MATERIALS TRANSACTIONS
Online ISSN : 1347-5320
Print ISSN : 1345-9678
ISSN-L : 1345-9678
Volume 57 , Issue 9
Showing 1-46 articles out of 46 articles from the selected issue
  • Naoya Kamikawa, Tomohiro Tsuru, Nobuhiro Tsuji
    2016 Volume 57 Issue 9 Pages 1385
    Published: 2016
    Released: August 25, 2016
    JOURNALS FREE ACCESS
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  • E. Bagherpour, F. Qods, R. Ebrahimi, H. Miyamoto
    2016 Volume 57 Issue 9 Pages 1386-1391
    Published: September 01, 2016
    Released: August 25, 2016
    [Advance publication] Released: May 13, 2016
    JOURNALS FREE ACCESS

    In the present paper texture changes of pure copper during and after a single pass of simple shear extrusion (SSE) was studied. For this reason, the samples were taken out from an SSE die during the process and investigated by electron back-scattering diffraction (EBSD). From the beginning to the middle of the deformation channel, the simple shear textures were formed gradually and the strongest one was observed on the 0.5 pass sample. The degree of the simple shear textures decreases with the distance from the middle plane where the shear is reversed, but the simple shear textures are still the major components after the exit of the channel. The major orientation component of the 0.5 pass sample was C component, whereas, it was A2* component of the 1 pass sample.

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  • Tomotsugu Shimokawa, Tomoaki Yamashita, Tomoaki Niiyama, Nobuhiro Tsuj ...
    2016 Volume 57 Issue 9 Pages 1392-1398
    Published: September 01, 2016
    Released: August 25, 2016
    JOURNALS FREE ACCESS

    Severe plastic deformation (SPD) processes can produce the bulk ultrafine-grained metals with grain sizes of less than 1 μm. However, the mechanism of grain refinement during SPD is not completely understood. In this study, we perform molecular dynamics simulations of a SPD process like equal-channel angular pressing and demonstrate grain refinement phenomena during the SPD simulations. We propose a new mechanism of grain subdivision related to the mobility of partial disclinations formed in strain-gradient regions during SPD.

    Fig. 4 Local shear strain dependence of the proportion of defect atoms after SPD processes. Fullsize Image
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  • Vinicius Aguiar de Souza, Ikumu Watanabe, Akira Yanagida
    2016 Volume 57 Issue 9 Pages 1399-1403
    Published: September 01, 2016
    Released: August 25, 2016
    [Advance publication] Released: June 24, 2016
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    The purpose of this study is to numerically estimate the friction coefficient for equal channel angular extrusion with and without back pressure. Three-dimensional finite element analysis is employed to estimate the coefficient of friction from the maximum pressing load, a crucial variable in die design. The finite element model consists of a billet, a plunger, a ram, and a die, where the interface between the billet and the die is modeled by the Coulomb friction model with truncated shear stress. The numerical model was validated by comparing the grid deformation patterns in the extrusion symmetry plane, and by comparing the load versus stroke curves for the ram (pressing load) and for the plunger (back pressure). Results indicate that the coefficient of friction can be accurately estimated from the maximum pressing load, but it is necessary to modify the traditional Coulomb friction model.

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  • Ikumu Watanabe, Daigo Setoyama
    2016 Volume 57 Issue 9 Pages 1404-1410
    Published: September 01, 2016
    Released: August 25, 2016
    [Advance publication] Released: June 24, 2016
    JOURNALS FREE ACCESS

    The heterogeneous deformation of a polycrystalline aggregate under severe plastic deformation was reproduced with finite element analysis by using single-crystal plasticity to characterize the evolution process of the heterogeneity. Finite element analyses of a periodic polycrystalline aggregate were carried out to simulate the deformation process corresponding to the multi-pass equal-channel angular extrusion process, which reached over 250% of the macroscopic logarithmic accumulated plastic strain. The numerical results were analyzed from multi-scale perspectives: the macroscopic response, evolution of the crystallographic orientation, and deformation state of the microstructure. This study addressed the importance of finite element discretization to reproduce the heterogeneous deformation of a polycrystalline aggregate, including that of the inside grains, which is a key element for investigating the underlying fine-graining mechanism.

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  • Yoji Miyajima, Midori Uchiyama, Hiroki Adachi, Toshiyuki Fujii, Susumu ...
    2016 Volume 57 Issue 9 Pages 1411-1417
    Published: September 01, 2016
    Released: August 25, 2016
    [Advance publication] Released: June 24, 2016
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    The microstructure and texture evolution of an accumulative roll bonding (ARB) processed 4N-Cu with and without lubrication were compared in addition to the mechanical properties, in order to understand the effect of additional shear strain caused by the friction between the rolls and a sheet. Furthermore, subsequent annealing at 423 K, 448 K and 473 K was applied for 4N-Cu ARB processed with and without lubrication, and, softening was observed for all temperatures. The texture change due to the ARB process and subsequent annealing were discussed using {111} pole figures and ODF maps. As a result, a 45° rotated Cube texture around ND was formed by additional shear strain, whereas the typical fcc rolling texture was formed by ARB with lubrication. At higher ARB cycles of 4N-Cu, discontinuous recrystallization occurs due to its medium stacking fault energy. Cube orientation appeared in annealed-ARB processed 4N-Cu with lubrication, whereas no specific texture appeared in annealed-ARB processed 4N-Cu without lubrication

    Fig. 6 {111} pole figures of ARB processed 4N-Cu: (a)–(d) are ARB 2c, (e)–(h) are ARB 4c, (i)–(l) are ARB 6c, and (m)–(p) are ARB 8c, respectively. The first column from the left is the results at quarter of ARB with lubrication. The second, third, and the fourth columns from the left are at centre, quarter, and surface of ARB without lubrication, respectively. (q) {111} pole figure of annealed (ARB 0c) 4N-Cu, and (r) ideal orientations of the rolling texture along β fibre, Cube and rotated Cube orientations. Fullsize Image
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  • H. Miura, M. Kobayashi, T. Benjanarasuth
    2016 Volume 57 Issue 9 Pages 1418-1423
    Published: September 01, 2016
    Released: August 25, 2016
    JOURNALS FREE ACCESS

    Samples of AZ80Mg alloy were multi-directionally forged (MDFed) at various strain rates in the rage from 3.0 × 10−3 s−1 to 3.0 × 10−1 s−1 under decreasing temperature conditions. The MDFing pass temperatures employed were 653 K, 605 K and 553 K. These passes, each of 0.5 strain, were applied up to a cumulative strain of ΣΔε = 1.5 at maximum. The average grain size decreased with increasing cumulative strain and depended only weakly on the strain rate. Microstructures with average grain sizes of 0.84 μm, 0.88 μm and 1.2 μm were attained when MDFed at strain rates of 3.0 × 10−1 s−1, 3.0 × 10−2 s−1 and 3.0 × 10−3 s−1. The microstructure evolved at 3.0 × 10−1 s−1 was less homogeneous. This difference is interpreted as being due to the higher stored energy causing static recrystallization in the latter MDFing condition. As a result, the best balance of the mechanical properties was attained by MDFing at 3.0 × 10−2 s−1. In this case, ultimate tensile strength (UTS) of 445 MPa was achieved together with a fracture strain of 22%. By comparison, MDFing at 3.0 × 10−1 s−1 led to lower UTS and ductility of 410 MPa and 15% while the yield stresses were comparable.

