Mechanism of shear band formation and dynamic softening in a two-phase (α2 + γ) titanium aluminide

The formation of shear bands during hot deformation of a two-phase (alpha(2) + gamma) titanium aluminide and its consequences on dynamics softening has been investigated. The starting material consists of a colony of lamellar grains along with the segregated vanadium and niobium which was subjected to hot deformation in the temperature range 1000-1175 degrees C at the strain rate 10 s(-1). Microstructures of the deformed samples indicate that, with increase in the deformation temperature, the orientation of shear bands changes. Moreover, the extent of dynamic recrystallization also increases with deformation temperature. The softening behaviour and crystallographic orientation change within lamellae during hot deformation have been explored. The nucleation of newly recrystallized grains has been observed at twin-parent grain boundary and within the twined gamma phase. Lamellae of the gamma and alpha(2) phase have been also observed to be twisted and tilted, leading to the band formations under the load, whose mechanisms have also been explored in the present study.