Air oxidation of commercial FeCrAlRE alloy foils between 800 and 950°C

Abstract

The oxidation behaviour of 30 mm and 50 mm thick Aluchrom YHf and 50 mm thick Kanthal AF foils have been examined during discontinuous exposure (100 h cycles) to laboratory air at 800, 850, 900 and 950uC. Oxidation was continued out to 3000 h or until chemical failure ensued, whichever was the shorter. Resulting observations include two oxidation temperature domains, a two-stage oxidation process leading to a duplex (transitional-a) alumina scale and ultimately, a two-stage chemical failure process of the oxide scale leading to breakaway/non-protective attack. To unravel the underlying mechanisms involved, the scales were examined by a range of microscopy and analytical techniques, including optical and scanning electron microscopy (SEM), electron microprobe analysis (EPMA), energy dispersive X-ray analysis (EDX) and X-ray diffraction (XRD).

Oxidation of a Dispersion-Strengthened Powder Metallurgical FeCrAl Alloy in the Presence of O2 at 1,100 °C: The Influence of Water Vapour

“…. Metastable aluminas are reported to form during early stages of high temperature oxidation of FeCrAl alloys and at intermediate temperatures [21,22,[37][38][39]. They are invariably found in the outer part of the scale, and grow by cation (outward) diffusion [40].…”

Oxidation of FeCrAlY Fibers at Low Oxygen Potentials

“…The Cr 2 O 3 is a suitable protective oxide below *950°C, and this growth region is termed ''pseudo-protective.'' This recent study of Tatlock et al [6] shows a chromium-rich oxide forming below the alumina after oxidation at 900°C for 700 h. The stability of the oxide/alloy in this pseudoprotective region needs to be more fully assessed.…”

“…A recent extensive study of FeCrAlRE (RE = rare earth metal) alloys between 800 and 950°C shows the importance of the transient oxides at these temperatures [6]. There still remain many questions about the structure of these transient oxides, but they are thought to be spinel-like and highly defective, which leads to rapid growth rates.…”

“…A critical issue for the oxidative lifetime of these alloys is the supply of aluminum [6]. These alloys have only * 5 wt.% aluminum to maintain their ductility.…”

“…At temperatures below 1,000°C the transient oxides play a critical role [5][6][7]. A recent extensive study of FeCrAlRE (RE = rare earth metal) alloys between 800 and 950°C shows the importance of the transient oxides at these temperatures [6].…”