Coating system for providing environmental protection to a metal substrate, and related processes

Abstract

A metal article which includes a protective coating system is described. The coating system includes a braze alloy layer and a plasma-sprayed bond coat. The bond coat may lie on top of the braze alloy layer, or the braze alloy layer may lie on top of the bond coat. In the case of a porous bond coat, partial or complete densification of the bond coat is sometimes carried out. Densification is achieved by heat treating the article, so that the braze alloy material migrates into the pores of the bond coat to a selected thickness. Related processes are also described.

What is claimed:  
     
         1 . An article, comprising a metal-based substrate, and at least two layers overlying the substrate, wherein one of the layers is a coating which comprises a braze alloy, and another layer is a plasma-sprayed bond coat.  
     
     
         2 . The article of    claim 1   , wherein the braze alloy comprises a nickel-base or cobalt-base material.  
     
     
         3 . The article of    claim 2   , wherein the braze alloy further comprises at least one component for lowering its melting point.  
     
     
         4 . The article of    claim 2   , wherein the braze alloy comprises silicon, chromium, and nickel.  
     
     
         5 . The article of article of    claim 1   , wherein the bond coat comprises an alloy of the formula MCrAlY, where M is selected from the group consisting of Fe, Ni, Co, and mixtures of any of the foregoing.  
     
     
         6 . The article of    claim 1   , wherein the bond coat is partially densified.  
     
     
         7 . The article of    claim 6   , wherein about 35% to about 65% of the depth of the bond coat is densified.  
     
     
         8 . The article of    claim 1   , wherein the layer comprising the braze alloy lies directly over the substrate.  
     
     
         9 . The article of    claim 8   , wherein the bond coat lies directly over the layer comprising the braze alloy.  
     
     
         10 . The article of    claim 9   , wherein the bond coat is partially densified.  
     
     
         11 . The article of    claim 9   , wherein a thermal barrier coating overlies the bond coat.  
     
     
         12 . The article of    claim 11   , wherein the thermal barrier coating is zirconia-based.  
     
     
         13 . The article of    claim 1   , wherein the bond coat lies directly over the substrate.  
     
     
         14 . The article of    claim 13   , wherein the layer comprising the braze alloy lies directly over the bond coat.  
     
     
         15 . The article of    claim 14   , wherein the layer comprising the braze alloy has been thermal-sprayed on the bond coat.  
     
     
         16 . The article of    claim 15   , wherein the layer comprising the braze alloy has been thermal-sprayed on the bond coat by APS.  
     
     
         17 . The article of    claim 14   , wherein a thermal barrier coating lies directly over the layer comprising the braze alloy.  
     
     
         18 . The article of    claim 14   , wherein the bond coat is partially densified.  
     
     
         19 . An article, comprising: 
 (i) a nickel-base superalloy substrate;    (ii) a braze alloy layer lying directly over the substrate, and comprising a nickel-base or cobalt-base material;    (iii) a plasma-sprayed bond coat lying directly over the braze alloy layer, and comprising an alloy of the formula MCrAlY, where M is selected from the group consisting of Fe, Ni, Co, and mixtures of any of the foregoing; and    (iv) a zirconia-based thermal barrier coating, applied directly over the bond coat.    
     
     
         20 . The article of    claim 19   , wherein at least a portion of the bond coat adjacent the braze alloy layer is densified.  
     
     
         21 . The article of    claim 19   , wherein the substrate is a component of a turbine engine.  
     
     
         22 . An article, comprising: 
 (i) a nickel-base superalloy substrate;    (ii) a plasma-sprayed bond coat lying directly over the substrate, and comprising an alloy of the formula MCrAlY, where M is selected from the group consisting of Fe, Ni, Co, and mixtures of any of the foregoing;    (iii) a braze alloy layer lying directly over the plasma-sprayed bond coat; and    (iv) a zirconia-based thermal barrier coating, applied directly over the braze alloy layer.    
     
     
         23 . The article of    claim 22   , wherein the braze alloy layer has been thermal-sprayed on the bond coat.  
     
     
         24 . The article of    claim 23   , wherein the braze alloy layer has been thermal-sprayed on the bond coat by APS.  
     
     
         25 . The article of    claim 22   , wherein at least a portion of the bond coat adjacent the braze alloy layer is densified.  
     
