Behaviour of cobalt infiltration and abnormal grain growth during sintering of diamond on cobalt substrate

The infiltration behaviour of molten cobalt into a diamond powder compact was examined when the latter was placed on a cobalt disc and held at high pressure of 5.8 GPa and high temperature of 1350 to 1500° C. The larger the grain size of the starting diamond powder and the higher the holding temperature, the more easily cobalt infiltrated into the diamond compact. The infiltration is considered to occur because of the negative pressure in the voids formed between diamond grains. Although diamond powder was consolidated in this process of cobalt infiltration, abnormal grain growth was also observed in the boundary between cobalt and diamond compact because of the dissolution and precipitation process of the compact into molten cobalt.