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

MATERIALS TRANSACTIONS Vol. 59 (2018), No. 11

  • Real Space Cluster Expansion for Total Energies of Pd-Rich PdX (X = Rh, Ru) Alloys, Based on Full-Potential KKR Calculations: An Approach from a Dilute Limit

    pp. 1669-1676

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    DOI:10.2320/matertrans.M2018194

    We study the accuracy and convergence of the real space cluster expansion (RSCE) for the internal energies in the free energies of Pd-rich PdX (X = Rh, Ru) alloys, being used to study the phase stability and phase equilibria of Pd-rich PdX alloys in fcc structure. In the present RSCE from a dilute limit, the X atoms of minor element are treated as impurities in Pd. The n-body interaction energies (IEs) among X impurities in Pd are determined uniquely and successively from the low body to high body, by the ab-initio calculations based on the full-potential Korringa-Kohn-Rostoker Green’s function method (FPKKR) for the perfect and impurity systems (Pd-host and Xn in Pd, n = 1∼4), combined with the generalized gradient approximation in the density functional theory. We show that the total energies of the ordered Pd3X (X = Rh, Ru; X-concentration = 25%) alloys in L12 structure, obtained by the screened FPKKR band calculations, are reproduced very well (within the error of ∼1 mRy per atom) by the present RSCE including the 2-body IEs up to the 20th nearest neighboring pair (X2) and the 3-body IEs up to the clusters (X3) in the two cubic cells in fcc structure. We clarify the contribution from each term (of the 0∼4 body terms) in the RSCE to the total energies of Pd-rich PdX alloys, the distance dependence of the 2-body (X2) IEs, and the cluster-size dependence of 3-body (X3) and 4-body (X4) IEs. It is also shown that the contribution from the n-body (n = 2∼4) IEs becomes smaller and smaller with the increase in n and that the contribution from the 4-body IEs is very small (less than ∼0.2 mRy per atom).
  • Copper Like Thermal Conductivity and Silicon Like Coefficient of Thermal Expansion Copper Graphene for High Power IGBT by Metal Injection Molding

    pp. 1677-1683

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    DOI:10.2320/matertrans.M2018136

    Enhanced stability, lifetime and safety of high power IGBT (Insulated Gate Bipolar Transistor) modules are a result of their progressive material selection, thereby necessitating the invention of new composite materials. High-end power modules are operated close to the maximum physical matching capability of their layered materials, leading to decreased lifetime and degraded performance, and thus creating demand for new composite materials with higher thermal conductivity and lower coefficient of thermal expansion (CTE). To eliminate failures caused by the CTE mismatch (∼300%) between metal and substrate material interface, we report for the first time Cu/Gr–Cu composite which exhibits similar thermal conductivity to pure copper (390 W/(m·K)), much higher than the range of metal injection molded copper heat sink (320–340 W/(m·K)), while featuring low silicon-like CTE (∼5 ppm/K). This is realized by injection parameter manipulation to not only reduce voids (vacancies) but increase the interface bonding through the use of electrodeposited copper on graphene (i.e., Gr–Cu). Such excellent property locates the Cu/Gr–Cu in the top of the Ashby map and shows excellent temperature stability with lower thermal distortion parameter (TDP). Thus, this excellent composite material is the only material simultaneously with high thermal conductivity and low CTE, making it uniquely suited for high power module applications, especially for hybrid and electric vehicles.
  • Interfacial Interaction between Carbon Nanotube and Stoichio- and Nonstoichiometric Ceramic Surfaces by Ab-Initio Calculations

    pp. 1684-1690

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    DOI:10.2320/matertrans.M2018244

    This work deals with the interfacial interaction between single-walled carbon nanotubes (CNTs) and ceramic surfaces of SiC(0001) and ZrO2(111) based on the density functional theory. The ab-initio calculations show that the adhesive energy per the projected contact area on the ceramic surfaces depends on not only the diameter of CNTs but also the stoichiometry of the surfaces. For stoichiometric surfaces, such as the O-terminated ZrO2(111), the structures of the adsorbed CNTs do not drastically change from the original cylindrical shape and the interfacial interaction is relatively weak. In the case of nonstoichiometric surfaces, such as Si- and C-terminated SiC surfaces and Zr-terminated ZrO2 surface, they have a strong interaction. Especially for the small-diameter CNTs, the structure was transformed into an arch-like shape. The strong interaction arises from the formation of the mixed covalent-ionic bonding and the subsequent opening of CNTs, which is catalytically induced by the nonstoichiometric surfaces. The covalent and ionic characteristics of the interfacial bonding states are discussed in terms of the integrated crystal orbital Hamilton populations calculation and the Bader charge transfer analysis. These properties of the interface might be related with how a crack propagates on the interface and how large fracture toughness the composite has. CNT-SiC, which has the lower adhesive energy and relatively large covalent strength, results in the slightly increased fracture toughness. And CNT-ZrO2 with the same lower adhesive energy but the lower covalent strength does in the decreased, as seen in the experimental data.
  • Nanometer-Sized Crystalline Clusters of IGZO Films Determined from the Grazing Incidence X-ray Scattering and Anomalous X-ray Scattering Data Combined with Reverse Monte Carlo Simulations

