Role of zirconia addition in pore development and grain growth in alumina compacts

The role of 12.4 vol% ZrO2 addition in the microstructure evolution of alumina compacts during the intermediate and final stages of sintering was investigated by means of small-angle neutron scattering measurements and stereological analysis. Both the pore-size evolution results and the grain-growth data indicate a narrowly defined onset density for the transition to the final sintering stage. The presence of ZrO2 as a second phase apparently maintains the stability of the intermediate sintering stage out to significantly higher density than in single-phase alumina and plays an important role in inhibiting grain growth and in preventing pore–grain boundary separation. The influence of the ZrO2 second phase on pore evolution, grain growth, and sinterability of the alumina–zirconia composite is discussed and compared to the behavior of single-phase alumina. The samples were prepared from commercially available powders, with naturally occurring porosity distributions, rather than from artifact(model) pore compacts prepared from nominally pure research-grade materials. The goal was to gain an improved understanding of microstructure development in real materials.