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ONLINE ISSN: 1347-5320
PRINT ISSN: 1345-9678

MATERIALS TRANSACTIONS Vol. 58 (2017), No. 8

  • Crystal Structure of the C-AlRuNi Phase

    Rayko Simura, Kazumasa Sugiyama, Shota Suzuki, Toru Kawamata

    pp. 1101-1105

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    DOI:10.2320/matertrans.M2017106

    Abstract

    The structure of C-AlRuNi was determined by single-crystal X-ray diffraction (space group Pm3 (No. 200); a = 0.77088(4) nm; R = 0.0401 for 268 independent reflections (Fo > 2σ(Fo)) measured by Mo Kα radiation). The fundamental structure of C-AlRuNi can be explained by the packing of two types of icosahedra. One is the regular icosahedron of transition metals (TMs; Ru and Ni) with a central TM atom at a 1a site (H-ICO), and the other is the irregular icosahedron of TMs with a central TM atom at a 1b site (HM-iICO). An H-ICO is in contact with six H-ICOs and eight HM-iICOs in the directions of the twofold and threefold axes, respectively. The interstitial spaces among the TM distribution are filled by Al atoms. An HM-iICO contains an Al icosahedron (Al-ICO) inside the HM-iICO and a large Al-cube outside of it. An H-ICO has a small Al-cube inside the H-ICO and an Al distorted icosidodecahedron outside of it, indicating the atomic arrangement associated with a pseudo-Mackay cluster (pMC). The structure of C-AlRuNi can also be explained by the CsCl-like packing of pMCs and Al-ICO clusters. The pMC and Al-ICO are the key clusters for explaining the structures of the C1 and C2 phases in the Al–TM–TM ternary system.

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  • Photophysical Behaviors at Interfaces between Poly(3-Hexylthiophene) and Zinc Oxide Nanostructures

    Lin Feng, Xiao-Tao Hao

    pp. 1106-1110

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    DOI:10.2320/matertrans.M2017080

    Abstract

    Development of design rules through understanding exciton dissociation and charge generation dynamics is an important pathway to improve the performance of hybrid inorganic–organic solar cells. In this work, we study the photophysical behavior and dynamics of charge generation in organic/inorganic hybrid based on poly(3-hexylthiophene) (P3HT) and zinc oxide (ZnO) nanostructures by steady-state and time-resolved fluorescence spectroscopy. Both films of P3HT:ZnO nanoparticle (NPs) blend as the active layer and pristine P3HT as the active layer on ZnO nanorod (NRs) array buffer layer can provide efficient interfaces for exciton dissociation and charge transfer. P3HT can infiltrate into inter-rod space of ZnO NRs and cover them to enhance the 0-0 band against the 0-1 one in the steady-state photoluminescence spectrum. However, the configuration of P3HT: ZnO NPs blend as the active layer on ZnO NRs buffer layer poorly further improves the exciton dissociation, due to the decreased organic-inorganic interface area.

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  • Preparation of Anhydrous Calcium Sulfate Whiskers from Phosphogypsum in H2O-H2SO4 Autoclave-Free Hydrothermal System

    Hongbin Tan, Faqin Dong, Liang Bian, Xiaochun He, Jingfeng Liu

    pp. 1111-1117

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    DOI:10.2320/matertrans.M2017042

    Abstract

    The anhydrous calcium sulfate (AH) whiskers were prepared in H2O-H2SO4 autoclave-free hydrothermal system by using phosphogypsum (PG) as raw materials. The influences of solid/solution ratio, reaction time, H2SO4 concentration and maleic acid on crystal growth were detected.The whiskers with smooth surface and high aspect ratio were obtained in a 20 mass% H2SO4 solution for hydrothermal 1 h with 1:60 ratio of solid/solution. The aspect ratio decreased but the amount of whiskers increased in sample by increasing the addition amount of maleic acid.The whiskers were not obtained in 30 mass% H2SO4 solution for hydrothermal 1, 2 and 3 h, respectively, with 1:60 ratio of solid/solution, and the whiskers were also not obtained by adding maleic acid in the solution.

