Abstract:
A seal assembly for a gas turbine engine includes a first seal member having a first surface, a second seal member having a second surface, with the second surface configured to generally abut at least a part of the first surface. At least a portion of at least one of the first surface and the second surface includes a coating that includes about 30 to about 80 weight percent of a hard carbide material, and about 20 to about 70 weight percent of lubricating material incorporated with the hard carbide material. The coating defines overlapping lenticular particles.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     The present application is a divisional application from U.S. patent application Ser. No. 13/164,131, filed Jun. 20, 2011, which is a divisional from U.S. patent application Ser. No. 11/376,455 (now U.S. Pat. No. 7,985,703), filed Mar. 15, 2006, both of which are herein incorporated by reference in their entireties. 
    
    
     BACKGROUND 
     The present invention relates generally to a coating. More particularly, the present invention relates to a coating suitable for use as a wear-resistant coating for a gas turbine engine component. 
     A wear-resistant coating is often applied to a component that is subject to high friction operating conditions. For example, a gas turbine engine component, such as a seal plate in a rotary seal mechanism, is often subject to high friction and high temperature operating conditions. After some time in service, the friction typically causes the surface of the component that is exposed to the friction to wear. The wear is generally undesirable, but may be especially undesirable and problematic for a sealing mechanism that acts to segregate two or more different compartments of the gas turbine engine. For example, if a sealing component wears (or erodes) and is no longer effective, fluid from one compartment may leak into another compartment. In some portions of a gas turbine engine, failure of the seal mechanism is detrimental to the operation of the gas turbine engine. In those cases, the gas turbine engine must be removed from service and repaired if a part of the seal mechanism wears to the point of seal failure. 
     A rotary seal mechanism separates two compartments of the gas turbine engine. A rotary seal mechanism typically includes a first component formed of a hard material, such as a carbon seal, that at least in part contacts a surface of a second component formed of a softer material, such as a seal plate, in order to segregate two or more compartments. In some applications, the seal plate rotates as the carbon seal remains fixed, while in other applications, the carbon seal rotates as the seal plate remains fixed. As the seal plate and carbon seal contact one another, the operating temperature and friction levels of both components increase. This may cause the seal plate and/or carbon seal to wear and deteriorate. The relative vibration between the seal plate and the carbon seal during the gas turbine engine operation may also cause frictional degradation and erosion of the seal plate. 
     It is important to minimize the wear of the seal plate in order to help prevent the rotary seal mechanism from failing. In order to mitigate the wear and deterioration of the seal plate and extend the life of the seal plate, a wear-resistant coating may be applied to the surface of the seal plate that contacts the carbon seal. However, it has been found that many existing wear-resistant coatings crack and spall under the increasingly high engine speeds and pressures. Regardless of the application, it is desirable to increase the life of a wear-resistant coating. Thus, it is also generally desirable to increase the life of wear-resistant coatings that are applied to components other than gas turbine engine components. 
     SUMMARY 
     A seal assembly for a gas turbine engine according to the present invention includes a first seal member having a first surface, a second seal member having a second surface, with the second surface configured to generally abut at least a part of the first surface. At least a portion of at least one of the first surface and the second surface includes a coating that includes about 30 to about 80 weight percent of a hard carbide material, and about 20 to about 70 weight percent of lubricating material incorporated with the hard carbide material. The coating defines overlapping lenticular particles. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The sole FIGURE is a partial cross-sectional view of a rotary seal, which includes a carbon seal and a seal plate. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention is both a coating suitable for use as a wear-resistant coating for a substrate and a method for coating a gas substrate with the inventive coating. A “substrate” is generally any underlying component, including gas turbine engine components. A coating in accordance with the present invention includes about 20 to about 70 percent of a lubricating material and about 30 to about 80 percent of a hard carbide material. The lubricating material includes, but is not limited to, polytetrafluoroethylene, molybdenum disulfide, boron nitride, cobalt oxide, graphite, and combinations thereof. The hard carbide material includes, but is not limited to, tungsten carbide, silicon carbide, nickel chrome/chromium carbide, titanium carbide, and combinations thereof. 
     The wear-resistant coating of the present invention is particularly suitable for applying onto a surface of a gas turbine engine component that is subject to high friction operating conditions, such as a seal plate of a rotary seal mechanism. However, the coating may be used with any suitable substrate that is subject to wearing conditions, including other gas turbine engine components having a hard-faced mating surface. It is believed that the inventive coating bonds to many substrate materials, including steel and nickel alloys, without the use of a bond coat. However, in embodiments, any suitable bond coat known in the art may be employed, if desired. 
     As turbine engine speeds and pressures have increased in order to increase engine efficiency, it has been found that many existing wear-resistant coatings that include a hard carbide material, such as nickel chrome/chromium carbide, crack and spall, as well as undergo excessive degradation under the increasingly strenuous operating conditions. Such cracking and spalling is undesirable and may shorten the life of the component on which the wear-resistant coating is applied. At the very least, the early failure of the wear-resistant coating causes the component to be prematurely removed from service in order to repair the wear-resistant coating. 
