Regensburg 2019 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 27: Methods in Computational Materials Modelling (methodological aspects, numerics)

MM 27.8: Vortrag

Mittwoch, 3. April 2019, 17:00–17:15, H44

Hydrogen enhanced cross-slip of dislocations in the vicinity of grain boundaries in nickel — •Ali Tehranchi, Tilmann Hickel, and Jörg Neugebauer — Max-Planck-Institut für Eisenforschung GmbH, D-40237 Düsseldorf, Germany

Extensive experimental observations indicate the presence of nano-voids and an increase of the free volume along grain boundaries in hydrogen contaminated metals. This phenomenon is rate-dependent and assumed to be connected to hydrogen embrittlement of Ni based alloys. However, an understanding of the underlying mechanism is lacking. In the present study a mechanism for an enhanced cross slip of the dislocations in the close vicinity of the grain boundaries is demonstrated by performing molecular dynamics (MD) simulations. The interaction of the screw dislocations with a variety of symmetric tilt grain boundaries in H-charged and H-free bicrystalline nickel specimens are examined. The presence of the segregated hydrogen atoms at the grain boundaries induces a stress field around them and thus the barrier for cross-slip of screw dislocations considerably decreases. The enhanced cross slip of dislocations facilitates the formation of jogs *below a critical loading rate *. These jogs are found to emit vacancies during glide processes. The mechanism discovered in this study shows nano-scale evidence of a rate sensitive enhanced vacancy formation and a subsequent increase in the free volume along the grain boundaries in the presence of H.