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 [1], dislocation distribution [2, 3] and the overall microstructure evolution, which is often extremely challenging. Microstructural processes during external mechanical loading are hard to observe due to the complex multiscale nature of the phenomenon.

If hydrogen is present in the solid (i.e. by wet electrochemical processes, introduced during manufacturing and  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. Direct H-detection within the lattice is an extremely challenging task, while one has to deal with continuous diffusion and outgassing issues from the studied samples. Microstructure observations are still mostly performed post mortem on bulk samples. Due to the mobility of H in metals it is critical to have continuous hydrogen charging on the test piece.

In situ H-charging is therefore essential for future experiments. Samples can be loaded electrochemically through the back surface [4], using a stage compatible with high-vacuum (HV) scanning electron microscopes (SEM). This way, H diffuses into the lattice from the back, avoiding contamination to the surface of interest. The current phase of such a development will be discussed in details during this talk, focusing on the coupling of the cell with the nanodeformation stage by performing nanoindentation experiments on H-charged metallic samples.

References

[1] S. Wang, S. Kalácska, X. Maeder, J. Michler, F. Giuliani, T. B. Britton, The effect of δ-hydride on the micromechanical de-formation of a Zr alloy studied by in situ high angular resolution electron backscatter diffraction, Scripta Materialia 173 (2019) 101-105. doi: 10.1016/j.scriptamat.2019.08.006

[2] S. Kalácska, Z. Dankházi, G. Zilahi, X. Maeder, J. Michler, P. D. Ispánovity, I. Groma, Investigation of geometrically necessary dislocation structures in compressed Cu micropillars by 3-dimensional HR-EBSD, Materials Science and Engineering A 770 (2020) 138499. doi: 10.1016/j.msea.2019.138499

[3] P. D. Ispánovity, D. Ugi, G. Péterffy, M. Knapek, S. Kalácska, D. Tüzes, Z. Dankházi, K. Máthis, F. Chmelík, I. Groma, Disloca-tion avalanches are like earthquakes on the micron scale, Nature Communications 13 (2022) 1975. doi: 10.1038/s41467-022-29044-7

[4] J. Kim, C. C. Tasan, Microstructural and micro-mechanical characterization during hydrogen charging: An in situ scanning electron microscopy study, International Journal of Hydrogen Energy 44 (12) (2019) 6333-6343. doi: 10.1016/j.ijhydene.2018.10.128