Cooling rate–mediated evolution of lamellar α colony microtexture in a near-α titanium alloy during β processing

This study systematically investigates how cooling rate mediates the evolution of lamellar α colony microtextured regions (MTRs) in a near-α titanium alloy during β processing. The initial MTRs formed after β processing can be inherited into subsequent processing steps, critically influencing dwell-fatigue life. To address this, two β processing routes—β deformation only (β-Def) versus β deformation plus β annealing (β-Def + HT)—were compared, with samples cooled from the β phase at rates between 2 and 0.125 °C/s. In the β-Def route, slower cooling (0.125 vs 2 °C/s) nearly doubled the mean α colony MTR size and significantly coarsened prior β grains. Conversely, the β-Def + HT route showed only a modest increase in MTR size under slow cooling. The β-Def route introduced an intragranular transformation texture (<11–20 > α), while complete β recrystallization in the β-Def + HT route randomized the MTR orientations. Double-colony MTRs (paired colonies spanning special β grain boundaries) formed only in β-Def at the slowest cooling rate, but occurred across all cooling rates in β-Def + HT, indicating that prior β crystallography governs double-colony formation. An optimized processing strategy using β deformation with an intermediate cooling rate (∼0.25 °C/s) produced relatively small (∼150 μm), randomly oriented α colonies without double-colony MTRs.