    pp. 1691-1700

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    DOI:10.2320/matertrans.M2018231

    Grazing incidence X-ray scattering measurements have been carried out on c-axis aligned crystalline-indium gallium zinc oxide (CAAC-IGZO) film and nanocrystalline category-indium gallium zinc oxide (NC-IGZO) film and the following results were obtained: (1) the characteristic layered structure of the IGZO crystal did not hold its shape and the X-ray scattering profile showed only a relatively sharp first peak at the wave vector (Q) = 21.8 for CAAC film and 23.1 nm−1 for NC film, respectively, and additional weak broad peaks were observed at a higher angle. (2) In the case of the CAAC film, tiny peaks were observed at Q = 7 and 14 nm−1, corresponding to the positions of the 003 and 006 reflections, respectively, of the IGZO crystal. Such tiny peaks were not detected in the case of NC film but the asymmetry of the first peak at the low angle side was clearly observed. (3) These structural features implied that more than three polyhedral units, such as InOx (x = 4–6), GaOy (y = 4–6), and ZnOz (z = 4–6), were likely to coexist. It is appropriate to call this structural feature as cluster-1. (4) A composite-type structure formed by combining these polyhedral units is also likely to exist and leads to middle-range ordering. This structure is called cluster-2. The size of such cluster-2 has been estimated to be 2.2 nm for CAAC film and 1.8 nm for NC film using the measured pair distribution function. To gain insights into the structural features of IGZO films, realistic atomic-scale models were obtained to fit not only the ordinary interference function of grazing incidence X-ray scattering but also the environmental interference function of the anomalous X-ray scattering (AXS) with Zn-absorption edge using reverse Monte Carlo (RMC) simulation. (5) The resultant models indicated the complex and irregular atomic arrangements of two types of IGZO films, which are well characterized by nanometer-sized crystalline clusters. This characteristic feature may be referred to as crystalline–cluster–composite (triple C) structure.
  • Effects of Impurities and Processing Conditions in Al–1%Mn Alloys on the Formation of Thermally Stabilized Substructures

    pp. 1701-1705

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    DOI:10.2320/matertrans.L-M2018841

    In this study, the effects of impurities and processing conditions on the thermal stability of substructures formed via hot deformation were investigated using a plane strain compression (PSC) test. Two types of Al–1%Mn alloys were prepared. One of the alloys had a low content of silicon and iron owing to the use of pure aluminum bare metal (4N–1Mn alloy). The other was cast by using A1050 alloy (1050–1Mn alloy). The PSC tests were performed between 300 and 500°C and were followed by annealing at 500°C for 120 s in a salt bath. After the salt bath treatment, the 4N–1Mn alloys exhibited a recrystallized structure, whereas the 1050–1Mn alloys retained their fiber structure. Although the 4N–1Mn alloys exhibited a small increase in conductivity after the PSC test, the conductivity of the 1050–1Mn alloys showed an apparent increase. The synchrotron radiation analysis confirmed Al–Mn–Si precipitations in the compressed 1050–1Mn alloys. These precipitations could be the reason for the change in conductivity in the compressed 1050–1Mn alloys. Precipitations were barely observed for the compressed 4N–1Mn alloys, and small precipitations formed during hot deformation seemed to affect the formation of the thermal stabilized substructures. In addition, the study results showed that impurities, such as silicon, contribute to precipitation during hot deformation.
  • Laves Phase Precipitation Behavior and the Orientation Relationship with BCC in Cr–Mo–Nb System

    pp. 1706-1715

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    DOI:10.2320/matertrans.M2018160

