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MATERIALS TRANSACTIONS Vol. 58 (2017), No. 6

ISIJ International
belloff
オンライン版ISSN: 1347-5320
冊子版ISSN: 1345-9678
発行機関: The Japan Institute of Metals and Materials

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キーワードランキング

22 Dec. (Last 30 Days)

MATERIALS TRANSACTIONS Vol. 58 (2017), No. 6

X-ray Study of Phason Strains in an AlCuFeMn Decagonal Phase

Wang Yang, Tomoyo Ando, Kazuki Yamamoto

pp. 847-851

DOI:

10.2320/matertrans.M2016446

抄録

The peak profiles, shifts, and splittings of Bragg reflections, which are inherent in the phason strain of a quasicrystal, are carefully examined using a precise powder X-ray diffraction method for a wide range of different AlCuFeMn alloys and annealing temperatures. Based on the peak-shift dependences of the Bragg reflections on the phason momentum Q⊥, two kinds of new approximant phases are identified. These phases have linear phason strains θ1 = τ−6 and θ2 = τ−5, and θ1 = τ−10 and θ2 = τ−5, corresponding to lattice spacings a = 3.814 nm and b = 2.005 nm, and a = 9.985 nm and b = 2.005 nm in the quasiperiodic plane of the orthorhombic system, respectively.

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Composition Dependence of Lattice Parameter, Thermal and Electrical Properties in ZrCx Compounds

Hiroyuki Nakayama, Kimihiro Ozaki, Takuji Nabeta, Yasushi Nakajima

pp. 852-856

DOI:

10.2320/matertrans.M2016283

抄録

The lattice parameter, thermal conductivity and electrical resistivity in off-stoichiometric ZrCx compounds were investigated and compared with previous research results. The change in the lattice constant as a function of carbon content in the present study was clearly different compared to results from previous studies. In the present study, the lattice constant decreased with the decrease in carbon content. In contrast, the lattice constant exhibited a maximum value at x = 0.8 in the previous studies. Moreover, the lattice constants obtained in this study were smaller than that of the previous studies at the same carbon contents. The changes in the thermal and electric properties as a function of carbon content and temperature exhibited the same trends in the present and previous studies. However, the values of the thermal conductivity at the same carbon content were different. The values in the present study were higher than those of the previous studies.

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Molecular Dynamics Study on Structural Relaxation Processes in Amorphous Germanium

Shigetaka Imabayashi, Manabu Ishimaru

pp. 857-861

DOI:

10.2320/matertrans.M2017036

抄録

The structural relaxation of amorphous germanium was examined by molecular dynamics simulations based on the empirical Tersoff interatomic potential. Although the Tersoff potential overestimated both the melting and glass transition temperatures, it was able to reproduce the structural relaxation behavior. The potential energy decreases with thermal annealing below the glass transition temperature, but occasionally increases during structural relaxation. The mean square displacement of atoms also increases in these periods. These changes were attributed to cooperative atomic motion during the structural relaxation. Atomic trajectories revealed that structural changes are induced by spatially- and temporally-inhomogeneous atomic motions: atomically mobile and immobile regions coexist during structural relaxation. This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 81 (2017) 66–70.

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The Microstructure of Mg98.5Zn0.5Y1 Alloy with Long-Period Stacking Ordered Structure

Zhi-chao Xu, Zhong-xue Feng, Qing-nan Shi, Ying-xiang Yang, Xiao-qi Wang

pp. 862-867

DOI:

10.2320/matertrans.M2016440

抄録

The microstructure of an Mg98.5Zn0.5Y1 alloy prepared by directional solidification (DS), synchronized with a long-period (LPSO) structure were systematically investigated using high-resolution transmission electron microscopy (HRTEM) and high-angle annular dark-field scanning transmission electron microscopy. The formation of 14H-type LPSO was observed to be accompanied by stacking faults. The lamellar 14H-type LPSO structure and stacking faults were both formed on (0001)α-Mg habit plane and grew along [1210]α-Mg direction in Mg98.5Zn0.5Y1 alloy prepared by DS. These findings demonstrated that the stacking faults have a great effect on crystal growth in LPSO structure. The stacking faults nucleation were proposed to explain the growth of LPSO in DS. For the DS polycrystals, the LPSO exhibited a lamellar shape, whose unit cell was composed of two twin-related building blocks (ABCA-type and ACBA-type) which determined the physical and chemical properties of Mg98.5Zn0.5Y1 alloy. There were three atomic layers between two building blocks. The clusters were observed in the 14H-type LPSO which played an important role on building blocks. Furthermore, the two building blocks arranged in opposite shear direction is 68.7°. Based on the present study, an atom model Mg142Zn12Y16, which considered as the characteristic structure of 14H-type LPSO in Mg98.5Zn0.5Y1 alloy prepared by DS, was constructed. The atomic model were verified by simulation. The simulated diffraction patterns were consistent with the experimental pattern.

