Massive Transformation Mechanisms in TG6 Titanium Alloy During Cooling

A kind of massive microstructure α_m along the primary α phase (α_P) has been characterized in the microstructure quenched from the α+β phase field. The obvious interface between α_m and α_P can be found under the optical observation, and the concentrations of Al, Sn and Zr elements in α_m are in between that of the α_P and β matrix, but the orientation of the α_m keeps consistent with that of the α_P as evidenced by EBSD analysis. The appearance of the α_m is considered as the result of limited diffusion controlled transformation from the β phase during the cooling, because the α_m initiates from the α/β interface and keeps the consistent orientation with α_P, and the growth is limited around the α/β interface. As the diffusion is limited by decreasing the solution periods from 30 min to 5 min, and the dissolving of α_P is accelerated by increasing the solution temperature from 1040℃ to 1060℃, the volume fraction of α_m increases from 5.2% to 30.7% significantly.