Microstructural Influences on Inhomogeneous Deformation in Superplastic Ti-6Al-4V

Abstract

The strong dependence of the superplastic behavior of Ti-6Al-4V on microstructural evolution has been presented, and it is found that this alloy cannot be adequately characterized by a single microstructural factor such as grain size. Distribution of grain size, grain aspect ratio, and volume fractions of two phases are also important for a complete description of microstructural parameters in superplasticity. In order to investigate the influences of microstructural evolution on deformation behavior, both uniform and non-uniform tensile tests were conducted under constant strain rate and constant velocity loading conditions at 900°C, respectively. Subsequent microstructural examination has been carried out using scanning electron microscopy, together with electron probe micro-analysis. The effects of volume fraction of two phases with concurrent grain growth were examined, and mechanical properties have been investigated in terms of the alpha-beta phase relations. A micromechanical approach is then presented for the material model in which heterogeneous q are coupled with deformation behavior. The evolution of grain size distribution and the effect of phase relations on the mechanical properties are predicted by the model, and an excellent agreement between experimental and predicted results has been obtained.