Tungsten Carbide-Cobalt Cermet Coating Powder Preparation

The traditional method of hard chromium plating on metal surface has many problems, such as complex process, low deposition rate, difficult to deposit thick coatings, softening of chromium plating layer when the temperature reaches above 260 ℃, leading to a significant decrease in wear resistance and environmental pollution caused by hard chromium plating.

Practice shows that tungsten carbide-cobalt cermet coatings can effectively protect the metal matrix, but the wear resistance and corrosion resistance of existing tungsten carbide-cobalt cermet coatings still need to be improved urgently. For this reason, some scholars have improved the preparation process of tungsten carbide-cobalt cermet coatings. The improved process is as follows:

A modified tungsten carbide-cobalt cermet coating powder consists of two different particle sizes of tungsten carbide and cobalt and trace rare earth yttrium. The mass percentage of tungsten carbide is 83%, that of cobalt metal is 16.5%, and that of yttrium oxide rare earth is 0.5%. The synthesis steps are as follows:

A. Preparing materials:
The nano-tungsten carbide with a mass percentage of 25-58% and a particle size of 0.05-0.2 micron was prepared. The prepared tungsten carbide with a mass percentage of 25-58% and a particle size of 2.0-8.0 micron was prepared.

B. Mixture:
Firstly, according to technological requirements, nano-tungsten carbide, medium-sized tungsten carbide and 16.5% cobalt powder were added to the ball milling equipment in step A. Then deionized water and polyvinyl alcohol, which accounted for 25% of the raw material mass and 2.0% of the mass, were added to the ball milling equipment. The milling time was 22 to 28 hours, and yttrium oxide, a grain growth inhibitor with 0.5% of the mass percentage, was added.

C. Granulation:
An open centrifugal spray drying tower was adopted to dry granulation and spherical mixture was obtained. The centrifugal atomizing disk was rotating at 8000 to 12000 rpm.

D. Sintering:
The mixture is loaded into graphite boat vessel, placed in molybdenum wire furnace and sintered continuously in hydrogen atmosphere. The pushing speed of boat is 9 12 minutes per boat, and the sintering temperature is 950 1250 ℃.

E. Fragmentation classification:
After sintering, the product is crushed by mechanical method, and the final product thermal spraying powder is obtained by sieving or airflow grading according to the size distribution range. The particle size is 15 45 micron, and the bulk density is 4.0-5.8 g/cm³.

The improved tungsten carbide-cobalt cermet coating powder was applied to supersonic flame spraying (HVOF), oxygen-acetylene surfacing, molten argon arc welding (MIG), submerged arc surfacing, subsonic spraying, explosive spraying or plasma melting-spraying, etc. Because rare earth was added to the coating material, the microstructure, microstructure and plasma melting-spraying of the coating material surface were improved. The micro-hardness and modulus of elasticity of WC/Co coating material are increased by 42% and 6.2%-14.9% respectively by structure, which improves the wear resistance of the material surface as a whole, and also improves the comprehensive mechanical properties of the modified layer.

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