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Journal Articles

Molecular dynamics simulations of phosphorus migration in a grain boundary of $$alpha$$-iron

Ebihara, Kenichi; Suzudo, Tomoaki

TMS 2020; 149th Annual Meeting & Exhibition Supplemental Proceedings, p.995 - 1002, 2020/02

Phosphorus (P) is known as an element which causes grain boundary (GB) embrittlement in steels. In addition, GB P segregation is promoted by the increase of vacancies and self interstitial atoms due to irradiation. Thus, the diffusion rate theory model for estimating irradiation-induced GB P segregation has been developed based on the atomic processes. Since the present model does not include the trapping and de-trapping processes at GBs, however, it cannot calculate the value which is directly compared with experimental results. In this study, we simulated the migration of a P atom in the $$Sigma$$3(111) symmetrical tilt GB. In addition, by tracking the migration of the P atom, the diffusion barrier energy was evaluated. As a result, the diffusion barrier energy was almost the same as the P segregation energy of an interstitial site in the GB, and it was found that P atoms migrate via interstitial sites in the GB.

Journal Articles

Austenite-based stainless steel irradiation behavior of the precipitate and void swelling

Inoue, Toshihiko; Sekio, Yoshihiro; Watanabe, Hideo*

Materia, 58(2), P. 92, 2019/02

For the evaluation of irradiated segregation behavior, Austenite-based stainless steel for the fast reactor, during irradiation was evaluated by utilizing TIARA facility (Irradiate temperature: 600 $$^{circ}$$C, Dose: 100 dpa) was observed by analytical electron microscope (JEM-ARM20FC). As a result of observation, the large-size void is observed in irradiation area, and MX segregation (containing Niobium) is not observed. In un-irradiation area the MX segregation is observed. And it is observed conspicuously that Nickel is segregation on the void surface. By the latest high-performance TEM utilization, these phenomenon are able to visualize. It is expected for the clarification of the irradiation damage and mechanism of void swelling, by the analyzing these phenomenon utilization with the latest high-performance TEM utilization.

Journal Articles

Atomistic simulation of phosphorus segregation to $$Sigma$$3(111) symmetrical tilt grain boundary in $$alpha$$-iron

Ebihara, Kenichi; Suzudo, Tomoaki

Modelling and Simulation in Materials Science and Engineering, 26(6), p.065005_1 - 065005_10, 2018/09

 Times Cited Count:1 Percentile:83.29(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 $$Sigma$$3(111) symmetrical tilt grain boundary in $$alpha$$-iron using molecular dynamics. We found that, in the vicinity of the grain boundary within $$sim$$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.

Journal Articles

Radiation enhanced precipitation of solute atoms in AlCu binary alloys; Energetic ion irradiation experiment and computer simulation

Mayumi, Ren*; Semboshi, Satoshi*; Okamoto, Yoshihiro; Saito, Yuichi*; Yoshiie, Toshimasa*; Iwase, Akihiro*

Transactions of the Materials Research Society of Japan, 42(1), p.9 - 14, 2017/02

AlCu binary alloys were irradiated with 16 MeV Au, 4.5 MeV Ni or 4.5 MeV Al ions at room temperature. Changes in surface hardness and the local atomic structure around Cu atoms were examined by using the Vickers hardness measurement and the EXAFS measurements, respectively. Some specimens were aged at 453 K and Vickers hardness was measured. The computer simulation was also performed by using the rate equation method. The hardness of irradiated specimens increased much faster than that of the aged specimens and it became larger than the maximum value of the hardness for the aged specimens. The comparison of the experimental EXAFS result with that of FEFF simulation suggests that the ion irradiation produced small Cu precipitates in the specimens. The computer simulation visualized the growth process of Cu precipitates during the irradiation, and the result qualitatively corresponds to the experimental result.

