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

MATERIALS TRANSACTIONS Vol. 59 (2018), No. 4

  • Crystallography and Energetics of Second Phases and Interfaces

    pp. 509-517

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    DOI:10.2320/matertrans.M2017310

    Morphology and crystallography of second phases, such as precipitates, martensites, inclusions, etc., embedded in a parent phase are discussed. The contribution of elastic strain energy is considered to find the most favorable shape of a second phase for given eigenstrains and elastic constants. Analyses based on the idea of invariant plane and invariant line deformations are conducted to discuss crystallography and energetics of second phases. Simple criteria are proposed to explain orientation relationship between the second phase and the parent phase as well as epitaxial relationship for substrate/thin film systems. Two types of stress effects are discussed; one on the morphology of the second phase and the other on variant selection. This Paper was Originally Published in Japanese in Materia Japan 56 (2017) 331–337. Since the maximum page allowance of this overview was larger than that for the Japanese version in Materia Japan, more detailed descriptions and explanations were possible. Accordingly, Chapters 2, 4 and 5 were made longer and Keywords and References were revised. Tables 1 and 2, and Figs. 6 and 8 as well as some equations were newly added.
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  • Effect of Microstructural Continuity on Room-Temperature Fracture Toughness of ZrC-Added Mo–Si–B Alloys

    pp. 518-527

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    DOI:10.2320/matertrans.MJ201613

    The room-temperature fracture toughness of ZrC-added Mo–Si–B alloys prepared using an arc-melting technique was investigated. The constituent phases of the heat-treated alloys were mainly molybdenum solid solution (Moss), Mo5SiB2 (T2), and ZrC, with a small amount of Mo2B in a few alloys. Four-point bending tests with a Chevron-notch were performed, and the average fracture-toughness values ranged from 12.4 to 20.3 MPa(m)1/2 depending on alloy composition. Here, the effects of the volume fractions of the constituent phases and the continuity of Moss on the fracture toughness are discussed. The fracture toughness improved with an increase in the volume fractions of the Moss and ZrC phases. Alloys with a higher Moss continuity exhibited higher fracture toughness, for example, the fracture toughness of 64.5Mo–3.2Si–6.5B–12.9Zr–12.9C (mol.%) was 19 MPa(m)1/2; the alloy contained a >95%-continuous Moss phase, even though it also contained 16 vol.% T2 and 23 vol.% ZrC.
  • Effects of Process Control Agents on the Mechanical Alloying Behavior of Nb-Ti-Si Based Alloy

    pp. 528-537

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    DOI:10.2320/matertrans.MJ201609

    Powder mixtures with the composition of Nb-20Ti-15Si-5Cr-3Hf-3Al (at.%) were mechanically milled in a planetary ball mill. Normal hexane (5 mass%), methyl alcohol (5 mass%) and different amount of stearic acid (0.625, 1.25, 2.5 and 5 mass%) were used respectively as the process control agent (PCA). The effects of the type and amount of PCAs on the mechanical alloying (MA) behavior of the powder mixtures have been investigated systematically. It has been shown that, compared with using 5 mass% methyl alcohol or stearic acid, ball milling with the same amount of normal hexane shows the fastest MA progress. However, the final powder particles have a coarse size as a result of severe cold welding. Ball milling with 5 mass% stearic acid shows a hyperslow MA progress due to its excessive lubrication effect. Milling with 5 mass% methyl alcohol yields a moderate MA rate and much fine particle size. However, HfC formed during milling due to the high carbon contamination of methyl alcohol. Moreover, it is found that decreasing the amount of stearic acid could accelerate the MA progress significantly. A suitable amount of PCA is necessary to restrain the excessive cold welding and avoid the formation of HfC. Finally, 1.25 mass% stearic acid is adopted as the PCA to fabricate the powder mixtures used for hot pressed sintering.
  • Grain Boundary Sliding-Induced Creep of Powder Metallurgically Produced Nb-20Si-23Ti-6Al-3Cr-4Hf

    pp. 538-545

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    DOI:10.2320/matertrans.MJ201610

