Influence of Cr content on sintering, textured structure, and properties of (Hf, Zr, Ta, Cr, Ti)B2 high-entropy boride ceramics

In order to provide insights into the influence of Cr content on the microstructure and corresponding properties of (Hf, Zr, Ta, Cr, Ti)B-2, the effects of 10 at.% to 30 at.% Cr contents on texture development, phase composition, microstructure, and mechanical properties of (Hf, Zr, Ta, Cr, Ti)B-2, which were prepared via a combination of boro/carbothermal reduction and SPS, were investigated in this study. The results showed that (Hf, Zr, Ta, Cr, Ti) B-2 added with 15 at.% Cr content samples formed a textured microstructure due to the formation of CrB in the (Hf, Zr, Ta, Cr, Ti)B-2 high-entropy boride powder. With the increase of Cr content up to 30 at.%, the density, grain size, and fracture toughness of (Hf, Zr, Ta, Cr, Ti)B-2 high entropy boride ceramics increased, then for higher content, they decreased, and tended to remain constant. The hardness of (Hf, Zr, Ta, Cr, Ti)B-2 decreased with the increase of Cr content. The (Hf, Zr, Ta, Cr, Ti)B-2 with 15 at.% Cr content possessed the best comprehensive mechanical performance (Hv(0.2): TS:26.9 +/- 0.8 GPa, SS: 26.5 +/- 0.6 GPa; K-Ic: TS:4.21 +/- 0.46 MPa.m1/2, SS: 3.16 +/- 0.18 MPa.m1/2) due to a combination of high relative density and unique textured structure.