Method for HVOF or LPPS restoration coating repair of a nickel-base superalloy article

Abstract

A method for repairing a nickel-base superalloy article, such as a gas turbine stationary flowpath shroud having flowpath cooling holes therein that has previously been in service, includes the steps of providing the nickel-base superalloy article that has previously been in service; and applying a restoration to a surface of the article. The restoration is applied by the steps of providing a restoration nickel-base alloy, wherein the restoration nickel-base alloy preferably has no more than about 15 weight percent chromium and no more than about 0.01 percent yttrium, thereafter applying a restoration coating of the restoration nickel-base alloy to the surface of the article by a hyper-velocity oxyfuel metal spray process or a low-pressure plasma spray process, and thereafter heating the article with the restoration coating applied to the surface thereof to a sufficiently high temperature to diffusion bond the restoration coating to the surface of the article. The article is then returned to service.

1 . A method for repairing a nickel-base superalloy article comprising the steps of 
 providing the nickel-base superalloy article that has previously been in service; and    applying a restoration to a surface of the article by the steps of 
 providing a restoration nickel-base alloy, thereafter  
 applying a restoration coating of the restoration nickel-base alloy to the surface of the article by a hyper-velocity oxyfuel metal spray process or a low-pressure plasma spray process, and thereafter  
 heating the article with the restoration coating applied to the surface thereof to a sufficiently high temperature to diffusion bond the restoration coating to the surface of the article.  
   
     
     
         2 . The method of  claim 1 , including an additional step, after the step of applying is fully completed, of returning the article to service.  
     
     
         3 . The method of  claim 1 , including an additional step, after the step of applying is fully completed, of 
 returning the article to service, wherein the article is heated to a temperature of not less than about 1800° F. during service.    
     
     
         4 . The method of  claim 1 , wherein the step of providing the nickel-base superalloy article includes the step of 
 providing a gas turbine stationary flowpath shroud as the article.    
     
     
         5 . The method of  claim 1 , wherein the step of providing the nickel-base superalloy article includes the step of 
 providing a gas turbine stationary flowpath shroud having flowpath cooling holes therein as the article.    
     
     
         6 . The method of  claim 1 , wherein the step of providing the nickel-base superalloy article includes the step of 
 providing a gas turbine stationary flowpath shroud having flowpath cooling holes therein as the article, and wherein the method includes an additional step, after the step of heating, of    redrilling the cooling holes.    
     
     
         7 . The method of  claim 1 , wherein the step of providing the nickel-base superalloy article includes the step of 
 providing the article having a nominal composition in weight percent of about 7.5 percent cobalt, about 7.0 percent chromium, about 1.5 percent molybdenum, about 5 percent tungsten, about 3 percent rhenium, about 6.5 percent tantalum, about 6.2 percent aluminum, about 0.15 percent hafnium, about 0.05 percent carbon, about 0.004 percent boron, about 0.01 percent yttrium, balance nickel and impurities.    
     
     
         8 . The method of  claim 1 , wherein the step of providing the restoration nickel-base alloy includes the step of 
 providing the restoration nickel-base alloy having no more than about 15 weight percent chromium and no more than about 0.01 percent yttrium    
     
     
         9 . The method of  claim 1 , wherein the step of providing the restoration nickel-base alloy includes the step of 
 providing the restoration nickel-base alloy having no more than about 12 weight percent chromium and no more than about 0.01 percent yttrium    
     
     
         10 . The method of  claim 1 , wherein the step of providing the restoration nickel-base alloy includes the step of 
 providing the restoration nickel-base alloy having a nominal composition in weight percent of about 3.1 percent cobalt, about 7.6 percent chromium, about 0.1 percent maximum molybdenum, about 3.85 percent tungsten, about 0.02 percent maximum titanium, about 1.65 percent rhenium, about 0.55 percent silicon, about 5.45 percent tantalum, about 7.8 percent aluminum, about 0.15 percent hafnium, about 0.02 percent carbon, balance nickel and impurities.    
     
