Materials doi: 10.3390/ma19183907

Authors: Arystanbek Kussainov Zarina Aringozhina Gulnara Zhunissova Lyaila Bayatanova Bauyrzhan Rakhadilov Moldir Kaliaskarova

This study investigates the effects of applied voltage and treatment duration during electrolytic-plasma hardening (EPH) on the microstructure, phase composition, hardness, surface condition, and tribological behavior of 20X steel. EPH was performed in a 12 wt.% Na2CO3 aqueous electrolyte at voltages of 280, 300, and 320 V for 4 and 6 s. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, instrumented indentation, surface profilometry, and ball-on-disk tribological testing were used to characterize the treated specimens. The 280 V/4 s, 300 V/4 s, 320 V/4 s, and 280 V/6 s conditions produced thermally modified surface layers without visible surface damage, whereas treatment at 300 and 320 V for 6 s resulted in localized surface melting. Among the undamaged specimens, the highest hardness was obtained at 280 V, reaching 329.6 ± 15.8 HV after 4 s and 332.1 ± 26.3 HV after 6 s, corresponding to an approximately 1.83–1.85-fold increase relative to the initial value of 180 HV. XRD revealed a predominantly α-Fe-based matrix, while weak secondary reflections could not be assigned reliably to specific phases. The minimum steady-state coefficient of friction was obtained at 300 V/4 s (0.444 ± 0.054), whereas the narrowest wear track was observed at 320 V/4 s (379.48 ± 36.24 μm). No direct correlation was found between hardness and tribological response, indicating that surface roughness and microstructural state should also be considered when selecting treatment parameters. The results define a stable EPH processing window for 20X steel and demonstrate that parameter selection should be based on a combined assessment of surface integrity, hardness, and tribological performance.

Materials doi: 10.3390/ma19183906

Authors: Juan Han Hai Fang

Pultruded glass fibre-reinforced polymer (GFRP) profiles are promising structural cores for lightweight sandwich panels, but their strong longitudinal response is accompanied by weak transverse resistance and local web instability. A matched experimental programme examined rectangular hollow pultruded GFRP profiles and vacuum-infused sandwich panels under four-point bending, short-span three-point bending and flatwise compression in H and V orientations. Changing from H to V increased the peak loads of individual profiles by 9.35% in four-point bending and by 26.06% in short-span loading but reduced the flatwise compressive peak load by 30.12%. For integrated panels, the same reorientation increased the four-point bending peak load by 22.74%, caused only a marginal change in short-span capacity and reduced the flatwise compressive peak load by 28.24%. Failure involved local web buckling, web shear damage, longitudinal splitting, laminate delamination and interfacial debonding. Continuous face sheets and wrapping laminates restrained local deformation and contributed to substantial post-damage resistance, consistent with load redistribution within the integrated section. Relative to a baseline comprising three individual profiles and the corresponding hollow FRP reference panel, integrated-panel capacities increased by 15.76%, 37.71% and 78.44% under four-point bending, short-span loading and flatwise compression, respectively. These results identify profile orientation and transverse web stability as key design parameters for pultruded-profile-core sandwich panels.

Materials doi: 10.3390/ma19183903

Authors: Danuta Barnat-Hunek Małgorzata Grzegorczyk-Frańczak Nikolas Robaczyński Wiktoria Puch

Waste calcareous opoka rock (WCOR) was investigated as a mass-based replacement for 0.5–1.5 mm granulated dolomite aggregate in thin-layer silicate and mineral renders intended for external thermal insulation composite systems (ETICS). Eight formulations with replacement levels ranging from 0% to 100% were evaluated in terms of fresh-state properties, moisture transport, adhesion, freeze–thaw and sodium sulphate crystallisation resistance, and microstructure using SEM/EDS. Increasing WCOR content reduced fresh-mixture density and flow diameter while increasing resistance to manual surface texturing. In silicate renders, capillary water absorption decreased by 84%, from 1.55 kg/(m2·24 h) for the WCOR-free reference to 0.25 kg/(m2·24 h) at 75% replacement. Conversely, in mineral renders, it increased by 52%, from 17.2 to 26.2 kg/(m2·24 h) at complete replacement. At 100% replacement, freeze–thaw resistance increased from 150 to 308 cycles in silicate renders and from 105 to 251 cycles in mineral renders, while salt-crystallisation resistance increased from 25 to 52 and from 16 to 52 cycles, respectively. Adhesion increased from 0.27 to 0.30 N/mm2 in silicate renders but decreased from 0.31 to 0.19 N/mm2 in mineral renders. SEM/EDS showed matrix-dependent differences in local morphology and aggregate–binder interfaces. Multi-criteria assessment identified 75% replacement as the most balanced option for silicate renders, whereas 25–50% provided the preferred compromise for mineral renders. Overall, the influence and preferred content of WCOR were strongly matrix-dependent.

Materials doi: 10.3390/ma19183905

Authors: Farjallah Alassaad Bechara Haddad Houssam Affan Ilyas Ennahal Walid Maherzi Amro Yaghi Anas Issa

The valorization of raw dredged sediments in concrete requires simultaneous verification of engineering performance and environmental safety during both service life and end-of-life conditions. This work focuses on raw marine sediment collected from a port area as a partial substitute for natural sand, through a global assessment of physical properties, mechanical performance, durability, simulated-rainfall release, and leaching after crushing. Four concretes with 0, 10, 20, and 30% of sediment, with the same contents of cement and effective water, and targeting the same SF2 consistency class, were manufactured. Increasing the replacement rate increased porosity, water absorption, shrinkage, and carbonation depth, while lowering the compressive strength. At 28 days, the compressive strength dropped from 43.91 MPa for the reference to 38.16 MPa at the 20% replacement and 24.63 MPa at the 30% replacement. The apparent chloride migration coefficient decreased by about 31 and 77% for the two replacement rates, respectively; given the initial chloride content of the sediment, this trend is interpreted comparatively and possible mechanisms are discussed cautiously. In the simulated-rainfall test, releases of anions, trace metals, and organic indicators measured from the intact concrete remained below the adopted screening thresholds; however, because only one slab per formulation was tested, these environmental observations are preliminary. After crushing, some sediment-containing mixtures exceeded inert-waste thresholds for chlorides, fluorides, or nickel, showing that stabilization was incomplete under end-of-life conditions. Among the sediment-containing mixtures tested, the 20% replacement provided the best overall balance between natural-resource substitution, technical performance, and the preliminary environmental observations.

Materials doi: 10.3390/ma19183904

Authors: Wenying Xu Jiawei Xu Yonglin Chen Dongyu Fan Yongbin Wang Tao Yu Siyu Chen Weidong Yang

Triply periodic minimal surface (TPMS) lattices are promising lightweight impact absorbers, but high-fidelity finite element modeling is costly, and uniform designs can develop high stress peaks during densification. This study presents a voxel-based finite element framework and a topology–density dual-gradient (TDDG) TPMS absorber. A convergence study selected a voxel size of 0.33 mm, yielding a 1.11% relative-density error and converged mechanical responses. Compared with a converged C3D4 tetrahedral model, the C3D8R voxel model reduced wall-clock time from 4222 to 497 s. Following validation against quasi-static compression tests, P, G, and IWP topologies at 20%, 30%, and 40% relative densities were screened. IWP20 and P40 were assigned to the impact- and support-facing regions and connected by normalized sigmoid interpolation. Under a 125 J impact, simulations predicted that TDDG-IWP20-P40 reduced peak nominal impact stress by 32.2% and 24.6% relative to U-P30 and DG-P20-P40, respectively, while maintaining comparable SEA. Additional simulations at 62.5 and 160 J confirmed lower peak stress than U-P30, with the added benefit over density-only grading becoming more pronounced at higher impact energy. Progressive crushing and delayed densification demonstrate the potential of TDDG TPMS absorbers for impact-load mitigation and future aerospace buffer designs.

Materials doi: 10.3390/ma19183902

Authors: Kateřina Hájková Josef Bárta Ida Skotnicová

Barley straw represents an underutilized agricultural residue with potential as a supplementary source of papermaking fibers. This study compared nitrate–alkaline, soda, and peracetic-acid delignification processes for the preparation of pulp from barley straw and evaluated the resulting laboratory paper sheets. The raw material was characterized by a cellulose content of 35.84%, an acid-insoluble lignin content of 18.79%, and ash content of 7.65%. Seven pulping variants were assessed in terms of total yield, reject content, Schöpper–Riegler degree, and Kappa number, while the paper sheets were tested for tear index, burst index, ISO brightness, Cobb60 water absorptiveness, and surface structure using optical microscopy. Total pulp yield ranged from 31.57% to 55.68%, and Kappa numbers varied from 13.50 to 47.86. Soda pulps had the highest Kappa numbers and the lowest brightness. Nitrate–alkaline treatments produced lower Kappa numbers than soda pulping but were generally accompanied by lower yields. Under the tested conditions, peracetic-acid delignification produced a pulp with a yield of 55.68%, a Kappa number of 13.50, an ISO brightness of 76.77%, a tear index of 6.26 mN·m2·g−1, and a burst index of 0.67 kPa·m2·g−1. Qualitative optical microscopy suggested a comparatively uniform fiber network. Among the evaluated variants, peracetic-acid delignification provided the most favorable combination of pulp yield, Kappa number, mechanical properties, and brightness; however, this finding is restricted to the specific treatment conditions applied in this study.

Materials doi: 10.3390/ma19183901

Authors: Shuai Zhang Bingbing Li Zhaofeng Wang Jiawei Han Qiang Shi

Traditional aluminum alloys have a mature industrial system, but their properties are still constrained by factors such as precipitation behavior, the grain boundary state, solidification defects, and residual impurities. This paper systematically reviews the microstructure formation, strengthening mechanisms, and performance regulation laws for major wrought and casting aluminum alloys. It also compares the characteristics of different alloy systems in terms of strength, ductility, corrosion resistance, fatigue performance, and manufacturing stability. The analysis shows that the development focus for traditional aluminum alloys has shifted from single performance improvement to multi-performance balance and precise control of the microstructure. With the increase in the proportion of recycled raw materials, the importance of impurity tolerance and the controllable transformation of second phases has further increased. At the same time, CALPHAD, physical models, and data-driven methods provide new means for alloy composition and process optimization, but their effectiveness still needs to be verified in actual components and engineering conditions. This paper can provide a reference for microstructure design, material selection, and performance optimization for the circular manufacturing of traditional aluminum alloys.

Materials doi: 10.3390/ma19183900

Authors: Victorien Bienvenu Abanda Well Mattia Giovini Francesco Genua Isabella Lancellotti Cristina Leonelli

The development of carbon-neutral construction materials has stimulated interest in alkali-activated systems for the valorization of industrial non-hazardous waste. This study proposes an original comparative approach to assess the cementing reactivity of several wastes, including black and white fly ash, bottom ash, fine glass dust, and float-glass polishing sludge, through their use as partial replacements for metakaolin (MK). Formulations containing 5–50 wt% of fine waste powders (<45 μm) were prepared and mechanically compared with a reference MK-based geopolymer. Formulations containing waste additions to the reference geopolymeric paste were also evaluated to investigate their role as aggregates/fillers. Mechanical testing identified float-glass polishing sludge as the most reactive precursor, achieving a compressive strength of 25 MPa at 10 w% addition, compared with 16 MPa for the reference material. Bottom ash and black and white fly ash reached approximately 19–21 MPa at 5–10% replacement or addition. Conversely, bottom ash at substitution levels above 5% reduced mechanical performance owing to its high crystallinity and unfavorable Si/Al molar ratio. Microstructural characterization by XRD, FT-IR, density measurements, and SEM was correlated with the observed cementing activity. These results provide a basis for performance-based design criteria aimed at the sustainable valorization of locally available industrial by-products in alkali-activated materials.

Materials doi: 10.3390/ma19183899

Authors: Gabriela Rutkowska Barbara Francke Mariusz Żółtowski Eryk Ostrzyżek

PE sheeting produced the most consistent crack-free final observations under the investigated conditions. This study investigated the combined effects of mixture composition, water-reducing admixture system, environmental exposure, surface finishing, reinforcement configuration, and curing method on the early-age cracking and mechanical performance of concrete under full-scale production conditions. Seven concrete mixtures were investigated, and 28 full-scale reinforced concrete slabs were produced and monitored for plastic shrinkage cracking. Fresh-concrete workability, slump retention, 28-day compressive strength, environmental conditions, and surface evaporation rates were evaluated. The actual water-to-cement ratio ranged from 0.58 to 0.85, and increasing water demand following the reduction or elimination of water-reducing admixtures resulted in a decrease in 28-day compressive strength (150 mm cube specimens) from 41.4 to 24.6 MPa. Under the investigated full-scale field-production scenarios, visible plastic shrinkage cracking varied with the combined material, environmental, construction, and curing conditions. The unprotected W4-P1 slab, cast during severe hot and dry exposure, developed 19 visible cracks, whereas 4 cracks were recorded for W5-P1 under more moderate conditions. Because these slabs also differed in mixture composition and reinforcement configuration, this comparison is interpreted as an association rather than a single-factor environmental effect. The estimated evaporation rate was 0.71 kg/m2/h for the initial W4 conditions and 0.22 kg/m2/h for W5. Surface-finishing and reinforcement comparisons were based on individual slabs and are therefore reported only as case-specific observations. PE sheeting showed the most consistent performance under the investigated conditions: all nine PE-protected slabs were free of visible cracks at final inspection, while the two water-cured slabs developed zero or one crack. These findings show that visible plastic shrinkage cracking in full-scale production cannot be interpreted from mixture composition or w/c ratio alone and should be assessed in the context of the complete field-production scenario.

Materials doi: 10.3390/ma19183898

Authors: Lirong Huang Minjie Huang Shun Ye Yuhang Chen Kai Ming Junhua Du Zhigang Liu

The inherent toxicity of antimony-based fillers in conventional resin-based friction materials necessitates the exploration of sustainable substitutes for wind turbine braking applications. This study therefore aims to formulate a high-performance, environmentally benign alternative using a ternary filler system comprising fly ash microspheres (industrial solid waste), molybdenum disulfide (MoS2), and talc. To optimize the filler proportions, an L9(34) orthogonal array design was implemented, systematically assessing the influence of each component on the friction coefficient, wear rate, and mechanical integrity. Dry sliding wear tests were conducted against an HT250 cast iron disc to simulate operational conditions. The experimental results identify the optimal composition (T3: 6 wt% MoS2, 6 wt% talc, 4 wt% fly ash) as achieving a low wear rate of 0.7 × 10−7 cm3/(N·m) at 350 °C, alongside an 88% recovery rate for the friction coefficient, with these key tribological metrics proving directly comparable to those of traditional antimony-containing formulations. The underlying mechanism for this improved performance lies in the synergistic interaction of the three fillers, which facilitates the development of a stable and cohesive tribofilm on the contact surface. Furthermore, analysis confirms that abrasive wear remains the prevailing material removal mechanism, thereby validating the practical feasibility of this newly developed, non-toxic composite material.

Materials doi: 10.3390/ma19183896

Authors: Jie Wen Yana Mao Yongfeng Wei

Bottom slag (BS), a coal combustion by-product, is an underutilized aluminosilicate resource with potential for alkali activation. In this study, the physicochemical characteristics of BS, including its chemical composition, mineralogy, morphology, and activity index, were systematically evaluated, and ground BS was blended with ground granulated blast-furnace slag (GGBFS) to prepare alkali-activated binders. The effects of BS content on mechanical properties, reaction products, and microstructural evolution were investigated using compressive strength tests and multi-scale characterization techniques. The results showed that BS contains abundant amorphous aluminosilicate phases with low residual carbon and exhibits considerable latent cementitious activity despite its relatively low intrinsic reactivity. The mechanical performance of the binders was strongly governed by precursor composition. Incorporating 20–40 wt.% BS achieved the optimum balance between precursor reactivity and strength development, whereas higher BS contents significantly inhibited alkali activation reaction because of the dilution of reactive glassy phases. Strength development was closely associated with the formation of C-(A)-S-H and N-A-S-H gels and the development of a dense microstructure. These results demonstrate that the synergistic activation of BS and GGBFS provides an effective route for producing low-carbon alkali-activated binders while enabling the high-value utilization of coal-fired BS.

Materials doi: 10.3390/ma19183897

Authors: Alex Lopes de Oliveira Rafael Rego dos Santos Caldeira Filipe Figueiredo Ramos Fábio Jesus Moreira de Almeida Bruno Luis Soares de Lima Marcos Massi

In this work, a methodology based on the finite element method is proposed for the design and simulation of optical modulators that exploit the magnetostrictive effect, aimed at enhancing the performance of magnetometers. The study focuses on a channel-type optical waveguide whose cross-section is carefully engineered to maximize opto-mechanical interaction while ensuring straightforward integration with magnetostrictive thin films. Fabrication follows the Induced Static Stress (ISS) technique: sputter deposition of a Terfenol-D (Tb0.3Dy0.7Fe1.92) layer onto a bismuth germanium oxide (Bi12GeO4) substrate creates residual stresses because of mismatched thermal expansion coefficients. During operation, applied magnetic fields induce magnetostrictive deformation, which, together with the pre-existing thermal stresses, modifies the local refractive index via the elasto-optic effect, thereby enabling dynamic guiding and modulation of guided light. Numerical analysis is carried out in COMSOL Multiphysics 5.6, employing coupled structural and optical modules. A fine mesh is generated along the waveguide core, while material parameters such as Young’s modulus, Poisson’s ratio, magnetostriction constant, and refractive indices are specified for each layer.

