EP B1 (19) (11) EP B1 (12) EUROPEAN PATENT SPECIFICATION

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1 (19) Europäisches Patentamt European Patent Office Office européen des brevets (11) EP B1 (12) EUROPEAN PATENT SPECIFICATION (4) Date of publication and mention of the grant of the patent: Bulletin 00/36 (1) Int. Cl. 7 : C23C 14/16, C23C /00, F01D /28, F16D 1/06 (21) Application number: (22) Date of filing: (4) Anti-fretting coating Beschichtung zum Schützen vor Reibkorrosion Revêtement pour protection contre la corrosion de contact (84) Designated Contracting States: DE FR GB (43) Date of publication of application: Bulletin 199/43 (73) Proprietor: UNITED TECHNOLOGIES CORPORATION Hartford, CT 061 (US) (72) Inventors: Beers, Russell A. Palm Beach Gardens, Florida (US) Machinchick, Michael F. Royal Palm Beach, Florida (US) Noetzel, Allan A. Palm Beach Gardens, Florida (US) (74) Representative: Tomlinson, Kerry John Frank B. Dehn & Co., European Patent Attorneys, 179 Queen Victoria Street London EC4V 4EL (GB) (6) References cited: US-A US-A US-A US-A WEAR, vol., 198, LAUSANNE/CH pages BILL 'Selected fretting-wear-resistant coatings for Ti-6%Al-4%V alloy' EP B1 Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). Printed by Xerox (UK) Business Services (HRS)/3.6

2 1 EP B1 2 Description BACKGROUND OF THE INVENTION Field of the invention [0001] This invention relates to a method for increasing the high temperature fretting wear resistance of surfaces, particularly of many nickel, cobalt, and titanium alloys. Description of the Prior Art [0002] Fretting wear occurs on the mating surfaces of two parts in contact which are designed to be static, but, through transmitted forces such as vibration, oscillate relative to each other with a high frequency, low amplitude motion. Since each surface contains many microscopic asperities in contact, the fretting motion tends to cause local adhesion at these junctions, which may fracture, producing material transfer, wear debris, or both. If the metals in contact are similar, or their constituent elements have good mutual solubilities, the majority of the fretting wear will be adhesive in nature. Elevated temperature will greatly accelerate the process, as may large loads and high frequencies. If the mating surfaces become extremely abraded and gnarled, stress concentrations will result in wear scarring, and a reduction in fatigue strength will result (known specifically as fretting fatigue), causing failure of the part(s). Specific examples of materials subject to fretting wear include turbofan airfoil bladeroots, friction dampers, bearings on shafts with loose fits, and drivecoupling components. [0003] Prior art efforts to overcome the onset of fretting have included providing anti-fretting coatings on the surfaces of the materials in contact. These coatings behave as soft metallic films, keeping the substrate surfaces from coming in contact and dissipating vibrational energy by intracoating shear mechanisms. Such prior art anti-fretting coatings for nickel, cobalt, and titanium alloys have been based on Cu-Ni or Cu-Ni-In compositions. Their success is well documented. However, at temperatures above about 00 F (38 C), accelerated oxidation will rapidly deteriorate the coatings, allowing the substrate surfaces to come in contact and fret. [0004] In addition, conventional application methods rely primarily on thermally spraying the constituents onto the desired part. This has further disadvantages due to the line-of-sight nature of thermal spraying, and the detrimental effects this type of operation has (e.g. warping) on thin-gauge materials. SUMMARY OF THE INVENTION [000] In accordance with the method of the present invention, force-transmitting and force-receiving bearing surfaces of nickel, cobalt, and titanium alloys may be protected from fretting wear at temperatures up to 10 F (649 C) or higher by coating either one or both of