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Kumagai, Masayoshi*; Kuroda, Masatoshi*; Matsuno, Takashi*; Harjo, S.; Akita, Koichi*
Materials & Design, 221, p.110965_1 - 110965_8, 2022/09
Times Cited Count：4 Percentile：41.53(Materials Science, Multidisciplinary)Kumagai, Masayoshi*; Akita, Koichi*; Kuroda, Masatoshi*; Harjo, S.
Materials Science & Engineering A, 820, p.141582_1 - 141582_9, 2021/07
Times Cited Count：9 Percentile：62.81(Nanoscience & Nanotechnology)
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martensitic transformation of biomedical Co-Cr-Mo alloys by introducing parent phase lattice defectsMori, Manami*; Yamanaka, Kenta*; Sato, Shigeo*; Tsubaki, Shinki*; Sato, Kozue*; Kumagai, Masayoshi*; Imafuku, Muneyuki*; Shobu, Takahisa; Chiba, Akihiko*
Journal of the Mechanical Behavior of Biomedical Materials, 90, p.523 - 529, 2019/02
Times Cited Count：19 Percentile：71.16(Engineering, Biomedical)Kumagai, Masayoshi*; Uchida, Tomohiro*; Murasawa, Kodai*; Takamura, Masato*; Ikeda, Yoshimasa*; Suzuki, Hiroshi; Otake, Yoshie*; Hama, Takayuki*; Suzuki, Shinsuke*
Materials Research Proceedings, Vol.6, p.57 - 62, 2018/10
Times Cited Count：0 Percentile：0.18(Metallurgy & Metallurgical Engineering)Murasawa, Kodai*; Takamura, Masato*; Kumagai, Masayoshi*; Ikeda, Yoshimasa*; Suzuki, Hiroshi; Otake, Yoshie*; Hama, Takayuki*; Suzuki, Shinsuke*
Materials Transactions, 59(7), p.1135 - 1141, 2018/07
Times Cited Count：7 Percentile：36.72(Materials Science, Multidisciplinary)Ikeda, Yoshimasa*; Takamura, Masato*; Hakoyama, Tomoyuki*; Otake, Yoshie*; Kumagai, Masayoshi*; Suzuki, Hiroshi
Tetsu To Hagane, 104(3), p.138 - 144, 2018/03
Times Cited Count：4 Percentile：22.67(Metallurgy & Metallurgical Engineering)Neutron engineering diffraction is a powerful technique which provides the information of the micro structure of steels in bulk-average, while X-ray diffraction or Electron backscatter diffraction can provide information only from the surface layer. However, such measurement using neutron diffraction is typically performed in a large facility such as a reactor and a synchrotron, while a compact neutron source has never been used for this purpose. Authors have recently developed a neutron diffractometer installed in Riken Accelerator driven compact Neutron Source (RANS) and succeeded in the measurement of texture evolution of a steel sheet. In this study, we made an attempt to measure the volume fraction of retained austenite by RANS. Background noise was carefully eliminated in order to detect as many diffraction peaks as possible with low flux neutrons. The volume fraction was estimated by Rietveld analysis. The accuracy of the measurement result was discussed by comparing with those obtained by a large neutron facility (J-PARC TAKUMI). The volume fraction obtained by RANS with reasonable measurement time, i.e. 30 to 300 min, showed only 1 to 2 % discrepancies with those obtained in J-PARC. These comparisons suggest that neutron diffraction by RANS is capable of quantitative analysis of the volume fraction of crystal phases, showing the possibility of practical use of an in-house compact neutron source in the industry.
observation of dislocation evolution in ferritic and austenitic stainless steels under tensile deformation by using neutron diffractionSato, Shigeo*; Kuroda, Asumi*; Sato, Kozue*; Kumagai, Masayoshi*; Harjo, S.; Tomota, Yo*; Saito, Yoichi*; Todoroki, Hidekazu*; Onuki, Yusuke*; Suzuki, Shigeru*
Tetsu To Hagane, 104(4), p.201 - 207, 2018/00
Times Cited Count：9 Percentile：44.29(Metallurgy & Metallurgical Engineering)Ikeda, Yoshimasa*; Taketani, Atsushi*; Takamura, Masato*; Sunaga, Hideyuki*; Kumagai, Masayoshi*; Oba, Yojiro*; Otake, Yoshie*; Suzuki, Hiroshi
Nuclear Instruments and Methods in Physics Research A, 833, p.61 - 67, 2016/10
Times Cited Count：38 Percentile：96.62(Instruments & Instrumentation)A compact accelerator-based neutron source has been lately discussed on engineering applications such as transmission imaging and small angle scattering as well as reflectometry. However, nobody considers using it for neutron diffraction experiment because of its low neutron flux. In this study, therefore, the neutron diffraction experiments are carried out using Riken Accelerator-driven Compact Neutron Source (RANS), to clarify the capability of the compact neutron source for neutron engineering diffraction. The diffraction pattern from a ferritic steel was successfully measured by suitable arrangement of the optical system to reduce the background noise, and it was confirmed that the recognizable diffraction pattern can be measured by the large sampling volume with 10 mm in cubic for an acceptable measurement time, i.e. 10 minutes. The minimum resolution of the 110 reflection for RANS is approximately 2.5 % at 8 
s of the proton pulse width, which is insufficient to perform the strain measurement by neutron diffraction. The moderation time width at the wavelength corresponding to the 110 reflection is estimated to be approximately 30 s, which is the most dominant factor to determine the resolution. Therefore, refinements of the moderator system to decrease the moderation time are important to improve the resolution of the diffraction experiment using the compact neutron source. In contrast, the texture evolution due to plastic deformation was successfully observed by measuring a change in the diffraction peak intensity by RANS. Furthermore, the volume fraction of the austenite phase was also successfully evaluated by fitting the diffraction pattern using a Rietveld code. Consequently, RANS was proved to be capable for neutron engineering diffraction aiming for the easy access measurement of the texture and the amount of retained austenite.
