Phase stability, mechanical, and thermal properties of high‐entropy transition and rare‐earth metal diborides from first‐principles calculations

Abstract The narrow composition design space of high‐entropy transition metal diborides (HE TMB 2 ) limits their further development. In this study we designed six quaternary and quinary high‐entropy transition metal and rare‐earth diborides (HE TMREB 2 ) and investigated their phase stability using the energy distribution of the local mixing enthalpy of all possible configurations. The results show that both quaternary and quinary HE TMREB 2 have higher enthalpic driving forces, which facilitates the formation of single‐phase AlB 2 ‐type structures between TMB 2 and REB 2 . Calculations of elastic constants show that the TMB 2 component has the greatest effect on the c 44 elastic constant and shear modulus G , while REB 2 significantly influences the bulk modulus B . Furthermore, LuB 2 and TmB 2 substantially affect the elastic modulus anisotropy of HE TMB 2 . Rare‐earth atoms in HE TMREB 2 can enhance the nonharmonic interactions between phonons, which results in a significant hindrance in the thermal transport of low‐frequency phonons as well as an increase in the volume thermal expansion coefficients. Thus, the incorporation of REB 2 into HE TMB 2 has a significant impact on the phase stability and properties.