Method for coating internal surfaces

Details Method for coating internal surfaces Method for coating internal surfaces

2001-09-21

2003-07-01

Barr, Michael (Department: 1762)

Coating processes

With post-treatment of coating or coating material

Heating or drying

C427S239000, C427S376200, C427S376600

Reexamination Certificate

active

06586052

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to coatings for superalloys such as nickel-based superalloys, and more particularly to a method for coating the internal surfaces of complex, superalloy parts.
BACKGROUND OF THE INVENTION
Nickel- and/or cobalt-based superalloys effective for use in high temperature environments are commonly used by the aerospace and power industries. While such alloys are inherently strong, they are generally not particularly resistant to corrosion by high temperature gases. Corrosion and oxidation-resistant coatings are therefore often applied to the metal to improve durability.
Internal coatings to protect those superalloy parts can be applied by several different methods. For example, chemical vapor deposition (CVD) methods using a reactor to generate a reactive Al-bearing species, or CVD methods that use above-the-pack technology, have been used. Both methods are generally effective, but require a sizable investment in equipment, etc. Moreover, in the case of above-the-pack processes, there is a significant amount of waste generated, including corrosive gases that require scrubbers to capture active species and/or convert them to innocuous products.
As an alternative to CVD methods, slurry methods have also been used. In those methods, an Al-bearing material is injected into the internal cavity and the part is heated to either produce an Al-bearing vapor and/or to diffuse the Al-bearing species into the metal surface.
One concern when using slurry methods is the amount of residue left after heat treating the component to diffuse the active species into the internal surface. Slurries that often contain halide activators also present additional problems since even trace amounts of these halides may initiate corrosion if not removed from the metal. Additional cleaning steps increase processing costs.
In addition, slurry methods often are difficult to use when the part being coated has small interior spaces. The slurry coating material doesn't always penetrate such spaces very effectively, and may leave some interior crevices uncoated.
Moreover, the coating methods of the prior art often make it difficult to control coating thickness. As a result, the interior coating may be thicker or thinner than necessary, adding weight and cost when the coating is too thick, and reducing coating efficacy when the coating is too thin.
A need therefore exists for new methods of applying a coating composition to Ni- and Co-based superalloy surfaces, and particularly to the inside of a jet engine turbine blade or vane. The present invention addresses that need.
SUMMARY OF THE INVENTION
Briefly describing one aspect of the present invention, there is provided a method for coating a nickel- or cobalt-based superalloy surface by slurry deposition followed by heat diffusion. The method comprises: (1) preparing a slurry of a metal coating powder mixed into an adhesive carrier that will burn off ash-free during a diffusion cycle; (2) depositing said slurry onto the surface of a Ni- or Co-based superalloy material to form a coated surface; and (3) heating said coated surface to a temperature of at least about 1600° F. to diffuse the metal coating powder into the metal substrate.
One object of the present invention is to provide an improved method of depositing a metal coating composition onto a superalloy surface.
Other objects and advantages will be apparent from the following description of the preferred embodiments.


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