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Journal of Materials Science & Technology 2021年第7期66卷 1-9页

作者： Xiaopei Wang Yoshiaki Morisada hidetoshi Fujii Joining and Welding Research Institute Osaka University11-1 MihogaokaIbarakiOsaka 567-0047Japan

2 mm low carbon steel plates were successfully welded by the flat friction stir spot welding(FSSW) using double side adjustable tools, by which the keyhole formed in the conventional FSSW was eliminated and a flat surface on both the top and bottom sides of the welded joints was obtained. In addition, the hook shape usually generated in the conventional FSSW was eliminated by this technique, and the unbonded interface was parallel to the surface of the sheets. Owing to the enlarged bonded interface width by eliminating the keyhole and the intermixed interface by the adjustable probe, the plug fracture occurred under all the welding conditions in the present study. Due to the suppression of the thickness thinning and elimination of the hook shape, the joint performance was improved in the plug fracture mode. The shear tensile performance was considered to strongly depend on the microstructure in the tip area of the unbonded interface and the maximum shear fracture load of 23.0 kN was achieved in this study.

关键词： Friction stir spot welding Interface structure Low carbon steel Mechanical properties Microstructure

Interface strengthening in dissimilar double-sided friction stir spot welding of AZ31/ZK60 magnesium alloys by adjustable probes

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Journal of Materials Science & Technology 2021年第26期85卷 158-168页

作者： Xiaopei Wang Yoshiaki Morisada hidetoshi Fujii Joining and Welding Research Institute Osaka University11-1 MihogaokaIbarakiOsaka 567-0047Japan

Dissimilar welding of AZ31/ZK60 magnesium alloys with a thickness of 2 mm was successfully carried out by the double-sided friction stir spot welding with adjustable probes.A dissimilar joint bearing flat surfaces on both sides without a keyhole was obtained and the shear failure load of 8.7±0.5 kN was *** role of the adjustable probes has been revealed in *** the center of the stir zone,the welding interface structure was heterogeneous around which some distinct oxides still remained,leading to a weak interface *** the contrary,the welding interface structure around the shoulder/probe interface was homogeneous with no oxides giving rise to a strong interface strength,which is attributed to the severe material flow introduced by the adjustable *** addition,the vicinity outside the shoulder/probe interface,where the fracture occurred during the shear tensile tests,was also strengthened owing to the shearing and torsion by the adju stable ***,a stable plug failure can be obtained and the joint properties can be improved.

关键词： Friction stir spot welding Dissimilar welding Interface strengthening Microstructure Magnesium alloys

On the Live Coloration and Partial Mitochondrial DNA Sequences in the Topotypic Population of Goniurosaurus kuroiwae orientalis(Squamata: Eublepharidae), with Description of a New Subspecies from Tokashikijima Island, Ryukyu Archipelago, Japan

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Asian Herpetological Research 2017年第2期18卷 96-107页

作者： Masanao HONDA hidetoshi OTA Faculty of Life and Environmental Sciences University of Tsukuba Institute of Natural and Environmental Sciences University of Hyogo and Museum of Nature and Human Activities

Careful investigations of live coloration and other characters in the eublepharid gecko Goniurosaurus kuroiwae orientalis from Tonakijima Island, the type locality of the subspecies in the Central Ryukyus, Japan, revealed its slight but consistent external differences from the consubspecific Tokashikijima population, whose phylogenetically divergent status against the former had been strongly suggested in a previous molecular study. A new subspecies, Goniurosaurus kuroiwae sengokui subsp. nov., is thus described for the Tokashikijima population. In life, Goniurosaurus k. sengokui subsp. nov. can be discriminated from G. k. orientalis in showing tint of reddish or pinkish, instead of yellowish, coloration in dorsal body pattern, and also usually darker and more or less reddish, instead of yellowish or grayish, iris in both adults and juveniles. Recalculation of sequence data at hand with relevant Gen Bank data confirmed substantial sequence divergences of G. k. sengokui from all other congeneric taxa of the Ryukyus described so far.

