Enthalpy driving force and chemical bond weakening: The solid-solution formation mechanism and densification behavior of high-entropy diborides (Hf1−x/4Zr1−x/4Nb1−x/4Ta1−x/4Scx)B2.

(Hf 0.2 Zr 0.2 Nb 0.2 Ta 0.2 Sc 0.2)B 2 was designed to improve the densification and solid-solution formation of high-entropy transition metal diborides, and its phase stability was predicted using the energy distribution of the local mixing enthalpy of all possible configurations. It was found that (Hf 0.2 Zr 0.2 Nb 0.2 Ta 0.2 Sc 0.2)B 2 are enthalpy-stabilized materials. The two-component metal diborides formed by transition metal diborides (HfB 2 , ZrB 2 , TaB 2 and NbB 2) with ScB 2 are thermodynamically favorable, based on the mixing enthalpy. Therefore, the introduction of ScB 2 in high-entropy metal diborides is beneficial to reduce the mixing Gibbs free energy during the boro/carbothermal reduction process, which enables the formation of single-phase solid solution at low temperatures. Even high-entropy metal diboride powders with large particle sizes, 25–57 µm, can achieve sintered density up to ~97% due to the introduction of ScB 2 in high-entropy metal diborides, owing to its weakening action on the TM d - B p and the TM dd bonding. [ABSTRACT FROM AUTHOR]