Diamond Coatings on Cutting Tools

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For machining many difficult-to-machine materials, such as high silicon aluminum-silicon alloys and composites, polycrystalline diamond tools made by the high pressure (50 kbars) -- high temperature (1500 C) (HP-HT) process are used. These tools are expensive because of the high cost of processing and finishing and need exists for an alternate tool material. The low pressure chemical vapor desposition (CVD) diamond synthesis, in contrast, is relatively simple and inexpensive, thus offering a potential for producing diamond coated cutting tools. The primary goal of this project is to develop the science base for strongly adherent diamond coatings on various cutting tool materials, including, cemented carbide (coated and uncoated) and ceramics (silicon nitride and SiAION) by the four activated CVD diamond synthesis techniques, namely, combustion synthesis, microwave CVD, hot filament CVD, and laser assisted CVD with emphasis on the first two. The conditions for each of the activated CVD diamond coating processes will be optimized for a given tool material based on good metallurgical coating, its thickness and morphology. These tools will be characterized by optical and scanning electron microscopy, and Raman spectroscopy. They will be evaluated in machining different work materials with the cutting speed and length of cut as variables. Various surface treatments including etching of the surface, different surface finishing conditions, surface interlayer coatings for the substrate will be considered. Tool wear mechanisms, tool life, and finish of the work material with diamond coated tools will be compared with that of the uncoated tools and/or polycrystalline diamond tools.