Corrosion Resistant Articles

Abstract

Gas turbine engine turbine blade includes a silicon-modified aluminide coating on at least an under platform region formed from a slurry composition being substantially free of hexavalent chromium. The silicon-modified aluminide coating provides oxidation resistance comparable to PtAl coatings without adding a weight penalty.

1 . A gas turbine engine turbine blade comprising:
 a superalloy substrate selected from the group consisting of nickel-base superalloys, iron-base superalloys, and cobalt-base superalloys, and combinations thereof;   an under platform region of the blade; and   a silicon-modified aluminide coating on at least a portion of the under platform region, the silicon-aluminide coating being formed from a slurry composition being substantially free of hexavalent chromium and comprising
 a binder selected from the group consisting of colloidal silica, organic resins, and combinations thereof; and 
 an aluminum-based powder; 
 wherein the silicon-modified aluminide coating has a coating thickness and an outer surface region, the outer surface region defines about 25% of the coating thickness and an outer surface of the silicon-modified aluminide coating, and the outer surface region comprises at least about 20% by weight aluminum and from about 1 to about 15% by weight silicon. 
   
     
     
         2 . The gas turbine engine blade according to  claim 1  wherein the silicon-modified aluminide coating has
 a concentration of silicon at the outer surface of the silicon-modified aluminide coating in the range of about 1 to about 15% by weight and a concentration of aluminum at the outer surface of the silicon-modified aluminide coating in the range of at least about 20% by weight. 
 
     
     
         3 . The gas turbine engine blade according to  claim 2  wherein the concentration of silicon at the outer surface of the silicon-modified aluminide coating is in the range of at least about 4% by weight. 
     
     
         4 . The gas turbine engine blade according to  claim 2  wherein the concentration of silicon at the outer surface of the silicon-modified aluminide coating is in the range of about 1 to about 10% by weight. 
     
     
         5 . The gas turbine engine according to  claim 1  wherein the blade comprises a new make blade. 
     
     
         6 . The gas turbine engine according to  claim 1 , wherein the blade comprises a repaired used blade. 
     
     
         7 . The gas turbine engine according to  claim 1  wherein the blade comprises the nickel-base superalloy. 
     
     
         8 . The gas turbine engine blade according to  claim 1  wherein the silicon-modified aluminide coating has a final coating thickness of about 0.064 mm. 
     
     
         9 . (canceled) 
     
     
         10 . The gas turbine engine blade according to  claim 1  wherein the slurry composition comprises
 (a) colloidal silica and 
 (b) particles of an aluminum-based powder 
 wherein the colloidal silica is present in the slurry composition in the range of about 5% by weight to about 20% by weight, based on silica solids, and wherein aluminum is present in the slurry composition in the range of about 0.5% by weight to about 45% by weight of the total composition. 
 
     
     
         11 . (canceled) 
     
     
         12 . The gas turbine blade according to  claim 8  wherein the thickness of the slurry composition is about 0.010 mm greater than the final coating thickness. 
     
     
         13 . The gas turbine blade according to  claim 1  wherein the aluminum-based powder comprises at least about 75% by weight aluminum. 
     
     
         14 . The gas turbine blade according to  claim 13  wherein the aluminum-based powder further comprises platinum group metals, rare earth metals, scandium, yttrium, and combinations thereof. 
     
     
         15 . The gas turbine blade according to  claim 1  wherein the aluminum-based powder comprises an aluminum-silicon alloy. 
     
     
         16 . The gas turbine blade according to  claim 1 , wherein the slurry composition further comprises an inert pyrolysable thickener. 
     
     
         17 . The gas turbine blade according to  claim 16  wherein the inert pyrolysable thickener is selected from the group consisting of solid organic particulate thickeners selected from the group consisting of acrylics and polymers, poly (methyl methacrylate), and water soluble polymers. 
     
     
         18 . The gas turbine blade according to  claim 17 , wherein the water soluble polymer comprises polyvinyl alcohol. 
     
     
         19 . The gas turbine blade according to  claim 1  wherein the binder comprises at least one synthetic resin or drying oil as a film-forming component and one or more solvents. 
     
     
         20 . The gas turbine blade according to  claim 19  wherein the at least one synthetic 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 thereof. 
     
     
         21 . The gas turbine blade according to  claim 19  wherein at least one of the one or more solvents is an organic solvent selected from the group consisting of alcohols, glycols, ketones, aldehydes, aromatic compounds, dimethylformamide, mineral spirits, naphtha, nitrated hydrocarbons, chlorinated hydrocarbons, and combinations thereof. 
     
     
         22 . The gas turbine blade according to  claim 1  wherein the silicon-modified aluminide coating includes a combination of β-NiAl and CrS 2  phases.