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

MATERIALS TRANSACTIONS Vol. 44 (2003), No. 10

  • Nanocrystallization of Steels by Severe Plastic Deformation

    pp. 1900-1911

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    DOI:10.2320/matertrans.44.1900

    The formation of nanocrystalline structure (NS) in steels by various severe plastic deformation processes, such as ball milling, a ball drop test, particle impact deformation and air blast shot peening are demonstrated. Layered or equiaxed nanograined region appeared near the specimen surface and dislocated cell structured region appeared interior of specimens. These regions are separated with clearly defined boundaries. The deformation induced nanograined regions have the following common specific characteristics: 1) with grains smaller than 100 nm and low dislocation density interior of grains, 2) extremely high hardness, 3) dissolution of cementite when it exist and 4) no recrystallization and slow grain growth by annealing. The deformation conditions to produce NS was discussed based on the available data in literatures. It was suggested that the most important condition is to impose a strain larger than about 7. High strain rates, low deformation temperature, multidirectional deformation, hydrostatic pressure are considered to be favorable conditions to produce NS. Introducing alloying elements, precipitates and second phase also enhance nanocrystallization by suppressing recovery. The mechanisms of the formation of sharply defined boundaries which separate nanograined structure region from dislocated cell structured region were discussed with respect to impurities, martensitic transformation and deformation. It was suggested several mechanisms may operate simultaneously in the formation of the clear boundaries.
  • Effect of Carbon on Nano-Crystallization in Steel during Mechanical Milling Treatment

    pp. 1912-1918

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    DOI:10.2320/matertrans.44.1912

    Mechanical milling (MM) treatment of metallic powder is suitable for fabricating nano-crystallized materials, because milling action by steel balls enables to give a huge amount of strain with multi-directional plastic deformation to powder particles. In this study, effect of carbon on the grain refining behavior during MM treatment was investigated in high purity iron material and Fe-C materials. The powder used in this study is electrolytic pure (9 ppmC) iron and cementite (6.2 mass%C) powder particles. The powders are mixed to set the chemical composition to be Fe-(0-2)mass%C. The mixed powder is subjected to MM treatment for various times (3.6-360 ks) and then microstructure was examined by means of X-ray diffractometry, TEM observation. With MM treatment, cementite decomposes into ferrite matrix and ferritic single structure is obtained after 360 ks MM treatment. On the other hand, microstructure of ferrite develops from dislocation cells structure to fine-grained structure through dynamic continuous recrystallization (DCR). The grain size is reduced gradually with MM treatment. However the grain size after reaching steady state is different between high purity iron and Fe-C materials. The grain size after 360 ks MM treatment decreases with increasing carbon content, and nano-crystallized structure with about 15 nm grain size was obtained in the Fe-0.8 mass%C. This indicates that carbon addition enhances grain refining and is necessary for nano-crystallization by severe plastic deformation. Considering the interaction between carbon atoms and dislocations, carbon addition would assist the increment of stored dislocations which contributes to DCR. This results in the effectiveness for the formation of nano-crystallized structure in carbon added iron.
  • Development of Nanostructures in Metallic Materials with Low Stacking Fault Energies During Surface Mechanical Attrition Treatment (SMAT)

    pp. 1919-1925

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    DOI:10.2320/matertrans.44.1919

    Surface mechanical attrition treatment (SMAT) technique was developed to synthesize a nanostructured surface layer on metallic materials for upgrading their overall properties and performance. In this paper, the grain refinement process during SMAT was investigated in materials with low stacking fault energies (SFE, Inconel 600 alloy and AISI 304 stainless steel) by means of transmission electron microscopy and high-resolution electron microscopy, respectively. Grain subdivision was performed by the interaction of mechanical microtwins with dislocations in Inconel 600. For AISI 304 stainless steel with a lower SFE, twin-twin intersections subdivide initial grains into refined blocks with sizes ranging from nanometers to submicrometers. Such grain subdivision processes of the interaction of microtwins with dislocations or microtwins obviously differ from those observed in the high SFE materials in which dislocation interactions predominate the grain refinement.
  • Dynamic Processes for Nanostructure Development in Cu after Severe Cryogenic Rolling Deformation

    pp. 1926-1934

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    DOI:10.2320/matertrans.44.1926

