Simulation of Slip-Oxidation Process by Mesh Adaptivity in a Cohesive Zone Framework

Adaptive oxide thickness was developed in a cohesive element based multi-physics model including a slip-oxidation and diffusion model. The model simulates the intergranular stress corrosion cracking (IGSCC) in boiling water reactors (BWR). The oxide thickness was derived from the slip-oxidation and updated in every structural iteration to fully couple the fracture properties of the cohesive element. The cyclic physics of the slip oxidation model was replicated. In the model, the thickness of the oxide was taken into consideration as the physical length of the cohesive element. The cyclic process was modelled with oxide film growth, oxide rupture, and re-passivation. The model results agreed with experiments in the literature for changes in stress intensity factor, yield stress representing cold work, and environmental factors such as conductivity and corrosion potential.

Investigation of IG-SCC growth kinetics in Al-Mg alloys in thin film environments

The effect of thin film environments on the intergranular stress corrosion cracking (IG-SCC) behavior of AA5083-H131 was investigated using fracture mechanics-based testing, high-fidelity monitoring of crack growth, and electrochemical potential measurements. A protocol for conducting thin film IG-SCC fracture mechanics experiments with anodized aluminum oxide (AAO) membranes is developed and the ability to maintain films of specific thicknesses without impeding oxygen diffusion during testing is validated via EIS testing and computational modelling. The IG-SCC susceptibility was found to increase once a critical thin film thickness of 82 µm was achieved; above this thickness a duality in IG-SCC susceptibility behavior was observed. These results are analyzed in the context of a coupled anodic dissolution and hydrogen (H) embrittlement mechanism, where susceptibility is found to scale with the cathodic limitation of the governing IG-SCC mechanism. Specifically, thinner film thicknesses led to limitations on the amount of cathodic current availability, which caused a decrease in the dissolution at the crack tip, a less aggressive crack chemistry development, and thus lower levels of H production. A close correlation between the open circuit potential of the bulk surface and the crack growth kinetics was also observed, consistent with trends reported in previous IG-SCC studies on this alloy.

Effect of Nitrogen on the Intergranular Stress Corrosion Cracking Resistance of 316LN Stainless Steel

Here the effect of nitrogen on the intergranular stress corrosion cracking (SCC) resistance of sensitized Type 316LN stainless steel containing different amounts of nitrogen is reported. SCC studies were performed at 70% of yield strength. Double-loop electrochemical potentiokinetic reactivation technique was used to quantify degree of sensitization (DOS) that was correlated with SCC resistance. SCC time to failure increased from 220 h to 285 h with increasing nitrogen content from 0.07 wt% to 0.14 wt%, but decreased drastically to approximately 120 h at 0.22 wt% nitrogen (i.e., beyond N solubility limit), due to excessive precipitation of Cr23C6 and Cr2N and drastic reduction in the coincidence site lattice (CSL) boundary distribution from 48% to approximately 32%. Scanning electron microscope images showed mixed mode of failure.