In this study, molecular dynamics simulations were conducted to investigate the factors influencing mechanical anisotropy in hetero-nanostructured titanium, focusing on (i) the intrinsic plastic characteristics of the HCP structure and (ii) the microstructural features specific to hetero-nanostructured titanium. Three types of models reflecting the crystallographic features of hetero-nanostructured titanium were employed: a polycrystalline model consisting of eight grains, a bicrystal model with a Σ15 grain boundary (tilt angle: 79°), and a bicrystal model with a Σ5 grain boundary (tilt angle: 101°). Uniaxial tensile simulations were performed along both the rolling direction (RD) and the transverse direction (TD) to assess the effects of grain size and boundary orientation on the deformation behavior. The results revealed that the TD consistently exhibited higher strength than the RD, and that the geometric relationship between the tensile direction and the grain boundary plane significantly affected the strength. In particular, differences in the mean free path of the activated slip systems during deformation were identified as a possible key factor governing the anisotropic strength. These findings suggest that both the plastic behavior and microstructural configuration play critical roles in determining the mechanical anisotropy of HCP metals.
MIYAZAKI et al. (Wed,) studied this question.