    The multi-component alloy Nb-20Si-23Ti-6Al-3Cr-4Hf was produced by powder injection molding or hot isostatic pressing of pre-alloyed, gas-atomized powder. The resulting microstructure comprises the Nb solid solution as well as the α- and γ-modifications of Nb5Si3. Creep is evaluated in constant true stress tests at 1000 and 1100 ℃. The analysis of the creep behavior regarding its dependence on microstructural and testing parameters such as grain size, stress, and temperature reveals grain boundary sliding as the prevalent deformation mechanism. This is backed up by SEM/EBSD and TEM observations in the undeformed and deformed state. This creep mechanism was found to be a direct result of the small grain/phase sizes after powder metallurgical processing and led to a creep resistance even lower than that of a single-phase niobium-based alloy.
  • Influence of Atomic Size Factors on the Phase Stability of Laves Phase in Nb-Cr-Ni-Al and Nb-V-Ni-Al Phase Diagrams

    pp. 546-555

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    DOI:10.2320/matertrans.MJ201604

    Phase equilibria among the refractory bcc solid solution (bccss), B2, and Laves phases in Nb-Cr-NiAl and Nb-V-NiAl isothermal sections were studied with the aim of introducing the NiAl-B2 phase and/or Al-containing Laves phase for improvement of the oxidation resistance of the bccss phase as an Al reservoir layer for the Al2O3 surface layer. Laves phases appear in a wide composition range in both of the isothermal sections, which prevent equilibration of NiAl-B2 with the Nb-rich bccss phase. The geometrical model proposed by Edwards was applied to understand the site-substitution behavior of the multi-component AB2 Laves phase. In the Nb-Cr-NiAl, Nb-V-NiAl, and Nb-Mo-NiAl systems, the site-substitution behavior of the Laves phases could be explained by comparison of the average atomic diameters of NiAl-B2, Cr, V, and Mo.
  • Microstructural Investigation of Oxidized Complex Refractory High Entropy Alloys

    pp. 556-562

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    DOI:10.2320/matertrans.MJ201611

    The microstructures of two newly developed refractory high entropy alloys were examined after isothermal oxidation at 1200°C for 10 hours. Scanning electron microscope analysis showed the formation of aluminosilicate layer on the sample surface, and the structure of oxide layers appears to be greatly affected by the content of Al and V. With increased Al content and decreased V content, the size of pores within the internal oxidation zone was decreased. Future directions to improve the oxidation resistance of complex refractory alloys were proposed.
  • Effect of Cr on the Oxidation Resistance of Co-Based Oxide Dispersion Strengthened Superalloys

    pp. 563-567

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    DOI:10.2320/matertrans.MJ201603

    Alumina-forming oxide dispersion strengthened (ODS) superalloys are favorable oxidation-resistant materials for extremely high temperature applications. In order to develop the advanced Co-based superalloys with high strength and superior oxidation resistance at elevated temperature of 1000℃, a new series of Co-Cr-Al ODS superalloys were designed and fabricated by mechanical alloying (MA) and spark plasma sintering (SPS), and then followed by hot rolling and annealing at 1200℃. In this work, the oxidation behavior of Co-10Al (mass%) ODS superalloys with/without 20Cr was investigated at 1000℃ in air to understand the effect of Cr on oxidation resistance. The results indicate that the addition of Cr improves the oxidation resistance significantly through optimizing the oxide scales from the multilevel scales with an external CoO/CoAl2O4 and an internal Al2O3 to a single layer of Al2O3. The alumina-forming Co-20Cr-10Al (mass%) ODS superalloys are expected to be applicable at 1000℃.
  • Numerical Analysis of Effects of Compressive Strain on the Evolution of Interfacial Strength of Steel/Nickel Solid-State Bonding

    pp. 568-574

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    DOI:10.2320/matertrans.MBW201708

