Effect of chromium on early stages of oxidation of Ni3Al alloys at 600°C

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. © 1988 Plenum Publishing Corporation.