Phase structure, mechanical properties and thermal properties of high-entropy diboride (Hf0.25Zr0.25Ta0.25Sc0.25)B2.

A new high-entropy diboride (Hf 0.25 Zr 0.25 Ta 0.25 Sc 0.25)B 2 was designed to investigate the effect of introducing rare-earth metal diboride ScB 2 into high-entropy diborides on its structure and properties. The local mixing enthalpy predicts that (Hf 0.25 Zr 0.25 Ta 0.25 Sc 0.25)B 2 has high enthalpy driving force, which more easily allows the formation of single-phase AlB 2 -type structures between components. The experiments further demonstrate that (Hf 0.25 Zr 0.25 Ta 0.25 Sc 0.25)B 2 possesses excellent phase stability, lattice integrity and nanoscale chemical homogeneity. (Hf 0.25 Zr 0.25 Ta 0.25 Sc 0.25)B 2 showed relatively high hardness (30.7 GPa), elastic modulus (E , G , and B of 522, 231 and 233 GPa, respectively), bending strength (454 MPa), and low thermal conductivity (13.9 W·m−1·K−1). The thermal expansion of (Hf 0.25 Zr 0.25 Ta 0.25 Sc 0.25)B 2 is higher than that of ZrB 2 and HfB 2 due to weakened bonding (M d - B p and M dd bonding) and enhanced anharmonic effects. Thus, incorporating Sc into high-entropy diborides can tailor the properties associated with the bonding, which further expands the compositional space of high-entropy diborides. [ABSTRACT FROM AUTHOR]