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

MATERIALS TRANSACTIONS Vol. 62 (2021), No. 10

  • Theoretical Approach for Long-Ranged Local Lattice Distortion in Al-Rich AlX (X = H∼Sn) Disordered Alloys by Kanzaki Model Combined with KKR Green’s Function Method

    pp. 1429-1438

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    DOI:10.2320/matertrans.MT-M2021110

    The local lattice distortion (LLD) effects in the disordered alloys with the large atomic-size misfit between the constituent elements are well known to be essential for reproducing theoretically the observed phase diagrams including order-disorder critical temperatures, although the theoretical approach from first principles remains a long-standing problem. We propose the Kanzaki model combined with the full potential (FP) Korringa-Kohn-Rostoker (KKR) Green’s function method, as an approximation for the direct FPKKR calculations, which is based on the harmonic approximation of the atomic displacements and enables us to study the long-ranged LLD effects in the disordered alloys. We first show that the present Kanzaki model may reproduce very accurately the LLD energies obtained by the direct FPKKR calculations with the restriction on the displacement of only the 1st-nearest neighboring atoms around a single impurity X in Al, although the discrepancy increases with the atomic-size misfit between Al and X atoms. Second we clarify the fundamental features of the LLD energies (over ∼10000 atoms) around a single impurity X (= H∼Sn) in Al, corresponding to the 1-body part in our real space cluster expansion for the LLD energy in the Al-rich AlX disordered alloy; the 1-body LLD energy becomes larger and more long-ranged with the atomic-size misfit between Al and X elements and also with the sp-d interaction of Al-X (X = d element).
  • Effects of B2O3 and CaO/Al2O3 on Structure of CaO–Al2O3–B2O3 System

    pp. 1439-1447

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    DOI:10.2320/matertrans.MT-M2021097

    CaO–Al2O3-based mould fluxes are the most significant slag systems for the continuous casting of high-Al steel. In this study, to investigate the structure of the CaO–Al2O3–B2O3 system, molecular dynamics simulation and infrared spectroscopy experiments with different amounts of B2O3 and CaO/Al2O3 ratio were carried out. The results showed that the structural unit of B–O and Al–O are of great stable while B atom is easier to bond with O atom than Al, and [BO3]3− trihedron is more stable than [AlO4]5− tetrahedron. With the content of B2O3 increases, the increased [BO3]3− trihedral structure units can balance the excessive negative charges in [AlO4]5− tetrahedron structure, and Al2O3, acts more acid in a highly alkaline surrounding, can absorb O2− and results in forming [AlO5]7− structure at high CaO/Al2O3 ratio, which promotes the transformation of Onb into Ob, while CaO results in an increase in the content of Onb with the increase of CaO/Al2O3 ratio. The results of infrared spectrum are consistent with simulation results that B2O3 addition promotes the complexity of the network structure, and the depolymerization of the large complex network structure with increased CaO/Al2O3 ratio.
  • Soft X-ray XAFS Analysis of Cluster Formation Behavior during Natural Aging on an Al–Mg–Si Alloy

    pp. 1448-1456

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    DOI:10.2320/matertrans.MT-L2021004

    This study investigated cluster formation in the early stages of natural aging in Al–1.04 mass%Si–0.55 mass%Mg alloys by soft X-ray XAFS measurements and first-principles calculation. XAFS measurements at the Mg-K and Si-K edges were carried out at the BL27SU beamline at SPring-8. It was found that the absorption edge energies changed as aging proceeded. Density functional theory (DFT) calculations were used to determine the valence electron densities near Si and Mg atoms and to simulate the Si-K and Mg-K edge spectra for some cluster models. On the basis of the results, it was demonstrated that Si and Mg atoms formed clusters in four stages (I–IV) during natural aging. In stage I, Si-vacancy pairs, Mg-vacancy pairs, and a combination of both were formed. In stage II, vacancies were released from the clusters formed in stage I. In stage III, Mg-vacancy pairs were included in the clusters. In stage IV, the clusters coarsened through the release of vacancies. These results indicate that soft X-ray XAFS, which is capable of identifying individual elements, has the ability to provide information on such clusters. This Paper was Originally Published in Japanese in J. JILM 71 (2021) 144–151.
  • Immobilization of Silver Nanoparticles on the Surface of Cellulose Nanofibers Using High-Pressure Wet-Type Jet Mill

    pp. 1457-1461

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    DOI:10.2320/matertrans.MT-Z2021009

