Anisotropic plasticity of nanocrystalline Ti: A molecular dynamics simulation

Using molecular dynamics simulations, the plastic deformation behavior of nanocrytalline Ti has been investigated under tension and compression normal to the 0001, 1010, and 1210 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 1010 and 1210), 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 <1210>_HCP||<110>_FCC, and 1010_HCP||110_FCC and <0001>_HCP||<010>_FCC between the HCP and FCC phases have been observed in the present work. For the transformation of HCP→BCC→HCP, the OR is 0001_α1||110_β||1010_α2 (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.