RESEARCH ARTICLE


High Temperature Corrosion Resistance of Pt-Based Superalloys in 0.2% SO2-N2 Gas



Johannes H. Potgieter*, Nthabiseng B. Maledi
NRF/DST Centre of Excellence in Strong Materials, School of Chemical and Metallurgical Engineering, University of the Witwatersrand, Private Bag 3, WITS, 2050, South Africa.


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© 2014 Potgieter and Maledi;

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: https://creativecommons.org/licenses/by/4.0/legalcode. This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

* Address correspondence to this author at the NRF/DST Centre of Excellence in Strong Materials, School of Chemical and Metallurgical Engineering, University of the Witwatersrand, Private Bag 3, WITS, 2050, South Africa.


Abstract

Pt-based superalloys are a new generation of materials intended to be used in various high temperature applications. Effluent gases emitted to the environment during combustion operations can lead to degradation of high temperature materials with deleterious effects on mechanical integrity and the corrosion of alloys. This paper focuses on sulphidation of one quaternary, and four ternary, Pt-based superalloys of various chemical compositions. Pt-based superalloys were exposed at 900°C in a reducing environment. The alloys were compared to coated and uncoated Ni-based superalloys (NBSAs). X-Ray diffraction (XRD), Scanning electron microscopy (SEM) and Raman spectroscopy were used to characterize corrosion products that formed. The Pt-based superalloys exhibited higher corrosion resistance than NBSAs as a result of the formation of a protective Al2O3 scale, whereas NBSAs suffered internal sulphidation and formed Cr and Ni sulphide corrosion compounds. The formation of brittle needle-like phases and the transformation of the NiAl phase to Ni3Al, led to early failure of the coated alloy. Pt-based superalloys alloyed with Co showed poor corrosion resistance as a result of depletion of alloying elements.

Keywords: Alumina, chromium, corrosion, high temperature, metals, NBSA, Pt-based superalloys, sulphidation.