Modified slurry compositions for forming improved chromium diffusion coatings

Abstract

Unique and improved chromium coatings derived from modified chromium-containing slurry formulations are disclosed. The slurry formulation includes a combination of a selected halide activator and buffer material that synergistically interact with each other to form chromium diffusion coatings with improved microstructure in comparison to chromium diffusion coatings produced from conventional chromizing processes. The coatings may be locally applied in a controlled manner with accuracy onto various parts, including those having internal sections with complex geometries, without masking any portion thereof.

1 . A chromium diffusion coating, comprising:
 an outer α-Cr layer comprising a thickness from about 0% to about 10% of a total coating thickness;   an inner nickel-chromium layer comprising between about 15% to about 50% chromium by weight;   wherein said coating is characterized by a substantial reduction of oxide and nitride inclusions in comparison to chromium diffusion coatings derived from conventional slurry chromizing processes.   
     
     
         2 . The chromium diffusion coating of claim  8 , wherein said inclusions comprise less than about 3% volume fraction. 
     
     
         3 . The chromium diffusion coating of claim  8 , wherein said outer α-Cr layer comprises a thickness of less than about 4% of a total coating thickness. 
     
     
         4 . The chromium diffusion coating of claim  8 , said coating applied onto a substrate along selected regions. 
     
     
         5 . The chromium diffusion coating of claim  8 , wherein said outer α-Cr layer comprises a thickness of less than about 2% of a total coating thickness.