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

MATERIALS TRANSACTIONS Vol. 57 (2016), No. 10

  • Extension of Structure Integration to Magnetic System

    Kazuhito Takeuchi, Takashi Ishikawa, Ryohei Tanaka, Koretaka Yuge

    pp. 1667-1670

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    DOI:10.2320/matertrans.M2016174

    Abstract

    We extend our previously developed method, “structure integration”, to evaluate free energy directly for magnetic large systems on a given lattice. The present method expresses the density of states (DOS) as parameters independent of the system but dependent on the lattice, and replaces the DOS unknown a priori as that known a priori. Through the two-dimensional square lattice Ising model, we find that the present method can evaluate magnetic free energy efficiently and accurately above the critical temperature without iterative methods like the Monte Carlo simulation.

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  • Flattening the Solidification Front by Varying the Wall Thickness of the Mould in Directional Solidification Technology

    Yuanyuan Lian, Dichen Li, Kai Zhang

    pp. 1671-1679

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    DOI:10.2320/matertrans.M2016157

    Abstract

    A non-planar solidification front can cause many defects in the directional solidification process. The irregular shape of the cross section of the cast leads to a non-uniform heat distribution and hence causes a non-planar solidification front. This paper provides a method to decrease the circumferential temperature gradient in the directional solidification process by varying the wall thickness of the mould. The relationship between the wall thickness and the control parameter has been determined. An optimization algorithm for obtaining the control parameter and the corresponding wall thickness of mould is presented with three simulation examples provided to verify the superiority of this method. According to the results the circumferential temperature gradients can be reduced by 68.7%, 72.0% and 88.2% respectively. Moreover, the transverse temperature gradients are reduced by 57.3%, 60.8% and 89.3% accordingly. The solidification front with a varying thickness mould is thus flattened compared with the un- optimized one.

  • Ligand-Driven Exchange Coupling in Graphene-Based Magnetic Materials

    Nguyen Van Thanh, Nguyen Anh Tuan, Phạm Thi Tuan Anh, Nguyen Viet Cuong, Dam Hieu Chi

    pp. 1680-1684

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    DOI:10.2320/matertrans.M2016092

    Abstract

    Several forms of graphene-based magnetic materials have been investigated via density-functional theory utilizing dispersion correction and full geometry optimization. Our calculated results show that the perinaphthenyl radical (R1) has a spin of 1/2. However, in its [R1]2 dimer structure, the net spin becomes zero due to an antiferromagnetic spin-exchange between radicals. To avoid antiferromagnetic spin-exchange of identical face-to-face radicals, the alternating stack of composition R1/D25/R1 (with D25 = graphene-based diamagnetic molecule C34H16) has been designed and investigated. As expected, our calculated results confirm that the alternating stack R1/D25/R1 has a ferromagnetic spin-exchange between two R1 radicals with the spin-exchange coupling of J/kB = 277 K, and the spin moment of m = 2 μB (Bohr magneton unit). In order to explore ways to tailor spin-exchange coupling in stacks, five other R1/D25/R1-based alternating stacks with different ligand configurations of R1 have been designed and investigated. Interestingly, ferromagnetic spin-exchange in stacks can be enhanced by substituting ligands having a weak electron affinity for H atoms of a R1 molecule, while it can be weakened by substituting ligands having high electron affinity for H atoms of a R1 radical. These results can be explained in terms of the competitive hybridization between the HOMO (highest occupied molecular orbital) of radicals and the HOMO and LUMO (lowest unoccupied molecular orbital) of diamagnetic molecules. These results would give some indication for how the spin-exchange coupling in graphene-based alternating stacks can be tailored.

  • Effect of Trace Ge on Wettability and High-Temperature Oxidation Resistance of Sn-0.7Cu Lead-Free Solder

    Qing-meng Wang, Gui-sheng Gan, Yunfei Du, Donghua Yang, Guoqi Meng, Huaishan Wang, Yi-ping Wu

    pp. 1685-1690

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    DOI:10.2320/matertrans.MD201521

    Abstract

    Sn-0.7Cu and Sn-0.7Cu-xGe solder alloys were prepared to investigate the influence of trace Ge on liquid Sn-0.7Cu lead-free solder at high temperature. The spreadability and the wetting force of solders were tested, and the oxidation-resistance was also evaluated by eye observation and skimming at 250℃～370℃. The results have shown that trace Ge can improve the spreading rate of Sn-0.7Cu, but have a few effect on the wettability. The oxide slag quantity of Sn-0.7Cu was three times more than the Sn-0.7Cu-0.012Ge at the same temperature and period, the optimal content of Ge to improve the oxidation resistance of Sn-0.7Cu was 0.012 mass%. The growth factor of oxide film on the surface of liquid Sn-0.7Cu solder (k250℃ = 1.59 × 10−6, k370℃ = 3.03 × 10−6) were both twice higher than the Sn-0.7Cu-0.012Ge (k250℃ = 0.56 × 10−6, k370℃ = 1.04 × 10−6) at 250℃ and 370℃ respectively.

