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

MATERIALS TRANSACTIONS Vol. 59 (2018), No. 2

  • Formation Mechanism of Lath Martensite in Steels

    Yoshinori Murata

    pp. 151-164

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    DOI:10.2320/matertrans.M2016430

    Abstract

    Lath martensite formed in low carbon steels plays a crucial role in the mechanical properties of heat-resistant steels containing approximately 0.1 mass%C. Lath martensite exhibits a hierarchical microstructure comprising packets, blocks and laths. Martensitic transformation is the phase transformation accompanying ordered shear deformation without atom diffusion. The hierarchical microstructure is formed as a result of the relaxation of the strain energy caused by the deformation; however, to the best of our knowledge, the formation mechanism of this microstructure has not been understood thus far. In this paper, the experimental results and phenomenological formation mechanism reported thus far are reviewed, and a new mechanism (including two types of slip deformation (TTSD) model) is introduced, which is constructed by independently considering two kinds of slip deformations using the slip deformation model proposed by Khachaturyan. In addition, the TTSD model allows for the simulation of the martensite phase formation by the phase-field method. Furthermore, the TTSD model permits the prediction of lath martensite features including the existence of sub-blocks and high density of dislocations in lath. In particular, the presence of laths in a block structure is clearly explained by the TTSD model for the first time. This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 80 (2016) 669–683.

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  • PREFACE

    Masanori Kajihara

    pp. 165-165

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    DOI:10.2320/matertrans.MPR2018901

  • Very Fine Structured DP Steel with Tempered-Martensite Matrix Fabricated by Fast Heating

    Nobuo Nakada, Masahiro Tsukahara, Kengo Fukazawa, Yoshitaka Misaka

    pp. 166-171

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    DOI:10.2320/matertrans.MC201705

    Abstract

    In order to fabricate new type of low carbon dual phase steel with excellent local deformability, cold-deformed lath martensite was intercritically annealed at ferrite and austenite two phase region at very high heating rate of 500 K/s by high-frequency induction heating in a low carbon chromium-molybdenum steel (0.15%C-1.15%Cr-0.15%Mo). No recrystallization of lath martensite to ferrite took place upon heating because of the fast heating and the pinning effect of very fine M3C particles. Consequently, austenite grains densely nucleated in the non-recrystallized lath martensite matrix during intercritical annealing, resulting in the formation of very fine dual phase structure consisting of tempered lath martensite matrix and finely dispersed fresh martensite grains. The very fine structured dual phase steel exhibited higher local deformability while maintaining good strength-elongation balance compared with the dual phase steel with recrystallized-ferrite matrix due to the high density of distribution of fine fresh martensite grains and low hardness ratio of fresh martensite to matrix.

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  • Molecular Dynamics Simulation of Local Structure Evolution in Cu Amorphous during Uniaxial Tension and Compression

    Ye Li, Hongye Liang, Xing Zhang

    pp. 172-175

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    DOI:10.2320/matertrans.MC201701

    Abstract

    The local structural arrangement of the Cu amorphous was investigated during uniaxial tensile strain and compressive strain using molecular dynamics simulation, respectively. The amorphous of pure Cu system was get through high cooling rate in simulated situation. The amorphous phase of the system did not change in the tension process, whereas in the compression process the amorphous phase transform to bcc crystal structure. The tensile deformation promoted the expansion of the shear transition zones, whereas there is no similar result was observed in the compressive deformation process.

  • Effect of Thermal Cycles on Microstructure of Er2O3 Thin Film on SUS316 Substrate with Y2O3 Buffer Layer Fabricated by MOCVD Method

    Masaki Tanaka, Seungwon Lee, Kenji Matsuda, Yoshimitsu Hishinuma, Katsuhiko Nishimura, Teruya Tanaka, Takeo Muroga

    pp. 176-181

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    DOI:10.2320/matertrans.MC201710

    Abstract

    Erbium oxide (Er2O3) and Yttrium oxide (Y2O3) are the promising materials to realize an advanced breeding blanket system because of good electrical resistivity and effective hydrogen permeation suppression. In this report, Er2O3 thin film fabricated via MOCVD process with the Y2O3 layer formed on SUS316 substrate before and after thermal cycles to investigate the effect of thermal cycling. Their microstructure was confirmed by SEM, AFM, TEM and STEM. The surface morphology of samples after thermal cycling has small granular structure than samples before thermal cycling and without buffer layer. According to cross sectional observation by TEM and STEM, Er2O3 and Y2O3 have different columnar structure, while buffer layer did not avoid diffusing elements from SUS316 substrate to Er2O3 layer. The thermal cycling test had not been affected to the growth direction of Er2O3 and Y2O3 layers, which is mostly cube-cube relationship.