    Composite material immobilized silver nanoparticles (NPs) on the surface of cellulose nanofibers (CNF) was prepared using a high-pressure wet-type jet mill. A mixture both containing an aqueous silver nitrate solution and a CNF suspension was prepared as a raw starting material. The mixture was pulverized with the high-pressure wet-type jet mill at a pressure of 100 or 200 MPa. An X-ray diffraction pattern of the obtained sample revealed the presence of not only cellulose type I crystallites but also silver metal crystallites. According to observation by field-emission scanning electron microscopy, it was found that many silver NPs were immobilized on the surface of CNF. Note that almost all the silver NPs were well dispersed on the surface of CNF. It was cleared that the silver NPs had a spherical in shape with an average particle size of about 3 nm by the transmission electron microscope observation. The average size of the silver NPs slightly increased with the number of jet milling cycles, however, the change in the discharge pressure of the high-pressure wet-type jet mill did not affect the NPs size. The silver content in the composite materials increased with increasing both the number of jet milling cycles and the discharge pressure. The silver NPs were deposited by using the thermal energy released in the jet milling process, and their grain growth was then inhibited because the suspension was cooled immediately through the cooling tube. Therefore, it was assumed that silver NPs with a narrow size distribution could be immobilized on the surface of CNF. This Paper was Originally Published in Japanese in J. Soc. Mater. Sci., Japan 70 (2021) 400–405. The Abstract and the caption of Fig. 1–7 are slightly modified.
  • Effect of Different Concentrations of Nano-Cubic Boron Nitride on the Preparation of TiO2/Ti/Fe Composite Materials by Thermal Sprayed and Micro-Arc Oxidation

    pp. 1462-1470

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    DOI:10.2320/matertrans.MT-M2021091

    In the mechanical, automobile, aerospace, and construction industries, Ti and steel are the mostly commercial materials be used. But the poor hardness, wear, and corrosion resistance limit their applications. In this study, we presented a composite material that consists of thermal-sprayed titanium (Ti) layer on AISI 1020 steel. Then we added different concentrations of c-BN to the electrolyte in the MAO process to enhance the wear resistance and corrosion resistance. The operating parameters of MAO were set to 35 A/dm2 current density, 450 V voltage and 10 minutes operating time. The concentration of c-BN added to the electrolytes were 0.1 g L−1, 0.3 g L−1, 0.5 g L−1, 0.7 g L−1, 0.9 g L−1, and denoted as Ti/MAO-BN1, Ti/MAO-BN3, Ti/MAO-BN5, Ti/MAO-BN7, Ti/MAO-BN9, respectively. To determine the properties of the composite coating, measurements of coating thickness, surface roughness, microstructure, hardness, XRD analysis, EDS observations were performed. Then potentiodynamic polarization test and a ball-on-disc wear test were used to determine the corrosion resistance and wear resistance. All the results indicated that all Ti/MAO contained c-BN (Ti/MAO-BN) have higher hardness, lower surface roughness, and thicker coatings thickness than that of Ti/MAO-free (Ti/MAO-F). In the corrosion resistance, Ti/MAO-BN was at least about 64% better than Ti/MAO-F, with Ti/MAO-BN9 being about 5 times better. In the wear resistance, Ti/MAO-BN reduces the wear volume at least about 59% compared to Ti/MAO-F, with Ti/MAO-BN9 reducing the wear volume by about 70%.
  • Effect of Plastic Anisotropy on Ironing Formability of 3104 Aluminum Alloy Hard Sheets

    pp. 1471-1478

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    DOI:10.2320/matertrans.MT-L2021007

