Grain-Boundary Sliding in a Superplastic Three-Phase Alumina-Zirconia-Mullite Ceramic Composite

Relative grain-boundary sliding at the surface of a three-phase superplastic ceramic after compressive deformation was measured using atomic force microscopy and scanning electron microscopy to investigate the x, y, and z strain contributions at different types of grain boundaries. This alumina (40 vol%), zirconia (30 vol%), and mullite (30 vol%) composite had an average grain size of 260 nm. The composite was deformed in compression under constant stress conditions in sequential increments of 5%-10% true strain at 1350 degrees C. Six different types of grain boundaries (alumina/alumina, zirconia/zirconia, mullite/mullite, alumina/zirconia, alumina/mullite, and zirconia/mullite) were characterized, for over 800 boundaries in all. It was found that all types of boundaries contributed significantly to the overall deformation with no differentiation between grain boundaries of the same phase and grain boundaries of dissimilar phases, with the exception of mullite/mullite boundaries that had a more complex surface topology due to the in situ formation of mullite during sintering.