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 re crystallization 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.

The molten salt corrosion performance of a Ni-Mo-Cr (GH3535) alloy weldment, produced using matching filler metal, was assessed. Corrosion testing was performed in FLiNaK molten salt at 750 degrees C for 500 h. Present results reveal that, despite a similar chemical composition, the weld metal has somewhat superior corrosion resistance to the parent metal. The difference is primarily attributed to the significantly lower density of high-angle grain boundaries (HAGBs) in the weld metal. Results further suggest that large M6C carbides present in the parent metal may contribute to corrosion attack of the alloy matrix via galvanic corrosion.

The mechanical performance of a Ni–Mo–Cr (GH3535) alloy weldment, produced using a matching filler metal, was assessed and compared to the surrounding parent metal. Ambient-temperature mechanical characterisation included hardness testing, small punch testing and uniaxial tensile testing, while a crystal plasticity finite element model was used to assess the impact of crystallographic texture on the mechanical properties. Despite the similar chemical composition, the weld metal exhibited superior strength and ductility to that of the parent metal. The higher strength was primarily attributed to the high dislocation density in the weld metal imbued by the welding-induced thermo-mechanical loading. In contrast, the ductility difference was attributed to M6C carbide stringers in the parent metal that initiated fracture at lower strains when compared to the weld metal, with the latter containing finer, well-dispersed M6C carbides.