Materials doi: 10.3390/ma19183895

Authors: Mao Jing Kang Peng Tao Chen

The deep-sea tunnels at the Sanshan Island Gold Mine are subjected to extreme conditions characterized by high stress and complex erosion resulting from high mineralization. Under these conditions, conventional shotcrete is prone to performance degradation and insufficient durability, posing a threat to the long-term safety of the tunnels. At the same time, mine water is difficult to recycle on-site. To address these engineering challenges, this study utilized fly ash (FA), S105-grade ground granulated blast furnace slag (GGBS), polypropylene coarse fiber (PPCF), and hydroxypropyl methylcellulose (HPMC) as modifying components and employed the response surface method (RSM) to optimize the mix design of mine water-blended shotcrete. The study selected compressive strength, direct shear strength, and chloride ion electrical flux at 6 h as response indicators and constructed a quadratic polynomial regression model. Analysis of variance and goodness-of-fit tests indicated that the model possessed good significance and reliability of fit. Based on this model, the optimal mix design was determined: an FA/GGBS blend ratio of 3:7, a cement replacement rate of 20%, a PPCF content of 3.3%, and an HPMC content of 0.18%. Performance testing showed that the optimal mixture achieved a compressive strength of 25.24 MPa, a direct shear strength of 8.08 MPa, and a chloride ion electrical flux of 778 C after 6 h. Compared to the control group, its peak compressive strength decreased by only 9.98%, while its residual strength increased significantly; direct shear strength increased by 18.1%, and electrical flux decreased by 33.8%. This indicates that the material’s mechanical load-bearing capacity, deformation coordination, and corrosion resistance have been enhanced in a synergistic manner. Field industrial trials have verified that this modified concrete possesses excellent ductile yield characteristics, can effectively suppress water seepage in mine tunnels, is capable of withstanding extreme underground operating conditions, and enables the efficient reuse of mine water resources.

Materials doi: 10.3390/ma19183894

Authors: Paulina Dziemiańczyk Dawid Łysik Francois Vernay Joanna Mystkowska

Polycaprolactone (PCL) is a widely used biodegradable polyester in tissue engineering, drug delivery, and temporary implant design. While its favorable processability, biocompatibility, and low melting temperature are highly advantageous, its slow and condition-dependent degradation remains a major limitation for precise temporal control in biomedical applications. Despite extensive literature on PCL, a critical knowledge gap remains in linking fundamental molecular chain scission directly to macroscopic structural evolution, mechanical failure, and predictable in vivo device performance. To address this, this review provides a comprehensive synthesis of PCL degradation mechanisms, with a particular emphasis on PCL-bioceramic composites designed for hard tissue engineering. We elucidate the progressive degradation pathway—distinguishing between initial hydrolytic chain scission, oligomer formation, the generation of low-molecular-weight degradation products, and their subsequent metabolic fate under physiological conditions. Furthermore, this review critically evaluates how fundamental variables—specifically molecular weight, crystallinity, bioceramic fillers, device geometry, and physiological environments—alter degradation kinetics. By connecting molecular weight reduction to subsequent mass loss, thermal behavior, and mechanical deterioration, we establish a framework for understanding how structural reorganization and crystallinity evolution govern material failure. This review bridges the gap between simplified in vitro models and complex in vivo realities, supporting the rational design of composite biomedical devices with tailored, predictable resorption profiles.

Materials doi: 10.3390/ma19183893

Authors: Yerbolat Koyanbayev Viktor Baklanov Nuriya Mukhamedova Arman Miniyazov Igor Sokolov Dilyara Belgibayeva Ospan Oken Aisara Sabyrtayeva Anel Raiko

This paper investigates the possibility of pressure-assisted thermomechanical consolidation and thermal treatment without applied pressure during the low-temperature consolidation of oil-saturated aluminosilicate sorbents for their subsequent application in the conditioning of liquid oil-containing radioactive waste (RAW). The Premium and Absorbent sorbents saturated with transformer oil not containing radionuclides were used as model RAW systems. It was established that pressure-assisted thermomechanical consolidation leads to the formation of a denser structure and a reduction in hydrocarbon-phase losses compared with thermal treatment without applied pressure. For Premium, mass losses decreased from 0.74 to 0.35 g (by 53%), and for Absorbent, from 0.75 to 0.47 g (by 37%), and the consolidated samples were characterized by a more homogeneous microstructure and increased resistance to exudation. It was established that the efficiency of hydrocarbon-phase retention is determined by both the treatment conditions and the mineral composition of the sorbent. The obtained results indicate the prospects of low-temperature pressure-assisted thermomechanical consolidation at a temperature of 150 °C, a pressure of 1.5 MPa, and a holding time of 20 s for the conditioning of oil-containing RAW without the use of additional binding components.

Materials doi: 10.3390/ma19183892

Authors: Przemysław Mania Mateusz Fertsch Magdalena Broda

Among wood types used in industry, ash wood is one of the most commonly heat-treated species. It is widely applied for outdoor applications such as cladding, terrace boards, and garden furniture, as well as in indoor applications that require high dimensional stability. Although the mechanical properties of thermally modified ash have been extensively studied, its creep behaviour under sustained load remains insufficiently described. This study evaluates the short-term creep behaviour of ash wood thermally modified at 210 °C under bending stress, based on deflection measurements at different stress levels and under controlled humidity conditions. Untreated ash wood with comparable moisture content served as a reference. The results show that thermally modified wood exhibited lower creep compliance than untreated wood at all applied stress levels. After 24 h of loading, the absolute reduction in total creep compliance was 3.7% at 40% stress and 20.3% at 60% stress relative to control wood. The difference between modified and unmodified wood became more pronounced as the load level increased. These findings indicate that thermal modification can reduce the tendency of ash wood to creep under short-term loading conditions. Given the limited test duration and the use of small specimens, the results should be interpreted with caution and cannot be directly extrapolated to structural-scale applications. Nevertheless, the study provides new knowledge and is an interesting basis for further investigation of the creep behaviour of thermally modified wood under long-term loading and variable environmental conditions.

Materials doi: 10.3390/ma19183891

Authors: Zbigniew Suchorab Magdalena Jastrzębska Anna Futa Magdalena Paśnikowska-Łukaszuk Magda Wlazło Krzysztof Tabiś

The article describes the problem of moisture in buildings and building materials as well as the Time Domain Reflectometry (TDR) measurement technique that can be applied for invasive and also noninvasive measurements of building materials. Moisture readings in such media rely on signal propagation time shift analysis and may be subject to errors, while the vast majority of models derived for TDR devices are based on this type of measurement. Multiple linear regression (MLR) is proposed as a method to improve the quality of the readouts achieved using TDR noninvasive sensors. The aim of this work was to improve the calibration methods of TDR surface sensors by taking into account the attenuation of the electromagnetic pulse caused by the presence of water and salt ions and to develop calibration formulas that are multiple linear regression equations considering both the time shift and signal attenuation. Within the research, two types of noninvasive TDR sensors were applied to measure the moisture of red ceramic, clinker and silicate bricks. Average RMSE values for all sensors and materials were 0.009 cm3/cm3 lower in the case of the proposed multiple regression calibration models and 0.005 cm3/cm3 in terms of RSE compared to the traditional calibration methods used in the TDR technique.

Materials doi: 10.3390/ma19183890

Authors: Martynas Statkauskas Danutė Vaičiukynienė Audrius Grinys Laura Vitola

The cement industry is a major source of global CO2 emissions, driving the development of low-carbon alternatives such as geopolymers. This study examines geopolymer binders produced from ceramic brick waste (CBW) and metakaolin waste (MKW), evaluating their fresh and hardened properties as well as their performance under elevated temperatures. Five binder compositions were formulated by progressively replacing CBW with MKW (25–100 wt.%). The alkaline activator ratio (Na2SiO3/NaOH = 1.5) and NaOH molality (8 M) were kept constant. Fresh-state behavior was evaluated using Suttard viscometry and Vicat testing, while hardened-state performance was assessed through compressive and flexural strength, softening coefficient, and drying shrinkage. Thermal resistance was examined at 200, 400, 600, and 800 °C, supported by XRD, FT IR, and SEM analyses. The present study investigates how waste-derived aluminosilicate precursors with differing crystallinity and reactivity affect geopolymerization mechanisms and high-temperature phase evolution. MKW-rich binders were found to form highly reactive amorphous gels, resulting in superior early mechanical strength, whereas CBW-rich binders retained thermally stable crystalline phases that enhanced resistance to structural degradation at elevated temperatures. The MKW-rich formulation (F5) demonstrated the highest ambient mechanical performance, reaching 82.8 MPa after curing at 200 °C, due to intensified secondary geopolymerization. In contrast, the CBW-only binder (F1) exhibited superior thermal stability, maintaining a compressive strength of 46.4 MPa even after exposure to 800 °C. These findings establish a clear structure–property relationship between precursor mineralogy, gel chemistry, and high-temperature performance, offering valuable insights for the tailored design of waste-derived geopolymers with optimized thermal and mechanical properties.

Materials doi: 10.3390/ma19183889

Authors: Donghe Zhang Yinghao Guo Xinhui Xu Yang Chen Shukai Hu Zexuan Han Lijun Yang Debin Shan Jie Xu Bin Guo

High-strength steels often require surface pretreatment before welding to remove contaminants and ensure weld quality. Compared with conventional mechanical grinding, which is time-consuming, labor-intensive, environmentally unfriendly, and potentially damaging to the substrate, laser cleaning offers a contact-free alternative to conventional surface-treatment methods and may reduce the use of abrasive or chemical cleaning agents. In this study, nanosecond laser cleaning of oxide films on 10CrNi2Mo3Cu2V steel was investigated in air and argon to determine the optimal process window. A 1064 nm, 100 ns pulsed fiber laser was employed for single-pass scanning at fluences of 5.10–10.19 J/cm2. The cleaned surfaces were characterized by SEM, EDS, XPS, laser confocal microscopy, microhardness testing, and vacuum electron-beam welding. In argon, the optimal fluence was 7.64 J/cm2, at which the oxide-related surface products were effectively removed in the analyzed area, the oxygen content decreased to 2.11 wt.%, the roughness reached 5.2 μm, and the hardness became comparable to that of the ground sample. At higher fluences, secondary oxidation increased and surface quality deteriorated. The optimized laser-cleaned joints were pore-free and achieved a tensile strength of 881.4 MPa, exceeding that of both the untreated and ground controls.

Materials doi: 10.3390/ma19183888

Authors: Gorka Barquero-Carmona Lorena Alcaraz Olga Rodríguez-Largo Félix A. López

The growing demand for electric vehicles has increased the need for rare earth elements (REEs), promoting the recycling of secondary sources such as end-of-life NdFeB permanent magnets. However, the selective separation of REEs with similar chemical properties, such as neodymium (Nd) and holmium (Ho), remains a major challenge. In this work, their separation from a real NdFeB permanent magnet leachate was investigated by liquid–liquid extraction using di-(2-ethylhexyl) phosphoric acid (D2EHPA) as an extractant. The effects of extractant concentration (0.05 M and 0.1 M), organic-to-aqueous phase ratio (1:1 and 2:1, O:A), and pH (0.6 and 2) on the extraction process were evaluated. Increasing extractant concentration and phase ratio improved Ho extraction, reaching above 90%, whereas Nd co-extraction remained relatively low at pH 0.6 (0.8–4.6%, depending on the conditions). However, pH was found to be the key parameter. At pH 2, Ho extraction exceeded 96% in all cases, while Nd co-extraction increased significantly (up to ~28%), reducing selectivity. Due to the high initial Nd:Ho concentration ratio (~12:1), even low Nd co-extraction percentages resulted in significant contamination of Ho-rich products, identifying product purity as the primary limiting factor. These results show a trade-off between recovery and selectivity, with low pH favoring selectivity and high pH favoring extraction efficiency.

Materials doi: 10.3390/ma19183887

Authors: Jinsu Yu Duc Anh Le Chao Zhang Ji Zhao

The quality of laser cladding is influenced by a combination of various process parameters, including laser power, powder feed rate, scanning speed, defocus amount, overlap ratio, and the flow rates of the powder feed gas and shielding gas. Taking into account the adjustment characteristics of laser cladding equipment, this paper selects laser power, powder feed rate, and scanning speed as the primary factors of study and systematically analyzes the patterns of their effects on the quality of the cladding layer. Based on the results of preliminary experiments, a single-factor experimental design was formulated, and the experimental results were analyzed according to the established cladding quality evaluation system. By developing an orthogonal experimental design and employing a combination of range analysis and analysis of variance, the optimal combination of process parameters was determined. Subsequently, the overlap ratio and Z-axis lift were derived and calculated using the equal-area method, providing a reference for the rapid estimation of multi-pass and multi-layer cladding coating process Windows.

Materials doi: 10.3390/ma19183886

Authors: Shaomin Luo Juan Li

This study investigates the effects of Cr content on the microstructure, room-temperature and 600 °C mechanical properties and high-temperature oxidation behavior of TiVNbTaCrx (x = 0, 0.25, and 0.5). Cr addition significantly intensified Ti segregation in the interdendritic regions during solidification, inducing the formation of an Face-Centered Cubic (FCC) Ti-rich precipitate phase. As the Cr content increases from 0 to 0.5, the Ti-rich phases evolve from a straw-like morphology to a blocky morphology, and the mechanical properties at room temperature continue to decrease. Fracture analysis reveals that cracks initiate at grain boundaries associated with the FCC Ti-rich phase, leading to a transition from ductile to brittle fracture in the Cr-containing alloys. At 600 °C, all Cr-containing alloys exhibit elongations below 0.20%, indicating that the precipitation of the FCC Ti-rich phase severely degrades the deformation capability of the alloys at 600 °C. Oxidation tests demonstrate that Cr addition provides only a marginal beneficial effect on the mass gain rate during the initial stage (0–10 h at 600 °C), while the Cr-containing alloys continue to gain mass upon prolonged exposure due to the reduced integrity of the oxide film. The oxide scale consists primarily of (Ta, Nb)9VO25, and no protective Cr2O3 scale was observed under the present experimental conditions. In summary, within the composition range studied, the FCC Ti-rich phase precipitates at Cr contents of 5.88 and 11.11 at.%, resulting in the fragmentation of the body-centered cubic lattice (BCC) matrix continuity and a comprehensive deterioration of mechanical properties at both room temperature and 600 °C, while failing to improve the oxidation resistance at 600–700 °C.

Materials doi: 10.3390/ma19183884

Authors: Kanchan Kumari Swastik Pradhan Monalin Mishra Abhishek Barua Chitrasen Samantra Trilochan Rout Manisha Priyadarshini

Electrified mobility regulations and lifecycle emissions targets have increased the demand for lightweight structural materials in vehicle architectures. Bioinspired composite materials offer microstructural configurations that alter conventional trade-offs among specific stiffness, crash energy absorption, and manufacturing energy requirements. This review evaluates the translation of biological structural archetypes including nacre, bamboo, cortical bone, and lotus leaves into load-bearing and functional automotive components. Quantitative benchmarks of continuous natural-fiber laminates, bio-cellular lattices, and mycelium-based acoustic cores are compared against high-strength steel and aluminum alloys. Key mechanical and functional metrics, including specific energy absorption (ranging from 35 to 48 kJ kg−1 for bioinspired crash structures), dynamic loss factors, and Cassie-Baxter superhydrophobic surface stability, are evaluated alongside high-throughput manufacturing routes such as high-pressure resin transfer molding (HP-RTM) and additive manufacturing. Methodological parameters for ISO 14040/14044-compliant Life Cycle Assessment (LCA) are synthesized, emphasizing component-level functional units over gravimetric mass equivalence. Furthermore, operational boundaries, specifically hygrothermal interfacial degradation, matrix glass transitions (Tg < 120 °C), and multi-axial loading sensitivity, are systematically outlined to define design limits for automotive deployment.

Materials doi: 10.3390/ma19183885

Authors: Zhe Wang Xi Chen Meng Jiang Zhijian Lu Yuan Chen Xuan Su Qingfeng Yang Dequan Yang Peng He Yanbin Chen

This work examines the response of Ti-6Al-4V fabricated by wire-laser directed energy deposition (DED) to heat inputs between 175 and 350 J/mm. Microstructure, tensile behavior, and rotating-bending fatigue were evaluated. As input increased, the transverse size of columnar prior β grains rose from about 642 to 1079 μm and the mean α-lath width increased from 0.65 to 1.32 μm. The α structure consequently changed from a fine acicular/basketweave form to a coarser lamellar form with clearer colonies. Tensile and yield strengths stayed near 900 and 840 MPa, whereas elongation fell from 14.3% to 10.3%. After a 600 °C, 4 h stress relief, fully reversed fatigue tests were performed at 500 MPa (R = −1). Specimens with 175 J/mm heat input reached about 3 × 107 cycles, while one with 350 J/mm fractured at roughly 1 × 105 cycles. The longer life of H175 coincided with its finer interwoven α structure, closer striations, more secondary cracks, and a more tortuous crack route.

