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

MATERIALS TRANSACTIONS Vol. 60 (2019), No. 5

  • Grain Boundary Engineering for Control of Fatigue Fracture in 316L Austenitic Stainless Steel

    pp. 623-630

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    DOI:10.2320/matertrans.MB201804

    Roles of grain boundaries in fatigue crack nucleation and propagation in 316L austenitic stainless steel were investigated to obtain a clue to the grain boundary engineering for control of high-cycle fatigue fracture. The fatigue crack nucleation preferentially occurred at grain boundaries at the low-stress amplitude conditions less than about 160 MPa. In particular, the 82% of cracked grain boundaries were random boundaries. The fatigue crack nucleation at the random boundaries occurred irrespective of the geometrical configuration of grain boundary plane to the stress axis and the persistent slip bands (PSBs) in the neighboring grains. Although the fatigue cracks nucleated even at the annealing twin boundaries, namely the {111}/Σ3 coincidence site lattice (CSL) boundaries the crack nucleation occurred only when the surface trace of the Σ3 CSL boundaries was parallel to the PSBs in the neighboring grains. Moreover, in-situ observations of the fatigue crack propagation revealed that the grain boundaries played important roles as crack path, crack deflection sites and barrier of crack propagation, depending their character. In particular, although the Σ3 CSL boundaries became crack propagation path, the crack propagation rate locally decreased when the crack propagated along the Σ3 CSL boundaries. On the other hand, the crack propagation rate considerably increased when the crack propagated along random boundaries. The usefulness of grain boundary engineering for control of high-cycle fatigue fracture was demonstrated. The higher fraction of CSL boundaries achieved higher fatigue strength and longer fatigue life in 316L stainless steel.
  • Phase Reaction and Diffusion Behavior between AuTi and CoTi Intermetallic Compounds

    pp. 631-635

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    DOI:10.2320/matertrans.MB201806

    The phase reaction and diffusion behavior of stoichiometric AuTi and CoTi intermetallic compounds were clarified using diffusion couple technique. It was found by scanning electron microscopy equipped with energy dispersive X-ray spectroscope that two intermetallic compounds of (Au,Co)Ti3 and (Au,Co)2Ti were produced near interface between the AuTi and CoTi when heat-treated at 1173 K and 1273 K, and that only (Au,Co)Ti3 was formed when heat-treated at 1373 K. The presence of these intermetallic compounds was explained by the concentration dependent diffusivity in the diffusion couple. With increasing the heat-treatment temperature from 1173 K to 1373 K, the thickness of the diffusion layer increased from 78 µm to 200 µm. The apparent activation energy for the layer growth was estimated as 127 kJ/mol. Furthermore, the diffusion path in the isothermal section at 1173 K–1373 K in the Au–Ti–Co system was also discussed.
  • Experimental Confirmation of Grain Boundary Magnetism in Fe–Si and Fe–Sn Alloys by TEM-EELS

    pp. 636-641

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    DOI:10.2320/matertrans.MB201803

    We measured the local magnetic moments at grain boundaries in Fe–Si and Fe–Sn alloys by electron energy loss spectroscopy with a transmission electron microscope and evaluated the relation between the grain boundary magnetism and grain boundary segregation in Fe–Si and Fe–Sn alloys. We found that the local magnetic moments at the random boundaries in these alloys were remarkably reduced in comparison with those in pure Fe, whereas there was no considerable change at the Σ5 grain boundary and low-angle boundary. The variation of the local magnetic moments at impurity-segregated grain boundaries was explained by the competition between magnetovolume effect and hybridizations of electrons. It was found that the grain boundary character remarkably affects this hybridization. The decrease in the magnetic moments at random grain boundaries was more pronounced in the Fe–Sn alloy than in the Fe–Si alloy.
  • Elucidation of Microstructure Formation Mechanism through Competitive Reactions during Initial Hydrogenation in Mg/Cu Super-Laminate Composites

    pp. 642-651

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    DOI:10.2320/matertrans.MB201807

    Microstructure formation mechanism through competitive reactions during initial hydrogenation in Mg/Cu super-laminate composites (SLCs) was investigated. Mg/Cu SLCs (Mg2Cu composition) were fabricated by accumulative roll bonding (ARB) and composed of laminate structures of Mg and Cu layers with the thickness of few hundreds nm. During the heating process of initial hydrogenation of Mg/Cu SLCs, hydrogenation of Mg and alloying of Mg with Cu followed by hydrogenation of Mg2Cu occurs competitively. It is found that microstructures of Mg/Cu SLCs during initial hydrogenation have changed drastically depending on the order of hydrogenation of Mg and Mg2Cu. The microstructures of Mg/Cu SLCs after initial hydrogenation can be categorized in three types such as (1) MgCu2 network, (2) MgCu2 sheath and (3) MgCu2 layer. Features of differential scanning calorimetry (DSC) profiles of the first cycle were well explained by this microstructure formation mechanism. In order to achieve only MgCu2 network structure, it is important to get fine, even and uniform microstructures in Mg/Cu SLCs. The large number of ARB cycles is inefficient. Changing flow properties such as annealing during ARB, warm-rolling and ultrasonic assisted rolling can be good strategies for that purpose.
  • Thermoelectric Properties of Nearly Single-Phase β-FeSi2 Alloys Fabricated by Gas-Atomized Powder Sintering

    pp. 652-661

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    DOI:10.2320/matertrans.MB201805