  • Microstructural Subsequence and Phase Equilibria in an Age-Hardenable Cu-Ni-Si Alloy

    Satoshi Semboshi, Mikio Ishikuro, Akihiro Iwase, Takayuki Takasugi

    pp. 182-187

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    DOI:10.2320/matertrans.MC201706

    Abstract

    We investigated the microstructural subsequence and phase equilibrium of Cu-4.3 at% Ni-2.2 at% Si alloy specimens during isothermal aging over a temperature range of 698 K to 873 K. During aging in this temperature range, the microstructure of the specimens evolved in the following sequence; continuous precipitation of fine disk-shaped δ-Ni2Si in the matrix, discontinuous precipitation of cellular components containing coarse fiber-shaped δ-Ni2Si at grain boundaries, and then occupation of the specimen with cellular components. By analyzing the variations in the hardness and electrical conductivity with aging time as well as temperature, we described the kinetics of the highest number density of fine δ-Ni2Si continuous precipitates. Based on the chemical analyses of the specimen in a phase equilibrium state using an extraction procedure, we proposed a revised solvus of solutes Ni and Si in the Cu solid solution phase, as well as Cu in the δ-Ni2Si intermetallic phase in a Cu–δ-Ni2Si pseudo-binary system.

  • Effects of Liquid Indium Particles on Recrystallization and Grain Growth of αFe in Fe-In Alloys

    Takehito Hagisawa, Toshihiro Omori, Ikuo Ohnuma, Ryosuke Kainuma, Kiyohito Ishida

    pp. 188-197

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    DOI:10.2320/matertrans.MC201707

    Abstract

    Recrystallization, grain growth, and particle ripening behaviors of pre-deformed Fe-In alloy specimens in liquid-particle dispersion microstructures were investigated by microstructural observation. Liquid In particles were trapped by grain boundaries of recrystallized grains, and the trapped particles were dragged by the grain boundaries during grain growth. The recrystallization and the grain growth of the αFe matrix were extremely retarded by the addition of In. The controlling diffusion mechanism of the growth of matrix grains and the ripening of intergranular liquid In particles changed from interfacial diffusion between matrix and particles to impurity diffusion through liquid In particles with increasing volume fraction of liquid In particles.

  • Growth Behavior of Compounds during Reactive Diffusion in the Solid-Cu/Liquid-Sn System

    S. Murakami, M. O, M. Kajihara

    pp. 198-203

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    DOI:10.2320/matertrans.MC201712

    Abstract

    Semi-infinite Cu/Sn diffusion couples prepared by an isothermal bonding technique were used to examine experimentally the kinetics of reactive diffusion in the solid-Cu/liquid-Sn system. Isothermal annealing of the diffusion couple was conducted in the temperature range of T = 753–793 K for various periods up to t = 144 ks (40 h). Owing to annealing, an intermetallic layer composed of ε-Cu3Sn with scallop morphology and δ-Cu4Sn with rather uniform thickness is formed at the original Cu/Sn interface in the diffusion couple. The total thickness of the intermetallic layer is proportional to a power function of the annealing time, and the exponent of the power function is close to unity at all the annealing temperatures. Such a power relationship holds also for the ε-Cu3Sn scallop and the δ-Cu4Sn layer. This means that volume diffusion controls the growth of the ε-Cu3Sn scallop and the morphology of the Cu3Sn/Sn interface influences the rate-controlling process. In contrast, the growth of the δ-Cu4Sn layer is governed by the interface reaction at the moving Cu4Sn/Cu interface. Adopting a mean value of 0.87 for the exponent, we obtain a value of 129 kJ/mol for the activation enthalpy of the intermetallic growth.

