The oxide morphology and transport processes occurring during the growth of α-aluminum oxide (α-Al2O3) at 1,200°C on an iron-aluminum (Fe-25 wt% Al) alloy and a nickel-aluminum (Ni-32 wt% Al) alloy (ß-NiAl) were investigated. Imaging secondary ion mass spectrometry (SIMS) was used to locate the different isotopic species following two-stage oxidations in 16O2 and 18O2. These images (with 0.1 μm lateral resolution) showed the growth of ridges of α-Al2O3 occurred by outward transport of Al for NiAl. As the ridges grew taller and wider, inward diffusion of oxygen played a role in the growth process. Mature alumina scales thickened by outward transport of Al and inward diffusion of oxygen. α-Al2O3 formed on Fe-25 wt% Al also grew through a combination of Al and oxygen diffusion, the latter appearing to take place along grain boundaries in the coarse-grained oxide.

Subject
Oxides, Diffusion, Oxide formation, Structures, Metal oxides, Oxide scales, Interfaces, Scale formation, Scale, Oxygen, Aluminum alloys, Grain, Oxidation
Keywords:
alloying, aluminum, diffusion, grain boundaries, grain morphology, iron, nickel, oxidation, oxygen, scaling
NACE International
1994
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