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Publication numberUS3741791 A
Publication typeGrant
Publication dateJun 26, 1973
Filing dateAug 5, 1971
Priority dateAug 5, 1971
Publication numberUS 3741791 A, US 3741791A, US-A-3741791, US3741791 A, US3741791A
InventorsGabriel J, Maxwell D
Original AssigneeUnited Aircraft Corp
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Slurry coating superalloys with fecraiy coatings
US 3741791 A
Abstract  available in
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Claims  available in
Description  (OCR text may contain errors)

United States Patent US. Cl. 117-46 CA 3 Claims ABSTRACT OF THE DISCLOSURE A slurry coating, particularly for the nickel-base and cobalt-base alloys, which comprises, by weight, 20-30 percent chromium, 8-12 percent aluminum, 10-16 percent silicon, 0.1-3 percent yttrium, scandium or lanthanum, balance iron is applied to a suitable substrate and diffusion heat treated to provide oxidation resistance thereto.

The invention herein described was made in the course of or under a contract with the Department of the Air Force. 7

BACKGROUND OF THE INVENTION The present invention relates in general to high temperature, oxidation resistant coatings and processes for achieving such coatings, particularly those of the iron/ chromium/ aluminum/ yttrium type.

In the patent to Talboom, Jr. et a1. 3,542,530 of common assignee with the present invention, there is described an advanced coating for the nickel-base and cobalt-base superalloys. The coating contemplated therein comprises, by weight, about 20-50 percent chromium, 10-20 percent aluminum, 0.03-2 percent yttrium or the like, balance iron. Because of the particular nature of this coating, specifically its high melting point, reference is made to the now conventional method of its application to a suitable substrate by vapor deposition from a molten pool of coating material in a vacuum chamber.

The vacuum vapor deposition techniques are essentially line-of-sight processes insofar as coating deposition is concerned and are, accordingly, most readily adapted to the coating of relatively small components, such as turbine blades or vanes. When the coating is desired on large parts or in internal passages shielded from the molten pool, the vapor deposition method becomes much more unwieldy and, in some instances, completely impractical.

In the patent to Joseph 3,102,044, also of common assignee with the present invention, there is described a slurry process for forming a protective aluminide coating on certain alloy parts. Since according to the Joseph technique a suitable coating slurry is merely painted or sprayed on the surfaces to be protected, with a subsequent heat treatment forming the desired protective aluminide, size of the part is of no importance, as distinguished from the vapor deposition methods.

The Joseph technique effects the generation of the protective coating by the reaction of aluminum in the slurry to form aluminides of the substrate metal from which the basic oxidation resistance is attained. The coatings of the iron/chromium/aluminum/yttrium type (hereinafter called FeCrAlY) depend, not as in Joseph on a reaction with the substrate, but rather on the formation of the FeCrAlY alloy at the surface-and within a certain compositional range for the reasons set forth in the Talboom, Jr. et al. patent.

The slurry of Joseph is also characterized by an active coating ingredient, i.e., aluminum, having a melting point substantially lower than the usual substrate alloy to be coated. In the Joseph process the applied coating becomes liquid during diffusion, and through reaction and diffusion with the base alloy resolidifies as the oxidation resistant aluminide having a melting point above the diffusion temperature.

With coatings of the FeCrAlY type, including CoCrAlY,

the melting point is typically higher than that of the substrate alloy or is at least so high that melting cannot take place wihout irreparable damage to the substrate. Thus, one cannot merely substitute the basic FeCrAlY coating components for the aluminum of Joseph and expect to generate the desired coating. Furthermore, in the slurry coating of the present invention, the coating components react with and dissolve a limited part of the base alloy, a combining of the elements in the coating with elements in the substrate, including those which may be harmful to oxidation resistance, providing oxidation resistant species. Thus the alloy microstructure as well as the coating mechanism differ from the aluminized parts and processes.

The generation of coating layers in the cobalt/chromium/aluminum/yttrium and nickel/chromium/aluminium/yttrium systems face similar problems. And in all of the coatings of the FeCrAlY-type, a substantial interchangeability of the iron group metals is tolerated.

SUMMARY OF THE INVENTION The present invention contemplates the inclusion of about 10-16 weight percent of silicon together with the other ingredients comprising the FeCrAlY-type coating in a suitable dispersant, forming a slurry for application to surfaces to be protected which are thereafter diffusion heat treated to form an oxidation-resistant layer.

The active ingredients for the FeCrAlY coating slurry comprise, by Weight, 20-30 percent chromium, 8-12 percent aluminum, 10-16 percent silicon, 0.1-3 percent yttrium, scandium or lanthanum, balance substantially iron. A suitable slurry is formed by mixing about 50 volume percent of suitably milled powders of the above composition with a volatile liquid dispersant, such as nitrocellulose.