    3104 aluminum alloy hard sheets are widely used for aluminum beverage can body stock (CBS) mainly because of their high ironing formability. The CBS has large anisotropy of r-value (Lankford value) and n-value (work hardening exponent), however, the effect of such anisotropy on the ironing formability remains unclear. In this study, cup and DI forming behavior was investigated using cold-rolled 3104 aluminum alloy hard sheets with different anisotropy of r and n-values. Magnitude of the anisotropy changes during drawing and ironing. Ironing fracture tests reveal that fracture occurs at angles between 10 and 20° in the can circumferential direction. From the strain distribution measurement of the can wall, it is found that the axial strain of the can wall at the fracture angle is larger. A theoretical analysis method of ironing stress introducing r and n-value anisotropy is devised based on the Hill’s anisotropic plasticity theory (quadratic yield function). The devised analysis reveals that as the anisotropy of r-value in the can wall becomes smaller, (1) the fracture is less likely occur, (2) the margin of stress which calculated from the ratio of the can axial tensile stress to fracture stress is larger. This Paper was Originally Published in Japanese in J. JILM 70 (2020) 422–428. Synopsis and keywords were slightly modified. Titles of Table 2 and Table 3 were slightly modified. Annotation in Table 1 was added. Annotation in Fig. 3 and Fig. 4 were slightly modified. Table 3, Fig. 3, Fig. 5, Fig. 11, Fig. 12 and Fig. 13 were slightly modified.
  • Effects of Grain Boundary Geometry and Boron Addition on the Local Mechanical Behavior of Interstitial-Free (IF) Steels

    pp. 1479-1488

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    DOI:10.2320/matertrans.MT-M2021128

    Nanoindentation measurements on various grain boundaries were performed to clarify the effects of the geometry of neighboring grains and the addition of boron (B) on plasticity resistance in the vicinity of grain boundaries in interstitial free (IF) steels. We define a parameter, α, which is measured by the slope of a P/hh curve with load, P, and displacement, h, to estimate the resistance against plastic deformation in the grain interior and at the grain boundaries. The value of α is almost constant with the geometric compatibility factor of the grain boundaries. This result shows that the geometry of the neighboring grains does not affect the plasticity resistance of the grain boundaries. However, the value of α increases by the addition of B due to the segregation of B and Ti to the grain boundaries. It is indicated that the elemental segregation to the grain boundaries enhances the resistance to the plastic deformation in the vicinity of the grain boundaries. This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 85 (2021) 30–39.
  • Numerical Simulation of Tribocorrosion of CoCr Alloy and Ti with Galvanic Coupling in Simulated Body Fluid

    pp. 1489-1494

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    DOI:10.2320/matertrans.MT-Z2021007

    The artificial hip joints have galvanic couple between femoral head made of CoCr alloy and stem made of Ti or Ti alloy, and are subjected to high levels of mechanical stress. Therefore, tribocorrosion of artificial hip joints has been frequently reported. In this study, we performed the first electrochemical numerical simulation for CoCr alloy and Ti with friction in simulated body fluid. We constructed single metal model and galvanic couple model to investigate the effect of the cathodic reaction on the tribocorrosion behavior. In single metal model, CoCr alloy with friction is referred to as CoCr(Tribo.). In galvanic couple model, CoCr alloy with friction in contact with Ti is referred to as CoCr(Tribo.)–Ti. In single metal model, the current density of CoCr(Tribo.) was higher than that of Ti(Tribo.). For the CoCr alloy with friction, the current density of galvanic couple model (CoCr(Tribo.)–Ti) was higher than that of single metal model (CoCr(Tribo.)). The current density of both single metal model and galvanic couple model increased as the increase in area of the non-friction part increased. The current density of CoCr(Tribo.)–Ti was highest, and the rate of increase in current density with the increase in area was also highest. This Paper was Originally Published in Japanese in J. Soc. Mater. Sci., Japan 69 (2020) 769–774.
  • Recovery of Palladium and Platinum Particles Suspended in the Al2O3–CaO–SiO2 Slag Using Copper-Based Extractants at 1723 K

    pp. 1495-1501

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    DOI:10.2320/matertrans.M-M2021844

