Phase evolution and microstructure analysis of CoCrFeNiMo high-entropy alloy for electro-spark-deposited coatings for geothermal environment

Sigrun N. Karlsdottir, Laura E. Geambazu, Ioana Csaki, Andri I. Thorhallsson, Radu Stefanoiu, Fridrik Magnus, Cosmin Cotrut

Research output: Contribution to journalArticle

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.

Original languageEnglish
Article number406
JournalCoatings
Volume9
Issue number6
DOIs
Publication statusPublished - 1 Jun 2019
Externally publishedYes

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sparks
Electric sparks
Entropy
entropy
coatings
Coatings
microstructure
Microstructure
vacuum melting
arc melting
casts
hardness
Melting
electrochemical corrosion
Hardness
Chemical analysis
corrosion tests
Vacuum
X ray diffraction
electrode materials

Keywords

  • Coating
  • Corrosion
  • Electro-spark deposition
  • Geothermal environment
  • High-entropy alloy
  • Microstructure
  • XRD

ASJC Scopus subject areas

  • Surfaces and Interfaces
  • Surfaces, Coatings and Films
  • Materials Chemistry

Cite this

Phase evolution and microstructure analysis of CoCrFeNiMo high-entropy alloy for electro-spark-deposited coatings for geothermal environment. / Karlsdottir, Sigrun N.; Geambazu, Laura E.; Csaki, Ioana; Thorhallsson, Andri I.; Stefanoiu, Radu; Magnus, Fridrik; Cotrut, Cosmin.

In: Coatings, Vol. 9, No. 6, 406, 01.06.2019.

Research output: Contribution to journalArticle

Karlsdottir, Sigrun N. ; Geambazu, Laura E. ; Csaki, Ioana ; Thorhallsson, Andri I. ; Stefanoiu, Radu ; Magnus, Fridrik ; Cotrut, Cosmin. / Phase evolution and microstructure analysis of CoCrFeNiMo high-entropy alloy for electro-spark-deposited coatings for geothermal environment. In: Coatings. 2019 ; Vol. 9, No. 6.
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AB - 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.

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