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

MATERIALS TRANSACTIONS Vol. 44 (2003), No. 12

  • Problems and Prospects of Halogen Element Contained Dust Treatment in Recycling

    pp. 2422-2426

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    DOI:10.2320/matertrans.44.2422

    For processing the halogen element contained dust (for example, Electric Arc Furnace Dust and Auto Shredder Residue) generated at the time of recovery of valuable metals by the smelting furnace, the problem of EAF dust processing, such as comparisons of the present technology in pyro-metallurgy and hydro-metallurgy, behavior of the zinc volatilization in pyro-metallurgy, mechanism of the impurities accumulation in hydro-metallurgy, and de-halogen processing were described using computer simulation.
  • Combination of Triboelectrostatic Separation and Air Tabling for Sorting Plastics from a Multi-Component Plastic Mixture

    pp. 2427-2435

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    DOI:10.2320/matertrans.44.2427

    This paper examines separation of waste plastics obtained from automotive shredder operations. Thus, a mixture of three kinds of plastic components (i.e. acrylonitrile-butadiene-styrene (ABS), polypropylene (PP), and polyvinyl chloride (PVC)) is sorted by using dry techniques i.e. without using water and hazardous chemicals. The separation process is characterized by the utilization of properties of triboelectric charge and density. Considering the relative position in triboelectric series (TES) and density of the each plastic component of the ABS, PP and PVC mixture, it is concluded that a satisfactory separation could not be obtained by either triboelectrostatic separation or air tabling alone. Thus, a system utilizing a combination of the two processes is developed. The triboelectrostatic separator is initially used to collect the ABS flakes as positively charged fraction and to produce a negatively charged fraction of PP and PVC flakes for further treatment on air table. Hence, at the end of the process, products of ABS, PP and PVC with a grade of 94.3%, 92.5% and 93.7% respectively are collected with a percentage mass distribution higher than 76.7% for all of them.
  • Novel Treatment Process of Harmful Organic Materials in Waste Water Using Temperature-Sensitive Gel Synthesized from PVA

    pp. 2436-2440

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    DOI:10.2320/matertrans.44.2436

    The adsorption removal of harmful organic materials in waste water has been carried out using the adsorption and desorption characteristics of a temperature-sensitive polymer gel which is synthesized from polyvinylalcohol (PVA). A new adsorption removal process using an air lifting type vessel has been designed and examined for practical use. Three types of polymerization degrees (1000, 1700 and 2500) of PVA were used in this experiment. The gel volume in water was induced the volume contraction at around 305 K for 1000, 310 K for 1700 and 320 K for 2500, respectively. At higher temperatures, the temperature-sensitive polymer gel shrinks because of discharging water, whereas, in contrast, at lower temperatures, the gel swells as a result of absorbing water. The reversibility of the volume change of the synthesized polymer gel is confirmed by changing temperature. The adsorption behavior of organic materials onto PVA polymer gels in water was investigated at various temperatures. The amount of adsorption of organic materials increases remarkably at temperatures higher than about 305 K for 1000, 310 K for 1700 and 320 K for 2500. The saturated amounts of adsorption are about 0.05 mmol/g-gel for 1000, 0.26 mmol/g-gel for 1700 and 0.20 mmol/g-gel for 2500, respectively. The organic material in waste water could be adsorbed and desorbed reversibly onto PVA polymer gel by the temperature swing. The mechanism of adsorption and desorption of organic materials onto the gel can be explained by the hydration and dehydration of the polymer gel. The driving force of the adsorption is considered to be the hydrophobic interaction between PVA polymer gel and organic compounds. The novel continuous removal process for organic materials in waste water was designed and discussed for practical use.
  • Thermodynamic Properties of Polybrominated/chlorinated Dibenzo-p-dioxins Calculated by Density Functional Theory

    pp. 2441-2451

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    DOI:10.2320/matertrans.44.2441

    Heat capacities, standard enthalpies of formation and entropies for 339 polybrominated/chlorinated dibenzo-p-dioxins (PXDDs) in the gas state were calculated using the density functional theory to construct a consistent set of thermodynamic values. The heat capacities and the entropies for PXDDs increase with increase in the substitute number of bromine and chlorine. As the degree of bromination increases, the standard enthalpies of formation and the Gibbs free energies of formation of PXDDs increase, while the degree of chlorination has only a small effect on their values compared with bromination. A much higher bromine potential than chlorine potential is needed for the formation of brominated dioxin congeners. However, the bromine-chlorine equilibrium potential for the formation of PXDDs suggested thermodynamically the possibility of their priority formation under the usual gaseous conditions where HBr and HCl are similar levels, because the bromine potential of the gas is much higher than the chlorine potential when the partial pressure of the two is similar.
  • Impurity Removal from Carbon Saturated Liquid Iron using Lead Solvent

    pp. 2452-2455

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    DOI:10.2320/matertrans.44.2452

    A new technique for removal of tramp-elements from steel scrap is required for saving energy and protecting the environment. An extraction method using phase separation in a liquid Fe-Pb-C system was investigated at 1453 K to obtain fundamental information on removal of copper, tin and zinc from molten iron. A mixture of iron, lead and carbon melted in a carbon crucible separates into two phases of lead and iron containing carbon. The compositions on the miscibility gap in the Fe-Pb-C system are 95.4 mass% Fe-4.5 mass% C-0.1 mass% Pb and 99.9 mass% Pb-0.1 mass% Fe. Distribution ratios of copper, tin and zinc between the lead and the iron phases, LX=[mass%X in molten Pb]/(mass%X in molten Fe), are 2.2, 2.2 and 1.4, respectively. By adding a same amount of lead to an iron scrap, 70% of copper and tin from the iron scrap can be eliminated. Gold, silver and palladium are enriched in the lead rich phase. However, platinum and rhodium are more distributed to the iron rich phase than to the lead phase.
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  • Processing of Refractory Organic Waste Water Using Ozone and Novel Agitation Method

    pp. 2456-2460

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    DOI:10.2320/matertrans.44.2456

    A novel agitation method using ozone was applied to removing BOD5, CODMn, color, and NH4-N in organic waste water filled in a cylindrical vessel. The organic waste water was agitated by injecting the same organic waste water into the bath through a centered bottom nozzle. Its flow rate was adjusted to form a jet above the nozzle. A pump was used for draining the organic waster water through four nozzles settled on the bottom of the vessel and circulating it until the aforementioned four quantities were sufficiently decreased. The swirl motion of the jet appeared under certain injection conditions. The bath was strongly agitated in the presence of the swirl motion. An ozone and air mixture therefore was supplied into the nozzle and then introduced into the bath with the jet. The rate constants of BOD5, CODMn, color, and NH4-N were highly enhanced by this method compared to the conventional method using aeration of an ozone-air mixture supplied through a perforated plate.
  • Novel Recycling System of Aluminum and Iron Wastes-in-situ Al-Al3Fe Functionally Graded Material Manufactured by a Centrifugal Method-

    pp. 2461-2467

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    DOI:10.2320/matertrans.44.2461

