ELECTROCHEMICAL CHARACTERISTICS OF FE-CR ALLOY THIN-FILMS PREPARED BYION-BEAM-SPUTTER DEPOSITION

A series of Fe-Cr alloy thin films having various Cr contents (11-34 m ass%) and thicknesses (60-550 nm) were prepared by ion-beam-sputter (I BS) deposition. The structure of the films was examined by transmissio n electron microscopy (TEM), electron diffraction (ED), glancing angle incidence X-ray diffraction (GIXRD), and atomic force microscopy (AFM ). The anodic polarization curves of IBS-Fe-Cr alloy films mere measur ed in 1 kmol.m(-3) Na2SO4 (pH 3.0), 1 kmol.m(-3) HCl (pH 0.0) and 1 km ol.m(-3) NaCl (pH 5.8) at 298 K, and then compared with those of vacuu m-indudion-melted (VIM) Fe-Cr alloys containing 10-25 mass%Cr. TEM ima ges and ED patterns of IBS-Fe-Cr alloy films indicated that the films consist of equiaxial bcc microcrystals with an average grain size of a pproximately 30 nn. The root-mean-square roughness value estimated fro m AFM images of IBS-Fe-Cr alloy films increases from 0.36 nm for a fil m 60 nm thick to 0.77 nm for a film 550 nm thick with increasing sim t hickness. This suggests that the surface microroughness becomes large as the film thickness increases. The critical passivation current dens ity, i(crit), of IBS-Fe-Cr alloy films in 1 kmol.m(-3) Na2SO4 (pH 3.0) is lower than that of VIM-Fe-Cr alloys: the value of i(crit) for an I BS-Fe-12Cr alloy film 140 nm thick is less than that for a VIM-Fe-14Cr alloy by a factor of about 100. The value of i(crit) for IBS-Fe-18Cr alloy films increases with increasing film thickness in the range of 6 0-550 nm, while it never exceeds that for a VIM-Fe-18Cr alloy. The IBS -Fe-21Cr alloy film 90 nm thick covered with a native oxide film does not show spontaneous activation in 1 kmol.m(-3) HCl under the open cir cuit condition. The alloy film never develops pitting under the subseq uent anodic polarization in 1 kmol.m(-3) HCl and 1 kmol.m(-3) NaCl.