Oxidation Induced Length Change of Thin Gauge Fe-Cr-Al Alloys

摘要

Alloys of Fe-20Cr-5Al have been used extensively as the material of choice in metallic catalytic converter substrates. The alloy chemistry has been developed through the last decade to provide the oxidation weight gain resistance that was thought to be adequate. Mainly by the addition of rare earth and active elements, the cyclic oxidation behavior has been improved to the point to meet the regulation requirements on the durability of catalytic converters. The major uncertainty on the understanding of oxidation behaviors of thin gauge Fe-Cr-Al foil is the cause of foil length change. It has been suggested that this length change is one of the causes of buckled honeycomb observed in the fractured substrate. Analysis on the stress and strain of thin gauge Fe-Cr-Al foil under the oxidation condition has been published to account for the length changes due to the oxidation. However, the potential metallurgical factors that control the length change has not been rationalized yet. In this paper we will present (1) the oxidation test results on Fe-Cr-Al foils with different gauge and chemistry, (2) the microstructure evolution and (3) oxide scale development during the oxidation test. The oxidation failure mechanisms will be demonstrated. A phenomenologi-cal model to incorporate the alloy chemistry, microstructure and oxide scale will be described to account for the oxidation behaviors of these Fe-Cr-Al alloys.