Dynamic transformation during the high temperature deformation of two-phase titanium alloys

The role of dynamic transformation in flow stress during the deformation of two-phase titanium alloys was evaluated using isothermal compression and self-consistent modeling. Dynamic transformation took place in both the equiaxed and lamellar microstructures at temperatures ranging from 815 degrees C to 950 degrees C. There was more flow softening in the lamellar than in the equiaxed microstructure. However, the extent of dynamic transformation and the associated flow softening were similar in the two microstructures. The softening proportion from texture evolution was analogous to that from dynamic transformation in the lamellar microstructure. Dynamic transformation served as the main source of flow softening in the equiaxed microstructure particularly at low strain rates, while its contribution to the flow softening in the lamellar microstructure was evidently reduced. An appropriate strain rate for observing dynamic transformation lay in the range from 0.01 s(-1) to 0.001 s(-1) based on the balance between inhibiting adiabatic heating and increasing driving forces. This approach was further applied on an IMI 834 alloy and its behavior was similar to that for Ti-6Al-4V.