Journal Articles

Modeling of Phosphorus Transport by Interstitial Dumbbell in $$alpha$$-Iron Using First-Principles-Based Kinetic Monte Carlo

Ebihara, Kenichi; Suzudo, Tomoaki; Yamaguchi, Masatake

Materials Transactions, 58(1), p.26 - 32, 2017/01

 Times Cited Count:3 Percentile:62.87(Materials Science, Multidisciplinary)

In order to evaluate grain boundary (GB) phosphorous (P) segregation in nuclear reactor pressure vessel steels under irradiation, the rate-theory model based on first-principles calculations is developed. In this study, we evaluated the diffusion coefficient of the mixed interstitial dumbbell of a P atom and an iron(Fe) atom using a kinetic Monte Carlo (kMC) simulation based on first-principles calculations. The evaluated diffusion coefficient was almost the same with the diffusion coefficient of P atoms which migrate via octahedral interstitial sites, and was much faster than that for P transport by vacancies. Furthermore, from the simulation of the irradiation induced GB P segregation using the model which was modified to include P atoms of octahedral interstitial sites, it was found that the boundary condition at GB is not valid for P atoms of octahedral interstitial sites

Journal Articles

Investigation of segregation during oxidation of Ni-Cu alloy by ${{it in situ}}$ photoelectron spectroscopy

Doi, Takashi*; Nishiyama, Yoshitaka*; Yoshigoe, Akitaka; Teraoka, Yuden

Surface and Interface Analysis, 48(7), p.685 - 688, 2016/07

 Times Cited Count:2 Percentile:91.81(Chemistry, Physical)

Ni-based alloys has been widely used for plant application because of their high strength and excellent oxidation resistance. In particular, the addition of Cu in Ni-based alloys significantly improves the metal dusting resistance. It is indicated that Cu is segregated on the alloy surface in the metal dusting environment; however, the details have not been clarified yet. The behavior of Ni-2Cu alloy under a high temperature oxidation environment was investigated using ${{it in situ}}$ X-ray photoelectron spectroscopy. It was confirmed that Cu have been segregated at the surface of Ni-2Cu alloy during oxidation. These results propose that the Cu segregation improves the metal dusting resistance.

Journal Articles

Study on the effect of phosphorous concentration on intergranular corrosion of stainless steel in boiling nitric acid solution

Ueno, Fumiyoshi; Komatsu, Atsushi; Igarashi, Takahiro; Yamamoto, Masahiro

Proceedings of European Corrosion Congress 2014 (EUROCORR 2014) (USB Flash Drive), 10 Pages, 2014/09

In this paper, the effect of phosphorous concentration in grain boundary (GB) on intergranular corrosion (IC) progress was studied to understand GB corrosion behavior of stainless steels in boiling nitric acid solution. Phosphorus (P) added extra high purity type 310 stainless alloy was corroded in boiling nitric acid solution, and P in GB was detected by three-dimensional atom probe. IC progress considering with P profile in GB was studied by numerical simulation using cellular automaton method. As the results, we concluded that P concentration change around 1.4at% in GB of the alloy caused IC rate change in boiling nitric acid solution. The developed numerical method could simulate GB corrosion change with P distribution in GB.

Journal Articles

Response to comment on "Grain Boundary Decohesion by Impurity Segregation in a Nickel-Sulfur System"

Yamaguchi, Masatake; Shiga, Motoyuki; Kaburaki, Hideo

Science, 309(5741), P. 1677d, 2005/09

Geng et al. claim in their comment that the segregation energy of sulfur atoms in a nickel grain boundary should be calculated not on average as we did but incrementally. From their own calculations using the incremental binding energies, they concluded that the two-monolayer (GB0 4/4, GB2 4/4) segregation that bring about the reduction of the tensile strength by one order of magnitude has only 1% occupation possibility. However, they miss the point that there are many paths to the (GB0 4/4, GB2 4/4) configuration. In our re-examined calculations, one path has the 50% possibility of the occupation even if we use the incremental binding energies. Furthermore, there may be other paths that have larger possibility. To begin with, Geng et al.'s claims are not meaningful because the prediction of the occupation possibility using the simple McLean's model is not quantitative but qualitative. On the other hand, they claim that another two-monolayer (GB1 4/4, GB2 4/4) configuration brings about the reduction of the tensile strength by one order of magnitude. Their results may be miscalculations, because that is not the case in our re-examined calculations. Furthremore, they suggest a new mechanism of the strong decohesion due to the directional change of the Ni-S bonds. However, they do not show any clear evidence.

