Mechanical Properties and Thermal Shock Resistance of Al2O3-TiC-Co Composites

Ductile cobalt was introduced into Al2O3-TiC (AT) composites by using a chemical deposition method to improve toughness and resistance to thermal shock. The mixture of Co-coated Al2O3 and TiC powders was hot-pressed into an Al2O3-TiC-Co (ATC) composite. The flexure strength and fracture toughness of the ATC composites have been improved considerably, compared with AT and Al2O3. The fracture surface of ATC shows a large proportion of transgranular cracks with some intergranular type, unlike the intergranular fracture modes of AT and Al2O3. The thermal shock properties of the composites were evaluated by water quenching technique and compared with the traditional AT and Al2O3. The composites containing only 3.96 vol.% cobalt exhibited higher critical temperature difference and retained flexure strength. The SEM examination of the fracture surfaces of the ATC composites after single thermal cycle showed that voids increased in number and size, and most isolated voids coalesced with increasing temperature difference, which caused the density and strength to decrease. The ATC composite is less sensitive to repeated thermal shock than the AT composite.