High temperature deformation behavior of a γ TiAl alloy determined using the load-relaxation test

The high temperature deformation behavior of a two-phase γ TiAl alloy was investigated as a function of temperature and γ/α2 volume fraction. For this purpose, load-relaxation and tension tests were conducted at temperatures ranging from 800 to 1050 °C. When a small amount of deformation was imposed (ε≈0.04), the experimental stress-versus-strain-rate data for the fine-grained TiAl alloy were well fit by predictions based on grain-matrix deformation and dislocation climb derived from the inelastic deformation theory. Evidence of grain-boundary sliding was not observed in this instance. However, after a large amount of pre-deformation (ε≈0.8), the constitutive behavior changed significantly, indicating that grain-boundary sliding was also operating, an effect attributable to the occurrence of dynamic recrystallization during the deformation. With an increase in the volume fraction of the α2 phase, the flow stress for grain-matrix deformation was not varied, but that of dislocation climb decreased significantly. It was also found that the γ/α2 boundaries were more susceptible to cavity initiation than the γ/γ boundaries.