  • Effects of Tungsten Addition and Isothermal Annealing on Microstructural Evolution and Hardening Behavior of Two-Phase Ni3Al-Ni3V Intermetallic Alloys

    Akinori Uekami, Satoshi Semboshi, Yasuyuki Kaneno, Takayuki Takasugi

    pp. 204-213

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    DOI:10.2320/matertrans.MC201702

    Abstract

    The effects of tungsten (W) addition and isothermal annealing on the microstructure and related hardening behavior were investigated for the dual two-phase Ni3Al-Ni3V intermetallic alloys. The microstructures in the homogenized alloys depended on the W substitution manner for Ni, Al or V. Distinctively fine and coherent dual two-phase microstructures were developed for the homogenized alloy in which W was substituted for Al and resulted in the largest hardness in the investigated alloys. Disk-shaped and fine Ni4W particles were precipitated in the channel region of the isothermally annealed alloy in which W was substituted for Ni. Hardness of the alloys increased with increasing annealing time and made a peak, followed by decrease, irrespective of the W substitution manner. The initial increase of hardness at early annealing time was attributed to the maturity of the eutectoid microstructure prematurely developed in the channel region before annealing. The simultaneous addition with W and Nb stabilized the eutectoid microstructure in the channel region and suppressed softening at a prolonged annealing time. Hardening mechanisms for the homogenized and annealed alloys were discussed in terms of the microstructural and phase stability and compared with the alloys with the simultaneous addition with W and Nb.

  • Anisotropic Ferrite Growth and Substructure Formation during Bainite Transformation in Fe-9Ni-C Alloys: In-Situ Measurement

    Tadashi Furuhara, Shin-ya Abe, Goro Miyamoto

    pp. 214-223

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    DOI:10.2320/matertrans.MC201714

    Abstract

    Growth kinetics of bainitic ferrite is re-examined in Fe-C-9%Ni alloys by taking the morphological anisotropy of bainitic ferrite due to crystallographic constraint in in-situ observation using confocal laser scanning microscopy. The true lengthening kinetics determined, after identifying crystallographic variants of bainitic ferrite in post-transformation EBSD measurement, is faster by a factor of about 4 than the apparent lengthening kinetics measured as a projection on the observed surface. The lengthening rate is mostly equal to or still slower than those predicted by carbon diffusion controlled kinetics. Variant pairing of bainitic ferrite belonging to the same Bain group occurred preferably in development of local substructure as previously reported in low-alloy low-carbon steels.

  • Martensitic Transformation and Magnetic Properties of Ni-Co-Mn-In-Gd Ferromagnetic Shape Memory Alloys

    Kaifeng Li, Li Gao, Yongcheng Liang

    pp. 224-229

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    DOI:10.2320/matertrans.M2017311

    Abstract

    The effect of rare earth Gd on the microstructure, martensitic transformation and magnetic properties of Ni45Co5Mn35In15−xGdx (0 ≤ x ≤ 1.6) alloys is investigated. The addition of Gd results in a change in the microstructure. With the increase of Gd content, the grain size is clearly reduced and the volume fraction of the second phase increases gradually. And then the second phase along the grain boundaries grows and connects to each other. Some disperse in the grains. One-step thermoelastic martensitic transformation is observed in Ni45Co5Mn35In15−xGdx alloys. When the Gd content reaches 0.8 (at%), the martensite transformation temperature decreases first, and then rises with the increase of Gd content. The near-room-temperature magnetocaloric effect (MCE) in polycrystalline Ni45Co5Mn35In14.2Gd0.8 alloys is observed. The magnetic-field-induced inverse phase transformation from martensite to austenite phase is confirmed. The inverse magnetic entropy change (ΔSM) reaches 17.78 J/kg K for Ni45Co5Mn35In14.2Gd0.8 alloy at 277 K and its Rc is about 356 J Kg−1 at an applied field of 5 T.

