On the mechanism of strain-enhanced grain growth during superplastic deformation

Superplastic deformation is often accompanied by grain growth, the rate of which depends on both strain and strain-rate, and is usually well in excess of that found in the absence of deformation. Two models for this process have been developed. In the first, which is most applicable to single phase materials, we assume that the deformation enhancement of grain growth is due to the damage created at triple junctions by grain boundary sliding. A geometrical model is used to show how the recovery of this damage by boundary migration, enhances the normal grain growth process. A second model, more suitable to microduplex alloys, is based on the postulate of Holm el al. [8, Acta metall.25, 1191 (1971)] that superplastic flow enhances the coarsening of particles which pin grain boundaries. Experimental data for a variety of materials give excellent agreement with these models.