Advanced or backward? Tungsten Carbide coating Technology is used to enhance aircraft engines and other components in Europe and the United States
Tungsten carbide materials are widely used in aerospace, petroleum, metallurgy, machinery and other fields because of their high hardness, wear resistance, high temperature resistance and corrosion resistance. In general industrial applications, we call it cemented carbide coating, usually using tungsten carbide / cobalt as raw material, supersonic spraying on the surface of nickel or iron-based materials to form a protective layer, which can increase the wear resistance and service life of the substrate. In principle, the implementation cost of this kind of process is not cheap, but compared with the damage of the whole parts and the overall replacement cost, the amount saved is considerable. In the field of aerospace engine research and development, surface reinforced coating is one of the most attractive technologies. Tungsten carbide is an important basic material for aircraft parts strengthening coating.
With the rapid development of high and new technology, the aviation industry continues to put forward a variety of performance requirements for materials. cermet? Yes, but most of the cermet mentioned in aviation are composite materials, and the technological composition is unknown, but most of them have added tungsten, such as zirconium tungstate, tungsten-aluminum ceramics, etc., which have advantages and disadvantages, and are certainly not omnipotent because of their differences in materials. Back to our theme, the existing coating processes include supersonic flame spraying tungsten carbide, hard chromium plating, physical vapor deposition of tungsten carbide and explosive spraying of tungsten carbide. Although these applications have been successful in some fields, each has its own limitations.
Among the most famous aviation manufacturing enterprises in Europe and the United States, they generally use a technology called low temperature chemical vapor deposition ((CVD)) coating, which is a process for deposition of tungsten carbide coating. It has been considered to be a practical, technically and commercially feasible solution, which can significantly increase the life of aircraft components and is widely used in the jet engine of the third generation fighter such as typhoon, F16 and so on. CVD coating technology is used because cobalt is needed in the general cemented carbide spraying technology, which can improve the compactness of the material, but cobalt will reduce the wear resistance and corrosion resistance of the material. CVD coating technology can not use cobalt, it belongs to nanostructured tungsten / tungsten carbide coating series, it is formed by atom-by-atom crystallization of low pressure gas medium. By constructing a dense tungsten layer and a protective layer bonded with tungsten carbide components, it is uniform and porous coating on the inner surface and complex shape of aircraft components, especially suitable for the design and complex geometry where spraying technology can not be used. Typical CVD coating applications include fuel metering valves, push rods, pins, bushes, bearings, hooks, catches, landing gear, flap tracks and strips, sleeves, rods, valves, pneumatic pistons and cylinders.
Compared with hard chromium electroplating method, CVD tungsten carbide coating technology can be directly converted to the design change of minimum precoated components, its thickness (50 μ m to 100 μ m) and hardness (800HV to 1200HV), the upper limit exceeds the maximum hardness of electroplating method. This is also because dispersed tungsten carbide nanoparticles give the material higher hardness, can control and adjust the hardness, so that the typical range of 800Vickers hardness and 1600 Vickers hardness, suitable for different coating types. The CVD coating is usually applied at a thickness of 50 μ m, which combines high hardness and enhanced toughness and extensibility, improves wear resistance and corrosion resistance, and can withstand impact and component deformation.
European and American engineers have used high frequency reciprocating test bench to test the wear resistance of CVD cemented carbide coating. The hard chromium electroplating stainless steel plate was compared with the CVD coated steel plate. The critical friction coefficient and 65N load of hard chromium electroplating stainless steel plate can not be further tested because of the rapid seizure of critical friction coefficient of 1.0 and 65N load. The dry friction coefficient of the sample coated with CVD is about 0.2. No wear was observed, even if subjected to the maximum load on the test-bed. The test results show that the hardness of CVD is 13 times higher than that of hard chromium electroplating coating. In the same way, it is about three times as good as supersonic flame spraying.
In addition, low temperature chemical vapor deposition of tungsten carbide coating technology can not use cobalt, which is easily affected by acid. Therefore, CVD tungsten carbide coating can resist more erosive chemicals and can be used as anticorrosion barrier. Due to the deposition mechanism, low temperature chemical vapor deposition of tungsten carbide coating has low porosity and does not need sealing. Tungsten and tungsten carbide have high chemical resistance. In the comparison with hard chromium plating and supersonic flame spraying, the low carbon steel plates coated with hard chromium electroplating, supersonic flame spraying and CVD coating were subjected to neutral salt spray test for 480 hours. The samples were seriously corroded and therefore removed from the test after 288hours. Supersonic flame spraying coating samples showed serious rust and coating blistering, while CVD samples showed only slight staining.
Another advantage of CVD tungsten carbide coatings is that they have no wear quality for seals, bearings and other reverse parts. Uniform nanostructures allow the coating to wear evenly and maintain or even improve surface finish-even in erosive or corrosive environments. For hydraulic actuators, rotating shafts and bearings, the coating maintains a good surface, reduces the wear of elastomers and PTFE seals, prevents oil leakage, and helps to reduce the maintenance requirements of aircraft actuators and transmission components.
In short, the tungsten carbide coating technology is very common in the application of the aerospace industry, whether it is a passenger plane or a fighter, it can effectively solve the wear of the aviation equipment and prolong the service life of the aviation equipment.
