Coating processes – Solid particles or fibers applied
Reexamination Certificate
2000-07-11
2001-11-13
Parker, Fred J. (Department: 1762)
Coating processes
Solid particles or fibers applied
C427S201000, C427S397700, C427S427000, C427S429000
Reexamination Certificate
active
06316048
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to gas turbine engines, and specifically to turbine components in the turbine portion of the gas turbine engine made of ceramic matrix composite materials.
BACKGROUND OF THE INVENTION
In order to increase the efficiency and the performance of gas turbine engines so as to provide increased thrust-to-weight ratios, lower emissions and improved specific fuel consumption, engine combustors are tasked to operate at higher temperatures. As the higher temperatures reach and surpass the limits of the material comprising the components in the combustor section of the engine and in the turbine section of the engine, new materials must be developed or methods of cooling the materials must be enhanced.
As the combustor operating temperatures have increased, new methods of cooling the high temperature alloys comprising the combustors and the turbine airfoils were developed. For example, ceramic thermal barrier coatings (TBCs) were applied to the surfaces of components in the stream of the hot effluent gases of combustion to reduce the heat transfer rate and to provide thermal protection to the underlying metal and allow the component to withstand higher temperatures. These improvements helped to reduce the peak temperatures and thermal gradients. Cooling holes were also introduced to provide film cooling to improve thermal capability or protection. Simultaneously, ceramic matrix composites were developed as substitutes for the high temperature alloys. The ceramic matrix composites (CMCs) in many cases provided an improved temperature advantage over the metals, making them the material of choice when higher operating temperatures were desired.
To compete with CMCs, additional improvements have been developed to allow metallic components to operate at temperatures that are comparable to the operating temperature of CMC components. For example, to counter the temperature advantage enjoyed by turbine components made from CMC materials, surface enhancements have been added to the metal components. These enhancements are referred to as turbulators and increase the cooling efficiency of the metal turbine components, allowing them to operate in higher temperature environments or conversely, with reduced cooling requirements. These turbulators increase the cooling efficiency of the component by increasing the surface area over which the channeled cooling air passes so that the metal component does not exceed its limits.
While in theory the temperature capability of turbine components made from CMC materials can similarly be improved by adding like surface enhancements, a cost effective process to apply these surface enhancements onto ceramic matrix composites previously did not exist. Attempts have been made to provide the surface enhancements in the form of turbulators to CMC turbine components by machining, but, as a result of the brittle nature of the ceramic, it is very susceptible to chipping and cracking during the machining process. Thus, it has not been feasible to fully take advantage of the higher temperature capabilities of components made from ceramic matrix composites. Without the economic incentive, the further development and incorporation of components made from ceramic matrix composites has not progressed.
What is needed is an effective process to apply surface enhancements such as turbulators to the surface of ceramic matrix composites.
SUMMARY OF THE INVENTION
Improvements in manufacturing technology and materials are the keys to increased performance and reduced costs for many articles. As an example, continuing and often interrelated improvements in processes and materials have resulted in major increases in the performance of aircraft gas turbine engines, such as the improvements of the present invention. A method for enhancing the cooling capability of a turbine component made from a ceramic matrix composite produces a surface having increased cooling capacity, thereby improving the thermal performance of the component by allowing the component to operate at a higher temperature. The method tailors the available surface area on the cooling surface of the composite component by depositing a particulate layer of coarse grained ceramic powders of preselected size onto the surface of the ceramic matrix composite component. The size of the particulate is selectively tailored to match the desired surface finish or surface roughness of the article. The article may be designed to have different surface finishes for different locations, so that the application of different sized powders can provide different cooling capabilities at different locations, if desired. The compositions of the particulates are chemically compatible with the ceramic material comprising the outer surface or portion of the ceramic matrix composite.
The method that is used to bond the particulates to the outer portion of the ceramic matrix composites is highly dependent upon the method to produce the ceramic matrix composite component. The ceramic matrix composites may be formed by chemical vapor infiltration (CVI), polymer impregnation pyrolysis (PIP) or melt infiltration (MI). The particulates may be applied by slurry processing methods, tape casting or spray forming. When any liquid medium is utilized as a carrier in the application of the particulates to the outer layer of the component, then it is an evaporable liquid that is removed by subjecting the component to relatively low heat, leaving the particulate attached to the outer layer of the component. The attached particles are bonded by heating the component to an elevated temperature sufficient to bond the particulates to the surface without melting either the surface or the particulates. Particulate melting is avoided by the present invention, as the high temperatures required for particulate melting can result in degradation of the reinforcing fibers.
An advantage of the present invention is that surface enhancements such as turbulators can be incorporated into the surface of the CMC component without utilizing potentially damaging machining techniques. The methods of the present invention thus reduce scrap; thereby making them more cost effective.
Another advantage of the present invention is that the effective heat transfer coefficient of the component surface readily can be tailored to vary the heat transfer capabilities across the surface so that a more uniform cooling profile can be achieved and hot spots can be eliminated.
Yet another advantage of the present invention is that the methods of tailoring the surface, as set forth by the present invention is not subject to limitations as a result of part size or part geometry.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, which illustrate, by way of example, the principles of the invention.
REFERENCES:
patent: 4182412 (1980-01-01), Shum
patent: 5780157 (1998-07-01), Tuffias et al.
patent: 5792544 (1998-08-01), Klein
patent: 5900277 (1999-05-01), Fox et al.
patent: 59-18394 (1984-01-01), None
Steibel James Dale
Utah David Alan
General Electric Company
Hess Andrew C.
Narciso David L.
Parker Fred J.
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