M. Itakura, H. Kaburaki, M. Yamaguchi, T. Okita
We investigate the effect of hydrogen on the mobility of a screw dislocation in body-centered cubic (bcc) iron using first-principles calculations, and show that the increase of screw dislocation velocity is expected in a temperature range between the upper and lower critical temperature. The interaction energy between a screw dislocation and hydrogen atoms is calculated for various hydrogen positions and dislocation configurations, and the strongest binding energy of a hydrogen atom to the stable screw dislocation configuration is estimated as $256\pm32$ meV. These results are incorporated into a line tension model of a curved dislocation line to elucidate the effect of hydrogen on the dislocation migration process, and the reduction of kink nucleation enthalpy in the presence of a hydrogen atom is estimated as 110 meV. Both the softening and hardening effect of hydrogen, caused by the reduction of kink nucleation enthalpy and kink trapping, respectively, are evaluated. A clear transition between softening and hardening behavior at the lower critical temperature is predicted, which is in qualitative agreement with the experimental observation.
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http://arxiv.org/abs/1304.0602
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