the surfaces with a coating of an alloy of copper as defined in claim 1. Preferably, the copper alloy comprises about 92 weight percent copper, and about 8 weight percent aluminium. The metallic structure and compressor airfoil root according to claims 11 and 17, respectively, are further embodiments of the invention. Additions of other elements, such as up to about weight percent iron, or nickel, may provide successful results at temperatures up to about 00 F (38 C), but generally not at the higher temperatures achieved using the above-identified alloys, as these additional elements usually degrade high temperature oxidation resistance. [0006] The thickness of the coating may be within the range of from 0.1 mils (2. micrometres) to about 4.0 mils (0 micrometres), and preferably within the range of from about 0.7 mils (19 micrometres) to about 1. mils (38 micrometres). [0007] The coating may be applied by typical physical vapour deposition techniques. Cathodic arc deposition is the preferred method, although other forms of ion vapour deposition are suitable. BRIEF DESCRIPTION OF THE DRAWING [0008] Figure 1 shows comparative results of fretting tests conducted on an uncoated nickel substrate, the same substrate having a conventional anti-fretting coating, and the same substrate having the antifretting coating of this invention. DESCRIPTION OF THE PREFERRED EMBODI- MENTS [0009] It has been determined that coating a thin nickel or nickel alloy work-piece in accordance with the present invention yields a significant improvement in durability as opposed to uncoated work-pieces at temperatures up to at least 10 F (649 C). The coating of the invention finds particular utility with such parts as compressor airfoil roots, but can be applied with beneficial effect to any nickel or nickel alloy surface where fretting wear is a problem, such as blade and vane airfoil damping systems. The anti-fretting coating is also beneficial for cobalt and titanium alloy surfaces. [00] Since the coating, in accordance with the invention, is beneficial at temperatures up to approximately 1 F (677 C), it has been found to provide advantages over conventional methods of minimizing fretting wear, which include the use of dry film lubricants and coatings of alloys, such as copper-nickel, and copper-nickel-indium, or silver plating. Such conventional coatings are deficient in being effective only at temperatures up to about 00 F (38 C), which temperature is below the temperature encountered in many applica- 2

3 3 EP B1 4 tions where fretting is a problem, such as in components of modern jet engines, e.g. compressor airfoil roots. [0011] With the coating of the present invention, it has been found that the copper and aluminium contents, particularly in the presence of silicon, minimize oxidation of the contact surfaces in the high-temperature environments encountered during use of the coated nickel-base alloy surfaces. This results in retention of the protective properties of the coating at temperatures exceeding 00 F (38 C), at which temperatures conventional coatings are rendered ineffective. By retaining oxidation resistant properties at these elevated temperatures, resistance against fretting is maintained in applications of nickel-based alloys for which conventional coating practices are not effective. [0012] In accordance with the method of the invention, test specimens of a nickel-base alloy corresponding to AMS 44, of the composition, in weight percent, Ni-19. Cr-13. Co-4.2 Mo-3Ti-1.4 Al-0.08 Zr-0.0C, were coated by ion vapour deposition coating. Coating was performed in a conventional low pressure inert gas vapour deposition chamber to deposit a coating thickness of 32 µm (1.2 mils) of an alloy comprising, in weight percent, Cu-7. Al. Test specimens prepared as above were tested in spring form on an oscillating spring-on-plate wear test facility, using plate specimens of alloy AMS 96 as the contacting