    The isothermal sections of the Cr–Mo–Nb ternary phase diagram have been studied. The C15 NbCr2 Laves precipitation behavior in three different alloys has been investigated in the Cr–Mo–Nb ternary system. The orientation relationship (OR) of NbCr2 in BCC matrix among BCC/Laves two-phase alloys and Cr-rich BCC1/Mo-rich BCC2/Laves three-phase alloy is different at 1473 K; OR 1: (011)BCC // (111)C15], [011]BCC] // [110]C15] and OR 2: (411)BCC] // (111)C15, [011]BCC] // [110]C15] with low lattice mismatch are both observed in Cr-rich alloys #3 (74Cr–16Mo–10Nb) and #2 (50Cr–30Mo–20Nb). OR 3: (011)BCC // (111)C15, [111]BCC] // [011]C15] with a lattice mismatch relatively larger than that of OR 1 and OR 2 is only observed in alloy #2, which may be due to the presence of BCC1 and BCC2 interphases formed after BCC decomposition. Only discontinuous precipitation is observed at grain boundaries in Cr-lean alloy #1 (42Cr–31Mo–27Nb) without obvious OR between the BCC matrix and Laves phase.
  • Formation of Black Striped Oxide Scale on Hot-Rolled Si-Containing Carbon Steel

    pp. 1716-1722

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    DOI:10.2320/matertrans.M2018060

    The black striped oxide scale formed on silicon (Si)-containing hot-rolled carbon steel sheets was investigated. The small black stripes of oxide scale became band shaped as the flow used in mill cooling was increased. The distance between the black oxide scale bands was the same as that of the overlapping areas in the hydraulic descaling system. The average thickness of the black striped oxide scale was larger than that of the normal scale region. No ferric oxide (Fe2O3) was observed in the scale, particularly in the fractured parts of the black striped oxide scale. Furthermore, Si did not obviously accumulate in the black striped oxide scale, indicating that the oxide scale was not induced by the residual secondary scale generated during rough milling. The cooling conditions in finish milling affected the deformability of the scale in the overlapping areas. Consequently, the difference in thickness between the overlapping areas and adjacent regions led to the formation of the black striped oxide scale.
  • Characteristics of Fine Particle Distribution at Cut Slope and Fill Slope Comprising Weathered Granite

    pp. 1723-1730

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    DOI:10.2320/matertrans.Z-M2018839

    In this study, fine particle distribution in artificial slopes comprising weathered granite, which may affect rainfall-triggered landslide, was investigated comprehensively, based on electrical resistivity, soil composition and unsaturated soil properties. The results showed that while degree of saturation plays a key factor on electrical resistivity in unsaturated soil, it has close correlation to pore-size distribution. Therefore, it can be considered that electrical prospecting is an effective method to investigate distribution of both coarse particle and fine particle. In addition, it was also pointed out that there is possibility that fine particle fraction involved in soil poorly compacted in artificial slopes may be eroded due to rainfall infiltration. This Paper was Originally Published in Japanese in J. Soc. Mater. Sci., Japan 67 (2018) 346–353.
  • Verification of the Inhibitory Effect of the Aquo-Siloxane Method on Material Migration in Porous Rock Using the µ-Focus X-ray Computed Tomography Method

    pp. 1731-1738

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    DOI:10.2320/matertrans.M-M2018840

    Kyushu Research Institute for Cultural Properties Inc. and Kumamoto University have introduced a new method, the Aquo-Siloxane method, to protect stone heritage sites. The application procedure of the method is very simple and it has been applied to several stone heritage sites. Here, one-dimensional diffusion tests using potassium iodide solution were conducted on two types of porous rock samples, Berea sandstone and Kimachi sandstone. The Aquo-Siloxane treatment was applied to the rock samples, and its inhibitory effect on diffusion phenomena was verified. The characteristic point of this study was that the diffusion phenomena was visualized using a µ-focus X-ray computed tomography (CT) scanner, and the density distribution inside the rock sample was quantitatively evaluated. When the Aquo-Siloxane treatment was applied, it was found that density increment resulting from diffusion was suppressed by nearly 1/2 to 1/3 of that without treatment in both the rock samples. The number of applications of Aquo-Siloxane treatment was also verified. It was found that there were no significant differences in the number of treatments, and it was proved that one application was sufficient to suppress the migration of solute into the rock sample.
  • Orientation Dependence on Fatigue Fracture Behavior in Uniaxial Fatigue Tests of Pure Mg Single Crystals

    pp. 1739-1746

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    DOI:10.2320/matertrans.M2018224

