Coalescence behavior of the antiphase domain in Ti3Al

Coalescence behavior of antiphase domains (APDs) in Ti3Al crystals with the stoichiometric and Al-rich composition was investigated, focusing on the influence of Al concentration on the shape and the growth rate of APDs, which are closely related to the anisotropy of diffusion and antiphase boundary (APB) energy due to the hcp-based ordered structure (D0(19)-type) of Ti3Al. The change in the domain size and the shape of APDs were observed by a transmission electron microscope. The growth was much faster in Al-rich crystals than in stoichiometric crystal. The change of average domain size was not associated with a parabolic law. The activation energy of APD coalescence, approximately estimated from the temperature dependence of the coalescence rate, was smaller than that of Al-self diffusion in both compositions. No anisotropy was observed in the shape of APDs. Factors which govern the growth rate and the shape of APDs were discussed considering the diffusion mechanism in D0(19) structure and the change of atomic arrangement in moving antiphase domain boundaries (APDBs).