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Intergranular Oxidation and Oxygen Transport in Ni-20Cr During Exposure to Model Dry and Wet Oxidation Environments

Picture for Competitive Grain Boundary Attack And Passivation Of Ni-Base Alloys In Model Dry And Wet Oxidation Environments
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The austenitic Ni-base Alloy 600 has been extensively used as structural material in primary water reactors (PWR). Despite good resistance against general corrosion in water-cooled nuclear power reactors, the material has been susceptible to stress corrosion cracking (SCC). These observations have led to ongoing discussions of the underlying embrittlement mechanism(s). Internal oxidation of the grain boundary (GB) at typical operating temperatures is one such mechanism, although debate continues on the exact mechanisms at play.

Product Number: ED22-17329-SG
Author: Martin Weiser, Daniel K. Schreiber, Karen Kruska, Mark H. Engelhard, Matthew J. Olszta
Publication Date: 2022
$20.00
$20.00
$20.00

Selective oxidation is a critical component of the proposed internal oxidation mechanism of stress corrosion cracking (SCC) for Ni-based alloys in primary water reactor (PWR) operation. To isolate and study this process, the binary Ni-20Cr was exposed to pressurized water and a CO/CO2 gas mixture. In both environments, the oxygen potential was kept under the Ni/NiO line to stimulate penetrative intergranular attack. A combination of electron microscopy and atom probe tomography 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 isotopic tracer exchange experiments to support classical theories of internal oxidation, revealing preferred oxygen transport paths were visualized with sub-nanometer resolution.

Selective oxidation is a critical component of the proposed internal oxidation mechanism of stress corrosion cracking (SCC) for Ni-based alloys in primary water reactor (PWR) operation. To isolate and study this process, the binary Ni-20Cr was exposed to pressurized water and a CO/CO2 gas mixture. In both environments, the oxygen potential was kept under the Ni/NiO line to stimulate penetrative intergranular attack. A combination of electron microscopy and atom probe tomography 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 isotopic tracer exchange experiments to support classical theories of internal oxidation, revealing preferred oxygen transport paths were visualized with sub-nanometer resolution.

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