Determination of Phase Transformation for TC21 Ti-Alloy by Dilatometry Method

The α + β ↔ β phase transformation kinetics of TC21 Ti-alloy during continuous heating and cooling were studied using a dilatometric technique. Dilatometric heating curve exhibited that two characteristic reflection points can be observed with increasing the heating temperature. Ts referred to the initial transformation temperature of α + β → β and Tf referred to the final transformation temperature of α + β → β. Ts was reported at 720°C, whereas the corresponding Tf was obtained at 950°C. The initial and final transforming temperatures by the first derivative curve were reported at 730°C and 955°C, respectively, which are close to the values obtained in the dilatometric heating curve. Dilatometric cooling curve showed that the starting temperature of β → β + α phase transformation was 880°C; however, the corresponding finishing temperature was 670°C. The starting and finishing temperatures using the first derivative curve were obtained at 665°C and 885°C, respectively. The first derivative for the studied dilatometric heating and cooling curves showed that the starting and finishing temperatures of α + β ↔ β phase transformation were more accurate and objective. Results show the α + β → β transformation heating curve exhibits a typical S-shaped pattern.