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Aluminides were formed on Ni-Cr-Fe based superalloy 690 substrates using pack aluminization process at 1273 K in controlled atmosphere. Thermal oxidation of aluminized specimens was carried out at 1273 K for a total period of 4 hours in air. The thermally grown oxide layer was examined using X-ray diffraction (XRD) studies on top surface and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) analysis along the cross-section of the sample. The oxide layer developed on aluminized superalloy 690 substrate consisted of Al2O3 layer with a thickness of about 2 μm. The oxidized specimens were exposed in nitrate-based environment (simulated high-level nuclear liquid waste) at 373 K for a total period of 216 hours. A good adherence of aluminide coatings was noticed even after prolonged exposure in nitrate-based solution with a little amount of material dissolution from the edges of the specimens. XRD studies on exposed specimen indicated existence of Al2O3 layer on the top surface, which is believed to have resulted in good adherence of aluminide coatings.

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