  • Fabrication of 2000 Series Aluminum Alloy Lap Joint Sheets by Magnetic Pulse Welding and Their Interfacial Microstructure Observations

    Takaomi Itoi, Syoichi Inoue, Keigo Okagawa

    pp. 1118-1126

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    DOI:10.2320/matertrans.L-M2017821

    Abstract

    Lap joint sheets of 2017-T3/2017-T3 and 2024-T3/2024-T3 were fabricated by magnetic pulse welding (MPW). Tensile shear tests were performed on the welded sheet, and a good lap joint was achieved at a discharge energy more than 3.0 kJ for both lap joint sheets. Weld interface showed wavy morphology when bonding at an adequate amount of discharge energy. Weld width of the lap joint sheets tend to increase with increasing of discharge energy. Collision speed calculated based on collision time was 211 m/s and estimated 1.5 GPa of the collision pressure at discharge energy of 3.5 kJ. SEM and EDS results showed that the weld interface exhibited no significant contrast of intermediate layer and oxides. A Metal jet was observed as aggregates of fine particles with size of less than 100 nm at the outside of bonded area. From TEM observation at the bonding interface, Al phases between flyer and parent sheets had direct contact without the intervention of the oxide, and localized melting was not recognized. From these obtained results, good lap joint is attributed to true-contact of Al phases, an increasing of weld width, the anchor effect, and work hardening at weld interface. This Paper was Originally Published in Japanese in J. JILM 67 (2017) 8–15.

  • Ultimate Rolling Texture in Pure Aluminum Highly Deformed by Accumulative Roll Bonding: Taylor Orientation Formed beyond Grain Subdivision

    Yoji Miyajima, Daisuke Kashioka, Nobuhiro Tsuji

    pp. 1127-1133

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    DOI:10.2320/matertrans.M2017131

    Abstract

    The texture evolution of an accumulative roll bonding (ARB) processed commercial purity aluminium with lubrication was measured by electron backscattering diffraction with a field emission-type scanning electron microscope. As a result of texture analysis using orientation distribution function maps, the highest intensity texture component was found to be Taylor orientation after ARB 6 cycle. The result suggests that the deformation of ultrafine grains is similar to Taylor model, which occurs in not only high purity aluminium but also commercial purity aluminium.

  • Electromagnetic Field Induced Structure Transition of Aluminum Alloys during Direct Chill Casting

    Lei Li, Qingfeng Zhu, Jianzhong Cui

    pp. 1134-1137

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    DOI:10.2320/matertrans.M2017071

    Abstract

    The structure transition induced by electromagnetic fields during the horizontal direct chill casting of 3004 aluminum alloy was investigated. Results show that the coarse columnar grains were transformed to medium-fine columnar and equiaxed grains with a transition region. Crystallographic analysis indicates that some arms were firstly detached from the coarse columnar dendrite and then formed fine grains with little change of orientation. With the increase of the electromagnetic fields, the grains growing from the later-detached arms exhibited a greater orientation deviation. When the electromagnetic fields approached the set value, more arms were detached and new grains showed totally random orientations. The structure transformation is related to the fragmentation of the dendrite arms by the forced convections.

  • Preparation of Graphite Dispersed Copper Composite on Copper Plate with Spot Welding

    Abdul Muizz Mohd Noor, Yoshikazu Ishikawa, Seiji Yokoyama

    pp. 1138-1144

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    DOI:10.2320/matertrans.M2017073

    Abstract

    It was attempted that copper-graphite composite was prepared only on the surface of a copper plate using a spot welding machine. Experiments were carried out with changing the compressive load, the repetition number of the compression and the electrical current in order to study their effects on carbon content and Vickers hardness of the composite. Generally, the carbon content of the composite prepared without an electrical current flow was smaller than that prepared with an electrical current flow. The former composite was prepared with that relatively small angular graphite particles were pushed into the copper plate. In the case of flowing electrical current, graphite particles was heated, and partially or wholly dissolved into molten copper. Therefore, the latter composite was prepared with undissolved graphite and precipitated graphite from the copper melt. In addition, the Vickers hardness of the copper matrix in the composite prepared without an electrical current flow was larger than that prepared with an electrical current flow, because energization heated and annealed the composite. The Vickers hardness of the copper matrix in the composite and the volume fraction of graphite were expressed by the rule of mixtures.

