Synthetic diamond grits in a metal bonded sintering tool are known to reduce the strength after heating at sintering process. In this study, a strength testing method with a single particle was applied to examine the strength of diamond before and after heating at an actual sintering temperature, and the thermal behaviour of diamond was investigated by the scanning electron microscope and the electron probe micro analyzer.
As the result, it was clarified that the deterioration of diamond is originated in rough surfaces caused by the chemical reaction of diamond with bonding metal, and a precoating method of diamond is found to prevent the deterioration.