WANG Tianci ¹, ZHAO Fangnan ¹, FAN Binbin ², ZHAO Lin ¹, XIE Zhipeng ²

(1. School of Materials Science and Engineering, Jingdezhen Ceramic University, Jingdezhen 333043, Jiangxi, China;

2. School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China)

Extended abstract:[Significance] High-entropy non-oxide ceramic materials demonstrate exceptional stability under extreme environments, such as ultra-high temperatures, strong corrosion, high wear and high radiation, thus exhibiting broad application prospects. For example, high-entropy carbides far exceed traditional carbide ceramics in hardness, thermal shock resistance and oxidation resistance, making them suitable for aerospace engine coatings or structural materials in nuclear reactors. The superior performance of high-entropy non-oxides primarily originates from four unique effects, including the high-entropy effect, sluggish diffusion effect, lattice distortion effect and "cocktail" effect. Multi-component synergistic enhancement results in significant improvement in fracture toughness, creep resistance and wear resistance, overcoming the brittleness and failure susceptibility of traditional ceramics. Therefore, regulating components to achieve entropy-stabilized states plays a decisive role in optimizing the structural stability and performance of high-entropy non-oxide ceramics. However, challenges, such as complex synthesis, intricate processing and high costs, have restricted their commercial applications. This review is aimed to summarize recent research progress in high-entropy borides, carbides, dual-anion high-entropy ceramics and multiphase/ composite high-entropy ceramics, emphasizing their mechanical and thermal advantages over traditional ceramics, identifying existing challenges and proposing future directions.[Progress] The development of high-entropy non-oxide ceramics, which are typically single-phase solid solutions formed by five or more non-oxide components, is first introduced. Then, material design, synthesis and structure-property of high-entropy borides, carbides, dual-anion ceramics and multiphase composites are elaborated. High-entropy carbides, mostly composed of five or more transition metal carbides, adopt phase formation criteria from high-entropy alloys as the theoretical design principles, supplemented by lattice distortion and entropy-forming ability criteria to determine single-phase formation. Current sintering methods for bulk high-entropy carbides include hot-pressing (HP), spark plasma sintering (SPS), pressureless sintering (PS), oscillatory pressure sintering (OPS) and ultra-fast high temperature sintering (UHTS). These materials generally exhibit higher hardness, elastic modulus and low thermal conductivity, as compared with their single-component counterparts. The enhanced elastic modulus and hardness are attributed to solid solution strengthening and unique deformation mechanisms. Adjusting solid-solution systems to modulate the high-entropy effect may alleviate brittleness. Secondly, typical high-entropy diborides possess hexagonal crystal structures, with SPS being the most common method for low-component systems. For octonary systems, ultra-high-temperature rapid sintering is preferred, due to the excessive synthesis temperatures. The formation of boride solid solutions depends on component melting points and vapor pressures. For instance, CrB₂ exhibits the highest vapor pressure, leading to Cr migration and non-equilibrium microstructures. Therefore, the content of Cr must be carefully controlled in the design. Unlike carbides, high-entropy borides excel in wear resistance and ultra-high melting points, showing promise for porous ceramics with low thermal conductivity. Thirdly, dual-anion high-entropy ceramics are formed through the incorporation of multiple anions, offering enhanced phase stability, broader tunability and unique properties, such as high strength and low thermal conductivity. Stronger lattice distortions and reduced Fermi-level density of states contribute to structural stability. Multiphase composites, including dual high-entropy phases or high-entropy/non-high-entropy hybrids, are synthesized via ball milling combined with HP or SPS. Additionally, the addition of SiC particle in high-entropy carbides promotes densification.[Conclusions and prospects] High-entropy non-oxide ceramics hold potential in energy, catalysis, environmental, and electronic fields, especially for high-temperature protection and wear-resistant coatings. This review is aimed to systematically discuss design theories, synthesis methods, microstructure control and performance optimization of these materials, with a focus on sintering techniques and structure-property for borides, carbides, dual-anion ceramics and composites. Finally, it is pointed out that the problems and challenges of synthesis, processing and cost of high-entropy non-oxide ceramic materials limit their practical applications. In future, novel synthesis approaches, refinement of microstructures to enhance reliability and durability and integration of AI/machine learning to decipher high-entropy solid-solution mechanisms and crystal structure principles should be explored to enable the design of cost-effective high-performance high-entropy non-oxide ceramics.

Key words: high-entropy ceramics; preparation method; microstructure regulation; high-temperature performance