Fundamental understanding of the corrosion mechanism of aluminium based quasicrystalline alloys

Ewa Ura-Bińczyk

Abstract

The quasicrystalline approximants (QA), which belong to a group of complex metallic alloys (CMA), are promising candidates for corrosion protection of aluminium parts. For such an application, a fundamental understanding and knowledge about corrosion behaviour is of key importance. In this PhD thesis, the resistance to uniform and localized corrosion of two QAs, namely Al65Cr27Fe8 and Al67Cu12Fe10Cr10, has been investigated. Microstructural characterization of both alloys was carried out using SEM, EDS, XRF and XRD techniques. The electrochemical behaviour was studied in aqueous solutions over a wide range of pH from 0 to 14 with a special focus on the surface stability and passivation mechanism. The resistance to localized attack was investigated in the presence of chloride ions. To determine corrosion resistance, a number of electrochemical techniques were used: potentiodynamic and potentiostatic polarization, electrochemical impedance spectroscopy (EIS) and a microelectrochemical method. The surface stability and dissolution rate of the alloying elements in highly acidic and alkaline solutions were examined using very sensitive methods: inductively coupled plasma–mass spectroscopy (ICP-MS) and inductively coupled plasma– optical emission spectroscopy (ICP-OES). X-ray photoelectron spectroscopy (XPS) combined with ion etching was applied to determine the chemical composition and structure of the passive oxides. The obtained results revealed the formation and remarkable thermodynamic stability of the passive film on AlCrFe QA over a whole range of pH. In the case of AlCuFeCr QA, the passivation process takes place in a narrower pH range and the stability and protective properties of the passive film are significantly lower in acidic and highly alkaline solutions. The excellent corrosion resistance of AlCrFe was attributed to the Cr enrichment of the outermost layer of the passive film and its interaction with Al oxi-hydroxide. The lower resistance to corrosion of AlCuFeCr alloy was attributed to the lower Cr content which was sufficient to stabilize the surface upon anodizing but not guaranteeing chemical stability of the passive film surface. It was also found that Cu represents an additional corrosion acceleration factors when active dissolution and subsequent deposition occur. In terms of resistance to localized corrosion, the microcell measurements revealed a high resistance to localized attack of pure Al65Cr27Fe8 and Al67Cu12Fe10Cr10 QA phases similar to that of 316LVM stainless steel.
Diploma typeDoctor of Philosophy
Author Ewa Ura-Bińczyk (FMSE / DMD)
Ewa Ura-Bińczyk,,
- Division of Materials Design
Title in EnglishFundamental understanding of the corrosion mechanism of aluminium based quasicrystalline alloys
Languageen angielski
Certifying UnitFaculty of Materials Science and Engineering (FMSE)
Disciplinematerial sciences and engineering / (technology domain) / (technological sciences)
Defense Date03-12-2001
Supervisor Małgorzata Lewandowska (FMSE / DMD)
Małgorzata Lewandowska,,
- Division of Materials Design

Patrick Schmutz
Patrick Schmutz,,
-

Internal reviewers Tadeusz Wierzchoń (FMSE / DSE)
Tadeusz Wierzchoń,,
- Division of Surface Engineering
External reviewers Jacek Banaś - [AGH University of Science and Technology (AGH)]
Jacek Banaś,,
-
- Akademia Górniczo-Hutnicza im. Stanisława Staszica w Krakowie
Pages109
Keywords in Englishxxx
Abstract in EnglishThe quasicrystalline approximants (QA), which belong to a group of complex metallic alloys (CMA), are promising candidates for corrosion protection of aluminium parts. For such an application, a fundamental understanding and knowledge about corrosion behaviour is of key importance. In this PhD thesis, the resistance to uniform and localized corrosion of two QAs, namely Al65Cr27Fe8 and Al67Cu12Fe10Cr10, has been investigated. Microstructural characterization of both alloys was carried out using SEM, EDS, XRF and XRD techniques. The electrochemical behaviour was studied in aqueous solutions over a wide range of pH from 0 to 14 with a special focus on the surface stability and passivation mechanism. The resistance to localized attack was investigated in the presence of chloride ions. To determine corrosion resistance, a number of electrochemical techniques were used: potentiodynamic and potentiostatic polarization, electrochemical impedance spectroscopy (EIS) and a microelectrochemical method. The surface stability and dissolution rate of the alloying elements in highly acidic and alkaline solutions were examined using very sensitive methods: inductively coupled plasma–mass spectroscopy (ICP-MS) and inductively coupled plasma– optical emission spectroscopy (ICP-OES). X-ray photoelectron spectroscopy (XPS) combined with ion etching was applied to determine the chemical composition and structure of the passive oxides. The obtained results revealed the formation and remarkable thermodynamic stability of the passive film on AlCrFe QA over a whole range of pH. In the case of AlCuFeCr QA, the passivation process takes place in a narrower pH range and the stability and protective properties of the passive film are significantly lower in acidic and highly alkaline solutions. The excellent corrosion resistance of AlCrFe was attributed to the Cr enrichment of the outermost layer of the passive film and its interaction with Al oxi-hydroxide. The lower resistance to corrosion of AlCuFeCr alloy was attributed to the lower Cr content which was sufficient to stabilize the surface upon anodizing but not guaranteeing chemical stability of the passive film surface. It was also found that Cu represents an additional corrosion acceleration factors when active dissolution and subsequent deposition occur. In terms of resistance to localized corrosion, the microcell measurements revealed a high resistance to localized attack of pure Al65Cr27Fe8 and Al67Cu12Fe10Cr10 QA phases similar to that of 316LVM stainless steel.
Thesis file
Ura-Binczyk.pdf 6.45 MB

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