Effect of Reactive Elements and of Increased Aluminum Contents on the Oxide Scale Formation on Fe-Cr-Al Alloys

摘要

Foils with a thickness of 50 μm of iron-chromium-aluminum alloys containing about 20 mass % chromium and 5.5 mass % aluminum are currently used as substrate in metal-supported automotive catalytic converters. These alloys achieve a high oxidation resistance forming at high temperatures a thin, protective alumina scale. Responding to the societal demand to reduce hazardous vehicle emissions an increase of the catalytic converters efficiency is of essential importance. Thinner foil dimensions down to 30 μm are therefore required and hence the danger of an accelerated Al consumption and thus a shorter life time due to breakaway oxidation is more likely. To reach the required life times using foils with reduced thicknesses, either the aluminum concentration has to be increased or the parabolic rate constant has to be decreased. New foil production techniques have been developed for achieving higher aluminum contents and the effect of reactive elements on the oxidation behavior of Fe-Cr-Al alloys has been extensively investigated. In the present research work in situ - studies by high temperature X-ray diffraction have been performed in order to investigate the oxidation behavior at 950℃ and 1100℃ of two Fe-Cr-Al alloys with 5.5 mass % Al containing different reactive element additions and of a prototype alloy with 7 mass % Al as well as of an Al - coated material. The method allows an in situ identification of the oxides and their modifications, and it monitors the formation of each phase as a function of time[7].