  • Enhanced Ductility of In Situ Synthesized (TiB+La2O3)/IMI834 Composite by TRIPLEX Heat Treatment

    Jiuxiao Li, Yuanfei Han, Liqiang Wang, Liangyu Chen, Weijie Lu

    pp. 1691-1697

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    DOI:10.2320/matertrans.M2015268

    Abstract

    The effects of a new TRIPLEX heat treatment on the microstructure and the mechanical properties of in situ synthesized (TiB+La2O3)/IMI834 composite (TMCs) were studied. The microstructures and the morphology of reinforcements after heat treatment were characterized by optical microscopy, scanning electron microscopy (SEM), electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM). The martensite variation was in situ observed in the processing of TRIPLEX heat treatment by confocal laser scanning microscope (CLSM). The results showed that the microstructure of specimens after TRIPLEX heat treatment exhibits laminar structure with high aspect ratio. The percent of low angle boundaries of TMCs treated by TRIPLEX heat treatment and β heat treatment is about 22.71% and 25.32%, respectively. Compared with β heat treatment, the ductility of titanium matrix composites after TRIPLEX heat treatment was improved significantly. Tiny perpendicular cracks on TiB reinforcement and the crack initiating in matrix were in situ observed at the same time by CLSM during tensile test.

  • Detection of Rhenium-Rich Particles at Grain Boundaries in Nickel-Base Superalloy Turbine Blades

    KeeHyun Kim, Paul Withey

    pp. 1698-1706

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    DOI:10.2320/matertrans.M2016131

    Abstract

    Ni-base single crystal superalloy turbine blades containing defect grains were investigated by high resolution electron microscopy. Several different types of defects, such as, stray grains, equiax grains and freckle chains which formed during casting, and recrystallized grains which formed during subsequent heat treatment, were selected. Regardless of the region of the turbine blade, many particles with large amounts of rhenium were detected at the boundary of the stray grain and matrix. The Re-rich particles were also detected at the boundary of the matrix and other defect grains, such as, equiax grains and freckle chain grains, and even at a low angle grain boundary. However, the boundary of the recrystallised grain and matrix which was formed after solution heat treatment showed just one Re-rich particle. Also, the composition of these Re-rich particles is different from any topologically close packed phases which have been reported in Ni-base superalloys. The results suggest that during solidification, the particles are formed from the melt and pushed ahead of each solidification front of the defect grain and the matrix, and piled up at the boundary of the matrix/defect grain.

  • Comparison of Reverse Transformation Behaviors of Thermally- and Deformation-Induced ε-Martensite in Fe-28Mn-6Si-5Cr Shape Memory Alloy

    Wataru Tasaki, Koichi Tsuchiya, Takahiro Sawaguchi, Susumu Takamori

    pp. 1707-1713

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    DOI:10.2320/matertrans.MAW201607

    Abstract

    Reverse transformation behavior and the microstructures of ε-martensite induced by two different methods of cooling and deformation in Fe-28Mn-6Si-5Cr shape memory alloy was investigated. In situ heating X-ray diffraction (up to 673 K) was applied to the cooled and deformed specimens to observe the reverse transformation behavior. The microstructures in the cooled and deformed specimens were analyzed by electron backscattering diffraction. From X-ray diffraction patterns, the reverse transformation start temperature (As) in the deformed specimens was found to be lower than that in the cooled specimen, while the reverse transformation finish temperature (Af) in the deformed specimens was higher than that in the cooled specimen. The electron back-scattering diffraction (EBSD) analysis revealed a higher fraction of low-angle misorientation boundaries in γ-austenite and ε-martensite in the deformed specimens than in the cooled specimens. Intersections of different ε-martensite variants with ε-twin were observed in the deformed specimens, while such intersections were not observed in the cooled specimens. A heterogeneous mixture of plastically deformed ε-martensite and γ-austenite were found in deformed specimens. It is considered that the heterogeneity of the microstructures led to the difference in reverse transformation temperatures of As and Af in the thermally-induced and deformation induced maretnsites.

  • Texture Development of α-Al2O3 Ceramic Coatings by Aerosol Deposition

    Makoto Hasegawa, Kota Akiyama, Yosuke Oki, Makoto Tanaka, Satoshi Kitaoka, Yutaka Kagawa

    pp. 1714-1719

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    DOI:10.2320/matertrans.M2016213

    Abstract

    X-ray diffraction and electron backscattering diffraction analyses of the surfaces of α-Al2O3 coatings formed by aerosol deposition and heat treatment up to 1573 K reveal that the coatings have textures. A texture with the (0001) plane inclined approximately 15° away from the coating plane is observed in an as-deposited specimen. During heat treatment, the (0001) plane becomes almost parallel to the coating plane. Texture development is observed with increasing heat treatment temperature.

