Search Results (142)

Steel components in thermal power plants are vulnerable to severe wear and wall thinning induced by the high-velocity impact of pulverized coal, which significantly compromises their service life and structural integrity. To address this issue, a TiC-reinforced AlCoCrFeNi high-entropy alloy (HEA) composite coating was fabricated via laser cladding, aiming to substantially enhance the wear resistance of these critical components. The phase composition, microstructure, microhardness and tribological behaviors of the coatings were systematically investigated by XRD, SEM, EDS and dry sliding wear tests. Results show that both coatings possess dense microstructures and reliable metallurgical bonding with the substrate. The AlCoCrFeNi coating consists of a single BCC solid solution phase, while the TiC/AlCoCrFeNi composite coating contains a BCC phase and a TiC ceramic phase without brittle intermetallic compounds. The average microhardness of the TiC/AlCoCrFeNi composite coating was measured to be 823 HV_0.3, which is 85.66% greater than that of the AlCoCrFeNi coating (443 HV_0.3). Under identical wear test conditions, the AlCoCrFeNi coating exhibits a mass loss of 31.4 mg and a volumetric wear rate of 24 × 10⁻³ mm³/min, whereas the TiC/AlCoCrFeNi composite coating exhibits a mass loss of 15.6 mg and a wear rate of 13 × 10⁻³ mm³/min, corresponding to reductions of approximately 50.32% and 45.83%, respectively. The wear mechanism of the AlCoCrFeNi coating is dominated by severe abrasive wear coupled with adhesive wear, while the addition of TiC converts the wear mechanism into mild abrasive wear and oxidative wear. The incorporation of TiC particles effectively enhances the microhardness and reduces the mass loss, thereby contributing to a marked improvement in the wear properties of the laser-clad AlCoCrFeNi coating. This research provides experimental data and theoretical support for the engineering application of TiC/AlCoCrFeNi composite coatings on wear-resistant components in thermal power units. Full article

High-entropy transition-metal diborides represent a promising class of ultra-high temperature ceramics. However, atomic insights into their high-temperature elastic response, anisotropic deformation, and fracture mechanisms remain elusive. Herein, we perform molecular dynamic simulations to study the thermomechanical behaviors of (Hf_0.2Zr_0.2Ta_0.2Ti_0.2Nb_0.2)B₂ from 900 to 3300 K by developing an ab initio accuracy deep-learning potential. The proposed potential accurately reproduces lattice parameters, equations of state, and elastic constants, in excellent agreement with density functional theory calculations and available experiments, and remains transferable under thermally expanded and compressed states. The simulations reveal anisotropic thermal expansion, with the out-of-plane expansion exceeding the in-plane expansion, together with progressive elastic softening while preserving C₁₁ > C₃₃ due to the dominant in-plane B-B bonding network. Furthermore, strain-rate- and temperature-dependent tensile and compressive responses show marked crystallographic anisotropy, tension–compression asymmetry, and severe thermomechanical degradation. Atomic structural evolution demonstrates that tensile fracture is dominated by bond stretching and progressive damage accumulation, whereas compressive failure is attributed to densification- and shear-mediated structural instability. These findings provide an atomistic understanding of the thermomechanical behavior and fracture mechanisms of the prototypical single-phase (Hf_0.2Zr_0.2Ta_0.2Ti_0.2Nb_0.2)B₂ high-entropy diboride, offering valuable insights into the design of ultra-high temperature ceramics under extreme service environments. Full article

We present a systematic study of thermal oxidation resistance of transition metal borides and carbides up to 1300 °C in a dry air environment. A High-Entropy Metal Boride (HEMB), of composition (Hf_0.2, Mo_0.2, Nb_0.2, Ta_0.2, Zr_0.2)B₂, and a similar High-Entropy Metal Carbide (HEMC) (Hf, Mo, Nb, Ta, Zr)C₅ were synthesized from precursor mixtures, under 30 MPa of pressure at a temperature of 1800 °C using a Spark Plasma Sintering Device. The synthesized phases were confirmed via X-ray Diffraction analysis, which showed a pure hexagonal AlB₂-type structure for HEMB and a face-centered cubic (FCC) structure for HEMC, with lattice parameters, a = 3.10 Å and c = 3.37 Å for HEMB and a = 4.524 Å for HEMC. Oxidation resistance was evaluated using a simultaneous thermogravimetric analysis and differential scanning calorimetry (TGA/DSC) stage in which HEMB and HEMC were heated up to 1300 °C at a rate of 2 °C/min in a dry air environment. Scanning electron microscopy (SEM) was used to analyze the resulting oxidized material. Our study demonstrates that HEMB shows better thermal oxidation resistance as compared to a similar metal composition HEMC at high temperatures. Full article

