A high-entropy B₄(HfMo₂TaTi)C and SiC ceramic composite

Prior research has shown that refractory carbides exhibit high hardness and thermal stability, but their use is limited by structural incompatibility and brittleness. Classical approaches to composite design often fail to integrate carbides with differing crystal structures. This gap motivated the exploration of high-entropy carbide systems that could overcome structural mismatches. It was already known that hexagonal close-packed (HCP) structures can accommodate multiple elements in a single lattice. However, no prior work had resolved how to form a single-phase ceramic from multiple carbides with distinct crystal structures. The challenge lies in achieving atomic-level mixing while preserving mechanical properties. This paper introduces a novel approach to composite design by leveraging high-entropy principles. The study addresses the need for a unified ceramic phase that combines multiple refractory carbides into a single structure.

The aim of this work is to synthesize and characterize a high-entropy B4(HfMo2TaTi)C ceramic composite with SiC as a secondary phase. The specific problem involves integrating multiple carbides with different crystal structures into a single-phase material. The motivation stems from the need for ceramics that retain mechanical strength at high temperatures while resisting oxidation. The researchers propose that a hexagonal lattice structure could accommodate multiple metal atoms and nonmetals in a single unit cell. The study also seeks to confirm the formation of a single-phase ceramic through experimental and computational methods. By combining B4C, HfC, Mo2C, TaC, TiC, and SiC, the team aimed to achieve structural compatibility and improved mechanical performance. The addition of SiC was intended to enhance oxidation resistance in the composite. The research tests whether high-entropy principles can be applied to refractory carbide systems to form a stable, single-phase material.

The research team used a combination of electron microscopy, X-ray diffraction, and density functional theory (DFT) calculations to analyze the ceramic composite. Electron microscopy was employed to observe the microstructure and crystallographic features of the composite. X-ray diffraction confirmed the formation of a single-phase B4(HfMo2TaTi)C ceramic with a hexagonal close-packed (HCP) structure. DFT calculations predicted the arrangement of metal atoms on the (0001) plane and carbon/boron atoms on the (0002) plane of the HCP lattice. Nanoindentation was used to measure the hardness of the high-entropy phase. The researchers also examined the role of SiC in tailoring the microstructure and improving oxidation resistance. The study compared experimental hardness values with theoretical predictions based on the rule of mixtures. The team validated the structural compatibility of the carbides by analyzing lattice parameters and crystal structure differences. The methods combined experimental and computational approaches to confirm the formation of a single-phase ceramic.

The study found that a single-phase B4(HfMo2TaTi)C ceramic with SiC formed successfully. Electron microscopy and X-ray diffraction confirmed the presence of a hexagonal close-packed (HCP) structure. DFT calculations showed that metal atoms occupied the (0001) plane while carbon/boron atoms formed hexagonal 2D grids on the (0002) plane. The nanoindentation results revealed a hardness of 35 GPa, which is higher than the theoretical value of 23 GPa based on the rule of mixtures. The increased hardness is attributed to solid solution strengthening in the multicomponent hexagonal structure. The addition of SiC as a secondary phase improved the microstructure and oxidation resistance of the composite. The study demonstrated that the metal and nonmetal atoms diffused independently to form a unique hexagonal lattice. The classical differences in crystal structures among the carbides were overcome in the final composite material. The results suggest that high-entropy principles can be applied to refractory carbide systems to form stable, single-phase ceramics.

The authors propose that the high-entropy B4(HfMo2TaTi)C ceramic with SiC can be formed successfully. The hexagonal close-packed structure accommodates multiple metal atoms and nonmetals in a single lattice. The study confirms that the classical differences in crystal structures among the carbides were overcome. The formation of a single-phase ceramic was validated through electron microscopy, X-ray diffraction, and DFT calculations. The hardness of the high-entropy phase was higher than expected based on the rule of mixtures. The solid solution strengthening effect in the multicomponent hexagonal structure contributed to the increased hardness. The addition of SiC improved the microstructure and oxidation resistance at high temperatures. The results suggest that high-entropy principles can be used to design refractory ceramic composites with enhanced mechanical properties.