Sintering behaviour of the diamond-cobalt system at high temperature and pressure

A powder mixture of diamond—8.9 vol % Co was consolidatedin situ on a WC-10 wt % Co base at temperatures of 1300 to 1500° C under a pressure of 5.8 GPa. The sintered body obtained at 1300° C, which is below the diamond—cobalt eutectic point, was not hard, and the surface of the diamond particle was partially graphitized. On the other hand, the sintered body obtained at 1400 to 1500° C was fairly hard. A strong correlation was also observed between hardness and the cobalt content found in the sintered body. The cobalt content in the harder sintered body was clearly lower compared with that of the softer one. The surface graphitization of the diamond particles is necessary to the transfer of cobalt during the sintering of diamond. In sintering the diamond-cobalt system, the sinterability of diamond was closely related to the feasibility of transformation from diamond to graphite.