Abstract: The paper has investigated the sticking or welding behaviour between diamond grain and adhesive Co-Si alloys in the man-made diamond compacts by SEM,EPMA and X-ray diffraction. It is found that element Si tends to the bondary of diamond grain; there are new chemical compounds SiC in the boundary between diamond grain and adhesives. This prolongs the service life of diamond tools. Perhaps the sintering time is the main factor of forming SiC.