Journal Articles

Effect of heat treatments on mechanical properties and microstructures of 8Cr-2W(F82H) steel doped with boron or boron and nitrogen

Wakai, Eiichi; Sato, Michitaka*; Okubo, Nariaki; Sawai, Tomotsugu; Shiba, Kiyoyuki; Jitsukawa, Shiro

Nippon Kinzoku Gakkai-Shi, 69(6), p.460 - 464, 2005/06

 Times Cited Count:1 Percentile:82.49(Metallurgy & Metallurgical Engineering)

no abstracts in English

Journal Articles

Energetics of segregation and embrittling potency for non-transition elements in the Ni $$Sigma$$5 (012) symmetrical tilt grain boundary; A First-principles study

Yamaguchi, Masatake; Shiga, Motoyuki; Kaburaki, Hideo

Journal of Physics; Condensed Matter, 16(23), p.3933 - 3956, 2004/06

 Times Cited Count:55 Percentile:11.07(Physics, Condensed Matter)

A series of non-transition elements bound to the Ni $$Sigma$$5(012) symmetrical tilt grain boundary (GB) and the (012) free surface (FS) systems has been studied by first-principles calculation using WIEN2k code. The multilayer relaxations in presence/absence of the solutes are determined by the force minimization. The binding energies at some GB/FS/bulk sites including both interstitial and substitutional sites are calculated for all the non-transition elements between $$_1$$H and $$_{86}$$Rn. The GB/FS segregation energy is obtained by calculating the binding energy difference between the GB/FS site and the bulk site. The embrittling potency energy is obtained by calculating the difference between the GB and FS segregation energies based on Rice-Wang model. Our results show that most of the non-transition elements have negative GB/FS segregation energies. Here, this means that there exists a segregation site in the GB/FS. The embrittling potency energies are positive for most of the solutes. However, some exceptions like Be, B, C, and Si having negative and large embrittling potency can enhance the GB cohesion. Our results are found to be consistent with the experimental findings.

Journal Articles

Grain boundary embrittlement of light water reactor pressure vessel steels

Nishiyama, Yutaka; Suzuki, Masahide

Kinzoku, 73(8), p.48 - 52, 2003/08

no abstracts in English

Journal Articles

Corrosion behavior of stainless steels simulating radiation-induced segregation

Miwa, Yukio; Tsukada, Takashi

Proceedings of Symposium on Water Chemistry and Corrosion in Nuclear Power Plants in Asia 2003, p.301 - 306, 2003/00

Local composition change at grain boundaries due to radiation-induced segregation (RIS) followed by loss of corrosion resistance is considered to be a key mechanism on irradiation-assisted stress corrosion cracking (IASCC). However it is not clear that the local composition change induces the loss of corrosion resistance at grain boundaries, because RIS results in not only depletion of Cr but also enrichment of Ni and Si. This chemical composition change is different from that of thermally-sensitized stainless steels. In this study, experimental alloys were manufactured simulating the composition at grain boundaries of irradiated type 304 stainless steel and corrosion behavior of the experimental alloys was examined by weight loss measurement in 573 K water and anode polarization measurement in 1N sulfuric acid and 1mol/l sodium sulfate at 303 K. Following results were obtained: (1) In oxygenated water (DO=10ppm) at 573 K, weight loss increased with decreasing the concentration of Cr and did not depend on the concentration of Ni and Si. (2) Results of anode polarization measurements showed that alloys contained lower Cr and higher Ni and Si concentration exhibited lower corrosion potential in oxygenated, lower pH solution. In de-aerated solutions both sulfuric acid and sodium sulfate, however, there was a little influence of chemical composition on the corrosion potential.

