Stress assisted oxidative failure of Inconel 601 for thermal energy storage

•Fracture behavior of Inconel 601 against carbonate molten salt was studied.•EBSD analysis revealed partial recovery with stress relieving in the sample.•TEM-EDS examination showed de-alloying among grain boundaries.•Stress assisted oxidation was found as the main reason for intergranular failure.

Degradation of an Inconel 601 superalloy subjected to a eutectic mixture of carbonate salt at 450 °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)3O4 oxide phase was formed at grain boundaries as a result of oxygen penetration. Intergranular cracking appeared due to the presence of residual stresses and microstructural heterogeneities facilitated the crack branching.

Graphical abstractFailure of Inconel 601 crucible containing a eutectic mixture of lithium carbonate, potassium carbonate and sodium carbonate at 450 °C: (a) intergranular morphology of crack, (b) and (c) TEM-EDS analysis of a grain boundary along a crack tip showing a de-alloyed zone surrounding the grain boundary and the subsequent formation of an oxide phase.Download high-res image (291KB)Download full-size image