    A molecular dynamics (MD) simulation of the solid-state bonding between single crystals of bcc iron and fcc nickel, i.e., dissimilar components, was conducted by hot-pressing with various initial compressive strains ranging from 14 to 20% and subsequent uncompressed isothermal holding at 873 K. Then, the intrinsic strength of the interfaces with various isothermal holding times was evaluated by uniaxial tensile technique. It was found that the interface separation follows the traction-separation law and that always take place either at the interface or close to the interface. The intrinsic strength of the interface is very low under an as-compressed condition and tends to rapidly increase in the early stage of isothermal holding. In addition, lower intrinsic strength was observed in a specimen with higher initial compressive strain. The significant increase in the intrinsic strength is attributed to the short-range atomic rearrangement of a layer of disordered atoms at the interface, driven by energy stored from the compressive deformation.
  • Isothermal Section of Ga–Ru–Cu Ternary Phase Diagram at 1073 K: Formation of New Ternary Phase, Ga4Ru3Cu, and Its Structural Relation with the GaRu β-Phase

    pp. 575-579

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    DOI:10.2320/matertrans.MBW201706

    We have investigated the isothermal phase diagram of the Ga–Ru–Cu ternary system at 1073 K by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and transmission electron microscopy to determine whether the stable icosahedral quasicrystal (i-phase) forms, as it does in the similar Al–Ru–Cu system, and new intermetallic phases exist. This is the first systematic investigation of the Ga–Ru–Cu system. No stable i-phase is identified in the Ga–Ru–Cu alloy system. However, we found a new ternary (τ) phase in the Ga–Ru–Cu system, which is characterized as a C-centered orthorhombic lattice with aτ = 11.80 Å, bτ = 6.04 Å, and cτ = 3.07 Å. The (ideal) chemical composition of the τ-phase is Ga50Ru37.5Cu12.5 (Ga4Ru3Cu). This new phase is stable up to 1073 K. Above 1173 K, the τ-phase transforms to the cubic GaRu (β) phase without any secondary phases. Thus, there is an order–disorder transition between the low-temperature τ-phase and the high-temperature cubic β-phase in this temperature range.
  • Description of Thermal Vacancies in the CALPHAD Method

    pp. 580-584

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    DOI:10.2320/matertrans.M2017328

    Thermal vacancies in solids have not been treated explicitly in the CALPHAD-type thermodynamic assessments because it was considered that their contributions to the Gibbs energy were limited, even at the melting point. However, the vacancy fraction is necessary for dynamic simulations, such as precipitations and diffusion processes. In this paper, a procedure is proposed to set parameters in the CALPHAD-type assessments, to reproduce the temperature dependency of thermal vacancies in pure metals and solid solutions. This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 81 (2017) 127–132. In order to more precisely explain how to set the Gibbs energy of the empty end-member, the 0GmVa term was explicitly described in eqs. (19) and (20). The reference 8) was changed. Eq. (21) was omitted. Eqs. (4), (5), (21), (22) and (23) were renumbered.
  • Tunnel-Type Magneto-Dielectric Effect and Its Annealing Study in Co–SiO2 Granular Films

    pp. 585-589

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    DOI:10.2320/matertrans.MBW201712

    Tunnel-type magneto-dielectric (TMD) effect arising from the spin-dependent quantum tunneling between nano-sized granular pairs, has opened up new route for room temperature magnetoelectric fields. We first investigated the TMD properties in metal-oxide (Co–SiO2) granular films and their annealing effect in this work. Results show that the films exhibit a TMD ratio () of 1% with high electrical resistivity of >108 µΩ·m and intermediate optical transmittance in Co0.24–(SiO2)0.76 films. Annealing investigations suggest that the samples remain TMD response up to 573 K, and further increment in annealing temperature leads to the inter-diffusion between Co and SiO2 interfaces, thus producing the increasing oxidation of metallic Co. This study demonstrates the possibility of TMD effect in metal-oxide composite materials, and may be desirable for a variety of other wide oxide-based candidates for magnetoelectric device applications.
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  • Effects of Scandium and Zirconium Addition on Recrystallization Behavior of Al–Mg–Si Alloy

    pp. 590-597

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    DOI:10.2320/matertrans.L-M2018802

