Characterisation of grain rearrangement during superplastic creep of Al 2 O 3 -ZrO 2 composite

An Al₂O₃-ZrO₂ composite specimen has been deformed at 1275°C up to a true compressive strain of 56%, by true strain increments of 14%. At each stage of the test, the same zones on a side face parallel to the compression axis have been investigated by scanning electron microscopy. Several elementary mechanisms occurring during superplastic flow and entailing grain rearrangement have been observed, the predominant one being the neighbour switching event. Neighbour switching is associated with grain disappearance corresponding to grain motion perpendicular to the investigated surface. This contributes to the maintenance of a nearly constant grain size and nearly stable structure. Grain boundary sliding is very active during the test, and involves individual grains, rather than rigid grain groups sliding along ‘supergrain’ boundaries. The results imply that pure Coble diffusion creep cannot account for deformation in the composite.