Basal stacking fault induced twin boundary gliding, twinning disconnection and twin growth in hcp Ti from the first-principles

First-principles calculations were performed to investigate the structures and energetics of coherent twin boundaries (CTBs) and glide twin boundaries (GTBs) in hexagonal close-packed (hcp) Ti. The formation mechanism of GTBs and their correlation with twin growth were fundamentally explored. Results suggested that GTBs can form from the gliding of CTBs, through their interaction with basal stacking fault. The gliding eventually restored the CTB structures by forming a pair of single-layer twinning disconnections. The pile-up of twinning disconnections should be responsible for the wide steps at twin boundaries as observed in high-resolution transmission electron microscopy, which can further promote twin growth. Possible effects of various alloying elements on pinning twin boundaries were also evaluated, to guide the strengthening design of Ti alloys.