    In this study, the concept of novel recycling system using waste Al and Fe is described. Taking advantage of the fact that due to its cyclic usage, aluminum scrap unavoidably contains iron and steel wastes, an in-situ Al-Al3Fe functionally graded material (FGM) is planned to be fabricated. A centrifugal method is applied to a model master alloy, Al-10 mass% Fe, obtained from virgin materials, the content of which is decided from the liquidus temperature. The resulting product is a thick-walled tube having a graded distribution of second phase particles in the Al matrix. It has been established that the shape of the particles varies depending on their position along the radial direction. The second phase is confirmed to be a stable Al3Fe intermetallic compound. Thin plates of Al-Al3Fe having homogeneously distributed Al3Fe particles, considering both the composition gradient and the particle morphology, were machined from the thick-walled Al-Al3Fe FGM tube and their mechanical properties measured. Based on the experimental observations, the potential and the advantages of the Al-Al3Fe alloy as a recyclable eco-FGM are discussed.
  • New Process to Fabricate Magnesium Composites Using SiO2 Glass Scraps

    pp. 2468-2474

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    DOI:10.2320/matertrans.44.2468

    To realize the lightweight effects by materials technology, a new process for fabricating high-performance magnesium composites via a solid-state reaction by using high purity SiO2 glass scraps has been established. From a viewpoint of the microstructures control of the composites, the core technologies to improve the physical and mechanical properties are; a solid-state synthesis of Mg2Si and MgO particles by the deoxidization of SiO2 glass by magnesium, and a refinement of both their dispersoids and the magnesium matrix grains by the RPW process. For example, when using the elemental AZ31 magnesium alloy and 2 mass% SiO2 glass powder mixture as starting raw materials, the hot extruded composite including Mg2Si and MgO shows 363 MPa of the ultimate tensile strength. The addition of only 2 mass% SiO2 powder also causes the remarkable improvement of the corrosion resistance because of the uniform distribution of refined Mg2Si not only at the particle boundary but also inside the grains. This process is quite safety and environmentally benign compared to the conventional re-melting process, because of utilizing course magnesium raw powder and no use of SF6 toxic gas. It also shows a possibility to employ SiO2 glass scraps as starting raw materials to fabricate magnesium alloys.
  • Reaction, Mechanism and Application of Various Zeolite Syntheses from Coal Fly Ash

    pp. 2475-2480

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    DOI:10.2320/matertrans.44.2475

    The hydrothermal syntheses of zeolites from coal fly ash were carried out using NaOH and KOH as an alkali source in order to clarify the reaction mechanism of zeolitization. The physical properties such as surface structure, crystal structure and cation exchange capacity (CEC), and the ion exchange properties were measured for the zeolites synthesized by hydrothermal treatment. From these results, the effective usage was investigated for various zeolites derived from coal fly ash. Zeolite P, HS (hydroxysodalite) and K-CHA (potassium-chabazite) are mainly formed as zeolite species in NaOH or KOH solution at 393 K. The zeolite P and K-CHA have a large exchange capacity as a cation exchanger. There are three reaction steps; the dissolution, deposition and crystallization reactions in a series of conversion process from coal fly ash to zeolitic materials. The selectivity of cation exchange of various zeolites is explained by the Coulomb’s attractive force between the ionic charge of metal ions and the surface charge of zeolites. The obtained zeolites can be used as a cation exchanger and a soil improvement agent. The usage of the synthesized zeolites as soil improvement makes a contribution to return coal residue to soil environmentally friendly.
  • Volatilization Mechanism of Pb from Fly Ash in Municipal Waste Incinerator

    pp. 2481-2488

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    DOI:10.2320/matertrans.44.2481

    Fly ash produced by waste combustion is designated as specially controlled waste in Japan due to harmful heavy metals contained in it and is legislated to be processed properly before disposal to landfill. As for technologies for making the fly ash harmless, several methods are recommended for the treatment, but each of them has some problems to be solved. The fly ash from a municipal solid waste incinerator contains large amounts of chlorinated compounds that make the harmful treatment difficult. A complete recycling of waste residue left behind after waste incineration, however, is required to solve the shortage of available final disposal sites. With this background, a new technology needs to be developed, that the heavy metals in the fly ash are removed sufficiently, no harmful heavy metals are leached and the residue ingredients are used effectively. In addition, Japanese government revised the Soil Contamination Countermeasures Law in February 2003 to strengthen the soil environmental evaluation standards. This could also promote the development of above technology. This paper focuses on lead that is particularly emphasized in the law, and proposes an advanced technology to remove lead from the fly ash, discussing the removal mechanism and removing conditions of lead. The newly developed technology is associated with the sintering process using a rotary kiln, and effectively uses only the chlorinated compounds contained in the fly ash to volatilize and remove the heavy metals. The technology achieves satisfactory low level of dioxins as well as prevention of lead leach. The fly ash treated by the technology also has passed a leaching test at pH 4 simulating typical acid rain circumstances.
  • Leaching of Zinc Oxide in Acidic Solution

    pp. 2489-2493

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    DOI:10.2320/matertrans.44.2489

    Leaching mechanism of zinc oxide is important not only to understand zinc smelting process but also to develop of new zinc recycling process. Recycling of zinc is mainly done by treatment of electric arc furnace dust (EAF dust). In Japan pyro metallurgical process is enhanced for EAF dust treatment, however only zinc oxide can be recovered by pyro metallurgical process. Hydro metallurgical process makes it possible to recover high purity zinc directly from EAF dust. One of the main components of zinc included in EAF dusts is zinc oxide. Thus the mechanism of zinc oxide leaching is important to develop the new hydro metallurgical zinc recycling process. Leaching test of zinc oxide in hydrochloric acid and sulfuric acid solution has been carried out kinetically. Zinc oxide disk was used for leaching test which the reaction area is clear. The experimental parameters of pH, temperature, leaching time and rotating speed of the disk specimen were varied. The results obtained are as follows;
    \\oindent(1) The activation energy of leaching reaction by sulfuric acid was 17.5 kJmol−1 and 11.6 kJmol−1 by hydrochloric acid solutions.
    \\oindent(2) The leaching rate increases in proportion to the square root of rotating speed of test specimen.
    These results indicate that the rate controlling factor of zinc oxide leaching reaction in acidic solution is mass transportation.
  • Influence of Magnetic Field Direction on Rearrangement of Martensite Variants in an Fe-Pd Alloy

    pp. 2495-2498

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    DOI:10.2320/matertrans.44.2495