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  • Sanjay Kumar Vajpai, Han Yu, Mie Ota, Ikumu Watanabe, Guy Dirras, Kei ...
    2016 Volume 57 Issue 9 Pages 1424-1432
    Published: September 01, 2016
    Released: August 25, 2016
    [Advance publication] Released: May 13, 2016
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    Creation of a unique “Harmonic Structure (HS)” with controlled bimodal grain size distribution in metals and alloys is a new material design paradigm allowing the improved mechanical performance of structural materials via enhancing strength without sacrificing ductility. A well designed powder metallurgy based processing approach has been developed to create such a controlled microstructure which consists of controlled mechanical milling (MM) of powder particles to create powder particles with bimodal grain size distribution, with a peculiar core-shell structure, followed by their hot consolidation. In the present study, full density compacts with HS were prepared and the effect of such a bimodal microstructure on the mechanical properties of commercially pure Ti with hexagonal close packed (HCP) crystal structure was investigated. The HS pure Ti exhibited considerably higher strength values, without sacrificing ductility, as compared to their coarse-grained (CG) counterparts. The numerical simulation results revealed that the initial stages of deformation and strength of the HS are governed by the characteristics of the interconnected network of the strong fine-grained (FG) shell regions whereas the extent of uniform deformation and overall ductility is governed by the ductile CG core region. It was also demonstrated that the unique HS design promotes uniform deformation very efficiently by avoiding strain localization during plastic deformation.

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  • Nur Zalikha Khalil, Sanjay Kumar Vajpai, Mie Ota, Kei Ameyama
    2016 Volume 57 Issue 9 Pages 1433-1439
    Published: September 01, 2016
    Released: August 25, 2016
    [Advance publication] Released: July 25, 2016
    JOURNALS FREE ACCESS

    The present work deals with a novel approach of fabricating harmonic structure in Al alloy through the application of semi-solid reaction between Al and Si. The harmonic structured Al was prepared by powder metallurgy route, where the Al and Si powder were subjected to controlled mechanical milling followed by subsequent spark plasma sintering to make a compact. The sintered compact resulted in a network structure of hard interconnected silicon dispersed region combined with Al-Si solid solution phase, known as “shell”, enclosing the soft phase of pure aluminum matrix known as “core”. The harmonic structured Al compact demonstrated retention of both uniform and total elongation as compared to its heterogeneous bimodal structure counterpart, which is the typical feature of the harmonic structured material. The application of semi-solid reaction between Al and Si in fabricating harmonic structure proved to be effective in improving mechanical properties of Al alloy. Present work also discusses the deformation behavior of the sintered compacts, with respect to its strain hardening behavior.

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  • Bhupendra Sharma, Sanjay Kumar Vajpai, Kei Ameyama
    2016 Volume 57 Issue 9 Pages 1440-1446
    Published: September 01, 2016
    Released: August 25, 2016
    [Advance publication] Released: June 03, 2016
    JOURNALS FREE ACCESS

    In the present work, Ti-25Nb-11Sn (mass%) alloys were successfully prepared by an advanced powder metallurgy method. The alloys were synthesized by mechanical milling of powder mixture, consisting of titanium hydride (TiH2), elemental niobium (Nb) and elemental tin (Sn) powders, followed by their consolidation via Spark Plasma Sintering (SPS) method. The use of brittle TiH2 powder, instead of ductile elemental Ti powder, resulted in ~100% powder yield of mechanically milled (MMed) powder even after long time mechanical milling. The resulting MMed powders consisted of homogeneously distributed nano-sized titanium/niobium hydride powder particles together with a few micron-sized pure Nb particles. The mechanical milling also led to the lowering of dehydrogenation temperature of the hydride particles. Sintering of short time mechanically milled powder (72 ks) resulted in the fine-grained heterogeneous microstructure consisting of β phase and orthorhombic martensitic α'' phase. On the other hand, sintering of long time mechanically milled powder (180 ks) resulted in the evolution of β-phase and α-phase. The specimen containing α+β phase exhibited higher average hardness as compared to the average hardness of specimen containing α''+β phase.

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  • Hiroki Adachi, Yui Karamatsu, Shota Nakayama, Tomotaka Miyazawa, Masug ...
    2016 Volume 57 Issue 9 Pages 1447-1453
    Published: September 01, 2016
    Released: August 25, 2016
    [Advance publication] Released: April 15, 2016
    JOURNALS FREE ACCESS

    In situ XRD measurements were conducted during the tensile deformation of both submicron-grained Ni specimens fabricated by accumulative roll bonding (having a grain size of 270 nm) and nanocrystalline Ni fabricated by electrodeposition (having a grain size of 52 nm). Variations in the dislocation density and the extent of elastic deformation could be determined with a time resolution of 1.0 s based on changes in the full width at half maximum of ten Bragg peaks and in the Bragg peak shifts, respectively. The dislocation density was found to vary in four different stages. Regions I and III were the elastic and plastic deformation regions, respectively, while Region II was the transition region. Here, the dislocation density rapidly increased to a value, ρII, necessary for plastic deformation. Since the increase in ρII was inversely proportional to grain size, it is evident that nanocrystalline materials require extremely high dislocation densities for deformation to progress solely by plastic deformation. In Region IV, the multiple dislocations were rapidly annihilated by unloading associated with fracture. In the case of the nanocrystalline Ni, there was little difference in the stress distribution in the grains depending on the crystal direction during plastic deformation and, accordingly, there was only minimal variation in the residual stress in the grain with different crystal directions after unloading.

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  • Yoshihiko Uematsu, Toshifumi Kakiuchi, Hiromi Miura, Taishi Nozaki
    2016 Volume 57 Issue 9 Pages 1454-1461
    Published: September 01, 2016
    Released: August 25, 2016
    [Advance publication] Released: June 03, 2016
    JOURNALS FREE ACCESS

    Magnesium (Mg) alloy AZ61 was multi-directionally forged (MDFed) under decreasing temperature conditions using a die. The average grain size decreased with increasing MDFing pass number. The initial grains size of 21.6 μm in the as-annealed specimen decreased gradually during MDFing and an average grain size of 0.3 μm could be attained after MDFing for 8 passes. The tensile strength and Vickers hardness were improved with increasing pass number from 1 to 8. Hall-Petch relationship was held for those static mechanical properties. Subsequently, tension-tension axial loading fatigue tests were performed using the as-annealed specimen and MDFed ones to 1, 3, 6 and 8 passes in which cumulative strains were 0.8, 2.4, 4.8 and 6.4 respectively. Fatigue strengths were highly improved by MDFing with increasing pass number of forging from 1 to 3. However, the improvement looked almost saturated over the pass number of 3. The observed breaking-up of the Hall-Petch relationship concerning with fatigue limits was attributed to grain-boundary sliding followed by crack initiation and propagation along grain boundaries.