  • Microstructure and Mechanical Properties of ARB Processed Aluminium with Different Purities

    Naoya Kamikawa, Nobuhiro Tsuji

    pp. 1720-1728

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    DOI:10.2320/matertrans.MH201519

    Abstract

    99.2% Al (2N-Al), 99.99%Al (4N-Al) and 99.999%Al (5N-Al) were deformed to high strains by accumulative roll-bonding (ARB) at room temperature, and microstructure and mechanical properties were systematically characterized. During the ARB process, original coarse grains were subdivided by deformation-induced high-angle boundaries into nano-scale grains, where redundant shear strain introduced in the near-surface layers by friction in the non-lubricated rolling significantly accelerated the formation of nanostructures. It was found that spacing and fraction of high-angle boundaries can be explained by total equivalent strain taking the effect of shear strain into account. Quite uniform nanostructures dominated by high-angle boundaries were obtained after 6 cycles of ARB for 2N-Al and 4N-Al, but the boundary spacing was smaller in the 2N-Al than in the 4N-Al. On the other hand, in the case of 5N-Al, recrystallization and grain growth occurred during the roll-bonding process, and nanostructures were not able to be obtained. It was suggested that an increase in the amount of impurities is effective to increase the stability of the nanostructures and to randomize the deformation texture leading to a high fraction of high-angle boundaries.

  • Correcting the Ultrasonic Scattering Attenuation Coefficient of a Metal Using an Equivalent Medium Layer

    Xiaoqin Han, Xiongbing Li, Yongfeng Song, Peijun Ni, Yiwei Shi

    pp. 1729-1734

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    DOI:10.2320/matertrans.M2016199

    Abstract

    The surface roughness and diffraction attenuation of a metal have an effect on the measurement accuracy of the ultrasonic scattering attenuation coefficient. In order to correct the scattering attenuation coefficient, the rough surface of the sample and its neighbouring couplant are assumed to be an equivalent medium layer, namely the sample is a multi-layered medium composed of a layer of the substrate medium and two layers of equivalent mediums. Based on the Lommel diffraction correction coefficient and the parameters of the equivalent medium layer, the expressions are developed for a circular planar piston transducer's sound field in a multi-layered structure with equivalent medium layers. As a result, a correction model of the scattering attenuation coefficient is established by using the surface roughness and diffraction attenuation. AISI 304 stainless steel samples with different surface roughnesses are used to conduct the ultrasonic experiment. The results show that the attenuation coefficient without correction increases in proportion to the roughness; and the average relative error is up to 182.8% compared to the theoretical attenuation coefficient, while the average relative error is only 1.28% after correction. This indicates that the model can limit the negative effects of the roughness and the sound field diffraction on the extraction of the scattering attenuation coefficient. Consequently, the corrected attenuation coefficient can improve the accuracy and reliability in the nondestructive evaluation of the microstructure.

  • Improved Combination of Strength and Ductility in Zirconium-Added Al-Zn-Mg-Cu Alloy Processed with High-Pressure Torsion

    Hiroyuki Kawabata, Ichiro Aoi, Keiichiro Oh-ishi, Takanori Nakagaki, Yoshihiro Shimizu, Shigeru Kuramoto

    pp. 1735-1740

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    DOI:10.2320/matertrans.M2016215

    Abstract

    To realize high-strength and high-ductility aluminum alloys, an Al-Zn-Mg-Cu-based alloy was produced by high-pressure torsion (HPT) processing. The chromium in the alloy was replaced with zirconium, and the iron content of the alloy was decreased to avoid ductility loss due to iron-containing intermetallic compounds formed during crystallization. The microstructures and mechanical properties of the processed alloy were investigated. The grains were elongated perpendicular to the rotation axis. The elongation of the alloy containing chromium decreased with increasing number of turns. In the case of the alloy in which chromium was replaced with zirconium, the strength increased with increasing number of turns, without reducing the elongation. The alloy exhibited an ultimate tensile strength of 929 MPa and an elongation of 6.4%.

  • Fatigue Crack Initiation Simulation in Pure Iron Polycrystalline Aggregate

    Fabien Briffod, Takayuki Shiraiwa, Manabu Enoki

    pp. 1741-1746

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    DOI:10.2320/matertrans.M2016216

    Abstract

    A numerical study was conducted to evaluate the fatigue crack initiation stage in pure α-iron. A two-dimensional synthetic polycrystalline aggregate was generated with Voronoi tessellation to represent the microstructure. Low-cycle fatigue experiments under fully reversed strain-controlled loading were conducted for different strain amplitudes. The stable stress-strain hysteresis loops were used to calibrate a non-linear kinematic hardening model for metal plasticity suitable for cyclic simulations. An existing procedure based on the Tanaka-Mura model for fatigue crack initiation was extended to body-centered cubic lattice to account for two orthogonal slip systems as potential crack locations. This procedure was applied for fully reversed fatigue simulations with various stress amplitudes ranging from low-cycle to high-cycle fatigue regime. The effect of the stress level on the crack morphology and the fatigue crack initiation life was evaluated. Finally the applicability and limitations of the proposed procedure was discussed.

