WEAR-RESISTANT DIAMOND COATINGS ON ALUMINA

Wear resistant diamond coating systems on alumina substrates with improved adhesion have been developed. These systems consist of single layer diamond coatings and multilayer composite diamond coatings. The multilayer diamond coating systems are made up of an embedding intermediate layer of TiC or TiN or TiC-TiN deposited by laser physical vapor deposition on a first layer of diamond. A second layer of diamond is also deposited on the embedding layers. Scanning electron microscopy and Raman spectroscopy have been used to characterize the coatings. Adhesion and wear resistance of the coatings have been tested using an indentation test and an overlap polishing test. The improvement in adhesion of the composite diamond coatings with TiC embedding layer is found to be highest. Mechanisms of the adhesion and wear resistance improvement of the composite films are investigated. The improvement in adhesion is explained by the epitaxial growth of TIC on alumina, Ti-C and C-C bondings between TiC and diamond, the small difference in the thermal expansion coefficients between TiC and alumina, and the close matching of lattice constants between TiC and diamond.