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Nature of current increase for a CoCrMo alloy: "transpassive" dissolution vs. water oxidation
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.ORCID iD: 0000-0002-9453-1333
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.ORCID iD: 0000-0002-4431-0671
2013 (English)In: International Journal of Electrochemical Science, ISSN 1452-3981, E-ISSN 1452-3981, Vol. 8, no 10, 11791-11804 p.Article in journal (Refereed) Published
Abstract [en]

The “transpassive” behavior of a CoCrMo alloy has been investigated to clarify the nature of the current increase at high anodic potential (0.5-0.7 VAg/AgCl). The total amount of released metal ions was determined after the potentiostatic measurements. According to the calculation through Faradays’ law, the metal dissolution only contributes to part of the total current recorded. Electrochemical AFM mapping did not show pronounced topography changes at 0.65 VAg/AgCl, while light optical microscopy observation revealed fast evolution of oxygen bubbles. Evidently water oxidation is another important process largely contributing to the current increase at the high potential.

Place, publisher, year, edition, pages
2013. Vol. 8, no 10, 11791-11804 p.
Keyword [en]
CoCrMo alloy, transpassivity, metal dissolution, water oxidation, AFM
National Category
Corrosion Engineering
Identifiers
URN: urn:nbn:se:kth:diva-129348ISI: 000326501800012Scopus ID: 2-s2.0-84886479232OAI: oai:DiVA.org:kth-129348DiVA: diva2:651791
Note

QC 20131203

Available from: 2013-09-27 Created: 2013-09-27 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Influence of carbides and nitrides on corrosion initiation of advanced alloys: A local probing study
Open this publication in new window or tab >>Influence of carbides and nitrides on corrosion initiation of advanced alloys: A local probing study
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Advanced alloys often present precipitated carbides and nitrides in their microstructure following exposure to elevated temperatures. These secondary phases are usually undesirable, because potentially deleterious for the corrosion and mechanical performances of the material. Carbides and nitrides are enriched in key alloying elements that are subtracted from their surrounding matrix areas, creating alloying element depleted zones, which might become initial sites for corrosion initiation. In this study, the influence of micro- and nano-sized precipitated carbides and nitrides on the corrosion initiation of biomedical CoCrMo alloys and duplex stainless steels has been investigated at microscopic scale, by using a combination of local probing techniques. The microstructures of the alloys were first characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and magnetic force microscopy (MFM). The Volta potential mapping of carbides and nitrides revealed their higher nobility compared to the matrix, and particularly compared to their surrounding areas, suggesting the occurrence of some alloying element depletion in the latter locations, which may lead to a higher susceptibility for corrosion initiation. In-situ electrochemical AFM studies performed at room temperature showed passive behavior for large potential ranges for both alloy families, despite the presence of the precipitated carbides or nitrides. At high anodic applied potential, at which transpassive dissolution occurs, preferential dissolution started from the areas adjacent to the precipitated carbides and nitrides, in accordance with the Volta potential results. Thus, the presence of carbides and nitrides doesn’t largely affect the corrosion resistance of the tested advanced alloys, which maintain passive behavior when exposed to highly concentrated chloride solutions at room temperature with no applied potential. The effect of nitrides on the corrosion initiation of duplex stainless steels was investigated also at temperatures above the critical pitting temperature (CPT). Depending on the type, distribution and size range of the precipitated nitrides different corrosion behaviors were observed. Intragranular (quenched-in) nano-sized nitrides (ca. 50-100 nm) finely dispersed in the ferrite grains have a minor influence on the corrosion resistance of the material at temperatures above the CPT, while larger intergranular (isothermal) nitrides (ca. 80-250 nm) precipitated along the phase boundaries cause a detrimental reduction of the corrosion resistance of the material, in particular of the austenite phase

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. xiv, 59 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2013:34
Keyword
carbides, nitrides, microstructure, CoCrMo alloys, duplex stainless steels, localized corrosion, transpassive dissoluti on, elemental depletion, AFM, TEM, SEM.
National Category
Corrosion Engineering
Identifiers
urn:nbn:se:kth:diva-129356 (URN)978-91-7501-841-6 (ISBN)
Public defence
2013-10-18, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20130927

Available from: 2013-09-27 Created: 2013-09-27 Last updated: 2013-09-27Bibliographically approved

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