The formation and anisotropic/isotropic diffusion behaviors of vacancy in typical twin boundaries of α-Ti: An ab initio study

Abstract

The distinct atomic structure of twin boundary (TB) significantly affects the physical and mechanical behaviors of materials. In this work, the local atomic structure, the formation and diffusion of vacancy in (101¯2), (112¯1), (112¯2) and (101¯1) TBs of α-Ti were investigated in details using ab initio calculations. Our calculations illustrated that most atoms at or close to the TBs have lower atom coordination number (CN), thereby experiencing the positive changes of local volume and tension strain. The CN and strain state significantly affect the vacancy formation. It’s shown that vacancy can easily form in these TBs, with the lower formation energy in the range of 1.26–1.59 eV. Our calculations further shown vacancy diffusion are somewhat anisotropic in 101¯2, 101¯1 and 112¯2 TBs planes. Vacancy prefers to diffuse along the direction of 1¯21¯0 in (101¯2) and (101¯1) TBs, and along the twinning direction of 112¯3¯ in 112¯2 TB, with the migration barriers of ∼0.43, ∼0.27, and ∼0.31 eV, respectively. Vacancy diffusion in (112¯1) TB plane is isotropic, with the migration barrier of ∼0.25 eV. Our calculations demonstrated that the fast diffusion channel mediated by vacancy for metallic atoms transport in these TBs can be mainly ascribed to the lower migration barrier and formation energy of vacancy in TBs.