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  • Ruixiao Zheng, Tilak Bhattacharjee, Akinobu Shibata, Nobuhiro Tsuji, C ...
    2016 Volume 57 Issue 9 Pages 1462-1470
    Published: September 01, 2016
    Released: August 25, 2016
    [Advance publication] Released: May 13, 2016
    JOURNALS FREE ACCESS

    In this study, bulk nanostructured 2024 Al alloy sheets with optimized strength and ductility were successfully prepared through an effective thermo-mechanical process including solution treatment, heavy deformation by accumulative roll bonding (ARB) and cold rolling (CR), and subsequent low temperature aging. A lamellar boundary structure with mean grain thickness of 40 nm could be clearly observed after 3-cycle ARB and 50% CR with total equivalent strain of 3.2. The ultimate tensile strength and elongation to failure of the ARB+CR processed sample were 599 MPa and 1.7%, respectively. After subsequent low temperature aging at 100℃ for 20 h, the ultimate tensile strength and elongation to failure became 635 MPa and 7%, respectively, showing simultaneously increased strength and ductility compared to the cold-worked state. The reasons for the superior mechanical properties were discussed.

    Fig. 10 TEM microstructures of the ARB+CR processed 2024 Al alloy sample aged at 100℃ for 20 h: (a) a bright field image and corresponding SAD pattern, (b) dark field image of (a), (c) higher magnification image of the region marked by the white-broken rectangular in (a), and (d) thickness distribution of the lamellas measured from (a). Fullsize Image
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  • Chihiro Watanabe, Masakazu Hibino, Ryoichi Monzen, Seiichiro Ii, Koich ...
    2016 Volume 57 Issue 9 Pages 1471-1475
    Published: September 01, 2016
    Released: August 25, 2016
    [Advance publication] Released: April 22, 2016
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    The microstructural change and aging behavior of Cu-1.8mass%Be-0.2mass%Co and Cu-3mass%Ti alloys severely deformed by high-pressure torsion (HPT) at room temperature were investigated on two-step aging condition; natural aging and subsequent artificial aging. Application of HPT processing under an applied pressure of 5 GPa for 10 revolutions at 1 rpm to the alloys produced ultra-fine grained structures. The hardnesses of the Cu-Be-Co and Cu-Ti alloys increased with equivalent strain up to 7, and then saturated to constant values of 400 and 330 Hv, respectively. Aging the HPT-processed alloys at 293 K gradually decreased the resistivities of the alloys; however, even after the longest natural aging period of 2.59 Ms (1 month), the hardnesses of the alloys remained essentially unchanged. The attained peak hardness of the Cu-Be-Co alloy on subsequent artificial aging at 593 K decreased with increasing natural aging time, while the age-hardening behavior of the Cu-Ti alloy during aging at 623 K was practically unaffected by natural aging at 293 K up to 2.59 Ms.

    Fig. 6 Age hardening curves of Cu-Ti specimens artificially aged at 623 K after HPT processing and then natural aging for 0 s (0s), 1 week (0.61 Ms; 1w) or 1 month (2.59 Ms; 1m). Fullsize Image
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  • Tomohito Tsuru, Yoshiteru Aoyagi, Tomotsugu Shimokawa
    2016 Volume 57 Issue 9 Pages 1476-1481
    Published: September 01, 2016
    Released: August 25, 2016
    [Advance publication] Released: June 24, 2016
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    The effects of grain size and intragranular dislocation on yield mechanism and subsequent plastic deformation in ultrafine-grained (UFG) Al and Cu were investigated by large-scale atomic simulations. Polycrystalline atomic models with and without intragranular dislocation sources were used to elucidate the relationship between mechanical properties and defect texture. It is found that the intragranular dislocation plays a significant role in both incipient yield and grain boundary mediated dislocation nucleation. In addition UFG Cu yields earlier than UFG Al because partial dislocations in Cu are more likely to activate from grain boundaries, where the partial dislocation leaves deformation twin and secondary dislocation tends to move on twin boundary accompanied by the shift of twin boundary plane.

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  • Kenjiro Fujimoto, Takuto Isa, Haruka Sakurai, Yuki Yamaguchi, Shigeru ...
    2016 Volume 57 Issue 9 Pages 1482-1488
    Published: September 01, 2016
    Released: August 25, 2016
    JOURNALS FREE ACCESS

    Ca3(Co1−xAlx)4O9+δ, Ca3(Co1−yCuy)4O9+δ, Ca3(Co1−x−yAlxCuy)4O9+δ thin-films and sintered bodies were prepared by electrostatic spray deposition, a solution-based process. The solid-solution region of Ca3(Co1−x−yAlxCuy)4O9+δ was narrower than the presumed region based on the results for single-element-substituted Ca3(Co1−xAlx)4O9+δ and Ca3(Co1−yCuy)4O9+δ. The electrical conductivity of Ca3(Co0.95Al0.025Cu0.025)4O9 were larger than that of the non-substituted-Ca9Co12O28. The power factor of Ca3(Co0.95Al0.025Cu0.025)4O9 was approximately the same as that of single phase compounds of Ca9Co12O28. This phenomenon was presumed to have resulted from the increased hole concentration and mobility of the material. Our evaluations of the thermoelectric performance showed similar trends for the thin-film and the sintered body. However, we observed uneven thickness and porosity in the prepared thin films. These flaws will have to be resolved through adjustments in the process used to prepare the thin films.

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  • Shinji Isogami, Tetsuroh Kawai, Masaaki Futamoto
    2016 Volume 57 Issue 9 Pages 1489-1493
    Published: September 01, 2016
    Released: August 25, 2016
    [Advance publication] Released: July 15, 2016
    JOURNALS FREE ACCESS

    A series of 40 nm-thick Fe100−xSix (x = 0, 6 or 10 at%) single-crystal films with an A2 phase were fabricated on MgO(001) substrates. Variations in the ferromagnetic resonant field (Hr) and linewidth (ΔH) values with changes in the azimuthal angle (ϕH) were subsequently evaluated, using an electron cyclotron resonant system with X-band (9.86 GHz) microwaves at room temperature. The Hr values exhibited fourfold symmetric behavior while varying the ϕH. In addition, the ΔH values demonstrated symmetric behavior, with intense peaks in the vicinity of the magnetization hard-axis, and so the ΔH variation was reduced with increasing Si content. An analysis of the data was performed, employing the magnetization coherent rotation model. It was determined that the appearance of strong peaks can be attributed to differences between ϕH and the magnetization angle (ϕM), based on the term [cos(ϕHϕM)]−1. This is believed to result from the insufficient Hr strength obtained during measurements with X-band microwaves relative to the anisotropy fields of the films.

