Advanced experiments for characterizing and understanding hydrogen-assisted mechanical degradation

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Presence of hydrogen in metals causes often a change in fracture mode from ductile transgranular to less ductile or brittle intergranular. For understanding the role and mechanisms of hydrogen induced degradation, it is necessary to know the local hydrogen concentration inside the grains and more especially at material inhomogeneities like grain boundaries (GBs). During this project, AFM-based scanning Kelvin probe force microscopy (SKPFM) will be used for studying local hydrogen distribution at coarse grained and pulse electrodeposited nanocrystalline nickel samples. The samples will be charged with hydrogen in a newly designed electrochemical cell. The incorporation of the cell into an AFM, enables us to study the impacts of i) type of GBs (e.g. tilt or twist), ii) segregations at the GBs, iii) pile-up of dislocations at the GBs and iv) grain sizes, on the local hydrogen content and hydrogen diffusion rate. In-situ nanoindentation measurements will be performed in order to evaluate the relationship between hydrogen content with local mechanical properties. Studying the contributions of applied external uniaxial tensile stress on the plasticity of a defined GB will be another subject of this work. Moreover, the influence of segregations at the GBs on work hardening and deformation processes in addition to their impact on the local hydrogen concentration will be evaluated.