    The dynamic grain refinement behavior upon severe plastic deformation has been systematically studied in commercial purity copper that was heavily cold rolled to large deformations at cryogenic temperatures. The low-temperature rolling allows the accumulation of extraordinarily high densities of dislocations in Cu, enabling an investigation of the various dynamic recrystallization phenomena upon further deformation. The eventual steady-state grain sizes achieved, as well as the dynamic recrystallization mechanisms, are studied using controlled deformation tests combined with transmission electron microscopy. The dominant mechanisms observed to contribute to grain refinement in Cu include the classical migration dynamic recrystallization process, the deformation twinning, as well as the continuous dynamic recrystallization via progressive lattice rotation upon deformation to extremely large strains. The strain rate and deformation temperature have strong effects on the operative mechanisms and the grain sizes achieved in the ultrafine and nanocrystalline regimes.
  • Processing Issues for Cryomilled WC-Co Nanopowders

    pp. 1935-1941

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    DOI:10.2320/matertrans.44.1935

    Processing issues of cryomilled WC-VC-Co nanopowders were investigated. A powder mixture of WC-9.8Co-0.8VC-xC was milled at −50°C in liquid nitrogen, using WC-Co balls. The particle sizes of the powders, in the form of agglomerates, were reduced to 18 nm and 13 nm for WC and Co, respectively by this process. The roles of some of the processing parameters such as compacting pressure, reduction of powders, and temperatures for the heating schedule were evaluated at a sintering temperature of 1450°C. The use of CIP resulted in a more uniform microstructure and enhanced mechanical properties: hardness (13-14 GPa) and KIC (12-15 MPam1⁄2). The findings herein suggest that carbon control and the use of a proper compaction technique were key factors in the successful production of nano-sized WC-Co alloys with no detectable η phase.
  • High Strength Ni-Fe-W and Ni-Fe-W-P Alloys Produced by Electrodeposition

    pp. 1942-1947

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    DOI:10.2320/matertrans.44.1942

    Ni-Fe-W alloys were produced by electrodeposition from an ammoniacal citrate bath having nickel sulphate, ferric sulphate and sodium tungstate as sources of nickel, iron and tungsten, respectively. The alloys prepared at low current densities have nanocrystalline structure, while those prepared at high current densities are amorphous. X-ray diffraction results show that the structure changes gradually from nanocrystalline to amorphous phase with an increase of current density. As the current density increases, tungsten content increases while iron content decreases. The hardness of the alloys increases with increasing tungsten content. The best mechanical properties among all the alloys are obtained for 51Ni-29Fe-20W alloy prepared at 600 A/m2. Effect of sodium hypophosphite on the composition of the alloys produced at 2000 A/m2 was also studied. Addition of hypophosphite causes a decrease in tungsten content of the alloys. Further increase in the hypophosphite content causes a decrease of both iron and tungsten contents and an increase of phosphorus and nickel contents. For the alloys deposited from solutions containing sodium hypophosphite more than 0.03 mol/L, the total molar content of tungsten and phosphorus remains constant at 20 at%.
  • Nanocrystalline structure and Mechanical Properties of Vapor Quenched Al-Zr-Fe Alloy Sheets Prepared by Electron-Beam Deposition

    pp. 1948-1954

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    DOI:10.2320/matertrans.44.1948

    Nanocrystalline Al-based ternary alloys with additions of Zr and Fe have been prepared by electron-beam deposition. The composition dependence of microstructures and mechanical properties has been investigated. Fine α-Al grains are observed and the grain size significantly decreases with the increase of Zr content. Al95.3-Zr4.0-Fe0.7 and Al96.5-Zr2.8-Fe0.7 alloys consist of α-Al containing the coherent meta-stable L12 precipitate. The addition of Fe, effectively refined the grain structure, increases hardness and improves the thermal stability of the meta-stable L12-Al3Zr phase. Al95.3-Zr4.0-Fe0.7 alloy exhibits remarkably high tensile strength both at room temperature and above 523 K, 817 MPa at room temperature, 536 MPa at 523 K and 434 MPa at 573 K, respectively. The microstructure of Al95.3-Zr4.0-Fe0.7 alloy exhibits excellent thermal stability under prolonged annealing at 523 K.
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  • Age Hardening of Ultrafine Grained Al-Ti-Cr Alloys Fabricated by Continuous Electron Beam Evaporation

    pp. 1955-1961

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    DOI:10.2320/matertrans.44.1955

