Growth mechanism of αp and interface relationships between αp and αs during cooling of a near α titanium alloy

Abstract

This paper focused on the interface relationships between primary α (αp) and the precipitation secondary α (αs) phase at different cooling rates from 965 °C. The rapid cooling rate favors the precipitation of the secondary αs. And the low cooling rate is conducive to the epitaxial growth of the primary αp. One key finding is that once the grain boundary (αGB) nucleated on the αp 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 αp particles share a common plane but not the same atomic arrangement direction in crystal spatial. Three precipitation types of the αs were discussed through EBSD and 3D spatial crystalline orientation. Specifically, the αs shares common {1 1 2¯ 0} plane with the αp 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 αs shares common {1 0 1¯ 0} plane with the primary αp, and the angle of c axis between them is 60°. Moreover, the primary αp do not maintain the BOR with the pre-existing β, except for Type-I.

Keywords

• Cooling rate
• Epitaxial growth
• Primary αp
• Duplex microstructure
• Secondary αs