By means of multistep techniques a serial of composite coatings of Cr and CeO_2 Containing nickel aluminide Ni(Cr)Al+CeO_2 for superalloy M_(38) have been developed. Firstly, the sandwich platings of Ni + CeO_2/Cr/Ni + CeO_2 with desired Cr and CeO_2 contents were successively electro deposited using conrentronal plating baths. Secondly, the plated samples with or without a post heat treatment were then aluminized through a high activity pack cementation process. In order to compare the oxidation performance of the new developed composite coatings of Ni(Cr)Al + CeO_2 with the coatings of Ni(Cr)Al without CeO_2, NiAl + CeO_2 without Cr and the simple aluminide of M_(38), they have been tested in air at 1100 ℃ for 200 hrs, and their hot corrosion behavior has also been examined by immersing the samples in crucibles with melten 75Na_2SO_4 + 25NaCl salt in air at 900 ℃ for 100 hrs. The morphology and phase constituents of oxidation and hot corrosion products are examined by optical metalloyraphy scanny electron microscopy, electroprobe microanalysis and X-ray diffraction. It follows that all the Ni(Cr)Al + CeO_2 composite coatings show better oxidation resistance than that of Ni(Cr)Al and simple alumimide coatings, However amount the CeO_2 coating Ni(Cr)Al coatings; the one with less CeO_2 content shows lower oxidation rate, it is also observed that the decrease in oxidation rate due to the addition of CeO_2 is primarily associated with improvement in scale adhesion. Higher Cr content and a heat treatment between the plating and the aluminizing steps are separatly beneficial to the oxidation resistance of the Ni(Cr)Al + CeO_2 coatings. The hot corrosion behavior of the Ni(Cr)Al type coatings is improved by the addition of CeO_2. The higher CeO_2 content shows the better corrosion reisistance of the coating. The matter maybe ascribed to the trapping effect for s by the cerium oxide. The degradation process of the coatings is discussed as well.
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