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Third Law Entropy of Silver Molybdate

Masao Morishita, Hiroki Houshiyama, Yoshiki Kinoshita, Ai Nozaki, Hiroaki Yamamoto

pp. 868-872

DOI:

10.2320/matertrans.M2017005

抄録

The isobaric heat capacities, C°p,m, for Ag2MoO4 at 2-300 K were measured by the relaxation method. Ag2MoO4 is harmful phase formed in nuclear fuel waste glasses. The third law entropy, S°m, determined via the Debye-Einstein function was: S°m(Ag2MoO4(cr), 298.15 K)/J K-1 mol-1 = 219.87 ± 2.20. The phase stability of Ag2MoO4 was discussed on the basis of its standard Gibbs energy of formation, ΔfG°m, which was derived by combining S°m determined in this study with the reference datum of the standard enthalpy of formation, ΔfH°m. Ag2MoO4 was found to exhibit greater phase stability in nuclear fuel waste glasses than transition metal molybdates such as NiMoO4 and ZrMo2O8.

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Effect of Tool Materials on Frictional Properties of Galvannealed Steel Sheets

Katsuya Hoshino, Yuji Yamasaki, Wataru Tanimoto, Masayasu Nagoshi, Shoichiro Taira, Naoto Yoshimi

pp. 873-879

DOI:

10.2320/matertrans.P-M2017813

抄録

The frictional behavior of galvannealed steel sheets (GA) depending on tool materials was investigated. GA having different ζ/δ1 phase intensity ratios was prepared as specimens. In addition, lubrication-treated GA was also prepared using these specimens as the base material. Four kinds of tools composed of zinc alloy die casting (ZAS), ductile cast iron (FCD), alloy tool steel (SKD) and Cr-coated FCD (CR) were used as sliding tools in order to simulate actual press tools used in trials and mass production. When the tool material was harder than the test specimens, the friction coefficient of the GA increased as the amount of the ζ phase increased, and the effect of the lubrication treatment was clearly observed. However when the tool material was softer than the test specimens, the friction coefficient was constant and independent of the existence of the ζ phase and lubrication treatment. The change in the frictional behavior was discussed from the viewpoint of the change in the friction mechanism depending on the relative hardness of the surfaces of the specimens to the tool materials. This Paper was Originally Published in Japanese in J. JSTP 56 (2015) 986–992.

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Effect of Parametric Variations on the Local Compression Deformation of Aluminum Foam Sandwich Panels

Ang Zhao, Sawei Qiu, Yuebo Hu

pp. 880-885

DOI:

10.2320/matertrans.M2016427

抄録

In this article, to study the local compression deformation of aluminum foam sandwich (AFS) panels by orthogonal method, two-dimensional random simulation models of AFS panels were constructed by C++ language combining with ANSYS software, and four parameters, including aluminum foam core's geometrical characteristic parameters porosity P and pore size R and experimental parameters loading force F and local compressing length L, were simultaneously considered. Furthermore, the dependences of the local compression deformation of AFS panels on the above-mentioned parameters were investigated by range analysis and variance analysis means and the related mechanisms were described. The results of range analysis confirmed that factors influencing local compressive deformation of AFS panels are in turn: porosity P, pore size R, local compressing length L, loading force F, in other words, P > R > L > F. Furthermore, variance analysis results showed, compared to loading conditions, geometrical parameters of samples were more influential on the local compressive deformation of AFS panels.