Sunaga, Hideyuki*; Takamura, Masato*; Ikeda, Yoshimasa*; Otake, Yoshie*; Hama, Takayuki*; Kumagai, Masayoshi*; Suzuki, Hiroshi; Suzuki, Shinsuke*
Journal of Physics; Conference Series, 734(Part B), p.032027_1 - 032027_4, 2016/09
Times Cited Count：0 Percentile：0.03(Physics, Applied)A neutron diffraction measurement was performed to reveal microstructural aspects of the ductile fracture in ferritic steel. The diffraction patterns were continuously measured at the center of the reduced area while a tensile specimen was loaded under tension until the end of the fracture process. The measurement results showed that the volume fraction of (110)-oriented grains increased when the texture evolved as a result of plastic deformation. But the mechanism of texture evolution may be changed during necking, decreasing an increase rate of the volume fraction.
Takamura, Masato*; Ikeda, Yoshimasa*; Sunaga, Hideyuki*; Taketani, Atsushi*; Otake, Yoshie*; Suzuki, Hiroshi; Kumagai, Masayoshi*; Hama, Takayuki*; Oba, Yojiro*
Journal of Physics; Conference Series, 734(Part B), p.032047_1 - 032047_4, 2016/08
Times Cited Count：5 Percentile：86.44(Physics, Applied)Neutron diffraction is well known to be a useful technique for measuring a bulk texture of metallic materials taking advantage of a large penetration depth of the neutron beam. However, this technique has not been widely utilized for the texture measurement because large facilities like a reactor or a large accelerator are required in general. In contrast, RANS (Riken Accelerator-driven Compact Neutron Source) has been developed as a neutron source which can be used easily in laboratories. In this study, texture evolution in steel sheets with plastic deformation was successfully measured using RANS. The results show the capability of the compact neutron source for the analysis of the crystal structure of metallic materials, which leads us to a better understanding of plastic deformation behavior.
Sato, Shigeo*; Shobu, Takahisa; Sato, Kozue*; Ogawa, Hiromi*; Wagatsuma, Kazuaki*; Kumagai, Masayoshi*; Imafuku, Muneyuki*; Tashiro, Hitoshi*; Suzuki, Shigeru*
ISIJ International, 55(7), p.1432 - 1438, 2015/07
Times Cited Count：13 Percentile：53.92(Metallurgy & Metallurgical Engineering)To characterize the distribution and anisotropy of dislocations in cold-drawn pearlitic steel wires, X-ray diffraction line-profile analysis was performed using synchrotron radiation micro-beams. The plastic shear strain was generally more severe near the surface than the center of the wire, whereas the dislocation density distribution was almost constant from the center to the surface. On the other hand, the dislocation rearrangement, which evolves the dislocation cell structure, progressed closer to the surface. It was also revealed that a difference between the hardness in axial and transverse wire directions could be explained by anisotropic dislocation density. Line-profile analysis based on diffraction data at elevated temperatures was performed. Whereas the cementite recovery progressed at a constant rate, the ferrite phase recovery rate was temperature-dependent, suggesting that the ferrite phase recovery was less related to that of the cementite phase.
Kumagai, Masayoshi*; Akita, Koichi; Imafuku, Muneyuki*; Oya, Shinichi*
Advanced Materials Research, 996, p.39 - 44, 2014/08
Times Cited Count：6 Percentile：93.39(Engineering, Mechanical)The microstructural features of shot and laser peened austenitic stainless steels were studied using line profile analysis with X-rays. Although both specimens had similar residual stress profiles toward the depth direction, the microstructural features were different not only on the original surfaces of the specimens but also to several micrometers in depth. The dislocation densities of the SP specimen were greater than that of the LP specimen. And the crystallite sizes of the SP specimen were smaller than that of the LP specimen.
