Oxidation properties of Fe-5Cr-4Al (wt.%) alloys in oxygen at temperatures 1000�C?1320�C

Abstract

Oxidation kinetics of a parent Fe-5Cr-4Al alloy subjected to two types of anneals were investigated at temperatures ranging from 1000°C to 1320°C. The alloy annealed at 850°C exhibited a rapid transient oxidation stage associated with growth of nodules containing iron oxides and internal precipitation of α-Al2O3 in the alloy beneath these nodules. The nodules nucleated and grew from sites located in the regions of the alloy grain boundaries during the period of rapid alloy grain growth. Nodular growth virtually ceased when a continuous α-Al2O3 film formed at the nodule-alloy interface. The alloy subjected to anneal at 1000°C and at the reaction temperature to stabilize the alloy grain size tended upon oxidation to form a protective α-Al2O3, layer by parabolic kinetics at temperatures to 1250°C. If this alloy was oxidized in stages at 1000°C, a protective α-Al2O3 scale was formed up to 1320°C. The temperature coefficient of the parabolic oxidation kinetics was consistent with diffusion processes at boundaries of the α-Al2O3 grains playing an essential role during growth of this protective oxide layer.