    Influence of magnetic field direction on rearrangement of martensite variants in an Fe-31.2Pd(at%) single crystal has been investigated using thermal expansion measurement in a cooling process under the magnetic field applied along [001]P, [011]P and [111]P (“P” represents “parent” phase). We also observe these rearrangements of variants in the cooling processes under the magnetic field applied along [001]P, [011]P and [111]P by optical microscope. From the thermal expansion measurement and the optical microscope observation, the following results are obtained: the variants are rearranged almost perfectly into the variants whose a axes are parallel to the magnetic field applied along [001]P, imperfectly into the variants whose c axis is perpendicular to the magnetic field applied along [011]P and hardly along [111]P. We explain these results considering the following criterion: rearrangement of variants proceeds when a kind of shear stress generated by applying a magnetic field acting on the twinning plane is larger than the stress required for the rearrangement of variants.
  • Effect of Co and Ni on Martensitic Transformation and Magnetic Properties in Fe-Pd Ferromagnetic Shape Memory Alloys

    pp. 2499-2502

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    DOI:10.2320/matertrans.44.2499

    Effects of Co and Ni addition on fcc-fct transformation temperature and magnetic properties have been investigated for Fe-Pd ferromagnetic shape memory alloys. The addition of Co shifts the fcc-fct transformation temperature slightly higher while the Ni addition shifts it lower. The results suggest that the relative stability between fcc and fct phases is significantly affected by the electronic structure. Saturation magnetization values for Fe-Pd-Co and Fe-Pd-Ni were found to be slightly higher than those for binary Fe-Pd.
  • Phase-Field Simulation of Microstructure Changes in Ni2MnGa Ferromagnetic Alloy Under External Stress and Magnetic Fields

    pp. 2503-2508

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    DOI:10.2320/matertrans.44.2503

    Since the factors that influence microstructure formation are extensive (e.g., alloy composition, applied stress, external magnetic field, etc.), quite a lot of experimental trial-and-error is often necessary when searching for the best combination of desired microstructure and material properties, even when the basic mechanism of microstructure formation is understood. During the last decade, the phase-field method has emerged across many fields in materials science as a powerful tool to simulate and predict complex microstructure evolution. Since the phase-field methodology can model complex microstructure changes quantitatively, it is possible to search for the most desirable microstructure by using this method as a design simulation, i.e., through computer trial-and-error testing. In order to establish this methodology, first of all, quantitative modeling of complex microstructure changes using the phase-field method is required.
    The objective of this study is to model the twin macrostructure developments in Ni2MnGa ferromagnetic alloy under external stress and magnetic field. This alloy has been actively investigated in the field of the magnetic induced shape memory effect, recently. Through the computer simulation, we show that it is possible to model the macrostructure changes in Ni2MnGa quantitatively using the phase-field method. This modeling method may also be applicable to another alloy systems that the magnetic shape memory effect will take place. The simulation result also suggests that the mobility of twin boundary motion is enhanced just below the Ms temperature. Using the phase-field method to model the microstructure evolutions is thought to be a very effective strategy in predicting and analyzing the complex microstructure formation where the magnetic and stress fields should be considered simultaneously.
  • Influence of Fe and Co on Phase Transitions in Ni-Mn-Ga Alloys

    pp. 2509-2512

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    DOI:10.2320/matertrans.44.2509

    Differential scanning calorimetry (DSC) and magnetic measurements were performed to study the influence of ferromagnetic 3-d transition elements Fe and Co on structural and magnetic properties of ferromagnetic shape memory alloys Ni2MnGa. Addition of Fe or Co on the Ni sites decreases the temperature of martensitic phase transition Tm, whereas addition of Co on the Mn sites results in a considerable increase of Tm. Magnetic measurement revealed that Curie temperature TC increases upon substitution of Fe or Co for Ni. This observation is of importance for design of high temperature ferromagnetic shape memory alloys.
  • Shape Memory Behavior of Ni-Mn-Ga Sputtered Films under a Magnetic Field

    pp. 2513-2519

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    DOI:10.2320/matertrans.44.2513

    The shape memory behavior under the magnetic field up to 5 T was observed in Ni-Mn-Ga sputtered films. The sputtered films were heat-treated at 1073 K for 36 ks for homogenization and aged at 673 K for 14.4 and 56.7 ks in a constraint condition. The martensitic transformation temperatures and Curie temperature of the obtained films were higher than room temperature. The martensitic transformation temperatures increased under a magnetic field. Furthermore, a shape memory effect was observed by increasing and decreasing of the magnetic field.
  • Phase Transformation of Polymeric Materials in High Magnetic Field

    pp. 2520-2523

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    DOI:10.2320/matertrans.44.2520

    A model to describe a non-rotation type magnetic alignment of crystalline polymers during crystallization from melts is presented. The model is based on the presence of mesophase existing between the melt phase and the crystalline phase, with an extremely small transformation enthalpy and a resultant large shift of melting point in the presence of a magnetic field. A calculation of the magnetic effect on the nucleation and growth rates of mesophase is carried out. It is shown that these rates are enhanced for the mesophase with a specific orientation with respect to the applied field, resulting in alignment.
  • Influence of Magnetic-Field Gradients on the Pearlitic Transformation in Steels

    pp. 2524-2528

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    DOI:10.2320/matertrans.44.2524

    Carbon steels of 1 wt%C were subjected to the pearlitic transformation in a helium-free superconducting magnet in search for some influence of the magnetic field gradient on the transformation. It was found that steels containing Mn and/or Cr got hardened proportional to the field gradient present during the transformation at 560°C. The hardness increase amounted to 8% at the field gradient of 50 T/m, the magnitude depending on the steel composition. It was confirmed that the hardening was irrelevant to the sign of the gradient and absent for homogeneous magnetic fields. This kind of hardening was not observed for a binary Fe-C alloy. The hardened specimens exhibited age hardening by annealing at 150∼200°C. TEM observations and internal friction measurements suggested that supersaturated carbon atoms were introduced into the ferrite layers of the pearlite phase under the field gradient. Such extra carbon atoms should have combined with Mn and/or Cr atoms during the quenching to impurity complexes responsible for the solution and age hardenings. Plausible arguments are made on the action of magnetic field gradients for the introduction of supersaturated carbon atoms in the pearlitic ferrite.
  • Effects of Magnetic Field and Prior Austenite Grain Size on the Structure Formed by Reverse Transformation from Lath Martensite to Austenite in an Fe-0.4C Alloy

    pp. 2529-2531

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    DOI:10.2320/matertrans.44.2529

    Effects of magnetic field strength and prior austenite grain size on the microstructure formed by the reverse transformation from lath martensite to austenite have been investigated in Fe-0.4C alloy. The degree of elongation of reverse-transformed austenite increases with increasing applied magnetic field, which is a similar result with that for austenite to ferrite transformation. However, well-elongated austenite is formed not only in small prior austenite grains but also in relatively large prior austenite grains, which is different from the case of austenite to ferrite transformation.
  • Structural Elongation and Alignment in an Fe-0.4C Alloy by Isothermal Ferrite Transformation in High Magnetic Fields

    pp. 2532-2536

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    DOI:10.2320/matertrans.44.2532

