Understanding passive film degradation and its effect on hydrogen embrittlement of super duplex stainless steel – Synchrotron X-ray and electrochemical measurements combined with CalPhaD and ab-initio computational studies

• Published in: Applied surface science Vol. 628; p. 157364
• Main Authors: Örnek, Cem, Zhang, Fan, Larsson, Alfred, Mansoor, Mubashir, Harlow, Gary S., Kroll, Robin, Carlà, Francesco, Hussain, Hadeel, Engelberg, Dirk L., Derin, Bora, Pan, Jinshan
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15-08-2023
• Subjects: Ab-initio density-functional theory; Cathodic polarization; Condensed Matter Physics; Den kondenserade materiens fysik; FactSage thermodynamics; Fysik; Hydrogen embrittlement; Natural Sciences; Naturvetenskap; Passive film; Physical Sciences; Super duplex stainless steel; Rct; C; HAXPES; PAW; GGA-PBE; Cathodic polarization; M-S; Passive film; DFT; SDSS; Ab-initio density-functional theory; XRR; Hydrogen embrittlement; Rs; GIXRD; DSS; Super duplex stainless steel; EIS; FactSage thermodynamics; HER; HAXPEEM; SCF; CPE; HE; OCP; SP-DFT
• ISSN: 0169-4332; 1873-5584; 1873-5584
• DOI: 10.1016/j.apsusc.2023.157364

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•Electrochemically generated hydrogen produces defects in the passive film.•The surface oxide degrades by defect generation, followed by phase decomposition and removal.•Surface degradation occurs most when the passive film’s electronic structure inverts from n-type to p-type.•Oxide removal by cathodic polarization does not happen immediately and requires energy and time.•The passive film provides an effective barrier against hydrogen embrittlement.
The passive film stability on stainless steel can be affected by hydrogen absorption and lead to microstructure embrittlement. This work shows that the absorption of hydrogen results in surface degradation due to oxide reduction and ionic defect generation within the passive film, which decomposes and eventually vanishes. The passive film provides a barrier to entering hydrogen, but when hydrogen is formed, atomic hydrogen infuses into the lattices of the austenite and ferrite phases, causing strain evolution, as shown by synchrotron x-ray diffraction data. The vacancy concentration and hence the strains increase with increasing electrochemical cathodic polarization. Under cathodic polarization, the surface oxides are thermodynamically unstable, but the complete reduction is kinetically restrained. As a result, surface oxides remain present under excessive cathodic polarization, contesting the classical assumption that oxides are easily removed. Density-functional theory calculations have shown that the degradation of the passive film is a reduction sequence of iron and chromium oxide, which causes thinning and change of the semiconductor properties of the passive film from n-type to p-type. As a result, the surface loses its passivity after long cathodic polarization and becomes only a weak barrier to hydrogen absorption and hence hydrogen embrittlement.