surface. Test springs of uncoated AMS 44 and AMS 44 coated with a conventional anti-fretting coating of 62 percent copper, 38 percent nickel were prepared and tested simultaneously for comparative results. Two springs of each specimen of 0.01 inch (0.38mm) thickness and containing a 0.00 inch (1.3mm) contact radius were loaded against two uncoated plates of 0.12 inch (3.2mm) thickness, with a load of 1 pounds (6.8kg), producing a maximum contact pressure of 10 psi (784 kpa). The springs were held rigid in the vertical plane while the plates were oscillated by an electromagnetic shaker at a frequency of 0 Hz and amplitude of 0.00 inches (0.13mm). The entire fixture was surrounded by a resistant-element furnace producing a temperature of 10 F (649 C). Thickness measurements were made on the spring and plate specimens at 2-hour intervals, and the test proceeded for either hours or failure, whichever came first. As shown in Figure 1, the coating of the present invention greatly reduced the fretting wear rate of the nickel substrate, as compared to the uncoated substrate and the conventional anti-fretting coating. Similar results are obtained when nickel, cobalt, and titanium substrates are tested using anti-fretting coatings of Cu-8Al, and Cu, 4-8 Al, 0-4 Si. [0013] It is to be understood that the above description of the invention is subject to considerable modification, change, and adaptation by those skilled in the art, and that such modifications, changes, and adaptations, are intended to be considered within the scope of the present invention, which is set forth by the claims which follow. Claims 1. A method for protecting an alloy surface selected from the group consisting of nickel, cobalt, and titanium alloys from fretting wear, said method comprising coating said surface with a coating consisting essentially of from 88 to 96 weight percent copper, from 4 to 8 weight percent aluminium, and from 0 to 4 weight percent silicon. 2. The method of claim 1, wherein said coating is deposited by physical vapor deposition. 3. The method of claim 1, wherein said coating is applied by cathodic arc deposition. 4. The method of any preceding claim, wherein said coating is characterized by anti-fretting capability at temperatures up to about 1 F (677 C).. The method of any preceding claim wherein the alloy surface is of a nickel-base alloy. 6. The method of any preceding claim, wherein said coating consists essentially of about 92 weight percent copper and about 8 weight percent aluminium. 7. The method of any one of claims 1 to, wherein said coating comprises about 92. weight percent copper and about 7. weight percent aluminium. 8. The method of any preceding claim, wherein said coating is from about 0.1 mils (2. micrometres) to about 4 mils (0 micrometres) thick. 9. The method of claim 8, wherein said coating is from about 0.7 mils (19 micrometres) to about 1. mils (38 micrometres) thick.. The method of claim 9, wherein said coating is from about 1.0 mils (2 micrometres) to about 1. mils (38 micrometres) thick. 11. A metallic structure comprising a substrate selected from the group consisting of nickel, cobalt, and titanium alloys, and an anti-fretting coating on said substrate, said coating consisting essentially of from 88 to 96 weight percent copper, from 4 to 8 weight percent aluminium, and from 0 to 4 weight percent silicon. 12. A structure as claimed in claim 11, wherein said substrate is a nickel-base alloy. 13. A structure as claimed in claim 11 or claim 12, 3

