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Journal Articles

Effect of nickel concentration on radiation-induced diffusion of point defects in high-nickel Fe-Cr-Ni model alloys during neutron and electron irradiation

Sekio, Yoshihiro; Sakaguchi, Norihito*

Materials Transactions, 60(5), p.678 - 687, 2019/05

 Times Cited Count:5 Percentile:29.51(Materials Science, Multidisciplinary)

The quantitative evaluation of vacancy migration energies in high nickel model alloy was conducted by analyzing the void denuded zone (VDZ) width formed near grain boundaries under neutron and electron irradiation. The microstructures of Fe-15Cr-xNi (x=15, 20, 25, 30 mass%) alloys that were neutron irradiated at 749 K and electron irradiated at 576 K-824 K were examined. The VDZ widths increased with increasing Ni content in both irradiation experiments, which implies an increase of the vacancy mobility. The vacancy migration energies were estimated from the temperature dependence of the VDZ widths, and the energies were 1.09, 0.97, 0.90, and 0.77 eV for the alloys containing 15, 20, 25, and 30 mass% Ni, respectively. From the obtained energies, the effective vacancy diffusivity and excess vacancy concentration were estimated using the analytical equation of the VDZ width, which quantitatively confirmed the increase of the vacancy mobility with increasing Ni content.

Journal Articles

Evaluation of irradiation-induced point defect migration energy during neutron irradiation in modified 316 stainless steel

Sekio, Yoshihiro; Yamagata, Ichiro; Akasaka, Naoaki; Sakaguchi, Norihito*

Proceedings of International Conference on Fast Reactors and Related Fuel Cycles; Next Generation Nuclear Systems for Sustainable Development (FR-17) (USB Flash Drive), 8 Pages, 2017/06

The widths of void denuded zones (VDZs) which were formed near random grain boundaries by neutron irradiation were analyzed in order to perform quantitative evaluations for the irradiation-induced point defect behavior in the modified 316 stainless steel (PNC316) having been developed by JAEA. Namely, the temperature dependence of VDZ width was investigated and vacancy migration energy of the PNC316 steel was estimated from the VDZ width analysis for the neutron-irradiated specimens. The obtained value of vacancy migration energy was estimated as 1.46 eV, which was consistent with that from the exiting method using electron in-situ examination. This indicates that VDZ analysis could be effective method to evaluate especially vacancy migration energy during irradiation, and this would be realized from not in-situ observation but post-irradiation examination in the case of neutron irradiation.

Journal Articles

Void denuded zone formation for Fe-15Cr-15Ni steel and PNC316 stainless steel under neutron and electron irradiations

Sekio, Yoshihiro; Yamashita, Shinichiro; Sakaguchi, Norihito*; Takahashi, Heishichiro*

Journal of Nuclear Materials, 458, p.355 - 360, 2015/03

 Times Cited Count:22 Percentile:88.3(Materials Science, Multidisciplinary)

Irradiation-induced void denuded zone (VDZ) formation near grain boundaries was studied to clarify the effects of minor alloying elements on vacancy diffusivity during irradiation in PNC316 steel. The test materials were Fe-15Cr-15Ni steel without additives and PNC316 stainless steel, which contains minor alloying elements. These steels were neutron-irradiated in the experimental fast reactor JOYO and electron-irradiation was also carried out using 1 MeV high voltage electron microscopy. VDZ formation was analyzed from the TEM microstructural observations after irradiation. VDZs were formed near random grain boundaries in both Fe-15Cr-15Ni and PNC316 steels. The VDZ widths in the PNC316 steel were narrower than those for the Fe-15Cr-15Ni steel for all neutron and electron irradiations. The VDZ width analysis implied that the vacancy diffusivity was reduced in PNC316 steel as a result of interaction of vacancies with minor alloying elements.

Journal Articles

Effect of additional minor elements on accumulation behavior of point defects under electron irradiation in austenitic stainless steels

Sekio, Yoshihiro; Yamashita, Shinichiro; Sakaguchi, Norihito*; Takahashi, Heishichiro

Materials Transactions, 55(3), p.438 - 442, 2014/03

 Times Cited Count:9 Percentile:42.45(Materials Science, Multidisciplinary)

In order to perform the comparative evaluations for vacancy diffusivity and flux between a base alloy and modified alloys, the void denuded zones (VDZ) widths were measured from the TEM in-situ observation during electron irradiation in the SUS316L, SUS316L-V and SUS316L-Zr steels. As a result, VDZs with given widths were formed near GBs. Then, the VDZ widths were different depending on steels, and the width was narrower due to addition of minor alloying elements which strongly interact with vacancies. Furthermore, from the analyses of measured VDZ widths in the SUS316L and SUS316L-V steels, the changes of vacancy diffusivity, vacancy flux and excess vacancy concentration were estimated as 0.50, 0.71 and 1.41, respectively. The decreases of vacancy diffusivity and flux during electron irradiation would be due to the interaction of vacancies with added minor elements, while the enhancement of the excess vacancy concentration would be caused by trapping effects due to alloying elements.

