MATERIALS TRANSACTIONS
Online ISSN : 1347-5320
Print ISSN : 1345-9678
ISSN-L : 1345-9678
Volume 60 , Issue 1
Showing 1-25 articles out of 25 articles from the selected issue
  • Type: Preface
    Subject area: Special Issue on New Casting Process and New Simulation Method for Casting
    2019 Volume 60 Issue 1 Pages 1
    Published: January 01, 2019
    Released: December 25, 2018
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  • Ikuzo Goto, Setsuo Aso, Ken-ichi Ohguchi, Kengo Kurosawa, Hiroyuki Suz ...
    Type: Regular Article
    Subject area: Special Issue on New Casting Process and New Simulation Method for Casting
    2019 Volume 60 Issue 1 Pages 2-9
    Published: January 01, 2019
    Released: December 25, 2018
    [Advance publication] Released: June 15, 2018
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    The effect of solidification conditions on the tensile deformation behavior of pure copper castings for electrical parts was investigated. Two main types of tensile deformation properties were distinguished on the basis of the difference in uniform elongation. For the castings fabricated under a superheat of 100°C or 150°C, larger and smaller uniform elongation types corresponded to the absence and presence, respectively, of the Cu–Cu2O eutectic phase in the microstructure. Meanwhile, for the castings fabricated under a superheat of 50°C, greater uniform elongation was sometimes obtained when the eutectic phase was present. In addition, irrespective of the presence or absence of the eutectic phase, greater uniform elongation was always obtained when chills were used. Cross-sectional observations showed the existence of considerable nonspherical porosity when the eutectic phase was present; the porosity was reduced when the pouring was conducted under the superheat of 50°C and when the chills were used because of lower hydrogen content in the melt and supersaturation of the hydrogen by rapid cooling, respectively. These results suggest that not only the presence of the eutectic phase but also the inferior casting soundness due to the existence of the porosity is a dominant factor responsible for the decrease in the uniform elongation. The findings presented here indicate that a decrease in the hydrogen content in the melt and/or the rapid cooling during solidification are effective measures to stably achieve practically sufficient deformation properties along with superior casting soundness.

  • Jun Yaokawa, Yasushi Iwata, Yuichi Furukawa
    Type: Regular Article
    Subject area: Special Issue on New Casting Process and New Simulation Method for Casting
    2019 Volume 60 Issue 1 Pages 10-18
    Published: January 01, 2019
    Released: December 25, 2018
    [Advance publication] Released: October 15, 2018
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    Capillary shaping is an attractive directional solidification process of fabricating lightweight aluminum frame components for automobiles. In this study, the strengths of capillary shaped A6005C aluminum alloys were investigated under various conditions. Tensile tests were performed parallel to and perpendicular to the pulling direction, to investigate columnar and equiaxed grain structures, as-cast and T6 heat-treated conditions, and different crystal orientations. In columnar grain specimens, the strength parallel to the pulling direction was higher than that perpendicular to the pulling direction in both as-cast and T6-treated conditions. Crystal orientation affected the work hardening behavior of as-cast specimens loaded perpendicular to the pulling direction. In equiaxed grain specimens, the anisotropy and the distribution of mechanical properties were quite low in both as-cast and T6-treated conditions.

  • Katsunari Oikawa, Kazuhiro Sakakibara, Youji Yamada, Koichi Anzai
    Type: Regular Article
    Subject area: Special Issue on New Casting Process and New Simulation Method for Casting
    2019 Volume 60 Issue 1 Pages 19-24
    Published: January 01, 2019
    Released: December 25, 2018
    [Advance publication] Released: October 01, 2018
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    The NaCl–Na2CO3 salt mixture is proposed as a water-soluble core material for aluminum die-casting processes. The mechanical properties and microstructures of NaCl–Na2CO3 samples prepared by gravity casting were investigated. The salt mixtures had superior properties compared to those of the pure salts. Plastic deformation occurred during compression tests at high temperatures because the eutectic region changed from lamellar to granular. Salt mixtures with NaCl primary phase and eutectic regions were found to be the most suitable core material.

