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Volume 79, Issue 12
Displaying 1-8 of 8 articles from this issue
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Regular Article
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Tetsuya Akiyama, Takanori Kitamura, Hirohiko Kakiuchi, Ryohei Hada, Ak ...2015 Volume 79 Issue 12 Pages 639-643
Published: 2015
Released on J-STAGE: November 25, 2015
Advance online publication: November 06, 2015JOURNAL FREE ACCESSBowl, saddle and twist curved surfaces are typical basic shapes shown in several industrial products. In recent days, laser forming is studied to form curved plate of industrial products. In laser forming process, twist curved plate is produced with many parallel heating lines put on both surface at right angles. On the other hand, it is already known that final shapes of products with many heating lines vary because of its order of heating lines. In this report, progress of twisted shape forming was measured step by step after every one heating line in following two cases. In the first case, heating lines lying inner part of a plate were finished first. In second case, heating lines on outer side of a plate were carried out first. As a result, during early stage of whole heating lines, twist angle in the first case is larger than the second case. After that, increase of twist angle in the first case was dropped gradually. After completion of all heating lines, twist angle in the second case was larger than the first case.
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Koji Tanaka, Hiroyuki T. Takeshita, Ho Shin, Kosuke Kurumatani, Tetsu ...2015 Volume 79 Issue 12 Pages 644-650
Published: 2015
Released on J-STAGE: November 25, 2015
Advance online publication: November 06, 2015JOURNAL FREE ACCESSThe micro/nano-structural transition and hydrogen absorption mechanism in Mg/Cu super-laminate composites (SLCs) were investigated. Differential scanning calorimetry (DSC) measurements were performed on Mg/Cu SLCs at several heating rates and till several repetition cycles up to twenty cycles, and micro/nano-structures of Mg/Cu SLCs were examined with stereomicroscope, digital-microscope, scanning electron microscope (SEM), and scanning transmission electron microscope (STEM). It is found that the micro/nano-structures of Mg/Cu SLCs change drastically at early cycles and reach a steady state after around the tenth cycle. The detailed examination of DSC profiles, and SEM and STEM observations of Mg/Cu SLCs suggest that the hydrogen absorption process consists of a fast and a slow reaction which shows a sharp exothermic peak around at 610 K and a broad exothermic peak around at 570 K connected with it in DSC profiles, respectively.
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Tatsuaki Sakamoto, Kazuki Takiue, Yuri Higaki, Sengo Kobayashi, Kiyomi ...2015 Volume 79 Issue 12 Pages 651-656
Published: 2015
Released on J-STAGE: November 25, 2015
Advance online publication: November 06, 2015JOURNAL FREE ACCESSEffects of α phase nucleating at a transient phase and at dislocations on mechanical properties in a metastable β titanium alloy, Ti-6.8Mo-4.5Fe-1.5Al(mass%), have been investigated by tensile test and optical, scanning and transmission electron microscopy. Two-step aging promotes the precipitation of fine α phase in grain interior because α phase nucleates at a transition phase of β′. Precipitate free zone appears at first, and finally disappears during aging. A specimen including precipitate free zone shows lower yield strength and larger elongation than that without precipitate free zone because dislocation can easily glide in the precipitate free zone, which can be verified from grain-boundary ductile fracture surface. The transition phase of β′ promotes the disappearance of precipitate free zone due to the promotion of α phase precipitation, resulting in enhancement of yield strength and in deterioration of elongation. Aging after tensile deformation produces α phase precipitation at dislocations. A specific variant of α phase is selected due to stress field around the dislocations included in a planar slip bands, resulting in the formation of a large colony of the specific α variant. Elongation is deteriorated because the large colony probably facilitates crack propagation.
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Motomichi Koyama, Takahiro Sawaguchi, Kaneaki Tsuzaki2015 Volume 79 Issue 12 Pages 657-663
Published: 2015
Released on J-STAGE: November 25, 2015
Advance online publication: November 06, 2015JOURNAL FREE ACCESSWe investigated the effect of Si on the tensile properties of Fe-33Mn, Fe-33Mn-4Si, and Fe-33Mn-6Si austenitic alloys (mass%) at 273, 294, 323, and 423 K. The Si addition promoted the deformation-induced ε-martensitic transformation, thereby enhancing the work-hardening capacity. In terms of Considère's criterion, the enhanced work-hardening capacity can improve uniform elongation. However, the Si addition simultaneously promoted brittle cracking associated with ε-martensite, tending toward decreasing elongation. As a result of the ambivalent roles of Si related to ε-martensite, the elongation-strength balance was improved by the addition of 4%Si, but was deteriorated when the Si content increased to 6%. As an additional effect, the Si addition changed the microvoid-formation behavior, resulting in decreasing local elongations.