    Three Mg single crystalline round-bar specimens with different crystal orientations were subjected to uniaxial tension-compression fatigue tests, and crystal orientation dependence on fatigue fracture behavior was investigated. Loading directions of AD, BC and EF specimens were [1120] [1100] and [0001] respectively. Results show that, at stress amplitude (σa) greater than or equal to 60 MPa, fatigue life of BC specimen was longest, while that of EF specimen was shortest. Under stress amplitude of 20 MPa, crystal orientation dependence on fatigue lives was not confirmed. Our study suggests that fatigue life in Mg single crystals show a high degree of dependence on crystal orientation and stress.
  • Bismuth Formation in Lead-Free Cu–Zn–Si Yellow Brass with Various Bismuth–Tin Alloy Additions

    pp. 1747-1752

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    DOI:10.2320/matertrans.M2018081

    Typically, bismuth added in traditional Cu–Zn brass segregates as films or particles along the alpha-beta phase boundary and induces cracks after casting. The present work investigated the bismuth formation in lead-free Cu–Zn–Si yellow brass with various amounts of recycled bismuth–tin (Bi–Sn) solder. The results showed that no bismuth film segregated at the phase boundaries. In contrast, round particles of bismuth formed in the beta phase and at the alpha-beta phase boundaries when added 1 mass% Bi–Sn alloy and the bismuth particles embedded only in the alpha phase when added 2 to 4 mass% Bi–Sn alloy, respectively. The morphology of the fracture surfaces was significantly modified when Bi–Sn alloy content was increased. More importantly, there was no crack observed in as-cast samples and samples did not subject to any heat treatment process unlike the bismuth formation in other work. Thus, this work suggests that the addition of recycled Bi–Sn solder in lead-free Cu–Zn–Si yellow brass is beneficial to avoid cracks in castings and offer an original lead-free brass alloy with superior properties.
  • Molecular Dynamics Study on Adhesion of Various Ni/Al Interface for Ni-Plated Aluminum Alloys

    pp. 1753-1760

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    DOI:10.2320/matertrans.M2018182

    As a fundamental study on the adhesion of Ni-plating on aluminum alloys, various molecular dynamics simulations are performed on Ni/Al infinite laminate structure under tension, by changing mixing concentration of Ni and Al at the interface. The adhesion shows the highest at the perfect (001) Ni/Al interface while it decreases with the rate of random mixing in Ni/Al phases (10%, 30% and 50% substitution in each phase). Especially the 50% substitution in Al phase remarkably decreases the adhesion compare to the same substitution in Ni phase. The (111) interface shows weaker adhesion than (001) for perfect Ni/Al interface, and the substitution doesn’t largely affect to the adhesion reduction as the (001) interface. The (001) interfaces are always ruptured in brittle manner near the interface in Al side, and few Ni atoms are observed on the fracture surface. The (111) interfaces shows shear-lip breakage by void formation and growth in Al side further away from the interface. We obtained simple conclusion that the Ni/Al interface is inherently strong and the delamination never takes place at the interface, since the surface energy and elastic coefficients of Ni is much larger than Al. The large reduction of adhesion by atom mixing in the (001) interfaces can be explained with the initial misfit at the interface while it doesn’t largely affect to the close-packed (111) interface. Assuming various phenomena in real Ni-plating, we also performed simulations with Ni3Al and NiAl interlayer, (001)–(110) surfaces combination; and all results in the same story above mentioned. Finally, we performed calculations on Ni–P system, and revealed that the surface energy of amorphous Ni–P is close to that of Al. Thus interfacial delamination can be occurred between the amorphous Ni–P plating and aluminum base.
  • Growth and Electrical Properties of Epitaxial ZnO Films Prepared by Chemical Bath Deposition Using a Flow Reactor

    pp. 1761-1766

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    DOI:10.2320/matertrans.M2018173

    Deposition methods using aqueous solutions have been developed as cost-effective routes to form transparent ZnO semiconductor films. Chemical bath deposition (CBD) employing a solution of zinc nitrate and hexamethylenetetramine is one of the most popular methods to grow ZnO using aqueous solutions. However, the electrical properties of ZnO films grown by CBD have not been extensively studied. In this study, epitaxial ZnO films were prepared by CBD using a flow reactor under various deposition conditions, and the temperature and reactant concentrations required for the growth of a transparent ZnO film with a smooth surface were determined. The electrical properties of the transparent ZnO films were examined by resistivity and Hall effect measurements. The optimum flow rate of the reaction solution, leading to the fastest growth of ZnO, was also identified. The ZnO film grown at such flow rate exhibited the highest electrical mobility. The carrier concentration and mobility of the ZnO film grown under the optimized conditions were 1.2 × 1018 cm−3 and 21 cm2 V−1 s−1, respectively.
  • Electrodeposition Behavior of Zn-Polyethyleneimine Composite from Sulfate Solution and Its Micro Structure

    pp. 1767-1776

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    DOI:10.2320/matertrans.M2018243

