Metal dusting of binary iron aluminium alloys at 600°C

In this work experiments on metal dusting of binary iron aluminium alloys with 15, 26 and 40 at.% Al were performed in strongly carburising CO-H-2-H2O gas mixtures at 600 degrees C. The mass gain kinetics was measured using thermogravimetric analysis (TGA). The carburised samples were characterised by means of light optical microscopy (LOM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). It was found that the mass gain kinetics depends on the CO content of the gas mixtures and on the Al content of the alloys. With decreasing carbon activity the carburisation reaction kinetics decreases and the onset of metal dusting is retarded for increasing time periods. With increasing Al content of the alloys the carburisation reaction is slower and metal dusting sets on at later times. The samples were not pre-treated for the formation of a protective oxide scale. By X-ray Photoelectron Spectroscopy (XPS) analyses of the carburised iron aluminium samples it was found that the formation of Al2O3 layers has taken place in the CO-H-2-H2O gas atmospheres. Needle- or plate-like kappa-phase (Fe3AlCx) precipitates close to the surface of the carburised Fc-15Al sample were detected by means of XRD and LOM. The coke on top of the carburised samples mainly consists of filamentous carbon with metal particles at their tips.