With the above slurry an oxidation-resistant coating can be generated on the nickel-base superalloys, after the slurry has dried, by diffusion heat treatments at 2100 F. and 2225 F., but in any event below that temperature at which irreparable damage to the substrate occurs.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the coatings of the FeCrAlY-type, chromium provides hot corrosion resistance; aluminum furnishes oxidation resistance through the generation upon exposure to an oxidizing environment of the protective aluminum oxide; and yttrium, scandium and lanthanum promote adherence of the oxide reducing the spallation of the protective oxide. In the present slurry coating, silicon lowers the melting point of the coating powders and, in addition, reacts to tie up the molybdenum, when present in the substrate metal, as an oxidation resistant nickel/silicon/ molybdenum or nickel/silicon/aluminum/molybdenum compound. Pure molybdenum or a very high molybdenum phase is typically not oxidation-resistant.

The process hereinafter described in detail has been utilized to increase the oxidation, sulfidation, erosion and thermal shock resistance of the nickel-base superalloys. A nickel-base alloy of the composition, by weight, comprising 17.5-18.5 percent molybdenum, 7.75-8.25 percent aluminum, 0-0.05 percent carbon, balance nickel was thoroughly cleaned and degreased. The surfaces to be protected were then sprayed with a milled slurry of 50 volume percent 400 mesh powders of the composition comprising, by weight, 24-26 percent chromium, -105 percent aluminum, 14.5-15.5 percent silicon, 0.8-1.2 percent yttrium, balance substantially iron; and 50 volume percent nitrocellulose base lacquer. Drying was accomplished in air in 4 hours, providing a green coating.

The coated parts were heated to 2100 F. at a rate of 30-40 F. per minute and held at temperature for 10 minutes, then heated to 2225 F. and held for 5 minutes, in the absence of air, typically in a vacuum or hydrogen atmosphere. In general, coating thicknesses of 0.004- 0.007 inch after diffusion have been found satisfactory.

It is, of course, inherent in this coating system that softening occurs at a lower temperature than that of the basic FeCrAlY system. Thus, its utility is confined to those applications where exposure is confined to temperatures about 200 F. below the acceptable exposure temperature of the unmodified coating. The utility of the system has been established in a variety of applications, however, such as jet engine afterburner seal flaps.

The invention in its broader aspects is not limited to the specific steps, process and compositions shown and described but departures may be made therefrom within the scope of the appended claims without departure from the principles of the invention and without sacrificing its chief advantages.

What we claim is:

1. In the coating of the nickel-base and cobalt-base alloys with a composition of the FeCrAlY-type for high temperature oxidation-resistance, the improvement which comprises:

forming a mixture of prealloyed powder-s consisting essentially of said composition and -16 weight percent silicon;

dispersing said mixture in a compatible volatizable liquid to form a slurry;

applying the slurry to the alloy surface to be protected;

drying the slurry on the alloy to form a green coatand diffusion heat treating the green coating in the absence of air at a temperature above about 2100 F. to form the desired oxidation-resistant coating.

2. The method of coating a nickel-base or cobaltbase alloy to impart oxidation-resistance thereto which comprises:

forming a slurry comprising a powder mixture consisting essentially of, by weight, 20-30 percent chromium, 8-12 percent aluminum, 10-16 percent silicon, 0.1-3 percent yttrium, lanthanum or scandium, balance substantially iron, together with suificient volatizable liquid dispersant to provide the desired viscosity for application;

applying the slurry to the alloy to be protected;

drying the slurry on the alloy to form a green coating;

and ditfusion heat treating the coated part to form the desired oxidation-resistant coating.

3. The method of coating a nickel-base or cobalt-base alloy to impart oxidation resistance thereto which comprises:

forming a slurry comprising a powder mixture consisting essentially of, by weight, 24-26 percent chromium, -105 percent aluminum, 14.5-15.5 percent silicon, 0.8-1.2 percent yttrium, balance iron, to-

gether with a nitrocellulose dispersant sufiicient in quantity to provide the desired slurry viscosity; applying the slurry to the surface to be protected; drying the slurry on the alloy;

and heating the coated part at about 2100 F. to effect diffusion and form the desired oxidation-resistant coating.

References Cited UNITED STATES PATENTS 3,542,530 11/1970 Talboom, Jr., et al. 29194 X 3,477,831 11/1969 Talboom, Jr., et al.

