Materials

13 pages, 3770 KiB

Open AccessArticle

Ductility Control via Nano-Precipitation at Grain Boundaries in Ti-Zr-Hf-Nb-Ta Multi-Principal Element Alloys

by Jiaying Li, Huibin Ke, Benpeng Wang, Liang Wang and Yunfei Xue

Materials 2025, 18(7), 1463; https://doi.org/10.3390/ma18071463 (registering DOI) - 25 Mar 2025

The formation of nano-sized Hf₂Fe precipitates at grain boundaries through Fe micro-alloying enhances the strength of Ti-Zr-Hf-Nb-Ta multi-principal element alloys (MPEAs), but this improvement comes at the cost of reduced ductility. Aging at 500 °C for just 30 min resulted in [...] Read more.

The formation of nano-sized Hf₂Fe precipitates at grain boundaries through Fe micro-alloying enhances the strength of Ti-Zr-Hf-Nb-Ta multi-principal element alloys (MPEAs), but this improvement comes at the cost of reduced ductility. Aging at 500 °C for just 30 min resulted in a marked reduction in elongation, from 17.5% to 7.5%. This decline is attributed to lattice mismatch between the precipitates and the matrix, as well as increased stacking stress at the grain boundaries. By adjusting the Fe composition and heat treatment parameters, the quantity of Hf₂Fe at the grain boundaries of (TiZrHfNbTa)_100−xFe_x alloy was effectively controlled, achieving a balanced combination of strength of 1037 MPa and elongation of 14%. Furthermore, this method enabled ductility modulation over a wide range, with elongation varying from 2.65% to 19% while maintaining alloy strength between 955 and 1081 MPa, providing valuable insights for tailoring these alloys to diverse application requirements. The precipitation thermodynamics of the (TiZrHfNbTa)_100−xFe_x alloy was also investigated using the CALPHAD method, with thermodynamic calculations validated against experimental results, laying a foundation for more in-depth kinetic study of nano-size precipitates in these alloys. Additionally, the relationships between thermodynamics, precipitates evolution, and mechanical properties were discussed. Full article

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34 pages, 1772 KiB

Open AccessArticle

On the Mechanical Performance of an L-PBF 316l Part Using the Performance-Line Instrumented Indentation Test (PL-IIT)

by Giovanni Maizza, Faisal Hafeez, Alessandra Varone and Roberto Montanari

Materials 2025, 18(7), 1462; https://doi.org/10.3390/ma18071462 (registering DOI) - 25 Mar 2025

Abstract

While L-PBF research continuously expands technologically towards more complex-shaped components and effective scanning strategies, the customization of the mechanical performance of these components to specific applications is still challenging. The presence of high process-induced residual stress levels frequently makes the current (standard) mechanical [...] Read more.

While L-PBF research continuously expands technologically towards more complex-shaped components and effective scanning strategies, the customization of the mechanical performance of these components to specific applications is still challenging. The presence of high process-induced residual stress levels frequently makes the current (standard) mechanical testing procedures ineffective or even inappropriate. The current engineering design principles cannot be applied to L-PBF components as the available mechanical properties are apparent (i.e., space and residual stress dependent properties). It is the aim of this work to overcome the aforementioned limitations by presenting a comprehensive methodology that can be used to determine the mechanical performance of an L-PBF 316L deposit along (five) pre-specified directions, denoted as performance lines (PLs), and in six special key regions, denoted as performance zones (PZs), through the nanoindentation test (PL-nIIT). The PLs determine the gradients of the indentation properties across the deposit, while the PZs exhibit the orientation-dependent mechanical performance in a specified number of regions of the deposit. The latter can be used for benchmarking, mechanical design, or performance customization. The frequently resorted to indentation modulus and hardness have thus been complemented with a new indentation size effect-free property (i.e., the loading stiffness rate, LSR) to help discriminate the presence of residual stress at different depths in the given deposit. A decreasing mild compressive residual stress was determined along the build direction of the deposit as revealed by the decreasing values of the relative LSR, H_IT, and E_IT (from the root to the top dome, i.e., 47.8 to 43.4, 2.57 to 2.49, and 216 to 202 GPa, respectively). Full article

(This article belongs to the Special Issue Additive Manufacturing of Metallic Alloys and Composite Materials—Process, Structure, Properties and Part Performance: Experimental and Computer Methods)

35 pages, 5707 KiB

Open AccessArticle

Comparative Analysis of the Dimensional Accuracy and Surface Characteristics of Gears Manufactured Using the 3D Printing (DMLS) Technique from 1.2709 Steel

by Jacek Sawicki, Wojciech Stachurski, Piotr Kuryło, Edward Tertel, Bartłomiej Januszewicz, Emila Brancewicz-Steinmetz and Aleksandra Bednarek

Materials 2025, 18(7), 1461; https://doi.org/10.3390/ma18071461 (registering DOI) - 25 Mar 2025

Abstract

This article provides a comparative analysis of the dimensional accuracy and post-surface characteristics of gears produced by the 3D printing technique Direct Metal Laser Sintering (DMLS) from 1.2709 steel immediately after printing and after grinding and grinding treatment. The following tests were performed [...] Read more.

