Abstract
A thin protective oxide formed on a Ni-19.7 Cr-2.4 Al alloy in air at 850°C. Microstructural examination of stripped films showed that the oxide was duplex with an inner chromium-rich layer of NiCr2O4 + Cr2O3 with probably some NiAl2O4 + Al2O3, and an outer nickel-rich layer, principally NiO. The oxide grew faster in the presence of NaCl and it differed significantly in microstructure and composition from a very early stage. The thicker regions of the oxide assumed regular polyhedral shapes in air + NaCl, rather than the irregular nodular shape exhibited in clean air, as well as becoming richer in chromium. The results suggest that chloride vapor increases cationic mobility in the oxide. It is proposed that Cl− ions are incorporated in the oxygen close-packed lattice, thereby increasing ionic mobility in Cr2O3.
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Hossain, M.K., Saunders, S.R.J. A microstructural study of the influence of NaCl vapor on the oxidation of a Ni-Cr-Al alloy at 850°C. Oxid Met 12, 1–22 (1978). https://doi.org/10.1007/BF00609972
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DOI: https://doi.org/10.1007/BF00609972