Materials

14 pages, 28158 KB

Open AccessArticle

Surface-Collision Analysis of Microscale-Confined ¹²⁹Xe in Pyrex Vapor Cells Based on Stem-Transport and Gradient Diffusion Dynamics

by Shangtao Jiang, Tengyue Wang, Xuyang Qiu and Heng Yuan

Materials 2026, 19(5), 956; https://doi.org/10.3390/ma19050956 (registering DOI) - 1 Mar 2026

Abstract

Surface collisions at Pyrex walls limit the spin coherence in nuclear magnetic resonance gyroscopes (NMRG) vapor cells, while the cavity–stem junction introduces geometry dependent exchange that perturbs the transverse spin relaxation time

T_{2}

of ¹²⁹Xe atoms. We combine

T_{2}

measurements [...] Read more.

Surface collisions at Pyrex walls limit the spin coherence in nuclear magnetic resonance gyroscopes (NMRG) vapor cells, while the cavity–stem junction introduces geometry dependent exchange that perturbs the transverse spin relaxation time

T_{2}

of ¹²⁹Xe atoms. We combine

T_{2}

measurements with Monte Carlo simulations of confined diffusion and surface collisions to decompose the relaxation of Xe atoms and derive a cavity–stem geometry correction for wall relaxation. A structural coupling factor (SCF) is introduced to compress stem length and aperture diameter into a dimensionless metric for diffusion-limited mixing, enabling prediction of the transverse relaxation rate versus geometry. Across eight simulated configurations, the model yields

R^{2} = 0.982

and agrees with experiments within 7–

9 %

, comparable to the measurement uncertainty (

\pm 0.015 s^{- 1}

). Using the validated framework, geometry optimization reduces the relaxation rate from

0.225

to

0.131 s^{- 1}

(a

41.8 %

improvement). This Pyrex surface-collisional analysis provides an in-situ,

T_{2}

-based route to compare effective surface depolarization across fabrication and surface-treatment protocols while accounting for cavity–stem coupling. Full article

(This article belongs to the Special Issue Advanced Materials for Electrical Engineering: Fabrication, Testing and Applications)

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18 pages, 6476 KB

Open AccessArticle

On the Adiabatic Shear Band Sensitivity of Extruded Ti-6Al-4V Alloy Under Dynamic Compression Along the Extrusion and Transverse Directions

by Chenxing Zheng, Weikang Fu, Tianyuan Gong, Yingqian Fu and Xinlu Yu

Materials 2026, 19(5), 955; https://doi.org/10.3390/ma19050955 (registering DOI) - 1 Mar 2026

Abstract

Adiabatic shear banding (ASB) is a critical failure mechanism in titanium alloys subjected to high-strain-rate deformation, and its initiation is strongly influenced by the initial crystallographic texture. The dynamic response and ASB sensitivity of extruded and annealed Ti-6Al-4V (TC4) alloy rods were investigated [...] Read more.

Adiabatic shear banding (ASB) is a critical failure mechanism in titanium alloys subjected to high-strain-rate deformation, and its initiation is strongly influenced by the initial crystallographic texture. The dynamic response and ASB sensitivity of extruded and annealed Ti-6Al-4V (TC4) alloy rods were investigated under dynamic compression of cubic specimens along the extrusion direction (ED) and the transverse direction (TD) at a strain rate of 2500 s⁻¹. Split Hopkinson pressure bar (SHPB) tests combined with digital image correlation (DIC) were employed to obtain the stress–strain response and the evolution of strain localization. A dislocation density-based crystal plasticity finite element model (CPFEM), incorporating the measured texture, was established to elucidate the correlation between texture and ASB behavior. The experimental results show that TD specimens exhibit a yield strength approximately 100 MPa higher than that of ED specimens, while both orientations display comparable post-yield hardening behavior. ASB initiation occurs earlier in TD (compressive strain ~0.13) than in ED (~0.23), indicating greater ASB sensitivity in the TD orientation. The CPFEM successfully reproduces the directional stress–strain responses and the observed localization morphology, enabling mechanistic interpretation in terms of slip activity and thermomechanical coupling. The simulations indicate that ED loading is dominated by prismatic ⟨a⟩ slip, resulting in lower flow stress and more dispersed strain localization. In contrast, TD loading is governed primarily by pyramidal ⟨c + a⟩ slip, leading to elevated flow stress and intensified localization. The higher ASB sensitivity in the TD orientation is therefore attributed to texture-controlled slip-mode partitioning, enhanced thermomechanical coupling, and a more concentrated crystallographic orientation distribution that facilitates intergranular slip transfer. These findings provide guidance for tailoring microtexture to mitigate dynamic failure in titanium alloys subjected to high-strain-rate loading. Full article

(This article belongs to the Section Metals and Alloys)

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19 pages, 2900 KB

Open AccessArticle

Densification and Mechanical Enhancement of Invasive South African Hardwoods: Prosopis glandulosa and Acacia mearnsii

by Matin Naghizadeh, Marthie E. Niemand, Ernst H. G. Langner, Aimin S. Sivanda and Karel G. von Eschwege

Materials 2026, 19(5), 954; https://doi.org/10.3390/ma19050954 (registering DOI) - 1 Mar 2026

Abstract

Wood used in construction varies in density, leading to differences in strength and rigidity. Wood densification has recently emerged as a promising technique to address these limitations and enhance material performance. This study explores the potential of two abundant and low-cost invasive hardwood [...] Read more.