Materials doi: 10.3390/ma19183881

Authors: Yassine Benali Rostom Lakhdar Daniela Predoi Simona Liliana Iconaru Carmen Steluta Ciobanu Krzysztof Rokosz Andrei Craifặleanu Khaled Boughzala

Hydroxyapatite (HAp) is a promising biomaterial with potential environmental and biomedical applications; however, its surface properties and functional performance can be improved through polymer modification. In this study, a novel hydroxyapatite xanthan (HAp-XAn) composite was developed and investigated for both environmental and biomedical applications. Comprehensive structural and surface analyses were carried out using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM) measurements. The biocompatibility of HAp and the HAp-XAn composite was assessed with the aid of the MG63 cell line using the MTT (3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) assay. The findings indicate that both HAp and HAp-XAn exhibit good in vitro cytocompatibility and favorable interactions with osteoblast-like cells, supporting their potential for use in bone-related biomedical applications. The antibacterial properties of HAp and HAp-XAn composites were studied in vitro against Staphylococcus aureus ATCC 25923 (S. aureus) and Escherichia coli ATCC 25922 (E. coli) bacterial strains. The results of the antibacterial assay revealed that HAp-XAn exhibited an improved antibacterial activity compared with HAp. The antibacterial assay highlighted that the inhibitory effect of HAp-XAn increased with the increase in incubation period. The HAp-XAn composite exhibited enhanced methylene blue (MB) adsorption compared with HAp, with the adsorption performance strongly dependent on pH, contact time, and initial dye concentration. Kinetic and equilibrium analyses indicated that the adsorption process was best described by the pseudo-second-order kinetic model and Langmuir isotherm. Overall, the incorporation of xanthan gum improved the adsorption and biological properties of HAp, demonstrating the potential of HAp-XAn as a multifunctional material for dye removal and biomedical applications.

Materials doi: 10.3390/ma19183883

Authors: Zhirui An Fahram Ayar Shiwen Sun Yicui Zheng Ruihuan Wang Yao Li Zhu Gao Qiangru Shen Yanchao Wang

Basalt-fiber textile-reinforced engineered cementitious composite (BTR-ECC) combines favorable durability, cost-effectiveness, and mechanics, making it a viable option for structural retrofitting. Although axial behavior is well-documented, off-axis loading zones often constitute structural weak points. To address this gap, this study experimentally and theoretically examines the mechanical responses and failure mechanisms of BTR-ECC at off-axis tensile angles of 0°, 15°, 30°, and 45°. The results demonstrate that: (1) The tensile stress–strain curves exhibit a distinct trilinear characteristic (linear elastic, strain-hardening, and fracture), featuring densely distributed microcracks confined to 30–50 μm. Dominant failure modes include textile rupture, interfacial debonding and pull-out, and PVA fiber bridging. (2) With increasing angles, tensile strength at 0°, 15°, 30°, and 45° surpasses plain ECC by 84.8%, 73.6%, 52.9%, and 54.0%, respectively, confirming effective synergistic load transfer between the basalt-fiber textile and the matrix. Despite progressive strength degradation, the strain energy density remains relatively stable across all orientations, indicating robust energy dissipation capacity. (3) A phenomenological constitutive model based on the tangent modulus approach is established to describe the off-axis tensile response. The model shows good agreement with the experimental data and may serve as a reference for the analysis of BTR-ECC structures within the calibrated range of the four tested angles.

Materials doi: 10.3390/ma19183880

Authors: Zirui Guo Zhongzhi Guan Yongzhen Zhang Ting Li Riguang Chi Yong Sun Zhiqiang Chen

To investigate the performance degradation patterns and underlying damage mechanisms of permeable concrete under freeze–thaw cycles in cold regions, permeable concrete with varying porosities was selected as the research subject. A total of 120 rapid low-temperature freeze–thaw cycles were conducted. The evolution of porosity, mass loss, skid resistance, permeability, and compressive strength was systematically analyzed. Exploratory numerical simulations, conducted under idealized assumptions, suggest that rising porosity may reduce effective thermal conductivity, extend phase-change duration, and amplify internal temperature gradients—trends that are consistent with the observed porosity-dependent frost damage but require experimental temperature validation for quantitative confirmation. With the increase in freeze–thaw cycles, mass loss and porosity continuously increase, while compressive strength and permeability gradually decrease. After 120 cycles, the mass loss of all specimen groups was below 1%, with compressive strength decreasing by 5.5% to 12.9%. Despite this, the specimens maintained good permeability and skid resistance. Numerical simulations indicate that permeable concrete exhibits a three-stage temperature response during both freezing and thawing processes. An increase in porosity reduces the material’s effective thermal conductivity, prolongs the phase transition duration, and intensifies the internal temperature gradient, thereby amplifying the thermo–mechanical coupling damage effects. Therefore, optimizing the pore structure is crucial for improving the long-term service performance of permeable pavements in cold regions.

Materials doi: 10.3390/ma19183882

Authors: Zhenyu Wang Liqing Li Faping Li

Lunar soil-based geopolymers are promising in situ construction materials, but their reliance on Earth-transported alkali activators limits sustainability. This study developed a nano-SiO2-modified simulated lunar soil-based geopolymer (NS-SLSG) with reduced activator demand by optimizing sodium hydroxide (SH), calcium hydroxide (CH), and sodium silicate (SS). Inductively coupled plasma atomic emission spectrometry (ICP-AES), orthogonal testing, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Scanning electron microscopy (SEM), Thermogravimetry–differential scanning calorimetry–derivative thermogravimetry (TG-DSC-DTG), Energy-dispersive X-ray spectroscopy (EDS), and Mercury intrusion porosimetry (MIP) were used to evaluate apparent elemental-release characteristics, flowability, mechanical properties, and microstructure. The experimental results indicated that the measured Al and Si concentrations were particularly sensitive to the SH dosage; SH and SS exerted comparatively greater effects on flowability, whereas SH and CH had greater effects on mechanical performance. Adding 0.75 wt.% NS reduced the total admixture mass in the experimental formulation by 23.9% while increasing compressive and flexural strengths by 26.0% and 19.5% to 36.15 and 8.26 MPa, respectively. Microstructural results suggested that SH promoted depolymerization, while CH may have enhanced Ca2+-assisted polycondensation, with corresponding variations in gel composition and pore structure. These findings indicate a viable strategy for improving the resource efficiency of lunar construction materials.

Materials doi: 10.3390/ma19183879

Authors: Anqi Cai Hairong Yin Cuicui Wang Hao Wan Yin Zhou

Infection associated with orthopedic implants and insufficient biological integration remain important clinical challenges. In this study, strontium-substituted hydroxyapatite (SrHA) was prepared by a chemical co-precipitation method, and a SrHA/polydopamine (SrHA@PDA) composite coating was constructed on porous tantalum (Ta) through the self-polymerization of polydopamine (PDA). The coating exhibited a photothermal conversion efficiency of 63.79% under 808 nm near-infrared (NIR) irradiation, with the temperature increasing to 62.7 °C within 10 min. The antibacterial activity was primarily attributed to PDA-mediated photothermal heating. After NIR irradiation, pronounced antibacterial effects were observed against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), while Sr2+ release remained controlled during the investigated period. In addition, the SrHA@PDA coating supported MC3T3-E1 osteoblast proliferation, indicating a favorable cellular response. Cross-sectional observations demonstrated the formation of a dense and continuous SrHA-containing coating on the porous Ta scaffold, and biomimetic mineralization further indicated favorable surface bioactivity. Overall, the SrHA@PDA coating integrates controlled Sr2+ release, favorable osteoblast response, and PDA-mediated photothermal antibacterial activity within a single surface modification strategy. This multifunctional approach provides a promising platform for improving the biological and antibacterial performance of porous tantalum implants for bone repair applications.

Materials doi: 10.3390/ma19183878

Authors: Yongbo Ye Sicheng Wang Jianfei Yang Dayu Zhang Xiaofei Ma

On-orbit assembly technology is the core method for constructing extremely large space structures, with assembly modules serving as the fundamental units for structural integration. Since ground dynamic verification of full-scale modules is often restricted by laboratory space, scaled models are required for equivalent evaluation. During the scaling of systems containing high-aspect-ratio flexible rods, traditional complete geometric similarity laws lead to severe dynamic distortion in these slender elements as dimensions are reduced. To address this issue, a dynamic equivalence method based on geometric distortion and material compensation specifically for space flexible rods is proposed. This theory permits non-proportional distortion of rod cross-sections by deriving distortion similarity laws and reconstructs dynamic consistency through material substitution. Numerical validation demonstrates that the method effectively eliminates prediction errors induced by size reduction. For free single rods, the prediction errors for the first three bending frequencies are maintained within 1%; for unconstrained two-bar mechanisms connected by spatial spherical joints, the error is maintained within 0.5%. Furthermore, upon introducing sliding rail boundary constraints, the scaled model accurately reproduces the spatial mode shapes of the prototype, with primary frequency errors converging to within 0.3%. This research provides a reliable theoretical basis for the ground experimental evaluation of on-orbit assembly equipment for extremely large space structures.

Materials doi: 10.3390/ma19183877

Authors: Zhongshuai Hu Shaoyuan Zheng Ping Lyu Chunhui Zhang Yuting Lv Yongkang Wang Yan Li Xinrong Zhao Weiqiang Zhang Liguo Ma

To investigate the corrosion resistance and service life of water-based epoxy-coated reinforcing bars under severe environmental conditions, HRB400 ribbed reinforcing bars were used as the substrate. Four types of water-based epoxy-coated reinforcing bars were prepared, containing 0.3% graphene–polyaniline (PAG), 0.3% iron oxide, 10% zinc phosphate, and 10% zinc–iron powder, respectively, with a bare reinforcing bar control group also included. In accordance with standards such as the ‘Design Standard for Durability of Concrete Structures’, durability tests were conducted under various conditions, including long-term immersion in marine chloride solutions, wet–dry cycling, de-icing salt freeze–thaw cycles, baking and immersion in saline soil, and concrete mixed with seawater. Corrosion current density (Icorr) was monitored using a three-electrode system and the linear polarisation method, and service life was predicted based on the Wiener process. The results indicate that, under all severe environmental conditions, the corrosion current density of the coated reinforcing bars was significantly lower than that of the bare reinforcing bars (BRBs). After 70 cycles of marine wet–dry cycling, the corrosion current density of the bare reinforcing bars reached 0.4569 μA·cm−2, whilst that of the 0.3% PAG coating was 0.1103 μA·cm−2, substantially lower than that of the bare bars (0.4569 μA·cm−2); after 110 freeze–thaw cycles in a de-icing salt environment, the corrosion current density of the bare reinforcing bars was 0.4480 μA·cm−2, whilst that of the PAG-coated bars was 0.1003 μA·cm−2. After 80 cycles of baking and immersion in a saline soil environment, the corrosion current density of the graphene–polyaniline-coated steel increased from 4.97 × 10−3 μA·cm−2 to 0.1021 μA·cm−2 (approximately a 20-fold increase), whilst that of the bare steel rose to 0.4489 μA·cm−2. In concrete mixed with seawater, the corrosion current density of bare reinforcing bars reached as high as 8.60 μA·cm−2 after 120 days, whereas that of coated reinforcing bars was 0.24 μA·cm−2, markedly lower than 8.60 μA·cm−2 for the bare bars. Lifespan predictions indicate that, provided that the specifications for concrete strength and protective layer thickness are met, water-based epoxy coatings have the potential to delay the onset of severe corrosion (Icorr ≥ 1 μA·cm−2) beyond the 50-year design threshold in seawater wet–dry cycling zones and saline soil environments, and are projected to meet the 100-year design requirements in de-icing salt environments. It should be noted that these projections are based on accelerated tests and require validation through long-term field performance data. Graphene-containing polyaniline nanocomposite coatings exhibited the best overall protective performance, whilst zinc phosphate coatings demonstrated outstanding stability in high-chloride environments. For the specific formulations tested in this study, the enhanced corrosion resistance is attributed to the synergistic combination of the epoxy matrix, inorganic fillers (TiO2 and BaSO4) and functional additives; these components collectively provide physical shielding, chemical passivation and dynamic pore-blocking effects. Within the scope of this study, the nanocomposite coating containing 0.3 per cent PAG exhibited the best overall protective performance.

Materials doi: 10.3390/ma19183876

Authors: Minseop Sim Seonbong Lee

Direct winding places magnet wires in direct contact with soft magnetic composite (SMC) stator cores, making the winding-corner response important for component design. This study evaluated an Fe–5.0 wt.%Si SMC stator core through finite element analysis and corner-loading tests. Based on a wire tension of 1.44 N/turn and a 90° change in winding direction, the resultant load was 2.04 N per turn and 38.7 N for 19 turns. An engineering verification load of 177 N was defined from the mean nominal 0.2% proof load of the AI-EIW wire. The equivalent distributed model at 38.7 N and the representative one-turn circular-contact model at 2.04 N predicted elastic responses without effective strain. At 177 N, the maximum effective stress and strain were 876.9 MPa and 0.0132, and the maximum resultant displacement after unloading was 0.85 μm. Component-level tests showed continuous force increases to the prescribed loads. Optical microscopy at 20× magnification identified no indentation, cracking, edge chipping, particle detachment, or corner-profile change after unloading, although the FEA-predicted sub-micrometer localized deformation was not directly quantified by the optical evaluation. These results characterize the local mechanical response under the defined reference winding and engineering verification conditions.

Materials doi: 10.3390/ma19183875

Authors: Yuhei Komaki Soo Han Oh Koki Nagao Tatsuya Mori Seiji Kojima

A universal excitation called a boson peak has been observed in glasses in the terahertz range. The terahertz time-domain spectroscopy (THz-TDS) enables the time-of-flight (TOF) detection of a boson peak. Volcanic obsidian is a typical natural inorganic glass. The broadband frequency dependence of complex dielectric constants was measured by TOF. The boson peak at 1.07 THz was observed at room temperature, which is lower than 1.2 THz of silica glass. The decrease in BP frequency may be attributed to the modulation of the SiO4 network by metal ions in obsidian. However, the IR light–vibration coupling coefficient CIR of obsidian is much higher than that of silica glass. The uncorrelated charge fluctuations, σ1=q1i2=0.481e were determined by CIR in Taraskin’s model. The value of obsidian is much higher than σ1 = 0.06e of silica glass. However, this value is comparable with σ1≈0.44e of sodosilicate glass, xNa2O(1−x)SiO2 at x = 0.2. As a common feature in silica-based glasses, the content of metal elements may lead to a nonlocal redistribution of all the atomic charges, which induces a weakening of Si-O bonds, and the uncorrelated charge fluctuations can be enhanced.

Materials doi: 10.3390/ma19183874

Authors: Daewoong Jung

NO2 sensing is shifting from the optimization of individual receptor materials toward integrated systems in which surface chemistry, interfacial charge transfer, transducer architecture, operating environment, and regeneration jointly determine performance. This review argues that deployment readiness is set not by peak response but by the coupled performance of five layers: (i) receptor and interface chemistry, (ii) transducer and device architecture, (iii) gas delivery and environmental conditions, (iv) regeneration and aging, and (v) calibration, uncertainty, and system integration. Within this mechanism-to-deployment framework, we examine how oxygen adsorption, depletion and accumulation layers, heterojunction and Schottky barriers, defects, catalytic sensitization, and percolation govern the electrical signal across metal oxides, carbon materials, transition-metal dichalcogenides, MXenes, porous and MOF-derived architectures, and organic semiconductors and how MEMS microheaters, FET/TFT/MOSFET transducers, flexible platforms, optical and electrical regeneration, and AI-assisted arrays read it out. Despite this progress, translation remains limited by environmental interference, incomplete recovery, transport-dependent response, aging, and device-to-device variability so that record responses seldom survive realistic operation. Reliable NO2 monitoring therefore requires application-specific validation of the complete measurement cycle—exposure, readout, recovery, environmental perturbation, calibration, and long-term operation—rather than isolated sensitivity metrics.

Materials doi: 10.3390/ma19183873

Authors: Adam D. Mumford Yon Ju-Nam Mohamed L. Merroun Jesús J. Ojeda

The long-term safety of geological disposal facilities (GDFs) depends in part on the integrity of metallic waste canisters exposed to evolving thermal, geochemical and microbial conditions. Although abiotic corrosion is comparatively well characterised, the significance of microbiologically influenced corrosion (MIC) remains uncertain. This review critically compares carbon steel, stainless steel, copper, and titanium under GDF-relevant conditions, distinguishing chemical MIC (CMIC) from electrical MIC (EMIC) and examining the roles of sulphate-reducing bacteria, biofilms, and extracellular electron transfer. Reported behaviour varies markedly: carbon-steel studies have reported localised attack approaching 1 mm within 12 months, while SRB-associated copper corrosion rates of up to 9.8 μm year−1 have been measured, yet other long-term experiments show little or no detectable microbial acceleration. These contrasts indicate that microbial presence alone is not predictive of corrosion severity; temperature, redox state, groundwater chemistry, bentonite density, nutrient availability, and passive-film stability are critical controls. The distinctive contribution of this review is an integrated, material-to-material assessment linking abiotic corrosion, CMIC and EMIC mechanisms with repository-specific environmental constraints, and current GDF development. It also identifies key uncertainties arising from methodological variability and short-term laboratory testing, supporting priorities for standardised, long-term, and in situ studies.