This article provides a comparative analysis of the dimensional accuracy and post-surface characteristics of gears produced by the 3D printing technique Direct Metal Laser Sintering (DMLS) from 1.2709 steel immediately after printing and after grinding and grinding treatment. The following tests were performed on the fabricated samples: metallography, hardness measurement, self-stress, surface roughness, and the gears’ shape were dimensioned and measured. The results show that post-processing influences the distribution of residual stress and the printed model’s hardness. The results show that heat treatment results in clear directionality marks and micropores, increasing the material’s hardness to 54.3 HRC ± 0.6 HRC, indicating effective strengthening. Grinding significantly improved the holes’ accuracy, changed the compressive intrinsic stresses to a tensile state, and reduced radial runout, improving gear geometries. In addition, it was noted that different results were obtained for roughness parameters depending on the gear tooth tested. Full article

(This article belongs to the Section Manufacturing Processes and Systems)

14 pages, 9297 KiB

Open AccessArticle

The Investigation of Ni-Doped SrFeO_3−δ Perovskite for a Symmetrical Electrode in Proton Ceramic Fuel Cells

by Jiajia Cui, Yueyue Sun, Chaofan Yin, Hao Wang, Zhengrong Liu, Zilin Zhou, Kai Wu and Jun Zhou

Materials 2025, 18(7), 1460; https://doi.org/10.3390/ma18071460 (registering DOI) - 25 Mar 2025

Abstract

The development of symmetrical solid oxide fuel cells with identical cathode and anode is beneficial for thermal matching and reducing the cost. Herein, proton-conducting electrolyte and novel high catalytic activity electrode material for symmetrical solid oxide fuel cells are proposed. Ni-doping at the [...] Read more.

The development of symmetrical solid oxide fuel cells with identical cathode and anode is beneficial for thermal matching and reducing the cost. Herein, proton-conducting electrolyte and novel high catalytic activity electrode material for symmetrical solid oxide fuel cells are proposed. Ni-doping at the B-site of (Sr_0.8Ce_0.2)_0.95FeO_3−δ (SCF) indicates reduced cell edge lengths, cell volume, and a more porous honeycomb structure. The B-site elements in oxide tend to have a high oxidation state via Ni-doping. Simple doping modification in SCF causes better thermal matching between the electrode and electrolyte and form more oxygen vacancies at the operating temperature. At the anode side, Ni-doping improves the stability of the symmetric electrode in reducing the atmosphere. The polarization resistance of symmetrical cells for new electrode material is half of the original both in oxidation and reduction atmosphere, which indicates boosted electrochemical performance for the cathode and anode. At the same time, Ni-doping reduces the impedance activation energy of the anode reaction in symmetric cells. The output performance of the cell is 210.4 mW·cm⁻² at 750 °C and the thickness of the electrolyte is 400 μm, achieving a highly efficient symmetrical electrode in proton ceramic fuel cells. The new finding of materials provides a novel high efficiency symmetrical electrode and proposes guidance for the improvement of solid oxide fuel cells at a reduced temperature. Full article

(This article belongs to the Special Issue Advances in the Manufacturing of Optical Materials, in Optical Sensing, and in Material Performance Analysis)

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16 pages, 8657 KiB

Open AccessArticle

Effect of Ce-Y Composite Addition on the Inclusion Evolution in T91 Heat-Resistant Steel

by Jun Liu, Gen Li, Chengbin Shi, Zhengxin Tang, Lei Jia, Yu Zhao, Shijun Wang and Xikou He

Materials 2025, 18(7), 1459; https://doi.org/10.3390/ma18071459 (registering DOI) - 25 Mar 2025

Abstract

This study investigates the influence of rare earth elements Ce and Y on the evolution of inclusions in T91 steel by melting experimental steels with varying Ce-Y contents in a vacuum induction melting furnace. The results show that the inclusions in the steel [...] Read more.

