Evident α/γ Interface Sliding in Fully Lamellar TiAl Alloy During Hot Deformation: Metallurgical Observation and Mesoscopic Modelling

Prominent interface sliding was noted in a fully lamellar Ti–43.5Al–8Nb–0.2W–0.2B alloy deformed in (α + γ) phase region with low strain rate, which is evidenced by the drastic α/γ lamellar offsets at the kink boundaries. Due to the effective accommodation of interface sliding, there were only a few substructures produced at the kink bands in spite of the high strain localization. By using the transmission electron microscopy, the interface sliding was demonstrated to be caused by the glide of pre-existing interfacial dislocations. Based on the metallurgical observations and kinetics analysis, two mesoscopic models for interface sliding were established corresponding to two alternative rate-controlling steps, i.e., intra-lamellar dislocation climb-controlled or interfacial dislocation glide-controlled. Both of them predicted a Newtonian viscous shear behavior but the latter was manifested to be more plausible to account for the interface sliding kinetics. In addition, the reliability of the model was discussed in detail, as well as the role of interface sliding during hot deformation. The developed mesoscopic model can be readily implemented into the crystal plasticity finite element method for a better understanding of the synergistic effects of the individual processes on the high temperature plastic flow of lamellar colonies in TiAl alloys.