Dresden 2011 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 28: Topical Session Electron Theory III

MM 28.5: Talk

Wednesday, March 16, 2011, 17:00–17:15, IFW A

Effect of H on homogeneous dislocation nucleation: Consequences for hydrogen embrittlement — •Johann von Pezold and Jörg Neugebauer — Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf, Germany

The embrittlement of modern high-strength steels is commonly explained by the HELP (Hydrogen-Enhanced Local Plasticity) mechanism. In its original form this mechanism attributes the embrittlement to a localized increase in plasticity resulting from a hydrogen-induced shielding of the stress fields of pre-existing dislocations. Recent in situ electrochemical nano-indentation experiments [1] suggest that H also reduces the critical shear stress for the homogeneous nucleation of dislocations in a range of metals. The observed reduction in the critical shear stress was correlated to a H-induced decrease in the stacking fault energy and/or shear modulus of the host material, as well as an increased dislocation core radius. In this study the model is evaluated using density-functional theory. In particular, the effect of H on the shear modulus and the stacking fault energy in Al, Ni and Cu was determined. Preliminary results indicate a significant reduction in the shear modulus and a moderate reduction in the stacking fault energy with increasing H content, in line with the originally proposed model. Whether or not the observed reduction in the critical shear stress for the dislocation nucleation can be explained by this model will depend on the H solubility under the elevated H chemical potential conditions in the in situ nano-indentation experiments.

[1] A. Barnoush and H. Vehoff, Acta. Mat. 58, 5274 (2010).