  • Ikuzo Goto, Kohei Tomita, Setsuo Aso
    Type: Regular Article
    Subject area: Special Issue on New Casting Process and New Simulation Method for Casting
    2019 Volume 60 Issue 1 Pages 25-32
    Published: January 01, 2019
    Released: December 25, 2018
    [Advance publication] Released: September 07, 2018
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    In this study, the solidification simulation of pure metal castings was conducted and the effects of open shrinkage cavity formation process on heat transfer behavior were investigated. The shrinkage cavity predicted by the conventional simulation method was shallower than the experimental results obtained using the proposed method, although an inverted conical shrinkage cavity was formed on top of cylindrical pure metal castings. The change in the heat transfer behavior during solidification was not modeled well using the conventional method, which was associated with the long duration of shrinkage cavity formation process and the resulting deep shrinkage cavity. On the contrary, when we altered the reduction of melt level based on solidification shrinkage and the proper interfacial heat release to the atmosphere, the predicted shape and depth of the shrinkage cavity were very close to the experimental results. Therefore, a comprehensive simulation of the effects of the shrinkage cavity formation process on the heat transfer behavior is important for predicting the shrinkage cavity formed in pure metal castings.

  • Naoya Hirata, Koichi Anzai
    Type: Regular Article
    Subject area: Special Issue on New Casting Process and New Simulation Method for Casting
    2019 Volume 60 Issue 1 Pages 33-40
    Published: January 01, 2019
    Released: December 25, 2018
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    Finer calculation elements (meshes) are required to conduct an accurate solidification simulation for castings with thin sections. Calculation methods using non-structural meshes can keep its efficiency even for complex shaped castings, because the methods can use adaptive mesh size for parts with various size and regions around interfaces. However, methods using non-structural mesh tend to have difficulty in mesh generation and complexed calculation program. In this study, we conducted heat transfer and solidification simulation using an adaptive resolution particle method (ARPM), which uses various kind of element size as adaptive resolution method with simple calculation program similar to the method using structural meshes. As a result, the ARPM showed good accuracy of solidification simulation and improve its efficiency of the computational time and the memory usage, slightly reducing an energy conservation quality.

    Fig. 10 Calculated temperature distribution at 1000 s using ARPM. Fullsize Image
  • Haruki Itofuji, Kazuya Edane, Tomokatsu Kotani, Masayuki Itamura, Koic ...
    Type: Regular Article
    Subject area: Special Issue on New Casting Process and New Simulation Method for Casting
    2019 Volume 60 Issue 1 Pages 41-48
    Published: January 01, 2019
    Released: December 25, 2018
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    Gravity die casting of spheroidal graphite iron had been attempted controlling free nitrogen during preparing base molten iron, magnesium treatment, inoculation and pouring. In this study, the actual CO/SiO2 reaction temperature of base molten irons was surveyed and magnesium treatment was conducted at that temperature. The mold was made of steel and the cavity size was thickness of 5.4 mm and diameter of 35 mm. As the results, ultrafine graphite nodules were obtained without chill in as-cast condition. They were average diameter of 7 µm and density count of over 3,000/mm2. Knuckle for automobile was also cast taking the same procedure. Knuckle had no meager defect like shrinkage, chill etc. in as-cast conditions. The possibility of no chill has become extremely higher than former study.

