Enhanced coating system for turbine airfoil applications

Abstract

A tightly adherent anti-stick coating applied over coated turbine components of gas turbine engines. The tightly adherent coating is an oxide of at least one metal selected from the group consisting of Pt, W, group 4 b and group 5 b metals of the periodic table and Si, Ge and Sn of group 4 a . The oxide is applied directly over existing environmental coatings, and thermal barrier coatings. It can also be applied directly to substrate material and to areas that are not within the combustion exhaust gases, such as platform portions and shank portions of airfoils including turbine blades. The oxide is conveniently applied to a uniform thickness of no greater than about 10 microns, and prevents the build-up of corrosion products and other products of combustion from the gases, thereby increasing the life expectancy of the component.

What is claimed is:  
     
         1 . A coated superalloy component for use in an atmosphere of hot, corrosive gases, comprising: 
 a substrate article formed of a superalloy;    a tightly adherent environmentally resistant coating applied over the superalloy substrate; and    a tightly adherent anti-stick coating applied over the environmentally resistant coating.    
     
     
         2 . The superalloy component of  claim 1  wherein the tightly adherent environmentally resistant coating is an aluminide coating selected from the group consisting of nickel aluminide, platinum aluminide and combinations thereof.  
     
     
         3 . The superalloy component of  claim 1  wherein the tightly environmentally resistant coating is a MCrAlY coating wherein M is an element selected from the group consisting of nickel, cobalt and iron and combinations thereof.  
     
     
         4 . The superalloy component of  claim 1  wherein the tightly adherent anti-stick coating is a thin oxide layer applied to reduce the adherence of deposits from the hot, corrosive atmosphere and to reduce the exposure of the environmentally resistant layer to oxygen.  
     
     
         5 . The superalloy component of  claim 4  wherein the tightly adherent anti-stick layer is a metallic oxide consisting of at least one metal selected from the group consisting of Pt, W, Si, Ge, Sn and groups  4   b  and  5   b  of the periodic table and combinations thereof.  
     
     
         6 . The superalloy component of  claim 5  wherein the tightly adherent metallic oxide is tantalum oxide.  
     
     
         7 . A coated superalloy component comprising: 
 a substrate article formed of a superalloy;    a tightly adherent bond coating applied over the superalloy substrate;    a thermal barrier coating applied over the bond coating; and    a tightly adherent anti-stick coating applied over the environmentally resistant coating.    
     
     
         8 . The coated superalloy component of  claim 7  wherein the bond coat is a MCrAlY coating wherein M is an element selected from the group consisting of nickel, cobalt and iron and combinations thereof.  
     
     
         9 . The coated superalloy component of  claim 7  wherein the thermal barrier coating is yttrium-stabilized zirconia.  
     
     
         10 . The coated superalloy  7  wherein the tightly adherent anti-stick layer is a metallic oxide consisting of at least one metal selected from the group consisting of Pt, W, Si, Ge, Sn and groups  4   b  and  5   b  of the periodic table and combinations thereof.  
     
     
         11 . The superalloy component of  claim 10  wherein the metallic oxide is tantalum oxide.  
     
     
         12 . A tightly adherent, high temperature, thin anti-stick coating applied over the surface of a turbine airfoil comprising a metallic oxide consisting essentially of at least one metal selected from the group consisting of Pt, W, Si, Ge, Sn and groups  4   b  and  5   b  of the periodic table and combinations thereof applied to a thickness of no greater than about 10 microns.  
     
     
         13 . The anti-stick coating of  claim 12  wherein the metallic oxide is tantalum oxide.  
     
     
         14 . The anti-stick coating or  claim 12  wherein the coating is applied to a thickness in the range of 0.5-2 microns.  
     
     
         15 . A superalloy turbine airfoil comprising: 
 a blade portion, a shank portion and a platform portion intermediate between the blade portion and the shank portion, each formed of a superalloy;    a tightly adherent environmentally resistant coating applied over at least the blade portion; and    a tightly adherent, high temperature, thin anti-stick coating applied to the platform portion of the airfoil and over at least a part of the shank portion of the airfoil.    
     
     
         16 . The airfoil of  claim 15  wherein the tightly adherent environmentally resistant coating is applied over the blade portion, the platform portion and at least a part of the shank portion, and a tightly adherent anti-stick portion applied over the blade portion, the platform portion and at least a part of the shank portion of the airfoil.  
     
     
         17 . A superalloy turbine airfoil comprising: 
 a blade portion, a shank portion and a platform portion intermediate between the blade portion and the shank portion, each formed of a superalloy;    a tightly adherent bond coating applied over at least the blade portion;    a thermal barrier coating applied over the bond coating on the blade portion; and    a tightly adherent, high temperature, thin anti-stick coating applied under the platform portion of the airfoil and over at least a part of the shank portion of the airfoil.    
     
     
         18 . The airfoil of  claim 17  wherein the tightly adherent bond coating is applied over the blade portion, the platform portion and at least a part of the shank portion, and a tightly adherent anti-stick portion applied over at the shank portion of the airfoil.  
     
     
         19 . A method for applying a tantalum oxide coating to a turbine airfoil, comprising the steps of: 
 cleaning the turbine airfoil;    optionally masking portions of the airfoil that are not to be coated;    placing at least one turbine airfoil in a CVD coater;    purging the chamber with a protective gas;    raising the temperature of the chamber to a predetermined temperature above about 500° F. (260° C.);    introducing a partial pressure of tantalum precursor gas into the chamber with the protective gas to deposit the precursor onto the airfoil;    maintaining the flow of the precursor gas for a predetermined time to achieve a predetermined thickness of tantalum oxide;    stopping the flow of precursor gas and protective gas; and    removing the airfoil from the CVD chamber.    
     
     
         20 . The method of  claim 19  wherein the protective gas is selected from the group consisting of nitrogen and inert gas.  
     
     
         21 . The method of  claim 19  wherein the predetermined temperature is in the range of about 720-900° F. (382-482° C.).  
     
     
         22 . The method of  claim 19  wherein the tantalum precursor gas is tantalum ethoxide.  
     
     
         23 . The method of  claim 21  wherein the tantalum precursor gas is tantalum ethoxide introduced at a partial pressure in the range of about 50-500 microinches of mercury for a predetermined time of about 1-3 hours.  
     
     
         24 . The method of  claim 19  wherein the predetermined thickness of tantalum oxide is up to about 5 microns.  
     
     
         25 . The method of  claim 24  wherein the thickness of tantalum oxide is in the range of about 0.5-2 microns.