Production, characterization, and wear behaviour of plasma jet CVD diamond films on hard metal cutting tools

The de plasma jet chemical vapour deposition (CVD) process is one of the most promising processes for the synthesis of polycrystalline diamond films. The obtainable linear growth rates in the range of 100 mu m/h are much higher than the growth rates for other CVD processes like microwave or hot filament CVD (1 to 10 mu m/h). Wear resistant diamond coatings on cutting tools are very interesting for industrial applications. The poor adhesion of the diamond films is the main problem with these systems. Therefore a mechanical or chemical pretreatment of the substrate surface is used to improve the adhesion of the coating. The influence of mechanical pretreatment by grinding and polishing with diamond powder as well as chemical etching with different solutions or combinations of these pretreatments were examined on WC-Co hard metals. The diamond films were synthesized on these pretreated cutting tools by de plasma jet CVD. Scanning electron microscopy, EDS analysis, X-ray diffraction: and Raman spectroscopy have been used to characterize the coatings. Adhesion and wear resistance of the diamond films have been investigated using turning tests on metal matrix composites without lubricant. The improvement in adhesion of the diamond coatings is found to be highest after a combined mechanical and chemical pretreatment.