Fluid reaction surfaces (i.e. – impellers) – Specific blade structure – Coating – specific composition or characteristic
Reexamination Certificate
2001-04-23
2002-05-07
Look, Edward K. (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
Specific blade structure
Coating, specific composition or characteristic
C416S24100B
Reexamination Certificate
active
06382920
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to an article of manufacture, in particular a component of a gas turbine, having a base body and a thermal barrier coating formed thereon. The invention also relates to a process for applying a thermal barrier coating to an article which can be exposed to a hot aggressive gas and has a base body, in particular a metallic base body.
U.S. Pat. No. 5,238,752 describes a thermal barrier coating system having an intermetallic bond coating. The thermal barrier coating system is applied to a metallic base body, in particular to a Cr—Co steel for an aircraft engine blade. An intermetallic bond coat, in particular of a nickel aluminide or a platinum aluminide, is applied directly on top of that metallic base body. The bond coat is adjoined by a thin ceramic layer of aluminum oxide, to which the actual thermal barrier coating, in particular made from yttrium-stabilized zirconium oxide, is applied. This ceramic thermal barrier coating of zirconium oxide has a columnar structure, the rod-shaped columns being oriented substantially perpendicular to the surface of the base body. This is intended to improve the ability to withstand cyclic thermal loading. The thermal barrier coating is deposited on the base body by means of an electron beam PVD (physical vapor deposition) process. The zirconium oxide is thereby vaporized out of a metal oxide body using an electron beam gun. The process is carried out in a corresponding device, in which the base body is preheated to a temperature of approximately 950° C. to 1000° C. During the coating operation, the base body is rotated at constant speed in the jet of metal oxide.
An electron beam PVD process for producing a ceramic coating is also described in U.S. Pat. No. 5,087,477. There, the ceramic coating has a layer thickness of between 250 and 375 &mgr;m.
U.S. Pat. Nos. 4,405,659 and 5,514,482 each describe components, in particular gas turbine blades, made from a nickel-base or cobalt-base alloy, and in each case a ceramic thermal barrier coating of columnar structure is applied to these components. The mean diameter of the columns is in that case over 2.5 &mgr;m, the layer thickness amounting to approximately 125 &mgr;m. The ceramic thermal barrier coating is applied by means of an EB (electron beam) PVD process.
International PCT publication WO 98/13531 describes a component, in particular a gas turbine blade, which has a ceramic thermal barrier coating of columnar fine structure on a metallic base body, the mean column diameter being less than 2.5 &mgr;m. This small mean column diameter for layer thicknesses of the order of magnitude of over 100 &mgr;m which are used in gas turbine construction is achieved by means of a reactive gas flow sputtering process. In this process, an ionizable gas is passed through a hollow cathode and, on account of the voltages prevailing in the hollow cathode, is ionized, and is thus accelerated toward the inner wall of the hollow cathode. The hollow cathode has the coating material, in particular metallic zirconium, on its inner wall, this material being thrown out by the ions and transported toward the base body which is to be coated.
U.S. Pat. No. 5,350,599 describes a thermal barrier coating for a turbine blade which has a plurality of layers positioned on top of one another. The outer surface layer is of erosion-resistant design, while the layer beneath it is of porous design. Both layers are made from ceramic material and are applied successively by means of a PVD process. The porous or sealed structure of the erosion-resistant outer layer is obtained by varying the process parameters during the coating process. The application of the outer erosion-resistant layer is intended to protect the turbine blade from damage caused by erosion.
European published patent application EP 0 139 396 A1 describes a coating system for a turbine blade in which different coatings are applied in different surface regions, specifically as a function of the temperature occurring on the turbine blade. In this case, a distinction is drawn between a hot end and a cold end of the turbine blade. The various coatings are adapted to the different temperature requirements in particular in terms of their ductility and their creep behavior. For this purpose, they have different chemical compositions. This requires a transition layer to be arranged between adjacent layers of different compositions.
SUMMARY OF THE INVENTION
The object of the present invention is to provide an article of manufacture that can be exposed to hot aggressive gases which overcomes the above-noted deficiencies and disadvantages of the prior art devices and methods of this general kind, and which is formed with a thermal barrier coating that satisfies the attendant requirements. A further object of the invention is to outline a process for coating an article with a thermal barrier coating.
With the above and other objects in view there is provided, in accordance with the invention, an article of manufacture that is to be exposed to hot aggressive gas. The article comprises a base body or substrate having a first surface region and a second surface region, and a thermal barrier coating of uniform chemical composition applied on the base body, the coating having a fine structure in the first surface region different from a fine structure in the second surface region.
In other words, the article of manufacture, in particular a component of a gas turbine, which can be exposed to a hot aggressive gas has a base body and a thermal barrier coating of uniform chemical composition applied to the base body. The coating has different microstructures in a first surface region and in a second surface region and is thus adapted to meet the requirements imposed by the thermomechanical stresses on the product which in each case prevail locally or are to be expected for the particular intended use. The two surface regions lie in the same surface plane or surface layer. They are in particular arranged next to one another. In the surface regions, the thermal barrier coating has a thermal barrier material which is uniform in terms of its chemical composition. The thermal barrier coating can therefore be referred to as a single-material barrier coating. This has the considerable advantage over multimaterial barrier coatings that problems which are inherent to a material transition are avoided. At the same time, on account of the different microstructures, the respective surface regions are designed for the expected loads.
In this case, it is likewise additionally or alternatively possible, in regions which are of geometrically different design, in particular with regard to surface curvature, convexity or concavity, if the local thermomechanical load to be expected is the same, for the fine structure in the geometrically different surface regions still to be of substantially identical form. This particular form of the coating is advantageous in particular in the case of curved components which are exposed to a hot gas stream which leads to locally different thermomechanical loads, since the thermal barrier coating is locally adapted to the thermomechanical stresses, such as temperature and the action of forces as a result of impinging particles, which occur. As a result, it is possible to locally influence, in particular extend, the service life of the thermal barrier coating in a controlled way, so that the duration of use and the service life of the product are also extended.
In accordance with an added feature of the invention, the thermal barrier coating has a fine structure with ceramic columns which are oriented substantially perpendicular to the surface of the base body. In this case, the ceramic columns may have a diameter of a few microns (&mgr;m) at a layer thickness of up to 100 &mgr;m or more. A fine structure with ceramic columns is particularly advantageous, since it is able to follow thermal expansion of the base body particularly in the event of cyclic temperature changes without being damaged.
In accor
Greenberg Laurence A.
Mayback Gregory L.
Siemens Aktiengesellschaft
Stemer Werner H.
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