EFFECT OF PRETREATMENT METHODS, CHAMBER PRESSURE AND SUBSTRATE TEMPERATURE ON MORPHOLOGY, QUALITY, ADHESION AND CUTTING PERFORMANCE OF HFCVD DIAMOND COATED TOOLS IN MACHINING ALUMINIUM ON CEMENTED CARBIDE INSERTS

The wide applications of aluminium in different industries have increased the necessity for researching on suitable cutting tool. It is observed that, comparing to ferrous materials; dry machining of aluminium, exhibits a greater challenge in view of heavy material built-up at the cutting edge. This not only enhances cutting force but also causes poor quality surface finish on the workpiece. This paper thoroughly investigated the effect of substrate treatments, micro structure, adhesive toughness and cutting force of Hot Filament Chemical Vapour Deposition (HFCVD) diamond coating on uncoated carbide cutting inserts (94%WC+6%Co). To restrict the formation of non-diamond carbon phases, such as graphite, and to improve the adhesion between diamond and WC substrates, etching with a combination of diluted HCL and HNO3 are used as substrate pretreatments. The pressure in the CVD chamber are set at 0.666, 1.333, 2.666 and 3.999 kPa and the substrate temperatures are kept at 650, 700, 750 0C while maintaining the filament temperature at 2100 0C. Characterization and purity (sp3 / sp2 ) of the obtained coatings are duly evaluated by Scanning Electron Microscope (SEM) and Raman Spectroscopy. The mechanical characterization of the coating is investigated by Rockwell indentation test under loads of 294 N, 588 N and 980 N to assess the coating-substrate adhesion.It is observed that the deposition pressure at 2.666 and 3.999 kPa and substrate temperature at 700 0C, coating with (111) habits is mostly preferred to achieve maximum coating substrate adhesion. These results suggest that during dry machining, compare to uncoated tool, a 4-5 µm HFCVD diamond coating exhibits remarkable inertness towards aluminium leading to substantial reduction of cutting force and improvement of work-piece surface finish.