  • Interface-Related Shear Banding Deformation of Amorphous/Crystalline CuZr/Cu Nanolaminates by Molecular Dynamics Simulations

    Yan Cui, Yoji Shibutani, Ping Huang, Fei Wang, Kewei Xu, Tianjian Lu

    pp. 230-236

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    DOI:10.2320/matertrans.M2017286

    Abstract

    Whereas adding a soft crystalline layer into metallic glasses can modify shear banding deformation and enhance plastic deformability, interface-related plastic behavior played a crucial role in the shear banding deformation of amorphous/crystalline nanolaminates (A/CNLs). In this work, the influence of amorphous/crystalline interface (ACI) and grain boundary (GB) on the shear banding deformation of amorphous Cu55(at%)Zr45(at%)/crystalline Cu nanolaminates were systemically studied using molecular dynamics (MD) simulations. On one hand, ACIs with both [110] and [111] interfacial crystal orientations were constructed. Results showed that localized interfacial sliding initiate at [111] interfacial orientation at an extremely low stress, due mainly to abrupt compositional mixing at the ACI. On the other hand, GB either vertical or parallel to ACI were specially designed. Large numbers of pre-existing boundary dislocation activations along the vertical GB were shown to facilitate the shear banding formation of A/CNLs. In contrast, interfacial dislocation emission and dislocation slip transmission across the parallel GB postponed the shear banding formation. These results enable controlling shear banding deformation of A/CNLs and ensure their reliable application via nanoscale interfacial design.

  • Water Droplet Erosion Resistance of Aluminizing Diffusion Coatings on Steel Tubes

    Yoshinori I. Oka, Keiji Ishikawa, Hideshi Tezuka

    pp. 237-243

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    DOI:10.2320/matertrans.M2017217

    Abstract

    Problems with erosion caused by water droplet impingement occur in high-temperature and high-pressure pipelines and in steam turbines in energy conservation systems and power plants. Advances in material development and the use of highly resistant materials are needed in order to insure a high-performance level of plant maintenance. The use of ceramic coatings or intermetallic diffusion coatings on pipe steels is thought to be beneficial for the improvement of corrosion and erosion resistance. Aluminizing diffusion coatings on a few types of steel tubes with different coating thicknesses were prepared for this experiment. Erosion tests on water droplet impingement were conducted on the internal surface of tubes at a droplet velocity of 148 m s−1 using a water droplet testing apparatus. Erosion resistance was evaluated based on the incubation period and an average damage-depth rate for aluminizing diffusion coatings and steel substrates. Hardness distributions of the coating materials on cross-sectional surfaces revealed a harder layer on the surface, a functional gradient hard layer, and a soft steel substrate. EDX analyses on aluminizing diffusion coatings showed irregularly large grains of alumina, a microstructural intermetallic compound of Al-Fe-C with small grains of alumina, and an Al-Fe-C gradient diffusion layer toward the substrate. Good erosion resistance was obtained with a microstructural intermetallic compound layer with small grains of alumina. However, the erosion resistance of the diffusion layer with large grains of alumina was inferior. The erosion resistance depended on the combinations of the diffusion layer, alumina grains, and steel substrate, but not necessarily on the thickness of the diffusion layers.

  • Observation of Cation Diffusion and Phase Formation between Solid Oxide Layers of Lanthanum Gallate-Based Fuel Cells

    Hiromi Eba, Chikako Anzai, Satoshi Ootsuka

    pp. 244-250

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    DOI:10.2320/matertrans.M2017257

    Abstract

    The structural irregularities of solid-oxide layers for fuel cells prepared by electrophoretic deposition and co-sintering were examined using electron-probe microanalysis (EPMA) and X-ray analysis. The solid-oxide electrolyte layer with Sr- and Mg-doped lanthanum gallate (LSGM) prepared on a NiO-yttria-stabilized zirconia (YSZ) anode with an inserted Gd-doped ceria (GDC) buffering interlayer was not rigid. EPMA of the cross-section showed diffusion of La and Sr out of LSGM, and Ni, Y, and Zr out of NiO-YSZ. Using synchrotron radiation, X-ray absorption near-edge structures of the layer cross-sections were examined using an X-ray fluorescence yield method. The spectral features supported the formation of SrLaG3O7 and La-doped GDC by a reaction between the layers. The formation of these and other oxides was also confirmed by X-ray powder diffraction patterns. Because the electrophoretic deposition layers were co-sintered, elemental diffusion must have occurred before the synthetic powders were well fused and fixed in each layer. As an alternative to GDC, La-doped ceria (LDC) was synthesized, and La diffusion between LSGM and LDC was examined using X-ray powder diffraction. LDC, which contains 40% La, seems to be the best material to suppress La migration.