This study investigates the influence of rare earth elements Ce and Y on the evolution of inclusions in T91 steel by melting experimental steels with varying Ce-Y contents in a vacuum induction melting furnace. The results show that the inclusions in the steel without rare earth are mainly composed of Mg-Al-O oxides, (Nb, V, Ti)(C, N) carbonitrides, and composite inclusions formed by carbonitrides coated oxides, and all of them have obvious edges and corners. Upon the addition of different concentrations of Ce and Y, the oxygen content in the steel significantly decreased, and the inclusions were modified into spherical rare earth oxides, sulfides, and oxy-sulfides. Additionally, no large-sized primary carbonitrides were observed. The average size of the inclusions was reduced from 2.8 μm in the non-rare-earth-added steel to 1.7 μm and 1.9 μm with rare earth addition. Thermodynamic analysis indicates that the possible inclusions precipitated in the steel with varying Ce contents include Ce₂O₃, Ce₂O₂S, Y₂O₃, Y₂S₃, and CeS. With the increase in Ce content, the rare earth inclusions Y₂S₃, Y₂O_3, and CeS can be transformed into Ce₂O₂S and Ce₂O₃. There are two kinds of reactions in the process of high-temperature homogenization: one is the internal transformation reaction of inclusions, which makes Y easier to aggregate in the inner layer, and the other is the reaction of Y₂S₃→CeS and Y₂O₃ + Y₂S₃→Ce₂O₂S due to the diffusion of Ce in the matrix to the inclusions. Combined with the mismatch analysis, it can be seen that Al₂O₃ has the best effect on the heterogeneous nucleation of carbonitrides during the solidification of molten steel. Among the rare earth inclusions, only Ce₂O₃ may become the nucleation core of carbonitrides, and the rest are more difficult to form heterogeneous nucleation. Therefore, by Ce-Y composite addition, increasing the Y/Ce ratio can reduce the formation of Ce₂O₃, which can avoid the precipitation of primary carbonitride and ultimately improve the dispersion strengthening effect. This study is of great significance for understanding the mechanism of rare earth elements in steel and provides theoretical guidance for the composition design and industrial trial production of rare earth steel. Full article

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24 pages, 10535 KiB

Open AccessArticle

Strategy to Enhance the Collapse Capacity of Composite Cylindrical Tubes: Experiments and Simulations

by Siddharth Jain, Akash Pandey and Arun Shukla

Materials 2025, 18(7), 1458; https://doi.org/10.3390/ma18071458 (registering DOI) - 25 Mar 2025

Abstract

The effects of adding circumferential groove geometries on the collapse capacity of carbon composite cylindrical tubes were investigated experimentally and numerically. Tubular specimens, both with and without grooves, were imploded hydrostatically in a water-filled pressure vessel facility. High-speed imaging captured the collapse behavior, [...] Read more.

The effects of adding circumferential groove geometries on the collapse capacity of carbon composite cylindrical tubes were investigated experimentally and numerically. Tubular specimens, both with and without grooves, were imploded hydrostatically in a water-filled pressure vessel facility. High-speed imaging captured the collapse behavior, while dynamic pressure transducers recorded the transient collapse pressure history of the implosion event. The results indicate that the collapse capacity is improved by up to 20% by adding a circumferential groove. A numerical model of the hydrostatic buckling was developed using ABAQUS 2022 software and validated against experimental results. A parametric study was conducted by varying the depth, steepness, and number of grooves. The results showed that deeper grooves tended to partition the tubes into sections that collapsed locally at higher pressures. Additionally, reducing the groove steepness increased the collapse capacity up to a certain threshold, beyond which the capacity decreased. Tubes with more grooves collapsed in higher modes and consequently at higher pressures. This provides a tool by which the groove geometry and pitch distance can be adjusted to achieve the desired collapse mode and capacity. Full article

(This article belongs to the Special Issue Carbon Fiber Reinforced Polymers (2nd Edition))

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22 pages, 2030 KiB

Open AccessArticle

Assessing the Influence of Cardinality Constraints on the Simultaneous Optimization of Truss Sizing, Shape, and Topology

by Nenad Petrović, Nenad Kostić, Nenad Marjanović, Ružica R. Nikolić and Robert Ulewicz

Materials 2025, 18(7), 1457; https://doi.org/10.3390/ma18071457 (registering DOI) - 25 Mar 2025

Abstract

The influence of cardinality constraints on the simultaneous optimization of truss sizing, shape, and topology, when used for weight minimization, is explored in this study. By integrating precise cardinality constraints, the implications for achieving global optimal solutions for different numbers of different cross-sections [...] Read more.

The influence of cardinality constraints on the simultaneous optimization of truss sizing, shape, and topology, when used for weight minimization, is explored in this study. By integrating precise cardinality constraints, the implications for achieving global optimal solutions for different numbers of different cross-sections were investigated. This research underscores the significance of these constraints in enhancing the practical applicability of optimization outcomes, particularly in complex structural configurations where traditional approaches may lead to excessive requirements of numerous different cross-sections. Comprehensive experimentation and comparative analysis, across various standard and practical truss examples, demonstrate the effectiveness of cardinality constraints in guiding optimal design configurations. Notably, the presented findings reveal a trend in weight savings, depending on the number of different cross-sections used relative to global optima, displaying the utility of this constraint in achieving practical and efficient designs. Case studies on a produced roof truss underscore the applicability of this approach in practical engineering scenarios. They offer insights into the optimal design configurations for problems that do not allow for drastic changes due to their restrictive design mandate. This research is part of continued advancements in truss optimization methodologies, with implications for promoting sustainability and cost-effectiveness in structural engineering practice. By elucidating the role of cardinality constraints in shaping the optimal design solutions, this study should contribute to the broader discourse on efficient structural design strategies. Full article

18 pages, 26462 KiB

Open AccessArticle

Combustion Characteristics and Thermochemistry of Selected Silicon-Based Compositions for Time-Delay Detonators

by Marcin Gerlich, Waldemar A. Trzciński and Marcin Hara

Materials 2025, 18(7), 1456; https://doi.org/10.3390/ma18071456 (registering DOI) - 25 Mar 2025

Abstract

This study investigates the combustion characteristics of silicon-based time-delay compositions with bismuth(III) oxide (Bi₂O₃), antimony(III) oxide (Sb₂O₃), and lead(II,IV) oxide (Pb₃O₄) to identify formulations with pressure-independent burn rates. Unlike conventional pyrotechnic [...] Read more.

