Untersuchung des Wasserstoffeinflusses auf die Nukleation und Bewegung von Versetzungen mit einem elektrochemischen nanoindentierenden AFM

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In the first phase of this project the effect of hydrogen on dislocation nucleation was studied with a NI-AFM. For this, a electrochemical three electrode setup was constructed and incorporated into the NI-AFM. The newly developed ECNI-AFM is capable of performing nanoindentation as well as imaging inside electrolytes. This setup was successfully used to study the effect of cathodically charged hydrogen on dislocation nucleation in pure metals and alloys. It was shown that hydrogen reduces the pop-in load by reducing the activation energy for dislocation nucleation. This new method was able to rank the sensitivity of materials to hydrogen embrittlement not only globally but also for the single phases and grains within a microstructure. The activation energy for dislocation nucleation is related to the shear modulus μ, dislocation core radius p and stacking fault energy, which in turn are altered by hydrogen. However, the effect of hydrogen on each of these parameters could not be measured separately. Therefore, in the planned project the same system will be converted to an electrochemical nano compression (ECNC) machine with the help of a flat punch instead of an indenter. The results of this new technique in combination with the ECNI-AFM results should provide the needed additional information to discriminate the effect of hydrogen on each of the above-mentioned parameters, μ, p, and by measuring the shear stress, strain rate sensitivity within defined slip band as well as the slip band nucleation stress in nano-pillars. Smooth specimens should mainly show the effect of surface and sub-surface enrichment on nucleation. Therefore, ECNC test on notched samples and bending tests are planned in order to study the effect of local hydrogen enrichment on notches. The advantage of this technique is, that the globally measured data, as yield stress and stress-strain curves can be directly correlated to local events.