  • Salicylic Acid Complex Imprinted Polymer Membranes: Preparation and Separation Characteristics

    Yan Dong, Lifang He, Xiahong Zhang, Xiurong Jiang

    pp. 1747-1752

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    DOI:10.2320/matertrans.M2016136

    Abstract

    Salicylic acid complex imprinted polymeric membranes have been prepared by thermal polymerization using polyvinilidene fluoride membrane as a support membrane, acrylamide as a functional monomer and ethylene glycol dimethacrylate as a crosslinker. The imprinted membranes are characterized by Fourier Transform Infrared Spectrometer (FT-IR), thermogravimetric analysis (TGA) and scanning electron microscope (SEM). It can be found that the structure of imprinted membranes is different from the supporting membrane, and the surface of the supporting membrane is covered with an imprinted polymer layer after polymerization. Adsorption and permeation binding experiments indicate that imprinted membranes show high specific binding capacity of template molecule, the selectivity factor of the imprinted membrane for the salicylic acid was 26.4, The optimum polymerization condition is 0.3 mmol salicylic acid, 1.2 mmol acrylamide and 6.0 mmol ethylene glycol dimethacrylate in acetonitrile at 60℃ for 24 h.

  • High Pressure Acid Leaching of Co Matte Converted from Co Concentrate

    Gunha Kim, Ga-hee Kang, Sangjun Kim, Sookyung Kim, Jeongsoo Sohn, Kyungjung Kwon

    pp. 1753-1758

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    DOI:10.2320/matertrans.M2015417

    Abstract

    Cobalt concentrates are often leached with an acid such as sulfuric acid. An alternative leaching process of using matte is suggested. Cobalt concentrates are first converted to matte, enriching their major elements of Co, Cu and Fe, and the matte is treated by sulfuric acid pressurized leaching. The Co concentrate includes Co oxides as valuable minerals, whereas Co, Cu and Fe exist predominantly as sulfides in the matte. The effect of experimental factors such as oxygen partial pressure, sulfuric acid concentration and sulfur content in the matte on the leaching efficiency of Co is investigated. The presence of oxygen as an oxidizing agent improves the leaching efficiency of Co. Sulfuric acid concentration of 0.19 M is sufficient for the full dissolution of Co from the matte in oxygen atmosphere. A higher sulfur content in the matte enhances leaching rate of matte slightly. The leaching results are well matched with physicochemical characterization of Co concentrate, matte and residues. This alternative leaching process using Co matte could lead to a higher Co leaching efficiency than the direct leaching process using Co concentrate.

  • An Aluminum/Polycarbonate (Al/PC) Joint by Homogeneous Low Voltage Electron Beam Irradiation (HLEBI) to PC Prior to Lamination Assembly and Hot-Press

    Masataka Tomizawa, Chisato Kubo, Masae Kanda, Michael C. Faudree, Itaru Jimbo, Yoshitake Nishi

    pp. 1759-1765

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    DOI:10.2320/matertrans.M2016058

    Abstract

    A 2-layer aluminum/polycarbonate (Al/PC) joint was fabricated between half specimens of typically difficult to adhere Al and PC without use of welding, fasteners, rivets, chemical treatment or glue by a new double-step adhesion method: applying a low dose of homogeneous low energy electron beam irradiation (HLEBI) to only the PC connecting surface, prior to lamination assembly and hot press at 418 K for 3.0 min under 15 MPa pressure. Experimental results showed 0.30 MGy along with 0.22 MGy had adhesion created in all 11 samples of their data sets [11/11], although data sets of untreated (hot press alone), 0.04, 0.13 and 0.43 MGy had adhesion created in less samples in their data sets at [2/11], [2/11], [6/11] and [10/11], respectively. Moreover, applying the 0.30 MGy HLEBI exhibited the highest mean adhesive force of peeling resistance, oFp over all the data sets, at all peeling probabilities (Pp). Notably, at high-Pp of 0.94 the 0.30 MGy HLEBI raised the oFp significantly, 1517% from 1.48 of the untreated to 23.95 Nm−1. Based on the 3-parameter Weibull equation, the statistically lowest oFp at Pp = 0 (Fs) from 0.30 MGy-HLEBI was the highest value over all other data sets at 3.10 N·m−1. XPS (X-ray photoelectron spectroscopy) of the peeled Al side revealed a C(1s) peak shift in binding energy from 283.8 eV (C-C) to 284.3 eV (C=C), along with increase in O(1s) C=O peak intensity (531.8 eV) indicating the 0.30 MGy HLEBI generates increased reactive double bond (π-bond) sites which can explain stronger oFp of Al/PC joint over the untreated. Since HLEBI cuts the chemical bonds and generates active terminated atoms with dangling bonds in PC polymer, the increased adhesion force in the Al/PC joint can be explained by the chemical bonding at the interface.

