Studies on as-cast microstructure and oxidation behavior of the Fe[sbnd]Cr[sbnd]B[sbnd]Al alloys at 1073 K

Abstract

Based on the FeCrB alloy, the Fe12Cr1.5BxAl (x = 0, 2, 4, 6 and 8 wt%) alloys were designed by adding Al. The as-cast microstructure and cyclic oxidation behavior have been investigated extensively in this study. The results reveal that the as-cast microstructure of FeCrB alloy consists of martensite (bcc), retained austenite (orthorhombic) and M2(B,C)-bct, M7(C,B)3-hcp, M23(C,B)6-complex fcc boron-carbides, gradually changing to α-(Fe,Al,Cr) solid solution (bcc), M2(B,C)-bct, M7(C,B)3-hcp, M23(C,B)6-complex fcc boron-carbides and Fe3Al intermetallic compound with the increasing of Al contents. The oxidation kinetics of all alloy samples follow a parabolic oxidation kinetic law. The oxidation rate constant kp in Al-free FeCrB alloy is nearly four times of that in FeCrB8Al alloy. The additions of Al refine the grains and make the distribution of elements more uniform, which results in forming a continuous and dense oxide film containing Al2O3 oxide with excellent fluidity and thermal stability, remarkably enhancing the high temperature oxidation resistance of FeCrBAl alloy.