    Thermoelectric alloys having nearly β-FeSi2 single-phase microstructure were fabricated by sintering gas-atomized powders using the hot pressing. Since the β-FeSi2 phase is formed by the peritectoid reaction between ε-FeSi and α-Fe2Si5 phases, the reaction rate for the completion of β-FeSi2 phase transition strongly depends on the diffusion path length which is governed by the morphology and size of solidified microstructure consisting of ε and α phases. It has been indicated by the wedge drop cast using arc melting that producing fine and fully eutectic microstructure by rapid solidification is quite effective for the completion of β-FeSi2 phase transition. An argon gas atomization process was chosen as a rapid solidification technique to produce fine and homogeneous alloy powder having fully ε and α eutectic microstructure, which was turned out to be beneficial for the formation of β-FeSi2 single-phase microstructure by a short time annealing even within 30 minutes at 1073 K for the gas-atomized powders with the averaged particles size of 20 µm and under in diameter. Thermoelectric properties were evaluated for these nearly single-phase β-FeSi2 sintered alloys with the addition of doping elements, n-type Co and p-type Mn, 1.67 at% respectively. The absolute value of Seebeck coefficient and electrical conductivity are higher in a p-type Mn alloy than an n-type Co alloy.
  • Compressive Deformation Behavior and Magnetic Susceptibility of Au2CuAl Biomedical Shape Memory Alloys

    pp. 662-665

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    DOI:10.2320/matertrans.MB201810

    The compressive deformation behavior and magnetic volume susceptibility were investigated for Au2CuAl biomedical shape memory alloys in a compositional range from 25 to 45 mol%Cu. Compression tests revealed that the stress for martensite variant reorientation was 282 MPa in Au2CuAl, and the value increased with the Cu content. On the other hand, the slip stress was higher at intermediate compositions. Moreover, intergranular fracture was suppressed during compressive deformation. Calculated antiphase boundary (APB) energies suggest the dissociation of superlattice dislocation, which leads to the active slip of 〈111〉-type. The measured magnetic volume susceptibility was −2.7 × 10−6 in Au2CuAl, hence, this alloy is judged to be metal-artifact-free in magnetic resonance imaging (MRI). The magnetic susceptibility increased up to +7.0 × 10−6 with increasing Cu content.
  • Effect of Cr Addition on the Phase Equilibria and Oxidation Behavior of NbSi2

    pp. 666-673

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    DOI:10.2320/matertrans.MB201809

    Effect of Cr addition on the phase equilibria and oxidation behavior of NbSi2 was investigated. Although the crystal structures of NbSi2 and CrSi2 are both C40, they form separated ranges of homogeneities in the Nb–Cr–Si ternary system. The vertical section passing through the NbSi2 and CrSi2 binary edges were experimentally determined. A binary NbSi2 alloy exhibited poor oxidation resistance, showing pest-like behavior upon cyclic oxidation at temperatures from 800 to 1200°C. On the other hand, Cr addition significantly improved the oxidation resistance of NbSi2. The oxide layers that developed on the Nb–Cr–Si ternary alloys consisted of NbCrO4, Cr2O3, and SiO2, and the formation of Cr2O3 and NbCrO4 suppresses the Nb2O5 formation, and thereby suppresses the pest-like behavior of the binary NbSi2 alloy. However large Cr additions that exceed the solubility limit of NbSi2 should not be suitable, because NbSi2/CrSi2 alloys were susceptible to spalling and disintegration of the oxide scales upon cyclic oxidation.
  • PREFACE

    pp. 674-674

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    DOI:10.2320/matertrans.MPR2019902

  • High-Voltage Scanning Transmission Electron Microscopy: A Tool for Structural Characterization of Micrometer-Thick Specimens

    pp. 675-677

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    DOI:10.2320/matertrans.MC201801

