Abstract
Initial oxide formation at 600°C in air on Ni3Al alloys with and without chromium additions was studied by TEM. Significant lateral nickel diffusion (apparently stress-induced) occurred in both alloys producing bands of nickel and nickel oxide-enriched hillocks. Chromium additions clearly alleviate dynamic embrittlement in Ni3Al; chromium additions were previously assumed to affect the oxidation process. Chromium additions significantly reduced the oxidation rate of the alloy. However, a continuous film of pure Cr2O3 had not yet formed after 45 sec oxidation. Grain boundaries preferentially oxidized to form Al2O3 or Cr2O3 and rejected nickel along both the surface and the grain boundary, deeper into the specimen. The dramatic effect of chromium on improving the ductility of Ni3Al when tested at high temperature in air is apparently a result of a process that occurs at or near the tip of a propagating crack that is both faster and on a finer scale than that studied here.
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Horton, J.A., Cathcart, J.V. & Liu, C.T. Effect of chromium on early stages of oxidation of Ni3Al alloys at 600°C. Oxid Met 29, 347–365 (1988). https://doi.org/10.1007/BF00751804
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DOI: https://doi.org/10.1007/BF00751804