This study investigates the combustion characteristics of silicon-based time-delay compositions with bismuth(III) oxide (Bi₂O₃), antimony(III) oxide (Sb₂O₃), and lead(II,IV) oxide (Pb₃O₄) to identify formulations with pressure-independent burn rates. Unlike conventional pyrotechnic compositions, silicon-based mixtures offer an improved energy density and reduced sensitivity to pressure variations. The linear combustion rate of the compositions was determined for a wide range of silicon contents and for different compaction pressures. Experimental results show that burn rates range from 8 mm s⁻¹ to 195 mm s⁻¹, depending on the metal oxide type and silicon content. The highest rate (195 mm s⁻¹) was observed for Si/Pb₃O₄ at 30 wt.% silicon, while Si/Sb₂O₃ had the lowest (10 ÷ 35 mm s⁻¹). The calorimetric heat of combustion varied between 1200 J g⁻¹ and 1400 J g⁻¹, with adiabatic combustion temperatures reaching 2200 K, calculated from this heat. DTA and XRD confirmed the condensed-phase combustion, forming reduced metal phases and silicon oxides. SEM and EDS revealed a porous residue structure. This work introduces a novel approach to time-delay compositions using silicon as a primary fuel. It shows that specific silicon oxide–metal systems maintain stable combustion for different loading pressures and advance pyrotechnic formulations for safer and more efficient industrial and defense applications. Full article

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12 pages, 5361 KiB

Open AccessArticle

Synthesis of Low-Defect Iron-Based Prussian Blue with Low Water Content for High-Stability Sodium-Ion Batteries

by Zhaoyue Li, Shenglin Zhong, Bingcheng Zhou, Denglian Chen, Zehai Qiu, Rui Zhang, Ruijuan Zheng, Chenhao Zhao and Jiangcong Zhou

Materials 2025, 18(7), 1455; https://doi.org/10.3390/ma18071455 (registering DOI) - 25 Mar 2025

Abstract

This study proposes an innovative two-step synthesis strategy to significantly enhance the performance of sodium-ion batteries by developing low-defect, low water content iron-based Prussian blue (PB) materials. Addressing the limitations of traditional co-precipitation methods—such as rapid reaction rates leading to excessive crystal defects [...] Read more.

This study proposes an innovative two-step synthesis strategy to significantly enhance the performance of sodium-ion batteries by developing low-defect, low water content iron-based Prussian blue (PB) materials. Addressing the limitations of traditional co-precipitation methods—such as rapid reaction rates leading to excessive crystal defects and interstitial water content—the research team introduced a synergistic approach combining non-aqueous phase precursor synthesis and controlled water-concentration secondary crystallization. The process involves preparing a PB precursor in a glycerol system, followed by secondary crystallization in a water-/ethanol-mixed solvent with a precisely regulated water content, achieving the dual objectives of water content reduction and crystal morphology optimization. Systematic characterization revealed that water concentration during secondary synthesis critically influences the material’s crystal structure, morphological features, and water content. The optimized PB50-24 material exhibited a highly regular cubic morphology with a sodium content of 9.2% and a remarkably low interstitial water content of 2.1%. Electrochemical tests demonstrated outstanding performance—an initial charge–discharge capacity of 120 mAh g⁻¹ at a 1C rate, the retention of 105 mAh g⁻¹ after 100 cycles, and a high rate capability of 86 mAh g⁻¹ at 10C, representing significant improvements in cycling stability and rate performance over conventional methods. This work not only establishes a cost-effective, scalable synthesis pathway for Prussian blue materials but also provides theoretical guidance for developing other metal-based Prussian blue analogs, offering substantial value for advancing the industrial application of sodium-ion batteries in next-generation energy storage systems. Full article

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9 pages, 4878 KiB

Open AccessCommunication

Influence of Carbon Nanotube Addition on Microstructure and Microwave Heating Performance of Polycarbosilane-Based Silicon Carbide

by Chang-Hun Hwang, Jong-Ha Beak and Se-Yun Kim

Materials 2025, 18(7), 1454; https://doi.org/10.3390/ma18071454 (registering DOI) - 25 Mar 2025

Abstract

The microwave heating of silicon carbide is induced at a specific frequency of 2.45 GHz, leading to rapid heating within a temperature range of several hundred degrees Celsius. In this study, a mechanochemical curing process using iodine was employed to cure polycarbosilane (PCS), [...] Read more.