  • Naoto Shirahata, Tetuo Uchikoshi, Thi Kim Ngan Nguyen, Yoshitake Masud ...
    Type: Regular Article
    2019 Volume 60 Issue 1 Pages 49-54
    Published: January 01, 2019
    Released: December 25, 2018
    [Advance publication] Released: November 16, 2018
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    Here we show an electrophoretic deposition process for a uniform coating of glass substrate surface with fluorescent silicon nanocrystals (SiNCs). The NCs with ∼35% of photoluminescence quantum yields (PLQYs) were synthesized by thermal disproportionation of hydrogen silsesquioxane, followed by hydrosilylation of 1-decence. Next, the hollow-silica particles that are crammed of the decane-terminated NCs were prepared by taking advantage of a vacuum impregnation process. The PL spectra were measured as a function of temperature for films of NCs before and after silica encapsulation. It was observed that a rapid decrease of PL intensity with elevated temperature for the hydrogen-terminated NCs whereas the silica capsule suppresses a thermal quenching to give PL stability at high temperature. The presence of a silica capsule also allows electrophoretic deposition of the NCs to the surface of an ITO glass substrate.

     

    This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 65 (2018) 108–113.

  • M. Yoneda, S. Obata, M. Niwa, N. Hirata, M. Motohashi
    Type: Regular Article
    2019 Volume 60 Issue 1 Pages 55-60
    Published: January 01, 2019
    Released: December 25, 2018
    [Advance publication] Released: November 09, 2018
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    We conducted a theoretical study on a phenomenon where an exchange bias effect appears in a Fe3O4 thin film containing an opposite phase boundary when a two-phase ferrimagnetic model is introduced using antiferromagnetic interlayer coupling. We studied the simulation technique for such a system and derived magnetic hysteresis loops in the exchange bias effect by computer simulations using the retarded-trace method.

  • Mei Liu, Atsushi Iizuka, Etsuro Shibata
    Type: Regular Article
    2019 Volume 60 Issue 1 Pages 61-67
    Published: January 01, 2019
    Released: December 25, 2018
    [Advance publication] Released: November 23, 2018
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    A large amount of sludge is generated from the neutralization of acid mine drainage (AMD) in Japan, which may cause severe environmental problems. This study showed there is potential to reuse such sludge in ceramic materials by thermal treatment. We sampled and characterized two types of iron-rich Japanese AMD sludge. Their phase compositions in the temperature range of 900–1200°C were identified by X-ray diffraction. α-Fe2O3 was the main crystalline phase in all sludge samples after thermal treatment. This can be used in ceramic enamels, porcelain bodies, and ferrite ceramics production. The results of leaching tests using acetic acid solution and distilled water as extraction fluids suggested that the stability of AMD sludge can be increased to a certain degree by thermal treatment; however, amorphous aluminosilicates formed by Al and Si impurities at lower temperatures weakened its stability. The enhanced mobility and volatilization of As impurity by thermal treatment also limits the application of AMD sludge. Applications that are insensitive to Al and Si impurities and products with higher arsenic stability are required when using sludges with high contents of impurities.

  • Yuki Koshino, Yasuhiro Aruga, Junpei Mukai, Kenji Kaneko
    Type: Regular Article
    2019 Volume 60 Issue 1 Pages 68-73
    Published: January 01, 2019
    Released: December 25, 2018
    [Advance publication] Released: November 16, 2018
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    Dislocation multiplication and dynamic recovery in the tensile deformed Al–Mg–Si–Cu alloys were characterized by transmission electron microscope (TEM), to reveal the correlation between the dislocation characteristics and the elongation behaviors. 6016 (Al–0.4%Mg–1.0%Si–0.2%Cu (mass%)) and 6014 (Al–0.6%Mg–0.7%Si–0.1%Cu) alloys were aged at 363 K for 18 ks after solution treated and quenched into water. The maximum n-value of 6016 alloy was found higher than that in the 6014 alloy. The n-value reduction rate after reaching its maximum of 6016 alloy was found smaller than that of 6014 alloy. Furthermore, the dislocation multiplication on {111} plane and the formation of dislocation band were formed in 6016 alloy with more than 10% of tensile deformation. Therefore, the slip lines observed by scanning electron microscope (SEM) are finely formed. The homogeneous dispersion of slip lines are probably the cause of higher elongation of 6016 alloy than that of 6014 alloy. It is believed that suppression of the cross slip dislocation may contribute to a higher elongation.