    Herein, the advantages of high-voltage scanning transmission electron microscopy (STEM) as a tool for structural characterization of micrometer-thick specimens are reported. Dislocations introduced in a wedge-shaped Si crystal were clearly observed by bright-field STEM operating at 1 MV. Many of the dislocations were straight and parallel to the 〈110〉, 〈112〉 or 〈113〉 directions. The widths of the dislocations in the STEM images were almost constant at 13–16 nm (i.e., 4–5 pixels) in the thickness range between 1 and 7.5 µm. The latest high-voltage STEM instrumentation is thus useful for imaging crystal defects in micrometer-thick materials, and enables multi-scale fields of view from a few nanometers squared to over 100 µm2.
  • Effect of Nickel Concentration on Radiation-Induced Diffusion of Point Defects in High-Nickel Fe–Cr–Ni Model Alloys during Neutron and Electron Irradiation

    pp. 678-687

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    DOI:10.2320/matertrans.MC201811

    The quantitative evaluation of vacancy mobility was conducted by analyzing the void denuded zone (VDZ) width formed near grain boundaries under neutron and electron irradiation. The microstructures of Fe–15Cr–xNi (x = 15, 20, 25, 30 mass%) alloys that were neutron irradiated at 749 K were examined, and the differences in the vacancy mobility among the four alloys were qualitatively investigated. We also investigated the VDZ widths formed under electron irradiation at various irradiation temperatures (576 K–824 K) in these alloys. The VDZ widths increased with increasing Ni content in both the neutron and electron irradiation experiments, which implies an increase of the vacancy mobility. The vacancy migration energies were estimated from the temperature dependence of the VDZ widths, and the estimated energies were 1.09, 0.97, 0.90, and 0.77 eV for the alloys containing 15, 20, 25, and 30 mass% Ni, respectively. It was confirmed that these estimated energies were approximately consistent with the ones estimated by well-known dislocation loop growth rate analysis through electron irradiation experiments. From the obtained vacancy migration energies by the VDZ analysis, the effective vacancy diffusivity and excess vacancy concentration were estimated using the analytical equation of the VDZ width, which quantitatively confirmed the increase of the vacancy mobility with increasing Ni content.
  • Crystalline Evaluation of Size-Controlled Silicon and Silicon Oxide Nanoparticles Produced by Solution Plasma Discharge

    pp. 688-692

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    DOI:10.2320/matertrans.MC201810

    Li-ion batteries using Si particles as anode materials have attracted attention because of their extremely high theoretical capacities. However, they experience extensive volume expansion during lithiation in the process of charging, dramatically affecting the battery lifetime. To mitigate these expansion effects and improve the capacity, Si nanoparticles and occasionally SiOx particles have been effective. Therefore, the production of Si nanoparticles is necessary. For these purposes, the solution plasma discharge method was applied. We improved previous work on the plasma discharge method by adjusting the electrolyte medium conditions via controlling the pH, solution conductivity, electrolyte concentration, and voltage, successfully generating Si nanoparticles with diameters of <10 nm and SiOx particles of <50 nm in diameter. These crystalline Si and amorphous SiOx particles were characterized using microscopy and spectroscopy.
  • Structure and Mechanical Properties of Multi-Functional Layer Deposited on Surface of Ni–Ti Shape Memory Alloy

    pp. 693-697

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    DOI:10.2320/matertrans.MC201805

    A thin layer, about 25 nm thick, was produced in glow discharge deposition process on the surface of the NiTi shape memory alloy. Structural and chemical studies revealed that the layer consisted of two sublayers. About 7 nm thick one, adhering closely to the NiTi substrate and formed from the nanocrystalline titanium nitride was followed by 17 nm of the amorphous titanium oxide layer. The technological parameters of the glow discharge process caused that the presence of the R-phase in the matrix was identified.
  • Suppressing Geometric Phase Shift Owing to Antiphase Boundaries in Dark-Field Electron Holography

    pp. 698-703

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    DOI:10.2320/matertrans.MC201809

    Antiphase boundaries (APBs) formed in Fe70Al30 alloy have attracted significant attention because they intensify ferromagnetic spin order by atomic disordering. Electron holography can be a useful tool for examining the magnetism in APB regions, although the observations suffer from an undesired contribution from an additional geometric phase shift in the incident electron wave. This paper proposes a method based on dark-field electron holography to suppress the unwanted geometric phase shift owing to APBs in electron holograms. The results of this study yield useful information for examining APBs and other planar defects in ordered crystals.
  • Microstructure of Mg–Zn Matrix Composite Reinforced with Nano-SiC Prepared by Thixomolding

    pp. 704-707

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    DOI:10.2320/matertrans.MC201807

    Thixomolding technology was successfully used to produce Mg–5 mass% Zn matrix composites reinforced with nano-SiC. The composites containing 5 mass% of SiC nano-particles were fabricated under pure Ar or Ar+CO2 atmosphere. Microstructure characterization has been carried out by scanning and transmission electron microscopy methods. It was found that regardless of the gas used, the composites consisted of unmelted globular α(Mg) grains surrounded by small areas of a magnesium solid solution formed directly from liquid and a mixture of SiC and MgO. Reaction of CO2 with liquid alloy during process leads to the in-situ formation of MgO nano-particles, which results in an increase in the amount of oxide particles and refinement of the microstructure compared to the composite produced in pure Ar. These microstructure changes increased the hardness to 70 HV.
  • Martensitic Transformation in Nanostructured NiTi Alloy Studied by X-ray Diffraction In-Situ Heating

    pp. 708-713

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    DOI:10.2320/matertrans.MC201808

