Chemical Vapor Spraying Tungsten Carbide Coatings

Tungsten carbide with high hardness, corrosion resistance, wear resistance, coating material is good, for metal ceramics, valves, bearings, tools and other industrial components in the long-term work wear and corrosion conditions, tungsten carbide spraying protective coating, can effectively alleviate the matrix failure, prolong the service life.

With the development of nanotechnology, the preparation and process of nanometer tungsten carbide powder are becoming more and more mature. When the particle size is reduced to the nanoscale range, the mechanical properties of the material will begin to change sharply, and the hardness and wear resistance will be greatly improved. The coating technology of tungsten carbide includes thermal spraying, supersonic flame spraying and physical vapor deposition. The chemical vapor deposition technology can be applied to prepare tungsten carbide coating with strong adhesion, low friction coefficient and uniform friction on the complex shaped matrix.

Chemical vapor deposition (CVD) tungsten carbide coatings are mostly carried out under low pressure, because the average free range of molecules at low pressure is larger and the coating is more uniform. However, the low pressure chemical vapor deposition (CVD) process is complex, the equipment performance is very high and the deposition rate is slow, which brings difficulties to the industrial application. In contrast, the chemical deposition of nanoscale tungsten carbide coating is more complex. Ultrafine and nanocrystalline tungsten carbide coating, which consists of lamellar fine structure and multilayer fiber structure. W and W₂C grains exist simultaneously in the lamellar fine structure. Only W₂C grains exist in the multilayer fibrous structure. The grain size is 3 ~ 5nm, and there is amorphous alloy at the same time. The interlayer bonding force and hardness of the layered fine crystal structure can be improved by the existence of multilayered fiber, and the microhardness of the coating can reach 28.8GPa.

After observing the tungsten carbide copper valve after thermal spraying, it can be found that the coating deposited on tungsten layer has layered structure and fibrous structure, and fiber structure penetrates multilayer lamellar fine structure. That is to say, compared with the ordinary tungsten carbide spray, the structure of nano tungsten carbide is more compact, and the wear resistance and corrosion resistance are stronger.

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