  • Formation of Antireflection Thin-Film Glasses Using Organopolysiloxane by Low-Temperature Process and Surface Modification

    Hiroyuki Miwa, Atsuki Kodama, Htay Win, Koichi Murakami, Taku Takahashi, Fumitaka Ohashi, Shuichi Nonomura

    pp. 251-254

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    DOI:10.2320/matertrans.M2017332

    Abstract

    Porous SiOx thin films were prepared using a commercial liquid glass (LG) based on organopolysiloxane to improve the conversion efficiency of photovoltaic modules as antireflection films. Optimization of the preparation of porous SiOx films such as the ink manufacturing process was carried out by adding isopropyl alcohol (IPA) to the LG, spin coating, and annealing. Adding an ultrapure water (UW) to the ink with subsequent annealing at 300℃ resulted in the formation of a porous SiOx thin film with 4.6% reflectance at 600 nm wavelength, whose refractive index was estimated to be 1.33, which is lower than that of conventional antireflection coating films such as MgF2. In addition, the antireflection effect of the antireflection film fabricated at room temperature without dilution with UW was improved by surface modification by performing excimer vacuum ultraviolet (VUV) irradiation at room temperature and atmospheric pressure. This treatment modified the reflectance of the film from 8.1% to 7.7% at 600 nm and the refractive index from 1.44 to 1.42, which is lower than that of normal glass.

  • Solidification Microstructure of AlCoCrFeNi2.1 Eutectic High Entropy Alloy Ingots

    Takeshi Nagase, Mamoru Takemura, Mitsuaki Matsumuro, Toru Maruyama

    pp. 255-264

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    DOI:10.2320/matertrans.F-M2017851

    Abstract

    AlCoCrFeNi2.1 eutectic high-entropy alloy (EHEA) ingots were successfully obtained by high-frequency melting and centrifugal metal-mold casting under an Ar flow. The microstructure of the ingots was investigated by trans-scale observations using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and scanning transmission electron microscopy (STEM). The constituent phases of the ingots were identified as fcc and bcc phases by X-ray diffraction (XRD) analysis, and were not dependent on the position of the ingot. The microstructure was observed to have a primary fcc dendrite and fcc+bcc eutectic structure at the inter-dendrite region, regardless of the position of the ingots. The size of the solidification structure was affected by the cooling rate. Faster cooling rates resulted in finer solidification structures. TEM observations clarified the development of L12 ordering structures in the primary fcc dendrite phase, while the ordering peak could not be detected by XRD analysis. This Paper was Originally Published in Japanese in J. JFS 89 (2017) 119–129. In order to more precisely explain the background, the purpose of the study, the experimental procedures, and the results, some parts of the contents were revised. The Refs. 21, 22), and 23) were added to clarify the source of pure elements. The Refs. 12) and 35) were added to discuss the solidification microstructure in more detail. Figure 1 was slightly modified to make the casting process and the position of the ingots clearly understandable. Figure 7 was slightly modified to discuss the solidification microstructure in more detail.

  • Viscous Sintering and Structural Stabilization of Amorphous B4C Powder

    Hiroshi Kimura

    pp. 265-271

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    DOI:10.2320/matertrans.M2017269

    Abstract

    This article reports the pulsed electric current bulk synthesis and high-temperature X-ray diffraction structure of the amorphous B4C powder prepared by planetary ball milling. Solid state synthesized amorphous B4C shows two-stage structural relaxation characterized by a significant increase to 2.1 in relative integrated X-ray intensity of first amorphous diffraction peak with increasing temperature to 1573 K. Amorphous B4C can be consolidated, avoiding visible submicron sized pore without the need for additives; its temperature decreases 1473 to 1073 K by decreasing 2.5 to 1.0 mm in final sample height in combination with an increasing applied stress 100 to 120 MPa. For the amorphous B4C, subjected to full structural relaxation; the rapid densification in heating can be fairly well expressed by an Arrhenius-type equation of Newtonian viscous flow, η = ηoexp(420 kJmol−1/RT) where η is the consolidation process viscosity. Progressive structural relaxation of amorphous B4C then is described as increase in viscosity constant (ηo) having a relationship of the form, ηo = ηooexp(−335 kJmol−1/RT). The density of the consolidated amorphous B4C is estimated at 2.02 Mgm−3 at the minimum, which is 0.8 of theoretical one for stoichiometric compound. The strain rate sensitivity for bulk amorphous B4C is determined to be a significantly low value of 0.043, characteristic of inhomogeneous plastic flow in Berkovich dynamic indentation testing.