    Platinum group metals (PGMs) are precious rare metals mined only in a few regions of the world. Recycling PGMs used in automotive catalytic converters is of utmost importance to meet increasing global demand. The Rose process is the main recycling process used in Japan to recover PGMs from spent automotive catalytic converters. The recycling process involves smelting a ceramic structure, in which PGMs are supported, with Cu, Cu2O, reductants, and fluxes such as CaO and SiO2.This study compared the Pd and Pt recovery capability of Cu or Cu2O as extractants. Pd and Pt particles were simultaneously suspended in Al2O3–CaO–SiO2 molten slag, and the extractant Cu or Cu2O was added. The concentration of Pd and Pt in the slag as a function of processing time was investigated at 1723 K of the operating temperature in the Rose process, under carbon saturation. The results show that the suspended Pd and Pt particles were combined by collisions in the slag, and the recovery ratio and recovery speed of Pd and Pt suspended particles were higher when using Cu2O than when using Cu. The Cu2O dissolved in the slag was reduced to metallic Cu in the slag and alloyed with the suspended PGMs particles to form Cu-PGMs alloys. As a result, the particle size of the PGMs increased and sedimentation motion in the slag is promoted.
  • Combined Effect of Gas Blow Induction Heating Nitriding and Post-Treatment with Fine Particle Peening on Surface Properties and Wear Resistance of Titanium Alloy

    pp. 1502-1509

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    DOI:10.2320/matertrans.Z-M2021845

    In order to fabricate a titanium alloy with superior wear resistance and fatigue strength, fine particle peening (FPP) was introduced as a post-treatment after gas blow induction heating (GBIH) nitriding. The surface characteristics of the treated alloy were examined using X-ray diffraction, scanning electron microscopy, laser microscopy and a micro-Vickers hardness tester. GBIH nitriding and post-treatment with FPP formed nitrided layers with high hardness and compressive residual stress at the surface of the alloy within a short period of time. This is due to the diffusion of nitrogen atoms during GBIH nitriding and plastic deformation of the surface layer during FPP. Reciprocating ball-on-disk wear tests were performed to investigate the wear resistance of the surface-treated alloy. The wear resistance of the titanium alloy was improved by the proposed surface treatment compared with samples that were only polished or FPP-treated. This is due to the presence of a nitrogen compound layer with high hardness at the surface. The abrasiveness toward the wear test counter material was also decreased by the combined surface treatment.
  • Development of a Powder Wettability Evaluation Technique by Analyzing the Increase in Internal Pressure due to Capillary Suction of Closed Powder Bed —Effect of Powder-Bed-Preparation Method and Powder Surface Area Estimation Method—

    pp. 1510-1518

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    DOI:10.2320/matertrans.MT-Y2021002

    Evaluation of powder wettability is important to prepare well dispersed slurries. Therefore, in this study, a technique for evaluating powder wettability was developed to analyze the increase in the internal pressure of a closed powder bed due to capillary suction to determine the contact angle of the powder. The effect of the powder-bed-preparation method and powder surface area estimation method on the determined value of the contact angle was discussed. We demonstrated that the improved air permeation test proposed in this research can accurately determine the powder surface area, resulting in a faithful determination of the contact angle of the powder. It was also shown that compression under the shearing method could result in a denser and more homogeneous powder bed when compared to the conventional tapping method, indicating high reproducibility for estimating the contact angle. This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 67 (2020) 629–640.
  • Negligible Temperature Dependence of Nitrogen Solubility in Molten Silicon–Chromium Alloys at Middle Composition Range

    pp. 1519-1523

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    DOI:10.2320/matertrans.MT-M2021074

    N solubility in molten Si-based alloys is an important property for controlling the concentration of N in SiC crystals, fabricated by the solution growth method. In this study, N solubility in Si–Cr alloys, which is the commonly used solvent for solution growth, was measured at 1953, 2023, and 2073 K, and then evaluated in terms of thermodynamics. The measured N solubilities in Si–40, 55, and 72.5 mol% Cr obeyed the Sieverts’ law, and increased with the increase in Cr concentration. For Si–40 and 55 mol% Cr alloys, the temperature dependence of the N solubility was negligibly small, or even slightly positive, which is opposite to those for pure Si and Cr. This reverse feature in the middle composition range was reproduced by the estimated activity coefficient of N by the quasi-chemical model, which assumes N as interstitial atoms in Si–Cr solvents. In addition, another feature was found for the estimated activity coefficient of N, that is, an upward convex against the Si–Cr composition. These characteristics arise from the negatively large heat of mixing of Si–Cr alloys and its relatively large temperature dependence.
  • Wettability of Pure Metals with Liquid Sodium and Liquid Tin

    pp. 1524-1532

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    DOI:10.2320/matertrans.MT-M2021107

