Visualizing ion transport mechanisms through oxide scales grown on mixed nickel- and cobalt-base model alloys at 900 °C using FIB-SIMS techniques

Abstract

A set of five model superalloys with a γ′-precipitate strengthened structure and a nominal composition of Ni-xCo-9Al-8 W-8Cr were oxidized at 900 °C by the two-step oxidation method in normal oxygen and tracer oxygen-18 enriched gas atmospheres. Analysis at a nanoscale resolution by gallium focused ion beam sputtering and quadrupole-based secondary ion mass spectrometry of the surface oxide cross-sections provided evidence of both anion and cation motion during the second oxygen-18 oxidation where parabolic oxidation rate conditions can be assumed. These experiments provide new insights into the mass transport vectors for modeling the important oxidation mechanisms at extreme service conditions in mixed cobalt- and nickel-base alloys.