    The effects of thermally stabilized particles on the recrystallization behavior of an Al–Mg–Si alloy were investigated to obtain the fundamental knowledge for controlling the microstructure, texture, and mechanical properties of this alloy. In this study, the Al–Mg–Si–Sc–Zr alloy was cast, homogenized, and hot-rolled. Three types of spherical Al3(Sc, Zr) particles with L12 structure, rod-like incoherent, spherical semi-coherent, and spherical incoherent particles, were observed in a hot-rolled sample of the Al–Mg–Si–Sc–Zr alloy using transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), and energy-dispersive X-ray spectroscopy (EDS). In addition, three-dimensional electron tomography (3D-ET) and STEM-EDS revealed that all particles have a core-shell structure with a Sc-enriched core and a Zr-enriched shell. It is considered that these particles are formed during casting, homogenized treatment, and hot rolling. The crystal orientation distribution of the sample after cold rolling indicated that the presence of Al3(Sc, Zr) particles may interfere with the recrystallization (grain growth) until 600°C. Comparison with the driving force of primary recrystallization and grain growth, and the pinning force of Al3(Sc, Zr) particles, showed that these particles mainly contribute to the suppression of grain growth. The results of an in-situ heating SEM/EBSD analysis of the cold-rolled Al–Mg–Si–Sc–Zr alloy supported this suggestion. This Paper was Originally Published in Japanese in J. JILM 66 (2016) 609–616.
  • Fabrication of Electrodeposited Permalloys with High Strength and High Ductility

    pp. 598-601

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    DOI:10.2320/matertrans.MBW201707

    The best electrodeposition conditions for fabricating artifact–free and ductile bulk nanocrystalline (nc) Ni–Fe alloys were investigated by evaluating the orientation indices of thin–film samples. Bulk nc Ni–Fe alloys electrodeposited under optimum conditions exhibited a high ultimate tensile strength of 1.9 GPa and a high tensile ductility of 9.1–12.2%. These alloys also showed a high Fe content of 25–29 mass%, achieving a permalloy composition. This study suggests that we succeeded in overcoming the trade–off between Fe content and elongations observed for previous electrodeposited Ni–Fe alloys.
  • Plastic Deformation Behavior of Mg-Y Alloy Single Crystals Observed Using In Situ Brinell Indentation

    pp. 602-611

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    DOI:10.2320/matertrans.M2017336

    A newly established in situ Brinell indentation technique was conducted to investigate the plastic deformation behavior of pure Mg and Mg-Y alloy single crystals under complex stress conditions. The deformation morphology on the upper surfaces of the specimen around the indent could not be sufficiently observed using the previously reported in situ indentation methods with an optically transparent indenter due to the refraction of rays at the indenter/air interface. In this study, the gap between the indenter and the specimen surface is filled with immersion liquids such as silicone oil and kerosene. This technique enables observation of the specimen surface during indentation. Application of the in situ Brinell indentation to pure Mg and Mg-Y alloy single crystals revealed that the shape of the indents is not circular but elliptical, even during loading. The aspect ratio of the indents decreases with increasing Y content. Moreover, the occurrence of plastic deformation around the indents and beneath the indenter could be observed during the loading and unloading processes using the in situ Brinell indentation method. This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 81 (2017) 198–205.
  • Effect of Sintering Temperature on Fatigue Crack Propagation Rate of Sintered Ag Nanoparticles

    pp. 612-619

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    DOI:10.2320/matertrans.M2017392