4 EP B1 6 wherein said coating consists essentially of copper and aluminium. 14. A structure as claimed in claim 13, wherein said coating consists essentially of about 92. weight percent copper and about 7. weight percent aluminium. 1. A structure as claimed in any one of claims 11 to 14 wherein said coating is from about 1.0 mils (2 micrometres) to about 1. mils (38 micrometres) thick. 16. A method for reducing fretting wear between contacting surfaces at a temperature of from about 00 F (38 C) to about 1 F (677 C), said method comprising applying to at least one of said contacting surfaces a coating consisting essentially of from about 88 to about 96 weight percent copper, from about 4 to about 8 percent aluminium, and from 0 to about 4 weight percent silicon. 17. A fretting-fatigue resistant compressor airfoil root for use at a temperature of from about 00 F (38 C) to about 1 F (677 C), comprising an airfoil root of a metal selected from nickel, cobalt and titanium alloys, the surface thereof having a coating of an alloy consisting essentially of from 88 to 96 weight percent copper, from 4 to 8 weight percent aluminium, and from 0 to 4 weight percent silicon, said coating being from 0.1 mils (2. micrometres) to 4 mils (0 micrometres) thick. Patentansprüche 1. Verfahren zum Schützen einer Legierungsoberfläche, die ausgewählt ist aus der Gruppe aus Nickel-, Kobalt- und Titanlegierungen, vor Reibverschleiß, wobei bei dem Verfahren die Oberfläche mit einer Beschichtung versehen wird, die im wesentlichen aus 88 bis 96 Gew.-% Kupfer, 4 bis 8 Gew.-% Aluminium und 0 bis 4 Gew.-% Silizium besteht, 2. Verfahren nach Anspruch 1, wobei die Beschichtung durch physikalische Abscheidung aus der Dampfphase (PVD-Abscheidung) aufgebracht wird. 3. Verfahren nach Anspruch 1, wobei die Beschichtung durch Kathoden-Lichtbogen-Abscheidung aufgebracht wird. 4. Verfahren nach einem der vorausgehenden wobei die Beschichtung gekennzeichnet ist durch Reibverschleißbeständigkeit bei Temperaturen von bis zu ca. 1 F (677 C) Verfahren nach einem der vorausgehenden wobei es sich bei der Legierungsoberfläche um eine Legierung auf Nickelbasis handelt. 6. Verfahren nach einem der vorausgehenden wobei die Beschichtung im wesentlichen aus etwa 92 Gew.-% Kupfer und etwa 8 Gew.-% Aluminium besteht. 7. Verfahren nach einem der Ansprüche 1 bis, wobei die Beschichtung etwa 92, Gew.-% Kupfer und etwa 7, Gew.-% Aluminium enthält. 8. Verfahren nach einem der vorausgehenden wobei die Beschichtung eine Dicke von etwa 0,1 mil (2, µm) bis etwa 4 mil (0 µm) aufweist. 9. Verfahren nach Anspruch 8, wobei die Beschichtung eine Dicke von etwa 0,7 mil (19 µm) bis etwa 1, mil (38 µm) aufweist.. Verfahren nach Anspruch 9, wobei die Beschichtung ein Dicke von etwa 1,0 mil (2 µm) bis etwa 1, mil (38 µm) aufweist. 11. Metallgebilde mit einem Substrat, das ausgewählt ist aus der Gruppe bestehend aus Nickel-, Kobaltund Titanlegierungen, und mit einer auf dem Substrat vorhandenen Beschichtung zum Schutz vor Reibverschleiß, wobei die Beschichtung im wesentlichen aus 88 bis 96 Gew.-% Kupfer, 4 bis 8 Gew.-% Aluminium und 0 bis 4 Gew.-% Silizium besteht. 12. Gebilde nach Anspruch 11, wobei es sich bei dem Substrat um eine Legierung auf Nickelbasis handelt. 13. Gebilde nach Anspruch 11 oder Anspruch 12, wobei die Beschichtung im wesentlichen aus Kupfer und Aluminium besteht. 14. Gebilde nach Anspruch 13, wobei die Beschichtung im wesentlichen aus etwa 92, Gew.-% Kupfer und etwa 7, Gew.-% Aluminium besteht. 1. Gebilde nach einem der Ansprüche 11 bis 14, wobei die Beschichtung eine Dicke von etwa 1,0 mil (2 µm) bis etwa 1, mil (38 µm) aufweist. 16. Verfahren zum Reduzieren von Reibverschleiß zwischen miteinander in Berührung stehenden Oberflächen bei einer Temperatur von etwa 00 F (38 C) bis etwa 1 F (677 C), wobei bei dem Verfahren auf wenigstens eine der miteinander in 4

