Effects of Hydrostatic Pressure On Superplastic Deformation Stability

It is well established that many superplastic alloys exhibit cavitation during deformation. Cavitation not only limits the superplastic ductility of the material, but also adversely affects the service properties and fatigue performance of the formed parts. In this paper, finite element simulations and stability analyses are carried out to study the effects of hydrostatic pressure on the superplastic deformation process. The finite element analysis is based on a three dimensional model, that utilizes experimentally calibrated microstructure-based equations, and takes both damage evolution and grain growth into account. Elements that can handle contact, large deformation and the generated triaxial stress state are used. The effect of hydrostatic pressure on the limiting strains is emphasized through an analytical stability model. Cavitation evolution paths are generated for uniaxial and biaxial loading conditions.