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Abe, Yosuke; Sasaki, Taisuke*; Yamashita, Shinichiro; Okubo, Nariaki; Ukai, Shigeharu
no journal, ,
In Fe-Cr-Al alloys, which are being developed as accident-resistant fuel cladding for light water reactors, it is a challenge to accurately predict the precipitation behavior of the Cr-rich embrittlement phase (
phase), which occurs at relatively low temperature irradiations. However, the formation behavior of the phase under neutron irradiation is not well understood due to global limitations of irradiation reactors. In this study, the influencing factors (Cr concentration, Al concentration, and damage rate) on phase formation were quantitatively evaluated by combining systematic irradiation experiments for 14 types of alloys at three levels of damage rate and multiple regression analysis. The results also contributed to the development of more accurate 
/(+) phase boundary curves based on Cr and Al concentrations, which are important in actual alloy design.
Suzudo, Tomoaki; Ebihara, Kenichi; Tsuru, Tomohito; Mori, Hideki*
no journal, ,
In the previous study, we have performed large-scale 3D cleavage simulations using the machine-learning interatomic potential of BCC iron and confirmed that at 0 K, dislocations are emitted from the crack tip of the 
plane and crack propagation is suppressed. This result confirms that {100} is the only crack plane observed experimentally at low temperatures. In the present study, we performed an atomic fracture simulation analysis at finite temperatures using the same interatomic potential for {100} planes and grain boundaries. As a result, plastic deformation was found to occur in some of the crack front directions, and the mechanism of plastic deformation was investigated in detail.
Lobzenko, I.; Shiihara, Yoshinori*; Mori, Hideki*; Matsunaka, Daisuke*; Tsuru, Tomohito
no journal, ,
Refractory multi-component alloys (MCA) form an important class of materials with high potential for use in severe conditions. One of the main problems hindering the application of these alloys is the low ductility inherited from the body-centred cubic (BCC) crystal structure. Dislocation motion is the factor significantly influencing the ductility of the material, so a comprehensive understanding of the dislocation dynamics in refractory MCAs should be achieved to pave the way for designing refractory alloys with increased ductility. To achieve high accuracy in classical molecular dynamics simulations of dislocation motion, we apply the technique of machine learning (ML) for interatomic potential development. It is known that alloys with hexagonal closed-packed (HCP) elements such as Zr exhibit higher ductility, which is why two medium-entropy alloys, MoNbTa and ZrNbTa, were chosen to study the influence of elements' constitution on dislocations dynamics. The inter-atomic potentials for MCAs built using ML need a specific dataset. In the process of the potential development, we identify which structures contribute to a better quality of materials' mechanical properties prediction by the potentials. Results of the simulations have shown qualitative and quantitative differences between the two alloys under study. One example of that difference can be seen in the shapes of the screw dislocation core. In contrast to MoNbTa, ZrNbTa demonstrates a non-compact core with an extension on a (110) plane.
Gong, W.; Harjo, S.; Kawasaki, Takuro; Aizawa, Kazuya; Tsuji, Nobuhiro*
no journal, ,
no abstracts in English
Harjo, S.; Mao, W.; Gong, W.; Kawasaki, Takuro; Gao, S.*
no journal, ,
no abstracts in English
Imatomi, Daisuke*; Ishikawa, Ryosuke*; Nakata, Akira*; Ito, Tatsuya; Han, K.*; Nagasako, Makoto*; Xu, X.*; Omori, Toshihiro*; Kainuma, Ryosuke*
no journal, ,
no abstracts in English
Shimizu, Raiki*; Xu, X.*; Ito, Tatsuya; Gong, W.; Harjo, S.; Omori, Toshihiro*; Kainuma, Ryosuke*
no journal, ,
no abstracts in English
Ito, Yuto*; Egusa, Daisuke*; Yamaguchi, Masatake; Abe, Eiji*
no journal, ,
Among HCP metals, Zn and Cd, which exhibit high c/a ratios, exhibit a peculiar deformation mode with crystal rotation called kink deformation under conditions where the main slip system is suppressed. Although a model of kink deformation has been proposed based on collective rearrangement of dislocations, the details of the kink deformation have not been clarified. In this study, we evaluate the phonon dispersion relation using first-principles calculations for HCP metals under uniaxial compression in the basal plane, where kink deformation is known to occur, and verify the generalized stacking fault energy, which is considered important for characterization of dislocations.
Mao, W.; Gao, S.*; Gong, W.; Harjo, S.; Kawasaki, Takuro
no journal, ,
Traditional austenitic stainless steels (ASSs), such as 304, have good low-temperature toughness and are the most commonly used low-temperature materials. However, due to the face-centered cubic (FCC) crystal structure, their yield strength remains relatively low at cryogenic temperatures. Recent studies reveal that ultrafine-grain (UFG) refinement of 304 ASS can be easily achieved by heavy cold-rolling and subsequent annealing. Compared to conventional 304 ASS with coarse grains, the UFG 304 ASS has significantly higher yield strength owing to the grain refinement strengthening, while it still maintains good ductility. However, current research mostly focused on the mechanical properties of UFG 304 ASS at room temperature, and its low-temperature mechanical properties are still unclear. In this study, we systematically investigated the tensile deformation behavior of an UFG 304 ASS at different temperatures ranging from 77 to 295K. The results showed that the optimal mechanical properties were achieved at 77 K, with extremely high yield strength and ultimate tensile strength as well as a relatively good elongation. The role of deformation-induced martensitic transformation in the low-temperature deformation process of UFG 304 ASS was discussed in light of in-situ neutron diffraction and microstructure observation.
Ito, Tatsuya; Ogawa, Yuhei*; Gong, W.; Kawasaki, Takuro; Okada, Kazuho*; Shibata, Akinobu*; Harjo, S.
no journal, ,
no abstracts in English