The microwave heating of silicon carbide is induced at a specific frequency of 2.45 GHz, leading to rapid heating within a temperature range of several hundred degrees Celsius. In this study, a mechanochemical curing process using iodine was employed to cure polycarbosilane (PCS), followed by the addition of carbon nanotubes (CNTs) to produce mixed polymer powders. The effects of the CNT addition on the microstructure, crystalline structure, and microwave heating properties were investigated. The findings indicated that the incorporation of CNTs generally led to a reduction in the number of micropores; however, when the CNT concentration exceeded 10 wt%, the aggregation of CNTs became evident. In terms of microwave heating properties, the sample containing 0.1 wt% CNTs achieved the highest temperature, whereas samples with a higher CNT content demonstrated a heating limit of approximately 500 °C. Remarkably, post-processing of the specimens with 10 wt% CNTs enabled rapid heating to approximately 1800 °C within 4 s of microwave exposure. Full article

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16 pages, 3316 KiB

Open AccessArticle

Synthesis, Structural and Magnetic Properties of BiFeO₃ Substituted with Ag

by Maria Čebela, Pavla Šenjug, Dejan Zagorac, Igor Popov, Jelena Zagorac, Milena Rosić and Damir Pajić

Materials 2025, 18(7), 1453; https://doi.org/10.3390/ma18071453 (registering DOI) - 25 Mar 2025

Abstract

Here, we report the hydrothermal synthesis of BFO (bismuth ferrite) and Bi_1−xAg_xFeO₃ (x = 0.01, 0.02) ultrafine nanopowders. The diffraction patterns show that all obtained particles belong to the R3c space group. On top of that, crystal structure [...] Read more.

Here, we report the hydrothermal synthesis of BFO (bismuth ferrite) and Bi_1−xAg_xFeO₃ (x = 0.01, 0.02) ultrafine nanopowders. The diffraction patterns show that all obtained particles belong to the R3c space group. On top of that, crystal structure prediction has been accomplished using bond valence calculations (BVCs). Several promising perovskite structures have been proposed together with experimentally observed modifications of BFO as a function of silver doping. Magnetization measurements were performed on BFO, both pure and substituted with 1% and 2% of Ag. The addition of Ag in BFO did not affect the Neel temperature, T_N = 630 K for all samples; instead, the influence of Ag was observed in the increase in the value and irreversibility of magnetization, which are usual characteristics of weak ferromagnetism. Our calculations based on density functional theory (DFT) are in agreement with the experimental finding of enhanced magnetization upon Ag doping of antiferromagnetic BFO, which is assigned to the perturbation of magnetic-type interactions between Fe atoms by Ag substitutional doping. Additionally, electronic and magnetic properties were studied for all phases predicted by the BVCs study. DFT predicted half-metallicity in the γ phase of BFO, which may be of great interest for further study and potential applications. Full article

(This article belongs to the Special Issue Advances in Process Metallurgy and Metal Recycling)

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15 pages, 5300 KiB

Open AccessArticle

HTPFA-Coated AlB₂ with Enhanced Combustion Performance as a High-Energy Fuel

by Jiangfeng Wang, Wanjun Zhao, Chen Shen, Yapeng Ou and Qingjie Jiao

Materials 2025, 18(7), 1452; https://doi.org/10.3390/ma18071452 (registering DOI) - 25 Mar 2025

Abstract

High-energy boron-based fuel aluminum-diboride (AlB₂) has attracted much attention in the field of solid propellants. However, the low reactivity of AlB₂ hindered its further application. In this study, highly reactive AlB₂@hydroxyl-terminated perfluoropolyether alcohol (AlB₂@HTPFA) composites with [...] Read more.

High-energy boron-based fuel aluminum-diboride (AlB₂) has attracted much attention in the field of solid propellants. However, the low reactivity of AlB₂ hindered its further application. In this study, highly reactive AlB₂@hydroxyl-terminated perfluoropolyether alcohol (AlB₂@HTPFA) composites with a core–shell structure were prepared by coating AlB₂ with functionalized fluoropolymers by using a facile one-step in situ polymerization method. AlB₂@HTPFA composites with varying polymer contents (0, 5, 10, and 15 wt%) were obtained. The in situ polymerization strategy enables precise control over the polymer coating thickness and interfacial interactions, which is critical for optimizing the reactivity and thermal stability of composites. The morphology and structure were characterized, and the microcore–shell structure of AlB₂@HTPFA was obtained. Compared with raw AlB₂, the combustion efficiency of coated fuel increased by 4.1%, 5.6%, and 7.5%, respectively, with varying polymer contents. Meanwhile, the reactivity of AlB₂@HTPFA (5 wt%) was 0.65 MPa/s, which is ~1.5 times that of AlB₂. Additionally, the ignition and combustion characteristics of AlB₂@HTPFA were investigated by laser ignition experiments with potassium perchlorate (KP) as an oxidant. The results revealed that AlB₂@HTPFA/KP composites showed a greatly reduced combustion duration compared to uncoated AlB₂. The ignition and combustion enhancement mechanism of AlB₂@HTPFA was proposed. During the ignition process, the existence of HTPFA can result in a pre-ignition reaction, thus raising its reaction activity. This work provided a promising candidate for high-energy fuel that can be used in energetic materials. Full article