    Structural elongation and alignment in an Fe-0.4C alloy transformed in high magnetic fields has been studied by quantitative microscopy analysis. An elongated and aligned two-phase structure is formed in high magnetic fields by isothermal ferrite transformation both below and above Curie temperature. Equiaxed ferrite grains nucleate randomly at austenite grain boundaries and they become elongated by preferred growth along the direction of applied magnetic field. Below Curie temperature, the degree of elongation increases with increasing transformation temperature, whereas it decreases above Curie temperature. Small chemical driving force for ferrite precipitation and large magnetization of ferrite in high magnetic fields favor the formation of elongated structure.
  • X-ray Diffraction Studies of Fe-N Bulk-Processed in a Magnetic Field Using Synchrotron Radiation

    pp. 2537-2540

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    DOI:10.2320/matertrans.44.2537

    The volume fractions of α″ phase Fe16N2 in bulk samples were estimated using X-ray diffraction data. The SPring-8 synchrotron radiation facility was utilized for data collection. Samples were prepared in an NH3+H2 atmosphere, and a magnetic field was applied to reduce the amount of remanent γ phase. Samples were then annealed for varying times (0.25-512 h). Rietveld analysis was applied to obtain the volume fractions of each phase generated in the samples. The results showed relatively small fractions of the α″ phase were present. The discrepancy between the present analyses and the results of Mössbauer measurements are also discussed.
  • Isothermal Martensitic Transformation of γ-FeN in a Magnetic Field

    pp. 2541-2544

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    DOI:10.2320/matertrans.44.2541

    Isothermal martensitic transformation of the γ-FeN was found to occur in magnetic field at temperatures above the Ms. Molar fraction of martensite monotonically increases with increasing isothermal aging time, and saturates at a value proportional to applied magnetic field. Temperature and magnetic field dependence of the saturation value indicates that the transformation does not proceed above the temperature where the value become zero in a given magnetic field. Application of magnetic field reveals intrinsic isothermal character of the martensitic transformation in the γ-FeN hidden behind the complication associated with magnetization process of the α′ phase.
  • Magnetic Field-Induced Martensitic Transformation of Fe-Co Particles in a Cu Matrix

    pp. 2545-2549

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    DOI:10.2320/matertrans.44.2545

    The fcc-to-bcc martensitic transformation in Fe-Co precipitate particles has been induced by applying magnetic field to Cu-Fe-Co alloy single crystals at a range of temperature between 4 K and 300 K. The volume fractions of martensite can be estimated from the values of saturation magnetization of the bulk specimens. The amount of transformation is strongly dependent on the cooling temperature, and reaches its peak at around 77 K. The existence of the peak temperature is explained by considering the antiferromagnetic transformation of fcc Fe-Co.
  • Alignment of BiMn Crystal Orientation in Bi-20 at%Mn alloys by Laser Melting under a Magnetic Field

    pp. 2550-2554

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    DOI:10.2320/matertrans.44.2550

    This paper presents results of preliminary work done on developing a new technique to produce magnetically aligned structure in selected regions of rapidly solidified alloys. Rapid solidification of the Bi-20 at%Mn alloy resulted in dispersion of the fine BiMn grains in the supersaturated Bi-rich matrix. Low magnetization could be achieved in the rapidly solidified specimen, as compared to the equilibrium condition. The rapidly solidified specimen when further subjected to the semi-solid processing under a magnetic filed of 4 T achieved the alignment of the BiMn grains due to the magnetic anisotropy and consequently exhibited a hysterisis loop in the magnetization curve. The semi-solid casting by laser melting of the rapidly solidified structure under a magnetic field of 10 T achieved the BiMn alignment in a small selected region (10 μm in diameter). The experimental results pointed out the potential of the semi-solid casting by the laser melting under a magnetic filed to fabricate the aligned structure in the desired region.
  • Formation of Crystallographically Aligned Grains during Coarsening in a Magnetic Field

    pp. 2555-2562

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    DOI:10.2320/matertrans.44.2555

    A model that considers combined effects of the interfacial energy and the magnetic anisotropy energy is proposed to examine development of the crystallographically aligned microstructure during annealing under a magnetic field. For ferromagnetic materials with rather large magnetic anisotropy energies, the model indicates the coarsening can take place in accordance with the magnetic anisotropy. The grain with favorite orientation survive during annealing, resulting in the alignment. The narrow distribution in the grain diameters significantly improves the alignment by coarsening. For Paramagnetic and diamagnetic materials, the coarsening is also effective to develop the aligned microstructures when low degree of the alignment can be achieved by using a magnetic field in the initial microstructure prior to the coarsening.
  • Controlled Alignments of Feeble Magnetic Particles Utilizing Induced Magnetic Dipole Interactions

    pp. 2563-2566

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    DOI:10.2320/matertrans.44.2563

    Some ordered alignments of feeble magnetic particles were obtained utilizing magnetic dipole interactions. The interactions among feeble magnetic substances under magnetic fields, that is, interactions among magnetic dipoles induced in feeble magnetic substances have been believed too small to be observed. However, by controlling experimental conditions carefully, we confirmed that such interactions can be observed visually even in feeble magnetic substances. Furthermore, by applying the interactions to many-particle systems, ordered alignments were obtained such as chain-like alignments parallel to and triangle-lattice alignments perpendicular to magnetic fields. These results suggest that structures of feeble magnetic substances can be controlled by magnetic fields, and such application would be of use in materials processing.
  • Ferromagnetic Domain Structure in La1-xSrxMnO3 (x=0.125)

    pp. 2567-2569

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    DOI:10.2320/matertrans.44.2567

    Low-temperature Lorentz microscopy is applied to the observation of the ferromagnetic (FM) domain structure in the colossal magnetoresistive manganite, La1−xSrxMnO3 with x=0.125. We found the emergence of two types of FM domain structures in the low-temperature phase characterized as the FM insulator phase. One is a large 180° FM domain structure with the Bloch-type wall and the other is a wavy stripe-shaped FM domain structure with the 100 nm size. These two distinct FM domain structures depend strongly on the crystal orientation. The response of the FM domains with the application of the magnetic field was also examined.
  • High Temperature In-situ Observations of Magnetic Domains in Fe-Co Alloys

    pp. 2570-2577

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    DOI:10.2320/matertrans.44.2570

    In-situ observations of magnetic domain structure in Fe-Co alloys with Co concentrations of 4.6∼50 at% were made by the optical Kerr microscopy in the temperature range from R.T. to the Curie temperature (1103 K ∼ 1253 K). The magnetic domain structures could be successively observed up to the Curie temperature (1103 K ∼ 1253 K) and the average domain width was found to increase with increasing temperature. The contrast of magnetic domains in an Fe-4.6 at%Co alloy gradually decreased with increasing temperature and disappeared near the Curie temperature (1103 K). On the other hand, the magnetic domain structure in an Fe-50 at%Co alloy could be clearly observed at immediately below the α/γ phase transformation temperature (1253 K). Furthermore, it was found that the magnetic domain walls tended to orient perpendicularly to the α/γ interphase boundaries in an Fe-50 at%Co alloy at the α/γ phase transformation temperature.
  • Magnetic Domain Structure of MnAs Thin Films as a Function of Temperature

    pp. 2578-2581

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    DOI:10.2320/matertrans.44.2578

