ZrB 2 ‐based solid solution ceramics and their mechanical and thermal properties

Abstract Zirconium diboride ceramics as one of the main members of ultrahigh‐temperature ceramics are capable of being used as structural components at ultrahigh temperatures. Entropy adjusting is a newly developed approach to improving the properties of ceramics. In this work, a series of ZrB 2 ‐based solid solution ceramics with different mixing entropies, formulated (Zr x Ti y Nb y Ta y )B 2 ( x = .25, .85, .925, .9625, 1; x + 3 y = 1), were prepared by adjusting the content of other diborides. Diboride solid solution powders were synthesized by boro/carbothermal reduction process and then densified by spark plasma sintering. The results show that the formation of a single‐phase solid solution is independent of the mixing entropy in (Zr x Ti y Nb y Ta y )B 2 system. The addition of other diborides into ZrB 2 is beneficial to reduce the particle size of the synthesized powder and promote the densification process. The dense sintered samples with higher mixing entropy have finer grain size, higher hardness, and modulus. The (Zr 0.25 Ti 0.25 Nb 0.25 Ta 0.25 )B 2 ceramic has the highest hardness of 31 GPa and a modulus of 682 GPa. Severe lattice distortion in samples with higher mixing entropy will result in increased phonon scattering and lower thermal conductivity.