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Home > Blog >

Advanced or backward? Tungsten carbide coating technology is used for enhancement aircraft engines

2019-05-16
What is tungsten carbide:
 
Tungsten carbide consists of tungsten and carbon and is a compound with a molecular formula of WC and a molecular weight of 195.85. Black hexagonal crystal with metallic luster. Tungsten carbide hardness similar to that of diamond. It is a good conductor for electricity and heat. Tungsten carbide is insoluble in water, hydrochloric acid and sulfuric acid, and is easily soluble in a mixed acid of nitric acid-hydrofluoric acid. Pure tungsten carbide is brittle, and if a small amount of metal such as titanium or cobalt is added, brittleness can be reduced. Tungsten carbide used as a steel cutting tool is often added with titanium carbide, tantalum carbide or a mixture thereof to improve the antiknock ability. The chemical properties of tungsten carbide are stable. Tungsten carbide powder is used in cemented carbide production materials.
 
Application of tungsten carbide coating technology:

Because tungsten carbide materials have high hardness, wear resistance, high temperature resistance and corrosion resistance, they are widely used in aerospace, petroleum, metallurgy, machinery and other fields. In general industrial applications, we call it cemented carbide coating, usually with 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 of the substrate. Service life. In principle, the implementation cost of this type of process is not cheap, but the amount saved is considerable compared to the damage of the entire component and the overall replacement cost. In the field of aerospace engine research and development, surface-enhanced coating is one of the most eye-catching technologies. Tungsten carbide is an important base material for strengthening the coating of aircraft parts.
 
In aerospace manufacturing companies, a technique called low temperature chemical vapor deposition (CVD) coating, a process for depositing tungsten carbide coatings, is considered to be practical, technically and commercially. A viable solution that can significantly increase the life of aircraft components is commonly used in jet engines of third-generation fighters such as typhoons and F16.
 
In the general cemented carbide spraying technology, cobalt and cobalt are needed as the binder phase of the tungsten carbide material, which can improve the compactness of the material, but in contrast, cobalt can reduce the wear resistance and corrosion resistance. CVD coating technology can be used without cobalt. It belongs to the nanostructured tungsten/tungsten carbide coating series, which is formed by atomic crystallization from a low pressure gas medium. It is a non-porous coating on the inner surface and complex shapes of aircraft components by constructing a protective layer of dense tungsten and tungsten carbide components, especially for designs and complexes where spray technology cannot be used. Geometry. Typical CVD coating applications include fuel metering valves, thrust pushers, 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 the minimum pre-coating part design change, thickness (50μm to 100μm) and hardness (800HV to 1,200HV), the upper limit exceeds the maximum hardness of the plating method. This is also because the dispersed tungsten carbide nanoparticles give the material a higher hardness, can control and adjust the hardness, so that the typical range is 800 Vickers hardness and 1600 Vickers hardness, suitable for different coating types. CVD coatings are typically applied at a thickness of 50 μm, combining high hardness and enhanced toughness and ductility, improving wear and erosion resistance, and withstanding impact and component deformation.
 
Engineers used high-frequency reciprocating test benches to test the wear resistance of CVD carbide coatings. A hard chrome plated stainless steel plate and a CVD coated steel plate were used for comparison. The hard chrome plated stainless steel plate quickly reached a critical 1.0 friction coefficient and a 65N load, and it was severely worn and could not be tested. The sample with CVD coating has a dry friction coefficient of about 0.2. No wear was observed, even under the maximum load of the test bench. Test results show that CVD material hardness is 13 times higher than hard chrome plating coating. In the same way, it is about 3 times the performance of supersonic flame spraying.
 
Low temperature chemical vapor deposition of tungsten carbide coating technology can eliminate the use of cobalt that is susceptible to acid. Therefore, the CVD tungsten carbide coating resists more aggressive chemicals and acts as a corrosion barrier. Due to the deposition mechanism, the low temperature chemical vapor deposition tungsten carbide coating has a low porosity and does not require a seal. Tungsten and tungsten carbide have high chemical resistance. In a comparison test with hard chrome plating and supersonic flame spraying, low carbon steel coated with hard chrome plating, supersonic flame spraying and CVD coating passed a 480-hour neutral salt spray test, hard chrome plating The sample was severely corroded and was therefore removed from the test after 288 hours. The supersonic flame sprayed coating sample showed severe rust and the coating foamed, and the CVD sample showed only slight staining.
 
Another advantage of CVD tungsten carbide coatings is that they have no wear quality for seals, bearings and other counter-body components. Uniform nanostructures allow the coating to wear evenly and maintain or even improve surface finish - even in abrasive or corrosive environments. For hydraulic actuators, rotating shafts and bearings, the coating maintains a good surface, reduces wear on elastomer and PTFE seals, prevents oil leakage, and helps to reduce maintenance requirements for aircraft actuators and transmission components.
 
In short, tungsten carbide is widely used in the aerospace industry, not only passenger aircraft, but also fighter aircraft, which can effectively solve the wear and tear of aviation equipment and extend the service life of aviation equipment.