Oral presentation

Irradiation resistance property of austenitic stainless steels prepared by grain boundary engineering processing, 1

Tanikawa, Ryusuke*; Sakaguchi, Norihito*; Watanabe, Seiichi*; Kinoshita, Hiroshi*; Kokawa, Hiroyuki*; Kawai, Masayoshi*; Yamashita, Shinichiro

no journal, , 

no abstracts in English

Oral presentation

Research and development of high performance FBR core materials based on grain boundary engineering, 1; Trial production

Yamashita, Shinichiro; Yano, Yasuhide; Endo, Masaki*; Sakaguchi, Norihito*; Watanabe, Seiichi*; Miyagi, Masanori*; Sato, Shinya*; Sato, Yutaka*; Kokawa, Hiroyuki*; Kawai, Masayoshi*

no journal, , 

no abstracts in English

Oral presentation

Research and development of high performance FBR core materials based on grain boundary engineering, 2; Evaluation of tensile properties

Yano, Yasuhide; Yamashita, Shinichiro; Endo, Masaki*; Sakaguchi, Norihito*; Watanabe, Seiichi*; Miyagi, Masanori*; Oyamada, Tetsuya*; Sato, Shinya*; Sato, Yutaka*; Kokawa, Hiroyuki*; et al.

no journal, , 

no abstracts in English

Oral presentation

Dependence evaluation on grain boundary characteristic for both irradiation and corrosion effects in austenitic stainless steels

Endo, Masaki*; Sakaguchi, Norihito*; Kinoshita, Hiroshi*; Watanabe, Seiichi*; Yamashita, Shinichiro; Yano, Yasuhide; Kawai, Masayoshi*

no journal, , 

no abstracts in English

Oral presentation

Dependence evaluation on grain boundary characteristic for corrosion effects after irradiaion

Endo, Masaki*; Sakaguchi, Norihito*; Kinoshita, Hiroshi*; Watanabe, Seiichi*; Kokawa, Hiroyuki*; Yamashita, Shinichiro; Yano, Yasuhide; Kawai, Masayoshi*

no journal, , 

no abstracts in English

Oral presentation

Effect of irradiation in grain boundary character distribution optimaized austenitic steel

Sakaguchi, Norihito*; Tanikawa, Ryusuke*; Endo, Masaki*; Watanabe, Seiichi*; Kokawa, Hiroyuki*; Kawai, Masayoshi*; Yamashita, Shinichiro; Yano, Yasuhide

no journal, , 

no abstracts in English

Oral presentation

Study on material damage in the high energy quantum beam fields and development of high performance materials, 4; Ion and HVEM irradiation of grain boundary engineered material and its properties

Sakaguchi, Norihito*; Endo, Masaki*; Kinoshita, Hiroshi*; Watanabe, Seiichi*; Kokawa, Hiroyuki*; Yano, Yasuhide; Yamashita, Shinichiro; Kawai, Masayoshi*

no journal, , 

no abstracts in English

Oral presentation

High performance FBR core material development by means of grain boundary engineering

Yamashita, Shinichiro; Yano, Yasuhide; Sakaguchi, Norihito*; Watanabe, Seiichi*; Kokawa, Hiroyuki*; Kawai, Masayoshi*

no journal, , 

In this study, grain boundary character distribution (GBCD)-optimized Type 316 corresponding austenitic stainless steel has been developed as a nuclear material for next generation energy systems. Some of steel sheets were cold-rolled additionally for making the GBCD-optimized and cold-worked (GBCD+CW) specimens. These specimens, including as GBCD-optimized, were examined tensile strength property, phase stability during high temperature thermal ageing and irradiation property. The GBCD was assessed by orientation imaging microscopy (OIM) and also the microstructure by TEM. The OIM results showed that the average grain sizes and the frequencies of CSL boundaries in the typical specimens were 40-47 $$mu$$m and more than 70%. Totally considered all experimental results, it was indicated that it is highly possible to develop high performance FBR core material by means of grain boundary engineering.

