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Journal Articles

Achieving excellent mechanical properties in type 316 stainless steel by tailoring grain size in homogeneously recovered or recrystallized nanostructures

Liu, M.*; Gong, W.; Zheng, R.*; Li, J.*; Zhang, Z.*; Gao, S.*; Ma, C.*; Tsuji, Nobuhiro*

Acta Materialia, 226, p.117629_1 - 117629_13, 2022/03

 Times Cited Count:1 Percentile:0.01(Materials Science, Multidisciplinary)

Journal Articles

Effect of hydrogen on evolution of deformation microstructure in low-carbon steel with ferrite microstructure

Okada, Kazuho*; Shibata, Akinobu*; Gong, W.; Tsuji, Nobuhiro*

Acta Materialia, 225, p.117549_1 - 117549_13, 2022/02

 Times Cited Count:1 Percentile:81.79(Materials Science, Multidisciplinary)

Journal Articles

Metalloid substitution elevates simultaneously the strength and ductility of face-centered-cubic high-entropy alloys

Wei, D.*; Wang, L.*; Zhang, Y.*; Gong, W.; Tsuru, Tomohito; Lobzenko, I.; Jiang, J.*; Harjo, S.; Kawasaki, Takuro; Bae, J. W.*; et al.

Acta Materialia, 225, p.117571_1 - 117571_16, 2022/02

 Times Cited Count:5 Percentile:94.39(Materials Science, Multidisciplinary)

Journal Articles

Temperature-dependent hardening contributions in CrFeCoNi high-entropy alloy

Naeem, M.*; He, H.*; Harjo, S.; Kawasaki, Takuro; Lin, W.*; Kai, J.-J.*; Wu, Z.*; Lan, S.*; Wang, X.-L.*

Acta Materialia, 221, p.117371_1 - 117371_18, 2021/12

 Times Cited Count:7 Percentile:83.24(Materials Science, Multidisciplinary)

Journal Articles

Density functional theory study of solute cluster growth processes in Mg-Y-Zn LPSO alloys

Itakura, Mitsuhiro; Yamaguchi, Masatake; Egusa, Daisuke*; Abe, Eiji*

Acta Materialia, 203, p.116491_1 - 116491_9, 2021/01

 Times Cited Count:7 Percentile:87.55(Materials Science, Multidisciplinary)

Solute cluster in LPSO alloys plays a key role in their idiosyncratic plastic behavior such as kink formation and kink strengthening. Identifying the atomistic details of the cluster structure is a prerequisite for any atomistic modeling of LPSO alloys aiming for their improved strength and ductility, but there have been uncertainty about interstitial atom in the cluster. While density functional theory calculations have shown that inclusion of interstitial atom is energetically favorable, it has been unclear how the extra atom is provided, how much of the cluster have interstitial atoms, and what kind of element they are. In the present work we use density functional theory calculations to investigate the growth process of the solute cluster, specifically that of Mg-Y-Zn LPSO alloy, to determine the precise atomistic structure of solute cluster. We show that a pair of an interstitial atom and a vacancy is spontaneously created when a certain number of solute atoms are absorbed into the cluster, and all the full-grown cluster should include interstitial atom. We also show that interstitial atom is either Mg or Y atom, while Zn interstitial atom is extremely rare. These knowledge greatly simplifies atomistic modeling of solute clusters in Mg-Y-Zn alloy. Owing to the vacancies emitted from the cluster, vacancy density should be over-saturated in regions where solute clusters are growing, and the increased vacancy density accelerates cluster growth.

Journal Articles

Enhancement of fatigue resistance by overload-induced deformation twinning in a CoCrFeMnNi high-entropy alloy

Lam, T.-N.*; Lee, S. Y.*; Tsou, N.-T.*; Chou, H.-S.*; Lai, B.-H.*; Chang, Y.-J.*; Feng, R.*; Kawasaki, Takuro; Harjo, S.; Liaw, P. K.*; et al.

