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 automotive industry, plasma-oriented armor materials in nuclear fusion devices, etc.

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.

The tungsten coating sprayed with 28 micron tungsten carbide powder is taken as an example. Oxygen-free copper wafer of 40mm *8mm was used as spraying base, which was sandblasted and cleaned by alcohol or acetone to obtain clean and rough surface. After drying tungsten carbide powder with 28 micron fineness at 100 for 30 minutes, atmospheric plasma spraying technology was used to spray on oxygen-free copper substrate. The power of atmospheric plasma spraying equipment was 35KW, and the powder feeding method was internal feeding. The arc voltage and arc current are 70V and 500A. Argon is the main gas, hydrogen is the auxiliary gas, argon is 45L/min, hydrogen is 6L/min, powder feeding rate is 25g/min, spraying distance is 100mm and coating thickness is 1.5mm. The porosity and microhardness of the coatings are 7.5% and 245.5% respectively. The bonding strength of the coating is 35 MPa at 20HV.

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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