Wood used in construction varies in density, leading to differences in strength and rigidity. Wood densification has recently emerged as a promising technique to address these limitations and enhance material performance. This study explores the potential of two abundant and low-cost invasive hardwood species in South Africa—Prosopis glandulosa (Honey Mesquite) and Acacia mearnsii (Black Wattle)—as sources for producing densified wood. A range of strengthening methods, including chemical, pressure, and heat treatments, were applied and compared. After partial delignification and hot pressing, sample thicknesses were reduced by 40% for Prosopis and 50% for Acacia, yielding substantial increases in flexural strength of 216% (22.61 MPa) for Prosopis and 334% (24.65 MPa) for Acacia. In addition to SEM anatomical imaging, analyses of lignosulphonate content, and thermogravimetric profiling, the study also evaluated several practical, carpentry-relevant mechanical properties. These included comparative tests for flexural and compressive strength, nailing and sanding performance, as well as assessments of water absorption, electrical resistivity, and flame-holding capacity. Full article

(This article belongs to the Special Issue Advances in Sustainable Construction and Building Materials (4th Edition))

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44 pages, 3959 KB

Open AccessReview

Duplex-Phase Fe-Mn-Al-C Low-Density Steels: A Review on Their Alloy Design, Processing, Mechanical and Application Performances

by Peng Chen, Yan Lin, Liu-Jiang Yue, Rong Chen, Yi Wang, Ting-Jun Zhang and Xiao-Wu Li

Materials 2026, 19(5), 953; https://doi.org/10.3390/ma19050953 (registering DOI) - 1 Mar 2026

Abstract

Duplex-phase low-density steels are attracting interest for lightweight structural applications, as reducing vehicle mass is an effective route to lower fuel consumption and emissions. This review summarizes recent progress in alloy design, processing, microstructure control, and performance of duplex-phase low-density steels. The roles [...] Read more.

Duplex-phase low-density steels are attracting interest for lightweight structural applications, as reducing vehicle mass is an effective route to lower fuel consumption and emissions. This review summarizes recent progress in alloy design, processing, microstructure control, and performance of duplex-phase low-density steels. The roles of major alloying elements are discussed in terms of phase stability and precipitation tendency, followed by an overview of typical processing routes from melting to hot and cold rolling and subsequent heat treatments used to tailor phase fractions and defect structures. Strengthening mechanisms are reviewed with emphasis on precipitation control, including the beneficial contribution of fine intragranular κ′ precipitates and the ductility penalty associated with coarse intergranular κ* films, as well as the use of B2-based particles for high specific strength. Deformation behavior is then discussed in terms of transformation-/twinning-induced plasticity (TRIP/TWIP), planar versus wavy slip, and strain partitioning between ferrite and austenite. Finally, key challenges are outlined, including quantitative interface-based mechanism description, gaps in service property data, stable industrial production and compositional uniformity, and the development of forming and welding windows for engineering implementation. Full article

(This article belongs to the Special Issue Advanced Steel Materials: Recrystallization, Phase Transformation and Microstructure Analysis (Second Edition))

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14 pages, 1413 KB

Open AccessArticle

Construction of Atomically Thin Boron Films on Si Heterojunctions Using A First Principles Approach

by Piet Xiaowen Fang, Stoyan Nihtianov and Changming Fang

Materials 2026, 19(5), 952; https://doi.org/10.3390/ma19050952 (registering DOI) - 28 Feb 2026

Abstract

Deposition of amorphous boron (a-B) onto Si substrates via chemical decomposition of B₂H₆ molecules produces a-B/Si, heterojunctions which are the core parts of photodetectors used in vacuum ultraviolet (VUV) and potentially in extreme ultraviolet (EUV) lithography. However, fundamental questions regarding [...] Read more.

Deposition of amorphous boron (a-B) onto Si substrates via chemical decomposition of B₂H₆ molecules produces a-B/Si, heterojunctions which are the core parts of photodetectors used in vacuum ultraviolet (VUV) and potentially in extreme ultraviolet (EUV) lithography. However, fundamental questions regarding the limit on the thickness of the deposited a-B thin films and the intrinsic electronic nature of the B atoms adjacent to the Si substrate remain unanswered. Here we investigated the local structural and electronic properties of atomic-thin a-B layers at the Si{001} substrates using ab initio molecular dynamics (AIMD) techniques. The investigation revealed a rich variety of local chemical bonding and consequently interfacial electronic properties. For thin a-B layer(s)/Si systems, most of the a-B atoms at the interface formed (-B-Si-B-Si-) chains on the Si{001} surface. These B atoms were found to occupy the positions of the missing Si atoms and were bonded to the surficial Si atoms. The surficial Si atoms predominantly have two B neighbors. Localized defect states at the Fermi level for the interfacial Si and B atoms were found in the pseudo-gap. These states have a major influence on the electrical properties of the device. The predicted minimum thickness of the a-B films is about 1 to 2 nm, a useful metric for the manufacturing of a-B/Si devices. The information obtained here further helps us to understand the working mechanisms of a-B/Si interfaces for photon detection and constructing new core devices for potential applications in the field of metal/semiconductor heterojunctions for photon detection, photovoltaics, Schottky diodes and semiconductor devices. Full article