    In this study, the effect of sintering temperatures on fatigue crack propagation rates of sintered Ag nanoparticles were investigated. Paris’ law type fatigue crack propagation law between the fatigue crack propagation rate and the inelastic strain energy density range was found to hold at all test temperatures. The power exponent in the fatigue crack propagation law for the Ag nanoparticles sintered at 423 K was large and the fatigue crack propagation rate was fast with excessively brittle behavior. The stress and strain concentrations at neck parts interlinked with each other in damaged areas, in addition to the brittle grain boundary fractures, resulted in the excessively brittle behavior. On the other hand, the Ag nanoparticles sintered at 473 K showed more ductile behavior as pores decreases with sintering progression and the local strain concentrations were fewer compared to the Ag nanoparticles sintered at 423 K. However, with test temperature increasing, the grain boundary became viscous, so the power exponent in the fatigue crack propagation law and fatigue crack propagation rate at any sintering temperature decreased, causing only minor differences by sintering temperature in fatigue crack propagation rates.
  • Lead-Based Anodes for Copper Electrowinning: Effect of Grain Size on Mechanical and Anticorrosion Properties

    pp. 620-624

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    DOI:10.2320/matertrans.M2017356

    The aim of this paper was to study the effect of the grain size of lead-based anodes for copper electrowinning on their mechanical and anticorrosion properties. Aged anodes were cold rolled to different thicknesses, achieving reductions varying from their standard 50% up to 75%. The grain size, yield stress, and corrosion behavior of the different rolled samples was evaluated by galvanostatic polarization essays. It was found that by lowering the grain size, the yield stress of the anodes increased up to 66 MPa and the improved anodes maintained a higher yield stress with time and throughout temperature operation in cells, as compared with the currently used anodes. Also, a significant diminution of the corroded mass, up to 30%, was observed as cold reduction increased due to the formation of a more compact and less permeable PbSO4 at lower grain size.
  • Microstructure and Compressive Properties of Aluminum Foams Made by 6063 Aluminum Alloy and Pure Aluminum

    pp. 625-633

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    DOI:10.2320/matertrans.M2017300

    Aluminum foams are new kind of structural-functional composite materials which comprised of aluminum matrix and gas pores. In this paper, aluminum foams with homogeneous pore structure made by 6063 aluminum alloy were fabricated by melt foaming method. As comparison, the aluminum foams were also fabricated by pure aluminum. Studies on process parameter, microstructure and mechanical properties have been carried out. Process optimization for aluminum foams made by 6063 alloys has been studied according to the orthogonal experimental design method. The cell wall of aluminum foam is comprised of Al matrix, Ca-thickening phase and Ti-containing phase. The difference between foams made by 6063 aluminum alloy and pure aluminum is that there is element Mg and element Si dissolved in the matrix in the 6063 aluminum foam, which are positive to the foam strength accordingly. For different base materials, the compressive strength of foams made by 6063 aluminum alloy is greater than that made by pure aluminum.
  • Equilibrium Modeling for Solvent Extraction of Nickel and Ammonia from Alkaline Media with the Extractant LIX84-I

    pp. 634-641

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    DOI:10.2320/matertrans.M-M2018801

    The equilibria for the extraction of nickel(II) and ammonia from ammonium salt solutions by using the extractant LIX84-I (active component, 2-hydroxy-5-nonylacetophenone oxime) dissolved in a non-polar diluent, ShellSol D70, were studied at pH 2–10 and 298 K under different ammonium salt concentrations, kinds of counter anions, aqueous phase pH values, and phase ratios. The distribution constant of the nickel–hydroxyoxime complex was independent of the kind and concentration of ammonium salt, and the logarithm of the extraction constant of nickel linearly increased with the ionic strength of the aqueous phase. By using the initial conditions and a model based on the present results and those of our previous study concerning copper extraction (Mater. Trans., 58 (2017), 1427–1433), we were able to predict the extraction behavior of nickel, copper, and ammonia from copper–nickel mixed ammonium sulfate solutions. The agreement between the predicted and experimental data confirmed the validity of our model.
  • Effect of Cr Diffused Layer Formed by AIH-FPP Treatment on Adhesion of DLC Films to a Carbon Steel Substrate

    pp. 642-647

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    DOI:10.2320/matertrans.M2017367

