From stacking fault to phase transformation: A quantitative model of plastic deformation of CoCrFeMnNi under different strain rates

Abstract

To explore the plastic deformation behavior of CoCrFeMnNi high entropy alloy (HEA) at extreme conditions, the effect of strain rate ranging from 1 × 108 s−1 to 5 × 1010 s−1 on microstructural evolution and deformation mechanism was investigated via molecular dynamics (MD) simulations. Our results show that the alloy exhibits completely different deformation mechanism under lower and higher strain rates conditions. The deformation mechanism of the alloy is mainly the formation and evolution of stacking faults and twins driven by Shockley dislocations at lower strain rates, and a continuous phase transformation from FCC to HCP with the BCC phase as the transition at higher strain rates. Between the lower and higher strain rates, there are intermediate strain rates where the two deformation mechanisms coexist. A quantitative model was established to describe the strength of the alloy at intermediate strain rates by considering the contributions of four microstructural features that occur during the plastic deformation. Fitted empirical model with single adjustable parameters can agree well with those calculated by MD simulations. The present work can help researchers better understand the deformation mechanism of the CoCrFeMnNi HEA at different strain rates, thereby pointing out directions for alloy strengthening.