Phase Transformation Assisted Twinning in Face-Centered-Cubic FeCrNiCoAl <sub>0.36</sub>

Abstract

The FeNiCoCr-based high entropy alloys (HEAs) exhibit excellent mechanical properties, such as twin-induced plasticity (TWIP) and phase transformation plasticity (TRIP) that can reach a remarkable combination of strength and ductility. In this work, the face-centered-cubic (FCC) single-crystal FeNiCoCrAl0.36 HEAs were studied, using the density functional theory (DFT) combined with the phonon calculation to estimate the stacking fault energies, temperature-dependent phase stabilities of different structures. And the kinetic Monte Carlo (kMC) is used to predict the substructures evolution based on the transition state energies obtained from DFT calculations. We proposed two different formation paths of nano-twins in this Al-composited HEA and found that short-range hexagonal-close-packed (HCP)-stacking could occur in this HEA. DFT calculations suggest that this HEA has negative stacking fault energy, HCP formation energy, and twin-formation energy at 0 K. Phonon calculations represent that at the finite temperature, the competing FCC/HCP phase stability and propensity for twinning makes it possible to form HCP-like twin boundaries. The kMC simulations suggest that under deformation, HCP substructures could form followed by twins which differs to the study of others. With the great agreement of results from kMC simulations and experiments, this twin-formation path offers a new concept of designing TWIP HEAs containing tunable twin structures with HCP and TWIN lamellae structures, which results in better mechanical properties of HEAs.