Chromium and Reactive Element Modified Aluminide Diffusion Coatings on Superalloys: Environmental Testing

Authors

Robert Bianco, The Ohio State University
Robert A. Rapp, The Ohio State University
James L. Smialek, NASA Glenn Research CenterFollow

Date of this Version

1993

Citation

J. Electrochem. Soc., Vol. 140, No. 4, April 1993

Comments

U.S. Government Work

Abstract

The isothermal oxidation of reactive element (RE)-doped aluminide coatings on IN 713LC alloy substrates at 1100 ˚C in air formed a continuous slow-growing α-Al₂O₃ scale after 44 h of exposure. RE-free (reactive element-free) aluminide coatings were characterized by a cracked oxide scale which exposed an underlying voided coating surface. The cyclicoxidation behavior of Cr/RE-modified aluminide diffusion coatings on René 80 and IN 713LC alloy substrates, and of RE-doped aluminide coatings on IN 713LC alloy substrates, at ll00~ in static air was determined. Coatings deposited by the above pack (AP) arrangement, as opposed to the powder contacting (PC) arrangement, showed improved resistance to cyclic oxidation attack. RE-doped and Cr/RE-modified aluminide coatings exhibited considerably more adherent protective Al₂O₃ scales compared to undeped aluminide coatings. The hot corrosion behavior of Cr/RE-medified aluminide coatings on René 80 and Mar-M247 alloy substrates at 900~ in a 0.1% SO2/Q gas mixture also was determined. The Cr/RE-modified aluminide coatings provided better resistance to hot corrosion attack (i.e., thin film studies) than a commercial low activity aluminide coating. Coating lifetimes were strongly dependent on the chromium surface composition, since a mixed (A1, Cr)₂O₃ scale better resists attack by the molten salt.