关键词： Eublepharidae Goniurosaurus morphology taxonomy Ryukyu Archipelago

Weld Shape Variation and Electrode Oxidation Behavior under Ar-(Ar-CO_2) Double Shielded GTA Welding

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Journal of Materials Science & Technology 2010年第2期26卷 170-176页

作者： Shanping Lu hidetoshi Fujii Kiyoshi Nogi Shenyang National Laboratory for Materials Science Institute of Metal Research Chinese Academy of ScienceShenyang 110016 China Joining and welding Research Institute Osaka University Osaka 567-0047 Japan

Double shielded gas tungsten arc welding （GTAW, also known as tungsten inert gas （TIG） welding） of an SUS304 stainless steel with pure inert argon as the inner layer shielding and the At-CO2 or CO2 active gas as the out layer shielding was proposed in this study to investigate its effect on the tungsten electrode protection and the weld shape variation. The experimental results showed that the inner inert argon gas can successfully prevent the outer layer active gas from contacting and oxidizing the tungsten electrode during the welding process. Active gas, carbon dioxide, in the outer layer shielding is decomposed in the arc and dissolves in the liquid pool, which effectively adjusts the active element, oxygen, content in the weld metal. When the weld metal oxygen content is over 70×10-6, the surface-tension induced Marangoni convection changes from outward into inward, and the weld shape varies from a wide shallow one to a narrow deep one. The effect of the inner layer gas flow rate on the weld bead morphology and the weld shape was investigated systematically. The results show that when the flow rate of the inner argon shielding gas is too low, the weld bead is easily oxidized and the weld shape is wide and shallow. A heavy continuous oxide layer on the liquid pool is a barrier to the liquid pool movement.

关键词： Double shielding Weld shape Marangoni convection Gas tungsten arc welding

Effect of Ca addition on the microstructure and the mechanical properties of asymmetric double-sided friction stir welded AZ61 magnesium alloy

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Journal of Magnesium and Alloys 2020年第1期8卷 91-102页

作者： Mengran Zhou Yoshiaki Morisada hidetoshi Fujii Joining and Welding Research Institute(JWRI) Osaka UniversityJapan

The effects of 2%Ca addition on the microstructure and the mechanical properties of the asymmetric double-sided friction stir welded magnesium alloy AZ61 were *** to the Ca-free AZ61magnesium alloy,the addition of 2%Ca significantly refines the grains in the stir zone after *** to the existence of thermally stable Al2Ca particles,there is no noticeable change in the grain size in the stir zone regardless of the welding heat *** electron backscattered diffraction analysis at the center of the stir zone confirmed the significant deterioration of the(0001)texture strength from the addition of 2%*** tensile test of the joint suggested that the addition of 2%Ca provides stable tensile properties to the joint regardless of the welding *** critical(0001)texture strength that determines the ultimate tensile strength decreased from 20 to 15 by the Ca *** addition of Ca enhanced the deterioration of the plastic elongation when the(0001)texture strength increased.

关键词： Mg alloy Friction stir welding Microstructure Mechanical properties Texture

Super-High Heat Flux Removal Using Sintered Metal Porous Media

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Journal of Thermal Science 2005年第3期14卷 272-280页

作者： Kazuhisa YUKI Jun ABEI hidetoshi HASHIZUME Saburo TODA Dept. of Quantum Sci. and Energy Eng. Tohoku University Aramaki-Aoba Aoba Sendai 980-8579 Japan DENSO Corporation 1-1 Showa-cho Kariya Aichi 448-8661 JAPANDept. of Quantum Sci. and Energy Eng. Tohoku University Aramaki-Aoba Aoba Sendai 980-8579 JapanTohoku Radiological Science Center 1-1-30 Ichibancho Aoba Sendai 980-1811 Japan

Heat transfer experiments using various porous materials are performed to verify the possibility of extremely high heat flux removal （several dozens of MW/m^2）. The porous media introduced in this experiment are bronze particle-sintered ones and copper fibers-sintered ones that have high thermal conductivity, each of which can enhance the thermal diffusion in the porous material. From the heat transfer experiments using a non-transferred type of plasma arcjet as a high heat flux source, the steady heat removal of 66.0 MV~/m2 is proved by using the bronze porous medium whose pore size and porosity are 100 μm and 0.38, respectively. Furthermore, as the result of evaluating the heat removal performance for various copper fiber porous media with the porosity from 0.5 to 0.7 and the fiber diameter from 30 to 90 μm, it is clarified that the maximum cooling performance exceeds 70.0 MW/m^2 at the porosity of 0.7 and the fiber diameter of 90μm, and that using the lower porosity material is useful for improving an evaporation rate in the porous media.

