Periodic Reporting for period 3 - HydMet (Fundamentals of Hydrogen in Structural Metals at the Atomic Scale)
Reporting period: 2021-12-01 to 2023-05-31
In this project we address the the microscopical origins of the degradation of the mechanical properties of metallic materials caused by the ingress of hydrogen. In many metallic materials, especially steels, the presence of hydrogen in the microstructure leads to embrittlement. This embrittlement is caused by the interaction of hydrogen with the crystal defects that govern the mechanical properties of the materials. In other cases, such as zirconium or titanium, the formation of hydride phases in the material causes degradation. This degradation is not the focus of this work. In this work, the ingress mechanisms and interactions of hydrogen with crystal defects are addressed. Since this is a long-standing topic, much work has been done on the these embrittlement phenomena, however, direct imaging of the interactions between hydrogen and the crystal defects has not been achieved so far. In this project, we therefore create the means to image hydrogen at crystal defects using atom probe tomography.
This degradation by hydrogen is a major roadblock in the development of cost effective hydrogen energy technologies and infrastructure. E.g. hydrogen storage in mobility applications (cars, trucks etc.) rely on storage tanks with 35 MPa or 70 MPa pressure hydrogen. At these pressures, hydrogen embrittlement has so far been a major roadblock for the use of cost and space effective steel tanks. The same is true for stationary high pressure thanks that can constitute a major part of the capex of hydrogen infrastructure.
The overall objective in this project is the qualitative and quantitative analysis of the interaction of hydrogen with the crystal defects in engineering materials. To achieve this, we are developing tomographic atom probe methods to achieve this. Tomographic atom probe experiments are experiments where very sharp needles of the material to be investigated are put unter an intense electric field, such that individual atoms or small molecules are emitted from the needle. These atoms are then collected on a 2D detector. In order to identify the atoms, the flight time with reference to a start pulse (high voltage) is taken. By using this time-of-flight principle, all chemical elements are detected with equal sensitivity, including hydrogen. Natural hydrogen however constitutes an exception, since all atom probe instruments (prior to this project) are made from stainless steel. This material outgases hydrogen, which impedes imaging. As a workaround, isotopic labelling with deuterium can however be used in some cases. In this project we are using isotopic labelling to fundamentally image hydrogen at crystal defects. We also went a step further, and built an ultra-low hydrogen atom probe, made from titanium, that can be used to directly image natural hydrogen at crystal defects. This will allow us to quantitatively image the interaction of hydrogen from high pressure experiments with the materials that can be used for hydrogen storage and distribution.
This degradation by hydrogen is a major roadblock in the development of cost effective hydrogen energy technologies and infrastructure. E.g. hydrogen storage in mobility applications (cars, trucks etc.) rely on storage tanks with 35 MPa or 70 MPa pressure hydrogen. At these pressures, hydrogen embrittlement has so far been a major roadblock for the use of cost and space effective steel tanks. The same is true for stationary high pressure thanks that can constitute a major part of the capex of hydrogen infrastructure.
The overall objective in this project is the qualitative and quantitative analysis of the interaction of hydrogen with the crystal defects in engineering materials. To achieve this, we are developing tomographic atom probe methods to achieve this. Tomographic atom probe experiments are experiments where very sharp needles of the material to be investigated are put unter an intense electric field, such that individual atoms or small molecules are emitted from the needle. These atoms are then collected on a 2D detector. In order to identify the atoms, the flight time with reference to a start pulse (high voltage) is taken. By using this time-of-flight principle, all chemical elements are detected with equal sensitivity, including hydrogen. Natural hydrogen however constitutes an exception, since all atom probe instruments (prior to this project) are made from stainless steel. This material outgases hydrogen, which impedes imaging. As a workaround, isotopic labelling with deuterium can however be used in some cases. In this project we are using isotopic labelling to fundamentally image hydrogen at crystal defects. We also went a step further, and built an ultra-low hydrogen atom probe, made from titanium, that can be used to directly image natural hydrogen at crystal defects. This will allow us to quantitatively image the interaction of hydrogen from high pressure experiments with the materials that can be used for hydrogen storage and distribution.
In the first period of the project, we simultaneously carried out experiments where we investigated the interaction of hydrogen in the form of deuterium with crystal defects in metallic materials (pure iron, iron alloys). This was possible using the commercial atom probe that is available in our lab. This, and similar experiment carried out by other groups in the same period, showed that quantitative imaging of hydrogen at crystal defects is in many cases not fully conclusive when using deuterium tracers due to preparation artefacts. In practical experiments, deuterium is charged via an electrochemical reaction into the specimen. We therefore also included the assessment of sample preparation in the work for the project. This requires us to use deuterated chemicals for the preparation of the specimens, but unfortunately due to covid related supply chain issues, non of the ordered deuterated chemicals have arrived at the lab as of today.
Due to the results of my group and other labs on the issues of using tracers, we focussed on the design and construction of an atom probe that does not have the issue of hydrogen contamination from a stainless steel measurement chamber. We chose a design based on titanium. The parts were procured and the instrument was built before the onset of COVID, however, issues with lockdown etc. slowed down the progress in testing the instrument. However, it is finished now and a first publication on the performance of the instrument is currently under review. An improvement of 2 orders of magnitude in the hydrogen background could be made, which is sufficient for the imaging of hydrogen in all materials in a wide range of analysis conditions. This will in the second half of the project allow us to directly image natural hydrogen. This greatly simplifies the charing process, since gaseous charing can be used. Gaseous charing is also much closer to the conditions in the application and reproducible as it constitutes a thermodynamically defined state for the material and its crystallographic defects. We are excited about the possibilites this opens up for the second half of the project.
Beyond the original scope of the project, we also build up an open source atom probe data analysis suite for FAIR (findable, accessible, interoperable and reusable) data analysis. This is owing to the COVID lockdowns, where during a period of several months, not lab work was possible. The research group used this period to build this analysis system and teach its use to the community in an international atom probe software school. A publication is currently in the write-up phase. We are highly delighted to see the use of this analysis in labs around the world.
Due to the results of my group and other labs on the issues of using tracers, we focussed on the design and construction of an atom probe that does not have the issue of hydrogen contamination from a stainless steel measurement chamber. We chose a design based on titanium. The parts were procured and the instrument was built before the onset of COVID, however, issues with lockdown etc. slowed down the progress in testing the instrument. However, it is finished now and a first publication on the performance of the instrument is currently under review. An improvement of 2 orders of magnitude in the hydrogen background could be made, which is sufficient for the imaging of hydrogen in all materials in a wide range of analysis conditions. This will in the second half of the project allow us to directly image natural hydrogen. This greatly simplifies the charing process, since gaseous charing can be used. Gaseous charing is also much closer to the conditions in the application and reproducible as it constitutes a thermodynamically defined state for the material and its crystallographic defects. We are excited about the possibilites this opens up for the second half of the project.
Beyond the original scope of the project, we also build up an open source atom probe data analysis suite for FAIR (findable, accessible, interoperable and reusable) data analysis. This is owing to the COVID lockdowns, where during a period of several months, not lab work was possible. The research group used this period to build this analysis system and teach its use to the community in an international atom probe software school. A publication is currently in the write-up phase. We are highly delighted to see the use of this analysis in labs around the world.
Since we now have the capability to directly image natural hydrogen in our new titanium atom probe, we will make heavy use of this capacity in the second half of the project. We will use gas charing at high pressures to quantitatively analyse the interaction of hydrogen with the most relevant crystal defects, including dislocations and grain boundaries. This will be correlated with mechanical properties.