Kumagai, Masayoshi*; Akita, Koichi; Imafuku, Muneyuki*; Oya, Shinichi*
Materials Science & Engineering A, 608, p.21 - 24, 2014/07
Times Cited Count：10 Percentile：45.35(Nanoscience & Nanotechnology)The mechanical properties of shot- and laser-peened austenitic stainless steels, AISI316, were evaluated via Vickers hardness tests, and the correlation between workhardening and microstructural characteristics were discussed. Dislocation density, which is a microstructural feature, was determined via X-ray line profile analysis. Martensite was generated only by the shot-peening process. A linear relationship is observed between the hardness and the square root of the dislocation density in spite of the martensite formation on the shot-peened specimen. Therefore, the hardness is increased only by workhardening and is not affected by the martensite. We also clarified that a compressive residual stress greater than the original yield strength of the bare material can be induced because of the increase in yield strength caused by workhardening due to dislocation density increase with the peening process.
Kumagai, Masayoshi*; Akita, Koichi; Itano, Yuta*; Imafuku, Muneyuki*; Oya, Shinichi*
Journal of Nuclear Materials, 443(1-3), p.107 - 111, 2013/11
Times Cited Count：26 Percentile：88.43(Materials Science, Multidisciplinary)Microstructural features of AISI316 stainless steels processed by shot peening (SP) and laser peening (LP) were studied using X-ray diffraction line profile analyses. Both specimens exhibited similar compressive residual stress profiles. Although the number of dislocations was increased and the crystallites were refined with both processes, the dislocation density in the SP specimen was significantly greater than that in the LP specimen. The crystallite size in the SP specimen was one-third that in the LP specimen. The SP process induced martensite transformation. The variations in the microstructural features differed between samples subjected to the two processes. The SP process resulted in a greater variation in the microstructural features in a sample in which residual stresses similar to that induced by the LP process were induced. Thus, the variations in the microstructural features differed depending on the deformation process.
Kumagai, Masayoshi*; Akita, Koichi; Imafuku, Muneyuki*; Oya, Shinichi*
Nihon Zairyo Gakkai Dai-62-Ki Tsujo Sokai, Gakujutsu Koenkai Rombunshu (USB Flash Drive), 2 Pages, 2013/05
Dislocation densities and crystallite sizes in shot- and laser-peened ANSI316 specimens were evaluated by X-ray line profile analysis. The both peened samples had almost the same depth-distributions of residual stress. Even though dislocations were increased and crystallites were refined in both processes, the dislocation density of SP was significantly higher than that of LP and the crystallite size of SP was one-third that of LP. Thus, the states of the microstructure variations were different depending on the nature of deformation process.
Shobu, Takahisa; Akita, Koichi; Shiro, Ayumi; Fujishiro, Tomoyuki*; Kiriyama, Koji*; Kumagai, Masayoshi*; Hisamori, Noriyuki*
no journal, ,
Kumagai, Masayoshi*; Akita, Koichi; Imafuku, Muneyuki*; Oya, Shinichi*
no journal, ,
Microstructure and residual stress in shot and laser peened AISI316 stainless steels were evaluated using X-ray line profile analysis and residual stress measurements. Although both specimens exhibited similar compressive residual stress profiles in the depth direction, the hardness and dislocation density on the two specimens were different. The hardness of the SP specimen was greater than that of the LP specimen. And the dislocation density in the SP specimen was greater than that in the LP specimen. Thus, although the residual stress profiles of both SP and LP specimens were similar, the microstructural features in the samples differed.
Kumagai, Masayoshi*; Iwata, Saori*; Akita, Koichi; Kuroda, Masatoshi*; Oya, Shinichi*
no journal, ,
no abstracts in English
Shobu, Takahisa; Yasuda, Ryo*; Shiro, Ayumi*; Yoshida, Yutaka*; Tokuda, Susumu*; Shibano, Junichi*; Kumagai, Masayoshi*
no journal, ,
A dislocation density increases and fatigue failure of the structure occur, when a metal is deformed. In this study, dislocation density of a broken 0.3 mm thick SUS316L specimen was calculated by line profile analysis obtained by high energy synchrotron X-ray diffraction method, and a relationship between fatigue fracture and dislocation density was evaluated. As a result of the analysis, it was revealed that the dislocation density abruptly increases as approaching the fracture part. In addition, it was revealed that the bcc structure appeared in the fcc structure which is the basic structure in the fracture part. In steel, the increase in dislocation density is closely related to the increase in material strength, and the material strength of steel with bcc structure is known to be higher than that with fcc structure. So, it seems that the structure has changed due to a sharp increase in dislocation density at the fracture part.
Kumagai, Masayoshi*; Akita, Koichi*; Kuroda, Masatoshi*; Harjo, S.
no journal, ,
no abstracts in English
