Electrochemical and microgravimetric characterization of magnetron-sputtered Fe-Cr-Ni-Ta and Fe-Cr-Ni alloy films in neutral and strongly acidic media

The Fe-Cr-Ni and Fe-Cr-Ni-Ta alloy films were deposited on quartz substrate s by magnetron-sputtering using targets of AISI 316 stainless steel and in combination with pure tantalum. The conventional melting of the Fe Cr Ni Ta alloy formed is virtually impossible because the melting point of tantalum is higher than the boiling points of the other components, Elemental conte nt of the films was determined by XPS analysis. Corrosion behaviour of both alloy films was studied in 5% NaCl and 10 M HCl by electrochemical quartz crystal microgravimetry (EQCM), electrochemical impedance spectroscopy (EIS ) and dc-voltammetry. The corrosion resistance of Fe-Cr-Ni-Ta appeared to b e significantly higher than that of Fe-Cr-Ni in both neutral (5% NaCl) and strongly acidic (10 M HCl) media. The Fe-Cr-Ni-Ta specimen exhibited an ext remely high corrosion resistance in 10 M HCl, where the corrosion rates wer e about one order of magnitude lower than those of Fe-Cr-Ni in neutral solu tion. EQCM measurements in NaCl solution indicated accumulation of corrosio n products on the Fe-Cr-Ni-Ta surface, which was evident from a distinctive increase in electrode mass, By contrast, the mass of the tantalum-free all oy film decreased with a constant rate, which indicated alloy dissolution t o prevail. The corrosion current calculated from the mass decrease was in g ood agreement with that derived from voltammetric measurements. The EQCM da ta showed that the corrosion resistance of the Fe-Cr-Ni-Ta alloy film in 10 M HCl was about two orders of magnitude higher than that of the Fe-Cr-Ni. (C) 2001 Elsevier Science BN, All rights reserved.