     The life of a hard carbide wear-resistant coating may be increased by incorporating a lubricating material into the coating in an amount sufficient enough to decrease the coefficient of friction of the wear-resistant coating. The percentage of the lubricating material varies from about 20 percent to about 70 percent, depending upon the type of hard carbide material in the coating, as well as the particular application of the wear-resistant coating. The presence of a lubricating material in the wear-resistant coating lowers the coefficient of friction of the coating, which allows the coating to wear slower than many existing hard carbide wear-resistant coatings. Also as a result of the lower coefficient of friction of the coating, less frictional heat is generated between the coating and the component the coating is engaged with. This also decreases the rate of wear of the coating. 
     The coating of the present invention may be applied to a substrate with any suitable method, such as thermal spraying, including plasma spraying and a high-velocity oxy-fuel (HVOF) thermal spray process. In the embodiment discussed below, a HVOF type of thermal spray process is used. In a HVOF thermal spray process, a high velocity gas stream is formed by continuously combusting oxygen and a fuel. A powdered form of the coating is then injected into the high velocity gas stream. The coating is heated to near its melting point, accelerated, and directed at the substrate to be coated. A coating applied with a HVOF process results in a dense coating. This is partially attributable to the overlapping, lenticular particles (or “splats”) of coating material that are formed on the substrate. A coating applied with a HVOF process is applied in compression, rather than tension, which also contributes to the increased density and hardness values as compared to other coating application methods. 
     A coating of the present invention is preferably applied in a thickness of about 0.0508 millimeters (about 2 mils) to about 0.508 millimeters (about 20 mils). In an embodiment of the present invention, the lubricating material and the hard carbide material are blended prior to applying the materials onto a substrate or co-sprayed onto the substrate through two separate powder feeders. The resulting wear-resistant coating is a uniform layer of the blended lubricating and hard carbide material. 
     The sole FIGURE is a partial cross-sectional view of a typical gas turbine engine sealing mechanism  10 . Sealing mechanism  10  includes an annular carbon seal ring  12 , which is carried by seal carrier  14 , and an annular seal plate  16 , which is carried by rotating shaft  18 . Sealing mechanism  10  is an example of a seal that may be used in a bearing compartment of a gas turbine engine to limit leakage of fluid, such as lubricating oil, from compartment  20  into other parts of the gas turbine engine. Carbon seal ring  12  is formed of a carbonaceous material and seal plate  16  is formed of a metal alloy, such as steel, a nickel alloy, or combinations thereof. 
     Seal carrier  14  biases face  12 A of carbon sealing ring  12  against face  16 A of seal plate  16 . The biasing is accomplished by any suitable method known in the art, such as by a spring force. Shaft  18  carries seal plate  16 , and as shaft  18  rotates, seal plate  16  engages with a surface of carbon seal  12  and frictional heat is generated, causing wear problems at the interface of seal plate  16  and carbon seal  12  (i.e., where face  12 A of carbon seal contacts face  16 A of seal plate  16 ). 
     In order to limit leakage of fluid from compartment  20 , it is important to maintain contact between face  12 A of carbon seal  12  and face  16 A of seal plate  16 . Yet, such contact causes seal plate  16  and/or carbon seal  12  to wear. In order to help maintain the functionality of the gas turbine engine, it is important for sealing mechanism  10  to withstand the high-speed conditions and high-temperatures generated as a result of the high-speed conditions. Coating  17 , which incorporates a lubricating material and a hard carbide material in accordance with the present invention, is applied to at least a part of face  16 A of seal plate  16  that contacts face  12 A of carbon seal  12  (coating  17  is not drawn to scale in FIGURE). Coating  17  helps prevent erosion and deterioration of face  16 A of seal plate  16  that results from contacting face  12 A of carbon seal  12  (e.g., from friction), which helps prevent seal mechanism  10  from failing. Carbon seal  12  is formed of a harder and more wear-resistant material than seal plate  16 , and the rate of wear is slower for carbon seal  12  than it is for seal plate  16 . 
     In the embodiment of the FIGURE, coating  17  is applied with a HVOF thermal spray process in a thickness of about 0.0508 millimeters (about 2 mils) to about 0.508 millimeters (about 20 mils). 
     In embodiments, the carbon seal  12  may be coated with coating  17 , either in addition to or instead of coating the seal plate  16  with coating  17 . 
     Sealing mechanism  10  is shown as a general example of a component (or substrate) that includes surfaces subject to wearing conditions. A coating in accordance with the present invention is also suitable for applying to components other than gas turbine engine components that are exposed to wearing conditions, such as the mating face of flanges. 
     The terminology used herein is for the purpose of description, not limitation. Specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as bases for teaching one skilled in the art to variously employ the present invention. Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. 
     While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.