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Slow Strain Rate Testing of Ti-6Al-4V Alloy in Hydrogen Gas at High Pressures and High Temperatures

Kenichi Koide, Toshirou Anraku, Akihiro Iwase, Hiroyuki Inoue

pp. 886-891

DOI:

10.2320/matertrans.M2017031

抄録

A series of slow strain rate tests (SSRTs) were carried out on a Ti-6Al-4V alloy in hydrogen gas at high temperatures (up to 300℃) and high pressures (up to 75 MPa). In order to evaluate the degree of embrittlement of the titanium alloy in a hydrogen gas environment, measurements of tensile strength, elongation and reduction of area were normalized using results obtained in air of atmospheric pressure and in the same temperature range. Results show that Ti-6Al-4V alloy does not exhibit any decrease in tensile strength, elongation or reduction of area in a high pressure hydrogen gas environment.

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Mechanical Properties, Thermal Stability, and Glass Transition Behaviors of a Waterborne Polyurethane/Graphene Oxide Nanocomposite

Hyung Joong Kim, Jihye Han, Younggon Son

pp. 892-897

DOI:

10.2320/matertrans.M2016411

抄録

We synthesized anionic waterborne polyurethane (aWPU) from IPDI (di-isocianate), PTMG (diol), DMPA (anionic ionomer), TEA (neutralizer), and BD (chain extender). Cationic WPU (cWPU) was also prepared using MDEA (cationic ionomer) and HCl (neutralizer) instead of DMPA and TEA. Since the graphene oxide (GO) is anionic due to the –COOH group, GO and aWPU are not compatible because of the repulsive force between identical ionic charges. Thus, we fabricated cationic surfactant treated GO/aWPU to increase the compatibility. cWPU/GO, where attractive forces act between anionic GO and cationic WPU, was also prepared. The thermal stability, glass transition temperature, and mechanical properties of the nanocomposites were investigated. The thermal stability of the WPU was enhanced with the incorporation of GO nanosheets. The glass transition temperature of the hard segment of WPU was increased by the incorporation of GO. These results are attributed the fine dispersion of GO in WPU and strong interfacial interactions between GO and WPU. Enhanced dispersion and interfacial interaction lead to better mechanical properties. Tensile strength, initial modulus, and elongation-at-break of WPU/GO nanocomposites were increased with the incorporation of GO nanosheets. By a simple method (anion-cation matching) we could prepare WPU/GO nanocomposites with enhanced stiffness and toughness.

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Wear Behavior of PAN- and Pitch-Based Carbon Fiber Reinforced Aluminum Alloy Composites under Dry Sliding Condition

Kazunori Asano, Muhammad Faiz Bin Zainuddin

pp. 898-905

DOI:

10.2320/matertrans.M2017002

抄録

The effects of carbon fiber-reinforcement on the wear behavior of aluminum alloy under a dry sliding conditions have been investigated. Two kinds of carbon fibers, PAN-based and pitch-based short carbon fibers, were used as the reinforcements. The composites were fabricated by squeeze casting, and wear testing was carried out using the pin-on-disk method. The wear loss of the alloy and counterpart decreased due to the fiber-reinforcement. The change in the coefficient of friction during the wear test and the scatter in the roughness of the worn surface also decreased by the reinforcement. Examination of the worn surfaces and temperature change of the specimens during the wear revealed that these results were mainly attributed to the crumbled fibers forming a solid lubricant film on the worn surfaces thus preventing seizure of the matrix with the counterpart. Under a high load and sliding speed, the wear loss of the pitch-based fiber composite was lower than that of the PAN-based fiber one. The examination described above revealed that the improvement in the wear and seizure resistance was mainly attributed to the higher thermal conductivity of the pitch-based fiber composite.

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Mechanical Properties of Aluminum Composites Reinforced with PAN- and Pitch-Based Short Carbon Fibers

Kazunori Asano

pp. 906-913

DOI:

10.2320/matertrans.M2017023

抄録

Pure aluminum and AC8A aluminum alloy matrix composites, which were reinforced with PAN- and pitch-based short carbon fibers, were fabricated by squeeze casting, then the composites were exposed to a heat treatment. The effects of the fiber types, composition of the matrix, and heat treatment on the mechanical properties of the composites were investigated. The fibers were in a random planar arrangement in the composites. Although the aluminum carbide was formed due to the reaction between the PAN-based fiber and pure aluminum during the casting process, there was no reaction products near the PAN-AC8A, pitch-pure aluminum and pitch-AC8A interfaces. Although the ultimate compressive strength of the PAN-based fiber composite was greater than that of the pitch-based fiber composite under every condition, the strength of the PAN-based fiber composite degraded due to the heat treatment when pure aluminum was used as the matrix. Examination of fracture surface indicated that the lower reinforcing effect of the pitch-based fiber would be due to delamination at the boundary between the highly-developed graphite crystallites in the fiber. A hardness measurement of the fibers in the composites using a nano-indenter revealed that the interfacial bonding strength between the pure aluminum and PAN-based fiber degraded due to the heat treatment.