(This article belongs to the Section Thin Films and Interfaces)

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23 pages, 5718 KB

Open AccessArticle

Strut Size-Dependent Compressive Behavior and Failure Mechanisms of Laser-Based Powder Bed Fusion NiTi Octahedral Porous Scaffolds

by Ning Zhang, Wangwei Zhan, Hongsen Liu, Chuanhui Huang, Guangqing Zhang, Yinghong Zhang and Jinguo Ge

Materials 2026, 19(5), 951; https://doi.org/10.3390/ma19050951 (registering DOI) - 28 Feb 2026

Abstract

Nickel-titanium (NiTi) alloys are attractive for functional and biomedical applications due to their shape memory effect, superelasticity, and favorable corrosion resistance and biocompatibility. In this work, the influence of strut size on the compressive response of laser-based powder bed fusion (PBF-LB/M) fabricated NiTi [...] Read more.

Nickel-titanium (NiTi) alloys are attractive for functional and biomedical applications due to their shape memory effect, superelasticity, and favorable corrosion resistance and biocompatibility. In this work, the influence of strut size on the compressive response of laser-based powder bed fusion (PBF-LB/M) fabricated NiTi ortho-octahedral porous scaffolds was systematically investigated using combined experiments and finite element simulations. Four scaffold designs with identical unit-cell size (2 mm) but different strut sizes (280, 320, 360, and 400 μm) were fabricated, and their forming quality and deformation behaviors were examined. The as-built scaffolds exhibited high geometric fidelity to the CAD models and stable manufacturability across the investigated parameter range. Quasi-static compression tests revealed a typical three-stage response (linear-elastic regime, plateau/collapse regime, and densification), with both elastic modulus and compressive strength increasing markedly with strut size. Specifically, the modulus increased from 1.17 to 4.28 GPa and the compressive strength increased from 155 to 564 MPa as the strut size increased from 280 to 400 μm. A pronounced oscillatory plateau was observed for the 280 μm scaffolds, indicating progressive layer-by-layer collapse, whereas larger struts promoted a shear-band-dominated failure mode characterized by an approximately 45° fracture zone. Explicit quasi-static simulations reproduced the experimentally observed collapse sequence and demonstrated that stress preferentially concentrates at nodal junctions, with load transfer dominated by struts aligned with the loading direction. The agreement between experiments and simulations confirms the predictive capability of the proposed modeling framework and provides mechanistic insights into geometry-controlled failure. These findings establish a structure-property-failure relationship for PBF-LB/M-fabricated NiTi octahedral scaffolds and offer practical guidance for tailoring stiffness, strength, and collapse mode through strut-size design. Full article

(This article belongs to the Special Issue Advances in 3D Printing Technologies: Design, Manufacturing, and Applications)

35 pages, 879 KB

Open AccessSystematic Review

Modifications of Resorbable Root Canal Filling Materials for Primary Teeth: A Systematic Review

by Anna Błaszczyk-Pośpiech, Sylwia Kiryk, Natalia Nawrot, Julia Kensy, Jan Kiryk, Agnieszka Kotela, Magdalena Wawrzyńska, Maria Szymonowicz, Jacek Matys and Maciej Dobrzyński

Materials 2026, 19(5), 950; https://doi.org/10.3390/ma19050950 (registering DOI) - 28 Feb 2026

Abstract

Objective: This systematic review aimed to evaluate material-based modifications of resorbable root canal filling materials for primary teeth, assessing how compositional changes—including bioactive additives, antimicrobial agents, and alternative base matrices—influence antimicrobial performance. Methods: A systematic search of PubMed, Scopus, Web of Science [...] Read more.