关键词： heat transfer porous media

Human PIWI(HIWI) is an azoospermia factor

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Science China(Life Sciences) 2018年第3期61卷 348-350页

作者： hidetoshi Hasuwa Kyoko Ishino Haruhiko Siomi Department of Molecular Biology Keio University School of Medicine

Transposable elements （TEs） make up nearly half of the mammalian genome. Recent probabilistic re-annotation of genome sequences indicated that as much as two-thirds or more of the human genome may be derived from TEs （de Koning et al., 2011）. Their ability to mobilize in the genome represents a constant threat to the host by creating insertion mutations, which may lead to progressive deterioration of genetic information. To counteract this threat, host cells have evolved adaptive control mechanisms to repress the activity of TEs. One such mechanism is the P1WI-piRNA pathway conserved in animals, from C. elegans to humans （Iwasaki et al., 2015）. The pathway is a germline-specific mechanism required to maintain genome integrity. In this pathway, piRNAs （short for PIWI-interacting RNAs） with 25-35 nucleotides （nt） in length form effector complexes or RNA-induced silencing complexes （RISCs） with PIWI clade proteins of Argonautes to trigger multiple forms of sequence-specific gene silencing by guiding RISCs to target RNAs by means of Watson-Crick base-pairing, piR- NA-loaded RISCs or piRISCs normally repress TEs either by cleaving their transcripts in the cytoplasm or by inducing heterochromatin formation at their insertion sites of the ge- nome.

关键词：精子 RISC 哺乳动物基因信息染色体 RNA 适应控制建筑群

Effect of Gravity on Arc Shape in GTA Welding-for Low Electric Arc Current

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Journal of Materials Science & Technology 2003年第z1期19卷 209-211页

作者： hidetoshi FUJII Yosuke SUMI Manabu TANAKA Kiyoshi NOGI Joining and Welding Research Institute Osaka University 11-1 Mihogaoka Ibaraki Osaka 567-0047 Japan Joining and Welding Research Institute Osaka University 11-1 Mihogaoka Ibaraki Osaka 567-0047 Japan Joining and Welding Research Institute Osaka University 11-1 Mihogaoka Ibaraki Osaka 567-0047 Japan Joining and Welding Research Institute Osaka University 11-1 Mihogaoka Ibaraki Osaka 567-0047 Japan

Gas tungsten arc (GTA) welding was performed both in a microgravity environment and in a terrestrial environment,and the arc shapes in both environments were compared. A microgravity condition was obtained using the free fallsystem at the Japan Microgravity Center. The system can maintain a 10 s microgravity of less than 10-5 g. Awater-cooled Cu plate was used to simplify the arc phenomenon. The electric arc current was between 15 and 80 A,and the shielding and atmospheric gas was 99.9995% Ar and its flowing rate was 10 l/min. The polarity was a directcurrent electrode negative (DCEN). The arc gap was 3 mm and careful attention was also paid to the arc gap in boththe terrestrial and microgravity environments being the same. As a result, it was found that no effect of gravity onthe arc shape is observed under general welding conditions (over 60 A). When the electric arc current is lower than25 A, the arc shape is determined by the initial position of the arc root and is constant with time. Accordingly, itcan not be judged whether or not the arc shape is affected by gravity for this range. When the electric arc current isbetween 25 A and 60 A, it is estimated that the arc shape is not affected by gravity though it is occasionally affectedby other minor effects.

关键词： Microgravity, Arc shape, Gas tungsten arc welding, Water-cooled Cu

Principle for obtaining high joint quality in dissimilar friction welding of Ti-6Al-4V alloy and SUS316L stainless steel

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Journal of Materials Science & Technology 2020年第11期42卷 211-224页

作者： Huihong Liu Yo Aoki Yasuhiro Aoki Kohsaku Ushioda hidetoshi Fujii Joining and Welding Research Institute Osaka UniversityIbarakiOsaka 567-0047Japan

Ti-6Al-4V alloy(Ti64)and SUS316 L stainless steel rods were dissimilarly friction *** focusing on the detailed observation of interface microstructural evolution during the friction welding(FW),the relationship between the processing conditions,weld interface microstructure,and mechanical properties of the obtained joints were systematically investigated to elucidate the principle for obtaining a high joint quality in the FW of Ti64 and SUS316L.A higher friction pressure produced a lower welding temperature in the FW,hence suppressing the thick intermetallic compound layer ***,hard and brittle Ti64/SUS316L mechanically mixed layers generally formed especially at the weld interface periphery due to the high temperature increasing rate,high rotation linear velocity and high outward flow velocity of the *** harmful layers tended to induce the cracks/voids formation at the weld interfaces hence deteriorating the joints’mechanical *** rotation speed reduction and liquid CO2 cooling during the entire processing decreased the temperature increasing rate,rotation linear velocity and outward flow velocity of the Ti64 at the weld interface ***,they suppressed the formation of the harmful mechanically mixed layers,facilitated the homogeneous and sound interface microstructure generation,and finally produced a high-quality dissimilar joint in the FW of Ti64 and SUS316L.

关键词： Friction welding Titanium alloy Stainless steel Microstructure formation mechanism Mechanically mixed layers