CoCrFeNi-based high-entropy alloys (HEAs) have shown great potential for widespread applications in aerospace, chemical, and medical equipment fields due to their high strength, wear resistance, corrosion resistance, and thermal stability. In the present study, a series of Ni₂CoCrFeV_xCu_y alloys were designed to obtain a ductile FCC matrix suitable for ceramic-particle reinforcement. Subsequently, two representative reinforcement strategies, namely, in situ TiC formation and direct TiN nanoparticle addition, were employed to investigate their effects on the microstructure and mechanical properties of the alloy. The results showed that Ni₂CoCrFeV_0.5Cu_0.2 exhibited the best strength–ductility balance, with a tensile elongation of 51.8% among the designed alloys. Besides, the comprehensive performance of high-entropy alloys can be effectively enhanced by in situ generation of TiC and addition of TiN particles. The in situ synthesized TiC exhibited a finer and more uniform distribution than the directly added TiN particles, resulting in a more favorable strength–ductility balance under the present processing conditions. Full article

High-entropy MAX phases (TiVNbTa)₂AlC have attracted increasing attention due to their potential advantages in structural stability, damage tolerance, and mechanical reliability under complex service environments. This work studied the crystal and electrical structures with the elastic properties, the synthesis reactions and further wear resistance of HE-MAX (TiVNbTa)₂AlC theoretically and experimentally. The charge transfer between both M-C atoms and M-Al atoms turned more intense, which correspondingly strengthened the M-C and M-Al bonds, respectively. Because of the dope on M-sites, (TiVNbTa)₂AlC exhibited larger fracture toughness K_IC and a lower brittle index M, which suggested lower brittleness, better crack extension resistance, and higher damage tolerance than Ti₂AlC. In this work, high-entropy (TiVNbTa)₂AlC MAX phase ceramics were successfully synthesized by a powder metallurgy route combined with pressureless sintering and spark plasma sintering (SPS). The effects of raw material composition and sintering temperature on phase evolution, microstructure formation, mechanical properties, and tribological behavior were systematically investigated. The results show that a highly pure (TiVNbTa)₂AlC phase with a phase fraction of 96.8% could be obtained at a molar ratio of M:Al:C = 2:1.2:0.8 and a sintering temperature of 1550 °C. Phase evolution analysis indicated that the reaction process followed the sequence of intermetallic compound (IMC) formation → carbide formation → MAX phase formation. Severe lattice distortion induced by the multi-principal-element solid solution significantly enhanced the hardness of the material, which was markedly higher than that of conventional ternary MAX phases. Owing to its higher hardness and more homogeneous solid-solution structure, HE-MAX (TiVNbTa)₂AlC could inhibit the formation of surface microcracks and reduce the driving force for crack propagation to some extent. Therefore, the lower wear rate not only reflected improved tribological performance but also demonstrated the beneficial role of high-entropy design in enhancing resistance to surface damage. Full article

