CVD Diamond Coated Carbide Cutting Tool——Technical Matters (2/2)

Last but not the least, the binding force or adhesion is the most important problem of diamond coating and tungsten carbide matrix, which is also the major technical matter of most of coated cutting tool confronted with. Theoretically, in the process of machining, if the adhesive force between diamond coating and the matrix is too low, CVD diamond coating will be peeled off and become invalid early under the collective effect of the cutting force and the friction (especially in the cutting process with high speed or high load), which largely decreases the cutting property and service life of coated cemented carbide cutting tool.

However, the most difficult problem of the binding force confronted with is cobalt (Co) in tungsten carbide. Due to Co will promote the conversion of graphite to diamond (graphite and diamond are allotrope, and Co can be synthesized to the catalytic of diamond under high pressure) under high temperature and high pressure. But it will promote the growth of graphite under low temperature and low pressure (the growth conditions of CVD diamond).

Thus, CVD diamond is hard to nucleate and it has a huge influence on the binding force of diamond film and becomes invalid. In order to improve the binding force of CVD diamond coating and tungsten carbide matrix, we should take advantage of pre-treatment. The related researchers has proposed some new process, such as acid erosion or plasma etching to remove cobalt (Co), applying a variety of over-plating, mechanical or chemical heat treatment and so on. Although these methods are still in a development stage, it indicates that CVD coated cemented carbide cutting tool has a broad application prospect.

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