Dynamic transformation during the high temperature deformation of titanium alloys

Dynamic transformation was first predicted by Gegel and Nadiv during hot deformation of a Ti-6Al-2Sn-4Zr-2Mo alloy. Later it was observed in near alpha and two-phase titanium alloys. In the present work, the roles of dynamic transformation and other dynamic phenomena during hot deformation are reviewed. In equiaxed microstructures, dynamic transformation acts as an additional stress accommodation mechanism and facilitates grain boundary sliding. In lamellar microstructures, such transformation is accompanied by dynamic globularization and these phenomena serve as sources of flow softening. The thermodynamics of dynamic transformation in both unstable and stable states are summarized. Dynamic transformation of alpha to beta can be activated on condition that equilibrium state is achieved prior to deformation. Unsolved issues that appear to have potential for further study are also outlined.