    In this work martensitic transformation of Ni-rich NiTi alloy subjected to 17, 20 and 35% cold-rolling in the martensitic state followed by annealing at 450°C for 15 min has been studied by in-situ X-ray Diffraction, Transmission Electron Microscopy and Differential Scanning Calorimetry. It has been found that the material after thermo-mechanical treatment has ultra-fine grained structure with small number of large grains with high dislocation density. Phase composition of that nanostructured alloy consists of B2 austenite, B19′ martensite and R rhombohedral phases. B2 and B19′ were stable at high as well as at low temperatures. DSC measurements revealed that the studied material shows multistage character of phase transformation. Therefore it was decided to adopt in-situ XRD analysis.
  • SEM and TEM Studies on In-Situ Cast Al–TiC Composites

    pp. 714-717

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    DOI:10.2320/matertrans.MC201806

    This work concerns microstructure investigation of aluminum based composites strengthened with the TiC nanoparticles. The composites were fabricated by the casting method combined with in-situ formation of TiC particles. Transmission electron microscopy observation shown that the average size of TiC particles was close to 140 nm. HRTEM investigation of the interface between Al matrix and TiC particles shown the existence of misfit dislocation located in the Al-matrix, 2 nm far from interface boundary. Two other, bigger kinds of particles with size of several micrometers and blocky shape of α-Al2O3 and TiAl3 phases were also identified in the investigated composites which can influence both strengthening mechanism and plasticity.
  • Correlation between the Effective Amounts of Elements in TbFeCo Thin Films and Their Magnetic Properties

    pp. 718-725

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    DOI:10.2320/matertrans.M2019001

    In this study, TbFeCo thin films were prepared using DC-magnetron sputtering technique utilizing a conventional batch-type sputtering machine. The properties such as magnetic hysteresis loops and magneto-optical properties of the obtained films were measured. Furthermore, we precisely evaluated the “effective” amounts of elements, i.e., the amounts of constituents released by oxidation, in TbFeCo thin films. We also attempted to control the amounts of effective elements by changing the pre-sputtering condition before film preparation. This is because the pre-sputtering process greatly affected the effective amounts of elements in the prepared TbFeCo thin films, such that the magnetic properties were drastically different from sample to sample by altering the pre-sputtering condition. Insufficient pre-sputtering led to a relatively high oxygen content in the films in comparison with those prepared with sufficient pre-sputtering. Outstanding perpendicular magnetic anisotropy in the out-of-plane direction was observed in a film prepared after 60 min of pre-sputtering, which exhibited a coercivity (Hc) value of 6.4 kOe from magnetic hysteresis measurements and 8.2 kOe from magneto-optical polar Kerr hysteresis measurements at an incident light of wavelength 700 nm. The saturation value of the polar Kerr rotation angle (θK) of this film was approximately 0.3°, which is comparable to the theoretically optimized value. Therefore, we demonstrated that high-quality TbFeCo films can be obtained with high reproducibility by using a simple batch-type sputtering machine and that there is a strong correlation between effective amounts of elements in TbFeCo thin films and their magnetic properties. This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 82 (2018) 140–146.
  • Evaluation of the Solidification Control Parameters in the Bridgman Process

    pp. 726-731

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    DOI:10.2320/matertrans.M2019021

    Single crystals are widely applied in semiconductors and turbine blades and manufactured by directional solidification. The solidification control parameters such as the withdrawal rate, axial temperature gradient and cooling rate are the key parameters in directional solidification. Through a mathematical analysis, we derive the explicit relationships between the solidification control parameters and the physical and geometrical parameters. The accuracy of these relationships is high which is proven by the comparisons between the accurate values and the approximate values. These relationships give deep understanding into the directional solidification process. Moreover, they provide guidance for the manufacturing of directionally solidified crystals. Additionally, these relationships establish a connection between the microstructure and the physical and geometrical parameters.
  • Corrosion Behavior of ASTM A1008 Carbon Steel in Mixtures of HNO3, H2SO4, and HCl Using Immersion and Polarization Methods

    pp. 732-736

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    DOI:10.2320/matertrans.M2018315

