Berlin 2008 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 47: SYM Hydrogen in Materials: New Developments V

MM 47.2: Vortrag

Freitag, 29. Februar 2008, 10:35–10:55, H 1058

Hydrogen embrittlement revisited by in-situ electrochemical nanoindentation — •Afrooz Barnoush and Horst Vehoff — Saarland University Bldg. D22 P.O. Box 151150, Postcode D-66041, Saarbruecken, Germany

Electrochemical NI-AFM was used to examine the effect of hydrogen on dislocation nucleation. It was shown that hydrogen reduces the pop-in load in all of the tested materials except Cu. The reduced pop-in load can be interpreted as the HELP mechanism. Classical dislocation theory was used to model the homogeneous dislocation nucleation and it was shown that H reduces the activation energy for dislocation nucleation. The activation energy for dislocation nucleation is related to the material specific parameters; shear modulus, dislocation core radius and in the case of partial dislocation nucleation, stacking fault energy. These material properties can be influenced by H resulting in a reduced activation energy for dislocation nucleation. The universality of cohesion in metals relates the reduction of the shear modulus to the reduction of the cohesion, meaning HEDE mechanism. The increase in the core radius of a dislocation due to H is a direct evidence of decrease in dislocation line energy and H segregation on the dislocation line. In the case of partial dislocations, the H can segregate on to the stacking fault ribbon and decrease stacking fault energy.

Thus, depending on the experimental approach utilized to probe the H effect, either HELP or HEDE can be observed. In this study by utilizing a proper experimental approach, it was possible to resolve the interconnected nature of the HE.