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Volume 76, Issue 9
Displaying 1-7 of 7 articles from this issue
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Regular Articles
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Masaaki Tsukamoto, Takuya Kajiura, Atsushi Yamamoto2012 Volume 76 Issue 9 Pages 521-527
Published: 2012
Released on J-STAGE: September 01, 2012
JOURNAL FREE ACCESSDiffusion bonding is an appropriate method for chromium copper which is difficult to weld due to its high thermal conductivity. However, there have been few reports on diffusion bonding of chromium copper. In the present study, diffusion bonding conditions for chromium copper were investigated to obtain excellent joint strength. The bonded specimens were scarcely deformed because grain growth was suppressed by chromium precipitations. The bonding could be achieved above a temperature of 1073 K and the tensile strength was increased with increasing bonding temperature and pressure. Bonding time had a small influence on the tensile strength. Grain boundary migration across the bonded interface did not occur in all the specimens. Voids and oxides remaining at the bonded interface would play a role of barrier to the migration. The specimens could not be bonded with decreasing roughness on the bonding surfaces. Chromium oxide layer as well as copper one is formed on the bonding surfaces of chromium copper and is not removed with chemical polishing. The oxide layer would be broken by deformation of irregularities on the bonding surfaces. The tensile strength was reduced when contact between the bonding surfaces was delayed until temperature was raised up to bonding condition. Copper oxides are decomposed at 1073 K under a high vacuum of 4.0×10−3 Pa on a free surface of copper, while chromium is segregated to the bonding surfaces and is oxidized. Consequently, chromium oxide layer is strengthened, which inhibits diffusion between the bonding surfaces.
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Takuya Kajiura, Masaaki Tsukamoto, Atsushi Yamamoto2012 Volume 76 Issue 9 Pages 528-534
Published: 2012
Released on J-STAGE: September 01, 2012
JOURNAL FREE ACCESSRecrystallization and recovery behaviors in A1050 aluminum cold-rolled at a reduction of 50% have been observed by means of SEM (Scanning Electron Microscope)-EBSD (Electron Back Scatter Diffraction) in detail. Intermittent annealing at 623 K, ion-polishing and EBSD measurement were repeated and changes in the microstructures were observed on the same view field in a specimen during annealing up to 3.6 ks. Dislocation cells surrounded with low and high angle boundaries were induced by cold-rolling. Two types of recovery behaviors were observed. The main difference between them was whether recovered subgrains were partly surrounded with high angle boundaries or not. The high angle boundary migrated to form a recrystallized grain. When low angle boundaries were formed surrounding the subgrain, a relatively coarse recovered region was formed. Such a region was invaded by recrystallized grains and disappeared. In some case, invading a recovered region with other recovered regions was also observed. Difference in these two types of recovery behaviors occurred depending on the orientation relationships among the subgrains. When they have a similar orientation with respect to each other, recrystallized grains were not formed but recovered regions were formed. Subgrains having orientations apart from those of surrounding subgrains grew into recrystallized grains.
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Mitsuharu Shiwa, Hiroyuki Masuda, Hisashi Yamawaki, Kaita Ito, Manabu ...2012 Volume 76 Issue 9 Pages 535-540
Published: 2012
Released on J-STAGE: September 01, 2012
JOURNAL FREE ACCESSAcoustic emission and optical video microscope monitoring was proposed to investigate the stress corrosion cracking of work-hardened SUS304 stainless steel caused by a small magnesium-chloride droplet. The crack propagation length could measure clearly under the droplet by VMS. The SCC started at 45–82 ks with pitting. The crack velocity was 3.2–4.7 µm/ks and it propagated almost continuously. AE signals were generated at early stage of SCC testing of 55 ks and 82 ks, after that they were generated discontinuously. With the SEM observations, the detected AE signals were mainly attributed to cracking of the oxidation products and discontinuous crack propagation at the falling-off surface grain.
