COMPARISON OF MICROSTRUCTURAL FEATURES OF DIAMOND COMPOSITE COATINGS WITH POLYCRYSTALLINE DIAMOND OR BORON-NITRIDE BRAZED ON TUNGSTEN CARBIDE TOOLS

We have investigated microstructure and properties of diamond composit e coatings on cemented tungsten carbide tool substrates, and compared wear resistance of these coatings with that of polycrystalline diamond (PCD) and polycrystalline boron nitride (PCBN) tools brazed on to cem ented tungsten carbide substrates. The diamond composite coatings cons ist of layers of discontinuous diamond, TiC, and continuous diamond. I n these composite layers, diamond is deposited by hot filament chemica l vapor deposition and TiC by pulsed laser physical vapor deposition. Thermal stresses in the composite layer and the substrate are reduced and thereby help to improve the adhesion of diamond to the tool substr ate. These tool coatings are characterized by scanning electron micros copy, Raman spectroscopy, secondary ion mass spectroscopy, and x-ray d iffraction. The results of microstructural characterization and analys is of chemical composition are correlated with wear resistance. The pr esent results demonstrate the advantages associated with composite dia mond coatings compared to PCD and PCBN tool coatings. (C) 1997 America n Vacuum Society.