Combined XPS / TEM study of the chemical composition and structure of the passive film formed on additive manufactured 17-4PH stainless steel

Abstract

Combined XPS / TEM study of the chemical composition and structure of the passive film formed on additive manufactured 17-4PH stainless steel. (2021) Surfaces and Interfaces, 22. 100874.

Electrochemical impedance spectroscopy study of the passive film for laser-beam-melted 17-4PH stainless steel

“…Those higher capacitance values for the conventional samples led to thickness values δ that were lower as compared to LBM samples. This result was in agreement with our previous results obtained by using both XPS and TEM [24]. Slight differences were noticeable, however, between the three sets of δ values: 3.9 and 4.4 nm from XPS calculations, 2.4 ± 0.1 nm and 3.0 ± 0.1 nm from TEM measurements [24] and ~ 1.1 nm and ~ 1.3 nm from EIS data fitting for conventional and LBM MSSs, respectively (Table 2).…”

“…This result was in agreement with our previous results obtained by using both XPS and TEM [24]. Slight differences were noticeable, however, between the three sets of δ values: 3.9 and 4.4 nm from XPS calculations, 2.4 ± 0.1 nm and 3.0 ± 0.1 nm from TEM measurements [24] and ~ 1.1 nm and ~ 1.3 nm from EIS data fitting for conventional and LBM MSSs, respectively (Table 2). The values given here from EIS data fitting are mean values calculated from the three δ values given in Table 2 for both LBM and conventional samples.…”

“…It was worth noting that, if the dielectric constant had a value of 25, as was reported by Revilla et al [11], about the same thickness would be obtained by EIS and TEM. Nevertheless, we showed in previous study [24] that the differences in microstructure between the LBM and conventional samples led to the formation of a two-layer structure for the passive films formed on both the conventional and LBM steels with, as previously reminded, differences in thickness, but also in chemical composition. Differences in compositional gradient in the passive film were shown, in particular concerning Cr distribution in both the inner and outer oxide layers [24].…”

“…The layers were assumed to be homogeneous in a plane parallel to the sample surface. This constituted a simplifying hypothesis if we refer to our previous work [24]. Indeed, we showed, first, that the passive film formed on NbCs was different from this one formed on the martensitic matrix, which was true for both MSSs.…”

“…We showed that LBM 17-4PH MSS had more noble pitting potentials, which was related to smaller niobium cai• bides (NbCs) acting as preferential pitting sites, as compared to conventional MSS. In another study [24], we perfo1med a combined X-ray photoelectron (XPS) spectroscopy and transmission electron microscopy (TEM) study of the passive films fom1ed on both the LBM and conventional 17-4PH…”