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Analysing corrosion resistance of hardfacing alloys using electrochemical impedance spectroscopy (EIS)

Krishnan, Radhesh (2015). Analysing corrosion resistance of hardfacing alloys using electrochemical impedance spectroscopy (EIS). Bachelor of Engineering (4th Year Project) Thesis, Charles Darwin University.

Document type: Thesis
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Author Krishnan, Radhesh
Title Analysing corrosion resistance of hardfacing alloys using electrochemical impedance spectroscopy (EIS)
Institution Charles Darwin University
Publication Date 2015
Thesis Type Bachelor of Engineering (4th Year Project)
Subjects ENGINEERING
0904 - Chemical Engineering
Abstract In this thesis, the corrosion behaviour of hardfacing alloys was investigated. Widely used hardfacing alloys in the industry are based on chromium carbides. These hardfacing alloys are not only used in conditions where good wear resistance is required but also in corrosive environments. In these alloys, chromium provides good corrosion resistance and the carbides provide good hardness. Chromium carbides remove chromium in solution thus rendering them susceptible to corrosion. Because of this combination it is unclear whether these alloys are able to form a passive film. This will be tested in the thesis.

Electrochemical Impedance Spectroscopy (EIS) is a method of applying an AC signal with an amplitude of 10mV at various frequencies and analysing the impedance response of a sample using Bode and Nyquist plots. EIS was used to analyse the corrosion behaviour of hardfacing alloys. Testing was conducted at rest potential and passive potential in a solution of 2M NaOH with a pH of 14 to simulate alumina industry conditions. Results were gathered for the electrochemical properties of each sample before and after 24 hours of soak. The data is interpreted by developing Bode and Nyquist plots. A high value of resistance and a low value of capacitance indicate high corrosion resistance or a passive film.

Testing conducted in this thesis indicates that it is very difficult to identify passive behaviour with the samples using EIS. However, the results did show which sample had the best corrosion resistance. The sample which contained the highest amount of chromium and carbon in the matrix had the highest corrosion resistance. This sample had the smallest change in resistance compared to the other samples over 24 hours when testing was conducted at rest potential and passive potential. However, it is not conclusive whether chromium content affects the corrosion resistance of a sample without further testing being conducted. There is great promise in the use of EIS as a testing method for analysing corrosion behaviour once refinements have been made to the testing process to make it more accurate.
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Created: Tue, 24 Nov 2015, 15:04:09 CST by Jessie Ng