Coating and coating method for gas turbine engine component

Abstract

The present invention provides a protective coating for a gas turbine blade or other component wherein the duplex coating includes an aluminum-bearing coating, such as a diffusion aluminide, formed on a first, relatively higher temperature region of the blade/component and a later-applied chromium-bearing diffusion coating formed on an adjacent relatively lower temperature region of the blade/component subject to hot corrosion in service. The chromium-bearing coating is applied after the aluminum-bearing coating by masking that coating and depositing a metallic chromium coating on the adjacent region followed by diffusing the chromium into the blade/component alloy to form a chromium-enriched diffusion coating thereon.

We claim: 
     
         1 . A method of forming a coating on a substrate, comprising the steps of first applying an aluminum-bearing coating on a first region of the substrate, then depositing a metallic coating comprising chromium on the substrate, and then diffusing the chromium into the substrate to form a chromium-enriched diffused layer thereon. 
     
     
         2 . The method of  claim 1  including applying masking on said second region before the aluminum-bearing coating is applied. 
     
     
         3 . The method of  claim 1  including applying masking on the aluminum-bearing coating before applying the metallic coating. 
     
     
         4 . The method of  claim 1  including applying the aluminum-bearing coating on both said first region and second region followed by removal of the aluminum-bearing coating from said adjacent region before the metallic coating is applied. 
     
     
         5 . The method of  claim 1  wherein the metallic coating is applied using a liquid deposition medium. 
     
     
         6 . The method of  claim 5  wherein the liquid deposition medium is a electroplating bath or electrophoretic bath. 
     
     
         7 . The method of  claim 5  wherein the liquid deposition medium is a slurry of chromium-bearing particles. 
     
     
         8 . The method of  claim 1  wherein the aluminum-bearing coating is applied as a diffusion aluminide. 
     
     
         9 . A method of forming a duplex coating on a nickel or cobalt based alloy turbine blade, comprising the steps of first applying an aluminum-bearing coating on an airfoil region of the blade, then depositing a metallic coating comprising chromium on at least a portion of a root region of the blade using a liquid deposition medium, and then diffusing the chromium into the alloy to form a chromium-enriched layer on said portion of said root region. 
     
     
         10 . The method of  claim 9  including applying masking on the root region before the aluminum-bearing coating is applied on the airfoil region. 
     
     
         11 . The method of  claim 9  including applying the aluminum-bearing coating on the airfoil region and on the root region followed by removal of the aluminum-bearing coating from the root region before the metallic overlay is applied to the root region. 
     
     
         12 . The method of  claim 9  including applying masking on the aluminum-bearing coating before applying the metallic coating. 
     
     
         13 . The method of  claim 9  wherein the metallic coating is electroplated at a temperature less than 212 degrees F. 
     
     
         14 . The method of  claim 9  wherein the aluminum-bearing coating is applied to also cover a shank portion of said root region such that the root region includes the shank portion covered by the aluminum-bearing coating and an adjacent portion covered by the chromium-enriched coating. 
     
     
         15 . The method of  claim 9  including leaving an attachment portion of the root region uncoated. 
     
     
         16 . The method of  claim 9  wherein the aluminum-bearing coating is applied as a diffusion aluminide. 
     
     
         17 . The method of  claim 9  wherein the liquid deposition medium is an electroplating bath or electrophoretic bath. 
     
     
         18 . The method of  claim 9  wherein the liquid deposition medium is a slurry of chromium-bearing particles. 
     
     
         19 . A nickel or cobalt based alloy turbine component precursor having an aluminum-bearing coating applied on an airfoil region of the precursor and a metallic electroplated or electrophoretic coating comprising chromium applied on at least a portion of a root region of the precursor. 
     
     
         20 . The precursor of  claim 19  wherein the metallic coating comprises a majority of chromium. 
     
     
         21 . The precursor of  claim 19  wherein the aluminum-bearing coating also covers a shank portion of said root region such that the root region includes a shank portion covered by the aluminum-bearing coating and an adjacent portion covered by the metallic coating. 
     
     
         22 . The precursor of  claim 19  wherein an attachment portion of the root region is left uncoated. 
     
     
         23 . The precursor of  claim 19  wherein the aluminum-bearing coating comprises a diffusion aluminide. 
     
     
         24 . The precursor of  claim 19  that includes a platform region between the airfoil region and the root region, wherein a surface of the platform facing toward the airfoil region includes the aluminum-bearing coating. 
     
     
         25 . The precursor of  claim 24  wherein a surface of the platform region facing away from the airfoil region includes the metallic coating. 
     
     
         26 . The precursor of  claim 24  wherein a surface of the platform region facing away from the airfoil region includes the aluminum-bearing coating. 
     
     
         27 . A nickel or cobalt based alloy turbine component precursor having an aluminum-bearing coating applied on an airfoil region of the precursor and a metallic coating comprising chromium-bearing slurry particles applied on at least a portion of a root region of the precursor. 
     
     
         28 . A nickel or cobalt based alloy turbine component having an aluminum-bearing coating applied on an airfoil region of the blade and a chromium-enriched coating formed on at least a portion of a root region by depositing a metallic electroplated or electrophoretic coating comprising chromium and diffusing the chromium into the alloy at said portion of said root region. 
     
     
         29 . The component of  claim 28  that includes a platform region between the airfoil region and the root region, wherein a surface of the platform facing toward the airfoil region includes the aluminum-bearing coating. 
     
     
         30 . The component of  claim 29  wherein a surface of the platform region facing away from the airfoil region includes the chromium-bearing coating. 
     
     
         31 . The component of  claim 29  wherein the surface of the platform region facing toward the airfoil region includes the aluminum-bearing coating. 
     
     
         32 . The component of  claim 31  wherein the aluminum-bearing coating comprises a diffusion aluminide. 
     
     
         33 . The component of  claim 31  wherein the aluminum-bearing coating also covers a shank portion of said root region such that the root region includes a shank portion covered by the aluminum-bearing coating and an adjacent portion covered by the chromium-enriched coating. 
     
     
         34 . The component of  claim 28  wherein an attachment portion of the root region is uncoated. 
     
     
         35 . A nickel or cobalt based alloy turbine component having an aluminum-bearing coating applied on an airfoil region of the blade and a chromium-enriched coating formed on at least a portion of a root region by depositing a metallic coating comprising chromium-bearing slurry particles and diffusing the chromium into the alloy at said portion of said root region.