Materials and Chemistry for Molten Salt Systems: Corrosion I
Sponsored by: TMS Structural Materials Division, TMS: Corrosion and Environmental Effects Committee, TMS: Nuclear Materials Committee
Program Organizers: Stephen Raiman, University Of Michigan; Raluca Scarlat, University of California, Berkeley; Jinsuo Zhang, Virginia Polytechnic Institute and State University; Kumar Sridharan, University of Wisconsin-Madison; Nathaniel Hoyt, Argonne National Laboratory; Michael Short, Massachusetts Institute of Technology
Monday 8:30 AM
February 28, 2022
Room: 203B
Location: Anaheim Convention Center
Session Chair: Kumar Sridharan, University of Wisconsin
8:30 AM
Effects of Molten Salt Corrosion Associated with Proton Irradiation on the Micro-tensile Strength of Grain Boundaries in a Ni-20Cr Alloy: Fei Teng1; Weiyue Zhou2; Yachun Wang1; Daniel Murray1; Michael Short2; Lingfeng He1; 1Idaho National Laboratory; 2Massachusetts Institute of Technology
Corrosion in molten salts is usually proceeded by selective leaching of Cr from the alloys into the salts. For molten salt reactor application, it is important to understand how radiation damage/corrosion changes the failure behavior of grain boundary for evaluating the mechanical stability of materials under such extreme conditions. To address this, in situ scanning electron microscopy push-to-pull test was performed on the grain boundary of a Ni-20Cr alloy, which was simultaneously proton irradiated and corrosion treated. The grain boundary strength under both corrosion and corrosion/radiation conditions was tested. The grain boundaries under corrosion/radiation conditions show lower yield strength and longer total elongation compared to those only under corrosion. Radiation has likely modified the distribution of free volumes due to corrosion, which can be a possible explanation behind the observed trend.
8:50 AM
Inconel 617 Corrosion Study in Molten NaF-KF-UF4-UF3 Salts: Qiufeng Yang1; Jinsuo Zhang1; 1Virginia Polytechnic Institute of Technology
The corrosion of structural materials directly contacted with molten salt media at high temperature is one of the major concerns for the application of molten salts in various fields, such as molten salt reactor and hydrogen production facility. Inconel 617 is among few alloys that demonstrate good corrosion resistance performance at high temperature (650-850℃) for long-term use in molten fluoride salts. In this work, static corrosion tests were conducted by immersing Inconel 617 in molten NaF-KF-UF4-UF3 salts at 800℃. The corrosion rate was estimated by measuring the major corrosion product metal elements in the salts before and after tests using ICP-MS analysis. The crystal phases of the corrosion products were characterized by X-Ray diffraction. Moreover, the morphology and microstructure of the Inconel 617 samples after corrosion tests were analyzed using SEM-EDS as well to further understand the intergranular corrosion in the alloy.
9:10 AM
Corrosion Resistance of Steel and Nickel Alloys in Molten Nitrate Salt: Andrew Dong1; Camilla Stitt2; Peter Hosemann1; George Young2; 1University of California Berkeley; 2Kairos Power
Solar salt (60%NaNO3-40%KNO3) is being investigated for use as an intermediate heat transfer fluid in the Kairos Power fluoride salt-cooled high-temperature reactor (KP-FHR). Significant operational experience with nitrate salt at lower temperatures (≤550°C) exists due to its use in concentrated solar applications. However, at temperatures around and above 600°C, elevated corrosion rates in structural alloys are observed, associated with thermal decomposition of the nitrate salt. This presentation will discuss examination into the corrosion resistance of various iron- and nickel-based alloys exposed to molten nitrate salt at temperatures around the salt decomposition temperature. Weight change and microscopy data on metal coupons submerged in static nitrate salt for around 600 hours at 630°C will be presented. Observed corrosion rates and corrosion scales will be compared between the various alloys and overall conclusions will be discussed.