    Acids provide corrosive environments that have their own behavior and characteristics when reacted with metal. Much research has been conducted to determine corrosion behavior of metals in acidic environments; however, little has been published concerning the corrosion behavior of ultralow carbon steel in mixed acid solutions, although such systems are widely used in the textile, chemical, and fertilizer industries. Corrosion behavior of ASTM A1008 ultralow carbon steel in mixtures of HNO3, H2SO4, and HCl was investigated using immersion and polarization methods. The HCl concentration was held constant at 1 M and the HNO3 and H2SO4 concentrations varied to 0.1 M, 0.5 M, and 1.0 M. Under these conditions, a synergistic effect between HNO3 and H2SO4 was observed, which thinned the metal, while HCl caused pitting of the metal surface. The results showed that the corrosion rate of the metal was enhanced as the acid concentrations increased, especially that of HNO3. The corrosion products were identified as iron(III) oxide [Fe2O3] and rhomboclase [H5Fe3+O2(SO4)2·2(H2O)].
  • Effect of Sc and Zr on Al6(Mn,Fe) Phase in Al–Mg–Mn Alloys

    pp. 737-742

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    DOI:10.2320/matertrans.M2018392

    The effects of Sc and Zr on the shape, size, and number density of Al6(Mn,Fe) phase in Al–5Mg–0.7Mn alloys were investigated by this article. The results showed that Sc and Zr can form strengthening particles of Al3Sc and Al3(Sc,Zr), which have the effect of refining grains and modifying the morphology and distribution of Al6(Mn,Fe) phase. The OM, SEM, and TEM images indicate that with the formation of primary Al3Sc and Al3(Sc,Zr), the shape of Al6(Mn,Fe) became more regular, size of Al6(Mn,Fe) became smaller, and the number density of Al6(Mn,Fe) increased when compared with base alloy. Zr could motivate the precipitation of primary Al3(Sc,Zr) and Al–5Mg–0.7Mn–0.2Sc–0.2Zr had better refining effect than Al–5Mg–0.7Mn–0.4Sc. The grain refinement and finely dispersed Al6(Mn,Fe) phase can improve the mechanical properties such as yield strength and ultimate tensile strength and the corrosion resistance by the results of intergranular corrosion (IGC) also improved.
  • Effect of Initial Grain Size on Thermal Fatigue Behavior and Changes in Microstructure of Ferritic Stainless Steel

    pp. 743-750

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    DOI:10.2320/matertrans.M2018382

    To understand the effect of grain size on the thermal fatigue behavior and dynamic recrystallization during the thermal fatigue process in ferritic stainless steel, interrupted testing of thermal fatigue in the temperature range from 473 K (minimum) to 1073 K (maximum) with a restriction ratio of 50% was conducted for fine-grained (diameter: 38 µm) and coarse-grained (diameter: 221 µm) specimens in a Nb- and Si-added ferritic stainless steel tube. The fine-grained specimen showed a small inelastic strain range during the thermal fatigue process and a longer life than the coarse-grained specimen. Microstructure observation by electron back-scatter diffraction revealed that dynamic recovery and recrystallization occurred during the thermal fatigue process. However, the coarse-grained specimen showed lower nucleus density and retardation of the recrystallization in comparison with the fine-grained specimen. From a supposition of the accumulation of the inelastic strain range during thermal fatigue cycles, the relationship between the accumulation strain and Zener-Hollomon parameter for dynamic recovery and recrystallization almost accorded with previous knowledge on this tendency. In addition, we found that for the steady-state recrystallized grain size in thermal fatigue cycles, there was little initial grain size dependence.
  • Refinement and Coarsening of Grains Caused by Tensile-Shear Tests in Ultra-Fine Grained Cu Processed by Severe Plastic Deformation

    pp. 751-757

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    DOI:10.2320/matertrans.M2018379

    Ultra-fine grained pure copper fabricated by equal-channel angular pressing was used as a sample. We made tensile-shear tests using specimens with notches cut from the sample and large shear deformation occurred between the notches. Microstructural changes between the notches caused by the large shear deformation were observed. Using micro scale lattices scribed on the surface of the specimen, we found both refinement and coarsening of grains caused by the large shear deformation. Although severe plastic deformation causes ultra-fine grained structure, it is known there is a limit of the grain refinement. The grain coarsening observed in the present study is considered to be the reason of the limit of the grain refinement caused by severe plastic deformation. This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 82 (2018) 442–448.
  • Applicability of Neural Network in Rock Classification of Mountain Tunnel

    pp. 758-764

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    DOI:10.2320/matertrans.Z-M2019809

    In construction projects of mountain tunnels, with a purpose of improving accuracies of rock classifications in preliminary survey, we have studied applicability of Artificial Neural Network (ANN). One characteristics of ANN is that it does not require defining clear formula correlating data input and output, by using its learning function. Leveraging the characteristics, accuracy of rock classification improved by using geophysical datasets (seismic velocity and resistivity) at a tunnel face and surrounding. Also, ANN has a problem of reduced applicability caused by over learning to training data. It is possible to avoid the over learning problem by increasing training dataset, but it is not easy to accumulate complete dataset of geophysical properties and actual rock classification obtained in construction stage. We found that it is important to collect various tunnel data without much deviation, for accumulating training datasets effectively in the future. This Paper was Originally Published in Japanese in Journal of the Society of Materials Science, Japan 67 (2018) 354–359. In order to more precisely explain, we add vertical axis label as Estimated rock mass class and horizontal axis label as Actual rock mass class in Fig. 3 and Fig. 4.
  • Effect on the Wear Resistance of Copper Alloy Surface Modification Layer by FSSP Implanting W Particles

    pp. 765-769

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    DOI:10.2320/matertrans.M2018316