Objective: This systematic review aimed to evaluate material-based modifications of resorbable root canal filling materials for primary teeth, assessing how compositional changes—including bioactive additives, antimicrobial agents, and alternative base matrices—influence antimicrobial performance. Methods: A systematic search of PubMed, Scopus, Web of Science (WoS), and Embase was performed in October 2025. Search terms included (primary teeth OR deciduous teeth) AND (root canal filling materials OR root canal filling OR canal obturation) AND (antibacterial agents OR antibacterial OR antimicrobial). Study selection adhered to PRISMA 2020 standards and was systematically organized through the PICO framework. From 199 identified records, 18 studies met the eligibility criteria. Results: Most studies evaluated modified zinc oxide-based materials. Additives such as propolis, Morinda citrifolia extract, Aloe vera, and olive oil enhanced antimicrobial activity or improved clinical and radiographic outcomes compared with conventional zinc oxide–eugenol. Triclosan-containing formulations consistently demonstrated strong antibacterial effects. In contrast, chlorhexidine yielded variable results, with some calcium hydroxide–based pastes showing superior performance in its absence. Antibiotic-enriched materials exhibited high antimicrobial efficacy; however, several studies raised concerns regarding the potential development of bacterial resistance. Conclusion: Most of the introduced modifications of resorbable root canal filling materials for primary teeth enhance antimicrobial activity and their physicochemical properties in vitro. Clinical evidence is limited and heterogeneous, and therefore, its superiority over conventional materials cannot be definitively determined. Further long-term, randomized clinical trials on large patient groups, evaluating the same modifications, are needed to confirm the effects observed in laboratory studies. Full article

(This article belongs to the Special Issue Recent Research in Restorative Dental Materials (2nd Edition))

16 pages, 1107 KB

Open AccessReview

Coal Gangue Recycling in Construction Materials: Strategies for Environmental Risk Mitigation via Heavy Metal Immobilization and Resource Utilization

by Yang Xue, Xiaoming Liu, Xuchao Wang and Wei Zhang

Materials 2026, 19(5), 949; https://doi.org/10.3390/ma19050949 (registering DOI) - 28 Feb 2026

Abstract

Coal gangue represents the predominant solid waste in the coal industry and poses significant risks to both the ecological environment and human health. It has been demonstrated that recycling it in building materials effectively reduces stockpiling, mitigates environmental harm, and minimizes heavy metal [...] Read more.

Coal gangue represents the predominant solid waste in the coal industry and poses significant risks to both the ecological environment and human health. It has been demonstrated that recycling it in building materials effectively reduces stockpiling, mitigates environmental harm, and minimizes heavy metal leaching. However, a comprehensive review systematically focusing on the recycling of coal gangue and the behavior of its associated heavy metals in building materials is still lacking. This work introduces the physicochemical properties and environmental hazards of coal gangue, including spontaneous combustion, land occupation, and pollution risks. It also summarizes the leaching patterns, speciation, and immobilization mechanisms of heavy metals such as Cr, Cu, and Pb in gangue-based building materials, and reviews adsorption behaviors, solidification pathways, and microstructural interactions at the molecular scale. Despite ongoing efforts, over five billion tons of coal gangue remain accumulated in China, with secondary pollution from heavy metals continuing to pose serious concerns. To address these challenges, recommendations are proposed for establishing standardized leaching evaluation methods, and a novel approach for transitioning from heavy metal solidification to active utilization is introduced. This review aims to provide strategic direction for the green and sustainable recycling of coal gangue. Full article

(This article belongs to the Special Issue Testing of Materials and Elements in Civil Engineering (5th Edition))

20 pages, 3664 KB

Open AccessCommunication

Interpretable Machine Learning with Prediction Uncertainty Quantification for d₃₃ in (K_0.5Na_0.5) NbO₃-Based Lead-Free Piezoelectric Ceramics

by Xiaohui Yuan, Yalong Liang, Bang Lu, Gaochao Zhao and Pei Li

Materials 2026, 19(5), 948; https://doi.org/10.3390/ma19050948 (registering DOI) - 28 Feb 2026

Abstract

The accelerated discovery of high-performance lead-free piezoelectric ceramics is hindered by the vast compositional space and the limited interpretability of conventional machine learning (ML) models. Here, we propose a physics-informed and interpretable ML framework with integrated uncertainty quantification to predict and understand the [...] Read more.

The accelerated discovery of high-performance lead-free piezoelectric ceramics is hindered by the vast compositional space and the limited interpretability of conventional machine learning (ML) models. Here, we propose a physics-informed and interpretable ML framework with integrated uncertainty quantification to predict and understand the piezoelectric coefficient d₃₃ of (K_0.5Na_0.5) NbO₃ (KNN)-based ceramics. A curated dataset of 1113 experimental samples is used to construct 65 descriptors by decoupling A-site and B-site ionic contributions. Pearson correlation analysis reduces these to an optimized 11-dimensional feature set for training deep neural networks, Wide & Deep networks, and residual networks. A Bayesian neural network further provides predictive uncertainty, which quantitatively reflects the confidence of machine-learning-based d₃₃ predictions rather than experimental measurement uncertainty. To achieve physical interpretability, SHapley Additive exPlanations (SHAP) are combined with the Sure Independence Screening and Sparsifying Operator (SISSO) to derive a compact analytical descriptor revealing that sintering temperature, B-site electronic anisotropy, and A-site ionic displacement jointly govern d₃₃. The proposed framework achieves high accuracy (R² ≈ 0.81) while offering transparent design rules for next-generation lead-free piezoelectrics. Full article

(This article belongs to the Special Issue The Parameters of Advanced Materials)

10 pages, 2192 KB

Open AccessCommunication

From Polar Clusters to Active Nematics: Experimental Signatures of Swarming Dynamics in Bacterial Monolayers

by Xiao Chen and Yaner Yan

Materials 2026, 19(5), 947; https://doi.org/10.3390/ma19050947 (registering DOI) - 28 Feb 2026

Abstract

Bacterial swarms provide a tractable natural model of active matter, where their dynamics illuminate the principles of collective behavior and self-organization phenomena. In particular, the mechanistic and dynamical features of monolayer swarming are critical in driving the transition to multilayer structures at the [...] Read more.

