Tungsten carbide-cobalt coatings

Thermal spray processes can be used to give coatings of chromium carbide or nickel chromium for erosion resistance, copper nickel indium for fretting resistance, tungsten carbide cobalt for wear and abrasion resistance, and even aluminum siHcon polyester mixtures for abradabiHty. 

In order to improve the wear resistance of machining tools made of hard metals, steel, tungsten carbide cobalt, titanium aluminide, titanium and silicon substrates have been coated with SiBNsC via CVD of TABB [107, 108]. Layers produced in this fashion are dense and exhibit a Vickers hardness of 1000-2300 kg mm S depending on the specific process parameters. 

Zinc, aluminum, nickel alloys, cobalt alloys and tungsten carbide are applied for sprayed coatings, which are slightly porous. Flame-sprayed zinc coatings are used for corrosion protection of steel and provide similar properties for galvanized coatings. 

Other potential applications are ceramic powders coated with their sintering aids, zirconia coated withyttria stabilizer, tungsten carbide coated with cobalt, or nickel, alumina abrasive powders coated with a relatively brittle second phase such as MgAl204 and plasma spray powders without the segregation of alloying elements. 

Thermal spray is a well-established, relatively low-cost, industrial processes which is used widely for the deposition of metals and compounds, including the refractory carbides and nitrides. Examples are coatings of tungsten carbide with a cobalt binder which are of major industrial importance. PI... 

The process is used to apply abrasion protective coats of cobalt and nickel-based alloys. Tungsten carbides (there is a choice of square or round carbides) are used to enhance abrasion protection on the screw flights, they are not used on the drive faces as the roughness which appears there during their use impedes the transportation of the ceramic material (Fig. 5). 

Substrates. Suitable substrates for TiC deposition are the cemented carbides, such as tungsten carbide (WC) bonded with cobalt (Co), which are widely used as cutting-tool materials (see Ch. 16). Other substrates coated by TiC are molybdenum and graphite. 1 1 In the case of molydenum, it is essential to maintain the deposition temperature below 950"C, otherwise recrystallization of the metal and reduction in mechanical strength will occur. 

Among the lefiactory carbides and nitrides, tungsten carbide with a cobalt binder is the most important material used widely in the coating of gas-turbine components for aircraft and industrial use, components of steam turbines and diesel engines, components for the oil and gas industry, paper and pulp industry, and chemical processing industry (see Ch. 16). 

Tungsten carbide -nl5% cobalt flame sprayed coatings 0.056 (234) —... 

Tungsten carbide + 9% cobalt flame sprayed coating 5.3 (9.2) —... 

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