Atomistic studies of stress effects on self-interstitial diffusion in α-titanium*

Abstract

The diffusion anisotropy of intrinsic point defects is an important factor governing the behavior of the HCP metals bombarded by energetic particles. The effects of stress on the diffusion and its anisotropy, although known to be important, have not been well understood. In this paper, we use a combination of molecular dynamics and molecular statics methods to investigate energy states of a self-interstitial in α-titanium, a typical HCP metal. Our calculation shows that the most stable configuration of the self-interstitial is the basal-split dumbbell configuration on the basal plane. Compression along the [0001] or the [1¯100] directions leads to an insignificant change in the migration energies, while compression along the [11¯20] direction leads to a larger migration energy. A significant change of the diffusion anisotropy is observed when a uni-axial compressive stress of 200 MPa is applied along the [11¯20] direction. Similar stress along the other two directions does not produce substantial changes of the anisotropy. We also show that an applied hydrostatic stress can significantly change the diffusion anisotropy of HCP metals and alloys. Thus, under irradiation, a hydrostatic stress can produce a significant creep-like deformation (i.e., with a deviatoric strain rate) through a stress-dependent change of the growth rate.