Thin Solid Films 415 (2002) 258–265 0040-6090/02/$ - see front matter  2002 Elsevier Science B.V. All rights reserved. PII: S0040-6090 Ž 02 . 00359-0 Surface modification of ion-implanted AISI 304 stainless steel after oxidation process: X-ray absorption spectroscopy analysis F.J. Perez *, A. Gutierrez , M.F. Lopez , M.P. Hierro , F. Pedraza a, b c a a ´ ´ Universidad Complutense de Madrid. Departamento CC Materiales, 28040 Madrid, Spain a Universidad Autonoma de Madrid. Dpto Fısica Aplicada. Cantoblanco. 28049, Madrid, Spain b ´ ´ Consejo Superior de Investigaciones Cientıficas. Instituto de Ciencia de Materiales de Madrid. Dpto. Fısica e Ingenierıa de Superficies. c ´ ´ ´ Cantoblanco 28049-Madrid, Spain Received 29 November 2001; received in revised form 20 February 2002; accepted 11 April 2002 Abstract The influence of implanted Si, Mo and Ce vs. the as-received austenitic AISI 304 stainless steel has been studied after isothermal oxidation in air at 900 8C for 32 h. The oxide layer formed was characterised by means of conventional X-ray diffraction, scanning electron microscopyyenergy-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 Ce 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.  2002 Elsevier Science B.V. All rights reserved. Keywords: Ion implantation; Oxidation; X-Ray absorption; X-Ray diffraction 1. Introduction Alloy steels with adequate high-temperature strength, such as those commonly employed in petrochemical or electric power plants, etc., have poor oxidation, sulfi- dation and hot corrosion resistance w1x. Steels designed to withstand these oxidising or sulfidising environments rely on the formation of Cr O or Al O scales w2–4x. 2 3 2 3 Specifically, the finishing sections of the tubing and the pipes that take steam to the high-pressure turbine in fossil-fuel-fired boilers are typically manufactured either in Cr–Mo ferritic steels or in the austenitic AISI 304 stainless steel w5x. These stainless steels are designed to develop a protective Cr O oxide scale upon oxidising 2 3 conditions up to approximately 900 8C, at which tem- perature further oxidation into volatile CrO species 3 takes place w6x. *Corresponding author. Tel.: q34-91-394-4215; fax: q34-91-394- 4357. E-mail address: fjperez@eucmos.sim.ucm.es (F.J. Perez). ´ One of the current trends (in research and production) is to slightly modify the surface of different metals and alloys in order to take advantage of their known manu- facturing techniques. Ion implantation offers the unique possibility to introduce a controlled concentration of an element to a thin surface layer. In addition, this tech- nique induces changes in the surface due to radiation damage w7–9x without changing the original dimensions of the part to be treated. Small amounts of the so-called reactive elements (RE) added to the outer surface of the metals, and alloys have been reported to decrease the oxidation rate and improve the scale adherence w10,11x, leading to an overall beneficial effect. The successful application of surface modification techniques also involves characterisation of the implant. To investigate the influence of ion implantation on the oxidation behaviour of AISI 304 stainless steel, it is important to evaluate the chemical composition of the oxide layer formed at high temperature. Due to the thickness of this outer layer, one of the most appropriate