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Tsuru, Tomohito; Aoyagi, Yoshiteru; Kaji, Yoshiyuki
Materials Research Society Symposium Proceedings, Vol.1298, 6 Pages, 2011/04
Dislocation channeling observed in irradiated metals is generated as the result of strain localization and it has been thought to be the dominant stress factor in irradiation assisted stress corrosion cracking. In the present study, a hierarchical computational modeling based on atomistic and continuum simulations were constructed to describe the fundamental characteristics of the plastic deformation in irradiated materials. Several anomalous defects are introduced under irradiation. At first individual influences of the irradiation defects on plastic deformation can be identified by atomistic simulations. Then local interaction events between glide dislocation and irradiation defects were introduced into the crystal plasticity finite element analysis. We found that softening after the first yield event observed in experimental study is caused by annihilation of irradiation defects resulting from unfaulting by dislocation sweeping.
Kim, G.; Shiba, Kiyoyuki; Sawai, Tomotsugu; Ioka, Ikuo; Kiuchi, Kiyoshi
Materials Research Society Symposium Proceedings, Vol.1298, p.61 - 66, 2011/04
The irradiation behaviour in two different precipitation hardening types of Ni-base alloys with the ultra high purity grade (EHP), namely, the 
' type and G phase type was investigated by multi-ion beam techniques simulated to the irradiation conditions in fuel cladding tubes used in sodium cooled FBRs. Single ion-beam irradiation tests were conducted up to 90 dpa (by Fe
or Ni) at 673 K. Triple ion-beam irradiation tests were conducted up to 90 dpa (by Ni, 90 appmHe and 1350 appmH) at 823 K. The irradiation behaviour was examined by nano-indentation tests to irradiation hardening, and the microscopic observation by TEM to the distribution of dislocations, cavities and voids. The behaviour was compared with those of PNC316. The dominating irradiation defects in EHP(') alloy at 673 K by single ion-beam are Frank loops, perfect unfaulted loops and line dislocations. Whereas, those of EHP(WSi) alloy are the irradiation-induced G phase precipitates along 
planes. Those dominating defect structures at 823 K by triple ion-beam are classified as followings, bimodal distributions in EHP('), bubbles in EHP(WSi) and voids in PNC316. The ratio of void swelling is estimated as nearly 0.01% in EHP(WSi), 0.2% in EHP('), 3.4% in PNC316. From those results, the excellent irradiation properties of EHP(WSi) alloy is clarified as the inhibition effects of secondary irradiation defects.
-ray irradiated high-temperature waterNakahara, Yukio; Kato, Chiaki; Yamamoto, Masahiro; Tsukada, Takashi; Watanabe, Atsushi*; Fuse, Motomasa*
no journal, ,
Irradiation effects on the corrosion of stainless steel (SS) in high-temperature water have been studied. The corrosion in diffusion-restricted environment was examined with simulated crevice-shape samples. Test specimens were made of Type 316L SS. The specimens have been immersed in deaerated high purity water of 288 
C with -ray irradiation for 500 hours. The source of the rays was 
Co. The maximum absorbed dose rate in the water was estimated to be about 30 kGy h
. Characteristics of the surface oxide formed on the tested secimens have been analyzed using SEM, laser Raman Spectrometer (LRS), and TEM/EDX. On the surface of the irradiated specimens immersed as the crevice-shape samples, precipitated particles were observed but the surface was not fully covered with the particles. Besides the particles, bigger particles were observed on the surface. The LRS spectra indicated that the smaller particles were Fe-Ni spinels and the bigger particles were 
-Fe
O
. In-depth profiles of the surface taken using TEM/EDX showed that the smaller particles were Fe-Ni spinels and the bigger particles were -FeO. The bigger particles of -FeO were only observed in -ray irradiated crevice portion. It indicated that oxidants created by the irradiation changed the potential to nobler direction in the crevice-like environment.
Itakura, Mitsuhiro; Kaburaki, Hideo; Yamaguchi, Masatake
no journal, ,
Irradiation hardening in nuclear structural materials is induced by microstructure change in the material which hinders motion of dislocation. To identify the exact mechanism of irradiation hardening, precise knowledge about dislocation motion in the material is required, but the motion itself can not directly observed in experiments, and large scale quantum mechanical calculation is the only available method. In this presentation we report the first high-precision calculation of migration energy of screw dislocation in BCC iron using plane wave basis and generalized gradient approximation. We also calculated kink formation energy under applied stress using line tension model, and investigated temperature dependence of average screw glide direction. This work enables quantitative simulation of dislocation motion in BCC iron at finite temperature, which will leads to qualitative simulation of irradiation hardening.
-iron single crystal containing a grain boundary; Molecular dynamics simulationKaburaki, Hideo; Kadoyoshi, Tomoko; Itakura, Mitsuhiro; Yamaguchi, Masatake
no journal, ,
Many single crystal metals 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. Since the atomistic picture of brittle-to-ductile transition is still unknown, we have performed molecular dynamics simulations on the fracture process of iron single crystal by varying the temperature and strain rate in a wide range. From the atomistic results, we have found that the transition point shifts to the higher temperature due to the high strain rate.
