Ball Milling Method for Tungsten Carbide-based Hard Alloy Thermal Spray Powder

Thermal spraying of cemented carbide powder is a technology of hardening and strengthening mechanical surface. This technology may effectively prolong the service life of machinery. Tungsten carbide is the most common raw material for thermal spray welding (coating). Nowadays, there are many new technologies on the market, such as high-energy plasma spraying, vacuum plasma spraying, supersonic flame spraying, explosive spraying and so on. Whatever process is adopted, the raw materials for spraying are not made of high-quality tungsten carbide powder.

It is generally believed that the spherical tungsten carbide powder is most suitable for thermal spraying. By using the most common solid-phase ball milling process in the industry, the spherical tungsten carbide powder can be mixed with cobalt to produce high-quality tungsten carbide thermal spraying materials. The production process is as follows:

The WC powder with 6.14% C content and 4 micron average fineness is 860g, the cobalt powder with 2 micron average fineness is 120g, the total carbon content is 6.2% and the average fineness is 30 micron is 20g, TaC is 20g, milling for 16 hours, pressing into lumps or flakes, such as 60 x8mm, sintering at vacuum of 20 Pa and temperature of 1420 ℃ for 1 hour, crushing and/or airflow. The physical properties of the cemented carbide are as follows: density 14.21 g/cm³, hardness HRA 87.2, coercive magnetic force 7.4 KA/m and flexural strength 1948 N/mm².

The above process is to use crusher to crush and classify the powder, so that the fineness of the powder can reach less than 100 microns, and the particle size of the powder is uniform. Then, more than one of the hard phase tungsten carbide, binder phase iron series elements Fe, Co and Ni (including one kind of metal and additive) is weighed proportionally, and the mixture is mixed by dry mixing or ball milling for 1-72 hours to achieve uniform dispersion of the material. The mixture is pressed into flakes, blocks or pellets, then sintered at high temperature, and the products are sintered. It is then crushed into powder by machinery or gas, screened and classified into products.

The prepared tungsten carbide powder has narrow fine distribution, stable chemical composition, good fluidity and high deposition rate. It is suitable for supersonic flame spraying, plasma spraying, explosive spraying and other thermal spraying methods to meet the requirements of tungsten carbide powder. The obtained coatings are uniform in thickness, fine in density and high in hardness. The coatings are abrasion resistant and corrosion resistant.

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