  • Effect of Calcium on the Combustion Behavior of Molten AZ91 Magnesium Alloy

    Hiroyuki Kawabata, Yusuke Yagi, Yuko Aoki, Hajime Kato, Koshiro Kitayama, Kazuma Hibi

    pp. 272-279

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    DOI:10.2320/matertrans.M2017288

    Abstract

    In this study, to obtain guidelines for inhibiting the combustion of the molten metal in magnesium alloys, AZ91D magnesium alloy and AZ91 magnesium alloy with added calcium were exposed to the atmosphere, and the surfaces of the alloys were observed. In the case of AZ91D magnesium alloy, aggregated products were observed on the surface of the molten alloy. In the case of AZ91 alloy with added calcium, aggregated products were not observed. A CaO layer was formed on the outermost surface of the molten alloy, and a MgO layer was formed below the CaO layer. With increasing exposure time, the thicknesses of these layers remained almost constant. It was considered that the CaO layer, in which aluminum did not appear, inhibited combustion by limiting the flow of magnesium vapor from the molten alloy to the atmosphere and the oxidation of magnesium over a long time.

  • Friction and Wear Behaviors of Carbon Nanotube Reinforced Silica and Alumina Matrix Composites Fabricated by Catalyst Sol-Gel and CVD Process

    Kuo-Jung Lee, Yu-Ting Yeh, Huy-Zu Cheng, Hsun-Yu Lin

    pp. 280-289

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    DOI:10.2320/matertrans.M2017266

    Abstract

    Fe(NO3)3/TEOS (tetraethoxysilane, Si(OC2H5)4)) and Fe(NO3)3/boehmite catalyst sol-gels combined with different chemical vapor deposition (CVD) growing/calcining processes were individually adopted to fabricate different carbon nanotube (CNT) composite powders and make different CNT/silica and CNT/alumina composites. Experimental results indicate that the Fe(NO3)3/TEOS and Fe(NO3)3/boehmite catalyst sol-gels with different CVD growing/calcining processes generate different products. Among those different products, CNTs could improve the tribological performance, stabilize the friction coefficient and reduce weight losses of specimens. Furthermore, ceramic products such as cristobalite, α-Al2O3 transformed from the Fe(NO3)3/TEOS and Fe(NO3)3/boehmite catalyst sol-gels at higher calcining temperatures could increase hardness and friction coefficient of specimens, however, they also result in more fluctuant friction coefficient curves and higher weight losses. The final products from different catalyst sol-gels via the two-step growing/calcining process could provide better mechanical and tribological properties of the specimens. The weight losses of CNT contained specimens with stable phase (α-Al2O3 or cristobalite) from different catalyst sol-gels via the two-step growing/calcining process are 1/4 to 1/2 of CNT free specimens and CNT contained specimens with metastable phase (γ-Al2O3 and amorphous SiO2) via the one-step growing/calcining process, respectively.

  • Recovery of Calcium Fluoride from Highly Contaminated Fluoric/Hexafluorosilicic Acid Wastewater

    Masao Morita, Giuseppe Granata, Chiharu Tokoro

    pp. 290-296

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    DOI:10.2320/matertrans.M-M2017850

    Abstract

    We investigated the recovery of calcium fluoride (CaF2) from highly concentrated hexafluorosilicic acid wastewater by neutralization–purification. Neutralization was achieved by dosing calcium hydroxide, whereas purification was carried out by alkaline leaching with sodium hydroxide. X-ray diffraction, X-ray absorption fine structure, mineral liberation analyzer, Fourier transform infrared spectroscopy and Inductively-coupled plasma atomic emission spectroscopy were used to quantify the neutralization and leaching performance and to elucidate their mechanisms. The precipitation behavior was strongly dependent on the calcium (Ca)/silicon (Si) molar ratio. For a Ca/Si ratio of 1.12, approximately 25% of the total fluorine was precipitated selectively as CaF2. By increasing the Ca/Si ratio to 3.91, the recovery yield increased to 100% because of the precipitation of CaSiF6 and the hydrolytic decomposition of hexafluorosilicate ion (SiF62−) to CaF2. The hydrolytic decomposition of SiF62− resulted in the precipitation of silicon dioxide on the surface of the previously formed CaF2. Alkaline leaching by sodium hydroxide at 70℃ resulted in an efficient removal of the silicon phase from the neutralized sludge with the formation of a CaF2 product with a grade above 90%. Leaching parameters, such as the kinetic constant and the activation energy, were determined by assuming first-order kinetics. The residual silicon phase in the final product could not be dissolved because of the formation of non-leachable SiO32−.

