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Advanced or backward?Tungsten carbide coating technology is used to enhance aircraft engines and other components in Europe and the United States

  • Mosten
  • 15 Feb

Tungsten carbide has high hardness, wear resistance, high temperature resistance and corrosion resistance. It is widely used in aerospace, petroleum, metallurgy, machinery and other fields. In general industrial applications, we call it hard alloy coating, usually take tungsten carbide/cobalt as the raw material, in the surface of nickel or fe-based material for supersonic spraying and form a protective layer, can increase the wear resistance and service life of the matrix. 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, the surface enhancement coating is one of the most attractive technologies.

With the rapid development of high and new technology, the aviation industry puts forward various performance requirements for materials. Cermet? There is, but most of the aviation said metal ceramics are composite materials, process composition is unknown, but most have added tungsten components, such as negative thermal expansion materials zirconium tungstate, tungsten aluminum ceramics, have advantages and disadvantages, due to different materials, certainly not universal. Returning to our theme, existing coating processes include supersonic flame spraying of tungsten carbide, hard chromium electroplating, physical vapor deposition of tungsten carbide and explosive spraying of tungsten carbide. Although these applications have been successful in some areas, each has its limitations.

In Europe and America's most famous aviation manufacturing enterprises, they are generally used is called a low temperature chemical vapor deposition (CVD) coating technology, it is a kind of used for deposition of tungsten carbide coating process, has been considered to be practical, technically and commercially viable solutions, can significantly increase the life of aircraft parts, is widely used in the typhoon, F16 gan the three generation fighter jet engines.

The reason why CVD coating technology is adopted is that in general hard alloy spraying technology, cobalt is required. As the bonding phase of tungsten carbide material, cobalt can improve the material's compact performance, but relatively, cobalt will reduce the wear resistance and corrosion resistance. CVD coating technology can be used without cobalt. It belongs to the nano-structured tungsten/tungsten carbide coating series, which is atomically crystallized from low-pressure gas medium. It provides uniform, nonporous coatings on the interior surfaces and complex shapes of aircraft parts by constructing a protective layer of dense tungsten and tungsten carbide components bonded together, particularly for designs and complex geometricshapes that are not possible using spray technology.Typical CVD coating applications include fuel metering valves on aircraft, pushback rods, pins, bushings, bearings, hooks, catches, landing gear, flap rails and slats, sleeves, rods, valves, pneumatic pistons and cylinders.

Compared to hard chrome plating, CVD tungsten carbide coating technology can be directly converted to minimum pre-coated component design changes with thickness (50 m to 100 m) and hardness (800HV to 1,200hv) exceeding the maximum hardness of the plating method. This is also because the dispersion of tungsten carbide nanoparticles gives the material a higher hardness that can be controlled and adjusted to a typical range of 800 and 1600 vickers hardness for different coating types. CVD coatings are typically applied at a thickness of 50 m, combining high hardness and enhanced toughness and ductility to improve wear resistance and corrosion resistance, and to withstand impact and component deformation.

High frequency reciprocating test bench has been used by European and American engineers to test the wear resistance of CVD cemented carbide coating.Hard chrome plated stainless steel plates were compared with CVD coated steel plates. The hard chrome plated stainless steel plate seized quickly reached the critical friction coefficient of 1.0 and the 65N load, which had been severely worn and could not be tested any longer. For the CVD coated samples, the dry friction coefficient was stable around 0.2.No wear was observed, even under the maximum load of the test bed. The results show that the hardness of CVD material is 13 times higher than that of hard chromium plating coating.In the same way, it is about three times better than supersonic flame spray.

In addition, low temperature chemical vapor deposition of tungsten carbide coating techniques can be done without the use of acid-sensitive cobalt. Thus, CVD tungsten carbide coatings are resistant to more aggressive chemicals and can be used as corrosion barriers. Due to the deposition mechanism, the low porosity of low temperature chemical vapor deposition tungsten carbide coating does not require sealing. Tungsten and tungsten carbide have high chemical resistance. In the contrast test with hard chromium plating and supersonic flame spraying, the low-carbon steel plate coated with hard chromium plating, supersonic flame spraying and CVD coating was removed from the test after 288 hours of severe corrosion after 480 hours of neutral salt spray test.The supersonic flame spray coating sample showed severe rust and frothing of the coating, while the CVD sample showed only slight staining.

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tungsten