    This study aims to control the wettability of pure transition metals by liquid sodium or liquid tin. Such wettability was evaluated by measuring the contact angles with the droplet method. Pure titanium, iron, nickel, copper, and molybdenum metals were selected as specimens in this experiment. All experiments were conducted in an environment with high pure argon gas and extremely low moisture to avoid the influence of oxygen on the liquid metals. The measurement temperature was just above the melting temperature of each liquid metal. Results showed that in both liquid sodium and liquid tin, the measured contact angle changed depending on the atomic number of the substrate metal. The electronic structure of the interface between a liquid metal and a substrate metal was calculated by the molecular orbital method. Simple cluster models of the interface between the liquid metal and substrate transition metal were used in this calculation. The calculation results confirmed that the electronic state of the interface was expressed well. The magnitude of the atomic bonding between the liquid metal and substrate metal changed in accordance with the atomic number of the substrate metal, and the magnitude of the atomic bonding between the substrate metals changed similarly. There was an evident relationship between the atomic bonding ratio and the contact angle. The atomic bonding ratio is the ratio of the liquid-metal-substrate metal-atomic bonding to the substrate metal atomic bonding. This finding implies that the atomic bonding affected the wettability between the liquid metal and the substrate metal. The atomic bonding was obtained as one of the indications was obtained to control the wettability by liquid metal. This Paper was Originally Published in Japanese in J. Japan Inst. Met Mater. 85 (2021) 110–119.
  • Reduction of Titanium Dioxide to Metallic Titanium by Thermal Decomposition via Titanium Disulfide

    pp. 1533-1540

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    DOI:10.2320/matertrans.MT-MAW2021002

    We have earlier reported the synthesis of metallic titanium ingot by thermal decomposition process using titanium nitride (TiN) as the intermediate material, with a significant low decomposition temperature of approximately 3500 K. The present study reports the manufacturing process of metallic titanium ingot via thermal decomposition using titanium sulfides (TiSX) as intermediate materials: decomposition temperature of one of the titanium sulfides, TiS, is approximately 4000 K. The thermal decomposition was performed by an arc-flame in a conventional arc melting equipment. The reduced product exhibiting a lustrous surface is analyzed by XRD, and is matched with diffraction pattern of metallic titanium.
  • Cobalt Alloying Effect on Improvement of Ni/YSZ Anode-Supported Solid Oxide Fuel Cell Operating with Dry Methane

    pp. 1541-1548

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    DOI:10.2320/matertrans.MT-M2020355

    Although the cermet consisting of nickel and zirconia is useful as the solid oxide fuel cell anode, the conventional cermet consisting of nickel and yttria-stabilized zirconia (Ni/YSZ) is prone to be deactivated for a direct supply of hydrocarbon fuels. This paper describes a method to retard the deactivation of the Ni/YSZ-based cermet anode by being modified with appropriate incorporation of Co as the alloying element into Ni. The single-type anode-supported solid oxide fuel cell (SOFC) consisting of the Ni0.75Co0.25/YSZ cermet anode, YSZ film electrolyte, and La0.8Sr0.2MnO3 cathode exhibited a prolonged stable SOFC performance at 750°C for dry methane (CH4) feeding compared to the one using the Ni/YSZ anode. The microstructural modification of the cermet anode caused a carbon tolerance effect against CH4 accompanied by a low anodic polarization resistance.
  • Evaluation of Porosity in Gas-Atomized Powder by Synchrotron X-ray CT and Investigation of the Effect of Gas Species

    pp. 1549-1555

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    DOI:10.2320/matertrans.MT-Y2021001