  • Effect of Retained β Phase on Mechanical Properties of Cast Ti-6Al-4V Alloy

    Seong-Tak Oh, Kee-Do Woo, Jae-Hwang Kim, Seung-Mi Kwak

    pp. 1145-1149

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    DOI:10.2320/matertrans.L-M2017818

    Abstract

    We investigated effect of retained β phase on mechanical properties of cast Ti-6Al-4V alloy, after solution treatment and subsequent aging for a short time. The alloy was solution-treated at 1123, 1223 K in the α + β phase region and 1323 K in the β phase region for 1800 s, followed by water quenching. After that, as-quenched specimens were aged at 823 K for 300 s. The peak hardness of heat-treated specimens was obtained by solution treatment at each solution temperature and followed by aging at 823 K for 300 s. It was due to fine α phase transformed from the retained β phase. The tensile strength of specimen as-quenched at 1223 K and subsequent aged at 823 K for 300 s was increased, without significantly decreased ductility. This was due to the fine α phase transformed from the retained β phase by subsequent aging for 300 s. This behavior of increased strength without dramatically decreased ductility might be caused by the transformation induced plasticity (TRIP) effect, which is the strain-induced martensite transformation from the retained β phase throughout deformation, even after aging at 823 K for 300 s.

  • Effect of Irradiation Treatment on Compressive Properties of Ultra-High-Molecular-Weight Polyethylene

    Masaru Kamiya, Hisao Kikugawa, Takashi Asaka, Masae Kanda, Yoshitake Nishi

    pp. 1150-1154

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    DOI:10.2320/matertrans.M2017054

    Abstract

    Ultra-high-molecular-weight polyethylene (UHMWPE) is used as a bearing material in total joint prostheses. One of the criterion that determines the strength of medical UHMWPE is its tensile properties. However, its compressive properties, which play an important role in determining the durability of the contact surfaces of prostheses, have not yet been considered. In this study, we examined the effect of gamma and electron beam irradiation treatment on the compressive properties of medical UHMWPE. The compressive properties (Young's modulus and proof stress) of the gamma-irradiated specimens were higher than those of the nonirradiated specimens. The plastic flow pressure of the electron-beam-irradiated specimens was higher than that of the nonirradiated specimens. The inhibition of plastic deformation of the noncrystalline structure due to electron beam irradiation is considered to have increased the plastic flow pressure. The electron beam irradiation treatment was found to be effective for the surface enhancement of medical UHMWPE. An electron spin resonance signal was clearly observed in the irradiated UHMWPE specimen. These results indicated that dangling bonds were probably formed in the irradiated UHMWPE. This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 80 (2016) 192–196.

  • Effects of Gas Blow Velocity on the Surface Properties of Ti-6Al-4V Alloy Treated by Gas Blow IH Nitriding

    Shogo Takesue, Shoichi Kikuchi, Hiroyuki Akebono, Jun Komotori, Kengo Fukazawa, Yoshitaka Misaka

    pp. 1155-1160

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    DOI:10.2320/matertrans.M2017111

    Abstract

    In the present study, gas blow IH (Induction Heating) nitrided specimens were produced under variable nitrogen gas blowing velocities. This was done to investigate the effects of nitrogen gas velocity on the surface properties of Ti-6Al-4V alloy. The surface properties of the specimens were characterized using X-ray diffraction, scanning electron microscopy, a micro-Vickers hardness tester and nano-indentation tester. The results showed that the surface hardness and thickness of the hardened layer increased with increasing gas blowing velocity. This occurred because of the elevated temperatures in the interior of the alloy relative to the surface temperatures at a higher gas blowing velocity. Furthermore, increasing the magnetic field strength around the IH coil and the eddy current density around the circumference of the specimen also accelerated the formation of a hardened layer on the surface of the titanium alloy. Consequently, a high-hardness layer can be formed by applying a treatment temperature less than the β transus of the Ti-6Al-4V alloy, while increasing the gas blowing velocity. This layer improves the wear resistance of the alloy by suppressing both grain coarsening and the formation of an acicular α phase. This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 81 (2017) 288–293.