  • Adsorption and Photocatalysis Performance of Bi4Ti3O12 Nanoparticles Synthesized via a Polyacrylamide Gel Route

    Z. M. Cui, H. Yang, M. Zhang, H. M. Zhang, J. Y. Su, R. S. Li

    pp. 1766-1770

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    DOI:10.2320/matertrans.M2016212

    Abstract

    A polyacrylamide gel route was adopted to synthesize Bi4Ti3O12 nanoparticles and the effect of chelating agents on the products was investigated. When citric acid and acetic acid is separately used as the chelating agent, single-phase Bi4Ti3O12 samples can be prepared at a calcination temperature of 500℃; however, when tartaric acid or EDTA is used as the chelating agent, a higher calcination temperature of 600℃ is required to produce single-phase samples. SEM observation shows that the as-prepared samples are composed of sphere-like or ellipsoid-like particles. The average particle size of the citric acid-, acetic acid-, tartaric acid-, and EDTA-resulted samples is centered around 32, 35, 90 and 120 nm, respectively. The bandgap energy of the four samples is measured to be 3.27 eV by ultraviolet-visible diffuse reflectance spectroscopy. The photocatalytic activity of Bi4Ti3O12 samples was evaluated by degrading RhB under simulated-sunlight irradiation, and the influence of pH value on the adsorption and photocatalytic degradation of the dye was also investigated. Ethanol, BQ and AO were respectively used as the scavengers of •OH, •O2− and h+ to investigate their effect on the photocatalytic degradation with the aim of revealing the photocatalytic mechanism involved. Based on the experimental results, the direct oxidation by h+ is suggested to be the main mechanism toward the dye degradation.

  • Thermodynamics of Oxygen in the Fe-Nd-O System for Production of Dy Free Nd-Fe-B Magnet

    Takahiro Oshino, Yoshinao Kobayashi, Taichi Abe, Toshiyuki Koyama

    pp. 1771-1775

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    DOI:10.2320/matertrans.M2016055

    Abstract

    To improve the coercivity of Dy free Nd2Fe14B magnet, it is necessary to prevent oxidization of Nd-rich phase formed in grain boundaries on the basis of the information of oxygen behavior in this material which has been not well revealed so far. The present study aims to clarify the thermodynamic property of oxygen in the Fe-Nd-O system. The solubility of oxygen in molten Fe-Nd alloy coexisting with solid Nd2O3 has been measured at 1473 and 1673 K. On the basis of this results, the standard Gibbs energies for the dissolution of oxygen into molten Fe-Nd alloy at 1473 and 1673 K have been determined to be −397.3～−411.6 and −314.6～−396.8 kJ/mol, respectively. The dissolution behavior of oxygen into molten Fe-Nd alloy is thermodynamically discussed and found to be dominated by chemical property of neodymium. Addition of calcium or neodymium fluoride is found promising for effective deoxidation of the present alloy.

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  • Effect of Confinement Layer on Laser Ablation and Cavitation Bubble during Laser Shock Peening

    Tomoki Takata, Manabu Enoki, Pornthep Chivavibul, Akinori Matsui, Yuji Kobayashi

    pp. 1776-1783

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    DOI:10.2320/matertrans.M2016150

    Abstract

    Laser shock peening (LSP) is one of surface treatments to induce residual compressive stresses near metal surface to improve the resistance of materials to surface-related failures, such as fatigue and stress corrosion cracking. In LSP process, short pulsed laser is focused and irradiated to the material covered by transparent overlay such as glass or water. This transparent overlay is also known as a confinement layer and has an important role to increase impact pressure during LSP process. When confinement layer is liquid, the characteristics of the layer such as temperature, viscosity, etc. affect the phenomena occurring during the peening process and undoubtedly influence the induced residual stress. In the present study, Acoustic Emission (AE) technique coupling with high speed camera was applied to study the effect of confinement layer on LSP process. The results were discussed using the impact force calculated by inverse analysis of detected AE waveforms and bubble parameters observed by high speed camera. The results showed that temperature, thickness and viscosity of confinement layer had strong influence on the generation and collapse of cavitation bubble. The optimization of process parameters could be obtained by AE technique.

  • Effect of Reaction between Alloying Element and VGCFs on Mechanical and Electrical Properties of PM Copper Alloy Composites Dispersed with VGCFs

    Hisashi Imai, Kuan-Yu Chen, Katsuyoshi Kondoh, Junko Umeda, Hung-Yin Tsai

    pp. 1784-1788

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    DOI:10.2320/matertrans.Y-M2016829

    Abstract

    In this research, the effect of alloying elements on the mechanical and electrical properties of powder metallurgy (PM) copper composite reinforced with vapor-grown carbon fibers (VGCFs) was investigated. The alloying elements were titanium (Ti) and silicon (Si) that could easily form their carbides at elevated temperatures. The VGCFs-doped Cu-Ti composites showed a slightly decreased yield stress in comparison with the unadulterated Cu-Ti alloy. The electrical conductivity of the composite materials increased with increasing VGCFs content. However, the VGCFs-doped Cu-Si composites exhibited the same mechanical and electrical properties as the Cu-Si alloy. It was found that the reaction between Ti and VGCFs in forming TiC particles consumed the Ti solutes in the matrix and led to a reduction of solid solution strengthening effect by Ti elements, whereas the reaction between Si and VGCFs in forming SiC was observed. In addition, VGCFs adulteration showed no effect on the strength and conductivity improvement of Cu-Si alloy. This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 63 (2016) 150–156.