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Carbon Dioxide (CO2) Released in the Electrochemical Reduction of Titanium Dioxide (TiO2) to Titanium Metal

Galam Govinda Rajulu, M. Girish Kumar, K. Srinivas Rao, B. Hari Babu, Chaganti RVS Nagesh

pp. 914-920

DOI:

10.2320/matertrans.MK201633

抄録

Studies pertaining to kinetic aspects of the direct electrochemical reduction process of titanium preparation from TiO2 have not been substantial for determining the conversion time precisely. The solid state reduction process does not permit measuring either the rate of formation of product or the rate of depletion of the feed stock. In this work an attempt has been made to study the applicability of variation of CO2 (the product gas) in the vent gases of the electrolytic cell to approximate the bulk process kinetics of the process. From the electrolysis current trend, it might be possible to estimate CO2 profile during the electrolysis time so as to utilize the same for inferring optimal time of the electrochemical reduction process.

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Influence of Bauschinger Effect and Anisotropy on Springback of Aluminum Alloy Sheets

Takeshi Uemori, Satoshi Sumikawa, Tetsuo Naka, Ninshu Ma, Fusahito Yoshida

pp. 921-926

DOI:

10.2320/matertrans.L-M2017812

抄録

For accurate springback calculations, the development of accurate constitutive equation “Yoshida-Uemori model” must always be taken into account. However, several springback calculations of other sheet metals by Yoshida-Uemori model have shown wrong agreements with the corresponding experimental data. The reason is why most of them have been calculated from the view point of the accuracy of Bauschinger effect without the strong anisotropy of sheet metal. In the present paper, we have investigated how the initial anisotropy affects the amount of springback for aluminum sheet metals with Bauschinger effect. Specifically, hat bending experiments in R.D. and T.D. were compared with the corresponding calculations. From the above mentioned comparisons, we found that the optimum combination of an anisotropic yield functions and Yoshida-Uemori model is very important for accurate springback analysis. This Paper was Originally Published in Japanese in J. JILM 65 (2015) 582–587.

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Effect of Co Addition on High Temperature Erosive Wear Characteristics of Fe-C-Cr-Mo-W-V Multi-Component White Cast Iron

Yao Zhang, Kazumichi Shimizu, Kenta Kusumoto, Kazuhiro Tamura, Hiroya Hara, Jun Ito

pp. 927-931

DOI:

10.2320/matertrans.F-M2017810

抄録

Hot hardness and oxidation property of target material influence greatly on the erosion behavior at elevated temperature. The correlation between hot hardness, oxidation properties of multi-component white cast irons with 5%Cr-5%Mo-5%W-5%V and their erosion resistance was investigated to estimate the high temperature erosion behavior. Three kinds of multi-component white cast irons containing 0～10%Co were used in this study. High temperature erosion tests were performed using alumina balls with average size of 1.16 mm at impact angle of 30 degree, particle velocity of 30 m/s and test temperature 1173 K.In order to clarify the correlation of hot hardness, oxidation characteristics and the erosion resistance of specimens, hot hardness test was carried out and erosion damage caused by solid particles was estimated. Hot hardness test of specimens showed a value close to 200 HV10. The results of erosion and oxidation tests revealed that V accelerated oxidation and enhanced the erosion rate, while the erosion rate became smaller with the increase in Co addition. Co formed a stable spinel type oxide film and suppressed the oxidation, thus reduce the erosion rate of multi-component white cast iron. This Paper was Originally Published in Japanese in J. JFS 88 (2016) 246–251.

