Corrosion of Inconel 601 in molten salts for thermal energy storage

Inconel 601 superalloy was examined for compatibility with the eutectic mixtures of NaCI + Na2SO4 and NaCI + Na2CO3 at 700 degrees C and Li2CO3 + K2CO3 + Na2CO3 at 450 degrees 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 degrees 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 degrees 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 degrees C was found to be uniform.