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27 pages, 15440 KiB

Open AccessArticle

Dynamic Performance of a Steel Road Sign with Multi-Material Electronic Signboard Under Mining-Induced Tremors from Different Mining Areas: Experimental and Numerical Research

by Paweł Boroń and Joanna Maria Dulińska

Materials 2025, 18(7), 1451; https://doi.org/10.3390/ma18071451 (registering DOI) - 25 Mar 2025

Abstract

This study investigates the dynamic performance of a road sign equipped with a multi-material electronic signboard subjected to mining-induced seismic tremors. The key innovative aspect lies in providing new insights into the dynamic performance of multi-material electronic signboards under high-energy mining tremors, enhancing [...] Read more.

This study investigates the dynamic performance of a road sign equipped with a multi-material electronic signboard subjected to mining-induced seismic tremors. The key innovative aspect lies in providing new insights into the dynamic performance of multi-material electronic signboards under high-energy mining tremors, enhancing their safety assessment in mining areas. Experimental modal analysis and finite element analysis were conducted, and the numerical model of the sign was calibrated by adjusting ground stiffness to align experimental and computational data. The fundamental natural frequencies and their corresponding mode shapes were identified as 2.75 Hz, 3.09 Hz, 8.46 Hz, and 13.50 Hz. Numerical results were validated using MAC methods, demonstrating strong agreement with experimental values and confirming the accuracy of the numerical predictions. Damping ratios of 3.79% and 3.71% for the first and second modes, respectively, were measured via hammer tests. To evaluate the sign’s dynamic performance under high-energy mining-induced tremors, two events were applied as kinematic excitation of the structure. These tremors, recorded in different mining regions, exhibited significant variations in peak ground acceleration (PGA) and dominant frequency range. A key finding was that frequency matching between the dominant frequencies of the tremor and the natural frequencies of the sign had a greater impact on the sign’s dynamic response than PGA. The Szombierki tremor, with dominant frequencies of 1.6–4.8 Hz, induced significantly higher stress and displacement compared to the Moskorzyn tremor (5–10 Hz) despite the latter having twice the PGA. These results highlight that a road sign structure can exhibit widely varying dynamic behaviors depending on the seismic characteristics of the mining zone. Therefore, a comprehensive assessment of mining-induced tremors in relation to the seismicity of specific areas is crucial for understanding their potential impact on such structures. The dynamic performance assessment also revealed that the electronic multi-material signboard did not undergo plastic deformation, confirming it as a safe material solution for use in mining areas. Full article

(This article belongs to the Special Issue Modeling and Simulations of the Dynamic Mechanical Performance of Materials and Structures)

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15 pages, 3819 KiB

Open AccessArticle

Multiscale Investigation of Modified Recycled Aggregate Concrete on Sulfate Attack Resistance

by Xue-Fei Chen, Xiu-Cheng Zhang and Guo-Hui Yan

Materials 2025, 18(7), 1450; https://doi.org/10.3390/ma18071450 (registering DOI) - 25 Mar 2025

Abstract

This study investigated the sulfate resistance of modified recycled aggregate concrete (RAC) by applying carbonation and nano-silica soaking methodologies. Recycled concrete aggregates (RCA) derived from concretes of C30 and C60 strength grades were subjected to these modification techniques and subsequently utilized in the [...] Read more.

This study investigated the sulfate resistance of modified recycled aggregate concrete (RAC) by applying carbonation and nano-silica soaking methodologies. Recycled concrete aggregates (RCA) derived from concretes of C30 and C60 strength grades were subjected to these modification techniques and subsequently utilized in the fabrication of RAC specimens. The results show notable porosity and crack density within the interfacial transition zone (ITZ) interfacing recycled aggregate and cement paste in recycled aggregate concrete (RAC). Specifically, the porosity within the ITZ of RAC is observed to be up to 30% higher than that of virgin aggregate concrete. These pathways facilitate the penetration of sulfate ions, subsequently inducing deterioration and resulting in a compression strength reduction of up to 40%. While carbonation treatment exhibits a moderate enhancement in sulfate resistance, decreasing the sulfate penetration depth by 15%, the incorporation of 2% nano-silica by weight of cement proves significantly more effective. This addition reduces the sulfate penetration depth by over 30% and lowers the sulfate concentration by 25%. Furthermore, the compressive strength of RAC modified with nano-silica increases by 15% following 28 days of sulfate exposure. Additionally, a 30% reduction in the sulfate ion mass equilibrium depth is observed in nano-silica-modified RAC, accompanied by a markedly lower sulfate concentration in the pore solution. After 56 days of sulfate attack, the compressive strength of nano-silica-modified RAC retains 85% of its initial value, whereas unmodified RAC decreases to 70%. Notably, the quality of recycled aggregate significantly impacts sulfate resistance, with high-strength RCA (exceeding 40 MPa) demonstrating superior resistance compared to low-strength RCA (below 20 MPa). Consequently, RAC produced with high-strength RCA experiences only a 20% loss in compressive strength under sulfate attack, whereas RAC containing low-strength RCA suffers a 40% loss. The novelty of this study is the effective use of nano-silica soaking and carbonation to enhance the sulfate resistance and compressive strength of recycled aggregate concrete originated from both normal and high-strength reference concrete. Full article

