Zhang Hanzhu, Hedman Daniel, Feng Peizhong, Han Gang, Akhtar Farid
Division of Materials Science, Luleå University of Technology, 971 87 Luleå, Sweden.
Dalton Trans. 2019 Apr 16;48(16):5161-5167. doi: 10.1039/c8dt04555k.
A multicomponent composite of refractory carbides, B4C, HfC, Mo2C, TaC, TiC and SiC, of rhombohedral, face-centered cubic (FCC) and hexagonal crystal structures is reported to form a single phase B4(HfMo2TaTi)C ceramic with SiC. The independent diffusion of the metal and nonmetal atoms led to a unique hexagonal lattice structure of the B4(HfMo2TaTi)C ceramic with alternating layers of metal atoms and C/B atoms. In addition, the classical differences in the crystal structures and lattice parameters among the utilized carbides were overcome. Electron microscopy, X-ray diffraction and calculations using density functional theory (DFT) confirmed the formation of a single phase B4(HfMo2TaTi)C ceramic with a hexagonal close-packed (HCP) crystal structure. The DFT based crystal structure prediction suggests that the metal atoms of Hf, Mo, Ta and Ti are distributed on the (0001) plane in the HCP lattice, while the carbon/boron atoms form hexagonal 2D grids on the (0002) plane in the HCP unit cell. The nanoindentation of the high-entropy phase showed hardness values of 35 GPa compared to the theoretical hardness value estimated based on the rule of mixtures (23 GPa). The higher hardness was contributed by the solid solution strengthening effect in the multicomponent hexagonal structure. The addition of SiC as the secondary phase in the sintered material tailored the microstructure of the composite and offered oxidation resistance to the high-entropy ceramic composite at high temperatures.
据报道，由菱形、面心立方（FCC）和六方晶体结构的难熔碳化物（B4C、HfC、Mo2C、TaC、TiC和SiC）组成的多组分复合材料与SiC形成单相B4(HfMo2TaTi)C陶瓷。金属和非金属原子的独立扩散导致了B4(HfMo2TaTi)C陶瓷独特的六方晶格结构，其中金属原子层与C/B原子层交替排列。此外，还克服了所用碳化物在晶体结构和晶格参数方面的经典差异。电子显微镜、X射线衍射以及使用密度泛函理论（DFT）的计算证实了具有六方密堆积（HCP）晶体结构的单相B4(HfMo2TaTi)C陶瓷的形成。基于DFT的晶体结构预测表明，Hf、Mo、Ta和Ti的金属原子分布在HCP晶格中的（(0001)）平面上，而碳/硼原子在HCP晶胞中的（(0002)）平面上形成六方二维网格。与基于混合法则估算的理论硬度值（(23)GPa）相比，高熵相的纳米压痕显示硬度值为(35)GPa。较高的硬度归因于多组分六方结构中的固溶强化效应。在烧结材料中添加SiC作为第二相，可调整复合材料的微观结构，并使高熵陶瓷复合材料在高温下具有抗氧化性。