Materials doi: 10.3390/ma19183871

Authors: Jun Yang Zenghui Wan Long Yu Changlin Yu

It is of technological significance to construct efficient electrocatalysts for hydrogen production. Here, a novel composite based on NiF2 microspheres in situ grown on nickel foam (NiF2/NF) has been synthesized by a facile solvothermal procedure. Benefiting from the synergistic contribution of NiF2 microspheres and NF substrate, the derived NiF2/NF composite demonstrated excellent electrocatalytic performance for the hydrogen evolution reaction (HER) in both acidic and alkaline media. Specifically, it can deliver current densities of 10, 100, and 300 mA cm−2 at low overpotentials of only 40, 134, and 195 mV in 0.5 M H2SO4 and 69, 132, and 175 mV in 1.0 M KOH. Furthermore, an alkaline electrolyzer assembled with NiF2/NF as both the cathode and anode only required a low cell voltage of 1.57 V to drive the current density of 10 mA cm−2 for overall water splitting. This work proposed a new way for developing wide-pH HER electrocatalysts with high performance.

Materials doi: 10.3390/ma19183872

Authors: Sofia Fares Mustapha Kaci Nadjet Dehouche Christelle Delaite Amira Zaouak José-Marie Lopez-Cuesta

In this work, a sustainable approach is proposed for upcycling recycled Acrylonitrile–Butadiene–Styrene (ABS) derived from electrical and electronic waste (e-waste) through a combination of electron beam irradiation (EBI) technique and halloysite nanotubes (HNTs) used as reinforcement. The study reveals that the application of EBI at an optimal dose of 10 kGy enhances the tensile properties of unfilled e-waste ABS, achieving an increase of almost 9% in tensile strength (TS) and about 40% in Young’s modulus (E). Incorporating 5 wt% HNTs into e-waste ABS not only improves the thermal stability of the composite material, but also modifies its behavior towards irradiation, shifting the optimal dose to 5 kGy. Another effect of the combination of HNTs and irradiation is noted with regard to the increase in storage modulus (E’). The findings present a promising and eco-friendly route to transform e-waste ABS into a higher-value engineering material.

Materials doi: 10.3390/ma19183870

Authors: Natalia Martynenko Eleonora Chistyukhina Ivan Nikitin Dmitry Prosvirnin Mikhail Kaplan Vladimir Andreev Alexey Kolmakov Olga Rybalchenko

The effect of rotary swaging (RS) at room temperature and subsequent annealing at 350 °C on the microstructure, mechanical properties, and fatigue strength of Cu–35.8%Zn two-phase brass was studied. A structure with grains of α and β′ phases elongated along the deformation direction was formed after RS. It was also shown that subgrains of 200–300 nm in size, shear bands 100–200 nm wide, and deformation twins 10–30 nm wide were formed inside the α-phase grains. RS caused the increase in the yield stress (YS) from 93 ± 4 to 717 ± 6 MPa and the ultimate tensile strength (UTS) from 332 ± 2 to 744 ± 19 MPa with a decrease in ductility (El) from 71.0 ± 2.0 to 10.3 ± 1.7%. The fatigue limit also increased from 240 to 415 MPa after RS. Subsequent annealing at 350 °C induced recrystallization of the α-phase with the formation of equiaxed grains 2.2–3.6 µm in size, which resulted in a decrease in UTS to 462–466 MPa and an increase in ductility to 44–45%. Extending the annealing time to 4 h did not affect the strength and ductility values of the alloy.

Materials doi: 10.3390/ma19183867

Authors: Chenyang Yuan Jingyu Qi Yunfei Xie Weifeng Bai Junfeng Guan Jing Liu Kai Wang Lielie Li

This study systematically investigated the effects of carbon fiber (CF) content (0%, 0.15%, 0.3%) and strain rate (10−5/s, 10−4/s, 10−3/s, 10−2/s) on the mechanical properties, microstructure, and microscopic damage evolution of carbon fiber-modified recycled concrete (CFRRAC) using uniaxial compression testing, scanning electron microscopy (SEM) observation, acoustic emission (AE), and statistical damage theory. The results indicate that the moderate addition of CF can effectively improve the compactness of the microstructure of the specimen, enhance the strain rate effect of CFRRAC, and improve its initial macroscopic mechanical properties. The microstructure characteristics of specimens with different CF contents and the Stefan effect related to strain rate further affect the initiation and propagation morphology, propagation path, and adjustment process of effective stress skeleton of microcracks during uniaxial compression, leading to regular changes in characteristic parameters characterizing microfracture and yield damage evolution with CF content and strain rate. The above factors collectively determine the evolution characteristics of the macroscopic nonlinear stress–strain behavior of CFRRAC, combined with the CF bridging toughening effect, ultimately resulting in an increase in strength with increasing strain rate and maintaining good ductility. Compared with the specimens without CF doping, the peak stress of CFRRAC increased by 37.16% to 41.18% and the peak strain increased by 22.94% to 36.57% in the strain rate range of 10−5 to 10−2/s at a dosage of 0.3%. Taking the CFRRAC specimen with a content of 0.3% as an example, compared with the strain rate of 10−5/s, the peak stress of the specimen increased by 9.31%, 18.66%, and 31.24% at strain rates ranging from 10−4 to 10−2/s, respectively. The research results can provide theoretical support for the promotion and application of CFRRAC in the engineering field.

Materials doi: 10.3390/ma19183869

Authors: Gang Wang Mengyao Dong Junfang Shen Xiangning Zhang Meiling Du Donglong Li Kun Li Xiaoli Zhang Jingbo Chen

Shape memory polymers (SMPs) and their multifunctional composites have become important material systems for 4D printing because they can be processed into structures with programmed deformation and stimulus-responsive actuation. After being fixed in a temporary configuration, SMPs are able to recover their permanent shape when exposed to heat, electric or magnetic fields, and so on. This reversible shape change gives printed SMP structures functions beyond those of conventional static components, making them useful for biomedical devices, flexible electronics, and soft robotics. The performance of 4D-printed SMPs is determined not only by material chemistry but also by the design of the printed architecture and the manner in which external stimuli are applied. This review begins by covering the basic mechanisms that govern shape memory behavior in SMPs, including molecular switching, thermomechanical programming, and stimulus-controlled recovery. On this basis, representative printing methods for SMPs are compared, including stereolithography (SLA), fused deposition modeling (FDM), direct-write printing, and polymer inkjet printing. Recent applications are then considered in areas where programmed shape change has practical value, such as biomedical devices, soft robotics, and flexible electronics. The discussion also identifies unresolved problems in printing resolution, response speed, cyclic stability, structural design, and multifunctional coupling, which remain central barriers to wider use of 4D-printed SMP systems.

Materials doi: 10.3390/ma19183868

Authors: Xiaoqin Fu Lei Wang Yingjie Li Xu Li Zhuyao Li Yuyang Huang Haiying Fu Qiang Dou Hao Peng

In this work, cyclic voltammetry, square wave voltammetry, and chronopotentiometry were employed to systematically investigate the electrochemical behavior of O2− in LiF–BeF2 (66.7: 33.3 mol%) (FLiBe) molten salt on a gold electrode. Comparative analysis demonstrated that square wave voltammetry is more suitable than cyclic voltammetry for studying the electrochemical behavior of O2−. The square wave voltammetry results confirmed that O2− is oxidized to O2, with the electrode reaction controlled by ion diffusion. chronopotentiometry confirmed that the electrochemical behavior of O2− obeyed the Sand law. The diffusion coefficient of O2− in FLiBe by chronopotentiometry followed Arrhenius’ law. Then, a well-fitted linear relationship between O2− concentration and square wave voltammetry peak current density was established, enabling rapid determination and real-time monitoring of oxide content in an unknown FLiBe molten salt. Furthermore, the electrochemical deoxygenation of FLiBe was performed using the potentiostatic electrolysis technique, and a satisfactory removal efficiency of O2− was achieved. This study presents an in situ electrochemical quantitative analysis method to monitor the O2− concentration in FLiBe, overcoming the drawback of the long testing cycle in conventional chemical analysis. Meanwhile, this study provides new technical support for the deoxygenation and purification of the fuel salt in molten salt reactors.

Materials doi: 10.3390/ma19183866

Authors: Marco Lezzerini Stefano Pagnotta Maria Pia Riccardi

Hydric deformation can contribute to progressive damage in building stones, particularly when moisture-induced strains interact with pre-existing fabric anisotropy and thermally induced microstructural changes. Six Macigno sandstone prisms (20 mm × 20 mm × 200 mm), three with the longitudinal axis orthogonal to bedding (MTO) and three parallel to bedding (MTP), were examined after drying at 60 °C and after sequential thermal conditioning at 350 and 500 °C. At each stage, hydric deformation was continuously monitored during 8400 min of water immersion, and at the end of each test, water absorption and ultrasonic pulse velocity were measured on the samples. Mean final hydric deformation in the 60 °C reference state was 0.54 mm m−1 for MTO and 0.44 mm m−1 for MTP. Along the sequential conditioning path, it decreased to 0.18 and 0.10 mm m−1, respectively, at 500 °C, whereas water absorption increased from about 0.42 to 0.58–0.59 wt.%. Ultrasonic pulse velocity decreased from 4347 to 3915 m s−1 for MTO and from 4770 to 4437 m s−1 for MTP. Bedding-related anisotropy persisted, while water absorption and hydric deformation followed divergent trends. Continuous acquisition further showed that the general temporal pattern of rapid initial deformation followed by a more gradual approach to a near-stable response was preserved after thermal conditioning, although the initial deformation rate decreased systematically.

Materials doi: 10.3390/ma19183865

Authors: Adam Wójcik Danuta Miedzińska Maciej Jan Spychała

Nowadays, industries are increasingly developing advanced materials that combine high durability, sustainability, and ease of fabrication. Aramid fibers, particularly Kevlar, are widely used in engineering applications due to their excellent mechanical properties, such as high tensile strength, impact resistance, and thermal stability. At the same time, growing concerns over environmental impacts have led to increased interest in the reuse of waste materials and the development of sustainable composite systems. In this paper, we review experimental studies on Kevlar-based composites, with particular emphasis placed on composites manufactured from waste Kevlar fibers. Particular attention is given to the influence of fiber fragmentation and surface modification performed using polyvinyl butyral (PVB) on mechanical properties. We also cover material characteristics, manufacturing techniques, and the mechanical behavior of various composite systems. We primarily focus on analyzing the methodologies and research results of studies in the literature to enable future researchers to verify the quality of existing research.

Materials doi: 10.3390/ma19183864

Authors: Anita Milosavljevic Vasilije Petrovic Jovana Stepanovic Profirovic Dragan Djordjic Marija Petrovic

The mechanical performance of sewn seams is commonly evaluated using parameters such as seam strength and seam efficiency, which primarily describe the behavior of the seam at ultimate failure. However, these parameters provide only limited information about the initiation of structural deterioration that precedes rupture. An operational definition of the Seam Yielding Point (SYP) is proposed as an experimentally identifiable indicator of the onset of seam degradation during tensile loading. Nine woven fabric variants differing in structural characteristics were sewn using four polyester sewing threads with different linear densities. Seam tensile tests were performed according to the relevant international standard, while force–elongation curves were continuously recorded. The SYP was identified as the first local decrease in force observed on the force–elongation curve. Photographic documentation was used only for qualitative interpretation of the deformation process. The experimental results showed that the proposed SYP could be consistently identified in all tested specimens prior to ultimate seam failure. The corresponding yielding force and elongation depended on both the sewing thread properties and the fabric structure. In addition to conventional seam strength measurements, the proposed approach provides valuable information regarding the initiation of irreversible structural changes within the seam. Overall, the proposed operational definition of the SYP represents a useful complementary parameter for evaluating seam mechanical behavior and contributes to a more comprehensive assessment of seam performance.

Materials doi: 10.3390/ma19183863

Authors: Mingzhu Qian Wenyong Zhao Hui Liu Dejun Yan Guoxiang Xu Wen Liu Qingxian Hu

Laser–MIG hybrid welding is increasingly used in shipbuilding for medium-thick steel plates, where assembly-induced gaps and misalignment often compromise weld quality. In this study, a three-dimensional transient numerical model is established to simulate the molten pool dynamics during full-penetration laser–MIG hybrid welding of 10CrNiCu steel under varying gaps and misalignment conditions. The model incorporates coupled heat transfer, fluid flow, keyhole behavior, and droplet transfer and is validated against experimental weld profiles. The simulation results reveal that increasing gap size broadens the heat distribution, reduces keyhole depth, and decreases the bridging capacity of the filler metal. Larger misalignment enhances the step effect, promotes gravity-driven downward flow of liquid metal, and increases keyhole instability and porosity risk. The adaptability to assembly errors is further assessed. As welding current increases, the gap tolerance slightly improves from 1.61 mm to 1.65 mm, whereas the misalignment tolerance markedly decreases from 3.00 mm to 1.82 mm due to the earlier onset of porosity defects. These findings provide quantitative guidance for optimizing welding parameters to accommodate realistic assembly variations in marine steel fabrication.

Materials doi: 10.3390/ma19183862

Authors: Shuyun Chang Wenqing Wei Xue Qi Xufeng Wang Zuyi Zhang Jian Gu Dahong Mo Hu Deng

Lithium aluminosilicate (LAS) ultra-low-expansion glass ceramics are core materials for precision optical systems, whose quality and dimensional stability are critically constrained by the uniformity of the coefficient of thermal expansion (CTE). This work proposes a nondestructive ultrasonic immersion pulse reflection (UIPR) method for rapid and low-cost characterization of the CTE in LAS glass ceramics. Key parameters of the ultrasonic measurement system are optimized via finite element method (FEM) simulations and experimental validation. Employing the correlation method, the ultrasonic longitudinal wave velocity is measured in LAS glass ceramic samples with distinctly different CTE values. The proposed method achieves an ultrasonic longitudinal wave velocity measurement uncertainty of 0.49 m/s, contributing 4.78 ppb/°C to the overall uncertainty of ultrasonic CTE determination. Within the investigated sample set, a negative relationship is observed between ultrasonic longitudinal wave velocity and the mean CTE (0–50 °C). The linear fit yields a slope of −9.75736 (ppb/°C)/(m/s), with a Pearson correlation coefficient of −0.84303. Featuring noncontact and nondestructive capabilities, this method lays a solid methodological foundation for CTE evaluation and efficient iterative optimization of material fabrication processes. Meanwhile, it shows great potential for rapid full-aperture characterization of CTE uniformity in large-size LAS glass ceramics.

Materials doi: 10.3390/ma19183861

Authors: Emna M. Benali Manuel P. F. Graça Essebti Dhahri Benilde F. O. Costa Adel Benali

Bi0.8Ba0.2FeO3 nanoparticles were synthesized using the sol–gel method. X-ray diffraction (XRD) analysis confirmed that the material crystallizes in a tetragonal structure with the P4/mmm space group. This structural transformation plays an important role in the microstructural distortion and phase modification of the material, which are favorable for enhancing the magnetic and dielectric properties. The substitution of Ba2+ ions in the Bi-site of the BiFeO3 lattice leads to a notable increase in the remanent (Mᵣ) and saturation magnetization (MS) along with the coercive field (HC). Furthermore, the Bi0.8Ba0.2FeO3 compound exhibits a high dielectric constant (ε′) accompanied by a low dielectric loss (tg(δ)), manifesting its strong potential for applications in capacitors and dynamic random-access memory (DRAM) devices.

Materials doi: 10.3390/ma19183860

Authors: Gündüz Ercan Kutluay Fatih Erdoğan Yaşar Mahsut Dinçel

An aging population and a rising revision burden are increasing demand for bone-compatible load-bearing implants. Because the elastic modulus of conventional Ti-6Al-4V (~110 GPa) exceeds that of cortical bone (7–30 GPa), stress shielding can drive bone resorption and aseptic loosening. Two solution lines have emerged: low-modulus β-type alloys and porous architectures. Focusing on additive manufacturing (AM), this critical narrative review synthesizes the evidence along the axis of clinical failure modes. Materials science has lowered β-Ti’s modulus to ~40 GPa in bulk, yet clinical implants rely predominantly on porous conventional Ti-6Al-4V: the low effective modulus (single-digit GPa) comes from architecture, not alloying. These architectures range from porous fixation surfaces on solid acetabular shells to predominantly porous constructs—revision knee cones and sleeves, acetabular augments, and spinal interbody cages. In the acetabular cohorts, where clinical evidence is concentrated, short- to mid-term survivorship is favorable though heterogeneous; revisions were driven mainly by infection and instability, with aseptic loosening low. Two tools are proposed: a synthesis matrix setting laboratory claims alongside clinical evidence for each design parameter, and a 16-item minimum reporting checklist. Applied to the 12 primary series reviewed, the checklist found manufacturing and architecture-verification parameters largely unreported even where clinical outcomes are well documented.

Materials doi: 10.3390/ma19183858

Authors: Christian Krämer Volker Schulze Stefan Dietrich

This study investigates the application of magnetic Barkhausen noise (MBN) measurements for assessing the microstructural and residual stress characteristics of additively manufactured AISI 4140 steel. The research explores the influence of part geometry, residual stresses, and material hardness on the MBN signal, particularly in thin-walled structures produced using laser-based powder bed fusion (PBF-LB). Results indicate a strong correlation between wall thickness and MBN intensity, attributed to the penetration depth of the magnetic field and the resulting amplification in thinner sections. Furthermore, an anisotropic MBN response is observed due to residual stress distributions, with tensile stresses leading to a higher Barkhausen signal. These findings highlight the potential of MBN as a non-destructive evaluation method for quality assessment in additively manufactured components supporting future approaches for non-destructive assessment of material conditions in additively manufactured components.