    Supersaturated Al-Ti-Cr alloys were produced by a continuous electron beam evaporation technique. The as-deposited alloy sheets were fcc supersaturated solid solution with an average grain size of about 400 nm. Due to the fine grain size, the hardness of the alloy was as high as 270 Hv. The sheet showed age hardening, and the peak hardness of 340 Hv was obtained after aging at 623 K for 900 s, in which ultrafine coherent precipitates of L12 Al3Ti phase were uniformly dispersed. As the annealing temperature increased up to 773 K, large D022 particles precipitate by the discontinuous precipitation mode and the hardness significantly decreased. Although Cr was confirmed to be enriched in the L12 particles, it did not completely stabilize the L12 phase probably due to the effect of oxygen.
  • Chemical Modification of Titanium Nitride Films via Ion Implantation

    pp. 1962-1970

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    DOI:10.2320/matertrans.44.1962

    Titanium nitride, TiN is a typical ceramic coating film for cutting tools and dies; it often suffers from low oxidation temperature and high friction coefficient and wear volume. Its wearing and oxidation resistance is drastically improved by chemical modification via ion implantation. Carbon-, aluminum- and chlorine-ion implantation is introduced to describe the difference in the modified microstructure at the vicinity of surface. Ion-plated TiN films on a high-speed tool steel substrate are employed as a common specimen to be implanted. Each modified titanium nitride has its intrinsic, as-implanted nanostructure to the selected species. In the carbon implantation, the near-surface structure of TiN film is modified to have the layered bonding state with Ti-C/C-C/Ti-C. The Al-implantation modifies TiN to have non-equilibrium solid solution phase of (Ti, Al) N and metallic aluminum cluster. No change is seen in the chlorine implanted TiN except for increase of dislocations or point defects. The wear resistance is improved by the above as-implanted nano-structuring in the case of carbon implantation. Al- and Cl-implantation significantly improves the original oxidation and wearing resistance of TiN by the post-implantation nano-structuring. The stable, dense aluminum oxide layer is in-situ formed as a tight protective shield during the oxidation test by surface reaction between penetrating oxygen and diffusing aluminum. The lubricious titanium oxide film is also in-situ formed in the wear track at the presence of chlorine to sustain low friction and wear rate even in dry, severe wearing conditions.
  • Nanoquasicrystallization in Metallic Glasses

    pp. 1971-1977

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    DOI:10.2320/matertrans.44.1971

    Nanoquasicrystallization in Zr-based glassy alloys was investigated. It is found that the nano scale icosahedral quasicrystalline phase (I-phase) is formed by addition of the elements, which obstruct the glass-forming ability (GFA) in the glassy alloy. The primary phase of fcc Zr2Ni phase in the Zr65Al7.5Ni10Cu17.5 glassy alloy with high GFA changes to the fcc Zr2Ni plus I-phases by substitution of noble metals or Zr for only 1 at% Cu. Since each phase is precipitated independently and the icosahedral local atomic configuration exits in the fcc Zr2Ni and I-phases, they are originated from the same local structure in the Zr-based glassy alloy with high GFA. We found that the icosahedral local structure is strongly correlated with the stability of the supercooled liquid state. The origin of the icosahedral local structure is combination of Zr + Cu and Zr + Al + Ni elements. In these alloy systems, the I-phase is easy to precipitate as a primary phase by addition of a very small amount of appropriate element. From the present results, it is concluded that the icosahedral local structure stabilizes the supercooled liquid state. We suggest that the high GFA for the preparation of bulk glassy alloy is attributed to the stability of icosahedral local structure.
  • Precipitation of Stable Icosahedral Phase in Ti-Based Amorphous Alloys

    pp. 1978-1981

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    DOI:10.2320/matertrans.44.1978