  • Influence of Calcium Chloride Addition on Coal-Based Reduction Roasting of Low-Nickel Garnierite Ore

    Jingcheng Dong, Yonggang Wei, Chao Lu, Shiwei Zhou, Bo Li, Zhiguang Ding, Chengyan Wang, Baozhong Ma

    pp. 1161-1168

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    DOI:10.2320/matertrans.M2017086

    Abstract

    This work investigates the influence of calcium chloride addition on coal-based reduction roasting low-nickel garnierite ore, and which is most evident in nickel enrichment and ferronickel particles aggregation. The results demonstrate that a concentrate with 11.83% nickel, corresponding to a nickel recovery of 97.38%, was obtained when the ore was reduced at 1150℃ for 40 min in the presence of 12 mass% CaCl2·2H2O, followed by magnetic separation at 250 mT. Compared with the ore reduced without calcium chloride, the nickel enrichment ratio of the concentrate was increased from 3 to 14 by the addition of 12 mass% CaCl2·2H2O. Duing to the vaporization of the nickel chloride formed and the emergence of a new reactive surface, the addition of calcium chloride makes NiO in the garnierite easier to be reduced. The X-ray diffraction and scanning electron microscopy and energy dispersive spectrometry (SEM-EDS) studies show that metallic nickel was mainly enriched into a kamacite phase, and the presence of CaCl2·2H2O significantly accelerated the aggregation and growth of ferronickel particles, attributing to the vaporization and precipitation of nickel chloride on carbon surface together with ferrou chloride.

  • Corrosion Resistance of New Copper Alloy Castings Registered in JIS H 5120:2016 Copper Alloy Castings

    Hiroshi Yamada, Masaaki Yamamoto, Toshimitsu Okane, Yoshiharu Kousaka, Yoshiyuki Goto, Tomoki Ito

    pp. 1169-1174

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    DOI:10.2320/matertrans.F-M2017819

    Abstract

    Four kinds of dezincification corrosion resistance brass casting (JIS symbols CAC211, CAC221, CAC231 and CAC232) and two kinds of Bismuth bronze castings (JIS symbols CAC905 and CAC906) were suggested to Japanese Industrial Standards (JIS H2210, H5120 and H5121) as alloys applicable to tools related to water supply appliances. For the corrosion-resistant evaluation of those six new alloys (registered new materials), dezincification-corrosion test (ISO 6509-1981), erosion-corrosion test (jet-in-slit test) and stress-corrosion-cracking test were carried out, and the results were compared with JIS copper alloys (CAC203, CAC804, CAC902 and C3771). The dezincification corrosion resistance of the registered materials was better than CAC203 and equal to CAC804 and CAC902. In the erosion-corrosion test of the JIS copper alloys, CAC902 was excellent, followed by CAC804, C3771, and CAC203 (CAC902 >> CAC804 > CAC3771 > CAC203) in this order. Among the registered alloys, CAC211, CAC231, CAC905 and CAC906 showed good erosion-corrosion resistance equal to CAC902. The erosion-corrosion resistance of CAC221 and CAC232 was worse than CAC902 and equal or slightly better than CAC804. In addition, it was revealed that the erosion-corrosion resistance improved when tin was contained. In the stress-corrosion-cracking test, the stress-corrosion-cracking sensitivity of the registered materials was lower than C3771 and CAC203. This Paper was Originally Published in Japanese in J. JFS 87 (2015) 830–835.

