Surface modification of ion-implanted AISI 304 stainless steel after oxidation process:: X-ray absorption spectroscopy analysis

The influence of implanted Si, Mo and Cc vs. the as-received austenitic AISI 304 stainless steel has been studied after isothermal oxidation in air at 900 degreesC for 32 It. The oxide layer formed was characterised by means of conventional X-ray diffraction, scanning electron microscopy/energy-dispersion spectroscopy and X-ray absorption spectroscopy (XAS) techniques. The projected ranges of the implantation were calculated using the TRIM code. The results obtained by the most sensitive technique, XAS, show slight differences in the chemical composition of the oxide layer of the different ion-implanted samples. However, these chemical differences could determine a threshold between acceptable and non-acceptable oxidation behaviour. The evolution of the chemical composition from the oxide-metal interface to the oxide surface has also been studied. XAS spectra show that Cu diffusion is favoured in the oxide layer for the non-implanted sample, which does not occur for implanted samples. Both Si and Cc ion implantation promotes active diffusion of Cr and Mn from the parent steel to form a protective oxide layer, whereas Mo implantation induces major participation of Fe in the oxide scale. This may have been caused because of volatilisation of molybdenum oxides. (C) 2002 Elsevier Science B.V. All rights reserved.