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Phase Evolution and Microstructure Analysis of CoCrFeNiMo High-Entropy Alloy for Electro-Spark-Deposited Coatings for Geothermal Environment

1
Department of Industrial Engineering, Mechanical Engineering and Computer Science, University of Iceland, Hjardarhagi 2-6, 107 Reykjavík, Iceland
2
University Politehnica Bucharest, Splaiul Independentei 313, Bucharest 060042, Romania
3
Science Institute, University of Iceland, Dunhaga 3, 107 Reykjavik, Iceland
*
Author to whom correspondence should be addressed.
Coatings 2019, 9(6), 406; https://doi.org/10.3390/coatings9060406
Received: 20 May 2019 / Revised: 14 June 2019 / Accepted: 18 June 2019 / Published: 21 June 2019
(This article belongs to the Special Issue Coatings for Harsh Environments)
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Abstract

In this work, a CoCrFeNiMo high-entropy alloy (HEA) material was prepared by the vacuum arc melting (VAM) method and used for electro-spark deposition (ESD). The purpose of this study was to investigate the phase evolution and microstructure of the CoCrFeNiMo HEA as as-cast and electro-spark-deposited (ESD) coating to assess its suitability for corrosvie environments encountered in geothermal energy production. The composition, morphology, and structure of the bulk material and the coating were analyzed using scanning electron microscopy (SEM) coupled with energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The hardness of the bulk material was measured to access the mechanical properties when preselecting the composition to be pursued for the ESD coating technique. For the same purpose, electrochemical corrosion tests were performed in a 3.5 wt.% NaCl solution on the bulk material. The results showed the VAM CoCrFeNiMo HEA material had high hardness (593 HV) and low corrosion rates (0.0072 mm/year), which is promising for the high wear and corrosion resistance needed in the harsh geothermal environment. The results from the phase evolution, chemical composition, and microstructural analysis showed an adherent and dense coating with the ESD technique, but with some variance in the distribution of elements in the coating. The crystal structure of the as-cast electrode CoCrFeNiMo material was identified as face centered cubic with XRD, but additional BCC and potentially σ phase was formed for the CoCrFeNiMo coating. View Full-Text
Keywords: high-entropy alloy; coating; electro-spark deposition; microstructure; corrosion; geothermal environment; XRD high-entropy alloy; coating; electro-spark deposition; microstructure; corrosion; geothermal environment; XRD
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Karlsdottir, S.N.; Geambazu, L.E.; Csaki, I.; Thorhallsson, A.I.; Stefanoiu, R.; Magnus, F.; Cotrut, C. Phase Evolution and Microstructure Analysis of CoCrFeNiMo High-Entropy Alloy for Electro-Spark-Deposited Coatings for Geothermal Environment. Coatings 2019, 9, 406.

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