Studying the synthesis, microstructure and mechanical properties of Alumina/zirconia-cobalt composites

The present study aimed to investigate the synthesis, microstructural and mechanical properties of alumina/zirconia-cobalt composite. The compositions containing 5, 10, 20 Vol.% of the sum of ZrO2 and Co were studied. The composite powders were prepared through mixing of alumina powder with partially stabilized zirconia and cobalt sulfate powders followed by calcination treatment at 1100 for 3h and reduction of cobalt by aluminum powder additive, in carbon bed at 950 for 3h. The XRD analysis showed the presence of Al2O3, t-ZrO2, Co and a little m-ZrO2. In order to investigate the properties of Al2O3/ZrO2-Co composite, composite powders were pressed uniaxial followed by Cold Isostatic Pressing (CIP) at 400MPa. The prepared discs were sintered in carbon bed at 1550 1600 , 1650 for 5h. The alumina specimen was also prepared with the same procedure. The final results showed that the highest relative density value was 83.9% obtained for the specimen with the composition containing 5vol.% ZrO2 and 5vol.% Co densified at 1650 for 5h. The bending strength and hardness of this specimen was 322MPa and 11.95MPa.m1/2 respectively. So 20.15% increment of bending strength and 15.96% decrease of hardness was observed compare to monolithic alumina. The decrease of hardness was due to the lower hardness of metallic phase and the increase of bending strength is occurred because of presence of zirconia and cobalt particles which prevent of alumina grains growth.