     
         11 . The method of  claim 1 , wherein the step of providing the restoration nickel-base alloy includes the step of 
 providing the restoration nickel-base alloy having a nominal composition in weight percent of 0.01-0.03 percent carbon, 0.1 percent maximum manganese, 0.5-0.6 percent silicon, 0.01 percent maximum phosphorus, 0.004 percent maximum sulfur, 7.4-7.8 percent chromium, 2.9-3.3 percent cobalt, 0.01 percent maximum molybdenum, 3.7-4.0 percent tungsten, 5.3-5.6 percent tantalum, 0.02 percent maximum titanium, 7.6-8.0 percent aluminum, 1.5-1.8 percent rhenium, 0.005 percent maximum selenium, 0.3 percent maximum platinum, 0.01-0.02 percent boron, 0.03 percent maximum zirconium, 0.12-0.18 percent hafnium, 0.1 percent maximum niobium, 0.1 percent maximum vanadium, 0.1 percent maximum copper, 0.2 percent maximum iron, 0.0035 percent maximum magnesium, 0.01 percent maximum oxygen, 0.01 percent maximum nitrogen, balance nickel with other elements 0.5 percent maximum.    
     
     
         12 . The method of  claim 1 , wherein the step of applying the restoration coating includes the step of 
 applying the restoration coating to a thickness of from about 0.030 to about 0.150 inches.    
     
     
         13 . The method of  claim 1 , wherein the step of heating includes the step of 
 heating the article to a temperature of from about 2025° F. to about 2075° F.    
     
     
         14 . The method of  claim 1 , wherein the step of heating includes the step of 
 heating the article to a temperature of from about 2025° F. to about 2075° F. for a time of at least about 3-½ hours.    
     
     
         15 . A method for repairing a nickel-base superalloy article comprising the steps of 
 providing the nickel-base superalloy article comprising a gas turbine stationary flowpath shroud having flowpath cooling holes therein that has previously been in service, wherein the article has a nominal composition in weight percent of about 7.5 percent cobalt, about 7.0 percent chromium, about 1.5 percent molybdenum, about 5 percent tungsten, about 3 percent rhenium, about 6.5 percent tantalum, about 6.2 percent aluminum, about 0.15 percent hafnium, about 0.05 percent carbon, about 0.004 percent boron, about 0.01 percent yttrium, balance nickel and impurities; and    applying a restoration to a surface of the article by the steps of 
 providing a restoration nickel-base alloy, wherein the restoration nickel-base alloy has a nominal composition in weight percent of about 3.1 percent cobalt, about 7.6 percent chromium, about 0.1 percent maximum molybdenum, about 3.85 percent tungsten, about 0.02 percent maximum titanium, about 1.65 percent rhenium, about 0.55 percent silicon, about 5.45 percent tantalum, about 7.8 percent aluminum, about 0.15 percent hafnium, about 0.02 percent carbon, balance nickel and impurities, thereafter  
 applying a restoration coating of the restoration nickel-base alloy to the surface of the article by a hyper-velocity oxyfuel metal spray process or a low-pressure plasma spray process, and thereafter  
 heating the article with the restoration coating applied to the surface thereof to a temperature of about 2050° F. to diffusion bond the restoration coating to the surface of the article, prior to returning the article to service.  
   
     
     
         16 . The method of  claim 15 , wherein the method includes an additional step, after the step of heating, of 
 redrilling the cooling holes.    
     
     
         17 . The method of  claim 15 , including an additional step, after the step of applying is fully completed, of 
 returning the article to service.    
     
     
         18 . The method of  claim 15 , including an additional step, after the step of applying is fully completed, of 
 returning the article to service, wherein the article is heated to a temperature of not less than about 1800° F. during service.    
     
     
         19 . The method of  claim 15 , wherein the step of applying the restoration coating includes the step of 
 applying the restoration coating to a thickness of from about 0.030 to about 0.150 inches.    
     
     
         20 . An article comprising: 
 a nickel-base superalloy article that has previously been in service; and    a restoration applied to a surface of the article, wherein the restoration is made of a nickel-base superalloy different from that of the nickel-base superalloy article, and wherein the restoration nickel-base superalloy has no more than about 15 weight percent chromium and no more than about 0.01 weight percent yttrium.