With the continuous advancement of thrust-to-weight ratios in modern aero-engines, turbine inlet temperatures have reached levels that far exceed the thermal endurance limits of conventional superalloys and emerging ceramic matrix composites (CMCs). Consequently, thermal barrier coatings (TBCs) and environmental barrier coatings (EBCs) have become indispensable multifunctional systems for hot-section component protection. This review systematically delineates the evolutionary trajectory of TBC/EBC systems, transitioning from traditional yttria-stabilized zirconia (YSZ) and simple silicates to advanced multi-rare-earth-doped oxides, A₂B₂O₇ pyrochlore structures, and high-entropy ceramic systems. A critical comparative assessment is provided regarding their phase stability, thermal-physical properties, and durability challenges above 1200 °C. Furthermore, this paper provides an in-depth analysis of high-temperature degradation mechanisms, focusing on the thermochemical and thermomechanical interactions under calcium-magnesium-alumino-silicate (CMAS) attack, water-oxygen corrosion, and molten salt infiltration. By synthesizing current research gaps, we highlight the trade-offs between low thermal conductivity, high toughness, and environmental resistance. Finally, a strategic roadmap for next-generation coatings is proposed, emphasizing the integration of high-entropy material design, multi-scale structural optimization, and AI-driven life prediction models to meet the stringent reliability requirements of future propulsion systems. Full article

Ultra-high-temperature ceramics (UHTCs), including transition-metal carbides, nitrides, and diborides, have emerged as a class of promising structural materials for applications in extreme aerospace and energy environments. Their strong covalent–metallic bonding endows them with exceptionally high melting points, elastic moduli, and thermal stability. Nevertheless, intrinsic brittleness, limited oxidation resistance, and poor sinterability remain key challenges for the engineering application of conventional UHTCs. Recently, novel material design strategies such as multiphase composites, microstructural engineering, and compositional complexity have emerged. Among these, high-entropy UHTCs (HE-UHTCs) have attracted significant attention due to their configurational entropy, lattice distortion, and sluggish diffusion effects, which collectively enhance oxidation resistance, thermal stability, sinterability, and mechanical performance. This review summarizes the crystal chemistry, mechanical behavior, oxidation, and ablation properties of conventional UHTCs and HE-UHTCs. The four core effects of HE-UHTCs—configurational entropy, lattice distortion, sluggish diffusion, and cocktail effects—are discussed in relation to their mechanical properties and oxidation resistance. The roles of computational materials science, including density functional theory (DFT), molecular dynamics (MD), and machine learning, in composition screening and property prediction are critically reviewed. Finally, key challenges and future directions for the rational design and engineering application of UHTCs are discussed. Full article

Non-stoichiometric high-entropy carbides (Nb_0.2Ta_0.2Ti_0.2W_0.2Zr_0.2)C_x (x = 0.71–0.85) nanoscale powders were prepared using oxides and carbon as raw materials via carbothermal reduction. The (Nb_0.2Ta_0.2Ti_0.2W_0.2Zr_0.2)C_0.73 synthesized at 1700 °C exhibited a grain size of approximately 400 nm, an oxygen content of 0.3 wt.%, and uniform nanoscale distribution of the five metal elements. After ball milling, (Nb_0.2Ta_0.2Ti_0.2W_0.2Zr_0.2)C_0.73 powder was sintered by spark plasma sintering to produce high-entropy ceramics with a relative density of 98.1% and an average particle size of about 5.3 μm. The Vickers hardness, nano-hardness, Young’s modulus, and fracture toughness were 17.6 GPa, 29.1 GPa, 514 GPa, and 5.3 MPa·m^1/2, respectively. The thermal conductivity of the ceramic at room-temperature was as low as 8.5 W/m·K. Full article

High-entropy MAX (HE-MAX) phases represent a new class of layered ceramics that combine the multi-principal-element chemistry of high-entropy materials with intrinsic damage tolerance, electrical conductivity, and multifunctionality of conventional MAX phases. Despite their promise, the synthesis of HE-MAX phases remains fundamentally constrained by sluggish multicomponent diffusion, narrow thermodynamic stability windows, and strong competition from thermodynamically favored binary and ternary carbides, borides, and nitrides. These challenges are further exacerbated by the volatility of A-site elements under near-equilibrium processing conditions. This review positions self-propagating high-temperature synthesis (SHS) as an energy-efficient, non-equilibrium processing route capable of stabilizing selected entropy-driven MAX chemistries through ultrafast thermal excursions and rapid quenching. A unified thermodynamic–kinetic framework is developed to elucidate the interplay among reaction enthalpy, configurational entropy, combustion wave sustainability, and phase evolution in HE-MAX systems. Predictions of thermochemical adiabatic temperature are systematically correlated with experimental SHS studies to delineate phase stability boundaries, stoichiometric sensitivity, and the roles of diluents and transient liquid formation. Finally, practical design principles for scalable SHS synthesis of HE-MAX phases are outlined, alongside strategies for their selective exfoliation into high-entropy MXenes and a critical assessment of their emerging functional applications. Full article

