Stress assisted oxidative failure of Inconel 601 for thermal energy storage

Degradation of an Inconel 601 superalloy subjected to a eutectic mixture of carbonate salt at 450 degrees C was studied using advanced microscopy and microanalysis techniques. On the outside of the vessel, long term exposure to elevated temperature led to intergranular stress corrosion cracking via a stress assisted oxidation process. Elemental analysis verified diffusion controlled de-alloying of Ni and Cr from grain boundaries. Transmission electron microscopy showed that a (CrFeNiAl)(3)O-4 oxide phase was formed at grain boundaries as a result of oxygen penetration. Intergranular cracking appeared due to the presence of residual stresses and micro structural heterogeneities facilitated the crack branching.