Superplastic compression, microstructural analysis and mechanical properties of a fine grain three-phase alumina-zirconia-mullite ceramic composite

The creep behavior, microstructure and mechanical properties of a three-phase 40 vol.% alumina-30 vol.% zirconia-30 vol.% mullite ceramic composite were investigated. This material was made from zirconia (3Y-TZP) and the reaction of nanoscale powders of alumina and a silica sol to form mullite. Only a few small (10-15 nm) silica pockets remained after sintering, although the original amount of silica was 5.9 wt.%. The material demonstrated a steady-state strain rate and showed superplastic flow under compression. Most grains were equiaxed and sharply facetted. Samples quenched from 1450 °C indicated that the high temperature microstructure is similar to the as-sintered state. Dislocations formed in both mullite and zirconia grains during deformation, suggesting that a dislocation mechanism plays a role during superplastic deformation. The hardness was 15 GPa and the fracture toughness was 6.5 MPa m1/2, with no degradation in properties with 100% deformation.