    In this study, a diffusion layer of Cr was formed on the surface of a carbon steel by atmospheric-controlled induction heating fine particle peening (AIH-FPP) treatment, followed by coating of a diamond-like carbon (DLC) film in an attempt to provide a less expensive and facile method for the production of DLC-coated steels with superior adhesion to conventional methods. Frictional wear tests and indentation tests with Vickers indenter were conducted on these DLC-coated steel specimens, and adhesion to the substrate was investigated experimentally. It was revealed that the formation of a Cr diffused layer on the surface of the substrate by AIH-FPP treatment significantly improved the adhesion of the DLC film to the substrate under a sliding load and a large plastic deformation. In addition, frictional wear tests revealed that the thickness of the Cr diffused layer formed by AIH-FPP treatment has a significant influence on the adhesion of the DLC film to the substrate. A thicker Cr diffused layer with a thickness of about 100 µm imparted better adhesion of the DLC film to the base material, and the superior friction and wear characteristics of the DLC film were sustained up to 49000 wear cycles while the specimens with a Cr diffused layer thickness of about 40 µm and without a Cr diffused layer maintained low friction coefficients up to 36000 and 8000 wear cycles, respectively. These results suggest that the proposed film forming method with a Cr diffused layer formed by AIH-FPP treatment is superior to the conventional method and is very efficient as a technique to improve the adhesion of DLC films to a carbon steel substrate. This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 81 (2017) 352–357. References (6) and (13) were added.
  • Visible-Light-Assisted Silver Ion Reduction through Silver Diammine and Citrate Aggregation, and Silver Nanoparticle Formation

    pp. 648-655

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    DOI:10.2320/matertrans.M2017405

    Hexagonal silver nanoparticles are directly formed in a solution of 6.6 mM silver citrate and 132 mM ammonia irradiated by 1.98–2.46 eV visible light. The corresponding silver ion concentration is 19.8 mM, which is several orders of magnitude higher than those employed in other silver-nanoparticle-formation experiments. In the present study, the roles of silver citrate and ammonia on nanoparticle formation are investigated through experiments in which the concentrations of silver citrate (SC) and ammonia (NH3) are altered. Silver nanoparticles are efficiently formed when [SC] is the 1.65–6.6 mM range and the [NH3]/[SC] ratio is ∼8–16. Further, hexagonal nanoplates are dominantly formed when [SC] = 1.65–6.6 mM and [NH3]/[SC] = ∼16. Within this range, hexagonal nanoplate formation is insensitive to solution concentration. Concentrations of SC less than 1.65 mM, or NH3 ≥ 132 mM, inhibit the formation of silver nanoparticles. These observations suggest that aggregates composed of diammine silver complexes and citrate are formed at specific concentration ranges of SC and NH3, and they assist in the photoreduction of silver ions by 1.98–2.46 eV visible light. Furthermore, the lateral growth of platelet seeds is proposed to be the dominant mechanism for the formation of hexagonal nanoplates at [SC] values of 1.65–6.6 mM and [NH3]/[SC] = ∼16.
  • Numerical Analysis of Effect of Pin Tip Radius on Residual Stress Distribution in Ultrasonic Impact Treatment

    pp. 656-662

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    DOI:10.2320/matertrans.P-M2018805

