β phase transformation kinetics in Ti60 alloy during continuous cooling

The phase transformation kinetics from β to α′ or α phase in Ti60 alloy during continuous cooling courses was investigated by the thermodilatometry and metallographic analysis. The expansion behaviors and microstructures of the alloy under different cooling rates from 120 °C/s to 3 °C/s were compared to realize the existence of both the shear and diffusional transformations during continuous cooling. Mixture of the α′ martensite and α lamellar transformed from the β phase was obtained in the microstructures under the middle cooling rates of 20 °C/s, 15 °C/s and 10 °C/s with just appearance of the α platelets which precipitated along grain boundaries and grew toward the grain inside. Besides that, only the α′ martensite occupied the original β grains in the microstructure under 120 °C/s, and so did the α lamellar in the microstructure under 3 °C/s. Under the middle cooling rates, the transformation rates can be considered as the combination of both the β to α′ and α phase transformations under the middle cooling rates.