5 7 EP B1 8 Berührung stehenden Oberflächen eine Beschichtung aufgebracht wird, die im wesentlichen aus 88 bis 96 Gew.-% Kupfer, 4 bis 8 Gew.-% Aluminium und 0 bis 4 Gew.-% Silizium besteht. 17. Gegen Reibermüdung beständiger Kompressor- Strömungsprofilfuß zur Verwendung bei einer Temperatur von etwa 00 F (38 C) bis etwa 1 F (677 C); mit einem Strömungsprofilfuß aus einem Metall, das ausgewählt ist aus Nickel-, Kobalt- und Titanlegierungen, wobei seine Oberfläche eine Beschichtung aus einer Legierung aufweist, die im wesentlichen aus 88 bis 96 Gew.-% Kupfer, 4 bis 8 Gew.-% Aluminium und 0 bis 4 Gew.-% Silizium besteht, wobei die Beschichtung eine Dicke von 0,1 mil (2, µm) bis etwa 4 mil (0 µm) aufweist. Revendications 1. Procédé de protection contre l'usure par frottement d'une surface d'alliage, choisi dans le groupe comprenant les alliages de nickel, de cobalt et de titane, ledit procédé comprenant le gainage de ladite surface avec un revêtement constitué essentiellement de 88 à 96 % en poids de cuivre, de 4 à 8 % en poids d'aluminium et de 0 à 4 % en poids de silicium. 2. Procédé selon la revendication 1, dans lequel ledit revêtement est appliqué par déposition physique en phase gazeuse. 3. Procédé selon la revendication 1, dans lequel ledit revêtement est appliqué par déposition à l'arc cathodique. 4. Procédé selon l'une quelconque des revendications précédentes, dans lequel ledit revêtement est caractérisé par un pouvoir anti-corrosion à des températures allant jusqu'à 677 C (1 F).. Procédé selon l'une quelconque des revendications précédentes, dans lequel la surface d'alliage est en alliage à base de nickel. 6. Procédé selon l'une quelconque des revendications précédentes, dans lequel ledit revêtement est constitué essentiellement d'environ 92 % en poids de cuivre et d'environ 8 % en poids d'aluminium. 7. Procédé selon l'une quelconque des revendications 1 à, dans lequel ledit revêtement est constitué d'environ 92, % en poids de cuivre et d'environ 7, % en poids d'aluminium. 8. Procédé selon l'une quelconque des revendications précédentes, dans lequel l'épaisseur dudit revêtement est comprise entre environ 2, µm (0,1 mils) et environ 0 µm (4 mils). 9. Procédé selon la revendication 8, dans lequel l'épaisseur dudit revêtement est comprise entre environ 19 µm (0,7 mils) et environ 38 µm (1, mils).. Procédé selon la revendication 9, dans lequel l'épaisseur dudit revêtement est comprise entre environ 2 µm (1,0 mils) et environ 38 µm (1, mils). 11. Structure métallique comprenant un substrat choisi dans le groupe comprenant les alliages de nickel, de cobalt et de titane, et un revêtement anti-frottement sur ledit substrat, ledit revêtement étant constitue essentiellement de 88 à 96 % en poids de cuivre, de 4 à 8 % en poids d'aluminium et de 0 à 4 % en poids de silicium. 12. Structure selon la revendication 11, dans laquelle ledit substrat est un alliage à base de nickel. 13. Structure selon la revendication 11 ou la revendication 12, dans laquelle ledit revêtement est constitué essentiellement de cuivre et d'aluminium. 14. Structure selon la revendication 13, dans laquelle ledit revêtement est constitué essentiellement d'environ 92, % en poids de cuivre et d'environ 7, % en poids d'aluminium. 1. Structure selon l'une quelconque des revendications 11 à 14, dans lequel l'épaisseur dudit revêtement est comprise entre environ 2 µm (1,0 mils) et environ 38 µm (1, mils). 16. Procédé de réduction de l'usure par frottement entre des surfaces en contact, à une température comprise entre environ 38 C (00 F) et environ 677 C (1 F), ledit procédé comprenant l'application sur au moins l'une desdites surfaces de contact d'un revêtement constitué essentiellement d'environ 88 à environ 96 % en poids de cuivre, d'environ 4 à environ 8 % en poids d'aluminium, et d'environ 0 à environ 4 % en poids de silicium. 17. Pied d'aube de compresseur résistant à la fatigue par corrosion, destiné à être utilisé à une température comprise entre environ 38 C (00 F) et environ 677 C (1 F), comprenant un pied d'aube constitué d'un métal choisi parmi les alliages de nickel, de cobalt et de titane, sa surface étant revêtue d'un alliage constitué essentiellement de 88 à 96 % en poids de cuivre, de 4 à 8 % en poids d'aluminium et de 0 à 4 % en poids de silicium, l'épaisseur dudit revêtement étant comprise entre environ 2, µm (0,1 mils) et environ 0 µm (4

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