Oxidation-resistant coatings bonded to metal substrates, and related articles and processes

Abstract

An article is described, which includes a metal-based substrate and an oxidation-resistant coating bonded to the substrate by a bonding agent, such as a braze material. The oxidation-resistant coating material is often an aluminide- or MCrAlX-type coating, and can be one which contains relatively high amounts of aluminum. The coating is often very smooth, for maximum aerodynamic efficiency. The oxidation-resistant coating can be applied and bonded to the substrate by a variety of methods, using slurries, braze tapes, or metal foils. Coating repair methods are also described.

1 . An article comprising: 
 (a) a metal-based substrate; and    (b) an oxidation-resistant coating bonded to the substrate by a bonding agent.    
   
   
       2 . The article of  claim 1 , wherein the oxidation-resistant coating comprises an alloy of the formula MCrAlX, where M is selected from the group consisting of Fe, Ni, Co, and mixtures of any of the foregoing; and where X is selected from the group consisting of Y, Ta, Si, Hf, Ti, Zr, B, C, and combinations thereof.  
   
   
       3 . The article of  claim 1 , wherein the oxidation-resistant coating is an aluminum-rich coating.  
   
   
       4 . The article of  claim 3 , wherein the aluminum-rich coating is a discontinuous layer of aluminum-rich particles in a matrix of a metallic alloy, and the amount of aluminum in the particles exceeds the amount of aluminum in the substrate by about 0.1 atomic % to about 40 atomic %.  
   
   
       5 . The article of  claim 3 , wherein the total amount of aluminum in the aluminum-rich coating is in the range of about 10 atomic % to about 50 atomic %.  
   
   
       6 . The article of  claim 3 , wherein the aluminum-rich coating is a discontinuous layer of aluminum-rich particles in a matrix of a metallic alloy, and the coating has a contiguity fraction of less than about 65%.  
   
   
       7 . The article of  claim 3 , wherein the aluminum-rich coating comprises particles of a first component (component I) and a second component (component II).  
   
   
       8 . The article of  claim 7 , wherein component (I) comprises particles of aluminum and a second metal, and component (II) comprises particles of an alloy of the formula MCrAlX, where M is selected from the group consisting of Fe, Ni, Co, and mixtures of any of the foregoing; and where X is selected from the group consisting of Y, Ta, Si, Hf, Ti, Zr, B, C, and combinations thereof.  
   
   
       9 . The article of  claim 8 , wherein the second metal for component (I) is nickel.  
   
   
       10 . The article of  claim 1 , wherein the oxidation-resistant coating comprises a material selected from the group consisting of [aluminide, platinum-aluminide; nickel-aluminide; platinum-nickel-aluminide; and mixtures thereof.] 
   
   
       11 . The article of  claim 1 , wherein the oxidation-resistant coating has an average roughness value “Ra” of less than about 200 micro-inches.  
   
   
       12 . The article of  claim 11 , wherein the oxidation-resistant coating has an average roughness value “Ra” of less than about 90 micro-inches.  
   
   
       13 . The article of  claim 1 , wherein the bonding agent is a braze material.  
   
   
       14 . The article of  claim 13 , wherein the braze material comprises at least one metal selected from the group consisting of nickel, cobalt, iron, a precious metal, and a mixture which includes at least one of the foregoing.  
   
   
       15 . The article of  claim 13 , wherein the braze material comprises at least about 40% by weight nickel.  
   
   
       16 . The article of  claim 1 , wherein the oxidation-resistant coating is applied to the substrate by a technique selected from the group consisting of slurry deposition, tape casting, foil application, and combinations of these techniques.  
   
   
       17 . A turbine engine component comprising a superalloy material, and including an oxidation-resistant coating bonded to at least a portion of a surface of the component, wherein the coating comprises an aluminide material or an alloy of the formula MCrAlX, where M is selected from the group consisting of Fe, Ni, Co, and mixtures of any of the foregoing; and where X is selected from the group consisting of Y, Ta, Si, Hf, Ti, Zr, B, C, and combinations thereof.  
   
