MECHANICAL-PROPERTIES AND MICROSTRUCTURES OF CO-PRECIPITATION DERIVED TETRAGONAL Y2O3-ZRO2-AL2O3 COMPOSITES

Y-TZP-Al//2O//3 specimens (2. 5 mol% Y//2O//3-ZrO//2 and 5 to 30 wt% Al//2O//3) were prepared from coprecipitated powders and their mechanical properties were studied. The addition of alumina improves the density after sintering at 1500 degree C and reduces the degradation of their densities due to porosity formation when the materials are sintered above 1500 degree C. Near theoretical density could be achieved for most of the samples after HlPing at 1500 degree C for one-half h at 200 MPa pressure. The fracture strength of the HlPed specimens was in the range 2. 0 to 2. 4 GPa and the stress intensity factor was in the range 3. 5 to 6. 0 MPam** one-half . The mechanical strength was not degraded seriously after autoclaving in water at 175 degree C for 24 h. The surface layer of transformed monoclinic zirconia was less than 70 mu m thick even after autoclaving at 175 degree C for 5 days.