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

在本项目的第一阶段，用NI-AFM研究了氢对位错形核的影响。为此，构建了一个电化学三电极装置，并将其集成到NI-AFM中。新开发的ECNI-AFM能够在电解液中进行纳米压痕和成像。利用该装置成功地研究了阴极荷氢对纯金属和合金中位错形核的影响。结果表明，氢降低了位错成核的激活能，从而降低了弹入载荷。这种新的方法不仅能够对材料的氢脆敏感性进行全局评级，而且能够对微观结构中的单相和颗粒进行评级。位错成核激活能与剪切模数μ、位错核半径p和层错能有关，而层错能又受氢的影响。然而，氢对这些参数的影响不能单独测量。因此，在计划的项目中，相同的系统将改装成电化学纳米压缩(ECNC)机床，并使用平板冲头而不是压头。这项新技术的结果与原子力显微镜的结果相结合，应该提供所需的额外信息，以区分氢对上述每个参数μ，p的影响，并通过测量定义的滑移带内的剪应力、应变率敏感性以及纳米柱中的滑移带成核应力。光滑的试件应主要表现出表面和亚表面富集物对形核的影响。因此，为了研究局部富氢对缺口的影响，计划进行缺口试件的电火花加工试验和弯曲试验。这种技术的优点是，全球测量的数据，如屈服应力和应力-应变曲线，可以直接与局部事件相关。

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.