Journal Articles

The State and trend of IASCC study

Tsukada, Takashi

Nippon Yosetsu Kyokai "Genshiryoku Kozo Kiki No Zairyo, Sekkei, Seko, Kensa Ni Kansuru Koshukai" Tekisuto, 40 Pages, 2002/00

no abstracts in English

JAEA Reports

None

*

JNC-TN1400 2001-013, 70 Pages, 2001/08

JNC-TN1400-2001-013.pdf:5.13MB

no abstracts in English

Journal Articles

Formation and migration of helium bubbles in Fe-16Cr-17Ni austenitic alloy at high temperature

Ono, K.*; Arakawa, Kazuto*; Ohashi, Masahiro*; Kurata, Hiroki; Hojo, Kiichi; Yoshida, Naoaki*

Journal of Nuclear Materials, 283-287(Part.1), p.210 - 214, 2000/12

 Times Cited Count:21 Percentile:19.3

no abstracts in English

JAEA Reports

None

Yamanaka, Shinsuke*; Uno, Masayoshi*; Kurosaki, Ken*; ; Namekawa, Takashi

JNC-TY9400 2000-011, 41 Pages, 2000/03

JNC-TY9400-2000-011.pdf:1.28MB

no abstracts in English

JAEA Reports

Post-lrradiation examination on Fe-15Cr-20Ni series model alloy irradiated by CMIR-2(1); Effect of defect sink and size of solute atom on radiation induced segregation(1)

; Yamagata, Ichiro; ; Akasaka, Naoaki

JNC-TN9400 2000-046, 24 Pages, 2000/02

JNC-TN9400-2000-046.pdf:1.1MB

lt is well known that solute atoms are segregated on surface, grain boundary, etc. and composition changed partially in irradiated austenitic stainless steel. For understanding radiation induced segregation (RIS), we adopt a Fe-15Cr-20Ni-x (x: Si, Mo) which is basically alloy system in PNC1520, and size of Si, Mo are different from matrix atoms to investigate RIS behaviors. The specimens were irradiated by "Joyo" fast reactor that irradiation condition is 3.5 $$times$$ 10$$^{26}$$ n/m$$^{2}$$ (E>0.1Mev) at 476$$^{circ}$$C. After irradiation, the specimen were observed and analyzed with EDS (Energy Dispersive X-ray Spectroscope) of 400kV TEM (Transmission Electron Microscope). The behavior of RIS depends on size of solute atoms of alloy. For example, oversized atoms are decreased and undersized atoms are increased in sink. RIS of voids are as same as or more than grain boundaries and smaller than precipitates. The void denuded zone was existed nearby G.B. in case of combinations between the grains from G.B.0ne of the reasons in this, the voids swepted by moving G.B. in radiation induced G.B. migration.

Journal Articles

Effects of neutron irradiation on tensile properties in high-purity Fe-(9-50)Cr and Fe-50Cr-xW alloys

Wakai, Eiichi; Hishinuma, Akimichi; Miwa, Yukio; Ouchi, Asao*; Isozaki, Seiichi*; Takaki, Seiichi*; Abiko, Kenji*

Materials Transactions, JIM, 41(1), p.136 - 140, 2000/01

no abstracts in English

Journal Articles

Phase transformation of high-purity Fe-50Cr-xW alloys during Fe$$^{+}$$ ion irradiation

Wakai, Eiichi; Hishinuma, Akimichi; Abe, Hiroaki; Miwa, Yukio; Takaki, Seiichi*; Abiko, Kenji*

Proc of Ultra-High-Purity Metallic-Base Materials (UHPM-98), p.35 - 45, 1998/00

no abstracts in English

JAEA Reports

None

; *; ; ; Takeda, Seiichiro

PNC-TN8410 97-104, 56 Pages, 1997/04

PNC-TN8410-97-104.pdf:2.1MB

None

51 (Records 1-20 displayed on this page)