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Akinori Nishide, Yousuke Kurosaki, Hiroyuki Yamamoto, Shin Yabuuchi, M ...2012 Volume 76 Issue 9 Pages 541-545
Published: 2012
Released on J-STAGE: September 01, 2012
JOURNAL FREE ACCESSWe investigated thermoelectric properties of full-Heusler type Fe2VAl thin films. In order to achieve high Seebeck coefficient (S) and low resistivity (ρ) with low thermal conductivity (κ), we fabricated Fe2VAl thin films with a MgO seed layer and annealed them at 800℃. The MgO seed layer and the annealing process transform the Fe2VAl thin films into L21-ordered Heusler structure. The films show S of 59.5 µV/K and ρ of 3.14 µV m together with κ of 4.43 W/m•K, which results in the ZT of as high as 0.079. The considerably small κ compared to the one of bulk samples may originate from an enhancement of the phonon scattering due to a reduction of the film thickness.
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Hajime Takada, Yasuo Tomura, Makoto Aratani, Takuya Yamasaki, Toshihir ...2012 Volume 76 Issue 9 Pages 546-554
Published: 2012
Released on J-STAGE: September 01, 2012
JOURNAL FREE ACCESSA new ultrasonic immersion test method for detecting internal flaws in a running steel strip has been developed. A transmitting probe array and a receiving probe array are arranged face-to-face on opposite sides of the strip in water, and two flaw echoes are received by the receiving probe array: (1) Flaw echo reflected first at an internal flaw and next at the surface wall of the strip; and (2) Flaw echo reflected first at the back wall of the strip and next at an internal flaw. A linear area in the strip can be tested within a cycle of ultrasonic pulse repetition by integrating the transmission of a line-focused ultrasonic beam (25 MHz in frequency) using all elements in the transmitting probe array at once with the parallel processing of signals received by the receiving probe array.
An ultrasonic detection system based on this method was subsequently installed in the No. 6 pickling line at JFE Steel, Chiba District. The steel strip being tested is immersed in water by using six additional deflector rolls. The transmitting probe array and receiving probe array cover the width of the strip so that testing of the entire volume of the strip is realized. It is confirmed that inclusions with a minimum volume of 5×10−5 mm3 can be detected at a signal-to-noise ratio in the range of 9-10 dB. The detection results are rapidly fed back to the steelmaking process to improve steel cleanliness. As a result, steel coils have maintained a high level of internal cleanliness with a dramatic reduction in defects found during the users' manufacturing process.
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Hajime Takada, Takahumi Ozeki, Rinsei Ikeda, Tomoyuki Hirose2012 Volume 76 Issue 9 Pages 555-562
Published: 2012
Released on J-STAGE: September 01, 2012
JOURNAL FREE ACCESSWe developed a technique for nondestructively evaluating spot-welds based on through-transmission of Lamb waves. The nugget diameter can be evaluated by measuring the width of the zone where attenuated transmitted waves are observed. A particularly important feature of the developed technique is that spot-welds with no weld metal can be reliably distinguished from spot-welds with weld metal. We also developed a measuring system using array transducers. The measurement results using the system agree well with the nugget diameters measured by cross-sectional observation.
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Hajime Takada, Takahumi Ozeki2012 Volume 76 Issue 9 Pages 563-571
Published: 2012
Released on J-STAGE: September 01, 2012
JOURNAL FREE ACCESSA new ultrasonic testing technique and a new test system using a transducer array have been developed. The test system works as follows: (1) Ultrasonic waves are transmitted from all the ultrasonic transducer elements in the array at the same time; and (2) By additively synthesizing time-converted ultrasound signals transformed from echo signals received by all the ultrasonic transducer elements in the array at the same time, lines of continuously focused receiving beam (receiving needle beam) are closely formed under the transducer array (parallel receiving needle beam). Also, internal flaws in a cross-section are detected at once using the parallel receiving needle beam. The results of experiments using a 50-MHz transducer array and the developed system have proven that ultra-minute internal flaws 20 µm in diameter can be detected at a scan speed of 1000 mm/s. In addition, the focal zone formed is very long as compared with conventional point-focused beam forming. It is concluded that the system is suitable for simultaneous testing of a cross-section of a test object at high scanning speed.
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