Bacterial swarms provide a tractable natural model of active matter, where their dynamics illuminate the principles of collective behavior and self-organization phenomena. In particular, the mechanistic and dynamical features of monolayer swarming are critical in driving the transition to multilayer structures at the onset of biofilm formation. Here, we investigate monolayer swarms of Serratia marcescens across varying cell body aspect ratios and area fractions. The results show that at intermediate-to-low densities, bacteria form local dynamic clusters, with the distribution of cluster sizes determined by aspect ratio and area fraction. At higher densities, elongated bacteria align into active nematic states with half-integer topological defects, which point to a potential nucleation mechanism for multilayer formation. These findings provide new physical insights into how cellular morphology and density govern bacterial swarming dynamics and drive the early transition from monolayer swarming to multilayered biofilm development. Full article

(This article belongs to the Section Soft Matter)

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15 pages, 2423 KB

Open AccessArticle

Effects of Platelet TiB₂ on the Formation and Mechanical Properties of (Zr,Ti)B₂ Ceramics Prepared by Spark Plasma Sintering

by Shaolei Song, Peiqi Jiang, Yuanyuan Liu, Lei Lei and Yan Li

Materials 2026, 19(5), 946; https://doi.org/10.3390/ma19050946 (registering DOI) - 28 Feb 2026

Abstract

(Zr,Ti)B₂ ceramics with enhanced hardness and fracture toughness were prepared by spark plasma sintering using platelet TiB₂ and irregular ZrB₂ as starting powders. The effects of sintering temperature (1700–1900 °C) and platelet TiB₂ content (0–30 wt.%) on the sinterability, [...] Read more.

(Zr,Ti)B₂ ceramics with enhanced hardness and fracture toughness were prepared by spark plasma sintering using platelet TiB₂ and irregular ZrB₂ as starting powders. The effects of sintering temperature (1700–1900 °C) and platelet TiB₂ content (0–30 wt.%) on the sinterability, phase composition, microstructure, and mechanical properties of the (Zr,Ti)B₂ ceramics were investigated. With increasing sintering temperature, the relative density of the solid solution increased from 89.9 ± 0.5% at 1700 °C to 97.7 ± 0.4% at 1800 °C, followed by no significant change upon further temperature elevation; however, the relative density showed an initial increase and subsequent decrease with increasing TiB₂ content. Under optimized parameters (1800 °C, 3 min, 50 MPa, with a TiB₂ content of 30 wt.%), (Zr,Ti)B₂ ceramics achieve a maximum hardness of 24.9 ± 1.0 GPa, a fracture toughness of 5.0 ± 0.3 MPa·m^1/2, and a relative density of 96.5 ± 0.5%. The high content of platelet TiB₂ refined the (Zr,Ti)B₂ grain size, reducing the D50 by 25.8% to 1.70 μm compared to the 20 wt.% content. This study provides a novel perspective for the design and preparation of high-performance ceramics. Full article

(This article belongs to the Section Advanced Composites)

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13 pages, 7268 KB

Open AccessArticle

Study on Microstructural Evolution, Strengthening and Deformation Mechanisms of a CoCrNi-Based Medium-Entropy Alloy with Different Annealing Times

by Pu Zhang, Chunjiang Zhao, Ruirui Wang, Yongping Liu and Yongan Chen

Materials 2026, 19(5), 945; https://doi.org/10.3390/ma19050945 (registering DOI) - 28 Feb 2026

Abstract

This study systematically investigates the influence of annealing time on the microstructure and mechanical properties of a (CoCrNi)_93.5Al₃Ti₃C_0.5 medium-entropy alloy. Following hot-rolling, the alloy was subjected to annealing treatments at 900 °C for 10 min (HA900-10) [...] Read more.

