In situ micromechanical investigation of solids under extreme conditions – INSTINCT

Understanding mechanisms of deformation at the sub-micron scale is the key for designing new materials and alloys for industrial applications, as the mechanical behaviour of materials at such small scale differs strongly from macroscale. It requires the determination of strains/stresses, dislocation distribution and the overall microstructure evolution, which is often extremely challenging. Industrial applications (i.e. micro-sensors) have become wide-spread and used every day as metal-based functional components. We can find them in the harshest, most demanding environments, such as satellites, mobile devices, etc. In order for these components to operate precisely and reliably, it is necessary to construct them according to the micro-scale deformation mechanisms. Microstructural processes during external mechanical loading are hard to observe due to the complex multiscale nature of the phenomenon. Materials’ behaviour has mostly been studied experimentally at low strain rates (below 1/s) and moderate temperatures (from room temperature up to ~400°C). Recent developments can now allow us to explore high strain rate (up to 1000/s) related effects and compare modelling results with experimental observations. It is thus essential to understand dislocation-related size effects at this small scale not only at normal conditions (room temperature, slow deformation) but also in case of extreme situations.
When hydrogen is present in the solid (i.e. by wet electrochemical processes, introduced during manufacturing / environmental exposure or after contact with high pressure gaseous H), it can cause embrittlement or enhanced cracking, when the material is subjected to stress. This would eventually lead to the reduced lifetime or critical failure of the component. Although it is known for a long time that hydrogen causes degradation of mechanical performance in metals, the microscale mechanisms remain a subject of debate.
Project INSTINCT aims at paving the way towards mechanical characterization of materials subjected to extreme environmental conditions at small scales. These extremities include high strain rates (<1000/s) and temperatures varying between cryogenic (down to -150°C) up to medium ranges (room temperature to ~400°C). In particular, project INSTINCT aims to study materials’ characteristics in the hydrogen context by gaining knowledge on how the presence of hydrogen modifies dislocation nucleation and mobility. The interaction of dislocations and H atoms with phase/grain boundaries will be investigated through the application of in situ high spatial resolution experiments within the framework of the project. An in situ H-charging setup will be designed to resolve the continuous H-outgassing issue. This device will be compatible with the nanoindentation stage and the scanning electron microscope, allowing simultaneous deformation and microstructural analysis of miniaturized specimens. The proposed innovative and unique approach will support the attempt to push towards zero-emission mobility and energy efficient development.
The project will not only contribute to fundamental science, but it will support the European Commission's (and France's newly presented) initiatives regarding hydrogen strategy by 2030. The proposed research topics show a novel approach in experimental physics. The unique combination of the involved experimental methods has never been implemented before to resolve the behaviour of dislocations in the presence of hydrogen, and therefore project INSTINCT has a great potential for innovative materials scientific research.