    The presence of pores in gas-atomized alloy powders induces a significant deterioration in the properties of the final product. However, there is no established technique to quantitatively analyze the porosity of gas-atomized powders. In this study, the pores in gas-atomized amorphous Fe76Si9B10P5 powder particles prepared under different atomization conditions were analyzed in detail using synchrotron radiation X-ray computed tomography. This technique allowed the detection of small pores with diameters below 10 µm. It also enabled the quantification of the porosity; thus, the pore diameter and volume ratio under different atomization conditions were determined. The volume ratio of the pores with the use of low-pressure Ar as the atomization gas was lower than that with the use of high-pressure Ar. The use of a low-pressure gas during spraying induced an increase in the diameter of the powder particles, thereby resulting in the presence of numerous irregular-shaped particles. The results of X-ray diffraction confirmed the partial precipitation of a crystalline phase with a decrease in the cooling rate. The use of 3 or 7% Ar–H2 mixtures as the atomization gas induced a decrease in the number and volume of pores, without affecting the particle size and cooling rate. The presence of H2 as a reducing gas suppressed the surface oxidation of the droplet during the atomization of the molten-metal stream, which allowed trapped gas bubbles to be efficiently removed before solidification. This study demonstrated that the total pore volume in a powder can be decreased using a H2-containing gas. The low cost and abundance of H2 could facilitate the use of this technique in various industrial applications. This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 68 (2021) 167–174.
  • Influence of Chunky Graphite on Fatigue Crack Propagation Characteristics in Heavy Section Spheroidal Graphite Cast Iron

    pp. 1556-1561

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    DOI:10.2320/matertrans.F-M2021841

    The purpose of this study is to investigate the influence of chunky graphite on the characteristics of fatigue crack propagation in heavy section spheroidal graphite cast iron. Samples containing and not containing chunky graphite were cut from a large ingot of spheroidal graphite cast iron. The fatigue crack propagation test conformed to ASTM. Stress ratio R was 0.1, and the specimen used was of the 1CT type with a thickness of 12.5 mm, and humidity RH = 0%.In the samples containing chunky graphite, the slope of the linear approximation m at the IIb stage of fatigue crack propagation becomes larger and fatigue crack growth rate becomes faster than the spheroidal graphite samples. The reason seems to be that crack propagates along the graphite connected to the chunky graphite. The decrease in the threshold stress intensity factor range ΔKth of the chunky graphite samples was smaller than the decrease in tensile strength. In the chunky graphite samples, the fracture surface roughness became large and the crack closure induced by fracture roughness occurred conspicuously. The threshold stress intensity factor range decreased due to the influence of the chunky graphite. However, it was found that threshold stress intensity factor range does not decrease as much as the tensile strength due to the effect of the crack closure induced by fractured surface roughness. This Paper was Originally Published in Japanese in J. JFS 91 (2019) 844–849.
  • Interface Formation Mechanism of Cemented Carbide Dipped in Molten Cast Iron

    pp. 1562-1568

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    DOI:10.2320/matertrans.F-M2021842

    When cemented carbide contacts molten cast iron during the insert casting process, the binder phase of the cemented carbide is thought to melt even if the molten temperature of the cast iron is lower than the solidus temperature of the cemented carbide (1593 K). It is important to understand the melting mechanism to clarify the interface formation mechanism, and subsequently control the interface structure. The purpose of this study is to clarify the interface formation mechanism from the microstructural change of cemented carbide dipped in molten cast iron. A round bar specimen made of cemented carbide was dipped in molten cast iron at 1473 to 1596 K, and pulled up after a predetermined time. Microstructure observation, elemental analysis, and hardness test were performed on the cross-section of the specimen. The specimen changed from a homogeneous sintered structure to a two-layer structure, the center side was a non-reacted layer that did not change, and the outer side was the transition layer where melting had occurred. The diffusion of Fe and C is thought to have decreased the solidus temperature of the binder phase significantly that the binder phase melted. The non-reacted layer radius could be expressed by the rate equation derived from the Nernst-Brunner equation. Structural changes were seen at the interface such as increased outer diameter of the cemented carbide round bar specimen, occurrence of shrinkage cavities in the transition layer, and characteristic concentration of Co at the boundary. These are thought to be due to liquid phase migration occurring in the molten binder phase and decreased WC solubility due to increase in Fe concentration. This Paper was Originally Published in Japanese in J. JFS 93 (2021) 67–73. The background, experimental procedures, results, and discussion have been revised.
  • Effects of Reduced Pressure and Casting Design on Mold Filling in Expendable Pattern Casting Process of Thin Wall Aluminum Alloy Castings

    pp. 1569-1575

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    DOI:10.2320/matertrans.F-M2021843