Materials doi: 10.3390/ma19183859

Authors: Linshu Li Shengzhi Li Manjie Fan Jun Cheng Wuhua Zhang Xin Huo Xia Liu Kejian Li Zhipeng Cai Qu Liu

The creep-rupture behavior and microstructural evolution of Ni–Fe-based alloy/Inconel 617 dissimilar welded joints were investigated by creep-rupture testing, interrupted creep testing, and microstructural characterization. Tests were conducted at 630–750 °C under stresses of 130–375 MPa. All joint specimens fractured in the heat-affected zone (HAZ) or base metal (BM) on the Ni–Fe-based alloy side, indicating that the Ni–Fe-based alloy side was the creep-critical region of the joint. Three failure regimes were identified according to the relative rupture lives of the joints and the Ni–Fe-based alloy BM. Fractographic observations revealed predominantly intergranular fracture, with creep cavities and cracks preferentially associated with grain-boundary discontinuous precipitation (DP) regions containing coarsened rod-like γ′ precipitates and precipitate-free zones (PFZs). Differences in DP evolution between the HAZ and BM were closely related to creep-damage localization and failure behavior. Interrupted creep tests showed that temperature was the dominant factor affecting DP formation and growth, while applied stress accelerated its evolution. DP developed rapidly during the initial exposure stage and subsequently grew more slowly. These findings clarify the relationship between grain-boundary DP evolution and creep-rupture failure in Ni–Fe-based alloy/Inconel 617 welded joints, and also provide microstructural guidance for assessing and mitigating creep degradation in dissimilar welded components used in high-temperature A-USC systems. Future work should combine longer-term creep testing, phase-resolved microstructural characterization, and predictive modeling to establish quantitative relationships among DP evolution, creep-damage accumulation, and rupture life.

Materials doi: 10.3390/ma19183857

Authors: Grzegorz Maciaszek Andrzej Nowotnik Julia Maciaszek

The surface condition of the bond coat is an important factor governing the growth and microstructural development of electron-beam physical vapour deposition (EB-PVD) TBCs. In this study, 7 wt.% yttria-stabilised zirconia (7YSZ) coatings were deposited by EB-PVD on vapour-phase aluminide bond coats with three distinct surface conditions, ranging from the as-coated state to ground and polished surfaces. The effect of bond coat roughness was evaluated through surface profilometry, scanning electron microscopy, X-ray diffraction, quantitative analysis of columnar architecture and porosity, scratch testing, and Vickers microindentation. Reducing the bond coat roughness resulted in a more uniform columnar architecture, reduced intercolumnar spacing, and a lower degree of column inclination, accompanied by a decrease in the coating surface roughness. XRD confirmed the formation of the expected tetragonal/cubic 7YSZ phase assemblage for all investigated conditions. Scratch testing revealed no delamination or spallation up to the maximum applied load of 200 N, indicating high interfacial integrity irrespective of bond coat roughness. Vickers measurements revealed a statistically significant through-thickness hardness gradient for all coatings, with hardness decreasing from the bond coat interface towards the column tips. Importantly, bond coat roughness had no statistically significant effect on hardness near the interface or in the central region, whereas significant differences were observed near the column tips. These results demonstrate that bond coat roughness strongly governs EB-PVD columnar architecture and surface morphology, while its influence on hardness is predominantly confined to the uppermost region of the coating.

Materials doi: 10.3390/ma19183856

Authors: José Damián Calan-Canche Alfredo Reda-Cruz Salatiel Pérez-Montejo Cristóbal Patiño-Carachure Sergio Martinez-Vargas José Enrique Flores-Chan

In this study, an Al–20 wt.% Mg alloy was synthesized to systematically correlate its electrochemical behavior in synthetic seawater with the microstructural evolution induced by heat treatment at 190, 300, and 350 °C for 6 h. The samples characterized by SEM and XRD reveal a progressive morphological evolution of the β–Al3Mg2 intermetallic phase. The open circuit potential, the potentiodynamic polarization and the electrochemical impedance spectroscopy showed that this microstructural evolution increased the microgalvanic corrosion, promoting passive-film breakdown, and reducing charge-transfer resistance. The Al–20 wt.% Mg alloy treated at 350 °C exhibited the highest corrosion current density, associated with β–Al3Mg2. These results demonstrated that controlling beta-phase precipitation through heat treatment provides an effective approach to tune the electrochemical behavior of high-magnesium aluminum alloys.

Materials doi: 10.3390/ma19183855

Authors: Junkai Pan Yu Zhang Xuexia Wang Zhaolin Yao Yao Ran Renjuan Sun Yanhua Guan Linglai Bu

To improve the high-value utilization of recycled concrete powder (RCP) and its carbon sequestration potential, this study developed a low-carbon recycled powder-based binder (LCRPB) incorporating RCP, silica fume (SF), granulated blast-furnace slag (GBFS), and fly ash (FA). A five-factor, five-level orthogonal design was used to evaluate workability, mechanical properties, hydration behavior, wet carbonation performance, and post-carbonation reusability. The water-to-binder ratio showed the greatest relative influence on flowability and compressive strength, whereas RCP content had a greater influence on 28-day flexural strength and wet carbonation behavior. At favorable dosage levels, 2% SF, 7.5% GBFS, and 10% FA increased the 28-day compressive strength by 17.43%, 12.43%, and 11.83%, respectively. Wet carbonation showed the highest efficiency at a liquid-to-solid ratio of 5 and a CO2 flow rate of 3 L/min, with CaCO3 identified as the main carbonation product. The carbonated powder retained reuse potential. Matrix analysis identified a balanced formulation of W/B = 0.40, 0% SF, 7.5% GBFS, 10% FA, and 10% RCP. The selected formulation reduced the material-related carbon footprint by 26.6% relative to the 100% OPC reference.

Materials doi: 10.3390/ma19183854

Authors: Mengxin Xu Feng Ju Meng Xiao Tengfei Wang Dong Wang Lidong Yin Yingbo Wang Lu Si Dongming Yang

To improve fly ash utilization in mine grouting materials and address the slow reaction and limited early-age strength of fly ash-based binders, a fly ash-based grout was prepared using fly ash and S95-grade ground granulated blast-furnace slag at a mass ratio of 70:30 and activated with NaOH-Na2SO4. A full-factorial experiment evaluated the effects of water-to-solid ratio, total activator dosage, and NaOH:Na2SO4 on fluidity, bleeding rate, stone formation rate, and compressive strength at 7 and 28 d. Representative 7 d specimens were characterized by SEM, EDS, and XRD. Increasing the water-to-solid ratio improved fluidity but increased the bleeding rate and reduced the stone formation rate and compressive strength. The preferred mixture had a water-to-solid ratio of 0.55, a total activator dosage of 5%, and NaOH:Na2SO4 = 2:1. It exhibited a fluidity of 195.0 mm, a bleeding rate of 1.70%, a stone formation rate of 99.50%, and compressive strengths of 8.5 MPa at 7 d and 11.3 MPa at 28 d. At NaOH:Na2SO4 = 2:1, the specimen showed a denser microstructure with fewer pores and cracks, a local Ca/Si ratio of approximately 0.94, and more evident reaction-product features. The results provide an experimental basis for mix-proportion selection of fly ash-based grouting materials.

Materials doi: 10.3390/ma19183853

Authors: Yiyang Ge Ying Li Wen Fu Rongzhen Song Xiang Zhao Shanyu Han Zehui Jiang Fuming Chen

Bamboo is a renewable material widely used in traditional Chinese musical instruments, but its vibration behavior is sensitive to moisture. This study investigated how moisture content affects the vibration behavior of Jinghu bamboo soundboxes. Three Xipi and three Erhuang specimens were conditioned by soaking and drying to obtain 11 moisture states (M0–M10). Time domain responses, frequency response functions, natural frequencies, damping ratios, mode shapes, and a frequency-mass-based estimated structural stiffness index were evaluated using impact hammer testing and experimental modal analysis. Three individual Xipi soundboxes with nominal storage durations of 3, 46, and 86 years were examined before and after conditioning at 20 °C and 60% relative humidity as an exploratory case comparison. Both types showed stronger vibration responses at intermediate moisture levels, whereas nearly dry and nearly saturated conditions produced weaker responses. Increasing moisture generally lowered resonance frequencies and estimated structural stiffness index, while damping ratios were higher at the moisture extremes. Under the present test conditions, Xipi specimens exhibited a higher estimated structural stiffness index and stronger mid- to high-frequency responses than Erhuang specimens. Given the differences in specimen geometry and mass, these variations are interpreted as reflecting whole-structure dynamic responses rather than intrinsic differences in material properties. In the exploratory comparison, XP-86 showed the largest change, with a 61.17% decrease in fundamental frequency and the development of surface cracks. Given the limited number of independent specimens, the results are interpreted descriptively rather than as statistically generalizable effects. These results s demonstrate the importance of humidity control during the use and preservation of Jinghu soundboxes.

Materials doi: 10.3390/ma19183851

Authors: Byong Sun Chun Jinseong Jeong

In this work, we investigate the magnetization switching behavior of IrMn/NiFe bilayers as a function of NiFe thickness, temperature, and cooling-field direction. An unusual double-loop hysteresis behavior is observed in IrMn 10 nm/NiFe 40 nm bilayers, whereas a conventional single-loop hysteresis behavior is obtained for thinner NiFe layers. The observed double-loop feature exhibits temperature- and cooling-field-dependent asymmetry, suggesting a spatially nonuniform exchange interaction at the IrMn/NiFe interface. The opposite evolution of switching fields under positive and negative cooling fields indicates competing exchange contributions within the bilayer system. These results are consistent with a model involving distinct interfacial exchange regions or nonuniform uncompensated spin configurations in the IrMn layer. Our findings provide insight into the complex interfacial exchange behavior responsible for double-loop hysteresis in IrMn/NiFe bilayers and highlight the importance of interfacial magnetic inhomogeneity in exchange-biased spintronic structures.

Materials doi: 10.3390/ma19183852

Authors: José Roberto Ferreira Neto Jhuliene Elen Muro Torrento Carlos Eduardo da Silva Fernanda de Freitas Quadros Carlos Roberto Grandini Sophia Alexandra Tsipas Diego Rafael Nespeque Correa

This study investigated the combined influence of the α/β phase proportion and Plasma Electrolytic Oxidation (PEO) on the wear behavior of Ti-6Al-4V alloy. Samples with distinct α/β phase ratios induced by previous heat treatments (600, 800, and 1000 °C) were subjected to dry sliding wear tests before and after PEO treatment. The untreated samples exhibited major abrasive and minor adhesive wear mechanisms, characterized by broad scratches and minor adhered debris. In contrast, PEO-treated samples exhibited predominant adhesive wear, indicating a significant tuning in the wear mechanism. The coefficient of friction (COF) was unaffected by phase proportions in untreated samples but was influenced by PEO treatment. Volume loss and wear rate were sensitive to phase composition, with the untreated samples heat-treated above 800 °C exhibiting the highest values, likely due to the retention of the metastable α′ phase. Conversely, PEO-treated samples demonstrated markedly reduced wear, confirming the protective role of the oxide layer. Energy-dispersive spectroscopy (EDS) revealed the counterbody’s particle adhesion in untreated tracks, whereas PEO-treated tracks retained the coating, evidencing superior wear resistance. These findings highlight that tailoring the α/β ratio through heat treatment combined with PEO treatment enhances wear performance, offering promising implications for clinical translation in biomedical implants.

Materials doi: 10.3390/ma19183850

Authors: Qian Qiao Dawei Guo Chi-Tat Kwok Lap-Mou Tam

Ultrasonic vibration-assisted machining (UVAM) can improve the machinability of difficult-to-machine titanium alloys; however, the relationship between machining-load fluctuations, subsurface microstructure, and electrochemical response remains insufficiently established. In this study, a wireless in-situ monitoring system was integrated with electron backscatter diffraction (EBSD), electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, and scanning electrochemical microscopy (SECM) to compare conventional milling (CM), low-excitation UVAM (L-UVAM), and high-excitation UVAM (H-UVAM) of Ti-6Al-4V. Under the investigated conditions, H-UVAM reduced the RMS value of the measured axial load signal by 43.3% compared with CM and decreased the variation in the resultant bending-moment signal. The EBSD results showed a reduction in the mean grain size from 11.67 μm for CM to 10.07 μm for H-UVAM, together with an increase in the measured high-angle grain-boundary fraction from 48.27% to 59.39%. Electrochemical measurements further indicated a lower corrosion current density and a higher fitted barrier resistance for the H-UVAM surface. SECM mapping showed a narrower local current distribution under H-UVAM than under CM. These results demonstrate a consistent association between reduced machining-load fluctuations, modified subsurface crystallographic features, and improved electrochemical response. Because surface roughness, residual stress, tool wear, and passive-film chemistry were not independently quantified, the present work does not attribute the corrosion response exclusively to microstructural changes. Instead, it provides a cross-scale experimental framework for correlating machining dynamics with surface integrity and corrosion-related performance in machined titanium alloys.

Materials doi: 10.3390/ma19183848

Authors: Nokhaiz Sabir Duncan Billson Stephen Grigg

Hydrogen embrittlement (HE) is a critical degradation mechanism in high-strength offshore fasteners, where early-stage hydrogen-induced cracking (HIC) is difficult to detect using conventional inspection methods, due to its subsurface and time-dependent nature. This study presents an automatic acoustic emission (AE) signal classification framework for identifying hydrogen-related damage mechanisms in high-strength offshore bolts subjected to in situ electrochemical hydrogen charging under cyclic loading. Fatigue experiments were performed on modified property class 10.9 steel bolts using a bespoke axial fatigue rig integrated with localized hydrogen charging and multi-channel AE monitoring. Baseline fatigue experiments performed under uncharged conditions were additionally used to compare hydrogen-assisted and non-hydrogen-assisted AE activity. AE data was analysed using a structured framework incorporating signal filtering, feature extraction, principal component analysis (PCA), and Gaussian mixture model (GMM) clustering. To improve signal discrimination, spectral and temporal energy-distribution features, supported by continuous wavelet transform analysis, including partial-power and energy-ratio parameters, were introduced. The proposed framework enabled separation of AE signals associated with hydrogen evolution, plastic deformation, hydrogen-induced cracking, and brittle fracture. Comparison with manually classified datasets demonstrated strong agreement between automatic and physically interpreted signal clusters, while scanning electron microscopy (SEM) supported the presence of hydrogen-assisted brittle-fracture features associated with HIC-related AE activity. The introduction of spectral and temporal energy-distribution features improved cluster separability under in situ hydrogen-charged conditions. The results demonstrate that physically informed feature engineering combined with automatic clustering provides a promising proof-of-concept approach for mechanism-informed identification of hydrogen-assisted AE activity in high-strength steel fasteners.

Materials doi: 10.3390/ma19183849

Authors: Yanmiao Qu Shiyu Li Weihui Xu Xinwei Guo Weishu Wang

When a thermal power unit operates under deep peak shaving and variable load conditions, the heat-resistant materials of the boiler’s heat exchange surfaces will suffer accelerated fatigue damage due to frequent thermal shocks. To grasp the evolution law of thermal shock damage in high-temperature heat-resistant steel for the key equipment of thermal power units, based on the 12Cr1MoVG heat-resistant steel, a plastic strain simulation analysis was conducted. Through numerical simulation, the coupling relationship among thermal shock duration, thermal stress evolution, equivalent plastic strain (PEEQ) accumulation, damage penetration depth, and fatigue life was investigated. The results show that extending the duration of thermal shock will increase the thermal stress of the material, causing the failure depth to increase from 2.24 mm to 2.6 mm, and the accumulation rate of PEEQ at different depths of the material to accelerate, with the theoretical life decreasing from 1.82 × 105 cycles to 1.72 × 105 cycles. Extending the duration of low-temperature exposure will reduce the thermal stress of the material, causing the failure depth to decrease from 2.24 mm to 2.03 mm, and the accumulation rate of PEEQ at different depths of the material to slow down, with the theoretical life increasing from 1.81 × 105 cycles to 1.94 × 105 cycles. The research results can provide reference for fatigue damage and life assessment of the high-temperature and high-pressure materials used in key equipment of thermal power.

Materials doi: 10.3390/ma19183847

Authors: Vojtěch Václavík Jana Seidlerová Rudolf Hela Tomáš Dvorský Klára Křížová Tomáš Široký Miroslav Škopán Jaroslav Kašpárek Jiří Frühbauer Lubomír Keim

The growing production of construction and demolition waste has been stimulating the need to look for sustainable alternatives to natural aggregate used in the production of cement composites. This study evaluates the potential use of recycled brick material as a substitute for natural coarse aggregate in terms of environmental safety, mechanical properties, the solidification effect of the cement matrix, and life cycle assessment (LCA). Recycled brick materials sourced from four recycling yards were characterized using physical, chemical, and leaching tests. Cement composites containing 50%, 70%, 80%, and 100% replacement of natural coarse aggregate with recycled brick material were subsequently designed. The results demonstrated significant variability in the environmental properties of the recycled materials depending on their origin. Compressive strength after 28 days ranged from 31.8 to 36.2 MPa, and all mixtures met the requirements for strength classes C20/25 to C25/30 according to ČSN EN 206+A2. At the same time, a significant solidification effect of the cement matrix was confirmed, leading to a reduction in the concentrations of dissolved substances by 68.0–80.1% and sulfates by 97.8–99.2% compared to the original recycled material. A life-cycle assessment demonstrated a gradual reduction in the environmental impacts as the proportion of recycled brick material increased, with the best results achieved by a mixture with 100% replacement of natural aggregate. The results confirm that recycled brick material can be safely used as a full-fledged substitute for natural coarse aggregate while maintaining the required mechanical properties and reducing environmental impacts.

