More than entropy in high-entropy alloys: Forming solid solutions or amorphous phase

• A two-parameter rule is revealed capturing the phase selection mechanism in HEAs.
• A critical atomic size polydispersity ∼0.065 determines the phase selection.
• A more negative ΔHmix (<−12 kJ/mol) favors the amorphous phase formation.
• The rule becomes sufficient only when intermetallic compounds are not formed.

Metastable solid solutions can form preferably over intermetallic compounds, in cast high-entropy alloys or multi-component alloys with equi- or nearly equi-atomic compositions, due to the entropy contribution at elevated temperatures. Meanwhile, the high mixing entropy also favors the amorphous phase formation. The phase selection between solid solutions and the amorphous phase upon alloying in high-entropy alloys is intriguing. A two-parameter physical scheme, utilizing the atomic size polydispersity and mixing enthalpy, is found to be capable of capturing this phase selection mechanism.