Method for applying a high-temperature bond coat on a metal substrate, and related compositions and articles

Abstract

A method for applying a bond coat on a metal-based substrate is described. A slurry which contains braze material and a volatile component is deposited on the substrate. The slurry can also include bond coat material. Alternatively, the bond coat material can be applied afterward, in solid form or in the form of a second slurry. The slurry and bond coat are then dried and fused to the substrate. A repair technique using this slurry is also described, along with related compositions and articles.

What is claimed:  
     
         1 . A method for applying a bond coat on a metal-based substrate, comprising the following steps: 
 a) applying a slurry which comprises braze material to the substrate, wherein the slurry also contains a volatile component;    b) applying bond coat material to the substrate;    c) drying the slurry and bond coat material to remove at least a portion of the volatile component; and    d) fusing the braze material and bond coat material to the substrate.    
     
     
         2 . The method of  claim 1 , 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.  
     
     
         3 . The method of  claim 2 , wherein the braze material comprises at least about 40% by weight nickel.  
     
     
         4 . The method of  claim 2 , wherein the braze material further comprises a constituent which lowers the melting point of the braze alloy.  
     
     
         5 . The method of  claim 4 , wherein the constituent is silicon, boron, or mixtures thereof.  
     
     
         6 . The method of  claim 1 , wherein the braze material has an average particle size in the range of about 20 microns to about 150 microns.  
     
     
         7 . The method of  claim 1 , wherein the slurry further comprises at least one additive selected from the group consisting of binders, stabilizers, thickening agents, dispersants, deflocculants, anti-settling agents, plasticizers, emollients, lubricants, surfactants, anti-foam agents, and curing modifiers.  
     
     
         8 . The method of  claim 1 , wherein the slurry is applied to the substrate by a technique selected from the group consisting of slip-casting, brushing, painting, dipping, flow-coating, roll-coating, spin coating, and spraying.  
     
     
         9 . The method of  claim 1 , wherein the bond coat material 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.  
     
     
         10 . The method of  claim 1 , wherein the bond coat comprises a material selected from the group consisting of aluminide, platinum-aluminide; nickel-aluminide; platinum-nickel-aluminide; and mixtures thereof.  
     
     
         11 . The method of  claim 1 , wherein the bond coat material has an average particle size of at least about 45 microns.  
     
     
         12 . The method of  claim 11 , wherein the bond coat material has an average particle size in the range of about 150 microns to about 300 microns.  
     
     
         13 . The method of  claim 1 , wherein the volatile component comprises at least one aqueous solvent or at least one organic solvent, or mixtures thereof.  
     
     
         14 . The method of  claim 1 , wherein step (c) is carried out by air-drying.  
     
     
         15 . The method of  claim 1 , wherein step (d) is carried out at a temperature in the range of about 525° C. to about 1650° C.  
     
     
         16 . The method of  claim 1 , wherein the metal-based substrate is a superalloy.  
     
     
         17 . The method of  claim 16 , wherein the superalloy is a nickel-base or cobalt-base material.  
     
     
         18 . The method of  claim 1 , wherein the bond coat has a root mean square roughness (R a ) value of greater than about 200 micro-inches, after step (d).  
     
     
         19 . The method of  claim 1 , wherein the slurry also contains the bond coat material, so that the braze material and the bond coat material are applied to the substrate simultaneously.  
     
     
         20 . The method of  claim 19 , wherein the slurry is prepared by combining the bond coat material and the braze material with a solvent and at least one additive selected from the group consisting of binders, stabilizers, thickening agents, dispersants, deflocculants, anti-settling agents, plasticizers, emollients, lubricants, surfactants, anti-foam agents, and curing modifiers.  
     
     
         21 . The method of  claim 19 , wherein the braze material has an average particle size in the range of about 20 microns to about 150 microns, and the bond coat material has an average particle size of at least about 45 microns.  
     
     
         22 . The method of  claim 1 , wherein the slurry of step (a) is substantially dried after being applied, thereby forming a green layer, prior to the application of the bond coat material.  
     
     
         23 . The method of  claim 22 , wherein an adhesive material is applied to the green layer, prior to the application of the bond coat material.  
     
     
         24 . The method of  claim 23 , wherein the bond coat material is in the form of dry particles, and is applied to the adhesive material.  
     
     
         25 . The method of  claim 24 , wherein the bond coat material is poured or sprinkled onto the adhesive.  
     
     
         26 . The method of  claim 1 , wherein the bond coat material is in the form of a second slurry, applied in step (b) on top of the slurry applied in step (a).  
     
     
         27 . The method of  claim 26 , wherein each slurry comprises at least one additive selected from the group consisting of binders, stabilizers, thickening agents, dispersants, deflocculants, anti-settling agents, plasticizers, emollients, lubricants, surfactants, anti-foam agents, and curing modifiers.  
     
     
         28 . The method of  claim 26 , wherein each slurry is applied to the substrate by a technique selected from the group consisting of slip-casting, brushing, painting, dipping, flow-coating, roll-coating, spin coating, and spraying.  
     
     
         29 . The method of  claim 1 , wherein the bond coat is in the form of a second slurry, and the second slurry is pre-mixed with the first slurry to form a pre-mixture, said pre-mixture being applied to the substrate prior to step (c).  
     
