Jörgen Westlinder

Cyclic oxidation of two FeCrAlRE foils at 1100 oC - The influence of the concentration of minor alloying elements on scale microstructure

Two FeCrAlRE alloys, a commercial, 0C404, and a model alloy in the form of thin foils, with different Mn, Nb, Mo and Ti concentrations were subjected to cyclic oxidation in lab air at 1100°C. The oxidized samples were studied by gravimetry, Grazing-Incidence X-ray Diffraction (GI-XRD), Scanning Transmission Electron Microscopy (STEM), and Energy Dispersive X-ray (EDX) analysis. The two FeCrAl alloys exhibit different oxidation kinetics; however, both alloys have the same weight gain after 500 hours exposure. During the early stages the scale consists mainly of α-Al2O3 together with some oxide particles containing Mn, Al, Fe and Cr formed on the alloys. After 500 hours the 0C404 scale locally also consists of larger polycrystalline regions of Mn-Cr-Al spinel. In addition, Si-rich oxide, chromia and Al-Cr oxide could be observed at the metal/oxide interface.

A Time Resolved Study of Precoated AISI 441 for SOFC Interconnects Using STEM-EELS - Part I

Precoated AISI441 for SOFC interconnectors were inv stigated by STEM-EELS looking at the diffusion processes in the initial stage of the oxidation. The electron beam physical vapour deposition (EB-PVD) coating contained Ce and Co/Mn-alloy in tw o layers with at total thickness of 800 nm. The samples were exposed up to 1000 hours at 800°C, and then characterized by STEM -E LS. Multiple linear least squares (MLLS) fitting of ref erence spectra aids the interpretation of the elemental maps due t o overlapping edges. Within 4 min heat treatment the oxidation fr t has reached the substrate steel and Cr 2O3 is forming at the stainless steel interface. CeO2 acts as the barrier line for Cr and is situated between the Cr-containing spinels and the (Co,Mn)-s pinel after up to 168 h heat treatment.