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  • Jianglong. Yi, Yupeng Zhang, Xinxin Wang, Chunlin Dong, Haichun Hu
    2016 Volume 57 Issue 9 Pages 1494-1497
    Published: September 01, 2016
    Released: August 25, 2016
    [Advance publication] Released: July 29, 2016
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    In this paper, a series of Al/Ti multilayers with different modulation periods were used in copper and Al2O3 ceramic diffusion bonding. The reactive multilayer was deposited by DC magnetron sputtering, and the diffusion bonding experiments were performed at 900℃ for 10 min with a pressure of 5 MPa. The interfacial joints were inspected by scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS), X-ray diffraction and tensile shear tests. As a result, no significant metallurgical defect was observed in the microstructures of the joints. The formation of several intermetallic compounds at the interface, such as Cu/Ti eutectic and Al2O3-X·TiO compound, has further confirmed the success of Cu-Al2O3 bonding as compared to the Al/Ni nano-multilayers, which use Al/Ti nano-foils as interlayer for diffusion bonding to bring more benefit to the quality of cermet joint.

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  • Pei-Shan Chang, Chun-Hung Chen, Chuen-Guang Chao
    2016 Volume 57 Issue 9 Pages 1498-1504
    Published: September 01, 2016
    Released: August 25, 2016
    JOURNALS FREE ACCESS

    The effect of microstructure on the stress corrosion behavior of Mg–Sn alloys was investigated using a bent-beam method. The effects of an Mg2Sn phase and Sn in the matrix on stress corrosion were investigated. Mg2Sn phase mainly formed at the grain boundary. The volume fraction of the Mg2Sn phase increased with increasing Sn content, and the morphology of Mg2Sn changed from spherical to a semi-continuous network. The average volume fractions of Mg2Sn phase increased from 0.07 ± 0.02% to 5.06 ± 0.92% as the Sn content was increased from 2 to 8 mass%. An increase in the amount of Mg2Sn phase increased the pit density, whereas dissolution of the Mg2Sn phase into the matrix resulted in decreased pit density. An intergranular cracking mode was observed. The solution heat treatment dissolved the Mg2Sn phase and eliminated the micro-galvanic corrosion due to Mg2Sn, thereby delaying crack initiation also enhancing stress corrosion resistance. Mg-8%Sn sample through solution heat treatment showed the best stress corrosion resistance.

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  • Ye Li, Ming Lv, Hongyu Liang
    2016 Volume 57 Issue 9 Pages 1505-1508
    Published: September 01, 2016
    Released: August 25, 2016
    [Advance publication] Released: July 29, 2016
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    The local structural arrangement of the amorphous alloy system Al45Ni50Co5, subject to uniaxial tensile strain, was investigated using molecular dynamics simulation. The amorphous phase of the alloy system did not change in the process. The degree of icosahedral order quantified by the Honeycutt-Andersen structural type, 1551, plays an important role in the formation and expansion of the shear transition zones in this amorphous system. The structural types 1551, 1441, and 1661 are found to evolve during the deformation process.

    Fig. 1 The stress-strain curve of the simulated Al45Ni50Co5 alloy. Inset shows snapshots of the system under tensile deformation at 0, 20, and 40 percent strain, respectively. Fullsize Image
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  • Meng Wang, Wilson Xu, Qingyou Han
    2016 Volume 57 Issue 9 Pages 1509-1513
    Published: September 01, 2016
    Released: August 25, 2016
    JOURNALS FREE ACCESS

    While aluminum-silicon (Al-Si) alloys are one of the most versatile aluminum alloys, iron is considered one of the most harmful elements in Al-Si diecasting application. Its presence leads to the precipitation of many AlFeSi intermetallic phases and unacceptable mechanical properties, such as reduction in ductility. Thus controlling the fraction and morphology of the AlFeSi phase, especially the β-AlFeSi phase is an important way to improve the ductility of Al-Si die casting alloys. In this article, Ca/Mn, Ca/Sr and Sr/Mn elements were added into A380 alloys to study the effect of combined element addition on the morphology change of the AlFeSi phase. Sr and Ca addition can impair the modification effect and introduce sludge. Mn and Ca, Mn and Sr can result in a microstructure consisting of fcc α-Al, modified eutectic Si, α-AlFeSi Chinese script phases and a refined platelet β-phase. However, use of high cooling rates can better refine the morphology of the AlFeSi phase and lead to a better alloy product.

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  • Kengo Hata, Masayuki Wakita, Kazuki Fujiwara, Kaori Kawano, Toshiro To ...
    2016 Volume 57 Issue 9 Pages 1514-1519
    Published: September 01, 2016
    Released: August 25, 2016
    JOURNALS FREE ACCESS

    The crystal orientation of nucleating austenite during reverse phase transformation of a C-Mn steel has been investigated by in situ EBSD technique using a heating stage of FE-SEM at temperatures ranging from RT to 800℃. It has been found that the multiple interfaces between a nucleating austenite grain and the surrounding parent ferrite grains are preferentially selected as the Kurdjumov-Sachs (K-S) relationship. More than 50% of austenite grains are surrounded with two or more parent ferrite grains satisfying the K-S relationship with a deviation within 7°. Based on these findings, a nucleation model at triple junction is proposed, which supposes that the orientation of nucleating austenite is selected to satisfy the K-S relationship or the orientation relationship close to K-S relationship at two of the interfaces to ferrite grains, and at the other interfaces to minimize the misorientation from the K-S relationship.

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  • Yong Zang, Zebo Zhao, Qin Qin
    2016 Volume 57 Issue 9 Pages 1520-1525
    Published: September 01, 2016
    Released: August 25, 2016
    [Advance publication] Released: July 29, 2016
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    A reverse process design method is established in this paper by reversely applying the Hodgson recrystallization models. The method allows a draft schedule to be designed according to the requirements of the resulting microstructure, and it is made up of the design equations of process parameters and the criteria-selected values of the parameters. First, the microstructural evolution is summarized as five paths, and the temperature and strain are set to fixed ranges according to the authors' experience. The mathematical models of the other parameters for each evolution path are established by applying the Hodgson recrystallization models. Secondly, criteria are established to select suitable values as a better draft schedule from uncountable groups of values. Finally, some examples are given and experiments are carried out according to the method. Metallographic observations showed that the final grain size was consistent with the design goals. The maximum relative error comparing the design goal was just 5.5%. These results prove that the method is sufficiently accurate and effective.

