Compatibility of inconel 617^R alloy with LIF-MGF²-kf thermal energy storage salts and vacuum at high temperature

Abstract

Thermal energy storage capsules made of Inconel 617 alloy were filled with high- purity LiF- MgF2- KF salts and thermally cycled at 983 ± 100 K in vacuum for up to 5 years. The containment life performance characteristics with fluoride salts and in vacuum were examined. Metallographic study indicated that the inside surfaces of the post- test containers had a corrosion damage of 100 um in depth after 5 years of thermal cycling. The outer surface showed a vaporization damage of 120 μm after the same period. After 5 years of thermal cycling, the aluminum concentration at the capsule interior surface was reduced to 0.424 wt% from a nominal concentration of 1.34 wt% and chromium was reduced to 18.7 wt% from a nominal concentration of 21.8 wt%. A more significant depletion of aluminum and chromium was observed at the outer surfaces. Atomic absorption spectroscopy (AAS) and differential thermal analysis (DTA) were used to reveal the alloying element dissolution and the changes in melting temperature and heat of fusion of fluoride salts during thermal cycling. A modified diffusion equation for a one-dimensional semi-infinite bar was applied to the depletion of aluminum on the interior surfaces of the containers. Good agreement was obtained between the analysis and the measured concentration profiles.