This study systematically investigates the influence of annealing time on the microstructure and mechanical properties of a (CoCrNi)_93.5Al₃Ti₃C_0.5 medium-entropy alloy. Following hot-rolling, the alloy was subjected to annealing treatments at 900 °C for 10 min (HA900-10) and 60 min (HA900-60). Microstructural characterization revealed that both alloys contained three types of precipitates: intergranular M₂₃C₆ and MC-type carbides, as well as γ′ phase. The HA900-10 specimen exhibited a low degree of recrystallization, whereas prolonged annealing promoted partial recrystallization, leading to the formation of a slightly heterogeneous structure (HA900-60). Additionally, the extended annealing facilitated the intragranular precipitation of nanoscale γ′ phase. Room-temperature tensile tests demonstrated that the HA900-10 and HA900-60 specimens achieved yield strengths of 1276 MPa and 1202 MPa, with total elongations reaching 26% and 28%, respectively. Quantitative strengthening analysis indicated that the strength of HA900-10 primarily originated from dislocation and grain boundary strengthening. For HA900-60, an additional significant contribution arose from the dislocation shearing mechanism induced by the intragranular γ′ precipitates. Analysis of the deformation mechanisms revealed that planar slip, assisted by the formation of stacking faults, dominated the room-temperature deformation, thereby ensuring sustained work-hardening capacity. This research provides a theoretical foundation for tailoring the microstructure and properties of multi-phase medium-entropy alloys through annealing process control. Full article

(This article belongs to the Special Issue Advanced Metal Alloys/Metal Matrix Composites for Automobile and Aerospace Engineering)

15 pages, 10766 KB

Open AccessArticle

The Combustion Behaviors and Flame-Retardant Mechanisms of Cu Coating as Protection for Titanium Alloys

by Jianjun Li, Shujing Wang, Pengfei Jin, Cheng Zhang and Congzheng Wang

Materials 2026, 19(5), 944; https://doi.org/10.3390/ma19050944 (registering DOI) - 28 Feb 2026

Abstract

This study investigates the influence of highly thermally conductive coatings on the combustion thresholds of a TC4 titanium alloy, aiming to address the flame-retardant protection requirements for titanium alloys. The findings reveal that, in terms of combustion thermodynamics, as the thickness of the [...] Read more.

This study investigates the influence of highly thermally conductive coatings on the combustion thresholds of a TC4 titanium alloy, aiming to address the flame-retardant protection requirements for titanium alloys. The findings reveal that, in terms of combustion thermodynamics, as the thickness of the copper coating increases from 100 μm to 300 μm, the critical ignition power rises by 125–170 W compared to the substrate (235 W). Additionally, the critical oxygen pressure increases by 0.21–0.51 MPa relative to the substrate (0.03 MPa), and the ignition temperature is elevated by 119–184 K above that of the substrate (848.80 K). This phenomenon is primarily due to the high thermal diffusivity of copper. Increased coating thickness further enhances heat dissipation, significantly suppressing the local heat accumulation rate and thereby improving the coating’s combustion resistance. In terms of combustion kinetics, under fixed experimental conditions, the copper coating extends the ignition delay time by 0.670 s and reduces the combustion propagation rate by approximately 21% compared to the substrate (26.772 mm/s). The post-combustion microstructural analysis indicates that during the reaction process, the copper coating forms a TiCu₂Al-type intermetallic compound (Ti_0.5Al_0.5)Cu. This structure exerts an “anchoring” effect on the substrate material, decreases the Ti/O reaction efficiency, and consequently achieves effective flame retardancy. These findings inform the subsequent design and optimization of copper-based abradable coatings with enhanced combustion resistance. Full article

(This article belongs to the Topic Advanced Manufacturing and Surface Technology, 2nd Edition)

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17 pages, 4757 KB

Open AccessArticle

Hydrogenation and Entanglement Effects on Tensile Properties and Energy Absorption of Entwined Coiled Carbon Nanotubes: A Molecular Dynamics Study

by Fenghua Nie, Xing Su and Hang Lin

Materials 2026, 19(5), 943; https://doi.org/10.3390/ma19050943 (registering DOI) - 28 Feb 2026

Abstract

Coiled carbon nanotubes and their entwined derivatives have attracted attention for their excellent mechanical properties and potential applications. Hydrogenation is an effective way to modify the mechanical response of CCNTs, but its effect on the tensile performance and energy absorption of ECCNTs remains [...] Read more.

Coiled carbon nanotubes and their entwined derivatives have attracted attention for their excellent mechanical properties and potential applications. Hydrogenation is an effective way to modify the mechanical response of CCNTs, but its effect on the tensile performance and energy absorption of ECCNTs remains unclear. In this study, molecular dynamics simulations are used to systematically investigate the regulatory effects of hydrogenation and entanglement on the tensile properties and energy absorption capacity of CCNTs and ECCNTs. Different hydrogenation degrees and structural configurations are designed for comparative analysis. Results show that hydrogenation exerts a dual regulatory effect on single CCNTs: moderate hydrogenation enhances tensile strength and total energy absorption, while excessive hydrogenation leads to brittleness, reduced ductility, and impaired energy dissipation. Entanglement significantly improves the tensile load-bearing capacity and energy absorption of CCNTs, with ECCNTs showing 1.5–2.0 times higher spring constants than single CCNTs. Among the ECCNT models, ECCNT2 achieves an optimal balance between tensile stiffness, ductility, and energy absorption efficiency. This study clarifies the mechanistic roles of hydrogenation and entanglement, providing valuable guidance for the rational design of high-performance CCNT-based structural and functional nanomaterials. Full article