(This article belongs to the Special Issue The Development of Sustainable Concrete with Solid Waste and By-Products)

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25 pages, 11548 KiB

Open AccessArticle

Response of Bare and CFRP-Retrofitted Multi-Column Piers Under Post-Fire-Coupled Vehicle Collision and Air Blast

by Qusai A. Alomari, Daniel G. Linzell and Mubarak F. Abu Zouriq

Materials 2025, 18(7), 1449; https://doi.org/10.3390/ma18071449 (registering DOI) - 25 Mar 2025

Abstract

Numerous catastrophic events, including fire, vehicle collisions, and air blasts, have highlighted the significance of examining bridge performance under multi-hazard scenarios. While these hazards cause extensive damage, the loss of life, and drastically impact economies, limited attention has been devoted to study the [...] Read more.

Numerous catastrophic events, including fire, vehicle collisions, and air blasts, have highlighted the significance of examining bridge performance under multi-hazard scenarios. While these hazards cause extensive damage, the loss of life, and drastically impact economies, limited attention has been devoted to study the behavior of bridge structural elements under such extreme demand combinations. Hence, comprehensive research to understand the resiliency of bridges and their response to combinations of fire, vehicular impact, and air blast is warranted so that effective retrofitting techniques can be developed and design recommendations be made. To address this research gap, present investigations utilized previously validated finite element (FE) models in LS-DYNA to study the structural behavior of two-, three-, and four-column piers under post-fire medium truck collision and subsequent air blast. The response of multi-column piers was quantified and evaluated based on damage propagation, failure patterns, and permanent deformation sets. The effectiveness of selected retrofitting techniques that employed carbon-fiber-reinforced polymers (CFRPs) to mitigate damage was investigated. Study findings enhance current understanding, provide valuable insights, and can ultimately be used to ensure safety and improve the structural integrity of bridge piers under coupled vehicle collision and air blast following fire exposure. Full article

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18 pages, 10317 KiB

Open AccessArticle

Advanced Thermal Imaging Processing and Deep Learning Integration for Enhanced Defect Detection in Carbon Fiber-Reinforced Polymer Laminates

by Renan Garcia Rosa, Bruno Pereira Barella, Iago Garcia Vargas, José Ricardo Tarpani, Hans-Georg Herrmann and Henrique Fernandes

Materials 2025, 18(7), 1448; https://doi.org/10.3390/ma18071448 (registering DOI) - 25 Mar 2025

Abstract

Carbon fiber-reinforced polymer (CFRP) laminates are widely used in aerospace, automotive, and infrastructure industries due to their high strength-to-weight ratio. However, defect detection in CFRP remains challenging, particularly in low signal-to-noise ratio (SNR) conditions. Conventional segmentation methods often struggle with noise interference and [...] Read more.

Carbon fiber-reinforced polymer (CFRP) laminates are widely used in aerospace, automotive, and infrastructure industries due to their high strength-to-weight ratio. However, defect detection in CFRP remains challenging, particularly in low signal-to-noise ratio (SNR) conditions. Conventional segmentation methods often struggle with noise interference and signal variations, leading to reduced detection accuracy. In this study, we evaluate the impact of thermal image preprocessing on improving defect segmentation in CFRP laminates inspected via pulsed thermography. Polynomial approximations and first- and second-order derivatives were applied to refine thermographic signals, enhancing defect visibility and SNR. The U-Net architecture was used to assess segmentation performance on datasets with and without preprocessing. The results demonstrated that preprocessing significantly improved defect detection, achieving an Intersection over Union (IoU) of 95% and an F1-Score of 99%, outperforming approaches without preprocessing. These findings emphasize the importance of preprocessing in enhancing segmentation accuracy and reliability, highlighting its potential for advancing non-destructive testing techniques across various industries. Full article

(This article belongs to the Special Issue Non-Destructive Testing of Materials and Parts: Techniques, Case Studies and Practical Applications)

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11 pages, 3973 KiB

Open AccessArticle

Impact of Processing Parameters on Ti Schottky Contacts on 4H-SiC

by Marilena Vivona, Gabriele Bellocchi, Valeria Puglisi, Corrado Bongiorno, Salvatore Adamo, Filippo Giannazzo, Simone Rascunà and Fabrizio Roccaforte

Materials 2025, 18(7), 1447; https://doi.org/10.3390/ma18071447 (registering DOI) - 25 Mar 2025

Abstract

In this paper, we investigated the effects of the processing parameters, such as deposition methods, annealing temperature, and metal thickness, on the electrical characteristics of Ti/4H-SiC contacts. A reduction of the Schottky barrier height from 1.19 to 1.00 eV following an increase of [...] Read more.

