Investigation of the Peculiar Stress Flow Behavior of a Novel TiAl Alloy under High Strain Rate Conditions

In this study, we investigated the peculiar flow behavior during the isothermal deformation of a novel TiAl composition at 1200 °C and 1300 °C under high strain rate conditions using Gleeble^® Thermal-Mechanical Simulators. The initial yield-point phenomenon, resembling strain hardening at both temperatures, is attributed to the remnant lamellar microstructure. Secondary hardening at 1200 ℃ is caused by dislocation accumulation at the grain boundaries of the α phase, without the formation of dynamically recrystallized γ lamellar grains. In-grain misorientation axes analysis revealed a shift in the dominant deformation slip mode of the α phase from the prismatic slip system to a combined prismatic and basal slip system. The disappearance of γ lamellar laths after the first strain hardening and during secondary hardening is likely initiated by a deformation-induced γ→α phase transition within the γ phase matrix by the extended dislocation with intrinsic stacking faults and occurred simultaneously in the whole γ lamellae.