Complementary use of electrochemical testing techniques to study corrosion processes of HVOF Inconel 625, CoNiCrAIY and WCCoCr coatings
Niaz, Akbar (2013) Complementary use of electrochemical testing techniques to study corrosion processes of HVOF Inconel 625, CoNiCrAIY and WCCoCr coatings. PhD thesis, University of Nottingham.
The purpose of coating is to get a blend of unique properties at low cost which is not possible from other manufacturing processes. High velocity oxygen fuel (HVOF) is one of the most commonly used thermal spraying processes to produce wear and corrosion resistant coatings. Alongside wear and corrosion resistant properties the HVOF thermally sprayed coating process also induces microstructural heterogeneities which decreased the corrosion resistant properties. Considerable research has been reported on corrosion testing of the HVOF sprayed coatings by using electrochemical techniques. Some electrochemical techniques give area average results whilst other allows the effect of different features to be determined. The complementary use of basic electrochemical techniques with more advance techniques is missing in most of the previous research. In this research work potentiodynamic polarization testing, electrochemical impedance spectroscopy and scanning electrochemical microscopy were used to see if the combined results could provide a broader picture of corrosion processes taking place at HVOF coatings. Three HVOF coatings of different microstructural complexity i.e. γ-phase Inconel 625, γ + β-phase CoNiCrAlY and WC-CoCr cermet coating were tested.
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