Berlin 2024 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 19: Topical Session: Hydrogen in Materials: from Storage to Embrittlement II

MM 19.4: Vortrag

Dienstag, 19. März 2024, 11:15–11:30, C 130

Hydrogen Effect on the Activation Enthalpy of Plastic Deformation — •Florian Schaefer, Rouven Schneider, Lukas Hasenfratz, and Christian Motz — Materials Science and Methods, Saarland University, Campus D2 3, 66123 Saarbruecken, Germany

The strain rate sensitivity of a material arises from a thermally activated contribution to the rate-determining deformation process, e.g. to dislocation slip or dislocation grain boundary interaction. For instance, nanocrystalline f.c.c. metals exhibit an increased strain rate sensitivity compared to a coarse-grained equivalent due to the constraints on dislocation plasticity caused by the multitude of grain boundaries. In this study, the extent to which hydrogen affects thermally activated dislocation mobility and thus the strain rate sensitivity was investigated. For this purpose, specimens were charged in situ, both cathodically and by low-pressure hydrogen plasma, and subjected to nanoindentation, micropillar compression, and strain-rate jump macro-tensile tests, and the results were contrasted. Hydrogen is shown to increase the strain rate sensitivity of f.c.c. nickel but not in a b.c.c structural steel. The temperature was then varied to the cryogenic level. For this purpose, the macro strain rate jump tests were carried out in a bath cryostat combined with ex situ charging. The low temperature prevents from outgassing. The activation volume for plastic deformation in a head-to-head comparison between nanocrystalline and coarsely grained f.c.c. nickel as well as the b.c.c. structural steel shows that the rate-determining deformation mechanism seems to change for f.c.c. but not for the b.c.c. material.

Keywords: Hydrogen; Strain rate sensitivity; plastic deformation; activation volume; activation enthalpy