    Electrodeposition of Zn-polyethyleneimine composite was performed at 100–12000 A·m−2 and 4.8 × 105 C·m−2 in agitated sulfate solutions containing 1.84 mol·dm−3 of ZnSO4 and 4 g·dm−3 of polyethyleneimine at pH 1.8 and at 313 K: the composite’s deposition behavior and the relevant deposits’ micro-structure were investigated. The films obtained at current densities above 4000 A·m−2 from solutions containing polyethyleneimine exhibited gloss, and the gloss was highest for solutions containing polyethyleneimine with the highest molecular weight (70000). The preferred orientation of deposited Zn crystals changed from {0001} to {1120} and {1010} in the presence of polyethyleneimine, and the size of the platelet-shaped Zn crystals decreased as the polyethyleneimine molecular weight and current density increased. The deposition of Zn was polarized in the presence of polyethyleneimine, and the degree of polarization increased with the current density and with polyethyleneimine’s molecular weight. The C and N contents in deposited films increased as the polyethyleneimine molecular weight and current density increased, indicating an increase in the tendency of polyethyleneimine to be adsorbed onto the cathode. During deposition, polyethyleneimine buffered somewhat the pH increase in the layer of the electrolyte solution in contact with the cathode. At this time, H+ ions are released from polyethyleneimine because of an increase in pH in the cathode’s vicinity, and consequently, the number of electron lone-pairs in N atoms of polyethyleneimine increased, resulting in an increase in the adsorption ability of polyethyleneimine onto the cathode. This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 82 (2018) 281–288.
  • Microstructure and Elongation Anisotropy of Cold Rolled and Solution Treated A356 Alloy Strips Fabricated via High-Speed Twin-Roll Casting

    pp. 1777-1783

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    DOI:10.2320/matertrans.F-M2018837

    A356 alloy strips fabricated via high-speed twin-roll casting were cold rolled at the reductions of 0%, 12%, 30%, 50% and 73% and then solution treated at 793 K for 1 h. Microstructure observations and tensile tests were performed for the processed strips. Upon increasing the reduction from 0% to 50%, an improvement in elongation with significant anisotropy was observed; the elongation along the transverse direction was inferior to that in the rolling direction. However, on further reduction up to 73%, this anisotropy was eliminated and an elongation above 20% was achieved. This behavior is caused by the characteristic changes occurring in the second-phase particles that are located in the mid-thickness region of the strip. To achieve a high elongation without anisotropy, a process for refining the coarse particles in the mid-thickness region of the twin-roll-cast strips and homogeneously dispersing them into the matrix needs to be developed.
  • Cure and Collapse Mechanism of Inorganic Mold Using Spherical Artificial Sand and Water Glass Binder

    pp. 1784-1790

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    DOI:10.2320/matertrans.F-M2018838

    Artificial spherical sands were cured using water glass as a binder with or without addition of porous silica to prepare the test piece and aluminum alloy casting core. In order to clarify the curing and collapsibility mechanism of inorganic sand mold, the cross-linked structure between their particles were evaluated by SEM observation. A three-dimensional network of crosslinking bridges derived from water glass formed between the spherical particles enables the preparation of a core with sufficient strength for casting. The water glass added to cure the core requires less than 2 wt% by weight for the sand prepared by the melting method and about a third as much as that prepared by the sintering method. The high collapsibility of such an inorganic mold is due to the rapid elongation of crosslinking bridges between the particles when heated above a certain temperature so that the particles are separated from each other. Especially for spherical particles with a smooth surface, the relatively small amount of water glass for curing would cause collapsibility accelerated by the thinning of the crosslinked body wall occurring simultaneously with elongation. Furthermore, the addition of porous silica would induce elongation at a lower temperature as compared to when porous silica is not added, and is extremely effective for improving the collapsibility of the inorganic sand mold. This Paper was Originally Published in Japanese in J. JFS 89 (2017) 470–476.
  • Numerical Simulation of Suspension Plasma Spraying with Axial Injection

    pp. 1791-1797

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    DOI:10.2320/matertrans.T-M2018842

