The Influence of Heating Rate on Phase Transformation Kinetics and Microstructures Evolutions at Ageing in Metastable Beta Titanium Alloy—Ti-B19

The present work is focused on the influence of heating rate on the kinetics of the beta phase decomposition and the microstructure evolution for ageing treatment of Ti-B19 alloy. After solution treated at 900°C for 10 minutes, the samples are heated to 500°C with 10°C/s, 1°C/s and 0.1°C/s heating rate, respectively, and then holding for 4 hours followed by fast cooling. The microstructures observations revealed a needle-like α phase for 10°C/s, while for 0.1°C/s its shape are needle-like and particle-like with a nanometers size. The transformation kinetics was investigated by in situ electrical resistivity revealing a strong difference in transformation sequence. For the lower heating rate, precipitation begins at nearly 300°C and progresses on heating and dwell at 500°C. For 10°C/s precipitation occurs mainly on holding at 500°C. To further analyses these differences, samples were quenched from different temperatures on heating and were analysis by synchrotron X-ray diffraction and TEM revealing namely the formation of ω precipitates at slow heating. These nano size precipitates are nucleation sites for the latter α"/α precipitation. For the higher heating rates, ω precipitation does not occur during the heating period and only α"/α phase precipitates.