Preheat method for EBPVD coating

Abstract

A method is described for reducing surface oxide growth which heating aluminum containing surfaces in a vacuum environment prior to the deposition of a ceramic coating. The method comprises flowing an inert or non reactive gas into the coating apparatus adjacent to the surface to be coated to reduce oxygen reaction with the surface.

I claim:  
     
         1 . A method for heating a part in a vacuum environment which comprises: heating said part while simultaneously providing a gas selected from the group comprising inert and non reactive gases and mixtures thereof to the region immediately surrounding the part and maintaining the part in a vacuum environment; whereby oxidation of said part due to oxygen in said vacuum environment is reduced.  
     
     
         2 . A method as in  claim 1  wherein said part comprises a superalloy substrate having an aluminum containing bond coat.  
     
     
         3 . A method as in  claim 2  wherein said bond coat comprises an MCrAlY coating.  
     
     
         4 . A method as in  claim 2  wherein said bond coat comprises an aluminide coating.  
     
     
         5 . A method as in  claim 1  wherein said part comprises an aluminum containing superalloy substrate without a bond coat.  
     
     
         6 . A method as in  claim 1  wherein said inert gas is selected from the group consisting of Ar, Ne, Kr, Xe and mixtures thereof.  
     
     
         7 . A method as in  claim 1  wherein said non reactive gas is selected from the group consisting of N, H and mixtures thereof.  
     
     
         8 . A method as in  claim 2  wherein said gas is provided during that part of the preheat cycle where the substrate temperature exceeds about 1000° F.  
     
     
         9 . A method as in  claim 2  wherein said gas is provided during that part of the preheat cycle where the part temperature exceeds about 1200° F.  
     
     
         10 . A method as in  claim 1  wherein said vacuum environment is maintained at a pressure of less than about 10 −2  during the preheat cycle. (unit?)  
     
     
         11 . A method as in  claim 1  wherein said gas is injected into a chamber which partially surrounds the part to be preheated.  
     
     
         12 . A method as in  claim 1  wherein said gas is injected into the region immediately surrounding the part through at least one nozzle.  
     
     
         13 . A method for preheating a gas turbine component in a vacuum environment prior to the application of a ceramic coating, wherein said gas turbine component has an outer surface which contains aluminum, which comprises: adding a gas selected from the group consisting of Ar, He, N, H, Xe, Kr, and mixtures thereof into the region immediately surrounding the part to reduce the rate of alumina formation during preheating.  
     
     
         14 . In an apparatus applying a ceramic coating to a substrate by EBPVD, of the type which includes a vacuum chamber, means for producing a vacuum in said chamber and means to preheat said substrate prior to application of said coating, the improvement which comprises: means to inject a gas selected from the group comprising inert and non reactive gases, and mixtures thereof into the region surrounding the substrate during the preheat step preceding ceramic coating application.