    Ultrasonic impact treatment (UIT) is currently used in several manufacturing processes. UIT is a process in which ultrasonic vibration is used to impact pins onto a metal surface. To clarify the mechanisms of deep compressive residual stress in UIT, the effects of the pin tip radius on residual stress distributions were analyzed by the dynamic explicit finite element method. The sonotrode vibration amplitude and frequency were 25 µm and 20 kHz, respectively. The pin velocity accelerated by the sonotrode was approximately 4.6 m·s−1 at the first impact. The depth of the residual compressive stress remained nearly constant after the first impact for pins of various tip radii (1.5, 3, 8 and 12 mm). During the first 10 ms, eleven impacts occurred between the 8 mm tip radius pin and the metal surface. The pin velocities were highly dependent on the sonotrode velocity in the collision range from 4 to 16 m·s−1. The depth of residual compressive stress increased with increasing impact number. After 10 ms, the depth of residual compressive stress was approximately 2.5 mm when using an 8 mm tip radius pin, and it increased with increasing tip radius. This Paper was Originally Published in Japanese in J. JSTP 58 (2017) 35–40.
  • Influence of Additives on Surface Roughness at Turned End Face of Fe–Cu–C Sintered Steel

    pp. 663-668

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    DOI:10.2320/matertrans.Y-M2018803

    Influence of additive material to surface roughness in turning of sintered steels is not well known. In this study, effect of manganese sulfide (MnS), silica and alumina powder was investigated on a viewpoint of material characteristics near turned surface. The surface roughness of the sintered steel added with MnS was smaller than the others. MnS was extended and dispersed finely in the deformed layer near the turned surface, while silica and alumina were localized but not extended. Nano indentation test showed that the deformed layer of the sintered steel added with MnS had lower hardness in comparison with others. We considered that a tear mark of the cutting chip separated from deformed layer was lowered by MnS and the trace of torn chips, namely the surface roughness became relatively small. However, the deformed layer of the sintered steel added with silica or alumina was close to that of the additive-free sintered steel and the surface roughness became similar to these cases. This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 64 (2017) 333–337.
  • Microstructure and Mechanical Properties of Mg–Gd–Y–Zn–Zr Alloy Prepared by Repetitive Upsetting and Extrusion

    pp. 669-673

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    DOI:10.2320/matertrans.M2017323

    The microstructure and room temperature tensile properties of Mg–12Gd–3Y–2Zn–0.5Zr (wt%) alloy processed by repetitive upsetting and extrusion (RUE) at decreasing temperature condition were investigated. The RUE was carried out up to cumulative strains of around 5.4 with decreasing temperature from 753 to 683 K pass-by-pass. With increasing RUE passes, average grain size was gradually decreased from 58 to 7.3 µm and microstructure became more homogeneous. Block-shaped long period stacking ordered (LPSO) phases at grain boundary were broken into small blocks or rods. Lamellar LPSO structures dissolved gradually and β-Mg5(Gd,Y) phase particles precipitated at grain boundaries. Both strength and ductility were improved simultaneously with increasing RUE passes. After 4 RUE passes, the ultimate tensile strength, yield strength and elongation to failure of the alloy reached to 351 MPa, 262 MPa and 10.3%, respectively. The significant improvement of mechanical properties could be ascribed to grain refinement, dispersion of β-Mg5(Gd,Y) phase particles and redistribution of fragmented block-shaped LPSO phases.
  • Pseudo-Superplastic Characteristics of ZK60 Alloy with Fibrous Microstructure

    pp. 674-678

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    DOI:10.2320/matertrans.M2017360

    The superplasticity of ZK60 alloy was investigated after thermomechanical treatments (combination of rolling at 473 K and 673 K). ZK60 alloy, with an equiaxial grains microstructure (average grain size 2.6 µm), showed a maximum elongation of 865.2% with the strain rate 1 × 10−4 s−1 under high temperature tensile test at 573 K. Surprisingly, hot-rolled ZK60 samples with fibrous microstructure also displayed pseudo-superplastic behavior with an elongation of 535.2% at the same temperature. Microstructures indicated that the hot-rolled samples with elongated grains exhibited dynamic recovery and recrystallization during high temperature deformation, transforming the fibrous to fine-grained crystals, and thus retaining pseudo-superplastic behavior.
  • Magnetostrictive Fe–Ga Wires for Application in the High-Temperature Waveguide Device

    pp. 679-684

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    DOI:10.2320/matertrans.M2017381

