Pulse electric current sintering of transition alumina/zirconia composite powders prepared by a novel sol-gel route

Zirconia-dispersed alumina ceramics were fabricated by pulse electric current sintering (PECS) using transition alumina/zirconia (ZrO2 = 5.7-21.0 mass%) composite powders. The composite powders were prepared through a novel sol-gel route using polyhydroxoaluminum (PHA) and polyhydroxozirconiurn (PHZ) solutions as starting materials. PHA-PHZ composite gels were calcined at 800-1100 degrees C and then ground by a planetary ball mill. Upon heating, the PHA-PHZ composite gels transformed into mixed phases of gamma- and chi-alumina and tetragonal ZrO2, depending on the temperature and ZrO2 content. In the case of low calcination temperature and/or low ZrO2 content, t-ZrO2 was highly dispersed in transition alumina matrix as nanocrystallites. PECS was effective in transforming the composite powders into fully dense sintered bodies at 1250-1500 degrees C under a uniaxial pressure of 40 MPa. Sinterability depended strongly on calcination temperature: the temperature required for full density decreased as calcination temperature increased. The incorporation of ZrO2 into the alumina matrix through the sol-gel route was very effective in inhibiting grain growth of alumina, leading to finer microstructures. Using composite powders calcined at 1000 degrees C, bending strengths as high as 1.2 GPa were obtained through PECS at 1350 degrees C by the addition of a small amount of ZrO2 (5.7 mass%). With increasing ZrO2 content, the bending strength gradually increased up to 1.4 GPa.