117131 X 2,878,554 3/1959 Long 117-131 X 3,000,755 9/1961 Hanink et a1 117131 X 3,102,044 8/1963 Joseph 117131 X 3,300,854 1/1967 Jackson et al 117-131 X 3,447,912 6/1969 Ortner et al. 117--131 X 3,540,863 11/1970 Priceman et al. 117-131 X ALFRED L. LEAVITT, Primary Examiner J. R. BATTEN, JR., Assistant Examiner US. Cl. X.R.

Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3869779 *Jan 24, 1974Mar 11, 1975NasaDuplex aluminized coatings
US4022587 *Sep 8, 1975May 10, 1977Cabot CorporationProtective nickel base alloy coatings
US4034142 *Dec 31, 1975Jul 5, 1977United Technologies CorporationSuperalloy base having a coating containing silicon for corrosion/oxidation protection
US4054723 *Aug 13, 1975Oct 18, 1977Rolls-Royce LimitedComposite articles
US4080486 *Sep 24, 1974Mar 21, 1978General Electric CompanyCoating system for superalloys
US4117179 *Nov 4, 1976Sep 26, 1978General Electric CompanyOxidation corrosion resistant superalloys and coatings
US4546052 *Jul 17, 1984Oct 8, 1985Bbc Aktiengesellschaft Brown, Boveri & CieHigh-temperature protective layer
US6060174 *May 26, 1999May 9, 2000Siemens Westinghouse Power CorporationBond coats for turbine components and method of applying the same
US6440499 *Feb 22, 1999Aug 27, 2002Mtu Aero Engines GmbhMethod for producing a slip layer which is resistant to corrosion and oxidation
US6485780Aug 23, 1999Nov 26, 2002General Electric CompanyMethod for applying coatings on substrates
US6613445Jan 16, 2002Sep 2, 2003General Electric CompanyMetal slurry coatings on substrates, and related articles
US7285151 *May 6, 2002Oct 23, 2007Alfa Laval Corpoarate AbMaterial for coating and product coated with the material
US7314674 *Dec 15, 2004Jan 1, 2008General Electric CompanyCorrosion resistant coating composition, coated turbine component and method for coating same
US8262812Apr 4, 2007Sep 11, 2012General Electric CompanyProcess for forming a chromium diffusion portion and articles made therefrom
US8708646Jan 23, 2009Apr 29, 2014Siemens AktiengesellschaftMCrAlY alloy, methods to produce a MCrAlY layer and a honeycomb seal
US9222164Sep 6, 2011Dec 29, 2015General Electric CompanyProcess for forming a chromium diffusion portion and articles made therefrom
US20050072268 *May 6, 2002Apr 7, 2005Sjodin Per ErikMaterial for coating and product coated with the material
US20060127694 *Dec 15, 2004Jun 15, 2006Hazel Brian TCorrosion resistant coating composition, coated turbine component and method for coating same
US20080245445 *Apr 4, 2007Oct 9, 2008David Andrew HelmickProcess for forming a chromium diffusion portion and articles made therefrom
US20110101619 *Jan 23, 2009May 5, 2011David FairbournA MCrAlY Alloy, Methods to Produce a MCrAlY Layer and a Honeycomb Seal
DE2830851A1 *Jul 13, 1978Jan 18, 1979Fiat SpaVerfahren zur bildung von metalldiffusionsschutzueberzuegen
DE19941228A1 *Aug 30, 1999Mar 8, 2001Asea Brown BoveriIron aluminide coating used as a binder layer comprises aluminum, chromium, molybdenum, tungsten, tantalum and niobium, zirconium, boron, yttrium, platinum or rhenium, and a balance of iron
EP1079002A1 *Aug 9, 2000Feb 28, 2001General Electric CompanyA method for applying coatings on substrates
EP1088907A1 *Sep 23, 2000Apr 4, 2001MTU Aero Engines GmbHMethod for producing a plating for a metal component
EP1980643A1 *Mar 27, 2008Oct 15, 2008General Electric CompanyProcess for forming a chromium diffusion portion and articles made therefrom
EP2098606A1 *Mar 4, 2008Sep 9, 2009Siemens AktiengesellschaftA MCrAlY alloy, methods to produce a MCrAlY layer and a honeycomb seal
WO1999042633A1 *Feb 22, 1999Aug 26, 1999Thomas CosackMethod for producing a slip layer which is resistant to corrosion and oxidation
WO2009109414A1 *Jan 23, 2009Sep 11, 2009Siemens AktiengesellschaftA MCrAlY ALLOY, METHODS TO PRODUCE A MCrAlY LAYER AND A HONEYCOMB SEAL
Classifications
U.S. Classification427/250, 427/380, 427/375, 75/246, 428/679, 428/553
International ClassificationC23C10/30, C23C10/00
Cooperative ClassificationC23C10/30
European ClassificationC23C10/30