    Two-dimensional simulation is performed for an annular-shaped plasma torch using argon gas under different operating currents and torch-substrate distances. The mathematical model is based on the conservation equations of mass, momentum, and total energy for gasdynamics and the steady-state Maxwell’s equations for electrodynamics. Suspension carrying zirconium particles are axially injected into plasma flow and their trajectories and heating histories are analyzed with the Lagrangian method. A simplified model is used to simulate the evaporation of suspension droplets and the emergence of solid particles. The numerical results show that current stream lines are sharply curved downstream of the torch. In-flight particles are strongly heated in the area where the current streams are curved. An increase in operating currents results in shortening the length of current stream lines and moving the curved area further upstream. The numerical results also indicate that the particle impacting positions on a substrate get closer to its center as the operating current gets larger and the torch-substrate distance becomes shorter. Furthermore, the numerical results suggest that setting an operating current to higher values, which leads to an increase in particle impacting velocity, is suitable for impacting particles with molten state on the substrate. This Paper was Originally Published in Japanese in J. Jpn. Thermal Spray Soc. 54 (2017) 48–54. The reference 18) was added.
  • Fabrication and Strength Behavior of MWCNT-Reinforced 5083 Aluminum Alloy Composite via Friction Stir Processing

    pp. 1798-1804

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    DOI:10.2320/matertrans.M2018191

    In order to improve the strength of 5083 Al alloy used in a wide range of industries, incorporation of multi-walled carbon nanotubes (MWCNTs) into 5083 Al alloy by the use of friction stir processing (FSP) was investigated. The MWCNT-reinforced Al alloy composites via FSP were successfully fabricated. The composites have no voids and other defects with the optimized conditions of FSP. The grain refining and uniform distribution of MWCNTs were achieved because the composite powder comprised of MWCNTs and 5083 Al alloy via ball milling was used as a reinforcement. Nanoparticles of MWCNTs and submicron particles were observed in the composite. The proof stresses of the composites increased by ranging from 53 to 61 percent compared with that of the base material and the tensile strengths increased by ranging from 13 to 16 percent.
  • Ball Mill Grinding Characteristics with Respect to the Chemical Composition of Pyrophyllite

    pp. 1805-1810

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    DOI:10.2320/matertrans.M2018157

    The quality and price of pyrophyllite, which is commercially available in the powder form, depends on its particle size. The grinding characteristics of pyrophyllite are affected by its Al2O3 content. The breakage of domestic pyrophyllite in a ball mill was evaluated via laboratory grinding tests conducted on a 1.18 × 0.85 mm size fraction. The tests were performed using a 20 (D) × 20 (H) cm laboratory ball mill containing 2.54-cm-diameter alumina balls at a volume filling of 30% with 70% critical speed for various grinding times. The breakage constants were calculated by the inverse method based on the particle size distribution of the ground product. Parameter A of the specific rate of breakage was found to be inversely proportional to the chemical composition of Al2O3, and the other breakage constants were similar for all pyrophyllite samples. The simulated and experimental results were in good correlation, and the correlation between A and the Al2O3 contents can be expressed by the exponential function 1.3(p.i.)−0.3.
  • Metal–Metal Joining Using Super-Spread Wetting into Interface Fine Mesh Structure

    pp. 1811-1816

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    DOI:10.2320/matertrans.MAW201804

    Our group has previously realized region-selective super-spread wetting through surface fine crevice structures fabricated by laser irradiation or reduction-sintering of oxide powder and joined metals in microscopic regions by super-spread wetting. A new approach suitable for wide-area joining was investigated in this study. Using a metal mesh with high porosity, we produced a new structure termed “interface fine mesh structure” that can promote super-spread wetting. As well as successful super-spread wetting of liquid tin into a copper interface fine mesh structure, copper blocks were also joined by super-spread wetting.
  • Microstructure and Mechanical Anisotropy of Ni–Mo–Cr-Based Alloy Manufactured by Laser Metal Deposition

    pp. 1817-1822

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    DOI:10.2320/matertrans.M2018163

