Nano Tungsten Carbide Thermal Spraying Technology

Thermal spraying technology can rapidly prepare a protective coating on the surface of the workpiece, giving the workpiece surface different properties such as wear resistance, corrosion resistance, wear reduction, sealing and so on. WC-based cermets with high hardness and toughness are widely used in aerospace, metallurgy, petrochemical, mechanical and other industries.

In industrial applications, supersonic flame spraying is the most suitable method for spraying tungsten carbide-based cermets because of its fast spraying speed, relatively low combustion temperature, less decarbonization of carbides and high bonding strength of coatings. The common tungsten carbide-based cermets for thermal spraying include WC-12Co, WC-17Co, WC-10Co₄Cr, WC-Cr₃C₂-Ni, WC-Ni, etc.

Thermal spraying nano-coatings in the existing technology, especially tungsten carbide-based coatings, mainly take nano tungsten carbide as raw material, and adopt supersonic flame spraying or cold spraying processes. It is very important to control the spraying process conditions. The preparation methods of such coatings include:

1.Raw materials such as tungsten powder, boron carbide powder, cobalt powder and tungsten carbide powder are selected. The boron carbide powder accounts for 1.2 to 10% of the total weight, and the cobalt powder occupies 8 to 25% of the total weight, and the tungsten carbide powder accounts for 30 to 75% of the total weight. The raw materials are uniformly mixed, granulated by agglomerating or spray drying, and then processed by debinding sintering process to obtain spray powder.

2.Tungsten carbide coatings with Micro-Nanostructure were prepared by supersonic flame spraying or cold spraying using the obtained spraying powder.

The particle size of tungsten powder is less than 2 micron, that of boron carbide powder is less than 2 micron, that of cobalt powder is less than 3 micron, and that of tungsten carbide powder is more than 0.8 micron. The sintering temperature in the process of degreasing sintering is 1230-1450 C.

The coatings were prepared by supersonic flame spraying, in which oxygen was 56 cubic meters per hour, kerosene was 28 liters per minute and spraying distance was 380 mm. The results show that the coating has uniform nanophase distribution, less carbon loss, and nano-tungsten carbide is contained in the coating, forming a micro-nano structure coating, which has high hardness and good toughness.

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