    This paper aims to study the surface modification of H62 copper alloy with W nanoparticles implanted on its surface by friction stir surface processing (FSSP). Three implantation methods were studied, with the total implantation depth of 0.2 mm in each method. The first process method is that W powder is extruded to the surface of the copper alloy at a depth of 0.2 mm directly and one-timely through the tool. The second process method is to extrude the W powder into the surface of the copper alloy at a depth of 0.15 mm by a tool firstly, then return the tool to the starting end, and rotate the tool again on the copper alloy surface at a depth of 0.05 mm. The third process method is also to extrude the W powder into the surface of the copper alloy at a depth of 0.15 mm by a tool firstly, then move the tool backward from the stirring end to the starting end on the copper alloy surface at a depth of 0.05 mm. The microstructure, hardness and wear properties of the modified layers of the samples obtained from the three FSSP modified copper alloy surface techniques were tested and analyzed. The results of the three process methods show that W particles can be used to modify the surface properties of copper alloys, but the second process method has the best effect. The second process method can well achieve the uniform distribution of W particles on the copper alloy surface. The hardness of the modified layer was improved compared with the base metal. Among them, the hardness of the modified layer obtained by the second process was increased by 41.4%, the third process method was increased by 35.1%, and the first process method was increased by 16.1%. The friction coefficient of the modified layer obtained by the three technological methods is smaller than that of the base metal, and the second method produces the smallest friction coefficient.
  • Reproduction of Hot Rolling Mill Roll with High-Speed Tool Steel Type Shell Material Manufactured by Continuous Pouring Process for Cladding

    pp. 770-776

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    DOI:10.2320/matertrans.F-M2019808

    The composite rolls manufactured by the continuous pouring process for cladding using a high-speed tool steel type shell material and a steel core exhibit extremely high wear resistance, surface roughening resistance and toughness in the finishing rolling train of hot strip mills and have been widely applied. The authors focused on the fact that the core material of this type roll can be welded. Therefore, using this cladding process and welding technology, we developed a recycling system for a new roll using a scraped-out roll of this type. This technology realized high-performance rolls at a low cost and established a recycling system for work rolls reading to a reduction of CO2 emissions. These new rolls are friendly and contribute to meeting social demands in ecology.
  • Influence of Ingate Size on the Formation of Micro Shrinkage Pore in Gray Cast Iron

    pp. 777-784

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    DOI:10.2320/matertrans.F-M2019807

    In this paper, the origin of micro shrinkage pores in gray cast irons is revealed, and a solidification process for the iron is proposed. Gray cast irons, casted under various casting conditions, were examined in terms of density and optical microscopy microstructures of the irons. The amount of the added inoculation agent affects the size and the number of graphite particles per unit area, but does not affect the volume fraction of the graphite. The density of the iron was affected by the cross-sectional area of the ingate, regardless of the amount of the added inoculation agent. When the cross-sectional area of the ingate is larger than the appropriate size, the density of the iron decrease. The reason is the formation of micro shrinkage pores in the iron. The relationship between the solidification process and micro shrinkage pores of the gray cast iron was discussed based on the above experimental results. When the completion of the solidification in the ingate occurs before than that in the cavity, the molten metal cannot flow between the cavity and the runner by passing through the ingate. Therefore, the expansion due to the crystallization of the graphite is equal to the shrinkage due to the crystallization of the austenite at the eutectic solidification in the cavity. As a result, gray cast iron without micro shrinkage pores was obtained. This Paper was Originally Published in Japanese in J. JFS 90 (2018) 443–449.
  • Inhibition Effect of Ti(C,N) Particle Dispersion on Grain Growth of WC-Co Cemented Carbide

    pp. 785-792

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    DOI:10.2320/matertrans.Y-M2019810

