Stock material or miscellaneous articles – All metal or with adjacent metals – Having metal particles
Reexamination Certificate
1992-04-23
2001-08-21
Gorgos, Kathryn (Department: 1741)
Stock material or miscellaneous articles
All metal or with adjacent metals
Having metal particles
C428S553000, C428S557000, C428S567000, C428S668000, C428S674000, C428S675000, C427S405000
Reexamination Certificate
active
06277499
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method for protecting copper and copper-based composites or monolithic structures from oxidation at elevated temperatures.
2. Description of the Prior Art
Copper alloys have generally superior thermal and electrical conductivity, especially pure copper or alloys having only minimal additions. Unfortunately, such materials also tend to oxidize rapidly at elevated temperatures, thus limiting their applicability for such purposes as high temperature heat exchangers, actively cooled gas flow channels, and air frame structures. For such applications, the alloys must have high strength and adequate oxidation resistance. Strengthening of copper alloys may be accomplished by compositing with a second metallic phase, such as niobium, tantalum, etc., known as microcompositing, or by reinforcement by high strength fibers, such as graphite.
Prior to the present invention, applicants have been unaware of any viable method to protect copper substrates for use at temperatures exceeding approximately 800° F. It has recently been proposed, however, that copper and copper alloys, as well as copper-graphite fiber composites, be utilized for very high temperature heat exchange in rocket engines and hypersonic combustion engines. To achieve this, it was found necessary to provide a means to protect such materials from oxidation in the temperature ranges anticipated, e.g. 1200° F. or higher. Moreover, for such utility, it was also necessary to provide protective coatings which would be compatible with the coefficient of thermal expansion of the substrate, and not substantially lower the thermal conductivity of the structure, while exhibiting fatigue resistance and resistance to diffusion.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a means to protect a predominately copper substrate from high temperature oxidation by application of a protective coating to the surface thereof. It is also an object of the present invention to provide high temperature heat exchange media comprising copper having a protective layer of a highly oxidation resistant material thereupon.
These and other objects of the present invention have been achieved by application of a copper-aluminum alloy protective layer to the surface of a copper substrate, utilizing specifically selected barrier layer materials to prevent diffusion of the aluminum from the coating layer into the substrate. In addition, it is critical that the barrier layers utilized be microstructurally stable, resistant to oxygen and aluminum diffusion, tolerant to strain, and retain ductility at elevated temperatures, while not dissolving in either the copper substrate or the copper-aluminum alloy coating.
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Beers Russell A.
Khan Abdus S.
Noetzel Allan A.
Carroll Chrisman D.
Gorgos Kathryn
United Technologies Corporation
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