Anomalies in the deformation mechanism and kinetics of coarse-grained high entropy alloy

Starting from the thermodynamics to thermal and mechanical properties, high entropy alloys (HEAs) always deviate from the behavior of conventional materials and stamp its uniqueness among the alloy systems. In this study, tensile deformation mechanisms of HEA was investigated. A simple system, an Al0.1CoCrFeNi HEA, with a single crystal structure (face-centered cubic, FCC), coarser grains (CG), and low dislocation density was chosen to exclusively study the effect of intrinsic lattice on the HEA deformation mechanisms and kinetics. Monotonic tests were done at the strain rate of 10−3 s−1, and all the transient tests were started at the initial strain rate of 10−3 s−1. Strain-jump tests were carried out at strain rates of 10−5 s−1 and 10−3 s−1. Repeated stress relaxation tests were performed along the stress-strain curve to calculate the physical activation volume. Surprisingly, a large rate sensitivity of the flow stress and low activation volume of dislocations were observed, which are unparalleled, as compared to conventional CG FCC metals and alloys. The observed trend has been explained in terms of the lattice distortion and dislocation-energy framework. As opposed to the constant dislocation line energy and Peierls potential energy (amplitude,ΔE) in conventional metals and alloys, both the line energy and Peierls potential undergo continuous variations in the case of HEAs. These energy fluctuations have greatly affected the dislocation mobility and can be distinctly noted from the activation volume of dislocations.