(This article belongs to the Special Issue Electronic, Optical, and Structural Properties of Carbon Nanotubes)

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30 pages, 1755 KB

Open AccessArticle

Shrinkage Crack Patterns of Rectangular Timber Beams and Their Influence on Load-Bearing Capacity

by Xiaoyi Hu, Jiawei Wu, Xuwei He, Lu Li, Wei Guo and Jingjing Yang

Materials 2026, 19(5), 942; https://doi.org/10.3390/ma19050942 (registering DOI) - 28 Feb 2026

Abstract

This study used finite element simulation and theoretical analysis to predict the crack distribution patterns that may occur during the shrinkage cracking process of rectangular timber beams. Based on the predictions, experimental specimens with six typical crack distribution patterns (I–VI) were designed. Subsequently, [...] Read more.

This study used finite element simulation and theoretical analysis to predict the crack distribution patterns that may occur during the shrinkage cracking process of rectangular timber beams. Based on the predictions, experimental specimens with six typical crack distribution patterns (I–VI) were designed. Subsequently, a four-point bending test method was employed to conduct large-sample size fracture tests on a total of 1200small-sized Pinus sylvestris var. mongolica specimens, quantifying the effects of the crack depth, location, and distribution patterns on the specimens’ load-bearing capacity. The results indicate that when multiple cracks exist in a timber beam, their collective effect is not a simple superposition of individual cracks but a spatial distribution coupling effect. Both the depth and location of the cracks play crucial roles in their interaction. This study introduces three coefficients for evaluating the influence of cracks on timber beams, namely the load-bearing capacity coefficient (R), the decline ratio of load-bearing capacity (D), and the comprehensive crack-influence coefficient (β), which can effectively quantitatively evaluate crack damage effects. The framework established in this study, which links shrinkage crack characteristics with the load-bearing capacity of timber beams, along with the experimental data provided, can serve as a reference for the safety evaluation and scientific maintenance of historical timber components and modern timber structures with shrinkage cracks. Full article

(This article belongs to the Section Biomaterials)

18 pages, 8398 KB

Open AccessArticle

A Green P–N–Al Synergistic System for Eco-Friendly Flame-Retardant Polystyrene

by Zhunzhun Li, Qimei Zhang, Jian Cui and Yehai Yan

Materials 2026, 19(5), 941; https://doi.org/10.3390/ma19050941 (registering DOI) - 28 Feb 2026

Abstract

Polystyrene (PS) is widely used yet highly flammable, and developing halogen-free flame retardants that ensure both high fire safety and mechanical performance remains a challenge. A green intumescent system comprising ammonium dihydrogen phosphate (ADP) and phytic acid–triethylenetetramine (PA–TETA) was incorporated into PS powder [...] Read more.

Polystyrene (PS) is widely used yet highly flammable, and developing halogen-free flame retardants that ensure both high fire safety and mechanical performance remains a challenge. A green intumescent system comprising ammonium dihydrogen phosphate (ADP) and phytic acid–triethylenetetramine (PA–TETA) was incorporated into PS powder via sequential solution grinding and hot pressing. The optimal formulation, PS/10ADP/15PA–TETA, achieved a limiting oxygen index of 28.5% with a UL-94 V-0 rating, and reduced the peak heat release rate and total heat release by 73.8% and 46.2%, respectively, while retaining 78.4% of the tensile strength of neat PS. The ADP/PA–TETA system operates via a cooperative condensed-phase charring and gas-phase dilution mechanism, achieving superior flame retardancy in PS composites. This work provides an effective and eco-friendly strategy for fabricating high-performance PS composites with balanced flame retardancy and mechanical properties. Full article

(This article belongs to the Special Issue Design and Development of Flame-Retardant Functional Materials)

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12 pages, 3959 KB

Open AccessArticle

Effect of Prior Austenite Grain Size on the Hydrogen Diffusion Behavior in 30MnB5 Steel

by Hyunbin Nam, Minseok Seo and Cheolho Park

Materials 2026, 19(5), 940; https://doi.org/10.3390/ma19050940 (registering DOI) - 28 Feb 2026

Abstract

In this study, we investigated the effect of heat treatment-induced grain size on the hydrogen embrittlement (HE) resistance of 30MnB5 steel, focusing particularly on the variation in prior austenite grain (PAG) size. As the heat treatment time increased, the PAGs coarsened, leading the [...] Read more.

