Growth mechanism of α_p and interface relationships between α_p and α_s during cooling of a near α titanium alloy

This paper focused on the interface relationships between primary α (α_p) and the precipitation secondary α (α_s) phase at different cooling rates from 965 °C. The rapid cooling rate favors the precipitation of the secondary α_s. And the low cooling rate is conducive to the epitaxial growth of the primary α_p. One key finding is that once the grain boundary (α_GB) nucleated on the α_p could grow forward without maintaining the Burgers orientation relationship (BOR) with adjacent β grains. What's more, HADDF and Fourier-filtered HRTEM images elucidated that two adjacent α_p particles share a common plane but not the same atomic arrangement direction in crystal spatial. Three precipitation types of the α_s were discussed through EBSD and 3D spatial crystalline orientation. Specifically, the α_s shares common {1 1 2¯ 0} plane with the α_p grains respectively in Type-I and Type-II, but displaying different c axis angle (60° in Type-I and 80° in Type-II). For the Type-III, the secondary α_s shares common {1 0 1¯ 0} plane with the primary α_p, and the angle of c axis between them is 60°. Moreover, the primary α_p do not maintain the BOR with the pre-existing β, except for Type-I.