Modeling of the effect of cavitation on tensile failure of superplastic alloys

A model for creep deformation due to combined diffusion and plastic flow is applied to tensile failure of superplastic alloys by cavitation. The model requires input of strain-rate sensitivity, initial void radius and its volume fraction. Failure due to void coalescence is detected by micro-necking of the intervoid matrix material. The void shape change due to plastic flow is incorporated in the model. It is found that the effect of grain-boundary sliding as described by the local stress system in vicinity of the cavitating facet has a major influence on predictions of cavity growth rate and hence the resulting fracture strains. The model is applied to predict fracture strains of various superplastic materials, e.g. Al–Li, Cu–Zn and Ti–Al alloys. Comparison of these predictions with experiments is in fair agreement. Discrepancies may be due to neglecting the occurrence of diffuse necking in reporting ductility at fracture. The lack of quantified micro-mechanical parameters and hence the inevitable resort to assuming their values represent another shortcoming in applying the model.