  • Effect of Joining Conditions on the Shear Strength of Barium Titanate Joint Brazed with Molten Aluminum

    Ikuzo Goto, Setsuo Aso, Ken-ichi Ohguchi

    pp. 1175-1180

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    DOI:10.2320/matertrans.L-M2017820

    Abstract

    The shear tests using barium titanate joint brazed with molten aluminum under several joining conditions were conducted to determine the optimum joining condition. The barium titanate joints brazed at 780℃ had estimative strength, while those brazed at 720℃ did not. The strengths of the joints brazed at 780℃ became higher with increase in the heat holding time. Especially, the heat holding time for more than 24 h gave higher joint strength than the original shear strength of barium titanate. To discuss the bonding mechanism, the fractured surfaces of the joints were observed and the cross-sectional element distributions in the vicinity of the joint interface were investigated. The observations demonstrated that pieces and grains of the fractured barium titanate were strongly bonded to the aluminum layer at longer holding times. Meanwhile, from the oxygen distributions, relatively thick alumina layers that formed between barium titanate and aluminum at longer holding times were observed. These facts suggest that interfacial bonding is achieved through the formation of an alumina interlayer due to progressive oxidation of molten aluminum during joining process.

  • Effects of Heat Treatment Conditions on Formation of Expanded-Austenite Phase in Austenitic Stainless Steels by Combining Active Screen and DC Plasma Carburizing Processes

    Nobuhiko Satomi, Nobuyuki Kanayama, Youichi Watanabe, Osamu Takai

    pp. 1181-1189

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    DOI:10.2320/matertrans.H-M2017822

    Abstract

    A low temperature plasma carburizing process can produce an expanded-austenite layer (generally called the S phase), which has high hardness and corrosion resistance at the surface of austenitic stainless steels. We have investigated S phase formation behaviors by using a combined process of active screen and DC plasma carburizing for austenitic stainless steels such as JIS SUS304 and 316 with the aim of developing a highly effective and efficient production technique. The influence of carburizing parameters (processing temperature, time, gas atmosphere, etc.) on the formation of the S phase was studied in terms of thickness, hardness, carbon concentration, lattice constant, and residual stress. The mechanical properties and corrosion resistances of the obtained S phases were also evaluated by using a ball-on-disk test and a salt spray test (SST). The results show that S phases produced efficiently by the combined process under a condition of 733 K and a 10.5 vol% of CH4 gas ratio have both excellent wear and corrosion resistances. This Paper was Originally Published in Japanese in J. Jpn. Soc. Heat Treatment 56 (2016) 352–360.

  • Investigation of Vacuum Hot-Press Sintering Temperatures on the Sintered Characteristics of Cr-31.2 mass% Ti Alloys

    Shih-Hsien Chang, Chien-Lun Li, Kuo-Tsung Huang

    pp. 1190-1196

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    DOI:10.2320/matertrans.M2017048

    Abstract

    The aim of this work is to find the optimal sintering parameters of Cr-31.2 mass% Ti alloys and simultaneously investigate the effects of the TiCr2 Laves phases. In this study, Cr-31.2 mass% Ti alloys are fabricated by vacuum hot-press sintering. Different compositions of submicron titanium (760 nm) powders are added to micron chromium (4.66 μm) powders. The experiments utilize various hot-press sintering temperatures (1250, 1300, 1350 and 1400℃) with the pressure maintained at 20 MPa for 1 h, respectively. The experimental results show the optimal parameters of the hot-press sintered Cr-31.2 mass% Ti alloys to be 1400℃ at 20 MPa for 1 h. The relative density reaches 99.96% and the hardness and TRS (transverse rupture strength) reach 81.93 HRA and 475.73 MPa, respectively. In addition, the increase in temperature of the hot-press sintering is effectively decreased the Cr3Ti3O and slightly enhanced TiCr2 phases, which will lead to the better mechanical properties. Significantly, the optimal hot-press sintered Cr-31.2 mass% Ti alloys possess a dense microstructure, excellent mechanical property and good electrical conductivity value (1.51 × 104 S·cm−1).

