Organic coating compositions for aluminizing metal substrates, and related methods and articles

Abstract

An organic coating composition is described, which can be used to enrich the surface region of a metal-based substrate with aluminum. The composition comprises an aluminum-based powder and at least one organic resin, e.g., alkyds, epoxies, or silicone materials. At least some of the aluminum-based powder is in the form of substantially spherical powder particles. The coating composition is substantially free of hexavalent chromium. It can be applied to the substrate by a variety of techniques, such as spraying. It is then heat-treated, to cause diffusion of aluminum into the surface region of the substrate, e.g., a turbine engine component. The composition exhibits good thermal and chemical stability for extended periods of time. Related articles are also described.

1 . An organic-based aluminizing composition, comprising an aluminum-based powder and at least one organic resin. 
   
   
       2 . The composition of  claim 1 , wherein the organic resin is selected from the group consisting of silicone resins, alkyd resins, acrylic resins, polyurethane resins, polyvinyl chloride resins, phenolic resins, polyester resins, urethane resins, polyamide resins, polyolefin resins, and combinations of any of the foregoing. 
   
   
       3 . A method for aluminiding the surface region of a metal substrate, comprising the following steps:
 (I) applying at least one layer of an organic-based aluminizing composition to the surface of the substrate; wherein the composition is substantially free of hexavalent chromium, and comprises an aluminum-based powder and at least one organic resin; and then   (II) heat treating the aluminizing composition, under conditions sufficient to cause diffusion of aluminum into the surface region of the substrate.   
   
   
       4 . The method of  claim 3 , wherein the organic resin is selected from the group consisting of epoxy resins, silicone resins, alkyd resins, acrylic resins, polyurethane resins, polyvinyl chloride resins, phenolic resins, polyester resins, urethane resins, polyamide resins, polyolefin resins, and combinations of any of the foregoing. 
   
   
       5 . The method of  claim 3 , wherein the aluminum powder comprises substantially spherical powder particles. 
   
   
       6 . The method of  claim 5 , wherein the substantially spherical powder particles have an average particle size in the range of about 0.5 micron to about 200 microns. 
   
   
       7 . The method of  claim 3 , wherein the aluminum-based powder in the composition comprises an alloy of aluminum and silicon. 
   
   
       8 . The method of  claim 3 , wherein the aluminum-based powder further comprises at least one metal selected from the group consisting of platinum group metals, rare earth metals, scandium, yttrium, iron, chromium, and cobalt. 
   
   
       9 . The method of  claim 3 , wherein the aluminizing composition is applied to the surface of the substrate by a technique selected from the group consisting of spraying, slip-casting, brush-painting, dipping, pouring, rolling, or spin-coating. 
   
   
       10 . The method of  claim 3 , wherein the heat treatment of step (II) comprises a preliminary heat treatment to remove at least some of the volatile components, and a final heat treatment to diffuse the aluminum into the substrate. 
   
   
       11 . The method of  claim 3 , wherein the heat treatment is carried out at a temperature in the range of about 650° C. to about 1100° C. 
   
   
       12 . The method of  claim 3 , wherein step (II) comprises a graduated heat treatment. 
   
   
       13 . A method for aluminiding the surface region of a turbine component formed from a material comprising a nickel-based superalloy, comprising the following steps:
 (i) spraying at least one layer of an organic-based aluminizing composition to the surface of the substrate; wherein the composition is substantially free of hexavalent chromium, and comprises an aluminum-based powder and at least one organic resin selected from the group consisting of epoxy resins, silicone resins, alkyd resins, acrylic resins, polyurethane resins, polyvinyl chloride resins, phenolic resins, polyester resins, urethane resins, polyamide resins, polyolefin resins, and combinations of any of the foregoing;   (ii) heating the aluminizing composition in a preliminary heat treatment, to remove at least some volatile components contained therein; and   (iii) heat treating the aluminizing composition at a temperature in the range of about 650° C. to about 1100° C., to diffuse aluminum into the surface region of the turbine component.   
   
   
       14 . A method for preparing an organic-based aluminizing composition, comprising the step of adding an aluminum-based powder to an organic coating composition, so that the total amount of aluminum in the organic coating composition is in the range of about 30% by weight to about 40% by weight. 
   
   
       15 . The method of  claim 14 , wherein the aluminum-based powder which is added to the organic coating composition comprises substantially spherical powder particles having an average particle size in the range of about 1 micron to about 50 microns. 
   
   
       16 . The method of  claim 15 , wherein the organic coating composition is a commercial paint. 
   
   
       17 . The method of  claim 16 , wherein the commercial paint contains aluminum flakes, prior to addition of the aluminum-based powder.