EFFECT OF CALCINATION ON THE SINTERING OF GEL-DERIVED, ZIRCONIA-TOUGHENED ALUMINA

The densification behavior of ZrO2 (+3 mol% Y2O3)/85 wt% Al2O3 powder compacts, prepared by the hydrolysis of metal chlorides, can be characterized by a transition- and an alpha-alumina densification stage. The sintering behavior is strongly determined by the densification of the transition alumina aggregates. Intra-aggregate porosity, resulting from calcination at 800 degrees C, partly persists during sintering and alumina phase transformation and negatively influences further macroscopic densification. Calcination at 1200 degrees C, however, densifies the transition alumina aggregates prior to sintering and enables densification to almost full density (96%) within 2 h at 1450 degrees C, thus obtaining a microstructure with an alumina and a zirconia grain size of 1 mu m and 0.3-0.4 mu m, respectively.