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Tsuru, Tomohito; Kaji, Yoshiyuki
no journal, ,
Since the solute impurities have an effect on the embrittlement through segregation under irradiation, the solute stability of impurity elements is of considerable importance. In addition, the influence of irradiation on the diffusion characteristics of impurities becomes prominent due to the several acceleration effects of high irradiance circumstances. In the present study, the diffusion characteristic of large-radius impurities in iron are investigated by first principles calculations. The vacancy formation energy and binding energy between impurity and vacancy were obtained by first principles density functional theory (DFT) calculations. And the migration energy was calculated by nudged elastic band method collaborated with DFT. Finally, the entropic contributions to all free energies and jump frequency are evaluated by considering vibrational phonon frequencies based on frozen phonon employing the harmonic approximation for the lattice dynamics.
Igarashi, Takahiro; Komatsu, Atsushi; Yamamoto, Masahiro; Kaji, Yoshiyuki
no journal, ,
no abstracts in English
Kaburaki, Hideo
no journal, ,
Many single crystal metals, such as BCC iron, intrinsically exhibit brittle-to-ductile transition (BDT) as a function of temperature and strain rate. These materials are generally brittle at low temperatures or high strain rates, and become ductile as the temperature rises or the strain rate decreases. Although there have been many experimental studies on BDT, its mechanism is not clearly identified. We employed the atomistic method, molecular dynamics method, to clarify the mechanism of BDT for BCC iron. We studied the pure iron system containing one grain boundary to realize the BDT. We have found that the BDT temperature is shifted to the higher temperature region, compared to experiment, due to the high strain rate used in the molecular dynamics method.