Synthesis and thermodynamic analysis of nanostructured CuNiCoZnAl high entropy alloy produced by mechanical alloying

Abstract

Mechanical alloying was used to fabricate CuNiCoZnAl equiatomic high entropy alloy by two routes. In one route where balls with similar radii were used, the alloy was not formed even after 50 h mechanical alloying. However, in the other route by increasing the velocity of ball milling and using balls with different radii the alloy was synthesized successfully. Characterization of the alloy indicated that a FCC single phase solid solution was formed and no indication of any amorphous phase or intermetallic compound was found in the microstructure. Energy analysis showed that the total energy transferred during ball milling in the second route was nearly 1.7 times compared to the first route. Parameters such as melting point, mixing enthalpy change, mixing entropy change, atomic size difference, electronegativity difference and valence electron concentration were calculated to investigate the criteria for high entropy alloy formation. Thermodynamic analysis using extended Miedema model confirmed the lowest Gibbs free energy for solid solution compared to amorphous and binary intermetallic phases indicating the formation of solid solution as the stable phase.