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

It is necessary to compare with gradient tungsten carbide. Gradient coating refers to gradient arrangement in coating structure, while coated cemented carbide is not only determined by the coating material, the more closely related to the properties of tungsten carbide matrix. Tungsten carbide matrix with gradient structure effectively solves the problem that the cracks of coating layer extend to tungsten carbide matrix. It adds a spot of TiN, (Ti,W)C and some phase with cubic structure in WC-Co system, and adopts nitrogen removal process to form no cubic phase and Co binder phase concentration with gradient structure, which has excellent toughness and in case of the cracks expanding to some extent. There is homogeneous tungsten carbide matrix and tungsten carbide with gradient structure pictures under optical microscope as follow:

It is distinct that there is a big difference between homogeneous tungsten carbide matrix and gradient structural tungsten carbide matrix. In addition, compared with the fracture morphology of coated cemented carbide cutting tool SEM (Scanning Electron Microscope) picture:

Viewed from the fracture morphology of coated cemented carbide SEM picture, we can find that the fracture morphology of tungsten carbide cutting tool with gradient structure is coarser and unevener than homogeneous tungsten carbide cutting tool. Due to high toughness of Co concentration, it can absorb almost energy of cracks expanding, which increases the plastic deformation. It proves that tungsten carbide with gradient structure has better impact resistance toughness and cutting edge toughness.

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