In this study, we investigated the effect of heat treatment-induced grain size on the hydrogen embrittlement (HE) resistance of 30MnB5 steel, focusing particularly on the variation in prior austenite grain (PAG) size. As the heat treatment time increased, the PAGs coarsened, leading the martensite packets, blocks, and lath sizes to also coarsen. As the microstructure became more refined, the boundary density of the packet–block–lath structure increased along with a significant increase in the low-angle grain boundary (LAGB) fraction. The microstructure refinement accelerated the initial permeation rate of hydrogen, while the high density of LAGBs and trap sites effectively suppressed its long-term diffusion/localization. The slow strain rate tensile test confirmed that the tensile strength and elongation of 30MnB5 steel in a hydrogen environment were lower than those in air, indicating HE. Furthermore, the results showed that the HE sensitivity decreased in the fine microstructure condition, as evidenced by the smaller reduction in elongation compared to the coarse microstructure. The study results will enhance the understanding of hydrogen-induced degradation in hot-stamped automotive steels and offer fundamental insights for optimizing heat treatment strategies applied to 30MnB5 steel for mitigating HE. Full article

(This article belongs to the Special Issue Welding and Joining Technologies for Advanced Structural Alloys and Multifunctional Materials)

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20 pages, 5057 KB

Open AccessArticle

Stepwise Recycling of Red Mud Through Electrochemical Activation for Enhanced Cementitious Performance and Magnetically Separable Iron Recovery

by Pei Tang, Meiyi Zhu and Pengjie Rong

Materials 2026, 19(5), 939; https://doi.org/10.3390/ma19050939 (registering DOI) - 28 Feb 2026

Abstract

Red mud, a major solid waste from the alumina industry, suffers from an extremely low utilization rate due to its high alkalinity, complex chemistry, and particularly low cementitious activity, which drives the need for novel activation strategies. This study presents a new method [...] Read more.

Red mud, a major solid waste from the alumina industry, suffers from an extremely low utilization rate due to its high alkalinity, complex chemistry, and particularly low cementitious activity, which drives the need for novel activation strategies. This study presents a new method for red mud activation through electrochemical treatment, which simultaneously enables iron recovery as a valuable by-product. The electrochemical activation was systematically investigated by performing experiments in alkaline, neutral, and acidic electrolytes. The alkaline system showed a pronounced enhancing effect on the electrochemical process. Under alkaline conditions, the average Faradaic efficiency exceeded 80%. The electrochemical treatment modified the microstructure of red mud particles and transformed iron oxides into magnetic species, which could be effectively separated via magnetic separation. More importantly, this activation process significantly enhanced the cementitious activity of the treated red mud by removing iron oxide that encapsulates reactive aluminosilicate phases and increasing surface reactivity. When used as a supplementary cementitious material with ordinary Portland cement and gypsum, the electrochemically activated red mud demonstrated remarkably improved mechanical properties, with 28-day compressive strength reaching up to 69 MPa. Characterization analysis revealed that the electrochemical activation promoted the formation of key hydration products, including C-S-H gel (formed through both OPC hydration and pozzolanic reactions between activated red mud and portlandite), ettringite, and portlandite. This work provides a green and low-carbon pathway for the stepwise utilization of red mud through activation and resource recovery. Full article

(This article belongs to the Section Construction and Building Materials)

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26 pages, 23897 KB

Open AccessArticle

Stress–Strain and Dimension Evolution of Wind Turbine Bearing Ring with Non-Standard Section During Hot Bulging Process

by Ruijie Gu, Yutong Fu, Ziyang Shang, Zhuangya Zhang, Shan Lan, Tongxun Wang, Qiang Wang and Liaoyuan Chen

Materials 2026, 19(5), 938; https://doi.org/10.3390/ma19050938 (registering DOI) - 28 Feb 2026

Abstract

As wind turbines trend toward larger sizes, higher rotational speeds, and extended service lives, higher demands are emerging for the dimensional accuracy, mechanical properties, and service reliability of the main shaft bearings. The hot bulging process is a critical process in bearing ring [...] Read more.

As wind turbines trend toward larger sizes, higher rotational speeds, and extended service lives, higher demands are emerging for the dimensional accuracy, mechanical properties, and service reliability of the main shaft bearings. The hot bulging process is a critical process in bearing ring manufacturing. The stress–strain and dimensional evolution during the hot bulging process are crucial for the fatigue life and dimensional accuracy of rings with non-circular cross-sections. Therefore, based on the residual stress field from rolling as an initial condition, this paper established a coupled finite element model for the entire rolling-to-bulging process of GCr15SiMn bearing steel rings and verified the accuracy of the model. A stepwise rotation hot bulging process was innovatively designed. The stresses, strains, and deformation rates of the rings were thoroughly evaluated at different steps of the bulging process. Additionally, the effect of the bulge amount on the stress–strain uniformity and dimensional accuracy of the fabricated rings was also evaluated. Results indicate that based on the stepwise rotation hot bulging process conducted at 870–930 °C, when the first-step bulging amount is 1.50 mm, the secondary and third-step amounts are both 0.50 mm, and the bulging speed is 1.00 mm/s, while the roundness error of ring #3 stabilizes within 0.28–0.35 mm. The standard deviation of the axial equivalent strain was decreased by 92%, and the stress peak was also decreased by 39%. Above all, the stepwise rotation hot bulging process is an effective approach to improve the distribution uniformity of the stress–strain and the dimensional consistency of the bearing rings. This paper provides theoretical foundations and process guidance for the precision forming of large wind turbine bearing rings with non-standard sections. Full article

(This article belongs to the Section Materials Simulation and Design)

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