A Rapidly Solidified Powder (RSP) metallurgical FeCrAl alloy, Kanthal APMT, was exposed in dry and humid O 2 for 72 h at 900-1,100°C. The formed oxide scales were characterized using gravimetry in combination with advanced analysis techniques (SEM, EDX, TEM, XRD, AES and SIMS). The oxide scales were at all exposures composed of two-layered a-Al 2 O 3 scales exhibiting a top layer of equiaxed grains and a bottom layer containing elongated grains. A Cr-rich zone, originating in the native oxide present before exposure, separated these two layers. The top a-Al 2 O 3 layer is suggested to have formed by transformation of outwardly grown metastable alumina, while the inward-grown bottom a-Al 2 O 3 layer had incorporated small Zr-, Hf-and Ti-rich oxide particles present in the alloy matrix. The scale also contained larger Y-rich oxide particles. Furthermore, in the temperature range studied, the presence of water vapour accelerated alloy oxidation somewhat and affected scale morphology.

The present study investigates the influence of H 2 O and KCl on the high temperature corrosion of an FeCrAl alloy at 600°C. Polished samples were exposed to O 2 or O 2 ? H 2 O and to O 2 ? H 2 O with KCl applied. The samples were investigated using SEM/EDX, XRD, IC, AES and SIMS. It was found that KCl accelerates corrosion and that a rapidly growing iron-rich oxide forms with time. Chromate formation is shown to initiate the formation of a non-protective oxide scale. Pre-oxidising the alloy before exposure in the presence of KCl had a strongly beneficial effect on the corrosion.

The KCl-induced corrosion of the FeCrAl alloy Kanthal Ò APMT in an O 2 ? N 2 ? H 2 O environment was studied at 600°C. The samples were pre-oxidized prior to exposure in order to investigate the protective nature of alumina scales in the present environment. The microstructure and composition of the corroded surface was investigated in detail. Corrosion started at flaws in the pre-formed a-alumina scales, i.e. a-alumina was protective in itself. Consequently, KCl-induced corrosion started locally and, subsequently, spread laterally. An electrochemical mechanism is proposed here by which a transition metal chloride forms in the alloy and K 2 CrO 4 forms at the scale/gas interface. Scale de-cohesion is attributed to the formation of a sub-scale transition metal chloride.

The corrosion behaviour of a FeCrAl alloy was investigated at 600°C in O 2 ? H 2 O with solid KCl applied. A kinetics and microstructural investigation showed that KCl accelerates corrosion and that potassium chromate formation depletes the protective scale in Cr, thus triggering the formation of a fast-growing iron-rich scale. Iron oxide was found to grow both inward and outward, on either side of the initial oxide. A chromia layer is formed with time underneath the iron oxide. It was found that although the alloy does not form a continuous pure alumina scale at the investigated temperature, aluminium is, however, always enriched at the oxide/alloy interface.

The present study investigates the influence of H 2 O and KCl on the high-temperature corrosion of the FeCrAl alloy Kanthal Ò AF. Polished samples, with and without applied KCl, were exposed isothermally to O 2 or O 2 ? H 2 O at 600°C. The samples were investigated using TGA, XRD, SEM/EDX, AES and IC. It was found that KCl accelerates corrosion and that a rapidly growing iron, chromium-rich oxide forms in both environments. Chromate formation and alloy chlorination are shown to initiate the formation of non-protective oxide scales. In addition, aluminium nitrides form in the alloy substrate in both environments.