Hot deformation behavior and microstructure evolution of TA15 titanium alloy with nonuniform microstructure

The flow behavior and microstructure evolution of a near a titanium alloy with nonuniform microstructure during hot deformation were studied by isothermal compression test and electron backscatter diffraction technique. It is found that the nonuniform microstructure prior to deformation consists of equiaxed alpha, lamellar a in the colony form and (beta phase, and the a colony keeps the Burgers orientation relationship with beta phase. The flow stress of nonuniform microstructure exhibits significant flow softening after reaching the peak stress at a low strain, which is similar to the lamellar alpha microstructure. Nevertheless, the existence of equiaxed alpha in nonuniform microstructure makes its flow stress and softening rate be lower than the lamellar microstructure. During deformation, the lamellar a undertakes most of the deformation and turns to be rotated, bended and globularized. Moreover, these phenomena exhibit significant heterogeneity due to the orientation dependence of the deformation of lamellar alpha. The continuous dynamic recrystallization and bending of lamellar a lead to the "fragmentation" during globularization of lamellar alpha. The bending of lamellar a is speculated as a form of plastic buckling, because the bending of lamellar alpha almost proceed in the manner of "rigid rotation" and presents opposite bending directions for the adjacent colonies.