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Numerical Simulation of Shrinkage Formation Behavior with Consideration of Solidification Progress during Mold Filling Using Stabilized Particle Method

Naoya Hirata, Koichi Anzai

pp. 932-937

DOI:

10.2320/matertrans.F-M2017811

抄録

Solidification begins during pouring in casting processes, and the pouring rate influences the solidification pattern and soundness of products. In this research, the combined simulation of fluid flow and solidification simulation was performed based on the MPS method (a particle method) to analyze the behavior of shrinkage formation from the beginning of pouring to the end of solidification, and the influence of pouring rate on the solidification pattern and shrinkage shape of pure Al casting was investigated. Solidification simulation and stabilized flow simulation programs based on the particle method were combined considering the temperature-dependency of density. The proposed method was applied to shrinkage formation analysis based on the influence of pouring velocity on the shrinkage formation behavior. The results showed that the depth and shape of shrinkage agreed well with corresponding experimental results. The shrinkage formation behavior could also be directly calculated. This Paper was Originally Published in Japanese in J. JFS 88 (2016) 11–17.

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Fabrication of Carbon Fiber Oriented Al–Based Composites by Hot Extrusion and Evaluation of Their Thermal Conductivity

Toko Tokunaga, Koichi Takahashi, Munekazu Ohno, Katsuhiko Sasaki, Terumitsu Imanishi, Kiyotaka Matsuura

pp. 938-944

DOI:

10.2320/matertrans.M2016426

抄録

New heatsink materials having higher thermal conductivities have recently been required due to the recent rapid improvements in performance of the central processing unit, CPU, with increasing heat generation from computer devices. As an alternative material to conventional heatsink materials such as Al and Cu, composites containing carbon fibers have recently been gaining much attentions because of their extremely high thermal conductivity. However, carbon fiber exhibits high thermal conductivity only in its longitudinal direction. Therefore, it is essential to control the orientation of the carbon fibers in the composite materials. In the present study, hot extrusion of a powder–fiber mixture is applied to realization of unidirectional array of carbon fibers in Al matrix, and the effects of volume fraction of the carbon fibers on the thermal conductivity of the carbon fiber oriented Al–based composite have been investigated. It has been demonstrated that the carbon fibers are unidirectionally oriented in the extrusion direction, and the thermal conductivity in this direction increases with the increase in volume fraction of the carbon fibers. For the composites with more than 30 vol% of carbon fibers, the addition of Al–Si alloy powder or the application of the spark plasma sintering, SPS, before the extrusion was found to be effective for improving the sinterability of the powder–fiber mixture. This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 80 (2016) 640–645.

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Effect of Ti Addition on Phase Constitution and Wear Resistance of Fe–B–C Hypereutectic Overlays Produced Using Powder-Wire Composite Arc Welding

Ming-Hui Zhuang, Mu-Qin Li, Jun Wang, Zhen Ma, Zhi-Yuan Zhou

pp. 945-950

DOI:

10.2320/matertrans.M2016392

抄録

The effects of the addition of small amounts of Ti on the phase constitution, microstructure, and wear resistance of Fe–B–C hypereutectic overlays produced using powder-wire composite arc welding were investigated. The Fe–B–C hypereutectic overlay phase consisted of TiB2 and TiC in addition to Fe and Fe2B with the addition of Ti. The addition of Ti inhibited growth of the Fe2B and Fe3(C,B) phases. When the Ti content reached 0.918 mass%, the daisy-like Fe3(C,B) phases disappeared, and precipitation of dispersed TiB2 and TiC began, which improved the wear resistance. Overlays without macroscopic cracks could be obtained. The wear mode of the Fe–B–C hypereutectic overlay changed from a mixture of microcutting and microfracture wear to microcutting wear.

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Change in Mechanical Properties of Biomechanical Ti–12Cr Subjected to Heat Treatment and Surface Modification Processing

Kentaro Niwa, Toshikazu Akahori, Mitsuo Niinomi, Tomokazu Hattori, Masaaki Nakai

pp. 951-957

DOI:

