Evolution of lamellar α phase during two-phase field heat treatment in TA15 alloy

Two-phase field heat treatment experiments have been performed to study the evolution of the primary lamellar α phase in TA15 alloy during the whole heat treatment process. Meanwhile both the evolutions of the primary and secondary lamellar α during air cooling with different insulation histories have been examined. Results indicate that the transformation mechanism for the primary lamellar α phase during heating is the transformation of the thin lamellae at lower α/β region and the dissolving of the small lamellae originated from the decomposition of the branched lamellae at higher α/β region. During the holding process, the volume fraction of the primary lamellar α decreased, the average thickness increased and the variation trend of the average length is complex. When the cooling mode after two-phase field heat treatment is coupled with the insulation history, the variation trend of the volume fraction shows a non-monotonous way.