Thermal spray processes like air plasma spray and High-Velocity Oxygen Fuel (HVOF) are usually thought of as being used primarily for applying protective coatings to new parts. While new part applications do indeed constitute the majority of their use, there are also a wide variety of repair techniques that employ thermal spray processes. VAC AERO has been a leader in developing repairs for aircraft structural components and gas turbine engine parts using thermal spray processes.
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Blade Tip Coating
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HPT Nozzle
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An example of a structural component repair involves a flap track from a popular turboprop aircraft. As the wing flaps of this aircraft are extended and retracted during landing and take-off, rollers run along the surfaces of a series of components known as flap tracks. For the original flap track design, the manufacturer applied a nickel-based electroplated coating to protect the roller wear surfaces. However, after a certain period of service, the electro-plated coating was worn away and significant wear also occurred in the base metal substrate beneath. VAC AERO was tasked with coming up with a method of re-building the worn substrate and applying a more durable coating to the wear surfaces. VAC AERO’s solution was to use the HVOF process to apply a tungsten carbide coating over the worn area. This coating was used for both the restoration of the damaged substrate and as a wear resistant overlay. Because this application requires high bond strength and fatigue resistance, several coating compositions were tested before the ideal candidate emerged. The development of the proper spray parameters also required significant effort to ensure the coating adhered properly, particularly where it “feathered” out at the edges of the overlay. VAC AERO’s repair technique was subsequently approved by the aircraft manufacturer.
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Shroud Segment
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Vane Buildup
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VAC AERO has also developed a wide variety of thermal spray repairs for gas turbine engine components. These repairs can be applied to turbine blades, vanes, ring segments and many other parts, even those suffering from what might be considered as catastrophic damage. One of VAC AERO’s more popular repair techniques involves air plasma spraying the damaged surface with a proprietary coating composition consisting of a superalloy base metal powder blended with a diffusion braze alloy powder. The exact composition of this mixture is tailored to suit the base metal alloy of the part being repaired. Because the coating can be applied in a thick overlay, it can be used to re-build even heavily damaged sections. After the coating is applied, it is fused in a vacuum brazing operation and the part is then re-heat treated to restore its mechanical properties. Comprehensive studies by VAC AERO confirm that with carefully controlled powder composition and proper post-spray thermal processing, the mechanical properties of the repair will closely approach those of the base metal. Using these techniques, VAC AERO has repaired hundred of components from both aero and land-based turbine engines.
VAC AERO’s skilled engineers have extensive experience in developing the best coating solutions for both new parts and those needing restoration or repair. Contact VAC AERO to discuss your coating requirements.
For more information on VAC AERO’s Coating Services please click here.