Coated Cemented Carbide Types——Gradient Coating (1 of 2)

Since coated cemented carbide developed, coating types were diverse, such as single-layer coating, multi-element composite coating, gradient coating, nano coating, super-hard coating and soft coating.

3. Gradient Coating

Due to the differences of friction factor and coefficient of thermal expansion between coating layer and the matrix, if it can not be effectively controlled, the binding force of coated cemented carbide will remarkably decrease. Gradient coating solves the problem perfectly, which has structural composition and micro-structure in the space. It can reduce the concentration of the stress, eliminate the surface of multi-layer, which improves the binding strength of coating layer and matrix, and extends the service life of coated cemented carbide.

It can be found that gradient coating has better micro-hardness and toughness by analyzing the section structure and composition distribution of gradient Ti(C,N) coating layer. The related researcher adopted magnetron sputtering to deposit gradient TiAlN coating on tungsten carbide matrix, and injected Ti atom between the gradient coating and the matrix by metal vapor vacuum arc (MEVVA), which formed a transition layer with a certain concentration of Ti. After that this kind of tungsten carbide with gradient coating performed perfectly in the test of dynamic impact, and has better wear resistance and toughness in high-speed cutting or milling and been a giant leap in the service life.

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