Deformation nanotwins suppress shear banding during impact test of CrCoNi medium-entropy alloy

We report deformation bands ahead of the crack tip in a CrCoNi alloy under impact loading, and analyze the effects of deformation twinning on strain localization in the form of shear banding. Due to low stacking fault energy, upon high-strain-rate deformation this medium-entropy alloy forms twins with thickness and spacing of only a few nanometers. These nano-twins are embedded dynamically not only ahead of any developing shear band to retard its advance, but also in its interior to work harden. This dual effect helps to suppress runaway shear banding instability that instigates failure and contributes to the energy absorption as recorded in instrumented Charpy tests. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.