  • Effect of Direct Chill Casting Process Parameters on the Microstructure and Macrosegregation of Mg-Al-Zn Ingot

    Xingwei Zheng, Peng Luo, Jie Dong, Wenjiang Ding

    pp. 1197-1202

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    DOI:10.2320/matertrans.M2017013

    Abstract

    It has been demonstrated that the microstructure and macrosegregation of ingot produced by direct chill casting would take remarkable effect on its deformation behavior. In the present study, the influence of casting speed and temperature on the microstructure and macrosegregation of AZ81 ingot prepared by a self-designed crystallizer (220 × 220 mm) was investigated. The results show that the volume fraction of β-Mg17Al12 predicted by the Gulliver-Scheil model agrees well with image analysis results of the ingots prepared at different casting parameters. Moreover, the casting speed affects the macrosegregation greatly while it has slight influence on the distribution of β-Mg17Al12, and the casting temperature has slight influence on macrosegregation of ingot while it has strong influence on the distribution of β-Mg17Al12. The optimal casting speed and casting temperature for the AZ81 ingot are 80 mm/min and 953 K, respectively. The corresponding maximum values of ultimate tensile strength, yield strength and elongation are 265 MPa, 210 MPa and 3.5%, respectively.

  • Facile Synthesis of Nail-Shaped ZnO Microrods by Thermal Evaporation Technique in Ambient Air

    Geun-Hyoung Lee

    pp. 1203-1206

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    DOI:10.2320/matertrans.M2016461

    Abstract

    ZnO microrods with inverted cone shape and nail-like shape were formed by thermal evaporation of ZnS powder and ZnS/Zn mixture under air atmosphere. No catalysts and substrates were used. When ZnS powder was used as a source material, ZnO crystals had an inverted hexagonal cone shape, where the diameter of the microrods increased gradually from about 10 μm at the bottom to 35 μm at the top. When a mixture of ZnS and Zn powders was used as a source material, the diameters of the ZnO microrods increased significantly up to 40～80 μm at the top, which makes the ZnO microrods a nail-like shape. X-ray diffraction patterns showed that all the ZnO microrods had a wurtzite crystallographic structure. Two emission peaks were observed in the cathodoluminescence spectra at room temperature. One was a peak at around 380 nm (ultraviolet) and the other was a peak at 510 nm (green). The high intensity ratio of ultraviolet emission to green emission was obtained for the nail-shaped ZnO microrods, indicating the high crystalline quality of the ZnO microrods.

  • Thermoelectric Properties of InxFeCo3Sb12 Consisting Mainly of In-Filled p-Type Skutterudites

    Jungmin Kim, Ken Kurosaki, Seongho Choi, Yuji Ohishi, Hiroaki Muta, Shinsuke Yamanaka, Misato Takahashi, Junya Tanaka

    pp. 1207-1211

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    DOI:10.2320/matertrans.M2017089

    Abstract

    Indium (In)-filled CoSb3 skutterudite is known as a good n-type thermoelectric (TE) material. Its p-type samples have not been intensively studied. In this study, we tried to reduce the electron concentration of (In)-filled CoSb3 by substitute Fe atoms for 1/4 of Co atoms in InxCo4Sb12. Polycrystalline samples were prepared with the nominal compositions of InxFeCo3Sb12 (x = 0.3, 0.5, 0.7, and 0.9) and their constituent phases, microstructure, high-temperature TE properties were carefully investigated. All the samples showed positive sign of Seebeck coefficient as we expected from the nominal compositions. The filling fraction of In in InxFeCo3Sb12, was revealed to extend to the value of x = 0.43. The largest dimensionless figure of merit zT = 0.39 was observed at 705 K for the sample prepared at x = 0.5.