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  • Yasushi Kamimura, Satoru Katakura, Keiichi Edagawa, Shin Takeuchi, Shi ...
    2016 Volume 57 Issue 9 Pages 1526-1534
    Published: September 01, 2016
    Released: August 25, 2016
    [Advance publication] Released: July 29, 2016
    JOURNALS FREE ACCESS

    Single crystals and cold-swaged polycrystalline specimens of Gum Metal of Ti-36Nb-2Ta-3Zr-0.3O (mass %) have been compressed with the stress-relaxation test in the temperature range from 77 K to 450 K. In both single crystals and cold-swaged specimens, the yield stress decreases with increasing temperature rapidly to the room temperature and then gently above it forming a plateau at high temperature. The activation analysis of plastic deformation showed that the applied shear stress dependence of activation enthalpy and that of activation volume for single crystals and those for cold swaged specimens are almost identical if we shift the stress scale by about 120 MPa, meaning that the basic deformation mechanism is common to both samples. The above results are contradictory with the previously proposed non-dislocation deformation mechanism at the ideal shear strength, but consistent with the established features of usual bcc alloys, i.e., the deformation is governed by the Peierls mechanism at low temperature and by defect hardening at high temperature. τχχ and ψ − χ relations of single crystals showed a typical slip asymmetry seen in bcc metals, where slip in Gum Metal belongs to the {112} slip type as in binary Ti-Nb single crystals reported previously (S. Hanada et al.: Metall. Trans. A 16 (1985) 789). Yielding by massive {332}〈113〉 twin formation in single crystals at low temperatures was observed for the first time in Gum Metal.

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  • Hai V. Pham, Makoto Nanko
    2016 Volume 57 Issue 9 Pages 1535-1538
    Published: September 01, 2016
    Released: August 25, 2016
    JOURNALS FREE ACCESS

    High-temperature oxidation of 5 vol% Ni dispersed mullite-based composites was investigated at temperatures ranging from 1200 to 1400℃ for 1 to 48 h in air. Oxidation behavior at high temperatures of Ni/mullite composites was compared with other ceramic-based composites and then discussed in the present paper. Oxidation of Ni particles within mullite matrix developed a surface layer of the oxidation products and an internally oxidized zone. Growth of the internally oxidized zone obeyed the parabolic law, which meant diffusion process in internally oxidized zone is the rate controlling process. Comparison in this investigation indicated that Ni/mullite has a greater oxidation resistance than these of reported composites such as Ni/MgO and Ni/Al2O3.

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  • Kyohei Otani, Masatoshi Sakairi, Akira Kaneko
    2016 Volume 57 Issue 9 Pages 1539-1546
    Published: September 01, 2016
    Released: August 25, 2016
    [Advance publication] Released: July 25, 2016
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    Effect of a kind of metal cation on corrosion mechanism of A3003 aluminum alloy in tap water was investigated by electrochemical techniques and immersion corrosion tests. Corrosion rate of the aluminum alloy decreased with increase in a hardness of cation, except for Mg2+. XPS analyses showed metal cations, classified as a hard acid in tap water were incorporated in hydroxides on the aluminum alloy. The results suggest that the incorporated cations have corrosion inhibitory effect (e.g., Ca2+ and Zn2+) or corrosion promotive effect (e.g., Mg2+). These different effects can be explained by difference in molar volume between hard metal cation's hydroxide and aluminum hydroxide.

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  • Wen-Tao Yu, Jing Li, Cheng-Bin Shi, Qin-Tian Zhu
    2016 Volume 57 Issue 9 Pages 1547-1551
    Published: September 01, 2016
    Released: August 25, 2016
    JOURNALS FREE ACCESS

    The solidification microstructure and primary carbides in stainless steel 8Cr13MoV produced by electroslag remelting (ESR) were studied. The microstructure is finer when ESR using lower current intensity or higher cooling intensity. The amount of carbides is larger but the fraction is lower when using lower current intensity in ESR. The current intensity has no effect on the morphology and type of primary carbides. Under the condition of higher cooling intensity, distribution of primary carbides is more even, the size and alloy elements content of primary carbides is smaller. With increasing cooling intensity, the primary carbides change from skeleton-like shape composed of many fine clusters to skeleton-like shape composed of regular and short bar-like crystals, and the internal structure of primary carbides become more compact.

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  • Khurram Shahzad, Chunyu Zhu, Etsushi Tsuji, Yoshitaka Aoki, Shinji Nag ...
    2016 Volume 57 Issue 9 Pages 1552-1559
    Published: September 01, 2016
    Released: August 25, 2016
    [Advance publication] Released: July 25, 2016
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    In this study, we report the formation of barrier-type anodic films on magnetron-sputtered magnesium films at a constant current density of 10 A m−2 in ethylene glycol (EG)-H2O electrolytes containing 0.1 mol dm−3 ammonium fluoride and 0.1 mol dm−3 dipotassium hydrogen phosphate. The growth efficiency is close to 100% up to 10 vol% H2O, but decreases to 52% in the EG-free aqueous electrolyte. Even at such a low efficiency in the aqueous electrolyte a uniform barrier-type anodic film with flat and parallel metal/film and film/electrolyte interfaces is developed over 100 V. This is contrast to the non-uniform film growth and low breakdown voltage in the phosphate-free aqueous electrolyte containing ammonium fluoride. The anodic films appear to be amorphous regardless of H2O concentration in the phosphate-containing electrolytes, and consist of phosphate-incorporated oxyfluoride. The phosphate incorporation is suppressed by an increase in H2O concentration. In addition, the anodic films consist of two layers with an inner layer containing less amount of phosphate. The outer layer is probably formed at the film/electrolyte interface by the migration of Mg2+ ions outwards, while the inner layer is formed at the metal/film interface. The film formation at the former interface even in the aqueous electrolyte at low efficiency is likely to contribute to the formation of barrier films, not porous anodic films.

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  • Guan-Jhou Chen, Jia-Shyan Shiau, Shih-Hsien Liu, Weng-Sing Hwang
    2016 Volume 57 Issue 9 Pages 1560-1566
    Published: September 01, 2016
    Released: August 25, 2016
    JOURNALS FREE ACCESS

    The optimal carbothermic reduction parameters of limonite ore and the influence of calcining temperature on these were investigated. In addition, the impact of the addition of Na2SO4 on limonite ore which had been calcined before reduction at optimal carbothermic conditions was also investigated. XRD analysis, BET-specific surface area analysis, bromine methyl alcohol solution analysis, and chemical compositional analysis were used in order to obtain the associated parameters.

    The best nickel grade and recovery rate of the 673 K-calcined limonite ore can reach >30 mass% and 90.2 mass%, respectively, when the reduction temperature is 1373 K, with a reduction time of 30 min, and a carbon-oxygen ratio of 0.6. This is because the 673 K-calcined limonite ores have the highest specific surface area of 46.8 m2/g with pores in the size of 29.7 Å. The addition of Na2SO4 by 5 mass% resulted in the best nickel grade of >30 mass% and the best recovery rate of 93.8 mass% at the same reduction temperature, time and carbon-oxygen ratio.

