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Tsuru, Tomohito; Lobzenko, I.; Wei, D.*
Modelling and Simulation in Materials Science and Engineering, 30(2), p.024003_1 - 024003_11, 2022/03
Times Cited Count：9 Percentile：77.62(Materials Science, Multidisciplinary)High-entropy alloys (HEA) have been receiving increased attention for their excellent mechanical properties. Our recent study revealed that Si-doped face-centered cubic (FCC) HEAs have great potential to improve both strength and ductility. Here, we carried out first-principles calculations in cooperation with Monte Carlo simulation and structural factor analysis to explore the effect of Si addition on the macroscopic mechanical properties. As a result, Si addition increased the local lattice distortion and the stacking fault energy. Furthermore, the SRO formation in Si-doped alloy caused highly fluctuated SF energy. Thus, the heterogeneous solid solution states in which low and high SF regions are distributed into the matrix were nucleated. This unique feature in Si-doped FCC-HEA induces ultrafine twin formation in Si-doped alloys, which can be a dominant factor in improving both strength and ductility.
Suzudo, Tomoaki; Onitsuka, Takashi*; Fukumoto, Kenichi*
Modelling and Simulation in Materials Science and Engineering, 27(6), p.064001_1 - 064001_15, 2019/08
Times Cited Count：16 Percentile：66.08(Materials Science, Multidisciplinary)Plasticity of body-centered-cubic (BCC) metals at low temperatures is determined by screw dislocation kinetics. Because the core of screw dislocation in these metals has non-planar structure, its motion is complex and unpredictable. For example, although density functional theory (DFT) predicts slip on a { 110 } plane, the actual slip plane at elevated temperatures departs from the prediction, its mechanism having been a mystery for decades. Here we conduct a series of molecular dynamics simulations to track the screw dislocation motion and successfully reproduced the transition of the slip plane. We then devised an algorithm to scrutinize the activation of dislocation jump over the Peierls barrier and discovered the possible origin of this unexpected phenomenon, i.e., a large fluctuation leads to the kink-pair nucleation for the cross-slip jump without transition of dislocation core structure.
3(111) symmetrical tilt grain boundary in 
-ironEbihara, Kenichi; Suzudo, Tomoaki
Modelling and Simulation in Materials Science and Engineering, 26(6), p.065005_1 - 065005_10, 2018/09
Times Cited Count：4 Percentile：20.17(Materials Science, Multidisciplinary)Irradiation-induced grain boundary phosphorus segregation is an important factor for estimating the embrittlement of nuclear reactor pressure vessel steels, but the physical process of phosphorus migration to grain boundaries is still unclear. We numerically studied phosphorus migration toward 3(111) symmetrical tilt grain boundary in -iron using molecular dynamics. We found that, in the vicinity of the grain boundary within 
1 nm distance, an iron-phosphorus mixed dumbbell and an octahedral interstitial phosphorus atom push a self-interstitial atom into the grain boundary, and the phosphorus atom becomes a substitutional atom. A phosphorus vacancy complex in the region also becomes dissociated, and the vacancy is absorbed in the grain boundary without dragging phosphorus. The results claim that a novel view of the segregation process is required.
Tsuru, Tomohito; Aoyagi, Yoshiteru*; Kaji, Yoshiyuki; Shimokawa, Tomotsugu*
Modelling and Simulation in Materials Science and Engineering, 24(3), p.035010_1 - 035010_10, 2016/03
Times Cited Count：12 Percentile：49.85(Materials Science, Multidisciplinary)The effect of the dislocation density on yield strength and subsequent plastic deformation of ultrafine-grained metals was investigated in large-scale atomistic simulations. Polycrystalline models were constructed and uniaxial tension and compression were applied to elucidate the heterogeneous plastic deformation and the Bauschinger effect. The initial yield becomes heterogeneous as the dislocation density decreases owing to a wide range of Schmid factors of activated slip systems in each grain. A different mechanism of the Bauschinger effect was proposed, where the Bauschinger effect of ultrafine-grained metals is caused by the change in dislocation density in the process of forward and backward loadings.
dislocation in magnesiumItakura, Mitsuhiro; Kaburaki, Hideo; Yamaguchi, Masatake; Tsuru, Tomohito
Modelling and Simulation in Materials Science and Engineering, 23(6), p.065002_1 - 065002_19, 2015/09
Times Cited Count：14 Percentile：49.9(Materials Science, Multidisciplinary)The cross-slip process of a screw dislocation from the basal to the prismatic plane in magnesium was studied using the density functional theory and the molecular dynamics calculations. An atomistic method for calculating the total Peierls energy map has been devised to track the transition path of a dissociated and/or constricted screw dislocation in the cross-slip process. The barrier of a screw dislocation from the basal to the prismatic plane is estimated by the density functional theory for the first time. The activation enthalpy for the cross slip is calculated using a line tension model based on the density functional theory to be 1.4 to 1.7 eV, which is in reasonable agreement with experiments. On the basis of the results, the effect of temperature on the cross-slip process of the dissociated screw dislocation on the basal plane is studied in detail using the molecular dynamics method.
Suzudo, Tomoaki; Yamaguchi, Masatake; Hasegawa, Akira*
Modelling and Simulation in Materials Science and Engineering, 22(7), p.075006_1 - 075006_13, 2014/10
Times Cited Count：78 Percentile：92.55(Materials Science, Multidisciplinary)We report a series of 
studies based upon density functional theory for the behavior of rhenium and osmium atoms in tungsten crystal. Contrary to the one-dimensional migration of self-interstitial atoms, interstitials of these solute elements in tungsten have three-dimensional motion. The diffusion of these solute elements strongly influences the effects of radiation upon the materials, and we found that the three-dimensional migration is a property that is key to the explanation of the radiation effects experimentally observed in tungsten-rhenium and tungsten-osmium alloys.
-Fe; A Common feature over different grain boundariesSuzudo, Tomoaki; Yamaguchi, Masatake; Tsuru, Tomohito
Modelling and Simulation in Materials Science and Engineering, 21(8), p.085013_1 - 085013_8, 2013/12
Times Cited Count：9 Percentile：37.98(Materials Science, Multidisciplinary)He atoms introduced to materials may lead them to intergranular fracture, and understanding such an effect is a key issue for the design of future fusion reactors. In the present study, we investigated the decrease of grain boundary (GB) strength caused by He segregation at several kinds of -Fe GBs by exploiting the first principles calculations and a set of empirical potentials. We found enough evidence to support the notion that the GB cohesive energy, a critical measure of GB strength, approximately scales with the He concentration at the GB surface, regardless of the GB type.