    We have investigated magnetic domain structures of MnAs thin films grown on GaAs substrates by a magnetic force microscope. We observed, by an atomic force microscope, rectangular defects along GaAs [110] direction which disperse randomly on the surface of MnAs/GaAs (001). The Curie temperature of MnAs is 45°C, and it is successfully confirmed directly by the variable temperature magnetic force microscope observation. We also investigated magnetic domain structures of MnAs/GaAs (111)B, and no apparent relation was observed between the topographic structure and the magnetic domain structure.
  • Metamagnetism and Magnetic Phase Diagrams of the Intermetallic Compound DyAg

    pp. 2582-2588

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    DOI:10.2320/matertrans.44.2582

    The high field magnetization of DyAg, which is an antiferromagnet with three successive magnetic transitions at TN=56 K, T2=49 K and T1=46.5 K, has been investigated up to 54 T by using pulsed magnet for the magnetic field applied along [100], [110] and [111] axes. At low temperatures below T1, for H||[111], a saturation of the magnetization is observed after four metamagnetic jumps and the saturated moment is obtained to be 9.7 μB/Dy. The magnetic phase diagrams have also been established in detail for the three axes with the complementary studies of the magnetic susceptibility and the specific heat. The obtained phase diagrams below 40 K are well consistent with the previous results for all the directions. Above 40 K, on the other hand, the present results reveal an existence of some new phases in the proximity region of TN.
  • Influence of Grain Boundary on Magnetoresistance in Hole Doped Manganites La0.7Ca0.3MnO3, La0.7Sr0.3MnO3 and (La0.75Y0.25)0.7Sr0.3MnO3

    pp. 2589-2593

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    DOI:10.2320/matertrans.44.2589

    Magnetoresistance (defined in the study as Δρ(T,H)⁄ρ(T,0)=(ρ(T,H)−ρ(T,0))⁄ρ(T,0), where ρ(T,H) and ρ(T,0) denote the resistivity at a temperature with and without a magnetic field, respectively) of single crystal and polycrystalline La0.7Ca0.3MnO3, polycrystalline La0.7Sr0.3MnO3 and (La0.75Y0.25)0.7Sr0.3MnO3 has been studied in order to know the influence of grain boundary on magnetoresistance. As a result, the following characteristics are found: (i) Magnetoresistance of polycrystalline La0.7Ca0.3MnO3 and (La0.75Y0.25)0.7Sr0.3MnO3, whose grain sizes are about 10 μm, drastically decreases at a low magnetic field about 200 kA/m (for example, about 20% decrease at 4.2 K), and gradually decreases with increasing magnetic field up to 5.6 MA/m used in the present study, being different in case of single crystal La0.7Ca0.3MnO3. This behaviour of magnetoresistance of the present polycrystalline specimens is quite similar to that of the polycrystalline La2⁄3Sr1⁄3MnO3 previously reported and cannot be explained quantitatively by the model proposed by Raychaudhuri et al., which is derived based on the tunneling conduction mechanism through the grain boundary. (ii) Magnetoresistance of La0.7Sr0.3MnO3 extremely depends on the grain size and its absolute value, |Δρ(T,H)⁄ρ(T,0)|, decreases with increasing the grain size (12 μm, 300 μm, 1200 μm) at 4.2 K in the range of magnetic field up to 5.6 MA/m. A characteristic feature is that there is a similar transformation of magnetoresistance for specimens with different grain sizes. (iii) Time-dependent nature of resistance exists for the present polycrystalline specimens, but not for the single crystal specimen, suggesting that the magnetism around the grain boundary should be a spin-glass like state.
  • Characteristics of Paramagnetic and Diamagnetic Anisotropy which Induce Magnetic Alignment of Micron-Sized Non-Ferromagnetic Particles

    pp. 2594-2598

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    DOI:10.2320/matertrans.44.2594

    The effect of temperature is discussed on the magnetic-alignment process of micron-sized particles dispersed in a fluid medium, based on the experimental data compiled on various non-ferromagnetic materials having different concentrations of paramagnetic impurity ion. The field-intensity required to achieve alignment decreased with temperature following the relation calculated from the Langevin theory, when the diamagnetic particles were free of paramagnetic ions. The rotational Brownian motion was considered to randomize the direction of the micro-crystals in the theory. The above-mentioned temperature dependence was expected to occur for most of the diamagnetic oxides, since the oxides were expected to posses a finite amount of diamagnetic anisotropy according to a model proposed recently to explain the origin of anisotropy. The decease of temperature caused additional reduction on the field-intensity to achieve alignment, when finite amount of paramagnetic ion was contained in the particle. This was because the paramagnetic anisotropy increased which the reduction of temperature. The doping of paramagnetic ion on non-ferromagnetic materials in the course of processing a material expected to reduce the field intensity to achieve magnetic alignment at room temperature. The above findings, concerned with the reduction of field intensity to achieve magnetic alignment, may increase the possibility of practical applications of the phenomena of magnetic alignment.
  • Cross Sectional TEM Observation of Gas-Ion-Irradiation Induced Surface Blisters and Their Precursors in SiC

    pp. 2599-2604

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    DOI:10.2320/matertrans.44.2599

    Cross sectional structures of surface blisters and their precursors in SiC formed by H+, D+ and He+ irradiation were examined with transmission electron microscopy and electron energy-loss spectroscopy. The substructures of the H+- and D+-irradiated samples showed similar features, and experimental results suggested that H2 and CH4 bubbles nucleated after H(D)-trapping sites were saturated and the first nucleated bubbles grew by absorbing the gas molecules formed by further ion irradiation, followed by lift-up of the surface layer with increasing the internal pressure. The implanted hydrogen atoms other than those forming bubbles were scattered in atomic form, preferably bonded to carbon atoms. On the other hand the substructure of He+ irradiated sample was very similar to that of metals and other materials irradiated by He+, and it is considered that the formation mechanism of He-blister is common for most materials.
  • Origin of Perpendicular Magnetic Anisotropy in Tb-Fe Amorphous Alloy

    pp. 2605-2610

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    DOI:10.2320/matertrans.44.2605

