Visualizing oxygen transport pathways during intergranular oxidation in Ni-Cr

The transport paths of O during intergranular oxidation in binary Ni-Cr were investigated. To isolate the selective oxidation of Cr, oxidation was performed with a CO/CO2 gas mixture in which the oxygen partial pressure was kept under the NiO dissociation pressure. A combination of electron microscopy and atom probe tomography (APT) was used to study the nanometer-scale details of the passivation and penetrative intergranular oxidation processes at high-energy grain boundaries. Oxygen transport towards the terminating oxidation front is elucidated with dedicated usage of oxygen tracer exchange experiments. Secondary ion mass spectroscopy and APT support classical theories of internal oxidation, revealing preferred transport paths at the oxide/alloy interface with sub-nanometer resolution.

Automated summary

The transport paths of oxygen during intergranular oxidation in binary Ni-Cr were studied using electron microscopy, atom probe tomography (APT), secondary ion mass spectroscopy, and oxygen tracer exchange experiments. The selective oxidation of Cr was isolated by performing oxidation with a CO/CO2 gas mixture. The results reveal nanometer-scale details of passivation and penetrative intergranular oxidation processes, as well as preferred transport paths at the oxide/alloy interface.