Acta Materialia, 201, p.412 - 424, 2020/12

 Times Cited Count:24 Percentile:95.69(Materials Science, Multidisciplinary)

Journal Articles

Continuous and discontinuous yielding behaviors in ferrite-cementite steels

Wang, Y.*; Tomota, Yo*; Omura, Takahito*; Gong, W.*; Harjo, S.; Tanaka, Masahiko*

Acta Materialia, 196, p.565 - 575, 2020/09

 Times Cited Count:17 Percentile:89.3(Materials Science, Multidisciplinary)

Journal Articles

Neutron diffraction monitoring of ductile cast iron under cyclic tension-compression

Harjo, S.; Kubota, Satoru*; Gong, W.*; Kawasaki, Takuro; Gao, S.*

Acta Materialia, 196, p.584 - 594, 2020/09

 Times Cited Count:6 Percentile:61.98(Materials Science, Multidisciplinary)

Journal Articles

Real time observation of martensite transformation for a 0.4C low alloyed steel by neutron diffraction

Wang, Y.*; Tomota, Yo*; Omura, Takahito*; Morooka, Satoshi; Gong, W.*; Harjo, S.

Acta Materialia, 184, p.30 - 40, 2020/02

 Times Cited Count:15 Percentile:89.3(Materials Science, Multidisciplinary)

Journal Articles

Neutron diffraction study of temperature-dependent elasticity of B19' NiTi; Elinvar effect and elastic softening

Ahadi, A.*; Khaledialidusti, R.*; Kawasaki, Takuro; Harjo, S.; Barnoush, A.*; Tsuchiya, Koichi*

Acta Materialia, 173, p.281 - 291, 2019/07

 Times Cited Count:12 Percentile:73.38(Materials Science, Multidisciplinary)

Journal Articles

Mechanism of hardening and damage initiation in oxygen embrittlement of body-centred-cubic niobium

Yang, P.-J.*; Li, Q.-J.*; Tsuru, Tomohito; Ogata, Shigenobu*; Zhang, J.-W.*; Sheng, H.-W.*; Shan, Z.-W.*; Sha, G.*; Han, W.-Z.*; Li, J.*; et al.

Acta Materialia, 168, p.331 - 342, 2019/04

 Times Cited Count:32 Percentile:95.27(Materials Science, Multidisciplinary)

Body-centred-cubic metallic materials, such as niobium (Nb) and other refractory metals, are prone to embrittlement due to low levels of oxygen solutes. The mechanisms responsible for the oxygen-induced rampant hardening and damage are unclear. Here we illustrate that screw dislocations moving through a random repulsive force field imposed by impurity oxygen interstitials readily form cross-kinks and emit excess vacancies in Nb. The vacancies bind strongly with oxygen and screw dislocation in a three-body fashion, rendering dislocation motion difficult and hence pronounced dislocation storage and hardening. This leads to unusually high strain hardening rates and fast breeding of nano-cavities that underlie damage and failure.

Journal Articles

Reversible elastocaloric effect at ultra-low temperatures in nanocrystalline shape memory alloys

Ahadi, A.*; Kawasaki, Takuro; Harjo, S.; Ko, W.-S.*; Sun, Q. P.*; Tsuchiya, Koichi*

Acta Materialia, 165, p.109 - 117, 2019/02

 Times Cited Count:27 Percentile:93.1(Materials Science, Multidisciplinary)

Journal Articles

Interfacial segregation and fracture in Mg-based binary alloys; Experimental and first-principles perspective

Tsuru, Tomohito; Somekawa, Hidetoshi*; Chrzan, D. C.*

Acta Materialia, 151, p.78 - 86, 2018/06

 Times Cited Count:45 Percentile:95.88(Materials Science, Multidisciplinary)

We investigated the effect of solute elements on interfacial segregation and fracture in Mg alloys by experiments and first-principles density functional theory calculations in conjunction with interfacial fracture mechanics. Based on the assumption of brittle fracture in Mg alloys, the interfacial separation caused by segregated solutes in Mg can be efficiently described by the energy-based criterion of fracture, which is in good agreement with the fracture toughness obtained by experimental tests of Mg-M binary alloys. The electronic interaction, that is, the change in the electronic state between the interface and surface, mainly influences the ideal work of separation regardless of the type of interface. We found that IIIB ($$d^{1}$$) and IVB ($$d^{2}$$) solutes, such as Zr, show distinctive hybridization between the p band of Mg and the d band of the solute, which characterizes the strong fracture toughness of Zr-doped Mg alloys in both the calculations and experiments.