     

    This Paper was Originally Published in Japanese in J. JILM 68 (2018) 201–205. In order to explain tensile properties clearly, Tables 2 and 3 were added. In order to explain the previous studies more precisely, references 1, 2, 7, 13, 14, 17, 18 and 19) were added.

  • Xue-Zheng Yue, Hiroshi Fukazawa, Kazuya Maruyama, Keiji Matsuo, Koichi ...
    Type: Regular Article
    2019 Volume 60 Issue 1 Pages 74-79
    Published: January 01, 2019
    Released: December 25, 2018
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    Ti–6Al–4V alloys are widely used as a structural material. Open-cell porous Ti–6Al–4V alloys with different porosities are manufactured through powder bed fusion process. Cylindrical specimens consisting of ordered truncated octahedron unit-cells are designed using a 3D-CAD software. After the building, porous Ti–6Al–4V alloy specimens are annealed at different temperatures of 1173 and 1323 K for 1 h in vacuum. Vickers hardness of the annealed specimens is lower than those of as-built specimens. This is due to the increased volume fraction of beta phase which is measured by SEM observation and X-ray diffraction analysis. On the other hand, initial peak stress and energy absorption increase after the annealing because of the enhanced ductility of cell edges. Most specimens show the macroscopic shear band formation during compression tests, which causes the reduction of energy absorption. The ordered cell structure which is one of the reasons of the shear band formation is not suitable for energy absorbing applications.

  • Masaki Tanaka, Yukihiro Hayashi, Yelm Okuyama, Tatsuya Morikawa, Kenji ...
    Type: Regular Article
    2019 Volume 60 Issue 1 Pages 80-85
    Published: December 01, 2019
    Released: December 25, 2018
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    The temperature dependence of 0.2% proof stress was investigated in Ti–0.49 mass%O with an α single phase. The 0.2% proof stress decreased as the temperature increased from 77 to 573 K. The athermal stress, which was defined as the average of the stress values for which the temperature dependence was absent above 573 K, was found to be 70 MPa. The temperature dependence of the effective stress indicates that the temperature dependence of the effective stress changed at around 400 K. To study the thermally activated process that controls the yielding in Ti, the temperature dependence of the activation volume was also measured. An inverse temperature dependence of the activation volume was found at between 325 and 400 K, suggesting that the thermally activated process of dislocation glide changed at this temperature. Prismatic slip with 〈a〉 dislocations was dominant at low temperatures, whereas other slips were activated at high temperatures. The activation enthalpy for the dislocation glide was also measured between 77 and 573 K.

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  • Tatsuya Okada, Hiromu Hisazawa, Akihiro Iwasaki, Shota Amimoto, Jun Mi ...
    Type: Regular Article
    2019 Volume 60 Issue 1 Pages 86-92
    Published: January 01, 2019
    Released: December 25, 2018
    [Advance publication] Released: November 02, 2018
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    The objective of the present study was to investigate the suppression of grain-boundary sliding and its accommodation at triple junctions. Tricrystals of pure aluminum and pure copper having 〈110〉-tilt Σs = 3, 3, and 9 boundaries were grown. Creep tests were carried out at temperatures above 0.8TM, where TM is the melting point on the absolute temperature scale. In all specimens, boundary sliding occurred only in the Σ9 boundary. In aluminum tricrystals, sharp folds formed as a result of the suppression of Σ9 boundary sliding at the triple junction. Slip lines parallel to the trace of the (100) plane were observed in the fold. In copper tricrystals, no fold formed but a wedge crack was initiated at the triple junction and extended along one of the Σ3 boundaries aligned perpendicularly to the tensile axis. These results suggest that the ease or difficulty of fold formation affects crack formation during creep.