Materials doi: 10.3390/ma19183846

Authors: Norbert Nizel Dariusz M. Bieliński Jakub Wręczycki Magdalena Maciejewska Rafał Anyszka

Rubber compounds intended for Mars exploration missions must remain elastic at extremely low temperatures while being manufactured in a reliable and energy-efficient manner. In this study, the effect of vulcanization temperature (100–160 °C) on the network structure and properties of butadiene/silicone rubber (BR/VMQ) blends was investigated, comparing a conventional sulfur curing system (REF) with the same system activated by fluoride anion obtained from tetra-n-butylammonium fluoride (TBAF). The fluoride anion acts as an in situ activator of elemental sulfur, through the opening of the S8 ring, facilitating the crosslinking process at significantly lower temperatures. Fluoride enabled rapid vulcanization at 100–120 °C, shortening the optimum cure time from 129.1 min to 61.4 min at 100 °C and from 36.7 min to 16.9 min at 120 °C. Equilibrium swelling and thiol-amine analysis revealed opposite structural responses to lowered curing temperature: the crosslink density of the reference compounds increased (from 1.25 × 10−4 to 1.56 × 10−4 mol/cm3 between 160 °C and 120 °C), whereas that of the TBAF-containing compounds decreased (from 1.32 × 10−4 to 0.60 × 10−4 mol/cm3 between 160 °C and 100 °C), yielding networks dominated by elastic polysulfidic crosslinks (up to 97.2%). We attribute this to a suppressed crosslink maturation under conditions of reduced thermal energy and shortened curing time. Low-temperature curing also suppressed the crystallization of the VMQ phase (melting enthalpy decreasing from 1.23 J/g to 0.21 J/g for TBAF compounds), which we hypothesize results from insufficient energy for phase separation and regular chain packing in this strongly immiscible blend. TBAF-cured compounds exhibited lower tanδ peaks, a stable tanδ plateau between approximately −60 °C and +20 °C, a tanδ-peak shift towards lower temperatures with decreasing curing temperature, and higher elongation at break and tensile strength at −40 °C. The results show that low-temperature, fluoride-activated vulcanization is a promising route for tailoring BR/VMQ networks towards stable dynamic performance across the Martian daily temperature range.

Materials doi: 10.3390/ma19183845

Authors: Qun Zhang Lin Yao Xing Zhao Lifang Zhang Haiyang Li Jin Wu

Mixed recycled brick-aggregate concrete (MRBAC), produced by substituting natural coarse aggregates with crushed waste bricks and waste concrete, serves as a promising approach for the resource utilization of construction solid waste and boasts broad engineering application prospects. At present, few studies have established uniaxial compressive constitutive models for MRBAC after accelerated carbonation, which restricts its structural application. In this study, 16 groups of specimens were fabricated with four replacement ratios of recycled brick aggregate (RBA)—0%, 10%, 20%, and 30%—as well as four accelerated carbonation durations—0 d, 40 d, 80 d, and 120 d. Accelerated carbonation tests were carried out to measure carbonation depth, cubic compressive strength, elastic modulus, and uniaxial compressive constitutive curves of MRBAC. Test results show that full 120-day carbonation increases cubic compressive strength and elastic modulus of MRBAC by 16.07–32.13% and 28.3–50.1%, respectively. Carbonation depth imposes a stronger effect on peak stress than RBA content, whereas strength-growth rate decreases with carbonation progress. Peak strain decreases with increasing carbonation depth but rises with higher RBA replacement ratios, and RBA addition improves concrete ductility. Based on experimental data, a constitutive model for MRBAC is proposed, which simultaneously accounts for the coupled effects of carbonation depth and RBA replacement ratio. This study provides a theoretical basis for the structural design and popularization of MRBAC under carbonation-service environments.

Materials doi: 10.3390/ma19183844

Authors: Mardan Mamatyusup Qun Wei Zhengzhe Lin Jing Luo Meiguang Zhang

Re3Zr has recently been proposed in the cubic Pm-3n structure. Its alternative atomic arrangements and thermodynamic position within the Re–Zr system have not been systematically resolved. In this work, CALYPSO particle-swarm structure searches combined with density functional theory identify five Re3Zr polymorphs with Cmcm, Fmmm, Immm, P4/mmm, and Fm-3m symmetries and compare them consistently with the reported Pm-3n phase. Formation enthalpies, a selected-phase partial convex hull, phonon dispersions, elastic properties, sound velocities, elastic Debye temperatures, electronic structures, and bonding characteristics are evaluated. All five CALYPSO structures lie below Pm-3n in fixed-composition energy, with Cmcm being the lowest. The Cmcm phase has a formation enthalpy of −0.257 eV atom−1 and lies approximately 0.042 eV atom−1 above the selected-phase partial hull, identifying it as a low-lying off-hull metastable candidate at 0 K. AIMD simulations at 300 and 1000 K show no obvious structural reconstruction of the Cmcm framework over the simulated time scales. All six structures exhibit no imaginary phonon frequencies and satisfy the corresponding mechanical-stability criteria. Their elastic responses are strongly structure dependent: P4/mmm has the largest Chen–Tian hardness estimates and elastic Debye temperature, whereas Fm-3m shows the weakest elastic anisotropy. All six polymorphs are metallic, with Fermi-level states dominated by Re-5d orbitals and predominantly delocalized bonding. These results provide a thermodynamically constrained 0 K reference for future synthesis, phase identification, and finite-temperature or kinetic investigations of hypothetical Re3Zr polymorphs.

Materials doi: 10.3390/ma19183843

Authors: Lin Wang Yongbin Yang Yinrui Dong Yan Zhang Shichao He Qian Li

Coke breeze, a solid waste generated during coke production, transportation and utilization, possesses physicochemical properties akin to metallurgical coke except for its finer particle size. Recycling this material offers an effective route to conserve and reuse coal resources, yielding notable environmental and economic benefits. In this study, a composite binder composed of phenolic resin (PR) and coal tar pitch (CTP) was developed for producing high-strength metallurgical coke substitutes from coke breeze. This strategy complementarily combines the excellent binding and curing properties of PR with the superior high-temperature carbonization performance of CTP. Thermal and structural analyses elucidated distinct pyrolysis characteristics and functional group distributions between the two binders, providing a theoretical foundation for their complementary interaction. Systematic investigations into briquette strength, performance, and microstructure established that the optimal composite binder dosage is 15 wt.% of coke breeze, with a CTP-to-PR mass ratio of 7:3. This complementary system substantially enhanced the compressive strength of the formed coke, reaching 37.73 MPa after carbonization at 1000 °C, and improved its thermal stability, as reflected by a Coke Strength after Reaction (CSR) of 41.21%. Compared to the individual binders, the composite binder exhibited superior consolidation efficiency and structural integrity, presenting a promising approach for solid waste valorization and sustainable coke production.

Materials doi: 10.3390/ma19183842

Authors: Francesca Villa Corrado Tomasi Francesca Passaretti Nicola Bennato Enrico Bassani Emanuele Bestetti Elena Villa

Among the ferromagnetic shape memory alloys (SMAs), Ni43Mn31Ga19Co7 (at%) alloys are well known as a promising ferromagnetic SMA (FeSMA) for magnetocaloric effect, and scientific interest has increased due to the possible exploitation of multicaloric function. This first example of multi-effect by coupling elastocaloric and magnetocaloric effect is still far from complete experimental validation, mainly due to the difficulty of testing conditions that require the simultaneous application of both fields. In this study, a low magnetic field (μ0H = 0.26 T and 0.56 T) is applied during elastocaloric deformation at different temperatures. Although the magnetic field values applied in this work are much lower than those usually considered in the magnetocaloric effect, the magnetic field improves the elastocaloric effect, increasing the total strain and reducing the critical stress and mechanical hysteresis. This synergic action allows us to obtain an increase in the ΔTad of about 13% and 25% upon loading and unloading, respectively.

Materials doi: 10.3390/ma19183841

Authors: Miruna S. Stan

Nanotechnology continues to be one of the most dynamic and transformative areas of modern science [...]

Materials doi: 10.3390/ma19183840

Authors: David Carter Jason P. Coumans Nail Zagrtdenov Dominique Duguay Dogan Paktunc

CaCl2-assisted Direct Reduction of Chromite (DRC) is a potentially lower energy alternative to conventional chromite smelting to produce ferrochrome (FeCr). This study investigates the technical feasibility of substituting petroleum coke (PC) with bio-carbon (BC) as the reductant in DRC and quantifies its effects on reduction behavior, alloy characteristics, and residual phase evolution. Chromite pellets containing CaCl2 flux and either PC or BC were reduced under controlled conditions using thermogravimetric analysis and electric tube furnace experiments with continuous off-gas monitoring. Products were characterized using various methods including 3D X-ray microtomography, Scanning Electron Microscope (SEM)-based quantitative mineralogy, and Wavelength Dispersive Spectrometry using an Electron Probe Microanalyzer (WDS-EPMA). BC accelerated reduction kinetics relative to PC due to its devolatilization, which generated a microporous network and increased the reactive surface area. Correspondingly, peak CO flux occurred 8 min earlier with BC during vertical tube furnace tests. BC also produced finer FeCr alloys, with 15% of alloy volume below the initial reductant particle size compared with 3% for PC, reflecting enhanced alloy densification. Alloy compositions using both reductants met high-carbon FeCr specifications. BC use also promoted the formation of non-olivine and Cl-bearing slag phases, indicating that reductant type can influence the partitioning behavior of non-alloying elements within slag phases.

Materials doi: 10.3390/ma19183839

Authors: Xin Zhang Ya Lu Xinhai Liu

Warm-mix asphalt (WMA) reduces mixing and compaction temperatures through wax additives, chemical additives, and foaming techniques, but their dominant mechanisms, performance trade-offs, and evaluation priorities differ. This structured narrative review synthesizes evidence for Sasobit, Evotherm, and Advera as representative technologies across mixture, binder and mastic, interfacial and microstructural, and molecular scale. Sasobit-type wax additives improve construction-stage fluidity and high-temperature stability through viscosity–temperature regulation and wax crystallization, while low-temperature and fatigue risks require attention. Evotherm-type chemical additives enhance wetting and moisture resistance through surface-active adsorption, thin-film lubrication, and improved interfacial adhesion, with high-temperature shear resistance requiring verification. Advera-type zeolite foaming extends the compaction window through water release and microbubble formation, but residual moisture and wet-condition durability remain critical concerns. On this basis, technology-specific cross-scale evidence chains are established, and a mechanism-oriented evaluation framework is proposed, linking engineering scenarios, dominant mechanisms, reduced-temperature mix design feasibility, durability constraints, and applicability assessment. Mixture performance serves as the final criterion, while binder and interfacial evidence supports risk screening and molecular evidence provides mechanistic interpretation. The framework supports targeted material selection, experimental design, risk diagnosis, and process optimization.

Materials doi: 10.3390/ma19183838

Authors: Jianfeng Yang Qin Du

SmNiO3 thin films on PMN-PT ferroelectric substrates enable electrically switchable strain engineering, an advantage over permanently fixed lattice-mismatch strain. However, strain-engineered resistive switching in SmNiO3 via ferroelectric substrates remains largely unexplored. Here, by stabilizing high-quality epitaxial SmNiO3 films on (011)-cut PMN-PT through a LaAlO3/SrTiO3 graded buffer interface, we demonstrate dual-mode resistive modulation in SmNiO3/PMN-PT heterostructures: reversible butterfly-shaped hysteresis under bipolar fields arising from dynamic electrostrain, and nonvolatile switching through non-180° ferroelastic domain reorientation. Moderate heating to 75 °C boosts the resistance modulation, correlated with enhanced strain output from the PMN-PT substrate near its phase transition. At the same bias of 12 kV/cm, the modulation increases from −6.4% at 25 °C to −11.9%; even at only 6 kV/cm, the modulation reaches −6.7%, exceeding the room-temperature value at 12 kV/cm. These results demonstrate the potential of SmNiO3/PMN-PT heterostructures for dual-mode resistive switching, integrating both volatile and nonvolatile modulation within a single material system through a thermally enhanced strain-coupling mechanism. This work serves as a proof-of-concept demonstration for future exploration in neuromorphic applications.

Materials doi: 10.3390/ma19183837

Authors: Li-Chun Chang Yan-Zhi Liao Yu-Ting Ye Yung-I Chen

Monolithic CrSiN and WSiN films, as well as multilayered CrSiN/WSiN coatings, were fabricated via magnetron sputtering. The effects of bilayer stacking periods on the multilayer coatings’ characteristics were investigated. The monolithic CrSiN and WSiN films exhibited crystalline and near-amorphous structures, respectively, whereas the multilayer coatings exhibited mixed crystalline and amorphous phases. Moreover, the crystallinity of individual sublayers was affected by the underlying sublayers. The multilayer architecture effectively combined the mechanical and tribological properties of constituent sublayers. The mechanical properties of the multilayer coatings increased with decreasing bilayer period. The multilayered CrSiN/WSiN coatings with 12 alternative sublayers and a bilayer period of 143 nm exhibited a hardness and elastic modulus of 20.7 and 257 GPa, respectively. The bilayer and four-layer coatings demonstrated excellent wear resistance. Overall, the design of CrSiN/WSiN multilayer coatings with an optimized bilayer period can significantly enhance mechanical strength and wear resistance, indicating promising potential for advanced protective coating applications.

Materials doi: 10.3390/ma19183836

Authors: Hui Lin Bowen Cao Xuefei Zhang Jiawei Wang Xiaohui Huang Min Chen Nan Wang

Converter slag and copper slag represent promising sources for ceramic materials, but their high total iron content leads to waste of iron resources and inferior ceramic performance. To address this issue, we propose a two-step utilization method for converter slag and copper slag, including iron extraction synergistic oxidation and ceramic fabrication for tailings. In this study, the effects of tailings content, sintering temperature, and sintering aid addition on the phase composition, microstructure, physico-mechanical properties, and leaching characteristics of the novel pyroxene-based ceramics were investigated. The results reveal that the ceramics containing 50 wt% tailings present a single pyroxene phase with uniformly dispersed fine closed pores. At a sintering temperature of 1190 °C, the optimized ceramic achieves a water absorption of 0.33% and a flexural strength of 80.5 MPa. Elevating the sintering temperature facilitates the grain growth of pyroxene crystals and the formation of a liquid phase. The addition of sintering aid effectively lowers the sintering temperature and improves the densification degree of ceramic matrices. In addition, the leaching toxicity of the prepared ceramics is well below the standard regulatory limits. This study provides a novel approach for the high-value recycling of tailings.

Materials doi: 10.3390/ma19183835

Authors: Chengyong Ma Zhen Li Jianwei Dong Qiren Zhao Zhen Luo

Surface remelting is an effective method for modifying surface microstructures and improving the mechanical properties of metallic materials. However, the influence of an underwater environment on the laser remelting behaviour of zirconium alloys remains insufficiently understood. In this study, commercially pure Zr60702 was subjected to laser surface remelting in air and underwater environments under identical processing parameters. The phase constitution, microstructure, microhardness, and wear resistance of the remelted samples were systematically investigated. The maximum remelting depth decreased from 507.08 μm in air to 191.35 μm underwater because of the enhanced heat extraction and reduced effective laser-energy input in the aqueous environment. Both remelted samples were dominated by α-Zr at room temperature, while underwater remelting produced finer acicular α′-Zr and refined Widmanstätten structures. The maximum hardness values of the underwater- and air-remelted samples reached 636.7 and 546.5 HV, respectively, compared with 198.3 HV for the base material. The wear volumes of the base material, air-remelted sample, and underwater-remelted sample were 7.04 × 107, 6.77 × 107, and 5.66 × 107 μm3, respectively. The improved wear resistance of the underwater-remelted sample was attributed to its refined microstructure and increased hardness, which suppressed plastic deformation and ploughing during sliding. These results demonstrate that underwater laser remelting is a promising method for improving the surface properties of Zr60702.

Materials doi: 10.3390/ma19183834

Authors: Mervat Youssef Eman H. El-Shenawy Wael Khair-Eldeen Tadaharu Adachi Adel Nofal Mohsen A. Hassan

In the original publication [...]

Materials doi: 10.3390/ma19183833

Authors: Mincen Wan Dayong Hu Baoqing Pei

In the original publication [...]