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Shin-ichiro Kondo, Akinori Masusaki, Kento Ogawa, Takao Morimura, Hiro ...2015 Volume 79 Issue 12 Pages 664-671
Published: 2015
Released on J-STAGE: November 25, 2015
Advance online publication: November 06, 2015JOURNAL FREE ACCESSWe investigate early stages of spinodal decomposition in a melt-spun Cu-15Ni-8Sn alloy (melt-spun samples) by X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM) and electron diffraction analysis through comparison against a quenched alloy of the same composition (quenched samples). In XRD measurements, no sidebands of (200) planes are found in the melt-spun sample after aging at 350℃ for 120 min, whereas they are found in the quenched sample after a heat treatment at 350℃ for 60 min. TEM observations of a quenched sample after aging at 350℃ for 60 min indicate the presence of a modulated structure (λ=5-10 nm) in the matrix, whereas those of a melt-spun sample after the same heat treatment also indicate the presence of a modulated structure (λ: too small to measure). Electron diffraction patterns reveal satellite structures in both samples, although with superlattice reflections from ordering phases visible in the quenched sample. These differences are presumably due to a difference in the size of clusters present in their respective quenched states; in melt-spun samples, cluster size was much smaller as a result of a high cooling rate (≈8×105℃/s).
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Kazuki Tobita, Naoki Sato, Koichi Kitahara, Yoshiki Takagiwa, Kaoru Ki ...2015 Volume 79 Issue 12 Pages 672-676
Published: 2015
Released on J-STAGE: November 25, 2015
JOURNAL FREE ACCESSIron Aluminide Fe2Al5 has a rigid framework of both fully occupied Al and Fe sites and chains of partially occupied Al sites. On the other hand, Fe4Al13 possesses a large unit cell with 102 atoms. These complex and peculiar crystal structures bring a low lattice thermal conductivity. Here, we report the thermoelectric properties and discuss how the chain structure and large unit cell can lead to a low lattice thermal conductivity.
The calculated room-temperature lattice thermal conductivity by using the Wiedemann-Franz law is approximately 1.5 W/mK and 0.8 W/mK for Fe2Al5 and Fe4Al13, respectively. From the comparison with other Fe-Al alloys, which have neither plural partially occupied sites nor a large unit cell, we found that (1) the heat capacity does not decrease at high temperature, i.e. Al atoms at partially occupied sites do not behave as liquid, (2) the speed of sound for Fe2Al5 and Fe4Al13 is almost identical among Fe-Al alloys, i.e. the average phonon group velocity of acoustic modes for Fe2Al5 and Fe4Al13 is not slower than that of Fe-Al alloys, (3) the electrical conductivities of Fe2Al5 and Fe4Al13 are lower than those of the other Fe-Al alloys. These results suggest that the low lattice thermal and electrical conductivities are brought by short relaxation times of both phonons and electrons due to chemical disorder such as the partially occupied sites. In particular, the unit cell of the Fe4Al13 includes 102 atoms, which beneficially reduce the lattice thermal conductivity. The maximum dimensionless figure of merit is approximately 0.02 for both Fe2Al5 and Fe4Al13 at 973 K.
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Toshihiro Miyake2015 Volume 79 Issue 12 Pages 677-682
Published: 2015
Released on J-STAGE: November 25, 2015
Advance online publication: November 06, 2015JOURNAL FREE ACCESSThe purpose of this paper is to develop a new long-life electrical contact. The ability of copper-reductant composite by which the reducing agent with a size of 50 nm or less was distributed inside to extend a sliding life as a slide member for electrical contact was studied. After investigating that L-ascorbic acid as a reductant reduces cupric oxide to copper at room temperature, formation of the copper-reductant composite was tried by the composite plating using the aqueous solutions of a mixed-ligand copper(II) complex with L-ascorbic acid and 1,10-phenanthroline. In the obtained composite film contact, L-ascorbic acid as a reductant and 1,10-phenanthroline were probably distributed in 20 nm or less size, and the sufficiently longer sliding life was shown in slide testing than the plated copper film contact.
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Kentaro Yoshioka, Yaw Wang Chai, Yoshisato Kimura2015 Volume 79 Issue 12 Pages 683-690
Published: 2015
Released on J-STAGE: November 25, 2015
JOURNAL FREE ACCESSZrNiSn and NbCoSn are half-Heusler compounds which have excellent n-type thermoelectric properties. In the present study, solid solution behavior of quaternary half-Heusler Nb(Co, Nix)1+xSn (x=0, 0.05, 0.10, 0.15) and quinary half-Heusler (Zrx, Nb1−x)(Niy, Co1−y)Sn (x, y=0.25, 0.50, 0.75) alloys has been investigated aiming at the reduction of lattice thermal conductivity of alloys due to the solid solution effect. In the quaternary alloys, it was revealed that Ni atoms tend to substitute for the Co-sites instead of occupying the vacancy-sites of half-Heusler NbCoSn. In the quinary (Zrx, Nb1−x)(Niy, Co1−y)Sn alloys, it is suggested that half-Heusler solid solution phase seems to be formed. As a result, the thermal conductivity of sintered (Zr0.5, Nb0.5)(Ni0.5, Co0.5)Sn alloys is reduced by about 40 and 60% from that of ZrNiSn and NbCoSn alloys, respectively.
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