9:30 AM
Voids Observed during Molten Salt Corrosion: Kirkendall or Not?: Weiyue Zhou1; Miaomiao Jin2; Yang Yang2; Michael Short1; 1Massachusetts Institute of Technology; 2Penn State University
Corrosion of Cr-bearing structural metals in molten salts proceeds mainly via selective leaching of Cr. Upon removing the same amount of Cr atoms, the resulting corrosion morphologies can be entirely different depending on the alloy and conditions. Historically corrosion in these systems was attributed to Kirkendall effects, because the resulting voids looked semi-spherical and disconnected. Therefore, the void space was considered internal and isolated, resulting from unbalanced diffusion. No counter-argument was proposed, despite difficulties in explaining intergranular void spaces and significant variation of morphology. However, our recent experimental results exclusively show the existence of the salt in the void space, proving their connectivity. Such percolating voids cannot be obtained solely by unbalanced fluxes. The breaking down of the salt-solid interface pushes us to reconsider the validity of interpreting molten salt corrosion morphologies as Kirkendall voids, calling for a re-examination of past molten salt corrosion experiments.
9:50 AM Break
10:10 AM
The Corrosion of Severely Plastically Deformed SS316 in LiCl-Li2O at 650 °C: Jeremy Moon1; Andrew Hoffman2; Haiming Wen3; Dev Chidambaram1; 1University of Nevada, Reno; 2GE Research; 3Missouri S&T
The corrosion of SS316/SS316L exposed to LiCl-Li2O molten salt with dissolved Li metal during the electrolytic reduction of commercial oxide nuclear fuel is a complex process mediated by the formation and dissolution of precipitates in grain boundaries and in the bulk material as well as transport of the electrolyte through grain boundaries. We have previously observed that low-angle and twin grain boundaries experience less severe intergranular attack. In the present work, severely plastically deformed (SPD) SS316 fabricated using equal channel angular pressing (ECAP) and high-pressure torsion (HPT) were exposed to LiCl-Li2O (1 wt.%) at 650 °C for 100 hours in order to observe the effects of ultrafine and nanocrystalline grain sizes on the corrosion of SS316. Results of characterization studies of the exposed surface of SPD SS316 using scanning electron microscopy, X-ray energy dispersive spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy will be presented and compared to traditionally manufactured SS316.
10:30 AM
Understanding Molten Salt Corrosion in Ni-20Cr Model Alloy Using Multimodal Characterization: Kaustubh Bawane1; Xiaoyang Liu2; Ruchi Gakhar1; Michael Woods1; Mingyuan Ge3; Xianghui Xiao3; Wah-Keat Lee3; Simon Pimblott1; James Wishart3; Yu-chen Karen Chen-Wiegart2; Lingfeng He1; 1Idaho National Laboratory; 2Stony Brook University; 3Brookhaven National Laboratory
Corrosion is a major concern for molten salt facing structural materials in molten salt reactors (MSRs) and concentrated solar power plant (CSPs) applications. In this work, we utilized quasi-in-situ TEM technique and in-situ synchrotron X-ray nanotomography to study microstructural/chemical evolution during molten salt corrosion in Ni-20Cr model alloy as a function of time. Ni-20Cr TEM disc was corroded outside the microscope in KCl-MgCl2 salt at 500oC for 60 s in subsequent 20 s iterations, followed by TEM investigations after every corrosion iteration. In-situ synchrotron X-ray nanotomography technique enabled direct observations of corrosion processes in Ni-20Cr microwire when exposed to KCl-MgCl2 at 500oC. Both techniques were complimentary and provided valuable insights on molten salt corrosion processes at their respective length and time scales. This work was supported as part of the Molten Salts in Extreme Environments (MSEE) Energy Frontier Research Center, funded by the U.S. Department of Energy Office of Science.
10:50 AM
NOW ON-DEMAND ONLY – ICME Development of a Cold Spray Enabled Corrosion Resistant Bimetallic Structure for Nuclear Reactors: Pin Lu1; Joseph Heelan2; Vilupanur Ravi3; 1Questek Innovations LLC; 2Solvus Global; 3Cal Poly Pomona
Bimetallic structure consisting of a corrosion resistant surface layer joined on top of ASME code approved nuclear reactor structural materials has become a promising solution to address the corrosion issue in molten salt reactors. This DOE-funded work aims to develop cold spray enabled bimetallic structures with a refractory-based coating on ASME code-certified substrate. ICME was employed to design novel alloy compositions that combine improved cold spray processability with high molten salt corrosion resistance and strong interfacial bonding. Initial cold spray trials depositing these compositions on 316 stainless steel were successfully performed. Coatings were proved to be of high quality by metallographic inspection and have strong adhesion by adhesion testing. Molten salt test protocols have been developed. Cold spray materials have been tested and characterized post-test. Observations indicated are that all the alloy compositions were promising in terms of corrosion resisting performance after 750°C for 100 hours in molten chloride salt.