Room temperature cyclic creep behaviour of equimolar CoCuFeMnNi high entropy alloy

Abstract

The room temperature ratcheting response of equiatomic FCC CoCuFeMnNi high entropy alloy containing Cu-rich nanoclusters in HEA matrix at different mean stress and stress amplitude indicated the critical role of interaction among dislocations as well as dislocations and Cu-rich nanoclusters in determining the deformation response and damage accumulation contributing to final failure. Detailed microstructural investigation using EBSD and TEM capture the evolution of complex defect microstructure for different cyclic loading conditions. Perennial network of Cu-rich nanoclusters transforming into entangled Cu-rich nanofibers during ratcheting was observed in the three-dimensional elemental maps obtained using APT. This can be attributed to shearing of spherical clusters followed with enhanced short-range diffusion contributing to the decoration of dislocation structure formed by cyclic loading with copper atoms. Further, an increase in the concentration of copper in the solid solution matrix contributes to additional solid solution strengthening, compensating for cluster strengthening and leading to a lower steady-state creep rate with better ratcheting performance. Thus, synergistic operation of cluster and solid solution strengthening in improved ratcheting response of CoCuFeMnNi HEA showcases the unique ability of HEAs to offer excellent mechanical properties beyond superior strength-ductility combination.