Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Controlling current distribution within bath
Reexamination Certificate
1999-08-11
2001-07-03
Gorgos, Kathryn (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Controlling current distribution within bath
C205S096000, C205S122000, C205S136000, C205S145000, C205S195000, C205S228000, C205S264000
Reexamination Certificate
active
06254756
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to protective coatings on articles, and, more particularly, to platinum and platinum-aluminide coatings on aircraft components such as airfoils.
BACKGROUND OF THE INVENTION
In an aircraft gas turbine (jet) engine, air is drawn into the front of the engine, compressed by a shaft-mounted compressor, and mixed with fuel. The mixture is combusted, and the resulting hot combustion gases are passed through a turbine mounted on the same shaft. The flow of gas turns the turbine by contacting an airfoil portion of the turbine blade, which turns the shaft and provides power to the compressor. The hot exhaust gases flow from the back of the engine, driving it and the aircraft forwardly.
The hotter the turbine gases, the more efficient is the operation of the jet engine. There is thus an incentive to raise the turbine operating temperature. However, the maximum temperature of the turbine gases is normally limited by the materials used to fabricate the turbine vanes and turbine blades of the turbine. In current engines, the turbine vanes and blades are made of nickel-based or cobalt-based superalloys that can operate at temperatures of up to 1900-2100° F.
Many approaches have been used to increase the operating temperature limits and operating lives of the airfoils of the turbine blades and vanes. The compositions and processing of the materials themselves have been improved. The articles may be formed as oriented single crystals to take advantage of superior properties observed in certain crystallographic directions. Physical cooling techniques are used. In one widely used approach, internal cooling channels are provided within the components, and cooler air is forced through the channels during engine operation.
In another approach, a protective layer in the form of an environmental coating or a ceramic/metal thermal barrier coating (TBC) system is applied to the airfoil of the turbine blade or turbine vane component, which acts as a substrate. One of the currently known protective layers is a diffusion aluminide layer. A diffusion aluminide protective layer may be formed, for example, by electrodepositing a layer of platinum onto the surface to be protected, depositing a layer of aluminum over the platinum layer, and interdiffusing the two deposited layers.
This protective layer, with no overlying ceramic layer, is useful in intermediate-temperature applications. For higher temperature applications, a ceramic thermal barrier coating layer may be applied overlying the protective layer, to form a thermal barrier coating system. The ceramic thermal barrier coating layer insulates the component from the exhaust gas, permitting the exhaust gas to be hotter than would otherwise be possible with the particular material and fabrication process of the substrate.
Platinum is expensive, and therefore care is taken not to deposit more platinum than necessary. However, in existing practice excessive platinum is still used. There is a need for an improved approach to the preparation of airfoils with a platinum aluminide protective layer, which reduces the use of platinum. The present invention fulfills this need, and further provides related advantages.
BRIEF SUMMARY OF THE INVENTION
The present approach provides a technique for depositing platinum at selected locations of a component such as a turbine blade or turbine vane airfoil, so that the platinum aluminide protective layer is deposited only where needed. Expensive platinum metal is conserved. This technique allows full utilization of the volume within the electrodeposition tank, so that there is no reduction in part throughput. High efficiency and cost reduction in the production operation are thereby achieved. The approach is compatible with further processing procedures.
A method for preparing an article comprises the steps of providing an article precursor having a curved surface with a first portion and a second portion, and positioning a deposition anode in facing relationship to the first portion of the curved surface, so that there is no anode in facing relationship to the second portion of the curved surface. The method further includes electrodepositing a platinum layer from solution onto the article precursor using the deposition anode, with deposition occurring primarily on the first portion of the curved surface.
In one implementation, two airfoil precursors are provided, with each airfoil precursor having a convex suction side and a concave pressure side. The two airfoil precursors are positioned with their convex sides in a facing relationship, and two deposition anodes are respectively positioned in facing relationship to the concave sides of the airfoil precursors. A platinum layer is electrodeposited from solution onto the two airfoil precursors using the two deposition anodes, with deposition occurring primarily on the concave sides and some deposition on the leading edge of the airfoil. Other configurations for electrodeposition onto multiple components may also be utilized.
The article precursor is a metallic article having the shape and substantially the dimensions of the final part, optionally with small dimensional reductions to account for the layers that are deposited in the processing. The article precursor is preferably a turbine blade airfoil or a turbine vane airfoil, but other articles such as a shroud or a combustor center body may be processed using the present approach. The preparation of the article may include depositing an aluminum layer overlying the platinum deposited on the precursor, and interdiffusing the platinum layer and the aluminum layer. The resulting coating serves as an environmental protection layer. To form a thermal barrier coating for even higher-temperature applications, a ceramic layer is deposited overlying the article precursor.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The scope of the invention is not, however, limited to this preferred embodiment.
REFERENCES:
patent: 4001093 (1977-01-01), Koontz et al.
patent: 4028198 (1977-06-01), Tuscher et al.
patent: 5813118 (1998-09-01), Roedl et al.
Clarke Jonathan P.
Conner Jeffrey A.
Fargher David G. W.
Mantkowski Thomas E.
Maricocchi Antonio F.
General Electric Company
Gorgos Kathryn
Hess Andrew C.
Leader William T.
Narciso David L.
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