Oral presentation

The Effects of irradiation defect distribution and the steel compositions on void denuded zone formations during neutron irradiation and electron irradiation

Sekio, Yoshihiro; Yamashita, Shinichiro; Sakaguchi, Norihito*; Takahashi, Heishichiro*

no journal, , 

The irradiation-induced void denuded zone (VDZ) formation behaviors near grain boundaries were studied in order to clarify the effects of irradiation defect distribution and chemical compositions of steels which were developed to retard their swelling because of the decrease in mobility of point defects during irradiation. The test materials were Fe-15Cr-15Ni model alloy and PNC316 stainless steel which was developed in order to improve the void swelling resistance. These steels were neutron-irradiated in the experimental fast reactor JOYO and electron-irradiated separately using the 1 MeV high voltage electron microscopy (HVEM). The VDZ widths of each steel were evaluated by the TEM microstructural observations after irradiation. From the results in this research, it is considered that VDZ formation would be affected by chemical compositions and that the decrease of VDZ width would be related to increase of the void swelling resistance.

Oral presentation

Void denuded zone formations under electron irradiation in austenitic stainless steels modified with oversized elements

Sekio, Yoshihiro; Yamashita, Shinichiro; Sakaguchi, Norihito*; Takahashi, Heishichiro

no journal, , 

To predict the changes of vacancy diffusivity and concentration in alloys with additional elements to those in the based alloy from the experimentally obtained widths of void denuded zone (VDZ) formations induced during irradiations near grain boundaries, the effects of oversized additional elements of V and Zr on VDZ widths were evaluated in the electron-irradiated SUS316L and the modified type SUS316L steels with V and Zr. These steels were electron-irradiated at the temperature of 450$$^{circ}$$C. The results showed that the VDZ widths were 116nm, 95nm and almost zero in the SUS316L, the SUS316L-V and SUS316L-Zr steels respectively. The addition of V and Zr elements would have a role to decreasing the VDZ widths as results of the decrease of vacancy diffusivity in matrix under irradiations. In particular, the lesser VDZ width induced in the SUS316L-Zr would be also affected by the effective vacancy concentration.

Oral presentation

High-temperature tensile properties of the grain boundary engineered NIMONIC PE16

Sekio, Yoshihiro; Yamashita, Shinichiro; Sakaguchi, Norihito*; Shibayama, Tamaki*; Watanabe, Seiichi*; Tokita, Shun*; Fujii, Hiromichi*; Sato, Yutaka*; Kokawa, Hiroyuki*

no journal, , 

In order to improve ductility loss by helium embrittlement (or grain boundary embrittlement) induced under high temperature and neutron irradiation dose in nickel alloys which are expected to have high-temperature phase stability under non-irradiation, the grain boundary engineering was applied for NIMONIC PE16 to enhance the grain boundary strength. And, its high temperature tensile properties under non-irradiation were investigated as the first approach. As a result, the temperature dependence of the yield stress in the grain boundary engineered (GBE) PE16 was similar to that in NIMINIC PE16, but the yield stress was slightly lower and the uniform elongation was slightly higher at each temperature in GBE PE16 comparing to NIMINIC PE16. This would be caused by grain coarsening due to some heat treatments. If the gain size of GBE PE16 is optimized, tensile properties of GBE PE16 would be the same or more than that of NIMONIC PE16.

Oral presentation

Evaluation of mechanical property in grain boundary character distribution-optimized Ni-based alloy

Yamashita, Shinichiro; Sekio, Yoshihiro; Sakaguchi, Norihito*; Shibayama, Tamaki*; Watanabe, Seiichi*; Kokawa, Hiroyuki*

no journal, , 

Recent grain boundary structure studies have shown that optimal distribution of a high frequency of coincidence site lattice boundaries and consequent discontinuity of random boundary network in the material is one of very effective methods to enhance the intergranular corrosion resistance. This advantageous property, one of important ones for structural material of nuclear reactor, can be obtained through simple thermomechanical treatment process without any change of original chemical composition. In this study, grain boundary character distribution(GBCD)-optimized Ni-based alloy (PE16) has been developed as a prospective high-performance nuclear reactor material by grain boundary engineering processing, and then tensile behavior of GBCD-optimized Ni-based alloy was investigated to evaluate the effect of grain boundary engineering processing on mechanical property. The result of tensile test at room temperature showed that tensile strength of GBCD-optimized PE16 was somewhat lower than that of as-received PE16. However, no significant change was confirmed in elongation property. Details on tensile behavior analyses would be discussed in the conference.

Oral presentation

High temperature tensile properties of the grain-boundary-engineered Ni-base alloy

Yamashita, Shinichiro; Sekio, Yoshihiro; Sakaguchi, Norihito*; Shibayama, Tamaki*; Watanabe, Seiichi*; Tokita, Shun*; Fujii, Hiromichi*; Sato, Yutaka*; Kokawa, Hiroyuki*

no journal, , 

no abstracts in English

Oral presentation

Evaluation of mechanical property in grain boundary character distribution-optimized Ni-based alloy

Yamashita, Shinichiro; Sekio, Yoshihiro; Sakaguchi, Norihito*; Shibayama, Tamaki*; Watanabe, Seiichi*; Kokawa, Hiroyuki*

no journal, , 

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