(Li_0.4Co_0.2Ni_0.2Cu_0.2Zn_0.2)WO₄ high-entropy ceramics were prepared by a conventional solid-state reaction route. This study thoroughly explores the interrelationships between their crystal structure, bond properties, and microwave dielectric characteristics. X-ray diffraction analysis verified that all specimens crystallized in a single-phase ZnWO₄-type structure. According to Rietveld refinement of the XRD data, the lattice parameters are affected by the ionic radii of the constituent elements, confirming their dissolution and random distribution at Zn sites. Relative density exhibited a strong dependence on sintering temperature. Bonding analysis highlights the crucial role of the W–O bond in governing the dielectric response of the (Li_0.4Co_0.2Ni_0.2Cu_0.2Zn_0.2)WO₄ (LCNCZW) ceramics. Moreover, sinterability can be improved through optimizing the sintering process. Notably, samples sintered at 850 °C attained suitable dielectric performance, characterized by εᵣ = 11.697 ± 0.204, Q × f = 23,851 ± 0.126 GHz, and τ_f = 21.335 ± 0.232 ppm/°C. These results demonstrate that high-entropy design can effectively improve the sinterability and microwave dielectric performance of wolframite-type ceramics, offering a promising strategy for the development of microwave dielectric ceramics for communication devices. Full article

Ceramic materials are indispensable to aerospace and defence technologies, where structural and functional components are required to withstand extreme thermal, mechanical, and chemically aggressive environments. Traditionally valued for their exceptional thermal stability, oxidation resistance, and corrosion resistance, ceramics have nonetheless been constrained by their inherent brittleness, which has limited their widespread adoption in load-bearing structural applications. This review surveys the principal tough ceramic systems currently employed in aerospace and defence, including SiC, Al₂O₃, ZrO₂, Si₃N₄, SiC/SiC composites, and ultra-high-temperature ceramics (UHTCs) such as ZrB₂ and HfB₂. In parallel, it outlines advanced processing and manufacturing routes that enable enhanced microstructural control, improved reliability, and scalability for industrial deployment. Special attention is devoted to thermal and environmental barrier coatings (TBCs and EBCs), which provide critical protection against oxidation, corrosion, and severe thermal cycling in propulsion, power-generation, and hypersonic systems. Finally, the review highlights key material selection criteria for aerospace and defence platforms and discusses emerging trends that integrate tough ceramics with next-generation manufacturing technologies, underscoring their pivotal role in enabling high-performance, durable, and resilient systems for future extreme-environment applications. Full article

This comparative study investigates binder-free binary WC-TiC and ternary WC-TiC-TaC carbide ceramics as alternatives to cobalt-bonded hard materials. Equimolar compositions were processed via high-energy ball milling (HEBM) and consolidated by spark plasma sintering (SPS) at 1700–2100 °C. X-ray diffraction analysis (XRD) revealed fundamentally different homogenization kinetics: the ternary system achieved a complete single-phase structure at 2000 °C, 100 °C earlier than the binary system. This acceleration correlates with finer initial particle size (2–5 μm vs. 3–10 μm) and near-stoichiometric TaC, facilitating interdiffusion. Lattice parameter evolution confirmed the formation of (W,Ti)C and (W,Ti,Ta)C substitutional solid solutions. Mechanical characterization showed contrasting behaviors: binary WC-TiC exhibits maximum hardness at 1900 °C (1793 HV30, fracture toughness 5.07 MPa·m^1/2), while ternary WC-TiC-TaC peaks at 1700–1800 °C (1947–1782 HV30) with higher toughness (max 5.42 MPa·m^1/2). Optimal processing windows with acceptable property uniformity are 1800–1900 °C (binary) and 1700–1900 °C (ternary). The binary system offers superior toughness and stability; the ternary system enables faster processing and higher initial hardness, defining distinct application domains. Full article