  • Removal of Chloride Ions from an Aqueous Solution Containing a High Chloride Concentration through the Chemical Precipitation of Friedel's Salt

    Li Pang Wang, Wei Hao Lee, Shu Man Tseng, Ta Wui Cheng

    pp. 297-302

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    DOI:10.2320/matertrans.M2017273

    Abstract

    This study explored the feasibility of removing chloride ions from an aqueous solution containing a high chloride concentration through the chemical precipitation of insoluble Friedel's salt, which was triggered by the addition of calcium and aluminum compounds. Calcium hydroxide (Ca(OH)2) and sodium aluminate (NaAlO2) were used as the reagents. Key factors for the removal of chloride ions, including the dosage of the reagents, reaction temperature, reaction time, initial pH, and initial chlorine concentration, were investigated.The results indicated that an optimal chloride removal efficiency of 84.0% was obtained when the molar ratio of Ca:Al:Cl was 10:4:1. The main crystal phases in the formed precipitates, confirmed through X-ray diffraction analysis, were Friedel's salt (Ca2Al(OH)6Cl·2H2O), portlandite (Ca(OH)2), and katoite (Ca3(Al(OH)6)2). In addition, the chloride removal efficiency increased when the reaction temperature, initial pH, and initial chlorine concentration were higher. Chlorine removal could be further improved by conducting a second-stage treatment, regardless of the residual concentrations of chloride, calcium, and aluminum ions after the first-stage treatment.

  • High Temperature Characterization of Binary and Ternary Bi Alloys Microalloyed with Cu and Ag

    Meiqi Yu, Kazuhiro Matsugi, Zhefeng Xu, Yongbum Choi, Jinku Yu, Satoshi Motozuka, Yoshiyuki Nishimura, Ken-ichiro Suetsugu

    pp. 303-310

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    DOI:10.2320/matertrans.MAW201710

    Abstract

    The s-orbital energy level (Mk) of alloying elements in a Bi cluster was used to determine the composition for alloys of this system for use as Pb-free high-temperature solders. Binary Bi-Cu and Bi-Ag alloys with ⊿Mk of 0.013–0.343 and ternary Bi-2.0Ag-0.5Cu and Bi-5.0Ag-0.5Cu alloys with ⊿Mk of 0.180 and 0.379, respectively, were fabricated and tensile tested at 423 K; here, ⊿Mk is the compositional average of Mk. The flow stress and fracture strain at 423 K increased after the alloying elements were added to the alloys. The relationships between the 0.2% proof stress, ultimate tensile strength or fracture strain, and ⊿Mk were similar to those determined previously through tests performed at 293 K. Thus, these relationships could be useful for predicting the stress and fractures strain levels based on ⊿Mk, regardless of the temperature and alloy composition. Moreover, a transition from ductility to brittleness was observed at 348–373 K for both ternary alloys. In addition, the melting points of the ternary alloys lay between 536 and 538 K, indicating that the alloys would be suitable as high-temperature solders. The contact angles of molten droplets of 10 of the experimental binary and ternary alloys on a Cu plate as determined at 973 K were 24–30°. This confirmed that the alloys exhibited good wettability with respect to Cu. Finally, the ternary Bi-2.0Ag-0.5Cu and Bi-5.0Ag-0.5Cu alloys showed thermal conductivities of 12.1 and 15.9 W/m/K, respectively, at 373 K; these were lower than that (30.4 W/m/K) of Pb-5Sn.