    (Fe83Ga17)99.4B0.6 wires with 0.5 mm diameter were prepared by hot forging, rolling and combining hot and cold drawing. Strong 〈110〉 fiber texture was obtained in the as-drawn and annealed wires by alternating current with short time. Compared with the fracture elongation of about 0.1% in the as-drawn wire, the property increased to 16.1% in the annealed wire. The Young’s modulus of annealed wire was up to 174.3 GPa. In the annealed wires, the maximum twist angle of 206′′/cm and magnetostriction λ of −48 ppm was achieved respectively. The obvious voltage signals of the torsional wave could be detected up to 400°C in the annealed wire, which was attributed to the high Curie temperature and highly thermal-stable magnetic properties of the Fe–Ga alloy. The linear downward trend of the velocity of the torsional wave was observed from room temperature to around 250°C. The results indicate that (Fe83Ga17)99.4B0.6 wire is suitable for the high-temperature waveguide device.
  • Microstructure and High Temperature Charge-Discharge Characteristics of 3D Additive Manufacturing Produced Mg-Ni Anode

    pp. 685-689

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    DOI:10.2320/matertrans.M2017348

    This study applied a 3D additive manufacturing technique to produce a stable and high performance Mg-Ni alloy anode for lithium ion batteries. This 3D process used Mg-Ni powders to printed two layers on copper foil to obtain the Mg-Ni anodes directly, the 3D printed anodes have not need the traditional stir-slurry, coating and baking processes, and process the performances of high efficiency and low coat. Experiment results show that Mg2Ni, MgNi2 and Mg2Cu intermetallic compounds (IMC) are benefit for 3D printed anode, the anode can slowly form a dense and thick SEI layer at 55°C high temperature charge-discharge; therefore, a better capacity than at 25°C can be achieved. The 85°C charge-discharge environment makes the volume expansion effect serious, which results in capacity decay slightly. The presented high temperature charge-discharge capacities are higher than that of the commercial lithium battery, demonstrate that 3D additive manufacturing can fabricate the novel alloy electrodes simply and quickly, and that 3D Mg-Ni anodes are very suitable for today’s high-end electronic products.
  • Dependence of Reduction Behavior of Ti in Molten CaCl2 on Various Calcium Titanate

    pp. 690-693

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    DOI:10.2320/matertrans.MBW201702

    The change in TiO2 solubility in molten CaCl2 at 1573 K with CaO addition was studied to clarify the influence of CaO on TiO2 dissolution. The solubility of TiO2 in molten CaCl2 remarkably enlarged with CaO addition, which suggests that a titanate ion (TixOyZ−) was preferentially formed in it. The cathodic behavior in molten CaCl2 containing various species of calcium titanate at 1373–1573 K was investigated by cyclic voltammetry, and electrodeposition of Ti metal was attempted by potentio-static electrolysis. The reduction behavior was affected by the species of calcium titanate, and the components in the deposit changed consequently. These results indicate that the reduction behavior of Ti was strongly influenced by the species of titanate ion, and that the bath consisting of Ca3Ti2O7 is found suitable.
  • Clinching of Similar and Dissimilar Sheet Materials of Galvanized Steel, Aluminium Alloy and Titanium Alloy

    pp. 694-697

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    DOI:10.2320/matertrans.M2017319

    Aimed to describe the clinching join-abilities of galvanized steel with aluminium alloy and titanium alloy, extensible die clinched joints were prepared for similar and dissimilar sheet materials combinations. The quality of the clinched joints was analysed from the aspects of material forming, load-bearing capacity and failure modes. The failure mechanism of the clinched joints was researched from macroscopic and microscopic aspects. The results show that the sheet materials which have better strength and hardness, are suitable to be used as upper sheets in the clinching process.

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