Corrosion performance comparison of CoCrFeNi-based high-entropy alloys and austenitic stainless steels in acidic oxidizing chloride solutions

• V.A. Vorkel¹, R.I. Bogdanov², N.A. Pukhareva², V.E. Ignatenko¹, A.A. Rybkina¹, A.V. Voennov³ and A.I. Marshakov¹

¹ A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky pr. 31, 119071 Moscow, Russian Federation
² Department of Materials Science, National Research Nuclear University MEPhI, 115409, Moscow, Russian Federation
³ Federal State Unitary Enterprise “NL Dukhov All-Russian Scientific Research Institute of Automation” (VNIIA), 127055, Moscow, Russian Federation

Abstract: The long-term corrosion resistance of the CoCrFeNi-based high-entropy alloys and austenitic stainless steels were investigated. According to the gravimetric tests, in the 0.6 M NaCl + 0.1 M HCl solution with and without 10 mM H₂O₂ the general corrosion rates of Mo-containing CoCrFeNiMo_0.4 and AISI 316L were higher than that of AISI 304 due to the uneven distribution of Cr and Mo and the lower Cr content, respectively. However, both steels were considerably prone to intergranular corrosion in the presence of hydrogen peroxide. As for CoCrFeNiMo_0.4, only the matrix areas depleted in Mo and located proximately to the (Cr, Mo)-rich σ-phase were slightly susceptible to pitting corrosion. The corrosion rate of CoCrFeNiMo_0.4 was also significantly lower than those of both steels in the 0.4 M FeCl₃ solution. The small σ-phase content in the CoCrFeNiMo_0.4 microstructure and overall Cr and Mo distribution effectively suppressed its selective corrosion. According to the anodic curves of CoCrFeNiMo_0.4, the onset of metastable pitting was possible, which could also explain the alloy’s weight loss during the long-term corrosion tests. CoCrFeNiAl_0.5Cu_0.5 did not passivate in any test solution, and the oxidizers intensified its active dissolution initiated in the Cu-based precipitates. Comparing the results of gravimetric tests and polarization measurements demonstrated quantitative discrepancies between them due to the onset of a steady state during the long-term tests and with the determination of the average corrosion rate rather than the instantaneous one. This phenomenon should be carefully considered when justifying the alloys’ potential applications.

Keywords: high-entropy alloy, selective dissolution, gravimetric test, corrosion rate, oxidizer

Int. J. Corros. Scale Inhib., 2024, 13, no. 3, 1394-1422
doi: 10.17675/2305-6894-2024-13-3-3

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