Microstructure after superplastic creep of alumina–zirconia composites prepared by powder alcoxide mixtures

The microstructural evolution during superplastic creep of alumina–zirconia composites prepared from alumina powder–zirconium alcoxide mixtures was studied, in order to determine the changes in the grain size and shapes. Zirconia reinforced alumina composites with up to 20 wt.% ZrO2 content were deformed in compression creep tests at constant load in air at 1350 °C. The microstructure was studied by means of SEM. The distribution of both phases, grain sizes and shapes were determined on sintered and tested materials. Grain size distributions are narrow, with typical zirconia particle sizes several times finer than alumina ones, resulting in intergranular small zirconia grains occupying most alumina triple points. Every composition was deformed in stationary creep to 100% true strain. Superplastic strains were achieved by the coupled dynamic movement of grains during grain boundary sliding and simultaneous accommodation at triple points by zirconia particles. The shape and size changes in alumina and zirconia grains revealed that transport of matter took place also by diffusion at the grain boundaries. Grain boundary diffusion at alumina–zirconia interphases resulted in significant grain shapes in the zirconia particles, with zirconia grains exhibiting protruding parts along the alumina grain boundaries aligned perpendicularly with the compression axis.