Abstract
Minor additions of reactive elements (Y, Ce, Hf, etc.) can improve the oxidation behavior of high temperature alloys and coatings such as aluminide coatings. In the current investigation cerium-modified aluminide coatings were developed via additions of CeO2 to the powder mixture of high activity pack cementation aluminizing. Nickel-based substrates were aluminized at 750 °C and then diffusion annealed at 1080 °C. Microstructure of the coatings was studied using scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. The results were compared with the characterization results of specimens achieved by aluminizing an electrodeposited Ni–CeO2 interlayer at 1030 °C. The coatings modified by CeO2 addition to the pack showed a dense Al-rich NiAl surface layer with cerium distributed in the coating, however, the coatings modified by Ni–CeO2 interlayer revealed a porous Ni-rich aluminide layer containing CeO2 particles. Increasing the CeO2 content of the pack decreased the thickness of the final coating, but the presence of CeO2 particles in the interlayer increased the thickness of the final aluminide coating. The observed microstructural features were explained using thermodynamic analysis of equilibrium concentration of the involved gaseous species.
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