A new criterion for formation capability of annealing twin in face-centered cubic metals/alloys

Annealing twins (ATs) are prevalent in face-centered cubic (FCC) metals/alloys and significantly influence their mechanical properties. Therefore, understanding the formation capability of ATs is crucial for controlling the mechanical properties of FCC metals/alloys. Although the "Stacking Fault Energy" is a widely used factor to characterize AT formation capability, it doesn't comprehensively explain the observed experimental rankings of AT formation capability. In this study, through a combination of experiments and molecular dynamics simulations, we demonstrated that AT growth is primarily driven by the migration of the Sigma 3 incoherent twin boundary. This migration arises from the elastic strain energy imbalance between grains on either side of the twin boundary caused by the elastic anisotropy of crystal. Based on these findings, we propose a new criterion, defined as a ratio of the coherent twin boundary energy to the anisotropy factor, to represent the AT formation capability (inverse relationship). Such new criterion well explains the experimental observation, and can be generalized to the zero macroscopic strain deformation twin.