    The origin of perpendicular magnetic anisotropy has been investigated in a thick Tb-Fe amorphous alloy plate prepared by dc high-rate sputtering. In the as-prepared samples with and without a Cu substrate, no distinct difference in perpendicular magnetic anisotropy was confirmed. After annealing, the perpendicular magnetic anisotropy in the sample with a Cu substrate was maintained, whereas that disappeared in the sample without a Cu substrate. Inducing thermal strains with an epoxy resin, the perpendicular magnetic anisotropy was restored. Therefore, it is concluded that the strong strains induced by the difference between the thermal expansion of the Tb-Fe amorphous alloy plate and the Cu substrate dominate to the origin of perpendicular magnetic anisotropy.
  • Influence of Sr and Mn Additions on Intermetallic Compound Morphologies in Al-Si-Cu-Fe Cast Alloys

    pp. 2611-2616

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    DOI:10.2320/matertrans.44.2611

    The influence of Sr or Sr and Mn combined additions on the Fe-containing intermetallic compounds in Al-Si-Cu-Fe cast alloys has been investigated using Al-6.5%Si-3.5%Cu-1.0%Fe and Al-6.5%Si-3.5%Cu-1.0%Fe-0.3%Mn alloys (in mass%) with a similar composition to the 319 aluminum alloy. The results show that Sr successfully modifies the large, highly branched β-needle-like phase (β: Al5FeSi) into the individual, less-branched and finer one. The combined addition of Mn and Sr results in modification of the needle-like β-phase as well as promotion of Chinese script and sludge morphology formation. The mechanism of the above morphological changes has been discussed in accordance with the mechanism of nucleation and growth of the β-needle-like phase during solidification.
  • Microstructure and Mechanical Properties of Strip Cast Al-Mg-Si-X Alloys

    pp. 2617-2624

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    DOI:10.2320/matertrans.44.2617

    A study has been conducted on the microstructure and mechanical properties of strip cast Al6061 alloy with and without a 0.5 mass% Mn addition. The microstructures of the as-cast alloys are characterized by the presence of Si particles (<1 μm) and clusters of fine α-AlFeSi particles (<50 nm) along grain boundaries. In addition, there is the development of well-defined subgrains caused by the effects of hot rolling during strip casting. By T6 heat treatment, Si particles along grain boundaries are replaced by fine α-AlFeSi particles. There is also a formation of α-AlFeSi particles within the Al matrix by heat treatment. The addition of Mn results in an increase in the volume fraction of α-AlFe(Mn)Si particles within the Al matrix, which is associated with a corresponding decrease in the volume fraction of Mg2Si precipitates within the Al matrix over that observed in the base alloy. Accordingly, the Mn containing alloy shows a lower yield strength but a higher ultimate tensile strength due to a greater work hardening rate than the base alloy. The increased work hardening rate of the Mn containing alloy is due to the presence of uniformly distributed fine α-AlFe(Mn)Si particles within the Al matrix. The present study shows that strip casting is a viable process for the fabrication of structural Al alloys.
  • Grain Refinement in a Mg AZ91 Alloy via Large Strain Hot Rolling

    pp. 2625-2630

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    DOI:10.2320/matertrans.44.2625

    Significant grain refinement has been achieved in a cast Mg-based AZ91 alloy via large strain hot rolling. This is a simple processing method consisting of one rolling pass at intermediate temperatures with a large thickness reduction. The as-cast material was first homogeneized in order to obtain a homogeneous and equiaxed grain structure with a random texture. During processing, a double-peak basal texture develops, typical of rolled Mg alloys, that results from the operation of basal, prismatic and pyramidal ⟨c+a⟩ slip. The stabilization of this deformation texture during rolling suggests that the mechanism for grain refinement is continuous dynamic recrystallization.
  • Experimental Consideration of Multistage Martensitic Transformation and Precipitation Behavior in Aged Ni-Rich Ti-Ni Shape Memory Alloys

    pp. 2631-2636

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    DOI:10.2320/matertrans.44.2631

    It has been demonstrated with systematic experiments that the appearance and disappearance of multistage martensitic transformation in aged Ni-rich Ti-Ni alloys depend on the heat treatment atmosphere. No multistage transformation occurs when the evaporation of Ti and Ni and/or the preferential oxidation of Ti in the specimen are prevented and the purification of heat treatment atmosphere in an evacuated quartz tube is achieved. The heterogeneity in precipitation morphology of Ti3Ni4 phase which is responsible for the multistage transformation can be suppressed with the regulation of heat treatment atmosphere as mentioned above. We have concluded that the multistage martensitic transformation in aged Ni-rich Ti-Ni alloys is an extrinsic nature, i.e., a kind of artifact during the heat treatment.
  • Dynamic Mechanical Properties and Fracture Behavior of a 304L Stainless Steel GTAW Joint under Shear Conditions

    pp. 2637-2645

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    DOI:10.2320/matertrans.44.2637

    This paper employs the torsional split-Hopkinson bar to investigate the dynamic shear deformation behavior and fracture characteristics of a 304L stainless steel Gas Tungsten Arc Welded (GTAW) joint at room temperature under strain rates in the range of 8×102 s−1 to 2.8×103 s−1. The experimental results indicate that the strain rate has a significant influence on the mechanical properties and fracture response of the tested GTAW joints. It is found that the flow stress, total shear strain to failure, work hardening exponent and strain rate sensitivity all increase with increasing strain rate, but that the activation volume decreases. The observed dynamic shear deformation behavior is modeled using the Kobayashi-Dodd constitutive law, and it is shown that the predicted results are in good agreement with the experimental data. Observation of the fractured specimens indicates that the fracture features are closely related to the preceding flow behavior. At all values of strain rate, it is noted that the specimens all fracture within their fusion zones, and that the primary failure mechanism is one of extensive localized shearing. The fracture surfaces are characterized by the presence of many dimples, which suggests a ductile fracture mode. It is shown the strain rate has a significant influence upon the appearance of the dimpled surface. A higher strain rate tends to reduce the size of the dimples and to increase their density. Finally, it is determined that the presence of weld inclusions also influences the appearance of the fracture. These inclusions cause the initiation of micro-voids, which grow and coalesce within the fusion zone, and eventually form a continuous fracture surface.
  • Production of Tantalum Powder by Magnesiothermic Reduction of Feed Preform

    pp. 2646-2653

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    DOI:10.2320/matertrans.44.2646

    To develop an effective process for tantalum powder production, a new preform reduction process (PRP) based on the magnesiothermic reduction of feed preform containing tantalum oxide (Ta2O5) was investigated. The feed preform was fabricated from slurry, which was made by mixing Ta2O5 powder, flux (e.g., CaCl2), and binder. Various compositions of preform in the form of plates were prepared using a conventional casting technique, and the fabricated preform was heated at 1273 K before reduction in order to remove the binder and water. The sintered solid preform, containing Ta2O5, was then placed in a stainless steel container, and reacted with magnesium vapor at a constant temperature ranging between 973 and 1273 K for 6 hours. Pure tantalum powder was recovered from the reduced preform after leaching it in acid. This process was found to be suitable for producing a fine homogeneous powder, when the composition of flux and reduction conditions are controlled.
  • Phase Relations and Activities in the Fe-Ni-As and Fe-Ni-Sb Systems at 1423 K

    pp. 2654-2658

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    DOI:10.2320/matertrans.44.2654