  • Comparison of Flip-Chip Bonding Characteristics on Rigid, Flexible, and Stretchable Substrates: Part I. Flip-Chip Bonding on Rigid Substrates

    Donghyun Park, Tae Sung Oh

    pp. 1212-1216

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    DOI:10.2320/matertrans.M2017065

    Abstract

    To compare the flip-chip bonding characteristics on rigid, flexible, and stretchable substrates, the contact-resistance and microstructure of the flip-chip joints processed using anisotropic conductive adhesive (ACA) were characterized on rigid Si and glass substrates. The average contact resistance of a flip-chip joint substantially decreased from 39.3 mΩ to 17.2 mΩ when the bonding pressure increased from 10 MPa to 100 MPa, which was attributed to the deformation of the ACA conductive particles that were trapped between the chip bump and the substrate pad. The average contact resistance at a bonding pressure of 200 MPa was further improved to 5.9 mΩ because of direct contact between the Au layer of the chip bump and the Cu substrate pad. After such direct contact occurred, the contact resistance hardly changed even when the bonding pressure increased to 300 MPa.

  • Comparison of Flip-Chip Bonding Characteristics on Rigid, Flexible, and Stretchable Substrates: Part II. Flip-Chip Bonding on Compliant Substrates

    Donghyun Park, Kee-Sun Han, Tae Sung Oh

    pp. 1217-1222

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    DOI:10.2320/matertrans.M2017066

    Abstract

    The contact resistance and microstructure of the flip-chip joints processed using anisotropic conductive adhesive (ACA) were characterized on flexible printed-circuit-board (FPCB) and stretchable FPCB/polydimethylsiloxane (FPCB/PDMS) substrates. On the FPCB substrate, the contact resistance was remarkably reduced from 56.9 mΩ to 13.3 mΩ when the bonding pressure increased from 10 MPa to 200 MPa. However, at a bonding pressure of 300 MPa, it substantially increased to 74.8 mΩ with an excessive deviation of ±37.7 mΩ. On the more compliant FPCB/PDMS substrate, the contact resistance decreased from 43.2 mΩ to 31.2 mΩ when the bonding pressure increased from 10 MPa to 50 MPa. Severe distortion of the FPCB/PDMS substrate occurred at bonding pressures above 50 MPa because of the softness of the PDMS. A more compliant substrate has a lower appropriate bonding pressure for the flip-chip process.

  • Heat Treatment to Improve Fatigue Strength of Friction Stir Welded Ti-6Al-4V Alloy Butt Joint

    Masaaki Nakai, Mitsuo Niinomi, Yu Ishida, Huihong Liu, Hidetoshi Fujii, Takashi Ninomiya

    pp. 1223-1226

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    DOI:10.2320/matertrans.M2017117

    Abstract

    A post-weld heat treatment process, that is, solution treatment and aging, was found to be effective in improving the fatigue strength of friction stir welded Ti-6Al-4V butt joints. The stir-zone microstructure was changed by friction stir welding, from an equiaxed-α structure to a lamellar structure, but equiaxed-α structure remained in the base metal. Subsequently, solution treatment and aging modified these microstructures to bimodal structures in both the stir zone and base metal. The hardness in the stir zone differed from the base metal after friction stir welding, but the difference was eliminated by solution treatment and aging. The fatigue strength of friction stir welded Ti-6Al-4V butt joints was successfully increased by solution treatment and aging, which was higher than that of the parent Ti-6Al-4V plate. This indicates that solution treatment and aging increases the fatigue strength of friction stir welded Ti-6Al-4V butt joints by the formation of similar bimodal structures in the stir zone and base metal, resulting in reduced stress concentration at these boundaries and retarded fatigue failure.

  • Mechanism of the Unusual Wetting of a Surface Fine Crevice Structure Created by Laser Irradiation

    Vilakazi Siboniso, Jaebong Yeon, Christian Grozescu, Hiroki Goto, Masashi Nakamoto, Ryo Matsumoto, Hiroshi Utsunomiya, Toshihiro Tanaka

    pp. 1227-1230

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    DOI:10.2320/matertrans.M2017115

    Abstract

    We investigated the detailed mechanism of the unusual wetting of liquid metal bismuth on the surface fine crevice structure of copper metal created with laser-irradiation by focusing on the wetting state during the course of wetting. It was observed that liquid bismuth infiltrates into the fine pore and the interspaces on the surface fine porous structure, and wets on the surface fine crevice structure itself ahead and behind the wetting front, respectively. This revealed that the unusual wetting on the surface of the fine crevice structure proceeded through a transition from microscopic wetting to macroscopic wetting.