    The WC-Co cemented carbides with the addition of Ti(C,N) base particles with different sizes were fabricated by liquid phase sintering and their microstructures were mainly investigated in detail comparing the microstructure of the alloys with VC and Cr3C2 addition. It was found that the WC grain growth was more strongly inhibited with increasing Ti(C,N) content and with decreasing Ti(C,N) particle size. The degree of inhibition by the addition of Ti(C,N) particle with about 0.1 µm size was lower than that of VC addition and was almost same as that Cr3C2 of addition. Considering the results about the relationship between WC grain size and Ti(C,N) particle size and the analysis of Co phase composition, it was seen that the mechanism of grain growth inhibition by the addition of Ti(C,N) particles was the pinning (Zener) effect by the second phase particle, which was different from the mechanism for the addition of VC and Cr3C2 reported previously. The case that one Ti(C,N) particle contacts plural WC grains was often observed, so that the pinning effect was considered to work by many Ti(C,N) particles neighboring one WC grain. The very important result that the pinning effect by Ti(C,N) addition enable to develop the new type of ultra-fine cemented carbide was obtained in this study. This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 65 (2018) 91–98.
  • Prediction of Laminations in Zinc Alloy Die-Casting by Gas-Liquid Two-Phase Flow Simulation

    pp. 793-801

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    DOI:10.2320/matertrans.M2018395

    In the manufacturing process of zinc alloy die-casting, laminations are a serious problem because they cause blister defects and the deposition of zinc on the mold surface. Thus, it is very important to analytically predict the risk of lamination formation before determining the mold design. In this study, we proposed a criterion for predicting the locations of laminations. The criterion value is estimated from the result of a molten metal flow simulation and can indirectly predict the locations of laminations. As the analytic method in the mold-filling simulation, we adopted a gas-liquid two-phase flow model with a finite element method, and the Cahn-Hilliard equation was adopted to determine the interface between the gas and the liquid. We predicted the locations of laminations for two different types of gating system using the mold-filling simulation. The validity of the proposed criterion for laminations was confirmed by comparison of the results of the simulation and the observation of laminations after practical die-casting.
  • Effect of Thiourea on the Properties of a Cu–Al2O3 Coating Prepared via Jet Electrodeposition

    pp. 802-807

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    DOI:10.2320/matertrans.M2019024

    Cu–Al2O3 nanocomposite coatings were jet electrodeposited from an electrolyte containing Al2O3 nanoparticles and added thiourea. The effects of the thiourea concentration on the surface morphologies, microstructures, growth structures, incorporated Al2O3 nanoparticle contents, and mechanical performances of the composite coatings were examined. The results revealed that the adsorption of Al2O3 increased from 4.6 at% to 9.3 at% with the addition of thiourea, and grain refinement from 61 nm to 33 nm was achieved. Thiourea additions in the concentration range of 0–15 mg/L increased the microhardness by 79% compared with that of the coating fabricated without thiourea. The mechanisms by which thiourea influenced the deposition quality and mechanical properties of the coating are discussed.
  • Evaluation of Apatite-Forming Ability and Antibacterial Activity of Raw Silk Fabrics Doped with Metal Ions

    pp. 808-814

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    DOI:10.2320/matertrans.Y-M2019802

    Raw silk can be doped with metal elements such as calcium and zinc due to the high affinity of sericin, which forms its outer layer. Raw silk doped in this manner is expected to possess various favourable properties as biomaterials. In this study, we investigated metal-doped raw silk fabric’s apatite-forming ability in simulated body fluid (SBF), as well as its antibacterial activity against Escherichia coli. The samples were prepared by soaking the fabric in aqueous solutions containing calcium, copper, or zinc ions. Both Cu-doped and Zn-doped raw silk fabric showed antibacterial activity, suggesting that antibacterial agents released from the samples killed the bacteria. Additionally, Ca-doped raw silk fabric showed both apatite-forming ability and antibacterial activity. The apatite formation on fabric might be because calcium ions released from the sample increased the degree of supersaturation of SBF with respect to apatite, and accelerated apatite formation. Additionally, the release of calcium ions caused local pH increases, resulting in bacterial hardly survival at the sample surface. Therefore, Ca-doped, Cu-doped, and Zn-doped raw silk fabrics may have applications as antibacterial biomaterials. Furthermore, Ca-doped raw silk fabric has the potential to bind to living bone. This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 65 (2018) 495–501.
  • Effect of Solution Treatment on the Hardness and Tensile Properties of Al–Mg–Si Alloys for Automotive Chassis

    pp. 815-823

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    DOI:10.2320/matertrans.M2018368

    Al–Mg–Si alloys, which are used mainly as wrought materials, can also be used as casting materials because of the development of casting technologies. To improve the mechanical properties of alloys, the casting materials are often subjected to different heat treatments. Therefore, the influence of heat treatment on the mechanical properties of aluminum alloys needs to be understood before wrought alloys can be used in automotive casting components. This study examined the effects of solution treatment on the microstructure and mechanical properties of casting Al–Mg–Si alloy for automotive chassis. After a solution treatment for 5 and 8 h at 535 to 565°C, the microstructures were examined depending on the heat treatment temperature and time by optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction. As a result, Al matrix, β-Al5FeSi and Mg2Si phases were observed in solution-treated Al–Mg–Si alloys. In addition, the solution treatment temperature and time had a significant effect on the hardness and tensile properties of the alloy. The hardness and tensile strength increased with increasing solution treatment temperature to 555°C due to the solid solution hardening with the dissolution of residual phases. In contrast, when the solution temperature increased further to 565°C and the solution treatment time was increased, the hardness and the tensile strength decreased due to softening by grain growth rather than the effects of the solid solution hardening. In addition, the uniformity of the mechanical properties by each location of the specimen increased with increasing solution treatment duration due to the increase in time needed to produce a sufficient solid solution.
  • Microstructure Evolution of Fe–Ni-Based Alloy HR6W during Isothermal Aging

    pp. 824-829

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    DOI:10.2320/matertrans.M2019032