Journal Articles

Effect of crystal orientation on incipient plasticity during nanoindentation of magnesium

Somekawa, Hidetoshi*; Tsuru, Tomohito; Singh, A.*; Miura, Seiji*; Schuh, C. A.*

Acta Materialia, 139, p.21 - 29, 2017/10

 Times Cited Count:23 Percentile:80.74(Materials Science, Multidisciplinary)

The effect of crystal orientation on incipient plasticity during nanoindentation was investigated by experiments and molecular statics simulation. Pop-in behavior is a result of dislocation activity, and is therefore influenced by crystal orientation. Experimental results using single crystals indicated that indentations on the basal plane had higher pop-in loads and larger pop-in displacements than those on the prismatic plane, an effect also captured by molecular statics simulation. The difference can be traced to the types of activated dislocations, with not only basal but also pyramidal dislocations active for indentations on the basal plane, but only basal dislocations triggered at the first pop-in on the prismatic plane.

Journal Articles

Chemical misfit origin of solute strengthening in iron alloys

Wakeda, Masato*; Tsuru, Tomohito; Koyama, Masanori*; Ozaki, Taisuke*; Sawada, Hideaki*; Itakura, Mitsuhiro; Ogata, Shigenobu*

Acta Materialia, 131, p.445 - 456, 2017/06

 Times Cited Count:18 Percentile:73.67(Materials Science, Multidisciplinary)

Most of the solute species show a significant interaction with the dislocation core, while only several solute species among them, such as Si, P, and Cu, significantly lower the Peierls potential of the screw dislocation motion. A first-principles interaction energy with the "Easy-core" structure excellently correlates with the change in the $$gamma$$-surface caused by solute atoms (i.e., chemical misfit). We show the availability of the interaction energy to predict the effect of each species on macroscopic critical resolved shear stress (CRSS) of the dilute Fe alloy. The CRSS at low and high temperature for various alloys basically agree with experiment CRSS. These results provide a novel understanding of the interaction between a screw dislocation and solute species from the first-principles.

Journal Articles

The Two-step nucleation of G-phase in ferrite

Matsukawa, Yoshitaka*; Takeuchi, Tomoaki; Kakubo, Yuta*; Suzudo, Tomoaki; Watanabe, Hideo*; Abe, Hiroaki*; Toyama, Takeshi*; Nagai, Yasuyoshi*

Acta Materialia, 116, p.104 - 113, 2016/09

 Times Cited Count:57 Percentile:95.61(Materials Science, Multidisciplinary)

Atom probe tomography (APT) and TEM were combined for identifying the stage at which solute clusters transform into compounds crystallographically distinct from the matrix, in the precipitation of the G-phase (Ni$$_{16}$$Si$$_{7}$$Mn$$_{6}$$) from ferrite solid solution subjected to isothermal annealing at 673 K. Based on a systematic analysis of solute clusters as a function of annealing time, the nucleation of the G-phase was found to occur via a two-step process. Moreover, the structural change was found to occur via another two-step process. There was a time lag between the end of cluster growth to become a critical size and the start of the structural change. During the incubation period solute enrichment occurred inside the clusters without further size growth, indicating that the nucleation of the G-phase occurs at the critical size with a critical composition. Judging from the results of APT, TEM and the simulation of electron diffraction patterns, the critical composition was estimated to be Ni$$_{16}$$Si$$_{3.5}$$(Fe,Cr)$$_{3.5}$$Mn$$_{6}$$.

