Instability of the O-phase in Ti-22Al-25Nb alloy during elevated-temperature deformation

The deformation behavior and microstructural evolution of a Ti-22Al-25Nb alloy during tensile deformation at 900 °C was systematically investigated. The true stress-strain curve exhibited an initial hardening transient, a peak flow stress, and then a flow softening. The alloy exhibited a microstructural instability during the tensile deformation, characterized by coarsening, fragmentation, and spheroidization of the O-phase. This microstructural instability was enhanced by the imposed strain rather than the applied stress. After a strain of ε = 0.56, a refined microstructure with equiaxed or near-equiaxed O-phase grains formed. Based on the results of the microstructural evolution, the origin of the flow softening behavior was suggested.