    This study investigated the microstructure and mechanical anisotropy of laser metal deposited Ni–Mo–Cr super alloy. The laser metal deposited Ni–Mo–Cr super alloy showed a unidirectional micro-columnar structure. The γ phase was observed in the form of fine dendrites, and M6C (fishbone type) was shown in inter-dendrite regions. A room temperature compression test was conducted on specimens prepared in different directions (ND, PD), with strain rates of 10−3∼1 s−1. As the strain rate increased, there was a tendency for strength to increase in both directions. As compression stress was applied, M6C fractured and aligned in the vertical direction of compression, and linear fracturing occurred in the PD (printing) direction, and zig-zag fracturing occurred in the ND (normal) direction. As the strain rate increased, the fractured M6C size became finer, and cracks were formed and developed along the carbides that caused the fracturing. In particular, while detachment occurred due to carbides in the ND direction, a more compressed form was observed in the PD direction. Therefore, it is considered that the PD direction has relatively higher yield strength and greater strain rate sensitivity than the ND direction.
  • Fabrication of Bulk Ni–Mo Alloys by Electrodeposition with Intermittent Addition of Sodium Molybdate

    pp. 1823-1828

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    DOI:10.2320/matertrans.MAW201801

    The electrocatalytic properties of Ni–Mo alloys are desirable for a wide range of electrochemical applications. However, electrodeposited Ni–Mo alloys suffer from high internal stress and low ductility. In this study, we electrodeposited Ni–Mo alloys by intermittently adding different concentrations of sodium molybdate. The microstructure and mechanical properties of the resulting alloys were examined. We identified a critical point for the Mo concentration in the deposition bath at which the properties of the electrodeposited alloys changed sharply. When the Mo concentration was below a certain threshold, the alloys consisted of relatively large grains (approximately 30–50 nm) and exhibited a tensile of approximately 10%. Conversely, when the concentration exceeded the threshold, the grain size decreased to approximately 15 nm and the ductility was limited. X-ray photoelectron spectroscopy indicated that the change of the properties corresponded to inclusion of oxides of molybdenum. On the basis of these results we suggest that producing ductile Ni–Mo alloys requires the Mo concentration in the deposition bath to be maintained at low levels.
  • An Attempt to Visualize the Scrap Behavior in the Converter for Steel Manufacturing Process Using Physical and Mathematical Methods

    pp. 1829-1836

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    DOI:10.2320/matertrans.M2018125

    The behavior of the scrap is an important factor affecting the transport phenomena in the converter for steel manufacturing process, especially for the performance of a certain heat such as temperature and chemistry composition. However, the observation and evaluation of the scrap behavior is very difficult. In this paper, a physical modeling based on the similarity principle is established for the study of the scrap behavior during converter steelmaking process. Specially-made ice pieces with different shapes and sizes are used to simulate the scrap, and its motion and melting are visualized in a transparent scaled-down model. Moreover, the dynamic melting characteristics of a given ice piece is numerically investigated. It has been indicated that the scrap behavior is closely related to the fluid characteristics in the converter. The enhancement of stirring and mixing can be of importance to the scrap controlling. The scrap with small size is more favorable for the actual production. As for the scrap melting, the shape of scrap is a crucial parameter. The large-size scrap with small specific surface area should be avoided during converter steelmaking process. In addition, more energy is needed when more scraps are charged. The obtained results can provide good references for the actual production.
  • Effects of the Intermetallic Phases on Microstructure and Properties of Biodegradable Magnesium Matrix and Zinc Matrix Prepared by Powder Metallurgy

    pp. 1837-1844

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    DOI:10.2320/matertrans.M2018142

    A series of Mg–Zn alloys, including Mg–1%Zn, Mg–2.5%Zn, Mg–25%Zn, Mg–50%Zn, Mg–75%Zn and Mg–99%Zn alloys (at%), were designed and produced by powder metallurgy for bone tissue engineering. The effects of Mg–Zn intermetallic phases on microstructures, mechanical properties and corrosion resistance of Mg matrix and Zn matrix were studied and compared to select the suitable candidates for biodegradable metallic implants. The results showed that Mg–2.5%Zn alloy could be treated as good candidate for bone tissue engineering due to its suitable mechanical properties, relatively low degradation rate and good biosafety. Mg–1%Zn alloy could be used as candidate for implants without high strength requirements. The typical dendrite structure between bulk intermetallic phases and matrix were found in Mg–25%Zn and Mg–50%Zn alloys, which caused obvious property heterogeneity, strength reduction, and severe galvanic corrosion. Mg–75%Zn and Mg–99%Zn alloys obtained the lower degradation rates and higher compressive strengths, but they were too brittle to be used as available biomaterials. Consequently, the Mg–Zn series alloys prepared by powder metallurgy have the potential to serve as biodegradable metals.
  • High-Temperature Stability of ThMn12 Magnet Materials

    pp. 1845-1853

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    DOI:10.2320/matertrans.M2018195

