The nucleation and migration mechanisms of asymmetric 1123 twin boundary in hexagonal close-packed titanium

H Guo and T Zhao and J Zhang and H Ju and Z Meng and Y Ma and Q Wang and H Wang and D Xu and R Yang, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 924, 147761 (2025).

DOI: 10.1016/j.msea.2024.147761

The 1123 twin, with a large twinning strain (1.89), hardly nucleated in hexagonal close-packed (HCP) titanium. This poses challenges for experimental detection, resulting in limited studies. Consequently, the twin boundary (TB) structure, nucleation, and migration mechanisms of this twin remain poorly understood. In this study, we use atomistic simulations and electron backscatter diffraction (EBSD) to elucidate these mechanisms. Contrary to classical theory, our results show that the 1123 TB with mirror symmetry deteriorates during relaxation and becomes asymmetric. This breakdown is attributed to the intense repulsive interactions between the short-bonded atom pairs located at mirrored positions, with a distance smaller than half of the lattice parameter a. During TB migration, a well-defined single-layer height twinning dislocation b1 with Burgers vectors of 1/( 4 Lambda 2 +6)1122 +/- 1/121100 was identified, which differs from the twinning dislocation b2 predicted by classical theory. Meanwhile, an inverse shuffling displacement occurs along the 1100 direction for the double- layered prismatic (1100) planes. Notably, our research indicates that the nucleation of individual 1123 twin within HCP structure is inherently challenging. Nevertheless, 1123 TB can nucleate via the interactions among TBs, specifically between the 1121 and 1122 TB. These insights advance our understanding of the plastic deformation inherent in titanium alloys.

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