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Journal Articles

${it In situ}$ WB-STEM observation of dislocation loop behavior in reactor pressure vessel steel during post-irradiation annealing

Du, Y.*; Yoshida, Kenta*; Shimada, Yusuke*; Toyama, Takeshi*; Inoue, Koji*; Arakawa, Kazuto*; Suzudo, Tomoaki; Milan, K. J.*; Gerard, R.*; Onuki, Somei*; et al.

Materialia, 12, p.100778_1 - 100778_10, 2020/08

In order to ensure the integrity of the reactor pressure vessel in the long term, it is necessary to understand the effects of irradiation on the materials. In this study, irradiation-induced dislocation loops were observed in neutron-irradiated reactor pressure vessel specimens during annealing using our newly developed WB-STEM. It was confirmed that the proportion of $$<100>$$ loops increased with increasing annealing temperature. We also succeeded in observing the phenomenon that two $$frac{1}{2}$$$$<111>$$ loops collide into a $$<100>$$ loop. Moreover, a phenomenon in which dislocation loops decorate dislocations was also observed, and the mechanism was successfully explained by molecular dynamics simulation.

Journal Articles

Improving fatigue performance of laser-welded 2024-T3 aluminum alloy using dry laser peening

Sano, Tomokazu*; Eimura, Takayuki*; Hirose, Akio*; Kawahito, Yosuke*; Katayama, Seiji*; Arakawa, Kazuto*; Masaki, Kiyotaka*; Shiro, Ayumi*; Shobu, Takahisa; Sano, Yuji*

Metals, 9(11), p.1192_1 - 1192_13, 2019/11

 Times Cited Count:2 Percentile:64.55(Materials Science, Multidisciplinary)

The purpose of the present study was to verify the effectiveness of dry laser peening (DryLP), which is the peening technique without a sacrificial overlay under atmospheric conditions using femtosecond laser pulses on the mechanical properties such as hardness, residual stress, and fatigue performance. After DryLP treatment of the laser-welded 2024 aluminum alloy, the softened weld metal recovered to the original hardness of base metal, while residual tensile stress in the weld metal and heat-affected zone changed to compressive stresses. The fatigue life almost doubled at a stress amplitude of 180 MPa and increased by a factor of more than 50 at 120 MPa. As a result, DryLP was found to be more effective for improving the fatigue performance of laser-welded aluminum specimens with welding defects at lower stress amplitudes.

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:23 Percentile:18.25(Materials Science, Multidisciplinary)

no abstracts in English

Oral presentation

Development of true coincidence summing correction for cascade $$gamma$$-ray emitters including $$^{134}$$Cs, 1; Collaborative experiment by the committee on preparation of reference materials for radioactivity analysis of JSAC

Yonezawa, Chushiro*; Kakita, Kazutoshi*; Takahashi, Takanori*; Aono, Tatsuo*; Maeda, Satoshi; Abe, Takaaki*; Arakawa, Fumihiro*; Kiho, Nobuharu*; Akiyama, Masakazu*; Muramatsu, Isamu*; et al.

no journal, , 

no abstracts in English

Oral presentation

In-situ weak-beam scanning transmission electron microscopy for quantitative dislocation analysis in nuclear materials during post-irradiation annealing

Yoshida, Kenta*; Du, Y.*; Shimada, Yusuke*; Suzudo, Tomoaki; Toyama, Takeshi*; Inoue, Koji*; Arakawa, Kazuto*; Milan, K. J.*; Gerard, R.*; Nagai, Yasuyoshi*

no journal, , 

We developed a weak-beam scanning transmission electron microscopy (WB-STEM) by installing a novel beam selector, annular detector, a high-speed CCD camera and imaging filter in a camera chamber of an aberration corrected electron microscope. In-situ observation confirmed that the newly-developed WB-STEM has improved the ability to observe the dynamic behavior of dislocation loops. In addition, we performed a numerical simulation of dislocation loop behavior using molecular dynamics, and confirmed that the experimental results were well explained by the theoretical analysis. Therefore, this WB-STEM is expected to be useful for understanding the embrittlement mechanism of nuclear materials such as reactor pressure vessel (RPV) steels.

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