    The nitrogenated alloys (Nd0.7Zr0.3)(Fe0.75Co0.25)11.5Ti0.5N1.3 (A) and Nd(Fe0.8Co0.2)11Mo1.0N1.0 (B) and the non-nitrogenated alloy (Sm0.8Zr0.2)(Fe0.75Co0.25)11.5Ti0.5 (C), having a ThMn12 structure, show interesting magnetic properties and are candidate materials for high-temperature magnets. In this study, the stability of these materials was studied using Curie temperature measurements, differential scanning calorimetry, differential thermal analysis, thermogravimetry from room temperature to 1573 K, and X-ray diffraction of treated samples. The nitrogenated samples (A) and (B) started to decompose into the α-(Fe, Co) phase and other X-ray amorphous phases from about 800 and 1000 K, respectively. Sample (C) exists as a metastable phase at room temperature and decomposed above 700 K at a relatively high oxygen partial pressure (PO2 > 10 Pa), but the ThMn12 structure remained up to at least 1373 K in an almost oxygen-free atmosphere (PO2 < 10−15 Pa). Sample (C) is intrinsically stable at temperatures higher than about 1000 K up to the melting temperature, which was estimated to be 1480 K. The ThMn12 structure in both R = Nd and Sm starting alloys is metastable at room temperature, and becomes unstable under 800–1000 K. The decomposition rate was clearly dependent on the PO2 in the heated atmosphere, as high PO2 led to sample oxidation, and on the sample composition.
  • Forming of Aluminum Foam Using Light-Transmitting Material as Die during Foaming by Optical Heating

    pp. 1854-1859

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    DOI:10.2320/matertrans.M2018218

    Aluminum (Al) foams are expected as components of vehicles and construction materials. Among the several routes for fabricating Al foams, a precursor foaming route has been commonly used to produce Al foam. In this study, optical heating, which can directly heat a precursor, was employed through light-transmitting materials of glass and sapphire to obtain ADC12 (Al–Si–Cu alloy) foam. Fundamental investigations on the forming of the ADC12 foam using a light-transmitting material as a die, which can transmit light during foaming, were conducted. From the free foaming of the ADC12 precursor by optical heating through the glass, through the sapphire and without those materials, it was found that, although a slight energy loss was observed, the ADC12 precursor can foam by optical heating through the light-transmitting materials. In addition, it was indicated that a similar foaming behavior was observed with the generally used electric furnace except that the foaming time was much shorter by the optical heating. Furthermore, from the foaming of the ADC12 precursor by optical heating through the light-transmitting materials, which restrict upward expansion, a flat ADC12 foam can be obtained. The pore structures similar to those of the free foaming were observed. In this forming process, cracks were observed in the case of the glass during the cooling of the ADC12 foam, which was not observed in the case of the sapphire. Therefore, it was indicated that sapphire can be used as the die for the forming of the ADC12 foam during the foaming.
  • Chalcopyrite Bioleaching Using Adapted Mesophilic Microorganisms: Effects of Temperature, Pulp Density, and Initial Ferrous Concentrations

    pp. 1860-1866

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    DOI:10.2320/matertrans.M2018247

    This study examines the effects of several operating parameters on copper leaching from chalcopyrite ores using an adapted mesophilic bacterial culture. Three temperatures (35, 40, and 45°C), three pulp density (1, 2, and 4% (w/v)), and three initial ferrous ion (Fe(II)) concentrations (5, 10, and 20 g/L) were employed as variable parameters, and their effects on the bioleaching efficiency of chalcopyrite were investigated. After 14 days, the maximum copper bioleaching efficiency was estimated to be ∼64% at a temperature of 45°C, a pH of 1.5, an initial ferrous concentration of 5 g/L, and a pulp density of 4%. More specifically, the chalcopyrite dissolution tests conducted at different temperatures showed a minimal effect of temperature and low leaching efficiency (<20%) regardless of temperature. The trend of chalcopyrite dissolution at different pulp densities showed that Cu extraction tended to increase with increases in pulp density. Moreover, the Cu leaching efficiency associated with mesophilic microorganisms largely decreased when the initial Fe(II) concentration was greater than 10 g/L. The Cu leaching behavior in different test conditions was evalauted with concentrations of total iron (Fe), Fe(II), and ferric ions (Fe(III)), as well as the oxidation-reduction potential (ORP) of the solution used in the test. The Cu leaching rate increased under lower ORP conditions, lower Fe(III):Fe(II) ratios, and balanced Fe(II)–Fe(III) cycles.

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