Manufacturing, structure and high temperature corrosion of palladium-modified aluminide coatings on nickel-base superalloy M38

Three palladium-modified aluminide coatings were prepared by conventional pack-cementation aluminizing process on the nickel-based superalloy M38, which was previously electroplated with pure palladium, Pd-20 wt.% Ni alloy, or Pd + Ni composite plating. The structure of all coatings was thoroughly analyzed. A major difference between Pt- and Pd-modified aluminide coatings resided in the fact that the Pd zone was single-phased and the constitutive phase was beta-(Pd-x,Ni1-x)Al. The isothermal oxidation resistance of the Pd-20 wt.% Ni alloy modified coatings was better than that of the other two palladium-containing and conventional aluminide coatings in air at 1000 degreesC. The hot corrosion performance of Pd-Ni-Al coatings was also tested in Na,SO, melt at 900 degreesC. As regards their hot corrosion resistance, they behaved at least as well as commercial Pt-Al coatings under the same testing conditions and remarkably better than conventional aluminide coatings. The behavior of cyclic oxidation of Pd-Ni-Al coating was inspected at 1050 degreesC and its corrosion mechanism was also preliminary discussed. (C) 2000 Elsevier Science S.A. All rights reserved.