Abstract
A new high-entropy diboride (Hf0.25Zr0.25Ta0.25Sc0.25)B2 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)B2 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)B2 possesses excellent phase stability, lattice integrity and nanoscale chemical homogeneity. (Hf0.25Zr0.25Ta0.25Sc0.25)B2 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)B2 is higher than that of ZrB2 and HfB2 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.
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