Microstructure refinement in Ti-6Al-4V during warm deformation

Plastic-flow-behavior and microstructure evolution during the warm working of Ti-6Al-4V with a colony-alpha preform structure have been established. For this purpose, samples were compressed at 600 degrees C to various height reductions. The plastic-flow response was characterized by successive stages of strain hardening, flow softening, and steady-state flow. During warm deformation, the lamellae spheroidized partially to produce a globular microstructure with an alpha grain size of similar to 0.5 mu m. Additional insight into the evolution of microstructure was obtained via electron-backscatter diffraction (EBSD), which revealed that spheroidization was associated initially with the rotation of the alpha lamellae and the loss of the coherence at the interphase boundaries. After the coherence was lost, deformation localized within each phase, thus intensifying division of lamellae into equiaxed segments.