  • Preparation of a Cu Surface with the Hierarchical Structure of a Lotus Leaf via Electroplating and Its Superhydrophobicity

    Kai Chen, Tianchi Wang, Yizhuo Zhao, Zhe Zhou, Ziheng Liu, Jian Kong, Hongfu Xiang

    pp. 1231-1234

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    DOI:10.2320/matertrans.M2017139

    Abstract

    A lotus leaf exhibits excellent superhydrophobic properties because of its hierarchical microstructure and a waxy hydrophobic material covering its surface. Herein, the lotus leaf was used as a template and a copper surface layer with a microstructure similar to the lotus leaf was prepared by electroplating. Experimental results show that the plating samples saved micron-sized structure of the lotus leaf, such as papillae. At the same time, owing to the specificity of the electroplating method, smaller grains were formed as the second-level structure on the papillae, forming a hierarchical structure that makes it possible to obtain a superhydrophobic surface. The plated copper surface exhibited excellent hydrophobic properties with a contact angle of 160°, which is higher than that of the lotus leaf (157°) and also much higher than that of smooth copper covered with an identical fluroalkyl silane (112°). This affords a novel idea for preparing of superhydrophobic surfaces.

  • Microstructures of Al3Ni Particles Reinforced Composites by Infiltration and Reaction Method and Their Properties

    Yongbum Choi, Zhefeng Zu, Kazuhiro Matsugi, Kenjiro Sugio, Gen Sasaki

    pp. 1235-1237

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    DOI:10.2320/matertrans.M2017056

    Abstract

    A new process, based on an infiltration and reaction method, is proposed to fabricate metal matrix composites reinforced with Al3Ni, intermetallic compounds. This study investigates the optimum conditions for refining intermetallic compound dispersion inside the metal matrix at the different reaction times (60 s, 300 s and 600 s) at molten alloy temperature of 973 K and applied pressure of 0.1 MPa; porous nickel with a specific surface areas of > 5800 m2/m3 was used. The counts, area fraction, and aspect ratio of the intermetallic compounds inside matrix are investigated by different of reaction times. In additions, Vickers hardness, three-point bending strength and thermal conductivity of intermetallic compounds reinforced matrix composites are investigated.

  • Synthesis and Characterization of Highly Elastic TiCu-Based Amorphous Micro-Wires

    Benard Odhiambo Obondo, Qiang Li, Chuntao Chang, Xinmin Wang, Deng Pan

    pp. 1238-1240

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    DOI:10.2320/matertrans.M2017153

    Abstract

    A series of TiCu-based quaternary amorphous wires from a deep eutectic alloy composition were prepared by arc-melting and melt-extraction methods. Continuous amorphous wires with good white luster and smooth surface were obtained in Ti25Zr15 Cu60−xNix (x = 0, 5, 10, 15 mol%) alloys. The TiCu-based amorphous wires exhibit high tensile strength exceeding 1.3 GPa and high elastic limit of over 1.4%. Good combine of mechanical properties make them viable for use in many micro mechanical systems.

  • Effects of Grain Size and Texture on Thermal Conductivity of AZ31 during Static Recrystallization

    Gun-Young Oh, Young-Kyun Kim, Shae K. Kim, Hyun Kyu Lim, Young-Jig Kim

    pp. 1241-1243

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    DOI:10.2320/matertrans.M2017126

    Abstract

    In this paper, we report the effect of grain size and texture on the thermal conductivity of AZ31 alloys during static recrystallization. The ND surface of the extruded sheet had higher thermal conductivity than the cast material with random texture. As the recrystallization progresses after extrusion, the thermal conductivity tends to increase. It is considered that this is a composite cause of the growth of the grain, decrease of the grain size and development of strong basal texture.

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  • © 2017 The Japan Institute of Metals and Materials

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