  • Hiroshi Shibamoto, Akihiko Kimura, Masayuki Hasegawa, Hideki Matsui
    Type: Regular Article
    2019 Volume 60 Issue 1 Pages 93-98
    Published: January 01, 2019
    Released: December 25, 2018
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    Micro-Vickers hardness and positron lifetime were measured after 1 MeV proton irradiation to a fluence of 3 × 1017 ions/cm2 at below 80°C and post-irradiation isochronal annealing to 650°C to investigate the effects of nickel (Ni), phosphorous (P) and sulfur (S) on the irradiation hardening of Fe–0.2 mass% C–0.3 mass% Cu model alloy. With increasing the Ni content to 0.6 mass%, irradiation hardening was increased, while a further increase to 1 mass% resulted in a small reduction. The addition of 0.05 mass% P increased the irradiation hardening of the model alloys irrespective of the addition of 0.6 mass% Ni, while the addition of 0.05 mass% S showed almost no effect on the hardening. Positron lifetime measurements revealed that the intensity of long-lifetime component, namely the number density of microvoids, increased and decreased for the alloy added with P and S, respectively. However, no significant effect of Ni content on the long-lifetime component was observed. Post-irradiation anneal-hardening was large and became a maximum at around 350–375°C in most of the alloys studied. The addition of 0.6 mass% Ni caused almost no effect on the annealing behavior, while further addition of 0.05 mass% P reduced the hardness change by the annealing to 400°C. During post-irradiation annealing to around 400°C, the long-lifetime component increased in the alloy with P, but it was so small in the alloy with S or manganese (Mn). These suggest that P enhances the growth of the microvoids but S as well as Mn suppress it.

  • Masaya Ukita, Ryota Nagahara, Yu Oshima, Atsutomo Nakamura, Tatsuya Yo ...
    Type: Regular Article
    2019 Volume 60 Issue 1 Pages 99-104
    Published: January 01, 2019
    Released: December 25, 2018
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    Generalized stacking fault energies were calculated to understand dislocation characters and stability in zinc sulfide (ZnS) by using the density functional theory calculations. Peierls stresses and dislocation self energies were estimated for perfect and dissociated dislocations on glide-set and shuffle-set planes in ZnS in a framework of the Peierls–Nabarro model. It was found that Peierls stresses of the shuffle-set dislocations are smaller than those of the glide-set dislocations whereas dislocation self energies of the shuffle set are larger. It is experimentally known that the dissociated glide-set dislocations can be more easily formed and multiplied during plastic deformation in darkness at room temperature. It is suggested that the glide-set dislocations can be primarily activated due to their lower self energy, in spite of their higher Peierls stress.

  • Hiroyuki Watanabe, Naoko Ikeo, Toshiji Mukai
    Type: Regular Article
    2019 Volume 60 Issue 1 Pages 105-110
    Published: January 01, 2019
    Released: December 25, 2018
    [Advance publication] Released: November 23, 2018
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    A magnesium matrix composite comprising Mg–0.5 mass%Ca and 10 vol.% β-tricalcium phosphate (TCP) particles was processed with the aim of developing biodegradable material. The composite was produced by extruding a mixture of two component powders at 538 K. The matrix of the extruded composite comprised fine equiaxed grains (grain size: 1.3 µm). Moreover, isolated β-TCP particles and agglomerated particles (size: 10–15 µm) were observed. Owing to grain refinement, the composite exhibited a high yield strength (>300 MPa) at room temperature and behaved in a superplastic manner at ∼548 K.

    Fig. 8 Inverse pole figure (IPF) maps (a) and (b) and IPFs (c) and (d) of the X0/β-TCP/10p composite before (a) and (c) and after (b) and (d) deformation at 548 K to a true plastic strain of ε = −0.5. Cross-sectional planes perpendicular to the extrusion direction were examined. The IPFs correspond to the extrusion/compression direction. Fullsize Image
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  • Yoshiki Kinoshita, Masao Morishita, Ai Nozaki, Hiroaki Yamamoto
    Type: Regular Article
    2019 Volume 60 Issue 1 Pages 111-120
    Published: January 01, 2019
    Released: December 25, 2018
    [Advance publication] Released: November 30, 2018
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    The thermodynamic properties for Nd2(MoO4)3 were investigated. Nd2(MoO4)3 is one of the end member of the yellow phases which are known as hygroscopic harmful phases in the nuclear fuel waste glasses. The standard molar entropy, , at 298.15 K of Nd2(MoO4)3 was determined by measuring its isobaric heat capacities, , from 2 K via the fitting functions including the Debye-Einstein formula and electronic- as well as magnetic terms. The Neel temperature, TN, estimated by extrapolating the magnetic-term in the fitting function. Its standard Gibbs energy of formation, , was determined by combining datum with the standard enthalpy of formation, , which were estimated from ones for Ce2(MoO4)3 and Sm2(MoO4)3. The unknown standard Gibbs energy of solution, , at 298.15 K of Nd2(MoO4)3 was predicted from the reference data for MoO42−(aq) and Nd3+(aq). The obtained thermodynamic values are as follows:

