Comparative study of the pitting corrosion resistance, passivation behavior and metastable pitting activity of NO7718, NO7208 and 439L super alloys in chloride/sulphate media

Loto, R. T. (2019) Comparative study of the pitting corrosion resistance, passivation behavior and metastable pitting activity of NO7718, NO7208 and 439L super alloys in chloride/sulphate media. journals of materials research and technology, 8 (1). pp. 623-629.

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Abstract

Comparative study of the corrosion resistance and passivation characteristics of NO7718,NO7208 and SS439L super alloys in 4 M H2SO4media at 0–6% NaCl concentration was doneby potentiodynamic polarization, open circuit potential measurement and optical micro-scopic analysis. The metal alloys showed relatively high resistance to corrosion as variationin Cl−ion concentration had no significant influence on their corrosion rate results. SS439Lshowed the weakest resistance to pitting despite its relatively low corrosion rate. Passi-vation behavior disappeared after 2% NaCl concentration. NO7208 displayed exceptionalpitting resistance characteristics, however, its metastable pitting and repassivation domainresponds to changes in Cl−ion concentration. The passivation domain of NO7718 signif-icantly decreased with increase in Cl−ion concentration due to delayed repassivation ofthe protective film after metastable pitting. NaCl concentration caused significant negativeshift in open circuit potential (OCP) for NO7718 and SS439L alloys, compared to NO7208.The OCP of NO7208 at comparatively positive values contrasts those of NO7718 and SS439Lalloys. Micro analytical studies shows a highly corrosion resistant morphology for NO7208with numerous macro-pits present but their effect on the overall corrosion resistance of thenickel alloy is negligible. The corrosion pits on SS439L coupled with the appearance of grainboundaries are deleterious to the overall viability of the alloy. Enlarged corrosion pits arepresent on NO7718 due to the action of Cl−ions.

Item Type:	Article
Uncontrolled Keywords:	Corrosion Pitting Passivation Alloy
Subjects:	T Technology > T Technology (General) T Technology > TJ Mechanical engineering and machinery
Divisions:	Faculty of Engineering, Science and Mathematics > School of Engineering Sciences
Depositing User:	Mrs Hannah Akinwumi
Date Deposited:	02 Jul 2019 10:20
Last Modified:	02 Jul 2019 10:20
URI:	http://eprints.covenantuniversity.edu.ng/id/eprint/12786

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