Method for Substrate Stabilization of Diffusion Aluminide Coated Nickel-Based Superalloys

Abstract

An article and method for stabilization of a nickel-based superalloy coated with a diffusion aluminide coating. The region below the aluminide coating is first carburized to form refractory carbides. The article is cleaned and masked as required so that regions that will not have an aluminide coating are not carburized. After placing the article into a furnace and heating in a non-oxidizing atmosphere to a carburizing temperature, a carburizing gas is introduced, and the near surface region is carburized to a depth of about 100 microns. Refractory carbides are formed in this region. When a diffusion aluminide coating is formed on the article, the refractory elements, being present as refractory carbides, are not available to form detrimental TCP phases.

1 . A nickel based superalloy article, comprising:
 a nickel-based superalloy substrate having a surface;   refractory carbide precipitates formed by carburizing to a preselected depth below the surface of at least a portion of the superalloy substrate, the remainder of the superalloy substrate being substantially free of refractory carbide precipitates from carburizing at or below the surface; and   a diffusion aluminide coating formed on that portion of the substrate surface having carbide precipitates extending a preselected distance below the surface, the diffusion aluminide extending below the substrate surface to a distance substantially no greater than that of the refractory carbides.   
   
   
       2 . The nickel-based superalloy article of  claim 1  wherein the nickel-based superalloy substrate is a turbine airfoil selected from the group consisting of blades and vanes. 
   
   
       3 . The superalloy article of  claim 1  wherein the refractory carbide precipitates are formed to a preselected depth below the substrate surface of between about 10-100 microns. 
   
   
       4 . The superalloy article of  claim 3  wherein the diffusion aluminide coating is formed to a distance of 10-50 microns below the substrate surface and wherein the distance is of the diffusion aluminide coating extends to substantially the same distance below the substrate surface as the refractory carbide precipitates. 
   
   
       5 . The superalloy article of  claim 1  further characterized by a substantial absence of TCP phases in a near-surface region. 
   
   
       6 . An article comprising:
 a substrate comprising a nickel-based superalloy, the substrate having a substrate surface;   a carbide precipitate region comprising refractory carbide precipitates, at least some of the refractory carbide precipitates being diffused into the substrate to a depth of about 10 to about 100 micrometers below the substrate surface, the carbide precipitate region being substantially free of acicular topologically close-packed (TCP) phase forms;   an aluminum-based layer; and   an aluminum-based diffusion region contiguous to the aluminum-based layer, the aluminum-based diffusion region extending from the aluminum-based layer into the carbide precipitate region, and into the substrate to a depth of about 25 to about 50 micrometers below the substrate surface.   
   
   
       7 . The article of  claim 6 , wherein the aluminum-based layer is contiguous to the carbide precipitate region. 
   
   
       8 . The article of  claim 6 , wherein the aluminum-based layer is the outermost layer. 
   
   
       9 . The article of  claim 6 , wherein the at least some of the refractory carbide precipitates diffused into the substrate are diffused therein to a depth of about 25 to about 100 micrometers below the substrate surface. 
   
   
       10 . The article of  claim 6 , wherein the article is a turbine airfoil blade. 
   
   
       11 . The article of  claim 6 , wherein the article is a turbine airfoil vane.