Rapid Dynamic Transformation in the Initial Stage of Hot Deformation of a Near Alpha Titanium Alloy

The peak flow stress of a near alpha high temperature titanium alloy exhibits a special rapid drop behavior at low strain during hot compression. The experimental result indicates that this rapid drop of peak flow stress is related to the rapid dynamic transformation from alpha phase into beta phase which is induced by the deformation at elevated temperature. Both peak flow stress and the dynamic transformation change with different hot deformation parameters, and the drop of peak flow stress keeps almost consistent variation with the evolution of dynamic transformation observed from the microstructural morphology. The higher deformation temperature and the lower strain rate with the small increase of strain are beneficial to accelerate the dynamic transformation and the drop of peak flow stress. The dynamic transformation is mainly controlled by the immigration of alpha/ beta interface shrinking from edge to center of equiaxed alpha phase or the penetration of beta phase into alpha phase from edge to inside.