Electrochemical corrosion behaviour of ion-beam-mixed Fe-Al alloy: A conversion electron Moessbauer spectroscopic study

The electrochemical corrosion behaviour of ion-beam-mixed Fe-Al composites has been studied by using the technique of interface-sensitive conversion electron Moessbauer spectroscopy (CEMS). Polycrystalline aluminium foils deposited with a film 50 A thick of the 57Fe Moessbauer isotope and an overlayer 250 A thick of natural iron have been bombarded with 100 keV Ar+ ions at a dose in the range of about (1-3) x 1016 ions cm-2 to induce atomic mixing at the interface. A number of as-deposited and ion-beam-mixed composites have been subjected to electrochemical corrosion treatment in a buffer solution by employing the three-sweep potentiokinetic polarization technique. It has been shown that the atomically mixed interface region exhibits corrosion behaviour considerably different from that exhibited by either iron or aluminium foils. The as-deposited as well as the ion-beam-mixed composites have been characterized by 57Fe CEMS prior to the corrosive attack and after passivation so as to identify the structural state of the interface and the transformations occurring in the interface as a result of the corrosive reactions. The standard Moessbauer fitting procedure was used in conjunction with a method of obtaining hyperfine field distributions to establish that the corrosive action of the aqueous medium on the ion-beam-mixed Fe-Al composite leads to the elimination of the magnetic spectral components and to the growth of passive non-magnetic phases such as β-γ-FeOOH and FeO. (orig.)