Strain rate dependent shear localization and deformation mechanisms in the CrMnFeCoNi high-entropy alloy with various microstructures

Abstract

CrMnFeCoNi high-entropy alloys (HEA) with various microstructures have been produced using cold rolling followed by critical annealing at various temperatures. Shear deformation behaviors of this HEA with various microstructures at a wide range of strain rates (2 × 10-3-5 × 104 s-1) have been characterized using hat-shaped specimens. Strain hardening exponent and strain rate sensitivity have been obtained for various microstructures. No shear localization was observed up to shear strain of 8 for all microstructures under lower strain rates (2 × 10-3-1 × 101 s-1), while stress drop and shear localization were found to occur at various critical shear strains for various microstructures under dynamic shear loading (5 × 104 s-1). A new formula, considering competition of strain hardening and strain rate hardening against thermal softening, was proposed to estimate the critical shear strains under dynamic shear loading and the predicted results were found to be in a fairly good agreement with the experimental data. Based on micro-hardness testing, the strain hardening due to the microstructure evolution was found be much stronger under dynamic shear loading than that under quasi-static loading at the same interrupted shear strain, which can be attributed to the more efficient grain refinement and the triggered hierarchical deformation nanotwins under dynamic shear deformation.