    The crystallization behavior of bulk amorphous Ti-Zr-Be-Cu-Ni alloys has been studied by using differential scanning calorimetry (DSC), X-ray diffractometry (XRD) and transmission electron microscopy (TEM). Detailed thermal analysis showed that Ti-Zr-Be-Cu-Ni amorphous alloys with the wide composition range crystallized through two exothermic reactions followed by one endothermic reaction. At first stage, nanometer scale primary icosahedral phase (I-phase) precipitated from an amorphous matrix and then the remaining amorphous phase crystallized into cubic β-Ti(Zr) phase or hexagonal Laves phase depending on the alloy composition. Finally, I- and β-Ti(Zr) phase or I- and Laves phase mixture transformed into the Laves phase by the high-temperature endothermic reaction, indicating that the I-phase is a thermally stable phase at the lower temperature range. Reversible transformation between the I-phase and Laves phase during cyclic heating and cooling confirmed the thermodynamic stability of the I-phase in Ti-Zr-Be-Cu-Ni system.
  • Nanocrystallization Reactions in Amorphous Aluminum Alloys

    pp. 1982-1992

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    DOI:10.2320/matertrans.44.1982

    Primary crystallization is the key reaction that controls the synthesis of nanostructured bulk volumes comprised of a high density (1021–1023 m−3) of nanocrystals (7–20 nm) within an amorphous matrix. The primary crystallization kinetics in response to the annealing and the deformation of amorphous Al alloys are assessed in specific sample types and selected thermal treatments to evaluate primary nanocrystallization reactions. All amorphous Al alloy compositions are hypereutectic so that the initial phase selection of primary Al proceeds at a reduced driving free energy compared to thermodynamically favored intermetallic phases. Differential scanning calorimetry (DSC) studies on powders and melt spun ribbon (MSR) samples based upon thermal cycling and annealing below the glass transition, Tg, demonstrate a strong sensitivity of the primary crystallization onset and reaction enthalpy to thermal history and the as-quenched state. Microcalorimetry investigations and careful analysis of nanocrystal size distributions for Al92Sm8 MSRs following sub-Tg anneals reveal a partial nanocrystallization reaction resulting from a transient, decaying nucleation rate and a limited supply of heterogeneous nucleation sites. While crystallization is generally thought of as a thermally activated process, it can also be induced in response to external forcing such as irradiation or mechanical alloying. Intense deformation of amorphous Al88Y7Fe5 MSR, for example, yields a distribution of Al-nanocrystallites in the amorphous matrix without thermal annealing. Moreover, the results of cold-rolling experiments with melt-spun amorphous Al85Ni10Ce5 ribbons show that the deformation process can alter the phase selection upon annealing. These results suggest that the shear process during rolling effects a local rearrangement of atoms in the amorphous matrix. The kinetics behavior highlights the important role of the as-synthesized amorphous structure, reaction pathways and transient conditions on the evolution of nanoscale microstructures during primary crystallization.
  • Microstructure of Rapidly Solidified High Strength Al94V4Fe2 Alloy

    pp. 1993-1998

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    DOI:10.2320/matertrans.44.1993

    Al94V4Fe2 alloy melt-spun at different wheel velocities in the range of 20-50 m/s has been studied. The microstructure of the alloy consists of a nanoquasicrystalline phase in an Al matrix at slow cooling rates, while at higher cooling rates it shows nanodomains of an amorphous phase embedded in the Al matrix. The tensile fracture strength of the alloy reaches a maximum when it exhibits a nanocomposite microstructure consisting of quasicrystalline phase and Al. The composition of the quasicrystalline and amorphous phases has been identified using three dimensional atom probe field ion microscopy.
  • Nanostructured Composites in Multicomponent Alloy Systems

    pp. 1999-2006

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    DOI:10.2320/matertrans.44.1999