Materials doi: 10.3390/ma19183832

Authors: Ruizhe Liu Yuchen Feng Hu Xu Xiaoyu Wang Tao Wen

Particle-reinforced metal matrix composites, wherein preform pore structure dominates liquid infiltration behavior and final composite quality, are essential for high-performance industries. Conventional empirical models predict pore characteristics for bimodal preforms based on ideal particle stacking assumptions yet ignore real compression-induced microstructural changes including particle contact compaction and particle fracture, yielding systematic deviations from actual pore characteristics. This study adopted high-resolution 3D X-ray micro-computed tomography (μ-CT) to quantify such discrepancies for bimodal SiCp preforms across six coarse-to-fine particle ratios (0–100%). Three-dimensional pore network models were extracted to quantify key characteristics including areal porosity, surface area, and pore/throat dimensions. The results demonstrated that the average areal porosity fell to a minimum at a 67% coarse fraction then rose, while the pore distribution homogeneity steadily declined. Additionally, μ-CT measurements revealed that particle contact compactness reduced the particle surface area per unit volume at coarse fractions below 25% whereas particle fracture increased it at fractions above 25%, deviating significantly from empirical predictions. Larger coarse particle fractions reduced pore/throat quantities but increased their average size and volume. Beyond using established pore network extraction, this work distinguishes these two competing micro mechanisms and provides reasonable datasets to support bimodal preform optimization for composite manufacturing.

Materials doi: 10.3390/ma19183831

Authors: Nilge Sarimehmetoglu Huseyin Simsek

Background: This in vitro study evaluated the effect of different finishing and polishing systems on the surface roughness of two 3D-printed crown resins. Methods: Eighty disc-shaped specimens were produced from two 3D-printed crown resins, Saremco Print Crowntec and VarseoSmile Crown Plus. Specimens were divided into four groups according to the finishing and polishing protocol: Lucida, TwistDia, OptiShine, and OptiGlaze. Surface roughness (Ra) was measured before and after finishing and polishing using a non-contact optical profilometer. Data were analyzed using ART ANOVA (p < 0.05). Results: All polishing protocols significantly reduced surface roughness, with the overall median Ra decreasing from 0.198 µm before polishing to 0.101 µm after polishing (p < 0.001). Among the tested protocols, OptiGlaze showed the lowest post-polishing median Ra values for both resin materials, whereas Lucida showed the lowest overall median Ra value across measurement times. Resin type had no significant effect on Ra, whereas the polishing system significantly influenced surface roughness. Pairwise comparisons revealed significant differences between OptiGlaze and OptiShine, OptiGlaze and TwistDia, and Lucida and TwistDia (p < 0.05). All post-polishing Ra values remained below the clinically relevant threshold of 0.2 µm. Conclusions: The surface quality of the tested 3D-printed crown resins was determined primarily by the polishing protocol rather than the resin type. Although all protocols provided clinically acceptable surfaces, the optimal polishing approach may depend on the resin–polishing system combination.

Materials doi: 10.3390/ma19183829

Authors: Sheng-Hsiung Hung Horng-Tay Jeng

In the original publication [...]

Materials doi: 10.3390/ma19183830

Authors: Qinggele Hua Jing Ding Wenjie Qin

The front end of the exhaust manifold in a high-power diesel engine is connected to the cylinder head with a bolted flange joint. The high-temperature gas discharged from the cylinder poses a great challenge to the sealing performance of the flange joint. In this paper, in order to provide a predictive foundation for the sealing design of the flange joint at the front end of a high-power diesel engine exhaust manifold, the finite element (FE) analysis was implemented to determine the contact stress distributions on the joint surfaces under the high-temperature working condition. An experiment was designed and conducted to obtain the contact stresses on the gasket in the testing flange joint under the critical bolt preload needed to meet the leakage rate requirement, which were used to compare with the contact stresses on the gasket in the actual flange joint to evaluate the sealing performance of the actual flange joint. The results show that the sealing performance of the actual flange joint is qualified. Considering the effect of material creep deformation on the sealing performance of the flange joint, the creep analysis was conducted based on the creep constitutive models of the materials obtained through creep tests, and the continuous sealing time of the flange joint at the high working temperature was predicted. This approach of combining numerical simulation with experimental testing can also be used for sealing prediction and design of other bolted flange joints working at high temperatures.

Materials doi: 10.3390/ma19183828

Authors: Lin Zhu Shi Zhao Ziyu Cheng Shiqi Sheng Yibao Liu Qianglin Wei Bao-Tian Wang

Helium accumulation is a major contributor to swelling, gas release, and mechanical degradation in oxide nuclear fuels under irradiation. This study employs first-principles density functional theory (DFT) to investigate helium behavior in thorium-based mixed oxide (MOX) fuels. A series of (Th1−xPux)O2 and (Th1−xUx)O2 solid solutions (x = 0, 0.25, 0.5, 0.75, and 1) was constructed, and the corresponding ground-state configurations were determined through total-energy minimization. The effects of 4.167 at.% helium incorporation on structural stability, electronic structure, elastic response, and thermal expansion were evaluated. Helium migration in ThO2, PuO2, and UO2 was further investigated at octahedral interstitial, metal-vacancy, and oxygen-vacancy sites. Positive helium incorporation energies indicated that helium incorporation is energetically unfavorable for all compositions. Vegard-like behavior was preserved for lattice constants and metal–oxygen bond lengths. The 2.06 eV band gap of UO2 disappeared after helium incorporation, whereas band-gap variations in most MOX compositions remained below 0.7 eV. Helium reduced the bulk moduli of (Th0.75U0.25)O2 and UO2 by 3.75% and 7.94%, respectively. Thermal expansion coefficients followed the order αL-UO2 > αL-PuO2 > αL-ThO2, with αL of UO2 nearly doubling. Metal vacancies acted as helium traps, whereas adjacent oxygen vacancies provided the lowest migration barrier of 0.42 eV. These results indicate that increasing ThO2 content improves the resistance of MOX fuels to helium-induced degradation.

Materials doi: 10.3390/ma19183827

Authors: Lushan Li Le Chang Jianping Zhao Xiaowei Wang Jizhong Yan Zechen Yang Shengping Wu

This study investigates the tensile behavior of polytetrafluoroethylene (PTFE) tube material across a wide range of temperatures, displacement rates, and sampling directions. Temperature has a dominant effect: flow stress decreases and ductility increase markedly as temperature rises, while displacement rate and sampling direction show only minor effects. A temperature-coupled three-part superposition quasi-static stress (TPS) model is developed, using Arrhenius-type relationships to describe how the model parameters evolve with temperature. This model outperforms the Johnson–Cook, Ogden, and Zhu–Wang–Tang (ZWT) models across the full strain range and the entire tested temperature range. Molecular dynamics simulations further show that rising temperature increases free volume and chain-segment mobility while reducing chain orientation, providing a molecular-scale explanation for the observed thermal softening.

Materials doi: 10.3390/ma19183826

Authors: Renate Fetzer Annette Heinzel Alfons Weisenburger Georg Müller

Heavy liquid metals such as liquid lead (Pb) are attractive heat transfer media for advanced energy applications, despite their corrosive nature. In the search for heat-resistant austenitic materials that are corrosion resistant to liquid Pb at high temperature, three new Fe24Ni15Cr3Al-based alumina-forming austenitic (AFA) steels with slightly varying compositions have been developed. The present study investigates the corrosion behavior of these AFA materials using static exposure tests to molten Pb containing 1 × 10−7 wt.% dissolved oxygen. The corrosion tests are performed at 500 °C, 600 °C, and 700 °C for 1000 h, 2000 h, and 5000 h each. In addition to the variation in material, temperature, and exposure time, two different surface finishes are also used for the tests. Examination of the specimens after exposure shows the formation of oxide scales for temperatures up to 600 °C on all three AFA materials, with minor material-specific variations. Furthermore, the scale characteristics depend on the surface finish. Coarse ground surfaces exhibit thin Al-rich protective oxide scales, while fine ground surfaces show the formation of thick multilayer oxide scales susceptible to Ni dissolution and Pb penetration. Pb exposure at 700 °C leads to a severe corrosion attack of all three Fe24Ni15Cr3Al-based AFA steels.

Materials doi: 10.3390/ma19183825

Authors: Alessandra Zanotti Stefano Cardea

Polymeric drug carriers have emerged as versatile platforms for improving therapeutic efficacy, drug stability and controlled and sustained release of active pharmaceutical ingredients. Conventional manufacturing techniques often rely on high processing temperatures, utilization of organic solvents and consequent purification procedures that may compromise morphology, encapsulation efficiency and carrier biocompatibility. Supercritical fluid technologies overcome the limitations of conventional methods and emerge as environmentally friendly, sustainable and flexible alternatives to produce advanced polymeric drug carriers. This review provides insights into the most widespread supercritical fluid technologies, encompassing the most recent advancements (2022–2026) made in the field of porous materials, micro- and nanoparticles and microcapsules. Emphasis was placed on carrier characteristics, features and applicative translation; this review aims at evidencing advantages, current limitations and future perspectives of supercritical fluid technologies, aiming at encouraging technological and industrial advancement of next-generation advanced polymeric drug carriers.

Materials doi: 10.3390/ma19183824

Authors: Joanna Szołtysik Wojciech Sorociak Sławomir Kwiecień Jarosław Rybak

This paper presents a comprehensive review of bituminous binder modification using Styrene–Butadiene–Styrene (SBS) copolymer. Bitumen is one of the most widely used binder types in road engineering, and its modification has been extensively studied to enhance performance characteristics. The review outlines the historical development of bitumen modification, discusses binder structural models, and examines the influence of SBS on binder properties. The review focuses on ageing process of Polymer-Modified Bitumen (PMB) and Highly Modified Bitumen (HiMA). The complexity of binder’s origin, polymer structure, ageing factors and the presence of cross-linking agents or other compounds creates significant challenges in predicting binder performance after technological and exploitation ageing. This uncertainty directly affects the assessment of long-term durability and recycling potential. Therefore, it is relevant to incorporate a broader range of ageing factors into standardized laboratory testing procedures to develop effective rejuvenation strategies for SBS-modified PMBs.

Materials doi: 10.3390/ma19183823

Authors: Xiao Liu Yilun Li Chaoyang Liu Haiwei Yao Liangyin Huang

Traditional brick masonry buildings in China are commonly constructed using fired clay grey bricks bonded with glutinous rice mortar, forming a unique historical masonry system with significant cultural value. During long-term service, these structures are vulnerable to environmental deterioration, material aging, and seismic actions, resulting in cracking, deformation, and degradation of structural integrity and load-carrying capacity. Carbon fiber-reinforced polymer (CFRP) sheets have been increasingly applied for strengthening masonry structures due to their high strength-to-weight ratio, corrosion resistance, and convenient installation. However, most existing studies on Fiber-reinforced polymer (FRP)–masonry interfaces have focused on conventional masonry systems, while the interfacial bond behavior and load-transfer characteristics between CFRP sheets and traditional grey brick masonry bonded with glutinous rice mortar remain insufficiently investigated. This study investigates the interfacial bond behavior of CFRP-strengthened traditional grey brick masonry through combined experimental testing and numerical analysis. First, uniaxial compression tests were conducted to determine the mechanical properties of glutinous rice mortar and fired clay grey bricks. Subsequently, double-shear tests considering different CFRP bond widths, bond lengths, and interface integrity conditions were performed to characterize the failure modes, force–displacement responses, and interfacial load-carrying behavior. The effects of interface geometric and integrity conditions were considered to evaluate the load-transfer characteristics of the strengthened interface. Based on the experimental results, a finite element model considering interface behavior was established and verified through comparison with the experimental results, which was subsequently employed to investigate the influence of bond width on interfacial stress transfer behavior beyond the experimental conditions. The results show that interfacial debonding accompanied by near-surface masonry damage dominates the failure process of CFRP–glutinous rice mortar masonry interfaces. Increasing the CFRP bond width enhances the interfacial load-carrying capacity and initial stiffness, while the ultimate capacity exhibits an approximately linear relationship with bond width within the investigated range. Numerical analyses further demonstrate that increasing bond width expands the effective load-transfer region, redistributes interfacial stresses, and delays stiffness degradation. These findings improve the understanding of interfacial bond behavior and load-transfer characteristics in CFRP-strengthened traditional masonry systems and provide references for the design and performance evaluation of strengthening applications in historic masonry structures.

Materials doi: 10.3390/ma19183822

Authors: Yangyang Xia Pengyu Li Lingli Shen Jifang Niu Huiguo Zhao

Fiber reinforced polymers (FRPs) have gained widespread application in civil engineering due to their light weight, high strength, and excellent corrosion resistance. Among various fibers, natural fibers have recently attracted increasing attention because of their renewability, low cost, and reduced environmental impact. However, natural fiber reinforced polymer composites (NFRPs) suffer from high moisture absorption and inferior mechanical properties, which are further deteriorated under hygrothermal environments, severely limiting their service conditions. This study focuses on flax fiber reinforced polymer composites (FFRPs) and, through systematic experimental testing, investigates their durability under hygrothermal conditions. Hygrothermal aging was conducted at 90% relative humidity and 40 °C for up to 30 days. Water uptake, mechanical properties, and thermomechanical behavior were evaluated for composites fabricated by two molding processes (autoclave and hand-laying) with varying ply numbers (10, 20, 30, 40, and 50 layers). The optimal ply number for mechanical performance was identified, and the influence of the different resin systems and fiber forms between the two processes on the cross-process comparison, as well as the rationale for the 30-layer laminate and the effect of laminate thickness, were clarified. Microstructural changes were examined via scanning electron microscopy. This work provides systematic experimental evidence and data for assessing the long-term durability of FFRP composites in humid and warm environments, offering valuable guidance for their practical application in civil infrastructure.

Materials doi: 10.3390/ma19183821

Authors: Yuekai Yao Min Mi Kuanghuai Wu Changkang Lao Yuqi Zheng

To quantitatively evaluate the skeleton design of the MaFF method, this study addresses five dimensions: gradation control, test method, quantitative model, correction conversion, and design method. First, the deviation coefficient method is proposed based on the Talbot method. Unlike conventional design restricted to n = 0.3–0.7, this method takes the maximum density curve at n = 0.45 as the reference and enables flexible adjustment of Vag by controlling the 4.75 mm sieve passing rate. This provides a theoretical basis for discontinuous gradation design. Second, the wet mixing test is developed to overcome aggregate segregation and inadequate lubrication inherent in the dry tamping method, offering a new detection approach that better reflects the actual skeleton structure in the mixture. The optimum parameters were determined as 2% asphalt content, layered loading, one-sided tamping and 75 blows. Using 11 gradations, the wet mixing tests show that Vag increases from 24.13% to 38.29% as λ increases from 0 to 1.0, with a strong linear correlation (R2 = 0.996). CT scanning validation indicates that the wet method results are 83–86% of those from 3D reconstruction, yielding a recommended reduction coefficient of 0.84. These findings systematically refine the MaFF method into a complete skeleton design framework. For the specific material system investigated (diabase aggregate, ultra-high-viscosity asphalt, maximum nominal particle size of 13.2 mm), this study provides a preliminary technical reference for FMA mix design. However, broader validation across diverse materials and field conditions is required before generalization.

Materials doi: 10.3390/ma19183820

Authors: Choi Seong-Woo Chenglin Li

This work investigated the effects of annealing temperature and holding time on recrystallization, grain growth, and tensile properties of cold-rolled biomedical Co–20Cr–15W–10Ni (L-605) alloy. The alloy was solution-treated at 1200 °C for 30 min, cold-rolled to 40% area reduction, and annealed at 800–950 °C for 15 min, 1000 °C for 5–60 min, or 1200 °C for 5–60 min. Annealing at 800–900 °C produced partially recrystallized microstructures; 950 °C yielded nearly full recrystallization with an average grain size of ~3.4 μm. At 1000 °C, the fully recrystallized microstructure retained ~5 μm fine grains even after 60 min, likely due to grain boundary migration inhibition by fine secondary-phase particles, whose composition and pinning effect remain unclarified. At 1200 °C, grains grew significantly to ~90 μm, attributed to higher grain boundary mobility and reduced particle pinning at elevated temperature. As annealing temperature rose from 800 °C to 950 °C, yield strength decreased from 1245 MPa to 800 MPa, and elongation increased from 12.6% to 45.9%. At 1200 °C, yield strength fell to 442–455 MPa and elongation reached 73.5–80.8%. The results confirm that the alloy’s strength–ductility performance is directly determined by microstructure evolution from retained cold rolling deformation substructures to fine recrystallized grains, and further to coarse recrystallized grains at higher temperatures.

Materials doi: 10.3390/ma19183819

Authors: Xudong Zhu Feifei Jiang Changwei Chen Hui Liu Pinghua Zhu Yang Li Tianyu Ma

This study investigates metakaolin-based geopolymer recycled mortar (GRM) in which recycled fine aggregate (RFA) was volumetrically replaced by pumice powder (PP) at 0% and 60–100%. Ambient compressive and tensile bond strengths were measured, followed by exposure to 600–800 °C for 1–3 h. The evaluation encompassed mass loss ratio, residual mechanical properties, temperature sensitivity, micro-phase evolution, and strength-normalized carbon intensity. Results demonstrated that PP replacement produced a non-monotonic response, governed by the trade-off between improved particle packing and the depletion of the rigid granular skeleton. Among the PP-containing mixtures, PP70 (70% replacement) showed a comparatively favorable mechanical response, with an ambient compressive strength of 31.7 MPa and a mean residual compressive strength of 18.8 MPa (59.3% of its initial value) after exposure to 800 °C for 3 h. Notably, tensile bond strength exhibited greater temperature sensitivity than compressive strength, with deterioration accelerating significantly above 700 °C. SEM and XRD analyses elucidated this macroscopic divergence via a two-stage damage mechanism: while dehydration and matrix contraction dominated at 600 °C, prolonged exposure at 800 °C induced structural rearrangement, with the dominant damage becoming increasingly concentrated at the RFA–matrix interface. Although substituting RFA with processed PP inherently increased the absolute embodied carbon, PP70 exhibited the lowest strength-normalized carbon intensity among the modified mixtures after exposure to 800 °C for 3 h. These findings indicate that, among the investigated high-volume PP mixtures, PP70 provided a comparatively favorable compromise between thermal-mechanical performance and environmental cost.