    Fig. 6 Schematic diagram of specific surface area and pore size. Fullsize Image
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  • Shunsuke Sasaki, Hiroto Goto, Tatsuro Katsumura, Masaru Miyake
    2016 Volume 57 Issue 9 Pages 1567-1574
    Published: September 01, 2016
    Released: August 25, 2016
    [Advance publication] Released: July 15, 2016
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    The sizing press process was developed to achieve extensive width reduction and yield improvement. The slab head and tail shapes after sizing pressing are important in crop loss reduction and stable operation. This study was carried out to investigate the deformation behavior of the slab head in sizing pressing with back pressure. Finite Element Analysis and a model experiment were conducted to study the deformation behaviors of the slab head thickness profile and plan-view pattern. It was found that width reduction by the back-pressure method enables control of the slab head shape. The maximum thickness of the central part of the slab head was reduced and the plan-view pattern changed from a fishtail shape to a tongue shape when back pressure was applied during sizing pressing.

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  • Akihiko Ikuta, Minoru Hatate, Tohru Nobuki
    2016 Volume 57 Issue 9 Pages 1575-1580
    Published: September 01, 2016
    Released: August 25, 2016
    [Advance publication] Released: July 01, 2016
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    The machinability of austempered spheroidal graphite cast iron made by continuous casting (A-FCD600) was investigated. In this study, spheroidal graphite cast iron made by continuous casting (FCD600) was used to examine the influence of the austempering on machinability. In addition, austempered gray cast iron made by continuous casting (FC250) was used to examine the influence of the morphology of graphite on machinability. From the results of a tool wear test using continuous turning, the machinability decreased in the order of FC600, A-FC250 and A-FCD600. When relative machinability ratings between each material were calculated using tool life equations decided by the result of the tool wear test, the machinability of A-FCD600 was approximately 1.9 times inferior to FCD600, and approximately 1.3 times inferior to A-FC250. One characteristic of A-FCD600 was that its mechanical properties were relatively near steel. Therefore, a similar tool wear test was carried out with a P10 cemented carbide tool for steel. In this case, the tool life extended 25% compared to the K10 cemented carbide tool for cast iron. These results suggest that tool life can be improved in A-FCD600 cutting when tools for steel are used.

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  • Sadatoshi Koroyasu
    2016 Volume 57 Issue 9 Pages 1581-1586
    Published: September 01, 2016
    Released: August 25, 2016
    [Advance publication] Released: July 08, 2016
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    The effect of the coat permeability on the melt velocity of molten aluminum alloy in the expendable pattern casting (EPC) process was investigated experimentally. For eight kinds of coats, the linear relationship between the inter-coat differential pressure and airflow rate was obtained. Coat permeabilities conforming JIS were determined from the gradient of the linear relationship. Using the eight kinds of coats, aluminum alloy plates were cast by the EPC process for three kinds of expansion ratios of expendable polystyrene (EPS) pattern, in the case of bottom pouring and without reduced pressure. The arrival time of the molten metal was measured and the melt velocity was obtained. The use of high expansion ratios of EPS pattern or high permeability coats led to higher melt velocities. In the high coat permeability region, the melt velocity did not increase so much, even when the coat permeability increased. The effects of the pouring temperature and casting thickness on the melt velocity were also examined. The application of high pouring temperature or large casting thickness, led to higher melt velocity. The experimental values of the melt velocity were compared with the calculated values based on the mold filling model used in the previous study. The experimental values were in relatively good agreement with the calculated values, except for when the coat permeability was high and the casting thickness was small.

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  • Osamu Furukimi, Hiroki Katafuchi, Masatoshi Aramaki, Muhammad Kozin, S ...
    2016 Volume 57 Issue 9 Pages 1587-1592
    Published: September 01, 2016
    Released: August 25, 2016
    JOURNALS FREE ACCESS

    The wear resistance of iron nitrides compound layers and a high nitrogen martensite phase formed in the material surface for industrial pure iron, treated by nitriding and quenching followed by aging process were studied experimentally. Both the compound layer without pores by lowering the nitriding temperature and the high nitrogen martensite phase, showed the same tendency to high wear resistance. On the other hand, the pores in the compound layer made by the longer nitriding time decreased the wear resistance due to the acceleration of crack propagation. Metal flows were observed at the ε-phase in the compound layer very close to the surface after a sliding test. However, no strain hardening was observed. It was also found that the metal flows on a large part of the martensite layer and the hardness increased considerably.

    These results revealed that the high hardness ε-phase shows high wear resistance due to the plastic deformation, whereas the nitrogen martensite shows high wear resistance by the plastic deformation accompanied with the strain hardening.

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  • Masayuki Koshiyama, Hazuki Sako, Munekazu Ohno, Kiyotaka Matsuura
    2016 Volume 57 Issue 9 Pages 1593-1596
    Published: September 01, 2016
    Released: August 25, 2016
    [Advance publication] Released: July 01, 2016
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    Combustion-synthesized Y-α-SiAlON and Ca-α-SiAlON powders were consolidated by spark plasma sintering (SPS) at 1300–1450℃ for 10 min, and the mechanical properties of the consolidated bulk samples were investigated. XRD analysis revealed that α-SiAlON partially transforms into β-SiAlON during the SPS and a bulk mixture of α/β-SiAlON was obtained. The fraction of β-SiAlON increased with the increase in sintering temperature and the α to β transformation ratio was higher for Y-α-SiAlON than for Ca-α-SiAlON. The hardness of the consolidated bulk increased with sintering temperature, and after reaching a maximum at 1350℃, the hardness gradually decreased with temperature in both the Y-α-SiAlON and Ca-α-SiAlON. The increase in hardness with temperature arises from the increased density of the sintered body, while the decrease in hardness results from grain growth due to an increase in temperature. The fracture toughness tended to increase with temperature and did not show a maximum for either α- or β-SiAlON, although the Y-α-SiAlON always exhibited a greater toughness than the Ca-α-SiAlON. The greater toughness of the Y-α-SiAlON is attributable to its higher fraction of transformed β-SiAlON, because the elongated shape of the β-SiAlON leads to the prevention of crack propagation.

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  • N. Setoudeh, Cyrus Zamani, Mohammad Sajjadnejad
    2016 Volume 57 Issue 9 Pages 1597-1601
    Published: September 01, 2016
    Released: August 25, 2016
    [Advance publication] Released: July 25, 2016
    JOURNALS FREE ACCESS

    Mixtures of Zn-NiO with stoichiometric compositions were milled for different times in open-valve milling cups. Although the gradual reduction of nickel oxide with zinc occurred during one hour of milling, it was found that nanometric mixtures of ZnO and Ni0.6Zn0.4O appear after 72000 seconds (20 hrs) of milling with the crystallite size of Ni0.6Zn0.4O phase being about 22 nm. On the other hand, and under the flow of argon gas, narrow and intense peaks of ZnO and Ni0.6Zn0.4O were observed after isothermal heating of 1800 seconds milled samples at 1273 K. Electron microscopy observations and elemental analysis of the products confirm formation of ZnO nano-needles distributed in the nickel zinc oxide matrix.