   
       18 . The turbine engine component of  claim 17 , wherein the oxidation-resistant coating is an aluminum-rich coating.  
   
   
       19 . The turbine engine component of  claim 17 , wherein the oxidation-resistant coating is bonded to the substrate by a braze material which forms a continuous matrix phase in which particles of the oxidation-resistant coating are embedded.  
   
   
       20 . A method for applying an oxidation-resistant coating on a metal-based substrate, comprising the following steps: 
 (i) applying the oxidation-resistant coating in the form of a slurry or a sheet to the substrate; and then    (ii) fusing the oxidation-resistant coating to the substrate with a bonding agent.    
   
   
       21 . The method of  claim 20 , wherein the oxidation-resistant coating comprises an aluminide material or an alloy of the formula MCrAlX, where M is selected from the group consisting of Fe, Ni, Co, and mixtures of any of the foregoing; and where X is selected from the group consisting of Y, Ta, Si, Hf, Ti, Zr, B, C, and combinations thereof.  
   
   
       22 . The method of  claim 20 , wherein the slurry further comprises the bonding agent.  
   
   
       23 . The method of  claim 22 , wherein the bonding agent is a braze alloy.  
   
   
       24 . The method of  claim 23 , wherein the braze alloy comprises at least one metal selected from the group consisting of nickel, cobalt, iron, a precious metal, and a mixture which includes at least one of the foregoing.  
   
   
       25 . The method of  claim 24 , wherein the slurry is applied to the substrate by at least one technique selected from the group consisting of slip-casting, brushing, painting, dipping, flow-coating, roll-coating, spin coating, and spraying.  
   
   
       26 . The method of  claim 25 , wherein the oxidation-resistant coating is fused to the substrate by a heat treatment at a temperature of about 525° C. to about 1650° C.  
   
   
       27 . The method of  claim 20 , wherein the sheet comprises a green braze tape.  
   
   
       28 . The method of  claim 20 , wherein the sheet comprises a metal foil.  
   
   
       29 . The method of  claim 20 , wherein the oxidation-resistant coating is in the form of a first green tape, and the bonding agent is in the form of a second green tape.  
   
   
       30 . The method of  claim 29 , wherein the first green tape is applied to the substrate, and the second green tape is applied over the first green tape, followed by a heating step which fuses the tapes to the substrate surface.  
   
   
       31 . The method of  claim 29 , wherein the first and second tapes are initially attached to each other to form a bilayer, which is then applied to the substrate, with the first green tape contacting the substrate surface, and the second green tape lying over the first green tape, said application being followed by a heating step which fuses the tapes to the substrate surface.  
   
   
       32 . A method for replacing an oxidation-resistant coating applied over a metal-based substrate, comprising the following steps: 
 (I) removing the existing oxidation-resistant coating from a selected area on the substrate;    (II) applying a new oxidation-resistant coating, in the form of a slurry or a sheet, to the selected area on the substrate; and then    (III) fusing the new oxidation-resistant coating to the substrate with a bonding agent.    
   
   
       33 . The method of  claim 32 , wherein the oxidation-resistant coating comprises an aluminide material or an alloy of the formula MCrAlX, where M is selected from the group consisting of Fe, Ni, Co, and mixtures of any of the foregoing; and where X is selected from the group consisting of Y, Ta, Si, Hf, Ti, Zr, B, C, and combinations thereof.  
   
   
       34 . The method of  claim 32 , wherein the slurry further comprises the bonding agent.  
   
   
       35 . The method of  claim 32 , wherein the sheet comprises a green braze tape or a metal foil.  
   
   
       36 . The method of  claim 32 , wherein the new oxidation-resistant coating is fused to the substrate by applying heat at a sufficient fusing temperature, by means of a localized heating means.