10.2320/matertrans.M2016432

抄録

In recent years, metallic biomaterial applications have demanded a relatively low Young's modulus that is nearly equal to that of bone (around 30 GPa). However, in the case of spinal fixture applications, metallic materials with a relatively high Young's modulus are required to suppress spring-back by elastic and plastic deformation during implantation. We recently proposed Young's modulus control by stress-induced transformation to produce the biomedical β-type Ti–12Cr alloy. However, the relationship between the microstructure and the mechanical properties of Ti–12Cr has not been fully investigated. In this study, the changes in the mechanical properties of Ti–12Cr were investigated through the heat treatment and the fine particle bombarding process (FPB), which is a surface modification process. Peak aging (PA) of Ti–12Cr heated at 673 K occurred for around 2.4 ks. The Vickers hardness of Ti–12Cr at the PA condition at 673 K (HV 524) was around 90% higher than that after solutionized treatment (ST) (HV 294). Both the 0.2% proof stress and tensile strength of Ti–12Cr at the PA condition at 673 K were also around 50% higher those after ST. However, the ductility of Ti–12Cr at the PA condition at each temperature significantly decreased. Therefore, only ST was judged to be optimal for Ti–12Cr with an excellent combination of strength and ductility. The Vickers hardness and Young's modulus of solutionized Ti–12Cr subjected to FPB increased by around 40% and 70%, respectively, at the edge of the specimen surface compared with the corresponding values of the unprocessed sample. Furthermore, the run-out (770 MPa) of Ti–12Cr subjected to FPB increased by around 70 MPa. The bone contact ratio of Ti–12Cr slightly increased with an increase in the implantation period from 24 to 52 weeks. This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 80 (2016) 764–771.

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Directional Control of Mature Osteoblast Derived from Juvenile Mouse Calvariae

Ryosuke Ozasa, Aira Matsugaki, Yoshihiro Isobe, Taro Saku, Takayoshi Nakano

pp. 958-962

DOI:

10.2320/matertrans.M2017077

抄録

Bone tissue has a highly anisotropic microstructure comprised of biological apatite (BAp) and collagen fibrils, which is closely related to bone mechanical function. The formation of anisotropic bone microstructure is governed by bone-forming osteoblasts; therefore, isolation of functional osteoblasts and regulation of their arrangement for generating bone tissue with optimally-oriented microstructure during bone reconstruction are important. In this study, we established the isolation and culture conditions of mature osteoblasts derived from juvenile mice (2-week-old). Osteoblasts from juvenile mice expressed significantly higher level of osteoblastic markers (alkaline phosphatase, osterix, and osteocalcin) than osteoblasts from neonatal mice, indicating that juvenile osteoblasts are promising materials for bone tissue engineering. Moreover, alignment of the mature osteoblasts was successfully regulated using oriented collagen substrates. This is the report that shows directional control of mature osteoblasts isolated from juvenile mice.

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Effect of Sn Addition on the Precipitation Behavior in AZ91 Magnesium Alloy

Jeong Kyun Kim, Seung Hyun Oh, Kang Cheol Kim, Won Tae Kim, Do Hyang Kim

pp. 963-966

DOI:

10.2320/matertrans.M2017011

抄録

The effect of Sn (1, 3 and 5 mass%) addition on the precipitation behavior of AZ91 alloy has been investigated in the present study. The addition of Sn is effective in suppression of discontinuous precipitation as well as acceleration of continuous precipitation. The Mg2Sn particles at the grain boundary effectively reduce the nucleation sites for discontinuous β precipitates, and slow down the movement of the grain boundary. The addition of Sn remarkably enhances the aging response of AZ91. The hardness increases steeply with the start of the aging treatment, resulting in significantly higher peak hardness within shorter aging time. The addition of Sn enhances the aging response by solid solution hardening effect as well as by co-precipitation of Mg17Al12 and Mg2Sn in the α-Mg matrix.

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Direct Temperature Measurement of Al-2mass%Si Alloy Strips during High-Speed Twin-Roll Casting and Its Application in Determining Melt/Roll Heat Transfer Coefficient for Simulation

Min-Seok Kim, Hyoung-Wook Kim, Shinji Kumai

pp. 967-970

DOI:

10.2320/matertrans.L-M2017814

抄録

In order to develop a numerical simulation model of the high-speed twin-roll casting (HSTRC) process, an appropriate melt/strip heat transfer coefficient (HTC) is required. In the present study, the strip temperature was directly measured by using the traveling thermocouple technique. Then, we tried to determine the reasonable HTC values, which conformed well with the temperature curves obtained experimentally. The results showed that the HTC values increased with increasing casting speed. Moreover, the overall HTCs were much higher than those reported so far. We believe that a large hydrostatic pressure, induced by a high melt pool level, and a sufficient roll separating force helped improve the contact condition between the solidifying shell and the roll surface.

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