Twin nucleation in Ti: A study using nudged elastic band (NEB) method

Capturing twin nucleation in full-field crystal plasticity is a long-standing problem in materials science. The challenge resides mainly in the biased regional lattice transformation associated with twin formation in defiance of its obedience to a threshold stress law which could be fulfilled in regions where twinning is deferred. Hence, determining a favorable site for nucleation of a twin variant remains a daunting task. We hypothesized that this site-specific nucleation is sensitive to the prior atomic structure of the lattice so twin embryos form in regions where the lattice transformation energy is minimum. Thus, quantifying the local strain energy required to trigger a stable twin underscores the non-pseudo-slip behavior of twin nucleation and growth. We performed atomistic calculations based on the nudged elastic band method to identify the minimum energy path and activation energy associated with {10-12} twin nucleation in titanium. Results of calculations demonstrate that the role of stress and atomic structure in twin nucleation could be understood in terms of the minimum energy path, energy barrier, and relaxed energy. Remarkably, for symmetric tilt grain boundaries, a linear correlation between the nucleation stress and grain boundary energy was observed.