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Strip process for superalloys

Inactive Publication Date: 2007-05-24
UNITED TECH CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

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Benefits of technology

[0006] In accordance with the present invention, it has been determined that alloys which contain high volume fractions of γ / γ′ eutectic phase can have their MCrAlY coatings stripped, with reduced amounts of pitting attack, by employing an improved chemical stripping process in accordance with the present invention.

Problems solved by technology

Solution heat treatment of such alloys does not fully eliminate these phases.

Method used

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  • Strip process for superalloys
  • Strip process for superalloys
  • Strip process for superalloys

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Embodiment Construction

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[0015] The present invention relates to a strip process for removing a coating from a substrate formed from a nickel-based superalloy and to a process for treating a nickel-base superalloy to improve removal of a coating such as a MCrAlY coating.

[0016] In accordance with the present invention, a turbine engine component formed from a nickel-based superalloy, such as one having a high volume fraction of γ / γ′ eutectic phase which is highly enriched in aluminum and of relatively large scale (up to about 5-10 mils in diameter) has a chromizing coating applied to surfaces to be coated. The chromizing coating may comprise a layer of chromium deposited onto each surface to be coated. Any suitable process known in the art may be used to deposit the chromium layer, such as, but not limited to, chemical vapor deposition processes with a deposit thickness of less than approximately 0.5 mils. The chromizing coating treatment may be applied during manufacture of the turbine engine component. A...

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Abstract

A process for forming a coated substrate comprises providing a nickel base alloy substrate, depositing a chromium coating onto the nickel base alloy substrate and diffusing chromium from said coating into the substrate, applying a MCrAlY coating onto the nickel base alloy substrate and heat treating the substrate with the deposited chromium and the MCrAlY coating so that chromium diffuses into an outer region of the substrate. Further, in accordance with the present invention, a strip process for removing a coating from a substrate broadly comprises the steps of providing a nickel base alloy substrate having chromium diffused into an outer region and a MCrAlY coating deposited over the substrate with the diffused chromium and removing the MCrAlY coating by immersing the nickel base alloy substrate in an acid solution containing a sulfuric acid-hydrochloric acid mixture in water.

Description

BACKGROUND OF THE INVENTION [0001](1) Field of the Invention [0002] The present invention relates to a process for removing a coating from a substrate made from a nickel-base superalloy and to a process for treating a nickel-base superalloy. [0003](2) Prior Art [0004] Cast nickel-base superalloys used in turbine engine components can be coated with MCrAlY type overlay coatings that typically contain about 8-12% aluminum. These coatings extend the life of the components that they are applied to. Some nickel-base superalloys contain a high volume fraction of γ / γ′ eutectic phase which is highly enriched in aluminum and of relatively large scale (up to about 5-10 mils in diameter) compared to the surrounding microstructure. Solution heat treatment of such alloys does not fully eliminate these phases. [0005] During manufacturing rework or aftermarket repair, coatings are removed using mineral acids. 70-100 v / o hydrochloric acid is typically used to remove MCrAlY type coatings which prefe...

Claims

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Application Information

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IPC IPC(8): B32B15/20C23C16/00
CPCC23C10/02C23C10/60C23C28/023C23F1/44Y10T428/12882F05D2300/132C23C28/022C23C28/028F01D5/288C23C10/38C23F1/38
Inventor CETEL, ALAN D.RIEWE, CURTIS HEALTHBRAITHWAITE, DWAYNE A.
Owner UNITED TECH CORP
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