A dual phase boride and carbide ceramic with the nominal composition (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)B2 and (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C was prepared by reactive synthesis and consolidated by spark plasma sintering. The resulting microstructure contained about 30% (in volume) boride and 70% carbide. Compositional inhomogeneities were observed within single grains that had core-shell structures and preferential accumulation of specific metals in the boride or carbide phases. Specifically, Ti and Nb had higher concentrations in the boride, whereas Hf and Ta in the carbide. The Zr concentration was relatively equally distributed in the two phases. The dual phase ceramic had additional, distinctive features including nanosized inclusions, possibly related to local miscibility gaps and supersaturation, linear defects, and strain due to adjustment of the crystal structure. As a consequence, the fracture mode was transgranular with the crack path deviated by these nanometric microstructure alterations. Nanoindentation under 5 mN measured higher hardness and modulus for the boride, 30 GPa and 525 GPa, as compared to the carbide phase, 22 GPa and 425 GPa, due to a higher concentration of dislocation tangles and strains deriving from the introduction of metals with different sizes (and properties) in a less compliant hexagonal lattice.

中文翻译：

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基于多阳离子硼化物和碳化物的双相陶瓷：纳米尺度的研究


采用反应合成制备了标称成分为（Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2）B2和（Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2）C的双相硼化物和碳化物陶瓷，并通过放电等离子烧结进行固结。所得微观结构包含约 30%（体积）硼化物和 70% 碳化物。在具有核壳结构的单个晶粒中观察到成分不均匀性，并且特定金属优先在硼化物或碳化物相中积累。具体来说，硼化物中的 Ti 和 Nb 浓度较高，而碳化物中的 Hf 和 Ta 浓度较高。Zr 浓度在两个相中分布相对均匀。双相陶瓷具有额外的独特特征，包括纳米级夹杂物，可能与局部混溶间隙和过饱和度、线性缺陷以及由于晶体结构调整引起的应变有关。因此，断裂模式是跨晶的，裂纹路径因这些纳米微观结构的变化而偏离。与碳化物相 22 GPa 和 425 GPa 相比，5 mN 下的纳米压痕测得的硼化物硬度和模量更高，分别为 30 GPa 和 525 GPa，这是由于在柔韧性较差的六方晶格中引入具有不同尺寸（和特性）的金属而产生的位错缠结和应变浓度更高。