AES depth profiling of passive overlayers formed on nickel alloys

Abstract

Depth profiling analysis of passive films grown on the surface of two nickel-based alloys (Inconel 600 and Hastelloy C4) in NaCl media was carried out using Auger electron spectroscopy (Am) aod ioo sputtering. Improvement to the sequeotid sputtering model of HofmaM (1976) should be performed when preferential sputtering occurs, especially in Mwxmtaining alloys. In this way, the kinetic model of preferential sputtering of Ho et ul. (1976) was extended to the case of ternary alloys. However, concentration gradients created by the electrochemical treatment in the metallic layers below the oxidized 6lm make it unsuitable. Passive layers (5-11 monolayers) mainly consist of chromium oxide, always located at the film-alloy interface. A layered depth distribution of oxidized species is generally observed: in Inconel, chromium oxide is successively covered with iron and nickel oxides; in Hastelloy, chromium oxide is covered with nickel oxide (only very few molybdenum atoms are depicted in these films). Increasing the passivation potential, the temperature or the NaCI concentration slightly enhances the nickel oxide amounts in the film, its thickness and the external chloride contents.

Passive and transpassive films formed on a nickel alloy in ammoniacal solution

“…This can be explained by preferential sputtering of Ni and Cr as also observed by Lorang et al for Hastelloy C4 and Mischler et al for Fe-Cr-Mo alloys. [21,23] However, previous work has also demonstrated that the kinetic order of dissolution is Mo<Ni<Cr at −0.46 V and Mo∼Cr Ni at −0.21 V in this particular ammoniacal test solution. [6] The surface layer enrichment in Mo may also be explained from this perspective.…”

“…The carbon intensity measured on the Hastelloy C4 was negligible within www.interscience.wiley.com/journal/sia approximately 25 monolayers or 6 nm of the surface. [21] Assuming similar contamination on alloy 625 we could approximate 6 nm of depth penetration after 360 s in our work (Fig. 6).…”

“…[16,21,22] According to the calculated sputter rate, the penetration depths in Figs 6 and 7 would correspond to approximately 30 and 60 nm, respectively. The oxygen concentrations shown in Figs 6 and 7 are extremely low even before depth profiling.…”

“…A qualitative approximation of the sputter rate can be made by comparison of the carbon penetration measured in this work with that measured by Lorang et al on a similar alloy, Hastelloy C4 (UNS N06455: Ni-16Cr-15Mo-3Fe-2Co), in 5 M NaCl solution after 2 h at 0 V SHE. [21] These authors cleaned and stored their sample before AES using the same methodology employed in this work. The carbon intensity measured on the Hastelloy C4 was negligible within www.interscience.wiley.com/journal/sia approximately 25 monolayers or 6 nm of the surface.…”

“…min −1 which is within the range reported by others through either calibration or model fitting for similar materials under similar sputtering conditions. [21,22] After 400 s of sputtering neither sample contained significant oxygen at the obtained depth: thus the oxide can be considered to be less than 7 nm thick. This oxide thickness is within 1 or 2 nm of those reported by Jabs et al for Ni-Cr alloys in NaOH, Boudin et al…”