  • Removal of Arsenic from Crude Tin by Vacuum Distillation

    Zhenghao Pu, Jibiao Han, Yifu Li, Yongnian Dai, Bin Yang, Anxiang Wang

    pp. 311-315

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    DOI:10.2320/matertrans.M2017303

    Abstract

    Arsenic is widely present in the process of ore-dressing, tailings recovery and smelting, which is poisonous and harmful. Current technologies which can treat tin ore or crude tin have not achieved satisfactory economic and environmental effects. In particular, the existing processes have poor effects on arsenic removal from raw materials. This paper adopted vacuum distillation to deal with crude tin. In the experimental research, tin was left as a residue after the distillation, and arsenic was volatilized into the gas phase as a volatile. The impurities in crude tin were effectively removed at 1473 K for 35 min and material weight of 80 g under 5 Pa. Under this condition, 98.67 mass% of tin in the residue can be recovered, and 84 mass% of arsenic in crude tin was removed by vacuum distillation. Arsenic can be removed effectively from crude tin by using vacuum distillation.

  • Nondestructive Evaluation by Reversible Magnetic Permeability of the Residual Life of Ferritic 9Cr Steel Subjected to Creep-Fatigue Damage

    Chungseok Kim

    pp. 316-319

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    DOI:10.2320/matertrans.M2017290

    Abstract

    This work presents a nondestructive and magnetic technique for evaluating the residual life of ferritic 9Cr steel using the peak interval of reversible magnetic permeability (PIRMP). The ferritic 9Cr steel was exposed to creep-fatigue damage, and samples were prepared with different damage levels using the interrupt test. The PIRMP decreased continuously with the fraction of creep-fatigue damage. The hardness (Hv) also decreased until failure. The rates of decrease of PIRMP and Hv were 18.2% and 11.8%, respectively, compared with the as-tempered sample. The hardness and PIRMP decreased as a function of the Larson-Miller parameter (LMP) and showed a good linear relationship with the LMP. Mechanical softening was caused by microstructural degradation during creep-fatigue damage. The microstructural features were analyzed and shown to support the variation in hardness and PIRMP. The results are of interest because mechanical softening of structural materials can be evaluated nondestructively by measuring the reversible magnetic permeability. Consequently, the PIRMP offers a useful tool for estimating the residual life of structural materials in a nondestructive and reliable manner.

  • Defect Imaging from a Remote Distance by Using Scanning Laser Source Technique with Acoustic Microphones

    Atsuya Maeda, Takahiro Hayashi

    pp. 320-323

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    DOI:10.2320/matertrans.M2017326

    Abstract

    Images of defects in plate-like structures can be generated using the scanning laser source (SLS) technique. When a laser Doppler vibrometer (LDV) is used as a receiving device in the SLS technique, images of defects can be obtained through measurements conducted from a distance. Because an LDV cannot receive vibrations reflected from outdoor structures that may have rough surfaces and large fluctuations in a stable manner, this paper discusses an imaging technique using a SLS with acoustic microphones as a receiving device. The results of the experiments that were conducted using various distances between the test plate and microphone showed that the quality of the defect images gradually degraded because of the attenuation of sound in air as the distance increased. Moreover, when the laser beam was reflected back to the microphone after scattering over the plate surface, the laser beam directly generated signals in the microphone due to the photovoltaic effect or alternating heat, preventing the acquisition of defect images. Thereafter, in order to establish remote defect imaging, an acoustic transmitter was connected to the microphone unit. Most of the experimental equipment were located at a remote distance except for the small microphone unit and transmitter. The experimental system enabled the generation of images of the defect in the test plate located at distances of 4 and 6 m.

  • Joining of Anodized and Stacked Aluminum Sheets by Copper Electrodeposition: Nano-Anchor Effect

    Masataka Hakamada, Yohei Kohashi, Yuriko Yamano, Mamoru Mabuchi

    pp. 324-326

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    DOI:10.2320/matertrans.M2017315

    Abstract

    A new manufacturing process for metallic layers is proposed, where no thermal process is required. Al sheets were anodized in H3PO4, and the anodized sheets were adhered by Cu electrodeposition. The interface shear strength of Al/Cu was increased significantly from 1.5 to 64.8 MPa by the anodizing. Cu deposition in a small space between the Al sheets was important for the strong adhesion. Microstructural observation showed that Cu deposition penetrated the nanopores of an anodic aluminum oxide (AAO) film, which indicates that the nano-anchor effect played a critical role in the strong adhesion.
  • © 2018 The Japan Institute of Metals and Materials

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