In this paper, we investigated the effects of the processing parameters, such as deposition methods, annealing temperature, and metal thickness, on the electrical characteristics of Ti/4H-SiC contacts. A reduction of the Schottky barrier height from 1.19 to 1.00 eV following an increase of the annealing temperature (475–700 °C) was observed for a reference contact with an 80 nm-thick Ti layer. The current transport mechanisms can be described according to the thermionic emission (TE) and thermionic field emission (TFE) models under forward and reverse biases, respectively. The comparison with an e-beam evaporated Ti(80 nm)/4H-SiC contact did not show significant differences for the forward characteristics, while an increase of the leakage current was observed under high reverse voltage (>500 V). Finally, a thickness variation from 10 to 80 nm induced a reduction of the Schottky barrier height, due to the reaction occurring at the interface with a Ti-Al region extended up to the 4H-SiC surface. In addition to a deeper understanding of the Schottky barrier properties, this work is useful for the development of Schottky barrier diodes with tailored characteristics. Full article

(This article belongs to the Section Electronic Materials)

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34 pages, 16470 KiB

Open AccessArticle

Study on the Dynamic Characteristics of Low-Frequency High-Stiffness Viscoelastic Damping Structures

by Zhangda Zhao, Wenjun Meng, Bijuan Yan, Huijun Liang, Yihang Geng and Zhengyu Sun

Materials 2025, 18(7), 1446; https://doi.org/10.3390/ma18071446 (registering DOI) - 25 Mar 2025

Abstract

Viscoelastic suspension systems serve as components essential for enhancing ride comfort and structural reliability in tracked bulldozers. However, traditional suspension-damping structures often exhibit high-stiffness and reduced-damping characteristics under low-frequency excitations, limiting their adaptability in complex off-road conditions. This limitation adversely affects the operational [...] Read more.

Viscoelastic suspension systems serve as components essential for enhancing ride comfort and structural reliability in tracked bulldozers. However, traditional suspension-damping structures often exhibit high-stiffness and reduced-damping characteristics under low-frequency excitations, limiting their adaptability in complex off-road conditions. This limitation adversely affects the operational safety and comfort of tracked bulldozers, particularly in extreme terrains. This study employs an elastic modulus gradient design, combined with the hysteretic properties of viscoelastic materials, aiming to develop five rubber materials with varying elastic moduli and constitutive parameters for damping-layer applications. Through parametric modeling and finite-element simulations, we systematically analyzed both static and dynamic performance across these five configurations while investigating how damping-layer elastic modulus variations influence dynamic vibration-damping characteristics. The results demonstrate that the S-NR3-NR3-S configuration exhibits superior dynamic vibration-damping performance. Further analysis focused on this optimal configuration’s stiffness characteristics and energy dissipation capacity under different harmonic excitations and maximum compression displacements. Finally, practical validation was conducted through static and dynamic performance testing of physical prototypes using a universal testing machine and electro-hydraulic servo-controlled instrumentation, based on operational conditions of high-power tracked bulldozers. The presented findings and methodologies establish a theoretical foundation for optimizing ride comfort in construction vehicles, demonstrating significant practical applicability and engineering value. Full article

(This article belongs to the Section Mechanics of Materials)

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16 pages, 2325 KiB

Open AccessSystematic Review

Meta-Analysis of Materials and Treatments Used in Contact Lenses: Implications for Lens Characteristics

by Ana Paula Oliveira and Clara Martinez-Perez

Materials 2025, 18(7), 1445; https://doi.org/10.3390/ma18071445 (registering DOI) - 25 Mar 2025

Abstract

A meta-analysis was conducted to assess the evolution of, applications of, and recent advancements in materials and surface treatments for contact lenses. This study aimed to comprehensively synthesize the available data, focusing on innovations that enhance vision correction, comfort, and safety while emphasizing [...] Read more.

A meta-analysis was conducted to assess the evolution of, applications of, and recent advancements in materials and surface treatments for contact lenses. This study aimed to comprehensively synthesize the available data, focusing on innovations that enhance vision correction, comfort, and safety while emphasizing sustainability as a critical factor in future development. Registered with PROSPERO, this analysis adhered to the PRISMA and AMSTAR-2 guidelines. A systematic review of databases including PubMed, Web of Science, and Scopus was performed for studies published between 2019 and 2024, without language restrictions. Observational studies on optical materials and lens treatments were included, and a random-effects model was used to address the high heterogeneity among the included studies. From the nine studies that were analyzed, significant advancements were identified regarding the functional properties of materials and treatments. Key advancements included technologies like self-lubricating lenses that reduce friction, nanogels for prolonged therapeutic drug delivery, and coatings that minimize protein and lipid deposition, ensuring greater comfort and extended wearability. Additionally, innovations in biodegradable and eco-friendly materials underscore the industry’s commitment to reducing the environmental impact of contact lenses, addressing challenges related to lens disposal and recycling. These advancements highlight the potential of integrating functional improvements with sustainability, paving the way for more effective and environmentally responsible contact lenses. Full article

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