Study on microstructure, mechanical properties and thermal performance of single-phase (Ti,Zr,Hf)B2 solid solution

Transition metal diborides are an important component of ultra-high temperature ceramics with particularly attractive high-temperature performance. In order to promote the application of borides in the field of high-temperature protection, a single-phase (Ti,Zr,Hf)B2 solid solution was synthesized, inspired by the concept of high-entropy effect. The mechanical, thermal conductivity and thermal expansion coefficient of (Ti,Zr,Hf)B2 ceramics were analyzed by experiments and First-principles calculations. Even compared with currently existing high-entropy diborides, the single-phase (Ti,Zr,Hf)B2 showed a higher Vicker hardness (30.22 ± 2.43 GPa). Furthermore, it possessed lower thermal conductivity (7.2–11.0 W·m−1·K−1) at 25–1000 °C and higher thermal expansion coefficient (8.7 ×10−6 K−1) at 25–1100 °C than transition metal diborides (TiB2, ZrB2, HfB2). The high-temperature oxidation behavior of (Ti,Zr,Hf)B2 ceramics was also investigated at 1000–1400 °C in air for 3 h. In this study, we provided a new strategy for designing transition diboride solid solutions.