Beta to alpha transformation kinetics and microstructure of Ti-6Al-4V alloy during continuous cooling

In the present paper, an approach based on the Kolmogorov-Johnson-Mehl-Avrami (KJMA) model has been developed and applied to study the transformation kinetics of the β phase in Ti-6Al-4V titanium alloy during cooling. To this purpose, Differential Scanning Calorimetry (DSC) tests have been conducted using a set of cooling rates ranging from 10 to 50 °C/min. This approach allows the kinetics parameters, particularly the activation energy, to be calculated from a single DSC test using a simple linear regression. The microstructural analysis indicates that the microstructure is dominated by the α Widmanstätten morphology (αW). Microstructural observations along with the calculated values of the Avrami index and of the activation energy suggest that the growth of the αW platelets obeys a mixed mode combining the vanadium diffusion and a displacive mechanism. •The kinetics of the β → α phase transformation is investigated.•An approach is proposed to adapt the KJMA model for continuous cooling.•The model permits the determination of the kinetics parameters for each cooling rate.•The growth of αW plates may obey a combined displacive-diffusional growth mode.•The growth involves shear mechanism and partitioning of vanadium between αW plates.