Active elements modified chromium diffusion patch coating

Abstract

There is provided a method for applying a diffusion coating on a specific area of targeted industrial item such as a turbine blade. The method uses a covering material such as a tape or slurry to cover the area where it is desired that the diffusion occur, for example above the root area of a turbine blade. The tape material includes a metallic source such as chromium and a master alloy of active elements for diffusion. The covering material thus defines the localized patch that is to be coated. An activator if any, such as a halide activator, can be included in the tape or slurry. Alternatively, the activator can be included in the pack material. The method uses known pack cementation methods to complete the diffusive process. The method results in a diffusion coating over a specific area of the target item.

1 . A method for diffusion coating a surface of a metallic target comprising the steps of: 
 applying a tape to a surface of a target wherein the tape is impregnated with metal powder comprising chromium and active elements containing master alloy powder with elements selected from the group consisting of silicon, hafnium, tantalum, rhenium, and yttrium; and wherein the tape further comprises a binder material;    placing a halide activator in proximity to the surface of the target; and    heating the target to a temperature sufficient to cause diffusion of the metals from the tape into the surface of the target.    
   
   
       2 . The method according to  claim 1  wherein the step of applying a tape further comprises applying a tape wherein the tape is impregnated with a halide activator.  
   
   
       3 . The method according to  claim 1  wherein the step of applying a tape further comprises a tape impregnated with metal powder comprising a chromium alloy and at least two elements selected from the group consisting of silicon, hafnium, tantalum, rhenium, and yttrium.  
   
   
       4 . The method according to  claim 1  further comprising shaping the tape to cover a desired area of the target.  
   
   
       5 . The method according to  claim 1  wherein the step of applying a tape further comprises tape comprising inert filler.  
   
   
       6 . The method according to  claim 1  wherein the step of heating the target further comprises heating the tape covered target to a temperature between approximately 1800° F. and 2100° F. and holding the temperature therebetween for between about 2 to about 16 hours.  
   
   
       7 . The method according to  claim 1  wherein the step of placing a halide activator further comprises placing an encapsulated halide activator.  
   
   
       8 . A method for diffusion coating a surface of a metallic target comprising the steps of: 
 providing a metal powder comprising chromium and at least two elements selected from the group consisting of silicon, hafnium, tantalum, rhenium, and yttrium wherein the metal powder has a mesh size of 140 or smaller;    mixing the metal powder with a binder material;    mixing a halide activator with the metal powder and binder material;    mixing an inert filler with the metal powder, binder material, and halide activator to form a tape;    covering a desired surface area of the target with the tape;    heating the tape covered target to a temperature between approximately 1800° F. and 2100° F. and holding the temperature therebetween for between about 2 to about 16 hours thereby causing diffusion of the metals into the target surface.    
   
   
       9 . A method for diffusion coating a surface of a metallic target comprising the steps of: 
 providing a metal powder comprising chromium and at least two elements selected from the group consisting of silicon, hafnium, tantalum, rhenium, and yttrium wherein the metal powder has a mesh size of 130 or smaller;    mixing the metal powder with a binder material;    mixing an inert filler with the metal powder, and binder material to form a tape;    covering a desired surface area of the target with the tape;    placing the tape-covered target in a diffusion box;    packing a mixture of halide activator and inert material in the diffusion box around the target;    heating the slurry covered target in the diffusion box to a temperature between approximately 1800° F. and 2100° F. and holding the temperature therebetween for between about 2 to about 16 hours thereby causing diffusion of the metals into the surface of the target.    
   
   
       10 . A method for preparing a slurry for use in diffusion coating a surface of a metallic target comprising the steps of: 
 providing a metal powder comprising chromium and at least two elements selected from the group consisting of silicon, hafnium, tantalum, rhenium, and yttrium wherein the metal powder has a mesh size of 140 or smaller;    mixing the metal powder with a binder material;    mixing a halide activator with the metal powder and binder material;    mixing an inert filler with the metal powder, binder material, and halide activator to form a slurry;    applying the slurry to a surface of a target in a desired thickness.    
   
   
       11 . The method according to  claim 10  wherein the step of providing a metal powder further comprises a metal powder comprising a chromium alloy and at least two elements selected from the group consisting of silicon, hafnium, tantalum, rhenium, and yttrium.  
   
   
       12 . The method according to  claim 10  further comprising covering a desired area of the target with the slurry.  
   
   
       13 . The method according to  claim 10  wherein the step of mixing a halide activator further comprises mixing an encapsulated halide activator.  
   
   
       14 . A method for diffusion coating a surface of a metallic target comprising the steps of: 
 providing a metal powder comprising chromium and at least two elements selected from the group consisting of silicon, hafnium, tantalum, rhenium, and yttrium wherein the metal powder has a mesh size of 140 or smaller;    mixing the metal powder with a binder material;    mixing a halide activator with the metal powder and binder material;    mixing an inert filler with the metal powder, binder material, and halide activator to form a slurry;    applying the slurry to a surface of a target in a desired thickness;    covering a desired area of the target with the slurry;    heating the slurry covered target to a temperature between approximately 1800° F. and 2100° F. and holding the temperature therebetween for between about 2 to about 16 hours.    
   
   
       15 . The method according to  claim 14  wherein the step of providing a metal powder further comprises a metal powder comprising a chromium alloy and at least two elements selected from the group consisting of silicon, hafnium, tantalum, rhenium, and yttrium.  
   
   
       16 . The method according to  claim 14  wherein the step of mixing a halide activator further comprises mixing an encapsulated halide activator.  
   
   
       17 . A method for diffusion coating a surface of a metallic target comprising the steps of: 
 providing a metal powder comprising chromium and at least two elements selected from the group consisting of silicon, hafnium, tantalum, rhenium, and yttrium wherein the metal powder has a mesh size of 140 or smaller;    mixing the metal powder with a binder material;    mixing an inert filler with the metal powder, and binder material to form a slurry;    applying the slurry to a surface of a target in a desired thickness;    covering a desired area of the target with the slurry;    placing the slurry-covered target in a diffusion box;    packing a mixture of halide activator and inert material in the diffusion box around the target;    heating the slurry covered target in the diffusion box to a temperature between approximately 1800° F. and 2100° F. and holding the temperature therebetween for between about 2 to about 16 hours.    
   
   
       18 . A turbine blade ready for diffusion comprising: 
 a turbine blade defining a surface;    a tape affixed to a surface of said turbine blade wherein said tape comprises a binder, an inert filler, a halide activator, a chromium containing powder, and a powder containing at least two metals selected from the group consisting of: silicon, hafnium, tantalum, rhenium, and yttrium.    
   
   
       19 . The turbine blade according to  claim 18  wherein said tape further comprises an adhesive.  
   
   
       20 . The turbine blade according to  claim 18  wherein said tape is affixed to the airfoil of the turbine blade.