Microstructural Investigation of the Initial Oxidation of the FeCrAlRE Alloy Kanthal AF in Dry and Wet O[sub 2] at 600 and 800°C

Abstract

The FeCrAlRE (where RE is reactive element) alloy Kanthal AF was exposed isothermally at 600 and 800°C for 72 h in dry normalO2 and in normalO2 with 10 vol % normalH2O . The mass gains were 3–5 times higher at the higher temperature. The presence of water vapor increased the oxidation rate at 800°C , while no significant effect was observed at 600°C . A thin two-layered oxide formed at 600°C : an outer (Fe,Cr)2normalO3 corundum-type oxide, containing some Al, and an inner, probably amorphous, Al-rich oxide. At 800°C a two-layered oxide formed in both environments. The inner layer consisted of inward grown α-Al2normalO3 . In dry normalO2 the originally formed outward grown γ-Al2normalO3 had transformed to α-Al2normalO3 after 72 h. Water vapor stabilized the outward grown γ-Al2normalO3 and hence no transformation occurred after 72 h in humid environment. RE-rich oxide particles with varying composition (Y, Zr, and Ti) were distributed in the base oxide at both temperatures and in both environments. The RE-rich particles were separated from the alloy substrate by a layer of Al-rich oxide. At 800°C the Y-rich RE particles were surrounded by thick oxide patches in both dry and humid normalO2 .

KCl-Induced Corrosion of the FeCrAl Alloy Kanthal ® AF at 600 °C and the Effect of H2O

“…The chromia band corresponds to Cr 2 O 3 which was identified using XRD while the alumina in the film was apparently non-crystalline. This is in accordance with a recent study of Canovic et al [20] who reports that the oxide film formed on Kanthal Ò AF in O 2 and O 2 ? H 2 O at 600°C consists of a top corundum-type layer and a bottom layer made up of non-crystalline alumina.…”

KCl-Induced Corrosion of an FeCrAl Alloy at 600 °C in O2 + H2O Environment: The Effect of Pre-oxidation

“…6,15), no crystalline aluminas can be detected with XRD. This is also in accordance with Josefsson et al [15] and Canovic et al [22], who reported that FeCrAl oxidation produces no crystalline aluminas at 500 and 600°C. However, Josefsson et al [15] detected a-Al 2 O 3 after 168 h at 700°C.…”

“…10b). [15,16,22]. It is notable that, although the oxide film is dominated by aluminium oxide (see Figs.…”

In Situ ESEM Investigation of KCl-Induced Corrosion of a FeCrAl and a Model FeNiCrAl Alloy in Lab Air at 450°C

“…15 In the present study, attempts to identify the alumina formed on the two alloys by nano-diffraction methods indicated that it was not crystalline. Formation of protective alumina layers -the role of Cr.-It is wellknown that the oxidation properties of alumina-forming alloys are improved by chromium.…”