    The data obtained in the present work are expected to be useful for geochemical simulations of the diffusion of radioactive elements through underground water.

     

    This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 81 (2017) 485–493. To more precisely express the physical meaning of the functions for fitting the heat capacity, some their coefficients and thermodynamic values for Nd2(MoO4)3 were revised. The thermodynamic values for the relevant molybdates were revised based on the updated standard entropy at 298.15 K of molybdenum as the standard states. See Appendix describing the revised details.

    Fig. 2 Experimental molar heat capacities, C°p,m, for Nd2(MoO4)3 at 2–300 K (open circle) and ones calculated from the fitting functions (eqs. (4)–(7), solid line), compared with C°p,m(17/4 MoO3) (solid circle) and C°p,m(17/5 Nd2O3) (solid triangle) at 298.15 K. Solid rectangle shows C°p,m at 298.15 K on the basis of the Neumann-Kopp law. Fullsize Image
  • Takaomi Itoi, Shoichi Inoue, Kouki Nakamura, Syunichi Kitta, Keigo Oka ...
    Type: Regular Article
    2019 Volume 60 Issue 1 Pages 121-129
    Published: January 01, 2019
    Released: December 25, 2018
    [Advance publication] Released: November 23, 2018
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    Lap joint sheets of 6061-T6/SPCC and 6061-T6/DP590 (Dual phase) steel were fabricated by magnetic pulse welding (MPW). Strong lap joints were achieved at discharge energy W of >2.0 kJ and gap length d of 1.0 mm for the 6061-T6/SPCC, and W of 3.0 kJ and d of 1.4 mm for the 6061-T6/DP590 steel, respectively. This result suggested that the high-collision speed is required for lap joint of the 6061-T6/DP590 steel compared with that of the 6061-T6/SPCC. Weld interface showed wavy joint interface and weld width of the lap joint sheets tend to increase with increasing of discharge energy for MPW. An intermediate layer consisted of FeAl, Fe2Al5 and FeAl3 was recognized at the weld interface discontinuously, due to localized melting and a subsequent high rate cooling of molten Fe and Al confined to the weld interface. Furthermore, work hardening by accumulated plastic strain and grain refinement of Al and Fe at the welded interface were recognized by SEM-EBSD.

    From microstructure observation, strong lap joint of the 6061-T6/DP590 steel by MPW was thought to be due to an increase in weld width, an anchor effect, and strengthening of the weld interface by work hardening and grain refinement.

     

    This Paper was Originally Published in Japanese in J. JILM 68 (2018) 141–147.

