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Tsuru, Tomohito; Yuge, Koretaka*; Aoyagi, Yoshiteru*; Shimokawa, Tomotsugu*; Kubo, Momoji*; Ogata, Shigenobu*
no journal, ,
High entropy alloys (HEAs) are chemically complex single- or multi-phase alloys with crystal structures. There are no major components but five or more elements are included with near equiatomic fraction. In such a situation, deformation behavior can no longer be described by conventional solid solution strengthening model. Some HEAs, indeed, show higher strengthening behavior and anomalous slip. However, the mechanisms of these features have yet to be understood. In the present study, we investigate the core structure of dislocations in BCC-HEAs using density functional theory (DFT) calculations. We found that core structure of a screw dislocation is identified as is the case with common BCC metals. On the other hand, dislocation motion should be different from pure BCC metals because of chemical and configurational disorder around dislocation core. We confirmed the specific feature of dislocation motion in HEAs by two-dimensional Peierls potential surface.
Tsuru, Tomohito
no journal, ,
We explored softening/strengthening behavior in various solutes in W matrix by density functional theory (DFT) calculations combined with a solid solution model. In addition, we proposed a method for the dynamics motion of a screw dislocation based on kink nucleation and kink migration, in which the Hamiltonian of a dislocation is described by line tension model. As a result of DFT calculations for various solutes, a clear trend was observed in the interaction energy between a solute and a screw dislocation, which has predominant influence on solid solution behavior. The predictions based on the solid solution model with DFT reasonably reproduced the complicated softening/strengthening as a function of temperature and solute concentration. Especially, some solutes such as Re with relatively-weak attractive interaction do not influence the pinning effect significantly while they can reduce the energy barrier for kink pair nucleation.
Okubo, Nariaki; Fujimura, Yuki
no journal, ,
An accelerator-driven subcritical system is a nuclear reactor design formed by coupling a substantially subcritical nuclear reactor core with a high-energy proton accelerator. In this system, lead-bismuth eutectic (LBE) is supposed to be used as coolant material of reactor core as well as neutron spallation sources. In this study, effect of irradiation on corrosion behavior was evaluated for 316L stainless steel and T91 ferritic/martensitic steel, which are ADS in-core candidate materials, through the immersion test under LBE with high and low oxygen concentration followed by ion irradiation experiment. Irradiations of 10 MeV-Fe
ions were conducted for T91 and SS316L steels at 450
C. After irradiation, the specimen was soaked in static LBE pod and started the corrosion test for about 400 hrs at 450C. The oxygen concentration in LBE was maintained at conditions of saturated concentration of around 10
wt% and at low concentration below 10
wt%. The surface morphology and cross sectional corrosion behavior were evaluated by SEM (Scanning Electron Microscope). In the case of soaking in LBE with saturated oxygen concentration for SS316L steels at 450C, 400hrs, non-irradiated region did not show clear oxide layer, however, irradiated region showed bi-layers of magnetite and spinel type oxide. In the case of low oxygen concentration, non-irradiated region showed pitting erosion, however, irradiated region showed bi-layer oxide formation. This result suggests that diffusion behavior after irradiation and mass transfer in the interface between LBE and steel surface is important for understanding of irradiation effect on liquid metal corrosion.
Ebihara, Kenichi; Suzudo, Tomoaki
no journal, ,
no abstracts in English
Y
alloy by neutron diffractionHarjo, S.; Aizawa, Kazuya; Gong, W.*; Kawasaki, Takuro
no journal, ,
no abstracts in English
Zn
clusterItakura, Mitsuhiro; Yamaguchi, Masatake
no journal, ,
no abstracts in English
Zhao, C.*; Suzudo, Tomoaki; Toyama, Takeshi*; Nagai, Yasuyoshi*
no journal, ,
Cu-rich precipitates play a significant role in embrittlement of nuclear reactor pressure vessel steels with high Cu concentration. It is important to understand the behavior of Cu atoms during precipitation. To evaluate the behavior of Cu atoms, diffusion coefficient of Cu is a key parameter. In this study, to understand the behavior of Cu atoms in Fe-Cu alloy, we aim to simulate the behavior of Cu atoms using kinetic Monte Carlo simulation, and to compare the corresponding experimental results which measured by 3D atom probe tomography.