Adhesion strength of diamond films on cemented carbide substrates

Abstract

Diamond-coated cemented carbides are expected to be superior cutting tools for Al-Si alloys. For practical use in cutting, the adhesion strength of the diamond film is a major problem which could be improved. The adhesion strength of diamond particles, deposited by hot filament chemical vapour deposition (CVD) of CH 4, was qualitatively measured in relation to the conditions of surface preparation of the carbide substrate and CVD. The adhesion strength is improved by deposition of diamond in pores formed by cobalt removal from near the surface of the substrate. Good adhesion is obtained when the size of the pore and the deposited particle is nearly equal. Better adhesion is obtained at a substrate temperature of 1000 °C compared with 800 and 900 °C. A diamond-coated carbide cutting insert was produced using the above results by microwave plasma CVD. The coating layer is mainly composed of diamond with a small amount of non-diamond carbon. The insert demonstrates a very small steady wear without flaking of the diamond film in cutting Al-10%Si alloy.