  • Yu Ogura, Mizuki Kanetake, Isao Matsui, Yorinobu Takigawa, Tokuteru Ue ...
    Type: Regular Article
    2019 Volume 60 Issue 1 Pages 130-135
    Published: January 01, 2019
    Released: December 25, 2018
    [Advance publication] Released: November 16, 2018
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    Contamination with sulfur causes deterioration of the mechanical properties of electrodeposited nanocrystalline iron (Fe) and its alloys. However, it is difficult to avoid this contamination for electrodeposition from a sulfate bath. In this study, we explored the processing parameters required to produce thick plates of electrodeposited Fe from a chloride bath containing no sulfur and examined the resulting mechanical properties. In a simple bath consisting only of iron chloride, the long electrodeposition required to produce bulk samples could not be performed due to the precipitation of hydroxide, which caused the voltage to increase beyond the limits of the equipment. The addition of ammonium chloride inhibited the generation of hydroxide and stabilized the voltage during the electrodeposition. In addition, a higher bath temperature suppressed the formation of micro-cracks on the surface of the electrodeposits. Furthermore, the appearance of voids on the surface was reduced by increasing the concentration of the iron source and decreasing the current density. On the basis of these results, we prepared a bulk sample of electrodeposited Fe with a body-centered cubic structure and average grain size of ∼5 µm. The electrodeposited bulk Fe exhibited a tensile strength of 649 MPa and good elongation of 13.9%.

  • Li-Fu Yi, Noriaki Yoshida, Tetsuhiko Onda, Zhong-Chun Chen
    Type: Regular Article
    2019 Volume 60 Issue 1 Pages 136-143
    Published: January 01, 2019
    Released: December 25, 2018
    [Advance publication] Released: December 07, 2018
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    Aluminum/graphite composites have been successfully prepared by a hot-extrusion technique. The effects of processing conditions such as graphite particle size, graphite content, and extrusion temperature on extrusion behavior, microstructure, texture, and thermal conductivity have been systematically investigated. During the hot extrusion, the graphite was subjected to deformation and hence distributed along the extrusion direction in the extruded Al/graphite composites. The (00l) basal planes of the graphite were preferentially orientated along the extrusion direction. The preferred orientation of the graphite resulted in an anisotropy of thermal conductivity in the extruded samples. On the other hand, the utilization of bimodal graphite powder consisting of coarse and fine particles is beneficial to the enhancement of both relative density and thermal conductivity. Moreover, when a pressed green compact was rotated 90° and then subjected to the hot extrusion, the resulting composite exhibited higher thermal conductivity due to its higher density, fewer Al/graphite interfaces, and higher orientation degree of the graphite.

  • Hiroyuki Takahashi, Takuya Ishimoto, Takayuki Inoue, Hiroomi Kimura, K ...
    Type: Regular Article
    2019 Volume 60 Issue 1 Pages 144-148
    Published: January 01, 2019
    Released: December 25, 2018
    [Advance publication] Released: November 23, 2018
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    A spinal cage is one of the primary spinal devices used for the treatment of spinal diseases such as lumbar spondylolisthesis. Since it is set in the intervertebral space that causes instability to promote the fusion of the adjacent vertebral bodies, it requires the early induction of healthy bones. For this reason, in most cases, an autogenous bone extracted from the patient’s ilium is implanted in the interior of the cage to stimulate bone formation. However, collecting autogenous bone involves secondary surgery and several clinical problems such as pain in the part from which it is collected. Additionally, the effect of the autogenous bone graft itself has not been sufficiently studied yet. Moreover, the mechanical functions of trabecular bones in a vertebral body are governed by the anisotropic structure of the trabeculae and the preferential orientation of the apatite/collagen in a trabecula with respect to the principal stress. Despite this fact, after the implantation of the cage, the mass of the bones is evaluated with soft X-ray photography, which does not guarantee an accurate measurement of bone functions. In this study, the effect of the autogenous bone graft on the spinal cage was verified based on structural anisotropy of trabecular bones and the preferential orientation of apatite/collagen in a trabecula using sheep. The autogenous bone graft demonstrated a significant effect on the increase of bone mass and anisotropy of the trabecular structure. However, compared to the trabecular anisotropy of normal parts, the anisotropy of the trabecular structure and apatite c-axis orientation of the parts with autogenous bone graft were considerably lower, indicating a minimal effect of the autogenous bone graft. Therefore, it was suggested that early stabilization of the spinal cage requires another strategy that rapidly forms the unique hierarchical anisotropic structure of trabecular bones.

