Corrosion of INCONEL Alloy 625 in Molten LiCl-Li₂O-Li

INCONEL alloy 625^® (I625) was exposed to molten LiCl-Li₂O-Li to evaluate the material reliability for applications involving the electrolytic reduction of uranium oxide. Samples of I625 were exposed to solutions of LiCl with 1 and 2 wt% Li₂O, containing either 0, 0.5, or 1 wt% metallic lithium for 20 h at 650°C. Additional experiments exposed samples to LiCl saturated with Li₂O to investigate the mechanism of interaction between materials and the melt. Postexposure sample surface morphology and chemistry were studied using scanning electron microscopy and X-ray photoelectron spectroscopy. Additionally, inductively coupled plasma–optical emission spectroscopy was used to analyze the melt to determine the alloy constituents that leached out of the coupon during the exposure. The inclusion of 0.5 wt% metallic lithium in the molten solution was found to increase the stability of chromium-rich surface films and suppress the dissolution rate of alloying elements, compared to melts of LiCl-Li₂O containing no metallic Li. Alternatively, samples exposed to solutions containing 1 wt% metallic lithium did not form surface films and demonstrated evidence of chromium depletion. The degradation of materials exposed to solutions containing 1 wt% metallic lithium was observed to be different from samples exposed to solutions saturated with lithium oxide, demonstrating a chemical effect other than, or in addition to, salt basicity.