Constitutive analysis on superplastic deformation mechanisms of two-phase Ti3Al-xNb alloy

In this study, superplastic deformation mechanisms of two-phase Ti3Al-xNb alloys were investigated in the context of inelastic deformation theory, which consists of grain matrix deformation (GMD) and grain boundary sliding (GBS). Flow stress-strain rate curves of the alloy were obtained by the load relaxation test as well as the strain rate change test at 950, 970 and 990 °C. The results showed that GMD and GBS of three specimens containing different amounts (21, 50 and 77%) of β were well described by the plastic deformation equation and viscous flow equation of the theory, respectively. Accommodation of deformation strains was found to occur in both α2 and β phase. The sliding resistance was analyzed for the different types of boundaries, which revealed the lowest resistance in the α2/α2 boundary and increased in the following order; α2/α2 ≪ α2/β < β/β.