Variant selection mechanism of α phase associated with initial texture and cooling rate in near-α titanium alloy Ti65

Abstract

The elucidation of the impact of the initial texture and cooling rate on the variant selection (VS) mechanism of α-phase in titanium alloys is essential for optimising their microstructure and mechanical properties. In this study, Ti65 foils featuring three different initial textures underwent annealing in the α + β phase region, followed by cooling at three different rates. Under slow cooling conditions (furnace cooling), the primary mechanism governing texture evolution of α-phase is the grain growth of the primary α (α_p) grains. Consequently, the effect of the initial texture on the texture evolution of α-phase under slow cooling is ascribed to variations in the α_p grains in the samples after heat treatments. Additionally, standard disorientation angle θ_m distribution maps of the α texture under different β textures are developed to predict the texture of the α_p grains. In contrast, during rapid cooling (200 °C/min cooling and air cooling), texture evolution of α-phase is driven by the precipitation of the secondary α (α_s) grains. In this case, a change in the cooling rate has no effect on the VS mechanism of α-phase at the α_p/β and β/β boundaries, but it changes the VS mechanism of α-phase at the parent β grain interior. Therefore, the influence of the initial texture on VS mechanism of α-phase under rapid cooling varies with cooling rates, depending on the ratio of α_s grains precipitated at α_p/β and β/β boundaries to the α_s grains precipitated at the parent β grain interior.