Corrosion of Inconel 601 in molten salts for thermal energy storage

- Corrosion behavior of Inconel 601 in three molten salts was studied.
- Oxidation was found as the primary attack.
- Solubility of surface films and alloying elements in NaCl + Na2CO3 was high.
- Oxidative pitting due to de-alloying was observed at 700 °C.
- Attack morphology at 450 °C was uniform oxidation.

Inconel 601 superalloy was examined for compatibility with the eutectic mixtures of NaCl + Na2SO4 and NaCl + Na2CO3 at 700 °C and Li2CO3 + K2CO3 + Na2CO3 at 450 °C in air for thermal energy storage. Electrochemical measurements combined with advanced microscopy and microanalysis techniques were employed. Oxidation was the primary attack leading to the development of oxide deposits on the alloy surface. The deposit was not stable in NaCl + Na2CO3 because of the fluxing action and high solubility of chromium in the salt leading to very high corrosion current density values. De-alloying threatened the material at 700 °C while the availability of oxygen controlled its rate. The availability of oxygen was seen to limit the corrosion rate in NaCl + Na2SO4 and NaCl + Na2CO3. De-alloying also appeared as pits on the metal surface at 700 °C. For the metal in contact with NaCl + Na2SO4 an additional layer attacked by sulfur was found under the pitting corroded layer. The attack morphology on the metal surface in contact with Li2CO3 + K2CO3 + Na2CO3 at 450 °C was found to be uniform.