Journal Articles

Effect of aluminum or zinc solute addition on enhancing impact fracture toughness in Mg-Ca alloys

Hase, Takayuki*; Otagaki, Tatsuya*; Yamaguchi, Masatake; Ikeo, Naoko*; Mukai, Toshiji*

Acta Materialia, 104, p.283 - 294, 2016/02

 Times Cited Count:37 Percentile:89.49(Materials Science, Multidisciplinary)

We measured the impact toughness of three alloys (Mg, Mg-0.3 at.% Ca-0.6 at.% Zn, and Mg-0.3 at.% Ca-0.6 at.% Al) by the impact three-point bending test. The plastic deformability and impact toughness were higher in the ternary alloys than in pure Mg. The generalized stacking fault energy and grain boundary cohesive energy were estimated by first-principles calculations for Mg, binary Mg-Ca, ternary Mg-Ca-Zn, and ternary Mg-Ca-Al alloys. The calculation results agreed with the trend in the experimental results. We suggest that addition of Ca along with Zn or Al reduced plastic anisotropy and strengthened the grain boundaries, leading to higher in impact toughness of Mg alloys.

Journal Articles

Hardening in thermally-aged Fe-Cr binary alloys; Statistical parameters of atomistic configuration

Suzudo, Tomoaki; Nagai, Yasuyoshi*; Schwen, D.*; Caro, A.*

Acta Materialia, 89, p.116 - 122, 2015/05

 Times Cited Count:11 Percentile:54.24(Materials Science, Multidisciplinary)

By exploiting Monte Carlo methodology and molecular dynamics, we computationally simulate the spinodal decomposition of iron-chromium binary alloys and analyze the relationship between the increase of yield stress induced by the phase separation phenomenon, and statistical parameters of the atomistic configuration. We successfully model the experimentally-discovered proportional relationship between the hardness and the variation parameter (or V), and also found that the adequacy of the parameter V as an empirical indicator of hardening is limited, because it does not properly capture short-range atomistic configurations that influence the hardening. We suggest that the short-range-order parameter has more potential to become universal descriptor of the phenomenon.

Journal Articles

Effect of prior martensite on bainite transformation in nanobainite steel

Gong, W.; Tomota, Yo*; Harjo, S.; Su, Y.; Aizawa, Kazuya

Acta Materialia, 85, p.243 - 249, 2015/02

 Times Cited Count:113 Percentile:98.9(Materials Science, Multidisciplinary)

Nanobainite transformation behavior was comparably studied using in situ neutron diffraction measurements, scanning electron microscopy and electron backscatter diffraction observations for two heat treatments: with and without partial quenching before isothermal holding at 523 or 573 K. Prior martensite transformation was found to accelerate the subsequent nanobainite transformation. Bainitic lathes formed adjacent to a pre-existing martensite plate exhibited an almost identical orientation. Dislocations introduced in austenite due to stress relaxation of transformation strains are believed to assist bainite transformation accompanying variant selection.

Journal Articles

The Effect of hydrogen atoms on the screw dislocation mobility in bcc iron; A First-principles study

Itakura, Mitsuhiro; Kaburaki, Hideo; Yamaguchi, Masatake; Okita, Taira*

Acta Materialia, 61(18), p.6857 - 6867, 2013/10

 Times Cited Count:82 Percentile:97.41(Materials Science, Multidisciplinary)

The interaction between dislocations and impurity atoms in metals determines various properties of plastic deformation, such as the dependence of the yield stress on the impurity contents. Since the direct observation of atomistic structure of screw dislocation is almost impossible, several hypothetical assumptions have been employed to explain conveniently experimental observations. Recent advancement of computational hardware, as well as the development of elaborated techniques to reduce the size-effect in the first-principles calculation, enabled direct calculations of dislocation-impurity interaction. We have succeeded to evaluate the effect of hydrogen atoms on the dislocation mobility in iron.

28 (Records 1-20 displayed on this page)