    The effects of reduced pressure and casting design on mold filling for thin wall aluminum alloy castings in the expendable pattern casting (EPC) process were investigated experimentally. Thin wall aluminum alloy plates were cast by the EPC process using several coats with different permeabilities. The fluidity length and melt velocity were measured. The application of the reduced pressure condition in the flask led to a larger melt velocity and longer melt fluidity length. There was no significant difference in the melt velocity depending on the casting design. However in the high coat permeability region, the melt fluidity length in top pouring was longer than that in bottom pouring. The distances of melt flow stop were predicted based on the heat transfer from the molten metal to the mold through the coat using measured melt velocities. Except with top pouring in the high coat permeability region, the predicted values more or less agreed with experimental fluidity length values. This Paper was Originally Published in Japanese in J. JFS 93 (2021) 121–127.
  • Spot Forge-Welding for Rapid Dissimilar Joining of Fe to Al to Produce an Intermetallic Compound-Free Interface

    pp. 1576-1582

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    DOI:10.2320/matertrans.MT-M2021080

    To solve the problem in joining dissimilar metals caused by intermetallic compound, dissimilar lap joining of SUS304 and A5083 was examined using a spot forge-welding method. The tensile shear load reached approximately 4.5 kN with a short bonding time of less than 0.1 s. Fatigue data were also acquired to confirm practical strength. The reaction layer of the bonded interface was approximately 10 nm thick, consistent with the calculated value. A high-strength dissimilar joining process that provides a highly productive and virtually intermetallic compound-free interface was established.
  • Effect of Glass Composition on Sinterability of Copper Terminal Paste for Multilayer Ceramic Capacitors

    pp. 1583-1588

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    DOI:10.2320/matertrans.MT-M2021067

    Low-melting glass with an optimal composition should be developed for application to Cu electrodes in multilayered ceramic capacitors (MLCCs). This study evaluated the glass transition temperature, plating solution resistance, and wettability of glass melts on Cu substrates for low-melting glass with a conventional composition and compositions of BaO, TiO2, ZnO, and V2O5 added to 46SiO2/27B2O3/27Na2O (mol%). Moreover, we produced a Cu electrode paste for an MLCC using the designed glasses and evaluated the characteristics in terms of terminal electrode sintering. The plating solution resistance was improved by adding TiO2 to 46SiO2/27B2O3/22Na2O/5BaO (mol%) glass. Furthermore, adding V2O5 improved the glass melt fluidity while maintaining the plating solution resistance, thereby improving the Cu base wettability. Compared with conventional glass, the 45.0SiO2/17.6B2O3/16.6Na2O/4.9BaO/2.1V2O5/8.8TiO2/4.9ZnO (mol%) composition formed glasses with low transition temperatures, good Cu wettabilities, and superior plating solution resistances. The fired film of the Cu electrode paste using this new glass was inferior in sintering as compared with the conventional glass and did not become densified. As a result of measuring the amount of carbon in the fired film, it was found that the new glass has a larger amount of residual carbon than the conventional glass. In addition, a reaction layer with ceramic is confirmed in the new glass, and there is concern about ceramic embrittlement due to crystal precipitation and cracks. For practical use of new glass as an electrode paste material, removal of residual carbon and suppression of ceramic reaction are considered to be future issues.
  • Advanced Electron Microscopy for Materials Science

    pp. 1589-1595

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    DOI:10.2320/matertrans.MT-M2021086

    This paper presents current research trends in advanced electron microscopy techniques for materials science. The survey is based on the special issue of Materials Transactions published in October 2019 (Vol. 60, No. 10). Advanced electron microscopy has been applied extensively to characterize various materials. The recent development and extension of analyses of electric fields and the collective motions of secondary electrons by in situ electron holography are discussed in detail.

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07 Dec. (Last 30 Days)

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