Water electrolysis is a key technology for sustainable hydrogen production and a cornerstone of future low-carbon energy systems. However, large-scale deployment is constrained not only by efficiency and cost, but increasingly by the sustainability and availability of materials used in electrocatalysts and membranes. This review provides a materials-centric assessment of state-of-the-art and emerging electrocatalysts for alkaline (AEL), proton exchange membrane (PEM), and solid oxide electrolysis (SOEC) technologies, emphasizing the interdependence of performance, durability, cost, and sustainability. Electrocatalyst activity and stability are linked to cell- and stack-level efficiency, energy demand, and the levelized cost of hydrogen. Life cycle assessment (LCA) and resource criticality analyses are integrated to quantify environmental impacts, supply risks, and recycling potential of key materials, including platinum group metals, nickel, rare earth elements, and ceramic oxides. Particular attention is given to recycling and circularity strategies, which are essential for mitigating material scarcity and reducing upstream emissions, especially in PEM electrolyzers. Emerging catalyst concepts such as single-atom catalysts, high-entropy alloys, and noble-metal-free systems are discussed as promising pathways to reduce critical material dependence. The review concludes by highlighting the need for integrated material–technology–system approaches to enable efficient, scalable, and truly sustainable hydrogen production. Full article

A high-entropy strategy has emerged as a promising approach to enhance the functional properties of piezoelectric ceramics for biomedical applications. For this reason, we have designed two novel high-entropy ceramics, (Bi_1/2Na_1/2)(Zr_1/3Sn_1/3Ti_1/3)O₃(BNZST) and (Bi_1/2Na_1/2)(Zr_1/4Sn_1/4Hf_1/4Ti_1/4)O₃(BNZSHT), which were synthesized via a two-step solid-state reaction. The phase structure, surface morphology, biocompatibility, and in vitro bioactivity were assessed. The results showed both ceramics adopted perovskite structures. BNZST and BNZSHT ceramics had relatively even crystallite sizes and element distribution, as well as achieving piezoelectric (d₃₃ ≥ 78 pC/N) properties. In vitro tests confirmed a high relative cell growth rate (RSG, >80%) after co-culturing BNZST or BNZSHT ceramic with murine fibroblasts L929 for more than 3 days. In particular, the surface with electric charge enhanced L929 with more extensive, widespread, and dense proliferation for the BNZST ceramic compared to ceramics without BNZST or unpolarized BNZST. The above indicated that multi-element doping and entropy stabilization established a novel pathway for developing a high-entropy bio-piezoelectric ceramics with high biocompatibility and bioactivity, providing the possibility for their use in bone repair materials. Full article

The simultaneous enhancement of hardness and toughness in WC-Co cemented carbides remains a critical and persistent challenge for advanced cutting-tool applications, where conventional materials often suffer from inherent property trade-offs. In this study, a novel composite ceramic material—WC-(TiZrHfNbTa) (C, N) high-entropy carbonitride (HECN)-Co composite—was successfully fabricated via dry ball milling and spark plasma sintering (SPS) at 1300 °C following 90 h of ball milling. By incorporating varying amounts of HECN (0–15%, mass fraction, same below), the microstructure and mechanical properties of the composites were systematically tailored. The results demonstrate that the addition of HECN effectively refines the WC grains and increases the material density, leading to a pronounced improvement in hardness. Notably, the composite with 10% HECN (WC-10%HECN-9Co) exhibits an optimal balance of hardness and fracture toughness, achieving a Vickers hardness of 2375 ± 25 HV30 and a fracture toughness of 12.9 ± 1.1 MPa·m^1/2. In contrast, excessive HECN addition (15 wt.%) induces excessive grain refinement, which significantly impairs toughness. Our study demonstrates that the introduction of (TiZrHfNbTa) (C, N) HECN as a reinforcing phase offers a viable and effective strategy for designing cemented carbides with an exceptional hardness–toughness synergy, showing great promise for demanding cutting applications such as high-speed machining and the processing of hard-to-cut materials. Full article