  • Influence of Cooling Roll Roughness on Nucleation and Growth of Primary Crystals in Strip Cast NdFeB Alloy

    Kazuhiko Yamamoto, Shinya Tabata, Takuya Onimura

    pp. 1789-1793

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    DOI:10.2320/matertrans.F-M2016830

    Abstract

    In general, the manufacturing process of NdFeB sintered magnets is as follows: preparing the starting alloys, crushing and pulverizing into fine powders, press-forming in magnetic fields for alignments, sintering, aging, crushing and cutting. It is well known that microstructure of starting alloys affect the ease of pulverization, press-forming for alignments in the magnetic field and sintering. A single roll casting process (hereinafter referred to as strip-casting) is a beneficial method for obtaining starting alloys with suitable microstructure. For this reason, strip-casting is regarded as a de-facto standard process for the production of starting alloys for NdFeB magnets. With this method, strips of 100–500 μm thickness are formed by pulling up from a melt by a single roll. For this reason, it is important to control primary crystal growth. In this study, we investigated primary crystal growth in starting alloys. First, Nd15.66Febal.B5.52 (atomic %) alloys were prepared using a strip-casting furnace. A batch size was 500 kg and roll diameter was 500 mm. Microstructures of obtained strip-casting samples were observed by electron probe micro-analyzer (EPMA). In this measurement, we focused on the morphologies of primary crystal growth and the distribution of constituent elements. Next we investigated the relation between the surface roughness of the rolls and frequencies of nucleation at the surface contacting a roll. The alloys were prepared using a strip-casting furnace. A batch scale was 5 kg and roll diameter was 300 mm. The alloy composition was Nd10.35Dy3.88Febal.B5.96 (atomic %). In this study, we also reviewed the method of reducing segregations of chill crystals existing in the microstructures of the starting alloys. This Paper was Originally Published in Japanese in J. JFS 88 (2016) 154–159.

  • Characteristics of Hypoeutectic Cu–Zr Alloy Rods Manufactured by Vertically Upwards Continuous Casting

    Naokuni Muramatsu, Masaaki Akaiwa

    pp. 1794-1800

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    DOI:10.2320/matertrans.M2016181

    Abstract

    This study applied a vertically upwards continuous casting (VUCC) mass-production method to the pilot-scale production of hypoeutectic Cu–xZr (x = 0.25–5 at%) alloy rods. The microstructures of these VUCC rods were investigated and compared with those of rods produced by copper mold casting (CMC). In addition, the wire-drawing ability of the VUCC rods was examined, and the adaptability of the VUCC method to the mass production of hypoeutectic Cu–Zr alloys was fully investigated. The results show that VUCC provides a higher rate of cooling than CMC, with the resulting dendritic microstructure expected to contribute to its arm-spacing refinement. Furthermore, the VUCC rods exhibit good wire-drawing ability. The ultimate tensile strength, total strain to fracture, and electrical conductivity of Cu–2.5Zr (at%) alloy wires with diameter of 13.8 μm drawn from a VUCC rod are 1882 ± 28 MPa, 2.2 ± 0.2%, and 21% IACS (i.e. 21% of the International Annealed Copper Standard conductivity of annealed copper), respectively. The results suggest that VUCC has good potential to be adapted for mass production of hypoeutectic Cu–Zr alloy rods. This Paper was Originally Published in Japanese in J. Japan Inst. Copper 54 (2015) 179–184.

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  • Surface Modification of Carbon Steel by Atmospheric-Controlled IH-FPP Treatment Using Mixed Chromium and High-Speed Steel Particles

    Shumpei Ota, Hiroyuki Akebono, Shoichi Kikuchi, Kazue Murai, Jun Komotori, Kengo Fukazawa, Yoshitaka Misaka, Kazuhiro Kawasaki

    pp. 1801-1806

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    DOI:10.2320/matertrans.M2016141

    Abstract

    First, in this paper, a new atmospheric-controlled induction heating and fine particle peening treatment system (vacuum AIH-FPP system) which reduces the oxygen concentration in the chamber to the order of ppm, much less than a conventional processing apparatus was presented. Next, in order to examine the effect on the formation of the surface modified layer of (i) mixing hard particles, (ii) the processing temperature, and (iii) the particle velocity, carbon steel AISI 1045 was treated with this system in conjunction with high-frequency induction heating, by peening Cr particles and mixed particles of Cr and high-speed tool steel. From the observation results by a scanning electron microscope and an energy dispersive X-ray spectrometer, it is clear that for the formation of a Cr diffused layer, using a mixture of Cr particles and high-speed tool steel particles is important. The treatment must be conducted at a higher temperature of approximately 1273 K to form a Cr diffused layer. Furthermore, by increasing the particle velocity, a thicker Cr transfer layer is formed at the surface under process. Therefore, an increased particle velocity accelerates the transfer of Cr. This Paper was Originally Published In Japanese in J. Japan Inst. Met. Mater. 79 (2015) 491–496.In order to establish an effective method of the surface treatment proposed in this paper, some parts of the contents were revised and Figure 10 was added. The sentences of abstract, conclusions, and references were slightly modified. Two contributed authors were also added.

