Search

Highlights • Amount of Mo 2 C precipitates is proportional to the amount of SiC in the initial powder mixture. • Mo 2 C precipitates readily dissolve into FLiNaK molten salt leaving behind empty voids. • The corrosion resistance of NiMo-SiC alloys is strongly dependent on the amount of SiC in the initial powder mixture. • The corrosion resistance of NiMo-SiC alloys with a low SiC content (<2 wt.%) is comparable to Hastelloy-N®. Abstract The corrosion performance of Ni-16%wt.Mo-X%wt.SiC (X = 0.5, 1.5, 2.0, 2.5 and 3.0) alloys prepared via mechanical alloying followed by consolidation using spark plasma sintering (SPS) from pure Ni, Mo and SiC powders is investigated. Corrosion testing at 650 °C/200 h in FLiNaK molten salt showed that increasing the volume fraction of SiC in the initial Ni-Mo-SiC powder mixture leads to formation of large amount of Mo 2 C precipitates, which readily dissolve into FLiNaK molten salt. Hence, only the corrosion resistance of NiMo-SiC alloys with a low SiC content (<2 wt.%) is comparable to that of Hastelloy-N® alloy. [ABSTRACT FROM AUTHOR]

• The state of the alloy's microstructure and its in-service evolution affects its corrosion behaviour. • High-temperature creep leads to the storage of dislocation and development of dislocation substructure. • Dislocation substructure promotes intragranular diffusion of alloying elements to the salt-alloy interface. • Accelerated diffusion of alloying elements leads to an increased corrosion attack of the alloy. Molten-salt-based energy-generation and energy-storage systems are expected to function under plasticity-imparting in-service operating conditions. It is thus of utmost importance to understand the effect of these operating conditions on the corrosion performance of molten-salt-facing structural alloys. Here, we investigate the impact of high-temperature creep on the molten salt corrosion of a NiMoCr alloy in FLiNaK molten salt. We show that high-temperature creep leads to an increased susceptibility of the alloy to molten salt corrosion via the development of a dislocation substructure, which promotes mass diffusion of alloying elements towards the salt–alloy interface (exposed surface). In addition, the corrosion-affected near-surface layer undergoes recrystallization leading to a significant increase in the amount of grain boundaries, which further promotes ongoing diffusion processes. This then causes increased molten salt corrosion attack resulting in an accelerated mass loss during the alloy's exposure to the molten salt. The present results thus unambiguously highlight the importance of the state of the microstructure as well as the evolution of the microstructure under in-service operating conditions on the alloy's molten salt corrosion performance. [ABSTRACT FROM AUTHOR]

Interactions between stainless steel 316L and eutectic Li 2 CO 3 + K 2 CO 3 + Na 2 CO 3 at 450 °C were investigated for thermal energy storage. Scanning Electron Microscopy (SEM), Electron Back-Scatter Diffraction (EBSD), Scanning Kelvin Probe Force Microscopy (SKPFM), X-ray Photoelectron Spectroscopy (XPS), neutron diffraction pattern, material loss, micro-hardness, polarization and impedance measurements were used to compare the alloy's response in unrolled (0%) condition versus 20% and 30% cold-rolled conditions. Cold-rolling increased the number of grains, grain boundaries and density of dislocations. Initially, faster corrosion accompanied by more areas of localized attack was confirmed by Volta potential measurements. However, recovery and the formation of a surface film were found to decelerate corrosion for longer times. Cold-rolling-induced dislocations were found to facilitate carbon diffusion and subsequently carburize the material leading to increased corrosion resistance. Consequently, the overall long-time corrosion rate was not noticeably affected by cold-rolling. Image 1 • Interaction of cold-rolled SS316L with a molten carbonate salt was studied. • Cold-rolling increased grains, grain boundaries and density of dislocations. • Volta potential confirmed initial fast corrosion rate due to localized attack. • Recovery and formation of an oxide layer decelerated corrosion rate after 1000 h. • Dislocations facilitated carburization leading to increased corrosion resistance. [ABSTRACT FROM AUTHOR]