Coated Cemented Carbide Process

Based on traditional chemical vapor deposition (CVD) and physical vapor deposition (PVD), some new coating technologies are emerging.

1. Chemical Vapor Deposition (CVD)

Since 1970s, chemical vapor deposition (CVD) has been widely used in semiconductor industry, which is suitable for most of metals and alloy materials. Theoretically, it uses two and more materials in gas state to react in chamber and forms new composite material to deposits on the surface of matrix. Viewed from coated cemented carbide, vacuum oven deposits the coating material on the surface of tungsten carbide cutting tool matrix by vacuum coating or arc evaporation at high temperature (about 800-1200℃).

In addition, CVD can be specifically divided into excess temperature controlling technology, medium temperature chemical vapor deposition (MTCVD), vacuum CVD, plasma chemical vapor deposition (PCVD), fluidized CVD, pyrolysis jet and so on. However, this kind of process has some defects, such as traditional CVD process will form brittle metal mesophase by deposited at high temperature, which has a bad effect on the properties in products.

2. Physical Vapor Deposition (PVD)

Physical vapor deposition (PVD) refers to transfer atoms and molecule to the surface of matrix, which uses low voltage, heavy current arc discharging and evaporate the target material. The evaporating material will ionized with the gas, which reaction products deposited on the matrix. Its advantage is that it can spray the grain with high hardness, high strength, good wear resistance and low coefficient of thermal expansion to tungsten carbide matrix, which makes it have better comprehensive properties. PVD also can be specifically divided into ion sputtering, vacuum evaporation, high-energy ion pulse, ion plating (arc ion plating, RF ion plating, hot cathode ion plating, hollow cathode deposition (HCD), DC discharge ion plating, activated reactive evaporation (ARE)) and so on.

Compared with CVD, PVD has lower deposited processing temperature (under 500℃) and it does not need heating process; there is no impact on the flexural strength of cutting tools under 600℃, and the internal stress of film is compression stress, which is more suitable for the coating of tungsten carbide precision or complex cutting tools. However, PVD has more complicate operation, higher demand of conditions and lower using cycles and uniformity than CVD process.

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