    Arsenic and antimony activities in the Fe-Ni-As and Fe-Ni-Sb ternary systems were measured at 1423 K by an isothermal isopiestic method to obtain fundamental information about the behaviour of arsenic and antimony in processing intermediate products, nickel arsenide or antimonide ores. Phase relations between the solid solution and liquid phase in a region of dilute arsenic or antimony in these systems were also determined at 1423 K with a quenching technique. The isoactivity lines of arsenic in the homogeneous liquid phase were almost parallel to the Ni-Fe axis of Fe-Ni-As ternary composition diagram, while those of antimony represented a negative gradient due to stronger chemical affinity of antimony to nickel as compared to iron. The iron and nickel activities in these ternary systems were derived from the measured arsenic or antimony activity and the determined phase relations. The Redlich-Kister-Muggianu polynomial formula was successfully applied to express the activities as a function of alloy compositions. Based on the obtained data, the total pressures of arsenic and antimony gas species were evaluated to discuss the possibility to recover or eliminate arsenic and antimony from the alloys by means of volatilization.
  • Determination of Macro-Contact Angle and Line Tension at High Temperatures for Au/Al2O3 System at 1373 K Using a Micro-Scale Wetting Method

    pp. 2659-2663

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    DOI:10.2320/matertrans.44.2659

    The size effect of a drop on the contact angle was discussed for the Au/Al2O3 system. As the size of the drop decreases, the shape of the drop closes to a sphere and the contact angle is obtained by the equation θ=cos−1(1−hRMax.), where θ is the contact angle between the drop and substrates, h is the height of the drop and RMax. is the maximum radius of the drop. The contact angle between liquid gold and alumina polycrystalline substrates having the roughness of 0.141 μm in RA number slightly increased as the sample size decreases to about 10 μm, yielding 134° and 3.50×10−7 N as the macro-scale contact angle and the line tension, respectively.
  • Characterization of the Surface Oxide Film on an Fe-Cr-N System Alloy in Environments Simulating the Human Body

    pp. 2664-2670

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    DOI:10.2320/matertrans.44.2664

    The objective of this study was to characterize the surface oxide film on nickel-free austenitic stainless steel with nitrogen absorption, Fe-24Cr-1N in mass% (Fe-26.4Cr-3.4N in at%), located in various environments, to estimate the reconstruction of the surface oxide film in the human body. The specimens were metallographically polished in deionized water, autoclaved after polishing, immersed in Hanks’ solution for 7 days after polishing and autoclaving, immersed in Eagle’s minimum essential medium containing fetal bovine serum for 7 days after polishing and autoclaving, and incubated with L929 fibroblasts for 7 days after polishing and autoclaving. L929 fibroblasts cultured on the specimen were removed with a flow of deionized water before surface analysis. X-ray photoelectron spectroscopy was performed to determine the composition of the surface oxide film and substrate and the thickness of the surface oxide film. The depth profiles of elements in the surface region were also characterized using Auger electron spectroscopy in combination with argon-ion-sputtering. The surface oxide film on Fe-24Cr-1N polished mechanically in deionized water consists of iron and chromium oxides. Large amounts of carbon, nitrogen, oxygen, and sulfur originating from proteins were detected after immersion in the medium. Sulfur existed as sulfide or sulfite. Calcium phosphate was formed on the surface oxide film after immersion in the Hanks’ solution and medium. On the other hand, calcium and sulfur were not detected after being incubated with the cells, indicating that a large amount of protein was absorbed on the top of the surface oxide film.
  • Characterization of the Surface Oxide Film on an Fe-Cr-Mo-N System Alloy in Environments Simulating the Human Body

    pp. 2671-2677

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    DOI:10.2320/matertrans.44.2671

    The objective of this study was to characterize the surface oxide film on nickel-free austenitic stainless steel, Fe-24Cr-2Mo-1N in mass% (Fe-26.7Cr-1.1Mo-3.6N in at%), with nitrogen absorption located in various environments, to estimate the reconstruction of the surface oxide film in the human body. The specimens were metallographically polished in deionized water, autoclaved after polishing, immersed in Hanks’ solution for 7 days after polishing and autoclaving, immersed in Eagle’s minimum essential medium containing fetal bovine serum for 7 days after polishing and autoclaving, and incubated with L929 fibroblasts for 7 days after polishing and autoclaving. L929 fibroblasts cultured on the specimen were removed with a flow of deionized water before surface analysis. X-ray photoelectron spectroscopy was performed to determine the composition of the surface oxide film and substrate and the thickness of the surface oxide film. The depth profiles of elements in the surface region were also characterized using Auger electron spectroscopy in combination with argon-ion-sputtering. The surface oxide film on the nickel-free austenitic stainless steel with nitrogen absorption, Fe-24Cr-2Mo-1N, polished mechanically in deionized water, consisted of iron and chromium oxides containing small amount of molybdenum oxide. A large amount of carbon, nitrogen, oxygen, and sulfur originating from proteins was detected after immersion in the medium and incubation with the cells. Sulfur existed as sulfide or sulfite. Calcium phosphate was formed on the surface oxide film after immersion in the Hanks’ solution and medium and incubation with the cells.
  • Synthesis and Characterization of Nanocrystalline Iron Aluminide Intermetallic Compounds

    pp. 2678-2687

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    DOI:10.2320/matertrans.44.2678

    Refining grain size to the nanocrystalline level has been suggested as a way of improving strength while enhancing ductility and toughness. In the present study, nanocrystalline iron aluminide intermetallic compounds were synthesized using mechanical alloying, sintering and high velocity oxy-fuel (HVOF) thermal spraying from the elemental powders. The phase changes occurred during milling, thermal spraying and annealing studied from magnetic and structural points of view. XRD, SEM, DSC and dynamic ultra-microhardness tester were used for examining the microstructure, thermal stability, mechanical properties and wear behavior of the milled powders and coatings. The current results demonstrated that, by controlling the experimental conditions, it was possible to prepare iron aluminide intermetallic compound with nano-size grains.
  • Mechanical Properties of Friction Surfaced 5052 Aluminum Alloy

    pp. 2688-2694

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    DOI:10.2320/matertrans.44.2688

    5052 aluminum alloy used for substrate and consumable rod, was friction surfaced using a numerical controlled full automatic friction welding machine. Effects of the surfacing conditions on some characteristics of deposits were investigated. It was clearly observed that the circularly pattern appeared on the surface of deposit by the rotation of consumable rod. The deposit has a tendency to incline toward the advancing side further than center of deposit for the feed direction of consumable rod. This deviation accompanied the decrease of the rotational speed of consumable rod. The width of deposit increased with increasing friction pressure, and decreasing rotational speed of consumable rod. The thickness of deposit became thinner when the consumable rod was high revolution. The surfacing efficiency decreased with increasing friction pressure and rotational speed of consumable rod, but increased with increasing feed speed. Microstructure of the deposit was finer than that of the substrate and consumable rod. The softened area was recognized at 3 mm distance from the weld interface of substrate. The tensile strength of deposit increased with increasing friction pressure. The maximum tensile strength of deposits showed 88.8% of the base metal of substrate.
  • Advanced Plasma Nitriding for Aluminum and Aluminum Alloys

    pp. 2695-2700

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    DOI:10.2320/matertrans.44.2695

