Abstract:
A coating with the ability to protect (1) the inside wall (i.e., lining) of a rocket engine combustion chamber and (2) parts of other apparatuses that utilize or are exposed to combustive or high-temperature environments. The novelty of this invention lies in the manner a protective coating is embedded into the lining.

Description:
CROSS-REFERENCE TO A RELATED APPLICATION 
     This application for patent is an original application and does not claim the benefit of any other previously filed application. 
    
    
     STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH OR DEVELOPMENT 
     The invention described in this patent was made with government support under contract NAS8-97240 awarded by the National Aeronautics and Space Administration. The Contractor has certain rights in this invention. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     In general, this invention pertains to rocket engines. Specifically, this invention pertains to a protective coating for the combustion chamber of a liquid-fueled rocket engine. 
     Although this invention was developed for rocket engines, the invention has application to parts of other apparatuses that utilize or are exposed to combustive or high-temperature environments (i.e., jet engines, gas turbines, incinerators, furnaces, heat exchangers, reactors, welders, etc.). 
     2. Background Information 
     The combustion chamber of a rocket engine is exposed to a very intense environment of heat and pressure during operation. In fact, the life of a rocket engine is highly dependent upon the ability of a combustion chamber to withstand the violent, combustive environment. Like many other high performance applications, several materials are combined to meet the demanding fabrication and performance requirements associated with a combustion chamber. For example, good thermal conductance is needed to keep the combustion chamber from getting too hot, and resistance to thermal corrosion and oxidation is needed to ensure a reasonable life expectancy of the chamber itself. A method of protecting the inside wall (i.e., lining) of a combustion chamber from thermal corrosion and oxidation consists of providing a thin protective coating on the lining of the combustion chamber. However, even with special intermediate adhesive or bond coatings, the protective coating has a strong tendency to delaminate in the combustive environment. 
     SUMMARY OF THE INVENTION 
     This invention has the ability to protect the inside wall (i.e., lining) of a rocket engine combustion chamber from the adverse effects of heat and oxidation. The novelty of this invention lies in the manner a protective coating is embedded into the lining. 
     An object of this invention is to protect the combustion chamber of a liquid-fueled rocket engine from the deleterious effects of thermal corrosion and oxidation. 
     Another object of this invention is to provide a protective coating for the combustion chamber of a rocket engine that is more durable than conventional coatings, and consequently, that extends the life of the rocket engine. 
     Still another object of this invention is to provide an insulative coating (i.e., thermal barrier) for the combustion chamber of a rocket engine that lowers the operating temperature of the combustion chamber and thereby extends the life of the rocket engine. 
     A further object of this invention is to provide a protective coating for parts of apparatuses that utilize or are exposed to combustive or high-temperature environments in order to protect such parts from corrosion associated with extreme heat and/or oxidation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The following discussion of the invention will refer to the accompanying drawings in which: 
     FIG. 1 is both an isometric view and a partial, cross-sectional view of a typical combustion chamber lining belonging to a liquid-fueled rocket engine. 
     FIG. 2 represents an enlarged and symbolic cross-sectional view of the combustion chamber lining from section  2  of FIG.  1  and demonstrates how the protective coating and lining are interlocked together in accordance with the present invention. 
     FIG. 3 is a graph showing how the proportions of materials associated with the combustion chamber lining and the protective coating change throughout the first transitional layer in accordance with the present invention. 
     FIG. 4 is an isometric view showing the layered components associated with the combustion chamber lining belonging to a liquid-fueled rocket engine. 
     FIG. 5 is a graph showing how the proportions of materials associated with the combustion chamber lining, a first protective coating, and a second protective coating change throughout the respective transitional layers in accordance with the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1 and 2, a preferred embodiment of this invention comprises a combustion chamber lining ( 10 ), a first protective coating ( 20 ), and a first transitional layer ( 30 ) that gradiently interlocks the combustion chamber lining ( 10 ) with the first protective coating ( 20 ). 
     The lining ( 10 ) of the combustion chamber can be fabricated from a variety of metallic materials. For example, any copper alloy within the following limitations would be suitable for the lining ( 10 ): 
     60 to 100 percent by weight copper (Cu) 
     0 to 30 percent by weight chromium (Cr) 
     0 to 10 percent by weight niobium (Nb) 
     0 to 4 percent by weight silver (Ag) 
     0 to 1 percent by weight zirconium (Zr) 
     A preferred lining can be fabricated from a copper alloy such as Cu—8Cr—4Nb. Other lining materials include rhenium, stainless steel, and nickel-based alloys. 
     The first protective coating ( 20 ) can also be fabricated from a variety of materials including metals and ceramics. A typical metallic coating is R 1 CrAlY where R 1  is selected from the group consisting of nickel (Ni), cobalt (Co), iron (Fe), or a combination thereof. Any R 1  alloy within the following limitations would be suitable for the first protective coating ( 20 ): 
     0 to 80 percent by weight R 1    
     15 to 35 percent by weight chromium (Cr) 
     5 to 15 percent by weight aluminum (Al) 
     0.1 to 1 percent by weight yttrium (Y) 
     A preferred R 1 -alloy is Ni—17Cr−6Al—0.5Y. Other metallic materials include stainless steel, nickel-based alloys, iridium, and Cu—30Cr. 
