Enthalpy driving force and chemical bond weakening: The solid-solution formation mechanism and densification behavior of high-entropy diborides (Hf_1−x/4Zr_1−x/4Nb_1−x/4Ta_1−x/4Sc_x)B₂

(Hf_0.2Zr_0.2Nb_0.2Ta_0.2Sc_0.2)B₂ 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_0.2Zr_0.2Nb_0.2Ta_0.2Sc_0.2)B₂ are enthalpy-stabilized materials. The two-component metal diborides formed by transition metal diborides (HfB₂, ZrB₂, TaB₂ and NbB₂) with ScB₂ are thermodynamically favorable, based on the mixing enthalpy. Therefore, the introduction of ScB₂ 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 ScB₂ in high-entropy metal diborides, owing to its weakening action on the TM d - B p and the TM dd bonding.