Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
1999-11-03
2001-08-21
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C428S652000, C428S668000, C428S670000, C428S678000, C428S680000, C416S24100B
Reexamination Certificate
active
06277500
ABSTRACT:
TECHNICAL FIELD
The invention relates to a gas turbine component in accordance with the preamble of the first claim.
It likewise relates to a method for protecting a gas turbine component in accordance with the preamble of the independent method claim.
BACKGROUND OF THE INVENTION
Latest turbine experience clearly shows that mechanical properties of coatings are one of the most critical material issues in advanced turbines. Progress in blading materials and technologies (i.e. single crystal blading) is not followed by today coating systems. Thermo-Mechanical-Fatigue (TMF) properties of coated alloys are far below those for uncoated single crystal (SX) material. The main effort in increasing of the TMF life of the coated component concentrates now in two directions. The first is to fit the coating composition to the composition of the substrate. That minimizes the difference in thermal expansion between coating and substrate. The second is in providing a fine grain structure to the coating in order to increase ductility and therefore reduce stress accumulation due to the difference in mechanical behavior of the coating and the substrate.
U.S. Pat. No. 4,758,480 discloses a class of coatings whose composition is based on the composition of the underlying substrate. The similarity in phase structure and in the chemical composition renders the mechanical properties of the coating similar to those of the substrate thereby reducing thermomechanically-reduced damage during service. However, when this coating is applied by traditional means on the single crystal substrate, the difference in the E-modulus between <010> oriented surface layer of the substrate and randomly oriented coating grains produce high TMF damage.
U.S. Pat. No. 5,232,789 discloses the further improvement of the TMF properties of the coating-substrate system. The coating, which has composition and phase structure similar to the substrate alloy, has at least 1000 times more fine-grained structure, produced by a special technology. The lowermost interface portion of the fine-grained coating grows epitaxially, and therefore has the same crystal orientation as the substrate. Epitaxial growth solves also coating/substrate interface adhesion problem.
However, the system of a single crystal substrate and the multicrystal coating still has a large difference in the mechanical behavior between the substrate and the coating as any equiaxed structure possesses E-modulus much higher than those for single crystal material in <001> direction. Higher E-modulus reflects in lower TMF life of the coating compared to the substrate (although the stresses on sub-strate-coating interface are significantly reduced compared to the traditional coating-substrate system). Multiple grain boundaries drastically reduce the creep resistance of the fine-grain coating, which finally determines life of the entire blading system.
SUMMARY OF THE INVENTION
Accordingly, one object of the invention is to provide coatings which mechanical properties which are adjusted to the substrate and which have a high TMF life.
According to the invention, this is achieved by the features of the first claim.
The core of the invention is therefore the fully single crystal structure of the coated gas turbine component, which with single crystall coating layer is grown epitaxially to the base material.
The advantages of the invention can be seen, inter alia, in the fact that a fully single crystal structure of the coated component, including a MCrAIY-type coating, grown epitaxially to the base material will minimise the difference in E-modulus and therefore in TMF life between single crystal substrate and the coating. The base material and the coating have the same crystallographic orientation and therefore E-modulus is almost constant over the substrate/coating system. Through optimization of the chemical composition of the coating it is possible to achieve very low mismatch in thermal expansion between coating and substrate. Creep properties of the epitaxial coating are made equal to those of the substrate by chemistry optimization, which is impossible for the system single crystal substrate-fine-grained coating. The entire system therefore will have mechanical properties close to those for the base material and the life-time is at least doubled compared to the traditional single crystal substrate-fine-grained coating systems.
Further advantageous embodiments of the invention emerge from the subclaims. Moreover, a method for protecting a gas turbine component is further specified.
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“Development of Two Rhenium-Containing Superalloys for Single-Crystal Blade and Directionally Solidified Vane Applications in Advanced Turbine Engines”, Harris, et al., Journal of Materials Engineering and Performance, vol. 2(4) Aug. 1993, pp.181-187.
Gaumann Matthias
Konter Maxim
Kurz Wilfried
ABB Research Ltd.
Burns Doane Swecker & Mathis L.L.P.
Jones Deborah
Young Bryant
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