     As stated, the first protective coating ( 20 ) can also consist of a ceramic. A typical ceramic is zirconium oxide (ZrO 2 ) that has been stabilized with yttrium oxide (Y 2 O 3 ). A preferred ceramic coating is ZrO 2 —8Y 2 O 3 . Other ceramic coatings include mullite, alumina, zircon, hafnium carbide, hafnium diboride, and hafnium nitride. 
     The first transitional layer ( 30 ) consists of a unique mixture of the lining ( 10 ) and the first protective coating ( 20 ). In one direction across the first transitional layer ( 30 ) (i.e., moving from the lining to the coating), the proportion of the lining ( 10 ) decreases on a gradient and the proportion of the first protective coating ( 20 ) increases on a gradient. In the other direction across the first transitional layer ( 30 ) (i.e., moving from the coating to the lining), the proportion of the lining ( 10 ) increases on a gradient and the proportion of the first protective coating ( 20 ) decreases on a gradient. 
     FIG. 3 is a graphical representation showing how the proportions of the two materials associated with lining ( 10 ) and the first protective coating ( 20 ) change in the first transitional layer ( 30 ). The x-axis represents the thickness or depth of both the lining ( 10 ) and the first protective coating ( 20 ). The thickness of the lining ( 10 ) is represented by (t 0 -t 1 ) on the x-axis, the thickness of the first protective coating ( 20 ) is represented by (t 2 -t 3 ) on the x-axis, and the thickness of the first transitional layer ( 30 ) is represented by (t 1  -t 2 ) on the x-axis. The y-axis simply represents proportion in percent. A first curve ( 11 ) represents various proportions of the lining ( 10 ) in the preferred embodiment and a second curve ( 21 ) represents various proportions of the first protective coating ( 20 ) in the preferred embodiment. 
     Continuing to refer to FIG. 3, the lining ( 10 ) and the first protective coating ( 20 ) are interlocked together in the first transitional layer ( 30 ). The first transitional layer ( 30 ) distinguishes the present invention over the prior art. In the first transitional layer ( 30 ), the presence of the lining ( 10 ) corresponds to a generally negative or decreasing gradient from t 1  to t 2  and the presence of the first protective coating ( 20 ) corresponds to a generally positive or increasing gradient from t 1  to t 2 . As indicated, even though the respective gradients will always be positive or negative, the gradients d o not have to be constant ( i.e., straight-line) gradients. In addition, the first transitional layer ( 30 ) can vary in thickness from a fraction of a millimeter to several millimeters. 
     FIGS. 4 and 5 represent an alternative embodiment of this invention in which a second transitional layer ( 40 ) is attached to the first protective coating ( 20 ) and a second protective coating ( 50 ) is attached to the second transitional layer ( 40 ). Typically, the second protective coating ( 50 ) consists of a ceramic or a metallic/ceramic mixture that is attached to the first protective coating ( 20 ). A preferred second coating is ZrO 2 —8Y 2 O 3 . Another preferred second coating is 50% (by weight) ZrO 2 —8Y 2 O 3  and 50% (by weight) R 1 CrAlY. 
     FIG. 5 is a graphical representation, similar to FIG. 3, showing how the second protective coating ( 50 ) is gradiently interlocked to the first protective coating ( 20 ). The thickness of the second transitional layer ( 40 ) is represented by (t 3 -t 4 ) on the x-axis and the thickness of the second protective coating ( 50 ) is represented by (t 4 -t 5 ) on the x-axis. A third curve ( 51 ) represents various proportions of the second protective coating ( 50 ) in this alternative embodiment. 
     Because of the transitional layers, the present invention is preferably fabricated from the inside to the outside. In other words, the second protective coating, if utilized, is made first; next, the first coating is made; and finally, the lining is made. The preferred process for making this invention comprises the steps of: first, making a second protective coating by applying a second coating material to a mandrel with a forming process; second, making a second transitional layer by gradiently adding a first coating material to the forming process and gradiently deleting the second coating material from the forming process; third, making a first protective coating by applying the first coating material to the second transitional layer with the forming process; fourth, making a first transitional layer by gradiently adding a lining material to the forming process and gradiently deleting the first coating material from the forming process; and finally, making a combustion chamber lining by applying the lining material to the first transitional layer with the forming process. If only a single protective coating is used, then the first two steps in the above procedure are eliminated and the first coating material is applied directly to the mandrel rather than the second transitional layer. 
     The preferred forming process is a plasmatic spray process that is carried out in a vacuum (also known in the art as the vacuum plasma spray (VPS) process). As indicated, the preferred process produces the transitional layer rather than the traditional material interface (i.e., bond line) of a simple coating. The result is a protective coating with substantially improved integrity against delamination, regardless of the respective coefficients of thermal expansion.