Toughened (Ti <sub>0.2</sub>Zr <sub>0.2</sub>Hf <sub>0.2</sub>Nb <sub>0.2</sub>Ta <sub>0.2</sub>)B <sub>2</sub>–SiC composites fabricated by one-step reactive sintering with a unique SiB <sub>6</sub> additive
Hao Wei, Xinzhe Lu, Ling Li, Tao Wang, Guoliang Ren, Huangyue Cai, Xiaofeng Zhao, Dongyun Wang, Na Ni
Abstract
High-entropy diboride has been arousing considerable interest in recent years. However, the low toughness and damage tolerance limit its application as ultra-high temperature structural materials. Here we report that a unique SiB<sub>6</sub> additive has been first incorporated as boron and silicon sources to fabricate a high-entropy boride (Ti<sub>0.2</sub>Zr<sub>0.2</sub>Hf<sub>0.2</sub>Nb<sub>0.2</sub>Ta<sub>0.2</sub>)B<sub>2</sub>-SiC composite though one-step boro/carbothermal reduction reactive sintering. A synergetic effect of high-entropy sluggish diffusion and SiC secondary phase retarded the grain growth of the (Ti<sub>0.2</sub>Zr<sub>0.2</sub>Hf<sub>0.2</sub>Nb<sub>0.2</sub>Ta<sub>0.2</sub>)B<sub>2</sub>-51SiC composites. The small grain size was beneficial to shorten the diffusion path for mass transport, thereby enhancing the relative density to ~99.3 %. These results in an increase of fracture toughness from ~5.2 in HEBS-1900 to ~7.7 MPa m<sup>1/2</sup> in HEBS-2000, which corresponded to a large improvement of 48 %. The improvement was attributed to a mixed mode of intergranular and transgranular cracking for offering effective pinning in crack propagation, resulting from a balanced grain boundary strength collectively affected by improved densification, solid solution strengthening, and the incorporation of SiC secondary phase.