  • Layered Microstructure Distribution and Forming Mechanism of Laser-Processed Ni-Fe-B-Si-Nb-C Amorphous Composite Coatings

    Shujin Chen, Ruifeng Li, Qichi Zheng, Zhuguo Li

    pp. 1807-1810

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    DOI:10.2320/matertrans.M2016189

    Abstract

    A Ni-based amorphous composite coating was fabricated via laser processing. Its microstructure was observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Cooling behavior during the laser remelting process was simulated using a finite element method. The results indicated that four layers with different microstructures were formed. The layers consist of coarse dendrites, fine dendrites, equiaxed dendrites, and a layer of NbC particles/amorphous phase. Heterogeneous nucleation from NbC particles was observed at the clad/remelt interface. An amorphous phase was the primary phase in the laser remelted layer. Numerical simulation results showed that the cooling rates decreased along the depth direction from the top coating surface. The cooling rate was on the order of 104 K/s. When the cooling rate was higher than the critical cooling rate threshold, an amorphous phase was formed in the remelted layer after the laser remelting process.

  • Effect of Surface Deposits on Nitriding Layer Formation of Active Screen Plasma Nitriding

    Akio Nishimoto, Takahiro Fukube, Toshiya Tanaka

    pp. 1811-1815

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    DOI:10.2320/matertrans.M2016209

    Abstract

    Austenitic stainless steel SUS 316L was nitrided by active-screen plasma nitriding (ASPN) to investigate the effect of surface deposits from the screen on the nitriding layer formation. ASPN experiments were carried out using a DC plasma-nitriding unit. The sample was placed on the sample stage in a floating potential (bias-off) and a cathodic potential (bias-on). The screen, which was SUS 316L expanded metal with 38% open area ratio, was mounted on the cathodic stage around the sample stage. Nitriding was performed in a nitrogen-hydrogen atmosphere with 25% N2 + 75% H2 for 18–180 ks at 673 K under 200 Pa by the ASPN process. After nitriding, the nitrided samples were examined using scanning electron microscopy, X-ray diffraction, Vickers microhardness and glow discharge optical emission spectroscopy. From the surface observation of the nitrided sample, deposits were observed on the top surface of the sample nitrided with bias-off whereas deposits were not on that nitrided with bias-on. The nitrogen-expanded austenite (S phase) was formed on the surface of both samples. Layer thickness of the S phase increased with increasing the nitriding time. Additionally, the degree of an increase of the layer thickness of the S phase nitrided with bias-on was approximately 2.5 times greater than that nitrided with bias-off. This result suggests that the ASPN treatment with bias-on is effective for the increase of the nitriding layer thickness.

  • Formation of Al-Ni Intermetallic Layers Lining Microchannels Produced by Powder-Metallurgical Process Using Aluminum Sacrificial Cores

    Tatsuya Ohmi, Naoya Hayashi

    pp. 1816-1822

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    DOI:10.2320/matertrans.M2016206

    Abstract

    The mechanism of in-situ formation of Al-Ni intermetallic lining layers during microchannel formation in nickel bodies by a powder-metallurgical process has been investigated. Aluminum wire was used as a sacrificial core that gives the shape of the microchannel and supplies the alloying element for the lining layer. Nickel powder compacts with 29(±1)% porosity containing aluminum wires were heated from room temperature and then quenched at various temperatures between 873 K and 1473 K. Porous intermetallic lining layers were clearly recognized at temperatures above 1073 K. Each lining layer was built up from an outward-growing layer and an inward-growing layer. Change in the voidage in the outward-growing layer during heat treatment and the formation of a high-voidage zone around the lining layer were accounted for in terms of phase equilibria and unequal diffusion rates of the alloy elements in the Al-Ni intermetallic compounds and nickel solid solution.

  • Quantitative Evaluation of Hydrogen Solubility and Diffusivity of V–Fe Alloys toward the Design of Hydrogen Permeable Membrane for Low Operative Temperature

    A. Suzuki, H. Yukawa, T. Nambu, Y. Matsumoto, Y. Murata

    pp. 1823-1831

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    DOI:10.2320/matertrans.MAW201604

    Abstract

    A concept for alloy design of hydrogen permeable membrane with high hydrogen permeability and long-term durability has been proposed in view of the PCT factor, fPCT, and the ductile-to-brittle transition hydrogen concentration, DBTC. As an example, V–10mol%Fe alloy has been designed for low operative temperature, which exhibits excellent and stable hydrogen permeability for at least 1000 hours at 573 K without brittle fracture.In addition, the alloying effects of iron on the hydriding property and the hydrogen diffusivity have been investigated quantitatively in order to establish a way to design optimal composition of V-Fe based hydrogen permeable alloy under any given conditions. It is found that the addition of iron into vanadium increases linearly the partial molar enthalpy change, ΔH0.2, of hydrogen for hydrogen dissolution, but scarcely affects on the partial molar entropy change, ΔS0.2. It is also found that both the activation energy, E and the pre-exponential factor, B0, of the mobility for hydrogen diffusion decrease linearly with increasing the mole fraction of iron, meaning that the addition of iron enhances the hydrogen diffusivity at low temperature below about 700 K. The evaluation in view of the four parameters, ΔH0.2, ΔS0.2, E and B0, is useful for deep understanding of the property of hydrogen permeable metal membrane. Following the concept for alloy design in view of these four parameters, optimal alloy composition can be designed under any given conditions. The hydrogen permeability of the designed alloy under the condition can also be estimated quantitatively.

