In-Situ Observation of β→α Phase Transformation of TA2 Commercial Pure Titanium during Continuous Cooling

The β→α phase transformation process of TA2 commercial pure titanium at the cooling rate of 20 ℃·min-1 was in-situ observed using a confocal laser scanning microscopy (CLSM). The results show that β→α phase transformation process could be divided into two stage, including the nucleation and growth of grain boundary α phase and widmanstatten α phase. Grain boundary α phase was formed by the growth and connection of several α nucleuses along β phase grain boundaries, and kept orientation relationship to at least one of the adjacent β grains. Widmanstatten α phase nucleated on α phase grain boundaries, and grew forward to β phase in the form of lamellar-type clustering. The lengthening speed was much higher than the widening speed.