US Patent 7730977 Cutting tool insert and drill bit so equipped

A polycrystalline diamond abrasive cutting element consists generally of a layer of high grade polycrystalline diamond bonded to a cemented carbide substrate. The polycrystalline diamond layer has a working surface and an outer peripheral surface and is characterized by having an annular region or a portion thereof adjacent the peripheral surface that is lean in catalyzing material. A region adjacent the working surface is also lean in catalyzing material such that in use, as a wear scar develops, both the leading edge and the trailing edge thereof are located in a region lean in catalyzing material.