Influence of Al and Cu elements on the microstructure and properties of (FeCrNiCo)AlxCuy high-entropy alloys

• Relationship between entropy and enthalpy on phase formation was specified.
• Phase changed from fcc to fcc plus bcc and then bcc phase.
• Mechanical properties changed from plasticity to brittleness.
• Young’s modulus, hardness and yield strength increased with Al element.

(FeCrNiCo)AlxCuy high-entropy alloys were designed using the strategy of equiatomic ratio, high entropy of mixing and different mixing enthalpies of atom-pairs. The effects of entropy and enthalpy on phase forming process of the alloys were clearly studied and the influences of Al and Cu elements on the microstructure and mechanical properties were investigated. As long as Al element level increased from 0.5 to 1, the microstructure of the alloy system changed from fcc structure to duplex fcc plus bcc structure and then a single bcc structure. Increase of Al element greatly enhanced the Young’s modulus, hardness and yield strength of these alloys. (FeCrNiCo)Al0.75Cu0.5 alloy got the most excellent comprehensive mechanical properties; its fracture strength and plastic strain were as high as 2270 MPa, and 42.70%, respectively. Cu-rich phase formed in the alloys when Cu element was in high levels. Increase of Cu element greatly decreased fracture strength of the high-entropy alloys when Al element was in the high level of x = 1.