Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Composite having voids in a component
Reexamination Certificate
1999-12-14
2001-10-09
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Composite having voids in a component
C428S316600, C428S212000, C427S373000, C427S255190, C427S255210, C427S255700
Reexamination Certificate
active
06299971
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of ceramic thermal barrier coatings and to abradable ceramics for use in gas turbine seal applications. More specifically this invention relates to ceramic thermal barrier coatings and abradable seals comprised of multiple layers in which at least one of the layers is porous.
DESCRIPTION OF RELATED ART
Gas turbine engines are widely used as sources of motive power, and for other purposes such as electric generation and fluid pumping. Gas turbine manufacturers face a constant customer demand for better performance, enhanced efficiency and improved life. One way to improve performance efficiency and performance is to increase operating temperatures. Increasing operating temperatures usually reduces engine life and is effective only within the limits of materials used in the engine.
Current gas turbine engines are predominantly constructed of metallic materials, with nickel base superalloys being widely used in high temperature portions of the engine. Such superalloys are currently used in engines where with gas temperatures which are very near their melting point of the superalloys. Increases in engine operating temperature are not possible without concurrent steps to protect the superalloys from direct exposure to gas temperatures at which melting occurs. Such steps include the provision of cooling air (which reduces engine efficiency) and the use of insulating coatings.
Insulating ceramic materials, particularly in the form of coatings or thermal barrier coatings, are the primary subject of this invention. Such coatings are most commonly ceramic and are commonly applied by plasma spraying or by electron beam vapor deposition. This invention focuses on coatings applied by electron beam vapor deposition. The electron beam vapor deposition process is described in U.S. Pat. Nos. 4,405,659; 4,676,994 and 5,087,477. Typical patents which discuss the current state of the art thermal barrier coatings are as follows: U.S. Pat. Nos. 4,405,660; 5,262,245 and 5,514,482.
The most widely used thermal barrier coating for application to rotating components in turbine engines comprises a bond coat material whose composition is described in U.S. Pat. No. 4,419,416, a thin layer of aluminum oxide on said bond coat, and a columnar grain ceramic coating adhered to the aluminum oxide layer as described in U.S. Pat. No. 4,405,659. This coating was developed by the assignee of the present invention and it is currently applied to more than 100,000 gas turbine components per year. Despite the success of this coating and its widespread acceptance there is a desire for advanced thermal barrier coatings, the principle desired enhancement being improved specific thermal insulation properties (thermal insulation corrected for density).
If a coating with improved density corrected insulation properties could be developed, such a coating could either be used at the same thickness as that now used commercially to reduce heat flow (allowing for a reduction in cooling air and thereby increasing engine efficiency) or could be used at a reduced thickness to provide the same degree of insulation and heat flow but with reduced coating weight. Such weight reductions are significant, especially on rotating components, since the weight of the thermal barrier coating results in centrifugal forces during engine operation of as much as two thousand pounds on a single turbine blade in a large aircraft engine. Reducing blade centrifugal forces has positive implications in the design requirements of engine components associated with the blade, in particular the supporting disc.
Gas turbine efficiency can also be improved by reducing gas leakage. In particular the clearance between the tips of the rotating blade and the surrounding case structure must be minimized. This is commonly accomplished by providing an abradable seal material on the case. In operation the blade tips cut a channel in the abradable, thus reducing gas leakage. The contents of U.S. Pat. Nos. 4,039,296 and 5,536,022 are incorporated herein by reference.
SUMMARY OF THE INVENTION
The present invention comprises a layered ceramic material, preferably applied as a coating. Different layers in the structure have different microstructures, with at least one of the layers being relatively dense and another of the layers being less dense and defective. The structure of the less dense defective layer can be modified by heat treatment to provide porosity. Porosity provides reduced thermal conductivity and increased abradability.
The layers are preferably deposited by electron beam physical vapor deposition. Sputtering is an alternative application technique for the invention process, but as currently practiced is a slow and generally uneconomic process.
Most frequently the layers will have different chemical compositions although under certain circumstances it is possible for the layers to have a common chemical composition. The layers are applied under conditions which produce the previously mentioned differences in density and porosity between alternating layers.
The relatively dense layers are applied by electron beam vapor deposition under conditions which result in the deposition of what those knowledgeable in the physical vapor deposition art refer to as zone II or zone III structures hereinafter the designation Zone II/III will be used to refer to structures having either a Zone II or Zone III type structure or a combination of Zone II and Zone III structures. The less dense layers (i.e. the layers which will become porous) are applied under conditions which result in microstructures that those skilled in the physical vapor deposition art referred to as Zone I structures. As used herein, the term Zone I means a layer having either an as deposited Zone I structure or an as deposited Zone I structure which has been heat treated to enhance porosity.
Preferably the resultant structure will be heat treated to enhance porosity through sintering which increases pore size and densifies the ceramic portions which surround the pores.
The invention coating finds particular application in the field of gas turbine components. Such components include turbine airfoils (blades and vanes) and abradable seals which are intended to interact with blade tips or knife edge seals to reduce unwanted gas flow.
REFERENCES:
patent: 3975165 (1976-08-01), Elbert et al.
patent: 4336276 (1982-06-01), Bill et al.
patent: 4566700 (1986-01-01), Shiembob
patent: 4936745 (1990-06-01), Vine et al.
patent: 5015502 (1991-05-01), Strangman et al.
patent: 5059095 (1991-10-01), Kushner et al.
patent: 5384200 (1995-01-01), Giles
patent: 5817372 (1998-10-01), Zheng
patent: 5834108 (1998-11-01), Shimai et al.
patent: 6957047 (2000-02-01), Maloney
Growth and Growth-Related Properties . . . Donald M. Mattox, ASM Handbook, vol. 5, 1994, 18 pgs.
Study of the Structure and Properties of Thick Vacuum . . . Movchan, Demchishin, Phys. Met. Metallogr. (USSR), vol. 28, 1969, 9 pgs.
Physical Vapor Deposition of Ceramic Coatings for Gas Turbine Engine Components, Demaray, Fairbanks, Boone, 8 pgs.
High Rate Thick Film Growth, John A. Thornton, Ann Rev. Mater Sci. 1977: 239-60, 12 pgs.
Jones Deborah
Sohl Charles E.
Stein Stephen
United Technologies Corporation
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