Tungsten Carbide Coating Prepared by Plasma Spraying

Tungsten has the advantages of high melting point, high strength, high hardness and high wear resistance. In addition, it has low thermal expansion coefficient, good corrosion resistance and oxidation resistance, and good conductivity and thermal conductivity. Therefore, tungsten has been widely used in cutting-edge scientific fields, national defense industry and civil industry.

In the application of surface engineering of hard surface materials, tungsten carbide can be coated on the surface of metal or workpiece by thermal spraying technology to form a strengthening coating, which can improve the performance of surface wear resistance, impact resistance, high temperature resistance and corrosion resistance, significantly prolong the service life of workpiece, and save a lot of metal materials and production costs. For example, it can be used as a surface wear-resistant protective layer for automotive parts in the automotive industry and plasma-oriented armor materials in nuclear fusion devices.

At present, chemical vapor deposition, physical vapor deposition and plasma spraying are the main methods to prepare tungsten carbide coatings. Compared with chemical vapor deposition technology and physical vapor deposition technology, plasma spraying technology has unique advantages: easy to operate, high deposition efficiency, easy to prepare thick coatings, and easy to repair damaged coatings in situ. Therefore, tungsten and molybdenum coatings prepared by plasma spraying technology as wear resistant and high temperature resistant coatings have attracted wide attention in fusion reactor.

The specific process steps of preparing tungsten carbide coating by plasma spraying are as follows:

A.Material preparation: The oxygen-free copper wafer, copper alloy sheet or stainless steel sheet of 40mm *8mm are used as spraying base material. After sandblasting pretreatment, the surface is cleaned by alcohol or acetone to obtain a clean and rough surface. Tungsten carbide powders with fineness of 30-30 microns were selected. Before spraying, the powder was dried for 30 minutes at 100 ℃ to avoid agglomeration and blockage of powder feeding tube during powder feeding.

B.Spraying: Equipment using atmospheric plasma spraying, the power of the equipment is 27KW-40KW. Argon is used as the main gas for spraying, hydrogen is used as the auxiliary gas to improve the power of spraying and prevent the oxidation of coating matrix, and internal powder feeding is used to improve the melting efficiency and inhibit oxidation. The spraying process parameters are as follows: arc voltage 60-70V, arc current 450-600A, main gas using argon, flow rate 40-50L/min, hydrogen flow rate 4-7L/min, powder feeding rate 15-30g/min, spraying distance about 100-120 mm.

Tungsten carbide coating prepared by plasma spraying technology has good mechanical properties and thermal shock resistance. It is suitable for wear-resistant surface protection layer of mechanical parts and high temperature plasma erosion parts, such as the first wall materials of nuclear fusion devices.

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