In Situ- Investigation of the Oxide Scale Formation and Recrystallization of a FeCrAl Foil

摘要

For practically all alumina formers like the FeCrAl alloys for automotive catalyst support foils a critical temperature interval exists, in which metastable phases like θ-Al_2O_3 are formed, that on further exposure to temperature transform into the stable α-Al_2O_3. An initially enhanced alumina scale growth and a faster Al consumption are the consequence. High temperature X-ray diffraction was applied to investigate the isothermal oxide scale formation of OC404 in air at 900℃ in situ. Low amounts of θ-Al_2O_3 were detected, but the accelerated formation of α-Al_2O_3 in the initial state and the micrographs indicate the presence of θ-Al_2O_3, which transforms very quickly to α-Al_2O_3. In in situ experiments it has been observed that on heating recrystallisation processes occur besides oxidation. For a better understanding samples exposed to 900℃ in air for different times were analysed by X-ray diffraction with a general area detector yielding meso-structure information like grain size and texture. The results show a grain coarsening at 900℃ with mostly reproducible texture obviously linked with the rolling direction.