     
         26 . The article of    claim 22   , wherein the substrate is a component of a turbine engine.  
     
     
         27 . An article, comprising: 
 (i) a metal-based substrate;    (ii) a dense bond layer over the substrate;    (iii) a substantially porous bond layer over the dense bond layer, having a microstructure which comprises an open network of interconnected pores; and    (iv) a thermal barrier coating over the substantially porous bond layer;    wherein the dense bond layer has been formed by a heat-induced infiltration of a braze material into a porous bond region immediately below layer (iii).    
     
     
         28 . A method for providing environmental protection to a metal-based substrate, comprising the steps of applying a coating which comprises a braze alloy over the substrate, and plasma-spraying a bond coat over the substrate.  
     
     
         29 . The method of    claim 28   , wherein the braze alloy comprises a nickel-base or cobalt-base material.  
     
     
         30 . The method of    claim 29   , wherein the braze alloy comprises silicon, chromium, and nickel.  
     
     
         31 . The method of    claim 28   , wherein the plasma-sprayed bond coat is substantially porous.  
     
     
         32 . The method of    claim 28   , wherein the bond coat comprises an alloy of the formula MCrAlY, where M is selected from the group consisting of Fe, Ni, Co, and mixtures of any of the foregoing.  
     
     
         33 . The method of    claim 28   , wherein the step of applying the coating which comprises a braze alloy over the substrate is carried out before the step of plasma-spraying the bond coat, said plasma-sprayed bond coat being applied directly to the coating comprising the braze alloy.  
     
     
         34 . The method of    claim 33   , wherein the coating comprising the braze alloy is fused to the substrate before the application of the plasma-sprayed bond coat.  
     
     
         35 . The method of    claim 33   , wherein the plasma-sprayed bond coat is substantially porous.  
     
     
         36 . The method of    claim 35   , wherein plasma-spraying of the bond coat is carried out by APS.  
     
     
         37 . The method of    claim 35   , wherein the braze alloy is heat-treated after the application of the plasma-sprayed bond coat, to at least partially densify the bond coat.  
     
     
         38 . The method of    claim 37   , wherein the heat-treatment is carried out in a vacuum.  
     
     
         39 . The method of    claim 37   , wherein about 35% to about 65% of the depth of the bond coat is densified.  
     
     
         40 . The method of    claim 37   , wherein the bond coat comprises an alloy of the formula MCrAlY, where M is selected from the group consisting of Fe, Ni, Co, and mixtures of any of the foregoing.  
     
     
         41 . The method of    claim 28   , wherein the step of applying the coating which comprises a braze alloy over the substrate is carried out after the step of plasma-spraying the bond coat, so that the plasma-sprayed bond coat is applied directly to the substrate, and the braze alloy overlies the bond coat.  
     
     
         42 . The method of    claim 41   , wherein the layer comprising the braze alloy is thermal-sprayed on the bond coat.  
     
     
         43 . The method of    claim 42   , wherein the layer comprising the braze alloy is thermal-sprayed on the bond coat by APS.  
     
     
         44 . The method of    claim 41   , wherein the plasma-sprayed bond coat is substantially porous.  
     
     
         45 . The method of    claim 44   , wherein the braze alloy is heat-treated after the application of the plasma-sprayed bond coat, to at least partially densify the bond coat.  
     
     
         46 . The method of    claim 45   , wherein the heat-treatment is carried out in a vacuum.  
     
     
         47 . The method of    claim 28   , wherein a thermal barrier coating is applied over the substrate after the application of the bond coat and the coating which comprises a braze alloy.  
     
     
         48 . The method of    claim 47   , wherein the braze alloy is heat-treated after the application of the thermal barrier coating, to at least partially densify the bond coat.  
     
     
         49 . A method for providing environmental protection to a nickel-base superalloy substrate, comprising the following steps: 
 (i) applying a braze alloy coating on the substrate, said coating comprising silicon, chromium, and nickel;    (ii) plasma-spraying a bond coat over the braze alloy coating, said bond coat comprising an alloy of the formula MCrAlY, where M is selected from the group consisting of Fe, Ni, Co, and mixtures of any of the foregoing;    (iii) applying a zirconia-yttria thermal barrier coating over the bond coat; and    (iv) heat treating the braze alloy coating, to at least partially densify the bond coat.