How to Strengthen Aircraft Components by New Tungsten Carbide Coating Technology

Tungsten carbide is widely used in aerospace, petroleum, metallurgy, machinery and other fields because of its high hardness, wear resistance, high temperature resistance and corrosion resistance. In general industrial applications, we call it cemented carbide coating. Usually, tungsten carbide/cobalt is used as raw material to form a protective layer on the surface of nickel or iron-based materials by supersonic spraying, which can increase wear resistance and service life. In principle, the implementation cost of this kind of process is not cheap, but relative to the damage and replacement cost of the whole parts, the savings are considerable. In the field of aerospace engine research and development, surface-enhanced coating is one of the most attractive technologies. Tungsten carbide is an important basic coating material for aircraft parts.

Among the most famous aviation manufacturers in Europe and the United States, they generally adopt a coating technology called low temperature chemical vapor deposition (CVD), which is a process used to deposit tungsten carbide coatings. It has been considered to be a practical, technically and commercially viable solution that can significantly increase the life of aircraft components. It is widely used in jet engines of typhoon, F16 and other three generations of fighters.

The reason why CVD coating technology is used is that in general cemented carbide spraying technology, cobalt is used as the binder phase of tungsten carbide material, which can improve the compactness of the material, but in contrast, cobalt will reduce the wear resistance and corrosion resistance. CVD coating technology does not need cobalt. It belongs to the nanostructured tungsten/tungsten carbide coating series. It is formed by atom-by-atom crystallization in low pressure gas medium. By constructing a dense tungsten layer and tungsten carbide composition bonded together, it can uniformly and porously coat the inner surface and complex shape of aircraft components, especially for design and complex geometry which can not use spraying technology. Typical CVD coating applications include fuel metering valves, push rods, pins, bushings, bearings, hooks, catches, landing gear, flapper tracks and slats, sleeves, rods, valves, pneumatic pistons and cylinders.

Compared with hard chromium plating, CVD tungsten carbide coating technology can be directly converted to the minimum pre-coated component design changes. Its thickness (50 to 100 microns) and hardness (800HV to 1,200 HV) exceed the maximum hardness of the plating method. This is also because the dispersed tungsten carbide nanoparticles give the material higher hardness, which can be controlled and adjusted. The typical range of hardness is 800 Vickers hardness and 1600 Vickers hardness, which is suitable for different coating types. CVD coatings are usually applied at a thickness of 50 um, which combines high hardness with enhanced toughness and ductility, improves wear resistance and corrosion resistance, and can withstand impact and component deformation.

European and American engineers have used high frequency reciprocating tester to test the wear resistance of CVD cemented carbide coatings. Hard chromium plated stainless steel plate and CVD coated steel plate were compared. The seizure of Hard Chromium Electroplated stainless steel plate quickly reached critical friction coefficient of 1.0 and 65N load, and it was already severely worn and unable to continue testing. The dry friction coefficient of CVD coated samples is about 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. Similarly, it is about three times the performance of supersonic flame spraying.

Another advantage of CVD tungsten carbide coatings is that they have no wear quality for seals, bearings and other inverted parts. Uniform nanostructures allow the coating to wear uniformly and maintain or even improve surface finish - even in abrasive or corrosive environments. For hydraulic actuators, rotating shafts and bearings, the coating keeps good surface, reduces wear of elastomers and PTFE seals, prevents oil leakage, and helps to reduce maintenance requirements for aircraft actuators and transmission components.

In a word, tungsten carbide coating technology is widely used in aerospace industry. It can effectively solve the wear and tear of aeronautical equipment and prolong the service life of Aeronautical equipment, whether for passenger aircraft or fighter aircraft.

• < Prev
• Next >