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

A new high-entropy diboride (Hf0.25Zr0.25Ta0.25Sc0.25)B-2 was designed to investigate the effect of introducing rare-earth metal diboride ScB2 into high-entropy diborides on its structure and properties. The local mixing enthalpy predicts that (Hf0.25Zr0.25Ta0.25Sc0.25)B-2 has high enthalpy driving force, which more easily allows the formation of single-phase AlB2-type structures between components. The experiments further demonstrate that (Hf0.25Zr0.25Ta0.25Sc0.25)B-2 possesses excellent phase stability, lattice integrity and nanoscale chemical homo-geneity. (Hf0.25Zr0.25Ta0.25Sc0.25)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 (Hf0.25Zr0.25Ta0.25Sc0.25)B-2 is higher than that of ZrB2 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.

Automated summary

A new high-entropy diboride (Hf0.25Zr0.25Ta0.25Sc0.25)B-2 was designed and studied for its structure and properties by introducing rare-earth metal diboride ScB2. The experiments showed that (Hf0.25Zr0.25Ta0.25Sc0.25)B-2 possesses excellent phase stability, hardness, and low thermal conductivity. The introduction of Sc into high-entropy diborides can tailor the properties associated with the bonding, expanding the compositional space.