Corrosion behavior of Inconel 625 deposited metal in molten KCl-MgCl₂

Abstract

In order to investigate the corrosion behavior of Inconel 625 deposited metal in molten KCl and MgCl2, the corrosion behavior of deposited metal immersed in molten salt for 60 h at 700 °C and 900 °C was studied by static corrosion immersion method. X-ray diffraction (XRD) and Geminisem300 were used to systematically study the phase composition, corrosion morphology and element distribution of the deposited metal. The results show that: the corrosion weight loss of the deposited metal showed an increasing trend at both temperatures, but the increasing range was different in different time intervals. The corrosion weight loss of the deposited metal increased slowly in the first 10 h, and increased sharply in the 10 h–60 h. It can be found that 10 h is the cut-off point of corrosion behavior. The corrosion rate is 0.03 mm/year at 700 °C and 0.50 mm/year at 900 °C for 10 h. The corrosion resistance of the deposited metal at 700 °C is better than that at 900 °C, which is due to the formation of dense MgO on the surface of the deposited metal at 700 °C, which hinders the corrosion reaction; at 900 °C, the content of CrCl3 on the surface of the deposited metal increases, resulting in a ‘shell breaking effect’, which destroys the MgO shell and forms NiCr2O4 with spinel structure. Its corrosion resistance is thus weakened.

Assessing the interfacial corrosion mechanism of Inconel 617 in chloride molten salt corrosion using multi-modal advanced characterization techniques

“…This argument is further supported by the fact that the OH − and O − signals detected by ToF-SIMS overlap with Mg − and Cl-signals corresponding to residual salt trapped within the pores. As noted, Cr 2 O 3 has been regularly cited by other investigators (Salinas-Solano et al, 2014;Zhu et al, 2016;Grégoire et al, 2020;Knosalla et al, 2020;Yang et al, 2020). In this investigation, intergranular Cr-O formation is an indicator of Cr 2 O 3 formation contributing to the propagation of the corrosion front.…”

“…Furthermore, the Frontiers in Nuclear Engineering frontiersin.org discontinuous porous network observed in this study corresponds to intergranular attack, which has been observed in Alloy 617 over shorter time scales (Sun et al, 2018a). The dealloying of Cr in Alloy 617 due to molten salt corrosion is commonly attributed to the formation of corrosion products, specifically Cr 2 O 3 , from Cr reacting with oxidant impurities in the salt, such as water (Salinas-Solano et al, 2014;Zhu et al, 2016;Guo et al, 2018;Grégoire et al, 2020;Knosalla et al, 2020;Yang et al, 2020). Several mechanisms explaining the role of Cr in propagating the corrosion front have been proposed.…”

“…Current regulations with the nuclear power section of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code are for traditional water-cooled reactors and cannot translate to MCFR structural materials. Many commercial structural alloys have been considered for construction of MCFRs, including alloys from the Inconel (Olson et al, 2009;Salinas-Solano et al, 2014;Grégoire et al, 2020;Yang et al, 2020;Lei et al, 2021;Pragnya et al, 2021) and Hastelloy series (Yang et al, 2016;Ye et al, 2016;Ding et al, 2018;Ezell et al, 2020;Knosalla et al, 2020). Informed qualification of structural materials for the construction of MCFRs in the future can only be ensured by expanding the fundamental knowledgebase pertaining to material performance under environmental stressors relevant to operation of the reactor, including corrosion susceptibility.…”

“…Elucidating molten salt corrosion susceptibility requires delving further into the corrosion mechanism of MCFR structural materials, expanding on the relationship between alloy composition and microstructure on the kinetics and thermodynamics of the corrosion process. To assess changes in alloy composition and microstructure at a length scale indicative for elucidating the corrosion mechanism, a suite of advanced characterization techniques is needed (Indacochea et al, 2001;Shankar et al, 2013;Salinas-Solano et al, 2014;Vignarooban et al, 2014;Gomez-Vidal and Tirawat, 2016;Liu et al, 2017;Wang et al, 2017;Sun et al, 2018a;Ding et al, 2018;Ding et al, 2019;Jalbuena et al, 2019;Yu et al, 2019;Grégoire et al, 2020;JagadeeswaraRao and Ningshen, 2020;Knosalla et al, 2020;Yang et al, 2020;Bawane et al, 2021;Caldwell et al, 2021;Gill et al, 2021;Patel et al, 2021;Pragnya et al, 2021). More importantly, these characterization techniques need to be employed in a corroborative manner through a multi-modal approach to develop a comprehensive assessment of the corrosion mechanism.…”

“…Together the two complimentary techniques captured key elements at different stages of the corrosion process to generate a comprehensive assessment. Assessing corrosion mechanisms in commercial alloys presents a more complex endeavor compared to that in model alloy systems (Indacochea et al, 2001;Shankar et al, 2013;Salinas-Solano et al, 2014;Gomez-Vidal and Tirawat, 2016;Zhu et al, 2016;Keny et al, 2019;Yu et al, 2019;Grégoire et al, 2020;Yang et al, 2020;Lei et al, 2021;Pragnya et al, 2021). An excellent example is Xi, et al analysis of microstructural changes in Hastelloy N in FLiNaK molten salt through a complementary application of x-ray diffraction (XRD), electron probe micro-analyzer, synchrotron scanning transmission x-ray microscopy (TXM), SEM, S/TEM, and XAS (Ye et al, 2016).…”