    Low hardness and wear resistance of aluminum alloys limit their use in practical application to automotive parts. Formation of hard aluminum nitride (AlN) layer on the surface can prolong the life time of aluminum automotive parts. Plasma nitriding was selected in the present study to form AlN layer on aluminum alloys. This processing is an environmental friendly method because of its low gas and energy consumption. Normal plasma nitriding requires long processing time to successfully form AlN layer. For advancing this surface treatment, refining microstructure and micro-alloying processes are proposed to activate the formation of AlN by plasma nitriding. Bulk Mechanical Alloying is used not only to make grain-size refinement but also to carry out micro alloying with addition of 1 mass%Ti. The formation rate of AlN layer is improved from 4.2×10−5 μm/s to 20.8×10−5 μm/s by microstructure refining. In particular, since the co-formed TiN with AlN works as a template in the initial state nitriding, the micro-alloyed aluminum can be nitrided even without pre-sputtering.
  • Solid State Diffusion Bonding of Silicon Nitride Using Vanadium Foils

    pp. 2701-2710

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    DOI:10.2320/matertrans.44.2701

    This paper describes the relation between the interfacial microstructure and the fracture strength of the joints of silicon nitride (Si3N4) and vanadium (V) formed by solid state diffusion bonding. At first, the interfacial microstructure and its evolution process were analyzed in detail. The phase sequence at the interface changes with the bonding time showing five typical stages. In the first stage, a V3Si layer and V2N grains are formed. The V2N grains contact with the V3Si layer at 1473 K and below, while the contact is prohibited at 1498 K and above. The Si3N4/V3Si interface is metastable. In the second stage, a V5Si3N1−X layer appears. In the third stage, V is annihilated. In the fourth stage, the V3Si layer is annihilated and VN grains are formed. In the fifth stage, V2N is annihilated. This evolution process of the interfacial microstructure agrees well with the proposed chemical potential diagram, except the metastable state of the interface. The increase and decrease behavior in the thickness of each reaction product interact with each other. The behavior of the V3Si layer is affected not only by the formation and growth of the V5Si3N1−X layer but also by the formation of a V(Si) zone at the V3Si/V interface. The formation of the V5Si3N1−X layer starts when the spatial gradient of the chemical potential of vanadium in the V3Si layer decreases to a certain value. The fracture strength of the joints changes depending on the bonding temperature and time. The higher bonding temperature leads to the higher maximum fracture strength. The maximum strength at each bonding temperature is achieved when the thickness of the V3Si layer is 2.0 μm. The prolonged bonding time gradually reduces the fracture strength down to 42 MPa.
  • Characterization of Pure Aluminum and Zinc Sprayed Coatings Produced by Flame Spraying

    pp. 2711-2717

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    DOI:10.2320/matertrans.44.2711

    We investigate flame spraying of pure aluminum and pure zinc powders on various different substrates and study shrinkage properties and thermal analysis curves of sprayed coatings during the forming process. We also examined effects of the spray distance on the porosity, tensile strength and hardness of sprayed coatings, and obtained the following results. With an increase in spray distance, shrinkage of the sprayed coating and the maximum temperature in the thermal analysis curve decrease. When the cooling ability of the substrate is higher, the shrinkage ratio and the maximum temperature become decrease. The porosity and the hardness of a sprayed coating increase with an increase in spray distance. This occurs because with the increase in the spray distance, the temperature of the sprayed particles decreases, the amount of air taken in the spray increases and, as a result, the cooling rate of the coating increases. The tensile strength of a pure aluminum coating decreases with an increase in spray distance due to the introduction of pores. On the contrary, the tensile strength of a pure zinc coating increases with an increase in spray distance. This occurs because when the spray distance is short, coating temperature is high and, as a result, a large quantity of zinc oxide is formed.
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  • Surface Integrity in Micro-Hole Drilling Using Micro-Electro Discharge Machining

    pp. 2718-2722

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    DOI:10.2320/matertrans.44.2718

    This paper presents an investigation into the drilling of micro-holes of diameter 0.3 mm in tool steel H13 by means of the Micro-EDM process. Scanning Electron Microscopy (SEM) and Scanning White Light Interferometry (SWLI) techniques are used to determine the influence of the drilling process parameters upon the surface roughness. The results reveal a series of randomly overlapped craters upon the machined surface, which represent the position and chronological sequence of individual sparks during the machining process. As the voltage and current increases, the crater appearance changes from a conical to a cylindrical shape, and its depth and diameter both increase. It is shown that surface roughness deteriorates as the pulse voltage increases. Finally a regression equation is established between the diameter of the crater and the pulse voltage, pulse current and pulse-on duration parameters. This equation enables the diameters of the craters, and hence the surface integrity of the machined surface, to be predicted for a given set of process parameters, and is therefore a valuable tool in achieving the goal of precision machining.
  • Re-examination of Phase Diagram of Fe-Pt System

    pp. 2723-2731

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    DOI:10.2320/matertrans.44.2723

    The phase boundaries pertaining to γ2 (FePt) and γ3 (FePt3) phases in the Fe-Pt system have been re-examined by measuring (1) the compositions of interphase boundaries in diffusion couples, (2) the equilibrium compositions in two-phase alloys and (3) the electrical resistivity as a function of temperature. The results obtained by the three methods are consistent with each other. The γ (fcc solid solution) ↔ γ23 eutectoid has been found to be located at a point higher in Pt concentration and lower in temperature than in the currently adopted phase diagram, the stability range of the γ2 phase exhibits considerable asymmetry. Other phase boundaries, as well as the ferromagnetic ↔ paramagnetic transition in the γ2 phase detected by the resistivity measurements, are in fair agreement with the data in the literature.
  • Shape Memory Effect Associated with FCC—HCP Martensitic Transformation in Co-Al Alloys

    pp. 2732-2735

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    DOI:10.2320/matertrans.44.2732

    The martensitic transformation and shape memory (SM) effect in Co-Al alloys containing 0–16 at%Al were investigated by differential scanning calorimetry (DSC) and bending tests. It was found that the martensitic transformation temperatures decrease and the thermal hystereses increase with increasing Al content. It was also found that an incomplete SM effect occurring in pure Co can be enhanced by the addition of Al over 4 at% and that Co-Al alloys containing Al over 10 at% show an excellent SM effect. Co-Al SM alloys possessing high reverse transformation temperatures over 200°C and martensitic transformation in the ferromagnetic state show promise as a new type of SM alloys.

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