Influence of cobalt phase on mechanical properties and thermal shock performance of Al2O3-TiC composites

Cobalt phase was introduced into Al2O3-TiC composites to improve resistance to thermal shock by hot pressing cobalt coated powders. The thermal shock properties of the composites were evaluated by water quenching method and compared with the traditional Al2O3-TiC composites. The composites containing only 4 vol.% cobalt exhibited higher critical temperature difference (ΔTc) and retained tensile strength. The calculation of thermal shock parameters (R parameters) indicates that the incorporation of cobalt improves the resistance to crack initiation and propagation under thermal shock, which should be attributed to enhanced tensile strength, fracture toughness and thermal conductivity as well as decreased Young's modulus. Noticeable improvement in crack deflection, bridging and blunting caused by cobalt phase are responsible for the increased crack stability in terms of the change in microstructure. The presence of cobalt in the matrix was also found to inhibit the oxidation of TiC.