Cobalt-Tungsten Carbide Alloy Thermal Spray Coating Applied in Aero Engines

Cobalt-tungsten carbide alloy thermal spray coating is the highest hardness wear resistant coating below 540 °C. Due to its combination of good hardness and toughness, it is widely used in aviation, aerospace, automotive, transportation, metallurgy, electric power, etc. Strengthen the wear resistance of the base metal and repair the worn fatigue parts.

In the field of aerial hair, tungsten carbide has good impact resistance, toughness and bond with the substrate, and has high density. It has been used as a fan blade damping boss, compressor blade damping boss, and crowned blade on an aero engine. The canopy damping surface and the turbine blade canopy damping surface have been successfully applied. For example, an AF-31 series engine equipped with a Su-27 or Desheng-10, J-11.

In the aero engine overhaul and consumable parts repair project, the coating of the wear-resistant boss on the surface of the nickel-base alloy parts to prepare high hardness and high wear resistance was selected to be carbonized with high cobalt content (>=21wt.%). Tungsten-cobalt thermal spray powder materials and thermal spray technology, in addition to compressor and intake rectifier blades, turbine blades, etc. For the high requirements of aerial hair, the thermal spray powder quality requirements of tungsten carbide cobalt alloy are extremely important.

As an important thermal spraying method, explosive spraying has the characteristics of lower, more stable gas temperature and higher air velocity, and is especially suitable for spraying tungsten carbide cobalt powder in the field of aviation. Explosive spraying undergoes two processes of explosion and pulse circulation, and a coating of 5-10 μm thick is formed on the workpiece in each working cycle. The spray pulse cycle ensures that the substrate material is exposed to very little heat (150 ° C - 200 ° C). In addition, all processes performed during explosive spraying have a short duration. The gas and the duration of the action of the gas on the powder does not exceed 3 x 10-3 seconds. The time during which the powder particles are impact-deformed at the instant of coating formation does not exceed 10-7 seconds. All of this helps to maintain the physical and mechanical properties of the material being sprayed.

In addition, the type of powder used for explosive spraying is not exactly the same as other thermal sprays. Explosive spraying requires that the powder has a certain structural strength and can withstand the impact of gas explosion waves without breaking. However, when heated to a certain temperature, particles composed of high-melting tungsten carbide and a molten cobalt-based liquid phase are required to be capable of generating sufficient plastic deformation, and when impinging on the substrate, 5 to 10 μm is formed from particles of 30 to 50 μm. The flakes are deposited on the substrate to form a coating. Therefore, the high cobalt tungsten cobalt alloy powder used for explosive spraying needs to satisfy a certain structural strength and can withstand the gas explosion wave impact without being shattered; and at the same time, it is easy to be heated and deformed sufficiently in the process of striking the substrate, and has a good combination with the substrate.

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