Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
1999-04-16
2001-02-27
Speer, Timothy M. (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C428S627000, C428S678000, C428S679000, C428S680000, C416S24100B, C416S24100B
Reexamination Certificate
active
06194086
ABSTRACT:
During the operation of a gas turbine engine, it is desired to maintain minimum clearance between the tips of the turbine blades and the corresponding seals. A large gap results in decreased efficiency of the turbine, due to the escape of high-energy gases. Conversely, friction between the blades and seals causes excessive component wear and wastes energy. Since aircraft turbines experience cyclic mechanical and thermal load variations during operation their geometry varies during the different stages of the operating cycle. It is therefore impossible to set the necessary minimum clearance at the time of assembly. Active clearance control and abrasive blade tips are currently used to establish and maintain optimum clearance during operation. Abrasive blade tips are used to enable the blades to cut their own path in the seals during the first few operating cycles of the engine. Ideally, those tips should retain their cutting action over many operating cycles compensating for any progressive changes in turbine geometry. The tips are usually comprised of an abrasive particulate phase such as CBN, coated SiC, or another hard ceramic phase embedded in a suitable oxidation-resistant alloy matrix, such as MCrAlY, the M standing for either Ni or Co or both.
Various methods have been described in the art for applying an abrasive coating on an article. U.S. Pat. No. 4,249,913 describes an alumina coated silicon carbide particle dispersed in an alloy attached to the end of a turbine blade by diffusion bonding, liquid phase bonding or brazing. U.S. Pat. No. 4,610,698 describes a combination of sintering, plasma arc spraying, hot isostatic pressing and chemical milling to form an abrasive surface. U.S. Pat. No. 4,227,703 describes a process of bonding a discrete shaped alloy to the tip, then entrapping thereon abrasive particles with a matrix containing Cr, Co and Ni applied by electrodeposition.
A more recent method is described in U.S. Pat. No. 5,076,897 wherein a binding coat of MCrAlY is applied by electrodeposition, anchoring to the binding coat abrasive particles by composite electrodeposition and then plating an infill around the abrasive particles. This method is attractive due to its low cost and ease of manufacture; however, a problem with these abrasive tips is the low mechanical strength. This is due primarily to the weakness of the plated matrix and the interface between the plated matrix and the base alloy of the blade.
Thus an object of this invention is to provide a cost effective means of applying durable abrasive coatings with a strong bond between the substrate and the abrasive coating.
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Fenton Richard
Fuggini Joseph A.
Howard Peter
Nenov Krassimir P.
Bittman Mitchell D.
Chromalloy Gas Turbine Corporation
Speer Timothy M.
Young Bryant
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