Passive film characterisation of duplex stainless steel using scanning Kelvin probe force microscopy in combination with electrochemical measurements

Abstract

The characterisation of passive oxide films on heterogeneous microstructures is needed to assess local degradation (corrosion, cracking) in aggressive environments. The Volta potential is a surface-sensitive parameter which can be used to assess the surface nobility and hence passive films. In this work, it is shown that the Volta potential, measured on super duplex stainless steel by scanning Kelvin probe force microscopy, correlates with the electrochemical properties of the passive film, measured by electrochemical impedance spectroscopy and potentiodynamic polarisation. Natural oxidation by ageing in ambient air as well as artificial oxidation by immersion in concentrated nitric acid improved the nobility, both reflected by increased Volta potentials and electrochemical parameters. Passivation was associated with vanishing of the inherent Volta potential difference between the ferrite and austenite, thereby reducing the galvanic coupling and hence improving the corrosion resistance of the material. Hydrogen-passive film interactions, triggered by cathodic polarisation, however, largely increased the Volta potential difference between the phases, resulting in loss of electrochemical nobility, with the ferrite being more affected than the austenite. A correlative approach of using the Volta potential in conjunction with electrochemical data has been introduced to characterise the nobility of passive films in global and local scale.

Characterization of Native Oxide and Passive Film on Austenite/Ferrite Phases of Duplex Stainless Steel Using Synchrotron HAXPEEM

“…Using this approach, it is possible to correlate the chemical information of the passive film as well as its changes caused by the electrochemical reactions (anodic oxide growth and/or dissolution) to the microstructural features, e.g., individual phases or even grains of the duplex stainless steel. Such knowledge will provide a scientific explanation for the experimental observations of the difference in the relative nobility and the selective dissolution of specific phases, 18,[23][24][25][26][27][28] thus contribute to a fundamental understanding of the corrosion mechanism of such alloys. Since advanced multicomponents alloys used today possess multi-phase microstructures, this method is valuable in the study of localized corrosion behavior of the alloys.…”

Swelling of Steel Film by Hydrogen Absorption at Cathodic Potential in Electrolyte

“…Metals and metallic alloys in electrolyte such as sea water suffer from galvanic corrosion caused by a gradient of the electrochemical potential between cathodic and anodic regions . In case of composite materials or alloys, such gradients arise also locally, even on the microscopic scale, because of the different nobilities, i.e., electrochemical potential of the contained elements/materials (see e.g., the study by Örnek et al). Exposed to electrolyte, local variations in nobility, i.e., variations in the electrochemical potentials, cause local potential differences, giving rise to local cathodic and anodic reactions and thus localized corrosion processes …”

Effect of Fibers on Durability of Concrete: A Practical Review

“…Corrosion is an electrochemical process in which the charge (electrons and ions) flow from the anode to the cathode. In general, a passive film forms spontaneously on the steel surface in the alkaline environment of hydrating concrete [ 33 ], protecting it from corrosion. However, this passive film can break down due to chloride ingress [ 34 , 35 ] or carbonation [ 36 , 37 ], leading to active corrosion [ 38 , 39 , 40 ].…”