Despite intense investigation over a long period of time, the micromechanisms involved in superplastic deformation remain controversial. No physically tenable model has gained widespread acceptance and it is clear that more information is required if a better understanding is to emerge. We have recently developed a method of milling fine surface markers onto the surface of specimens using focused ion beams that has proved capable of providing such information. The novelty compared with the many previous surface studies is that the grids can be made with a line spacing substantially less than a micrometer so that any deformation within the grains can be unambiguously identified and measured. Mesoscale grids with larger line spacings can also be produced to allow the homogeneity of deformation to be studied at all length scales. Our previous work has shown that there is negligible deformation within the grains under optimum superplastic conditions (Region II). The present paper extends this work using 3D stereographic reconstruction to demonstrate that grain boundary sliding is accommodated by diffusion flow in Region II and also includes results for superplasticity in Regions I and III. A new view of superplastic deformation is presented based on the results and the relevance to commercial forming in terms of the desired conditions for good surface finish and requirements for improved process modelling are briefly discussed.
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