The development of cavity growth maps for superplastic materials

Abstract

Superplastic alloys usually deform to very large extents but excessive cavitation can lead to premature cavitation failure in these materials. Several mechanisms can contribute to the growth of cavities during superplastic deformation although, generally, there is only one mechanism that controls cavity growth. Cavity growth mechanisms of relevance to superplastic materials are analysed in detail and the possible transitions in rate-controlling cavity growth mechanisms are considered. The contribution of lattice diffusion to the diffusional growth of cavities is included in the overall analysis of cavity growth. Cavity growth maps are constructed to show the dominant cavity growth mechanisms under different experimental conditions. Equations are developed to predict the appropriate transitions in cavity growth mechanisms with increasing cavity radii. Finally, it is demonstrated that the predictions of the cavity growth maps are consistent with the experimental results in several superplastic materials.