Anisotropic plasticity of nanocrystalline Ti: A molecular dynamics simulation**Project supported by the National Natural Science Foundation of China (Grant No. 11572259), the Natural Science Foundation of Shaanxi Province, China (Grant Nos. 2019JQ-827, 2018JM1013, and 2018JQ5108), and the Scientific Research Program Funded by Shaanxi Provincial Education Department, China(Grant No. 19JK0672).

Abstract

Using molecular dynamics simulations, the plastic deformation behavior of nanocrytalline Ti has been investigated under tension and compression normal to the {0001}, , and planes. The results indicate that the plastic deformation strongly depends on crystal orientation and loading directions. Under tension normal to basal plane, the deformation mechanism is mainly the grain reorientation and the subsequent deformation twinning. Under compression, the transformation of hexagonal-close packed (HCP)-Ti to face-centered cubic (FCC)-Ti dominates the deformation. When loading is normal to the prismatic planes (both and ), the deformation mechanism is primarily the phase transformation among HCP, body-centered cubic (BCC), and FCC structures, regardless of loading mode. The orientation relations (OR) of {0001}HCP║{111}FCC and , and and between the HCP and FCC phases have been observed in the present work. For the transformation of HCP → BCC → HCP, the OR is (HCP phase before the critical strain is defined as α1-Ti, BCC phase is defined as β-Ti, and the HCP phase after the critical strain is defined as α2-Ti). Energy evolution during the various loading processes further shows the plastic anisotropy of nanocrystalline Ti is determined by the stacking order of the atoms. The results in the present work will promote the in-depth study of the plastic deformation mechanism of HCP materials.