Materials doi: 10.3390/ma19183818

Authors: Wiktoria Kapusta Mateusz Walerzak Andrzej Sołtyk Małgorzata Ponto-Wolska Artur Winiarski Leopold Wagner Łukasz Zadrożny

The increasing use of photopolymer resins in dental three-dimensional (3D) printing has raised concerns regarding occupational exposure to volatile organic compounds (VOCs). This study aimed to characterize and compare formaldehyde (HCHO) and total volatile organic compound (TVOC) emission profiles of five commercially available dental 3D-printing resins and to explore their relationship with subjective odor perception. Subjective odor perception was assessed during routine educational laboratory activities using a numerical rating scale (0–10). Time-resolved HCHO and TVOC measurements were subsequently performed under standardized chamber conditions using a portable air-quality monitor, with three consecutive 10 min measurement cycles conducted for each resin using the same standardized 200 mL sample. Two participants reporting upper respiratory tract infection symptoms were excluded, resulting in a final sensory sample of 50 participants. Perceived odor intensity differed significantly among the tested resins (Friedman test, χ2(4) = 55.54, p < 0.001; Kendall’s W = 0.278). A positive resin-level association was observed between mean odor intensity and TVOC concentration at the 10 min endpoint of the first post-agitation measurement cycle (Spearman’s ρ = 0.70); however, this relationship was not statistically significant in the exact two-sided permutation analysis (p = 0.233) and was considered exploratory. HCHO–odor correlation analysis was not performed because HCHO concentrations for three of the five resins exceeded the upper measurement range of the instrument. Notably, a plant-based resin exhibited relatively high odor intensity despite comparatively low TVOC emissions, suggesting that total emission magnitude alone may not fully explain odor perception. The tested dental photopolymer resins exhibited distinct material-dependent emission and odor-perception characteristics. Odor perception should therefore be considered complementary to, rather than a substitute for, instrumental emission characterization. Integrating sensory assessment with instrumental emission measurements may support a more comprehensive evaluation of dental photopolymer resins and inform future occupational-safety studies.

Materials doi: 10.3390/ma19183817

Authors: Chao Zhou Rui Zhu Shengzhu Cao Jun Yang Binhua Gui

With the rapid advancement of space-based laser weapon technologies, on-orbit safety of spacecraft such as satellites is confronted with severe laser threats. To meet the demands for film system optimization and reliability improvement of thin films integrating space laser protection and thermal control functions, this study takes the Graphene/Ag/Al2O3/SiO2/ITO multilayer thin film structure as the research object. Combined with the space alternating high-low temperature environment and the action of ultra-high-density transient directional heat flux, systematic simulation research on the evolution laws of temperature and stress fields inside the multilayer thin films under laser irradiation in alternating space high-low temperature environments is carried out via COMSOL Multiphysics, and the influencing mechanisms of ambient temperature and laser operating parameters on thermal stress and temperature distribution are revealed. The simulation results demonstrate that the thin film structure reaches thermal equilibrium within several seconds under a given transient directional heat flux. As laser power rises, the peak temperature of each layer increases nonlinearly and the time required to reach thermal equilibrium shortens. The laser heat flux density acts as the dominant factor governing the temperature and thermal stress distribution. Under alternating space high-low temperature conditions, the thermal stress of the thin film varies approximately linearly with temperature while the overall stress magnitude remains low, and thermal stress is mainly concentrated in the Al2O3 layers. Laser loading exerts a remarkable impact on film thermal stress: the amplitude of thermal stress in all film layers rises synchronously with increasing laser power, and interlayer temperature gradients as well as stress concentration are further intensified. The stress growth of Ag and Al2O3 layers is the most significant, which can be attributed to the synergistic effect of interlayer thermal expansion coefficient mismatch and temperature gradients. The alternating high-low temperature and laser irradiation experiments indicate that the maximum temperature and maximum stress borne by the muti-layer film under alternating temperatures ranging from −150 °C to 150 °C and laser irradiation of 200 W/cm2 will not lead to macroscopic failure behaviors and degradation of thermal control performance.

Materials doi: 10.3390/ma19183816

Authors: Marcin Mikulewicz Katarzyna Chojnacka

Clear orthodontic aligners are removable polymer devices worn about 22 h a day for 12 to 24 months, increasingly by children. A growing in vitro literature shows that thermoformed and 3D-printed aligners shed micro- and nanoplastics and co-release elemental or organic constituents under oral, gastric and mechanical conditions, yet aligner-derived particle burden and systemic dose in wearers have not been measured. This review sets aligner-derived release against the wider human micro- and nanoplastic record and evaluates saliva as a biomonitoring matrix. Directly printed devices release more and larger microplastics under mechanical stress, whereas thermoformed materials show acid-related degradation, with Sb/Sn release and nanometre-scale particles reported in a single, not yet replicated in vitro study. Particles below 5 microns, especially below 1 micron, are plausible translocation candidates, but translocation of aligner-derived particles has not been demonstrated. In vitro work reports macrophage and oxidative responses, whereas detections in blood, placenta and atheroma are not source-specific and remain associative. The EU amalgam phase-out does not regulate aligners but highlights a substitution question, because device and chemicals law addresses intentionally added microplastics, not wear-generated secondary particles. ICP-MS for antimony and tin, with Raman, micro-FTIR and electron microscopy, forms a plausible analytical toolbox. We propose harmonised release testing and validated salivary biomonitoring, prioritising children, to characterise source-proximal exposure before use expands.

Materials doi: 10.3390/ma19183815

Authors: Yongqiang Xu Hao Chen Dapeng Zhang Guangyao Hu Hongjun Li Kerui Xiong

Floating involute splines are widely used in aviation power transmission systems for torque transmission. In this study, a finite element model considering the dynamic deformation of a floating involute spline shaft was established to analyze the influence of shaft deformation on the misalignment state of the spline pair under various typical dynamic overload conditions. Furthermore, a contact simulation model of the floating spline pair with an actual tooth profile was developed to investigate the effect of deformation-induced misalignment on the contact pressure distribution over the tooth surface. In addition, the contact fatigue strength of the spline pair under dynamic loading conditions, including limit loads and ultimate loads, was evaluated. The results indicate that axial overload can induce axial displacement of the mating surfaces of the floating spline, thereby reducing the effective axial contact length. Radial overload and gyroscopic moments can lead to parallel misalignment and angular misalignment of the spline, respectively. Under combined overload conditions, angular misalignment is dominant under limit loads, whereas parallel misalignment becomes more pronounced under ultimate loads. Moreover, significant stress concentration and non-uniform load distribution are observed in the contact stress field under both limit and ultimate loading conditions. A quantitative analysis method for floating spline misalignment under the superposition of multiple maneuvering loads has been established.

Materials doi: 10.3390/ma19183814

Authors: Lin Wang Tao Han Mou Lv Tingting Luo Maolin Liu Bing Xue Junwei Zhang Yongsheng Ji

The consumption of concrete is enormous during coal mine construction in the Xinjie Taigemiao mining area. During the concrete production process, the cleaning of concrete tank trucks and mixer equipment generates a large amount of waste sludge separated from fresh concrete. How to successfully recycle waste sludge has become a key issue that urgently needs to be solved in mine construction. In this work, a method is proposed for reactivating waste sludge into cementitious materials by wet grinding to peel off hydration products from the surface of cement particles, and the influence of aging time and wet-grinding time on the mechanical properties and frost resistance of reactivated waste sludge paste are investigated; furthermore, through testing methods such as hydration heat analysis, XRD, and SEM, the hydration and hardening mechanisms of waste sludge treated by wet grinding are analyzed. The results show that wet grinding can break the adhesion between agglomerated waste particles and peel off the hydration products from the surface of the waste particles to obtain fresh cement particles, thereby restoring the cement’s hydration activity and bonding properties. The cementitious properties of reactivated waste sludge first increase and then decrease with the increase in aging time, and they first increase and then tend to stabilize with the increase in wet-grinding time; the frost resistance of the reactivated waste sludge is improved. The optimal aging time and optimal wet-grinding time for reactivated waste sludge are 14–18 h and 10 min, respectively.

Materials doi: 10.3390/ma19183813

Authors: Zhixiang Wang Zhijian Yi Ya Li Jiaming Zhang Kang Su Jie Liu

Conventional concrete pavement materials remain limited in flexural strength, deformability, post-cracking load-carrying capacity, and impact resistance. To address these deficiencies, this study investigates the effects of polymer modification and ultrashort ultrafine steel fiber reinforcement on the static and dynamic mechanical responses and crack evolution of concrete. The results show that polymer modification enhances deformability, while steel fiber incorporation further increases flexural strength and ultimate flexural strain and improves post-cracking load-carrying capacity. Under repeated impact loading, the nominal impact energy input required for initial cracking and final failure increased; in particular, polymer-modified concrete containing 5% steel fibers showed increases of 938.76% in ultimate flexural strain and 8682.63% in the number of impacts to failure relative to ordinary concrete. The matrix and interfacial morphologies observed by scanning electron microscopy (SEM) were consistent with the macroscopic mechanical responses, supporting the interpretation that polymer modification improves matrix and interfacial integrity, while steel fibers contribute to post-cracking load transfer through crack bridging. Overall, the material exhibited high deformability and damage tolerance, indicating its potential for specialized pavement applications.

Materials doi: 10.3390/ma19183812

Authors: Jixin Yang Zhiqin Yang Xu Gu Ying Bao Huaping Tang

In situ rolling-assisted laser directed energy deposition (IR-LDED) was employed to fabricate Ti-6Al-4V titanium alloy samples, focusing on the microstructural characteristics under various rolling strategies. The results indicate that the microstructure was primarily governed by the interplay between temperature-dependent deformation and recrystallization processes. In situ rolling at elevated temperature, combined with complex thermal cycling, promoted recrystallization within the deposited material, leading to significant grain refinement. After remelting and high-temperature rolling, the average grain size in the middle region of the sample was refined to 21 μm, accompanied by high kernel average misorientation (KAMavg) value of 1.92. Increasing the number of rolling passes at lower temperatures further reduced the grain size and decreased the KAMavg. Following in situ rolling, the deposited material underwent remelting, and additional rolling at elevated temperatures increased both deformation and KAMavg. The rearrangement of dislocations, formation of subgrain boundaries, and enhanced solute diffusion collectively facilitated the globularization of lamellar α phases, ultimately forming a microstructure composed of globular α, lamellar α/β, and dot-like β phases.

Materials doi: 10.3390/ma19183811

Authors: Haiming Li Ziqiu Cheng Zhenzhen Zhou Chen Hu Junhao Ye Dong Huang Yanbin Wang Tingsong Li Heng Liu Shisheng Lin Denis Yu. Kosyanov Daqin Chen Duyou Lu Jiang Li

Despite the success of using Al2O3 as a secondary phase in Ce:LuAG phosphor ceramics (PCs), there is still room for improvement in the compositional design of biphasic PCs, as well as in their luminescent and thermal performance. In this study, nanopowders with 40 wt.% Al2O3-0.4at.% Ce:LuAG stoichiometry were synthesized via a co-precipitation approach. Subsequently, a series of compositionally uniform PCs was successfully fabricated by adjusting the vacuum sintering temperature and dwelling time. The grain size distributions of the Al2O3 and LuAG phases, as well as the evolution of porosity and pore size, were systematically analyzed and correlated with the sintering conditions. The addition of Al2O3 has been demonstrated to enhance the thermal properties of ceramics. The thermal conductivity of the “1750 °C × 10 h” sample was 15.6 W·m−1·K−1 at room temperature. Concurrently, it exhibited excellent thermal quenching behavior, retaining 96% of its luminescence intensity upon heating to 450 K. Its fluorescence lifetime was determined to be 21.06 ns. Under 450 nm laser excitation, the optimized PC attained a luminous efficacy of 286 lm·W−1 at 1 W·mm−2. In addition, the luminous flux increased continuously with laser power from 1 to 20 W·mm−2 without any sign of saturation, reaching a maximum of 2500 lm. The findings indicate that biphasic 40 wt.% Al2O3-0.4at.% Ce:LuAG PCs have potential as high-flux, green-color converters for next-generation high-power laser lighting. Furthermore, a laser illumination prototype device incorporating 40 wt.% Al2O3-0.4at.% Ce:LuAG ceramic samples and a 10 W blue laser was constructed. This device emits white light with an illumination range exceeding 500 m, thereby demonstrating its potential applications in laser-driven lighting.

Materials doi: 10.3390/ma19183810

Authors: Xiaoming Ren Hui Song He Li Yuanren Zhou Muqing Li Shihao Yang Chenxi Liu Yunxiang Lu Xin Li Nan Jiang Kazuhito Nishimura

Water-lubricated seal interfaces are particularly vulnerable to fluid-film instability, which accelerates interfacial friction and wear and compromises the reliability and service life of underwater equipment. Here, a novel graphite-microcrystalline diamond (Graphite-MCD) soft–hard seal-face tribopair was proposed and systematically benchmarked against SiC-SiC and Graphite-SiC tribopairs under high-pressure water lubrication. Their sealing capacity, friction and wear behavior, and interfacial evolution were evaluated. The polished Graphite-MCD pair achieved the highest limiting PcV (90.73 MPa·m·s−1) and the lowest wear rate, markedly outperforming the SiC-SiC and Graphite-SiC pairs. Multiscale interfacial characterization showed that the SiC-SiC pair failed primarily through adhesive instability after breakdown of the water film. Although the Graphite-SiC pair reduced interfacial shear resistance, sliding generated a continuous triboreaction layer accompanied by third-body wear. In contrast, the Graphite-MCD pair preserved interfacial structural integrity and suppressed the formation of an unstable continuous reaction layer and abundant abrasive debris. This behavior enabled a synergistic combination of a low-shear lubricating interface and a stiff load-bearing counterface. These results demonstrate that improving the limiting PcV of mechanical seals cannot be achieved by reducing the friction coefficient alone; rather, it requires simultaneous control of lubricity and interfacial stability. The findings provide a mechanistic basis for designing soft–hard tribopairs for high-pressure, water-lubricated mechanical seals.

Materials doi: 10.3390/ma19173809

Authors: Huidong Cao Hao Niu Xiufeng Wu Jinli Wang Qiao Zhang Jianfeng Zhao Yang Yu

To address the resource utilization of waste tires and the fire-safety concerns in engineering applications of rubber concrete (RC), this study systematically investigates the residual static and dynamic mechanical properties of RC after exposure to elevated temperatures and subsequent cooling to room temperature. Specimens are prepared by replacing fine aggregate with rubber particles at equal volume replacement ratios of 0%, 5%, 15%, and 30%. After undergoing gradient heating to target temperatures ranging from 20 °C to 300 °C, the specimens are naturally cooled to room temperature prior to testing. Subsequently, static compressive and splitting tensile tests, along with dynamic impact tests using a Split Hopkinson Pressure Bar (SHPB), are performed. These experiments are supplemented by scanning electron microscopy (SEM) to elucidate the microscale mechanisms. The results show that the residual static strength decreases monotonically with increasing rubber content and temperature. For the 30% rubber content mixture, the compressive strength decreased by approximately 40.6% from ambient temperature to 300 °C, and its strength is 64.6% lower than that of NC at 300 °C. Dynamic strength exhibits a pronounced strain-rate effect, with the strain-rate sensitivity of DIF being enhanced by higher rubber content. Energy dissipation increases substantially with strain rate; rubberized mixtures generally exhibit higher energy dissipation than NC at lower strain rates, though this effect becomes less evident at higher strain rates. These findings provide a theoretical foundation for the application of RC in complex thermo-mechanical loading scenarios, particularly in evaluating its post-fire residual load-bearing capacity.

Materials doi: 10.3390/ma19173808

Authors: Qian Zhang En-San Fu Ze Yang Le-Xiao Tian

Underground coal mining operations remain significantly threatened by the accumulation of methane (CH4) and carbon monoxide (CO): Methane poses an acute explosion risk, and carbon monoxide serves as a critical biomarker for spontaneous coal combustion. Consequently, rigorous real-time monitoring to ensure environmental safety is necessitated, which is based on superior gas sensor devices. Although various detection modalities exist, conventional methods are frequently constrained by environmental sensitivity and limitations regarding long-term sensor stability. This review provides a comprehensive analysis of recent advancements in chemiresistive gas sensors based on metal oxide (MO) semiconductor materials with low cost, high stability, high sensitivity, and easy preparation, which are engineered for the detection of methane and carbon monoxide in coal mining environments. This study examines the redox-sensing mechanisms of both n-type and p-type MO semiconductors, for which special attention is directed toward optimization strategies designed to overcome the high activation energy of methane and improve carbon monoxide response kinetics. Importantly, novel approaches to lower high operating temperatures and improve the selectivity of MO sensors under complex mine environments have been comprehensively discussed.