An apparatus and method of forming a composite body. The invention includes the steps of heating diamond crystals to a temperature about 1900.degree. C. and simultaneously subjecting the diamond crystals to a pressure above about 40 k-bar, forming a diamond material layer having a first surface from the diamond crystals, providing a substrate, and bonding the first surface of the diamond material layer and the substrate under high pressure and high temperature. The composite body has a diamond material layer formed from diamond crystals. The diamond material layer has a first surface and a substrate. The first surface of the diamond material layer and the substrate are bonded together under high pressure and high temperature.