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  • Takahiro Hayashi, Rei Fujishima
    2016 Volume 57 Issue 9 Pages 1602-1608
    Published: September 01, 2016
    Released: August 25, 2016
    [Advance publication] Released: July 29, 2016
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    Ultrasonic guided waves achieve non-destructive inspection of thin plates. However, issues such as large energy leakage and attenuation often plague guided wave inspection of storage tanks and pipes filled with fluid. This study experimentally investigated the non-destructive testing of a water-loaded flat aluminum alloy plate through the application of a quasi-Scholte (QS) wave that propagated along the fluid-plate interface without experiencing attenuation due to leakage. A QS wave was confirmed as having been generated and propagated in a plate loaded with water on the bottom surface using ultrasonic incidence and detection at the top water-free surface. Two-dimensional Fourier transform images of the waveforms revealed reflection of the QS wave from a defect as well as a forward incident QS wave. The visualization results experimentally confirmed—via measurements of waves in water using a laser Doppler vibrometer—that QS waves propagated along a plate surface, while scattered waves were generated by defects.

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  • Yoshitomo Kamiura, Kenji Umezawa, Yuden Teraoka, Akitaka Yoshigoe
    2016 Volume 57 Issue 9 Pages 1609-1614
    Published: September 01, 2016
    Released: August 25, 2016
    [Advance publication] Released: July 29, 2016
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    Polycrystalline tungsten surfaces were irradiated at room temperature with two kinds of nitrogen ions—N+ and N2+—at 2.5 keV by using an ion beam apparatus. Results of X-ray photoelectron spectroscopy (XPS) experiments performed using synchrotron radiation at SPring-8 showed that upon irradiation of the tungsten sample with either kind of ion, the full widths at half maximum (FWHM) of the W 4f7/2 and W 4f5/2 peaks broadened and the peaks at 35.8 eV and 37.8 eV—which correspond to WO3 binding energies—increased slightly; this indicated the formation of tungsten nitride at the subsurface below the interface. The N 1s spectra of tungsten after nitrogen ion beam irradiation were decomposed into four component peaks. The positions of these component peaks were observed to be the same as those of the standard tungsten oxynitride W0.62(N0.62O0.38), which exhibited W2N peaks in X-ray diffraction analysis. The main decomposed peaks at 397.3 eV and 398.1 eV were attributed to W-N bonds and W-N-O bonds, respectively. The variation of the intensity ratio of the N 1s peak at 397.3 eV to the W 4f doublet peaks (corresponding to W-N bonds) as a function of the escape depth, which was measured by angle-resolved XPS, apparently followed a normal distribution for the irradiated samples. This indicates that the W-N bond density of the tungsten surface irradiated with N2+ ions is higher than that of the surface irradiated with N+ ions and also that the N2+ ions penetrate slightly deeper than the N+ ions.

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  • Xian-rui Zhao, Dun-wen Zuo, Meng-xian Zhang, Feng Xu, Jin-fang Wang, S ...
    2016 Volume 57 Issue 9 Pages 1615-1619
    Published: September 01, 2016
    Released: August 25, 2016
    [Advance publication] Released: July 25, 2016
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    Ultra-fine Ti(C,N)-TiB2-Co cermets were fabricated from Co, Ti, C, and BN powder mixtures via a reactive hot pressing (RHP) process, and the effect of sintering temperature on their microstructure and properties was explored. An elevated temperature was conducive to the full conversion of Ti(C,N) phase, thus leading to microstructure homogenization and the production of cermets with a high relative density and purity. With increasing temperature, the relative density, hardness, and fracture toughness first increased, and then decreased. A sample sintered at 1150℃ therefore displayed the best overall performance in terms of its maximum relative density and ultra-fine particle size, with relative density, hardness, and fracture toughness of 99.9%, 1947 HV10 and 6.6 MPa.m1/2, respectively. Compared with P10 cemented carbide, Ti(C,N)-TiB2-Co displayed superior wear resistance because of its higher hardness, as well as the formation of an oxidation layer on the worn surface during dry sliding friction and wear.

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  • Kai Narita, Equo Kobayashi, Tatsuo Sato
    2016 Volume 57 Issue 9 Pages 1620-1627
    Published: September 01, 2016
    Released: August 25, 2016
    [Advance publication] Released: August 12, 2016
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    Mg/bioceramic composites fabricated by powder metallurgy technique have been explored for biodegradable load-bearing implants. Although sintering behavior including densification and reaction has a significant effect on mechanical properties of the composites, little studies have been conducted focusing on both sintering behavior and mechanical properties. In this study, Mg/10 and 20 vol.% β-tricalcium phosphate (β-TCP) composites were fabricated by spark plasma sintering, which achieved high densification. Distinct sintering behavior of Mg/β-TCP composites involving reaction was investigated by estimating relative densities during sintering, thermal analyses, X-ray diffractometry and auger electron spectroscopy. The results suggest that Ca solid diffusion into Mg during sintering resulted in melting and penetrating Mg into gaps between β-TCP particles, and finally led to high densification. The reaction between Mg and β-TCP produced MgO. Compression tests showed that Mg/β-TCP composites enhanced their mechanical properties compared with Mg sintered at the same route. That's because the high densification of Mg/β-TCP composites and high hardness of MgO potentially caused good load transfer from Mg-matrix to the formed MgO as reinforcement. The discoveries regarding the reactions can help the design of Mg/calcium phosphate composites including Mg/β-TCP composites.

    Fig. 11 Schematic diagrams of reaction behavior of Mg/β-TCP composites. Direction and thickness of arrows refer to direction and rate of elements diffusion respectively. Fullsize Image
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  • Satoshi Hiroi, Masashi Mikami, Tsunehiro Takeuchi
    2016 Volume 57 Issue 9 Pages 1628-1632
    Published: September 01, 2016
    Released: August 25, 2016
    JOURNALS FREE ACCESS

    Fe2VAl-based thin-films were prepared using radio frequency magnetron sputtering technique at various substrate temperatures up to 1073 K. At low substrate temperature below 773 K, we did not observe any evidences of L21 Heusler phase but the epitaxially grown B2-phase, which is considered as a chemically disordered structure of Heusler-phase. At high substrate temperatures above 773 K, L21 ordering became observable and its volume fraction was increased with increasing the substrate temperature. The sample deposited at 1073 K, that was considered as the highly ordered L21-phase, possessed S ≈ −120 μV K−1 at around 340 K, and this value is almost the same with that previously reported for bulk samples. The power factor indicated large values exceeding 2.0 mWm−1K−2 at the room temperature. The thermal conductivity of Fe2VAl thin-film was reduced to a half value of the bulk. As a result, the maximum figure of merit was almost doubled to 0.07 at 400 K from 0.04 of bulk samples.

