High Cobalt-Tungsten Carbide Powder for Explosive Spraying in Jet Fighter Engine

In the field of aero-engines in China, 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 and compressor blade damping boss on the aero engine. Crown blade canopy damping surface and turbine blade canopy damping surface have been successfully applied. For example, the Russian-made AF-31 series engine equipped with Su-27, J-10, J-11 or China's WS Series engine.

In the aircraft 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 alloy thermal spray powder materials and thermal spray technology, in addition to compressor and intake rectifier blades, turbine blades and so on. For the high requirements of aerial hair, the thermal spray powder quality requirements of tungsten carbide cobalt alloy are extremely important.

It is generally believed that explosive spraying is an effective process that can be used for aero-engine coating strengthening. It uses a high cobalt content (>=21wt.%) of tungsten carbide-cobalt alloy powder, which can withstand the impact of gas explosion waves without shredding. It is easy to heat in the process of impacting the substrate and can be fully deformed and combined with the substrate in good condition, but this requires higher requirements for tungsten carbide powder.

The high cobalt-tungsten carbide powder for explosive spraying needs to meet the two contradictory characteristics of having a certain structural strength and being able to be fully deformed during the process of easily melting and damaging the substrate. The researchers used the following scheme to prepare :

1) Mixing

The metal cobalt powder (≤3um) and the tungsten carbide powder (≤4um) are initially mixed in the material tray and then ball-milled and mixed, and the ball milling time is 8 to 24 hours.

2) Granulation

The uniformly mixed powder is uniformly added to 200 to 2000 ml of a binder (polyvinyl alcohol, polyvinylpyrrolidone, etc.) per 10 kg of the mixed powder for 5 to 30 minutes. The powder is granulated by a mechanical agitation granulation method or a spray drying granulation method.

3) High temperature sintering

The powder is placed in a graphite crucible, and a layer of activated carbon powder is placed on the crucible to form a stable carbon potential. A sintering-supporting element powder (phosphorus, magnesium, etc.) is added to the powder, and a phase-stabilizing element powder (a rare earth metal such as lanthanum or cerium) is added to the powder.

4) Crushing and screening

The sintered bulk powder is crushed and classified and sieved.

5) High temperature heat source densification treatment

The powder is subjected to high-temperature densification treatment using a high-temperature heat source such as plasma, flame, laser, microwave, etc., and finally a high cobalt-tungsten carbide powder having a high cobalt content is obtained.

The high cobalt-tungsten carbide powder thermal spray powder may contain spherical particles or a mixture of spherical, spheroidal or non-spherical particles. During the explosive spraying process of the engine, the powder may be subjected to blast waves due to its high structural strength. The impact is not broken and can fully meet the maintenance requirements of the jet fighter engine.

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