FCC-BCC phase transformation induced simultaneous enhancement of tensile strength and ductility at high strain rate in high-entropy alloy

FCC-BCC phase transformation-induced plasticity (TRIP) has been extensively studied in high-entropy alloys (HEAs) to customize their mechanical properties through compression/tension loading or thermal fabrication processes. In this study, we employed a combination of molecular dynamics (MD) and Monte-Carlo (MC) simulations to investigate the effects of TRIP on the uniaxial strain tensile deformation of Co₂₅Ni₂₅Fe₂₅Al_7.5Cu_17.5 HEA. Our results demonstrate that a complete FCC-BCC phase transformation occurs, in accordance with the N-W relationship, resulting in a simultaneous enhancement of strength and ductility. This is attributed to the HEA's significantly low stacking fault energy and pronounced lattice distortion (LD). However, short-range order (SRO) acts as an obstacle on atomic sliding, which further reduces the degree of phase transformation, leading to an increase in Young's modulus but a decrease in ductility. Furthermore, an increase in strain rate can promote the occurrence of the phase transformation to a certain extent but also leads to an increase in the degree of disorder defects. We also found that the HEA maintains excellent thermal stability up to 900 K, but the amount of phase transformation decreases with increasing initial temperature. Our systematic study of FCC-BCC transformation, considering the effects of SRO, LD, strain rate, and temperature, provides insights into tailoring the mechanical properties of HEAs for practical design purposes.