Papers by Author: Mats Halvarsson

Abstract: The oxidation of iron in dry O2 and in wet O2 (40% H2O) has been studied at 600°C. The oxide microstructure was investigated by SEM/EDX, FIB and XRD. Iron forms a layered scale in dry and wet oxygen at 600°C. The scale consists of a top hematite layer, a middle magnetite layer and a wüstite layer close to the scale metal interface. All three layers grow with time, but with different growth rates, the overall growth being approximately parabolic. The presence of water vapour increases the rate of oxidation and affects the evolution of the oxide microstructure. The higher rate of oxidation in the presence of water vapour is due to an increased growth rate of the magnetite layer and, especially, of the hematite layer, while the growth of the wüstite layer is not affected. It is suggested that water vapour influences grain boundary transport in the hematite layer.

Abstract: 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.