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  • Huy D. Vu, Makoto Nanko
    Type: Regular Article
    2019 Volume 60 Issue 1 Pages 149-155
    Published: January 01, 2019
    Released: December 25, 2018
    [Advance publication] Released: December 07, 2018
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    Crack-healing effectiveness was investigated as functions of heat treatment time and temperature on 5 vol% SiC-dispersed Y2SiO5-based composites. Dense specimens of SiC/Y2SiO5 composite were fabricated by the pulsed current sintering technique. Thermal oxidation for crack-healing was conducted at temperatures ranging from 1000 to 1300°C for from 1 to 24 h in air. Bending tests were carried out at room temperature on samples before and after heat treatment in order to clarify the crack-healing performance. The results show that SiC/Y2SiO5 composites possess a considerable crack-healing ability. The surface cracks with approximately 200 µm in length introduced on the sample surface were disappeared completely after heat treatment at 1300°C for 1 h in air. Mechanism of crack-healing was considered as filling up of cracks by Y2Si2O7 oxidation product which is formed by outward diffusion of cations. Bending strength of samples introduced surface cracks after heat treatment was recovered up to the level as high as that of as-sintered samples.

  • Enrique Hernández-Sánchez, Julio C. Velázquez, José. L. Castrejón-Flor ...
    Type: Regular Article
    2019 Volume 60 Issue 1 Pages 156-164
    Published: January 01, 2019
    Released: December 25, 2018
    [Advance publication] Released: November 30, 2018
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    This study evaluates the tribological behavior of borided AISI 316L steel. The treatment time was set to 2, 4, and 6 h at temperatures of 850, 900, and 950°C for each time duration. The morphology and microstructure of the boride layers were analyzed by scanning electron microscopy (SEM) and X ray diffraction (XRD), respectively. The mechanical properties were evaluated by an instrumented nanoindentation test. The tribological behaviors of the layers were evaluated using a sand/rubber apparatus following the ASTM G-65 standard. The friction coefficient of the boride layers was estimated by means of the tribological pin-on-disk test. The results show that the experimental parameters had a clear influence on the thickness of the boride layers and on their mechanical properties. The volume loss was established in the range of 0.0741 ± 0.011 µg to 1.6148 ± 0.150 µg. Wear mechanisms such as adhesion and micro-fatigue were mainly observed in the samples exposed for 6 h at 950°C. Finally, the friction coefficient was reduced from 0.7 for the as-received material down to 0.29 for the borided samples. The wear mechanisms were discussed as a function of the scanning electron microscopy observations. It is possible to conclude that single-phase layers of Fe2B are more apt to face wear than the FeB/Fe2B biphasic layers.

  • Hiroyuki Dannoshita, Toshio Ogawa, Kuniaki Maruoka, Kohsaku Ushioda
    Type: Rapid Publication
    2019 Volume 60 Issue 1 Pages 165-168
    Published: January 01, 2019
    Released: December 25, 2018
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    The effect of initial microstructures of low-carbon steel on austenite formation behavior during intercritical annealing was investigated. Three types of hot-rolled sheet specimens with different microstructures were used; specimen P consisting of ferrite and pearlite, specimen B consisting of bainitic structures, and specimen M consisting of fully martensitic structures. After the hot rolling, these specimens were cold-rolled, and subsequently heated to target temperature, and then water-quenched to room temperature. The martensite and/or bainite fraction corresponds to the fraction of austenite during intercritical annealing since the austenite transforms into martensite and/or bainite during the cooling process. The austenite fraction in specimen M was larger than that in specimens P and B below 730°C, whereas the order of specimens changed to P > B > M above 740°C. Below 730°C, austenite connected along the rolling direction was observed in specimens P and B, while the distribution of austenite in specimen M was uniform. In contrast, austenite was connected and elongated along the rolling direction in all the specimens above 740°C. The nucleation and growth of austenite can proceed under local equilibrium in specimens P and B, whereas that can proceed under paraequilibrium in specimen M below 730°C. Moreover, the austenite growth can progress under local equilibrium in all specimens above 740°C.

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