The α₂ precipitation from equiaxed γ phase in as-cast Ti-44Al-4Nb-2Cr-0.1B alloy

This paper presents the novel duplex microstructure in Ti-44Al-4Nb-2Cr-0.1B alloy during the heat-treatment of 1200 °C/24 h + 1300 °C/1h/FC, which precipitate two kinds of α₂ phases from the equiaxed γ grains. The mechanisms of γ → α₂ transformation in equiaxed γ grains were investigated. Two needle-like α₂ variants can be observed inside one parent γ grain with the intersection angle of 71.4°. The irregular α₂ were preferentially precipitated at γ grain boundaries with large disorientation, nucleated selectively in the γ grain whose {1 1 1}_γ plane nearly parallel the γ/γ grain boundary, and grew into the neighbor γ grains with no orientation relationship.