  • High-Pressure Synthesis of New Magnetic Compound in Mn–Li–N System

    Itsuki Matsushita, Atsunori Kamegawa, Satoshi Sugimoto

    pp. 1832-1836

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    DOI:10.2320/matertrans.M2016096

    Abstract

    A new magnetic compound in the Mn–Li–N system was synthesized at GPa-order pressure. This compound had a body-centered-tetragonal (bct) structure (space group: I4/mmm, No. 139) with lattice parameters a = 0.29186 nm and c = 0.39108 nm. The compound composition ratio was Mn:N = 2:1. The saturation magnetization and coercivity of a sample synthesized under 5 GPa at 1100℃ for 2 h were 17.73 A∙m2/kg and 310.7 kA/m, respectively.

  • Mobility of Twin Boundaries in Fe-Pd-Based Ferromagnetic Shape Memory Alloys

    Federico Guillermo Bonifacich, Osvaldo Agustín Lambri, José Ignacio Pérez-Landazábal, Damián Gargicevich, Vicente Recarte, Vicente Sánchez-Alarcos

    pp. 1837-1844

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    DOI:10.2320/matertrans.M2016243

    Abstract

    The mobility of twin boundaries in (at.%) Fe70Pd30, Fe67Pd30Co3 and Fe66.8Pd30.7Mn2.5 has been studied by mechanical spectroscopy. Measurements were carried out in amplitude dependent damping regime. A new model based on the Friedel theory was developed to obtain the activation energy (～2 kJ/mol) for twin boundaries motion. The model describes the amplitude dependent damping from thermally assisted break-away of dislocations. Interaction processes among twin boundaries, dislocations and vacancies during the recovery of the structure are also discussed. Moreover, a damping peak related to a dislocation dragging mechanism controlled by vacancies migration without break-away, earlier reported in Fe-Pd alloys, was also found in Fe-Pd-Co and Fe-Pd-Mn alloys.

  • Phase Stability of Nickel-Base Single Crystal Superalloys Containing Iridium Substituting for Ruthenium

    Yuhi Mori, Tadaharu Yokokawa, Toshiharu Kobayashi, Hiroshi Harada, Shinsuke Suzuki

    pp. 1845-1848

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    DOI:10.2320/matertrans.MAW201606

    Abstract

    Phase stability of Ni-base single crystal superalloys was compared between Ir addition and Ru addition. Investigated alloys were TMS-238 and its derivative alloys. The thermodynamic equilibrium microstructures obtained by a strain aging showed that the volume fractions of γ, γ' and topologically close packed (TCP) phases in the alloys were virtually the same to each other without depending on Ir substitution for Ru. On the other hand, the time temperature transformation diagrams obtained by an ordinary aging showed a significant delay in TCP precipitation in the alloys with Ir substitution. The delay in the TCP precipitation might be attributed to the smaller interdiffusion coefficient of Ir-Ni, compared with one of Ru-Ni. The smaller interdiffusion coefficient may affect the kinetics of the TCP precipitation.

  • Investigations of Join-Ability and Energy Absorption of Clinched Joints in Titanium and Aluminum-Lithium Sheet Materials

    Xiaocong He, Tongxin Yu, Aifeng Gao, Yue Zhang

    pp. 1849-1852

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    DOI:10.2320/matertrans.M2016223

    Abstract

    The join-ability and energy absorption of extensible die clinched joints in titanium and aluminum-lithium sheet materials were investigated in this paper. Tensile-shear tests were carried out to characterize the mechanical properties of different clinched joints made of the similar and dissimilar alloy sheets combinations. The quality assessment, load-bearing capacity and energy absorption of different clinched joints were studied. Results showed that the load-bearing capacity and energy absorption of clinched joints with titanium as upper sheets are higher than that of the clinched joints with aluminum-lithium as upper sheets.

  • Effect of Al Composition on the Corrosion Resistance of Mg-14 mass% Li System Alloy

    Taiki Morishige, Yutaro Obata, Takayuki Goto, Tomoki Fukagawa, Eiji Nakamura, Toshihide Takenaka

    pp. 1853-1856

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    DOI:10.2320/matertrans.M2016247

    Abstract

    Mg-Li system alloys have poor corrosion properties, especially cold-rolled sheet leads to exfoliation corrosion as a result of long-term immersion test. Addition of aluminum element to Mg-14 mass% Li alloy could be suppressed the occurrence of exfoliation corrosion. However, excess addition of aluminum to Mg-14 mass% Li alloy causes the degradation of corrosion resistance. In this study, the composition of aluminum in Mg-14 mass% Li was optimized to improve the corrosion property. 3 mass% of Al addition could be suppressed the corrosion rate because enough aluminum element dissolved into matrix and precipitation of the second phase was inhibited.

  • Editor's Announcement

    pp. 1857-1857

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    DOI:10.2320/matertrans.EAM2016701

  • © 2016 The Japan Institute of Metals and Materials

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