    The age-hardening behavior of the Fe–Ni-based alloy HR6W was investigated in the temperature range between 973 K and 1073 K. A two-step increase of hardness was detected for the alloy at every aging temperature; the first increase of hardness results from the precipitation of M23C6 carbides, and the second increase corresponds to precipitation of the C14–Fe2W Laves phase. The time–temperature–precipitation diagram for the alloy was established on the basis of the results of hardness measurements and microstructure observations, where the precipitation of the C14–Fe2W Laves phase was slower than that of the M23C6 carbides by three orders of magnitude and the nose temperature of the Laves phase was greater than 1073 K. The M23C6 carbides precipitated with a plate-like morphology along grain boundaries at the early stage of aging, followed by the precipitation of the C14–Fe2W Laves phase with a granular morphology with increasing aging time. The M23C6 carbides and C14–Fe2W Laves phase are aligned under the stress condition because of their precipitation on the dislocations introduced during creep deformation. This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 83 (2019) 30–35.
  • Fabrication of Anisotropic Nd–Fe–B Powders by Ta Sputtering

    pp. 830-836

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    DOI:10.2320/matertrans.M2019003

    The influence of Ta sputtering on the fabrication of anisotropic Nd–Fe–B powders was investigated. X-ray fluorescence and secondary electron microscopy analysis revealed that the measured Ta content after sputtering was 5.6 mass% and the Ta particles were located on the surfaces of the Nd–Fe–B grains. Ta coating on Nd–Fe–B grain could prevent necking between Nd–Fe–B grains after annealing at 700°C for Nd–Fe–B powders with and without Ta sputtering, and the Ta-sputtered powder could be easily crushed.After crushing and sieving under 75 µm, the coercivity value of the powders with and without Ta sputtering were almost the same, while the anisotropy of Ta-sputtered powder was higher. Upon annealing and crushing, the degree of texture (λ), which is used to evaluate anisotropy, improved from 0.08 to 0.73 for the Ta-sputtered Nd–Fe–B powder and was higher than that for the non-Ta-sputtered Nd–Fe–B powder. The results demonstrate that Ta sputtering can be an effective technique for the fabrication of anisotropic Nd–Fe–B powders.
  • Effect of Cl Removal in MSWI Bottom Ash via Carbonation with CO2 and Decomposition Kinetics of Friedel’s Salt

    pp. 837-844

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    DOI:10.2320/matertrans.M-M2019811

    In this study, the effect of Cl removal in bottom ash via a carbonation treatment with CO2 was investigated by comparing it with a water washing treatment. First, this was also focused on examining the existence of Cl contained in the bottom ash. The overall (soluble and insoluble) Cl content was close to that of bottom ash with fine particle. Next, the washing with water was confirmed and it was not effective in decreasing the Cl content because of the existence of insoluble Cl. Whereas, the removal effect of Cl via carbonation with CO2 was very high compared to the washing treatment because of the decomposition of Friedel’s salt (main insoluble Cl).In addition, the kinetics data pertaining to the decomposed Friedel’s salt as the carbonation process proceeds was confirmed. The theoretical was well fitted to the kinetics data. The variation of the rate is constant upon decomposition with the reaction temperature followed the Arrhenius equation (19.676 kJ/mol of activation energy) and the orders with respect to water-to-solution and particle size were also obtained. The decomposition rate of Friedel’s salt based on diffusion through the product layer of shrinking core model could be expressed by the equation.
  • Hydrogen Generation from Ammonia Borane over Ru/Nanoporous CeO2 Catalysts Prepared from Amorphous Alloys

    pp. 845-848

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    DOI:10.2320/matertrans.M2019017

    CeO2 supports were prepared via a dealloying method from amorphous alloy. The activities of Ru/CeO2 catalysts were examined in the hydrogen generation reaction from ammonia borane. To investigate the effects of atomic arrangement of CeO2 precursor on the activities of Ru/CeO2 catalysts, CeO2 supports were prepared from amorphous alloys and crystalline alloys. The use of amorphous alloys as the precursor of CeO2 created fine porous structures, resulting in high catalytic activities of Ru/CeO2 catalysts.

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