Publications Details
Validating Hydrogen Concentrations Ahead of Crack Tips
Ronevich, Joseph A.; Fonseca, Paulo
Current models for hydrogen embrittlement rely on adjustable parameters to correct for uncertainties in crack tip stress fields and subsequent H2-concentrations. Techniques are needed to quantify these concentrations ahead of crack tips in mechanically loaded materials, providing data for model calibration and validation. The goal of this work was to establish advanced analytical techniques to detect and quantitatively measure hydrogen ahead of cracks in stressed solids. Two advanced analytical techniques, kelvin probe force microscopy (KPFM) and nuclear reaction analysis (NRA), were explored to evaluate the feasibility to provide qualitative and quantitative H2-concentration fields in geometries designed to be 'loaded' while under observation. The feasibility of the KPFM technique at detecting hydrogen was evaluated using electrochemically precharged hydrogen as well as a mixed hydrogen gas atmosphere. The KPFM technique was able to detect the presence of elevated stress and hydrogen concentrations ahead of a tensile loaded crack tip. The results suggest that KPFM is a viable technique for qualitatively imaging changes in stress and hydrogen concentrations on the scale needed to inform predictive models. KPFM could be used to provide local stress and hydrogen variations associated with hydrogen traps or different phases which require sensitive measurements on the micron scale. NRA provided quantitative measurements of the hydrogen-isotope deuterium ahead of a tensile loaded notch, however, the vacancy formation due to the incident high energy He 3 beam overwhelmed stress-assisted enhancement of deuterium concentrations such that the effect of stress was overshadowed in this analysis. Modeling of the chemo- mechanical hydrogen concentration change was used to verify this observation.