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  • Hajime Kato, Koshiro Kitayama, Kazuma Hibi, Hiroyuki Kawabata
    2016 Volume 57 Issue 9 Pages 1633-1638
    Published: September 01, 2016
    Released: August 25, 2016
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    In a previous study, we reported that adding tin to Mg-Al-Ca alloys inhibits cast cracking while maintaining excellent heat resistance. In this study, to clarify the mechanism resulting in the improved castability, Mg-Al-Ca alloys with different compositions were cast by high-pressure die casting into an I-shaped die with strain gauge instrumentation. The solidification shrinkage and thermal contraction of the alloys during the solidification and cooling process were investigated. The addition of tin decreased the solidification shrinkage of the alloys, and the tensile stress in the alloys was relaxed. On the basis of these results, the addition of tin is considered to improve the castability.

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  • Atsushi Unemoto, Koji Yoshida, Tamio Ikeshoji, Shin-ichi Orimo
    2016 Volume 57 Issue 9 Pages 1639-1644
    Published: September 01, 2016
    Released: August 25, 2016
    [Advance publication] Released: July 25, 2016
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    In this study, we incorporated fast lithium ion conducting complex hydrides containing cluster anions, namely icosahedral dodecahydro-closo-dodecaborate anions, [B12H12]2−, into a bulk-type all-solid-state battery. Li2B12H12, TiS2 and Li were used as an electrolyte, a positive electrode active material and a negative electrolyte, respectively, for a battery assembly to investigate its battery performance. “Bulk-type” battery contains high quantity of electrode active materials in the electrode layer, and thereby the enhanced energy-storage density is expected. In addition, nonflammable solid-state electrolyte would ensure the safety, which is currently problematic for the conventional lithium rechargeable battery that uses organic liquid electrolyte. Li2B12H12 has a high lithium ionic conductivity of log(σ/S cm−1) = −2.6 at 393 K. It exhibits a relatively higher conductivity of log(σ/S cm−1) = −3.5 at reduced temperatures such as 333 K. These high lithium ionic conductivity allows for the repeated operation of the bulk-type all-solid-state TiS2/Li battery for at least 10 cycles at not only 393 K but also 333 K with the discharge capacities higher than 190 mAh g−1. Li2B12H12 exhibits higher oxidative stability. Thus, our battery realized high coulombic efficiencies of over 92% during the battery operation. This information will be beneficial for the further development of novel complex hydride-based electrolyte to have high-performance bulk-type all-solid-state batteries.

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  • S. Fujieda, W. Miyamura, K. Shinoda, S. Suzuki, B. Jeyadevan
    2016 Volume 57 Issue 9 Pages 1645-1651
    Published: September 01, 2016
    Released: August 25, 2016
    [Advance publication] Released: July 29, 2016
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    Fe-Ni hydroxide fine particles with a layered double hydroxide-type structure were precipitated as an intermediate in polyol (ethyleneglycol) solution with Fe compositions ranging between about 10 and 90 at%. Subsequent reduction-annealing of the above polyol-derived particles with 13–56 at% Fe at 673 K resulted in the synthesis of fcc Fe-Ni alloy fine particles with their sizes less than about 50 nm. The lattice constants of fcc Fe-Ni alloy particles were close to those of the bulk fcc Fe-Ni alloy with similar compositions. X-ray absorption spectroscopy measurements suggested that fcc Fe-Ni alloy was formed through simultaneous reduction of Fe and Ni in Fe-Ni hydroxide. Consequently, the reduction-annealing of polyol-derived Fe-Ni hydroxide fine particles is proved to be an effective process for obtaining composition-controlled Fe-Ni alloy fine particles.

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  • Motoaki Morita, Osamu Umezawa
    2016 Volume 57 Issue 9 Pages 1652-1659
    Published: September 01, 2016
    Released: August 25, 2016
    JOURNALS FREE ACCESS

    The microstructures of scales adhered to the inner walls of elbow steel pipes, used in the transport of hot spring water, are analyzed. The system examined in this study is from a geothermal plant in Obama town, Unzen city, Nagasaki, Japan, using pipes with 3.5 months of prior use. The adhered substance consists of four layers: amorphous magnesium silicate, aragonite, amorphous magnesium silicate, and iron corrosion products, on the carbon steel from the inside of the pipe to the outside. The corrosion product fully covers the steel surface. The magnesium silicate (1–2 mm thick) is initially generated as an adhesion substance on the corrosion product. The layer thickness of aragonite (orthorhombic calcium carbonate (λ-CaCO3)) is 15–70 mm. Carbon, oxygen and calcium are dissolved in the magnesium silicate, which later precipitates as calcium carbonate with large and/or stratiform features. The chemical contents in the magnesium silicate layers on both the top and bottom sides are nearly identical. Therefore, the precipitation of aragonite and its growth in the magnesium silicate may form the aragonite layer, which shows a columnar structure along the heat flux direction.

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  • Zhiyuan Chen, Kuo-Chih Chou, Kazuki Morita
    2016 Volume 57 Issue 9 Pages 1660-1663
    Published: September 01, 2016
    Released: August 25, 2016
    [Advance publication] Released: July 15, 2016
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    The possibility of metastable wüstite below 570℃ during the reduction of iron oxides was discussed. There was uncertainty regarding the formation of metastable wüstite in the reduction of hematite below 570℃. Planar disregistry (1/δ) was employed to predict the probability of metastable wüstite formation during the reduction process. The calculated results showed that the δ of wüstite/magnetite is similar to that of iron/magnetite with plain and normal structures, but less than flake and finger structures. The difference in disregistry of different geometries of interfaces was suggested to be the principal driving force for the formation of metastable wüstite. This implies that the formation of metastable wüstite always accompanies the nucleation of iron structures with high δ relative to magnetite. The latter structures form easily in supported iron, leading to the relatively common observation of metastable wüstite in an iron catalyst. The analysis showed that the temperature range for metastable wüstite formation, 400℃~500℃, was most likely to occur where it created a predominance of flake and finger structures.

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  • Li Pang Wang, Wei Sheng Chen, Chih Mei Chou, Kenji Murata, Toyohisa Fu ...
    2016 Volume 57 Issue 9 Pages 1664-1666
    Published: September 01, 2016
    Released: August 25, 2016
    [Advance publication] Released: July 29, 2016
    JOURNALS FREE ACCESS

    Prior to applying metallurgical processes for the recovery of rare earth elements from neodymium magnets in used rotors, it is necessary to separate the neodymium magnets from the rotors as effectively as possible. Due to the characteristics of the rotors such as hard steel cover, complex inner structure, and strong magnetic fields of neodymium magnet, it is difficult to disintegrate the neodymium magnet rotors by traditional mechanical crushing methods.

    This research letter presents the result of a preliminary experiment on applying underwater explosion for the liberation of neodymium magnet rotor followed by thermal treatment for recycling. The neodymium magnet rotor used in the compressor unit of an air conditioner can be effectively disintegrated by underwater explosion. The crushed products contain several steel pieces with neodymium magnet powder attached to their surfaces. After the crushed products are heated above the Curie temperature of the neodymium magnet, the neodymium magnet powder is demagnetized. After it is sieved, the neodymium magnet powder can be separated from the steel pieces. The separated powder can be subsequently treated by developed metallurgical processes for rare earth elements recovery.

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