WEB Imaging of Hydrogen in Metals at the Atomic ScaleWednesday (23.09.2020) 09:00 - 09:30 S: Structural Materials 1 Part of:
The damage that hydrogen causes to metallic materials is a major issue for the implementation of infrastructure for the hydrogen economy. This damage is fundamentally happening at the atomic scale, mostly at crystal defects such as grain boundaries and dislocations. At these crystal defects, it is expected that locally higher concentrations of H alter the mechanical behavior by e.g. causing decohesion or enhancing dislocation mobility. So far, much of this information had to be deduced indirectly, but recently atom probe tomography has been employed to quantify localization of hydrogen at individual crystal defects. This was done using deuterium (D) as a tracer, since H present as a contaminant in generally available atom probe instruments occludes any H that would be present in the sample.
In this talk, we will present first results on the atom probe measurement of H at individual grain boundaries via D charging. In this approach, individual grain boundaries of bcc and fcc Fe are prepared either via electrochemical sample preparation or focused ion beam, and then exposed to a water splitting reaction in heavy water (D20). This way, D is driven into the material, most likely until saturation sets in. Thus, this is a good method to assess the general ability of grain boundaries and other crystal defects to take up hydrogen. Via short time exposure of the sample to room temperature or elevated temperatures, the diffusion and loss of D can also be assessed.
While the above electrochemical approach is a great tool for fundamental research on the interaction of H with crystal defects, to assess the influence of H on the microstructure in bulk materials, the direct measurement of 1H is desired. This is due to the fact that exposure to high pressure H gas is the most relevant for the current aim of building up hydrogen infrastructure. Such experiments would be excessively expensive using D2 gas. We have therefore built an atom probe instrument with a measurement chamber made of titanium, which circumvents the issue of H bleeding into the measurement chamber from the usually used austenitic stainless steel. Using this atom probe, we will show first experiments of the influence of high pressure H on the composition of crystal defects such as grain boundaries and dislocations.