Chemical vapor deposited diamond films have many industrial applications but are assuming increasing importance in the area of micro engineering, most notably in the development of diamond coated micromilling tools. For these applications the control of structure and morphology is of critical importance. The crystallite size, orientation, surface roughness, and the degree of sp3 character have a profound effect on the tribological properties of the films deposited. In this paper we present experimental results on the effects of nitrogen doping on the surface morphology, crystallite size, and wear of micromilling tools. The sp3 character optimises at 200 ppm of nitrogen and above this value the surface becomes much smoother and crystal sizes decrease considerably. Fracture induced wear of the diamond grain is the most important mechanism of material removal from a micromilling tool during the grinding process. Fracture occurs as a consequence of tensile stresses induced into diamond grains by grinding forces to which they are subjected. The relationship between the wear of diamond coated milling tools, component machining forces, and induced stresses in the model diamond grains is described in detail. A significant correlation is found between the maximum value of tensile stress induced in the diamond grain and the appropriate wear parameter, in this case the grinding ratio. It is concluded that the magnitude of tensile stresses induced in the diamond grain by machining forces at the rake face is the best indicator of tool wear during the micromachining process.

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