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.