     
         30 . The method of  claim 29 , wherein the pre-mixture is applied to the substrate by a technique selected from the group consisting of slip-casting, brushing, painting, dipping, flow-coating, roll-coating, spin coating, and spraying.  
     
     
         31 . The method of  claim 1 , wherein an overcoat is applied over the bond coat after step (d).  
     
     
         32 . The method of  claim 31 , wherein the overcoat is a thermal barrier coating.  
     
     
         33 . The method of  claim 32 , wherein the thermal barrier coating is zirconia-based.  
     
     
         34 . The method of  claim 32 , wherein the thermal barrier coating is applied by a thermal spray technique.  
     
     
         35 . The method of  claim 34 , wherein the thermal spray technique is a plasma spray process.  
     
     
         36 . The method of  claim 31 , wherein the overcoat is a wear-resistant coating.  
     
     
         37 . The method of  claim 31 , wherein the overcoat comprises a material selected from the group consisting of metal carbides; alumina, mullite, zircon, cobalt-molybdenum-chromium-silicon; strontium-calcium-zirconate glass; and mixtures thereof.  
     
     
         38 . A method for applying a metal aluminide- or MCrAlY-based bond coat on a superalloy substrate, where M is nickel, cobalt, or a mixture thereof, comprising the following steps: 
 (I) applying a slurry which comprises a volatile component and a mixture of braze material and bond coat material to the substrate, wherein the braze material contains at least about 40% by weight nickel;    (II) drying the slurry under conditions sufficient to remove at least a portion of the volatile component, forming a green coating; and    (III) brazing the green coating to the substrate.    
     
     
         39 . The method of  claim 38 , wherein the braze material has an average particle size in the range of about 40 microns to about 80 microns, and the bond coat material has an average particle size in the range of about 150 microns to about 300 microns.  
     
     
         40 . The method of  claim 38 , wherein a zirconia-based thermal barrier coating is applied over the bond coat.  
     
     
         41 . A method for replacing a bond coat applied over a metal-based substrate, comprising the following steps: 
 (i) removing the existing bond coat from a selected area on the substrate;    (ii) applying a slurry which comprises braze material to the selected area, wherein the slurry also contains a volatile component;    (iii) applying additional bond coat material to the selected area; and    (iv) fusing the braze material and bond coat material to the selected area.    
     
     
         42 . The method of  claim 41 , wherein the slurry also contains the bond coat material, so that the braze material and the bond coat material are applied to the substrate simultaneously.  
     
     
         43 . The method of  claim 41 , wherein the bond coat material 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.  
     
     
         44 . The method of  claim 41 , wherein the metal-based substrate is a portion of a turbine engine.  
     
     
         45 . A slurry composition, comprising a braze material and a bond coat material.  
     
     
         46 . The composition of  claim 45 , 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.  
     
     
         47 . The composition of  claim 46 , wherein the braze material comprises at least about 40% by weight nickel.  
     
     
         48 . The composition of  claim 46 , wherein the bond coat material 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.  
     
     
         49 . The composition of  claim 46 , wherein the bond coat comprises a material selected from the group consisting of aluminide, platinum-aluminide, nickel-aluminide; platinum-nickel-aluminide; and mixtures thereof.  
     
     
         50 . The composition of  claim 46 , wherein the bond coat material is in the form of particles, and the particles have an average size of at least about 45 microns.  
     
     
         51 . An article, comprising: 
 (a) a metal-based substrate; and    (b) a volatile-containing slurry on the substrate, comprising braze material and bond coat material.    
     
     
         52 . The article of  claim 51 , wherein the substrate is a superalloy.  
     
     
         53 . The article of  claim 51 , wherein the substrate is a component of a turbine engine.  
     
     
         54 . The article of  claim 51 , wherein the braze material comprises at least about 40% by weight nickel, and the bond coat material 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.  
     
     
         55 . The article of  claim 51 , wherein the volatile component in the slurry has been substantially removed, so as to form a green coating.  
     
     
         56 . The article of  claim 55 , wherein the green coating is fused to the substrate, forming a bond coat.  
     
     
         57 . The article of  claim 56 , wherein the braze material forms a continuous matrix phase in which the bond coat particles are embedded.  
     
     
         58 . The article of  claim 57 , wherein an overcoat is disposed over the bond coat.  
     
     
         59 . The article of  claim 58 , wherein the overcoat is a zirconia-based TBC.  
     
     
         60 . The article of  58 , wherein the overcoat is a wear-resistant coating.  
     
     
         61 . An article, comprising: 
 (i) a metal-based substrate, and    (ii) a brazed bond coat comprising bond coat particles, disposed over the substrate, wherein the braze material forms a continuous matrix phase in which the bond coat particles are embedded.    
     
     
         62 . The article of  claim 61 , wherein the brazed bond coat has a root mean square roughness (R a ) value of greater than about 200 micro-inches.  
     
     
         63 . The article of  claim 61 , wherein the brazed bond coat is characterized by micro-roughness.  
     
     
         64 . The article of  claim 61 , wherein the brazed material is nickel-based or cobalt-based.  
     
     
         65 . The article of  claim 61 , wherein the bond coat is a higher-temperature material.  
     
     
         66 . The article of  claim 61 , wherein the bond coat particles are roughness-producing.