    A group of novel nanostructured composites fabricated by different casting methods is presented. Nb, Ta and Mo are added into Ti-base bulk metallic glass (BMG)-forming alloys and Nb is added to the Zr-base BMG-forming alloy to induce the formation of dendrite/nanostructured matrix composites. These composites exhibit high fracture strength of up to 2400 MPa. Both Nb-bearing Ti- and Zr-base composites exhibit over 14% plastic strain upon room temperature compression. The Ti60Cu14Ni12Sn4Nb10 composite also exhibits over 7% room temperature tensile plastic strain. The high strength of the composites is attributed to the nanostructured matrix. The large plasticity is due to the retardation of excessive localized shear banding in the matrix by the presence of the ductile dendrites. The significant work hardening before fracture is attributed to the deformation behavior of the dendritic solid solution.
  • Correlation between Glass Formation and Type of Eutectic Coupled Zone in Eutectic Alloys

    pp. 2007-2010

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    DOI:10.2320/matertrans.44.2007

    Glass formation is basically to avoid nucleation upon quenching. However, the growth of each nucleus is also important as certain undercooling is needed. Thus the subsequent competition between the growth of crystalline phases and the formation of amorphous phase should be considered. In this paper, we summarized our recent studies in Pd-Ni-Cu-P system and La-Cu-Ni-Al alloy systems. It is concluded that the glass forming ability of a eutectic alloy system depends on the type of the eutectics, i.e. symmetric or asymmetric eutectic coupled zone. For the alloy systems with symmetric eutectic coupled zone, the best glass forming alloys should be at or very close to the eutectic composition. For the alloys with asymmetric eutectic coupled zone, the best glass forming alloys should be at off-eutectic compositions.
  • Random Anisotropy Model for Nanocrystalline Soft Magnetic Alloys with Grain-Size Distribution

    pp. 2011-2019

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    DOI:10.2320/matertrans.44.2011

    A simple model considering grain-size distribution is proposed based on the random anisotropy model. When the maximum grain size (Dm) is less than the exchange correlation length and induced anisotropies are sufficiently small, the effective magnetic anisotropy constant (⟨K1⟩) is given by using a distribution function (f(D)) for the grain size (D) as ⟨K1⟩≈K14{∫0DmD3f(D)dD}2⁄(\\varphi6Ac3), where K1 is the magnetocrystalline anisotropy constant, \\varphi is a parameter which reflects both the symmetry of ⟨K1⟩ and the total spin rotation angle over the exchange-correlated coupling chain and Ac is the exchange stiffness constant. The log-normal distribution function reproduces well the observed grain-size distribution and yields ⟨K1⟩≈K14D6exp(6σD2)⁄(\\varphi6Ac3), where ⟨D⟩ is the mean grain size and σD is the geometric standard deviation for the distribution. This result satisfies the well-known ⟨D6 law. However, ⟨K1⟩ increases with increasing σD even if ⟨D⟩ is constant. Our model has been extended by taking into account the effect of the coherent induced anisotropies on the exchange correlation length. The coercivity (Hc∝⟨K1⟩⁄Js, where Js is the saturation magnetization) of the nanocrystalline Fe-Nb-B(-P-Cu) alloys with different grain-size distribution have been calculated. Our model explains well the dependence of Hc on the grain-size distribution. These results suggest that one should pay attention on not only the mean grain size but also on the grain-size distribution since the inhomogeneity of the grain size increases Hc.
  • Origin of Low Coercivity of Fe-(Al, Ga)-(P, C, B, Si, Ge) Bulk Glassy Alloys

    pp. 2020-2024

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    DOI:10.2320/matertrans.44.2020

    The magnetic properties of the glassy Fe-(Al, Ga)-(P, C, B, Si, Ge) alloys have been compared with those of the conventional Fe-based amorphous alloys to clarify the feature of the glassy alloys as a soft magnetic material. The glassy Fe-(Al, Ga)-(P, C, B, Si, Ge) alloys exhibit lower saturation magnetization (Js) than that of the conventional Fe-(B, Si, C) amorphous alloys with the same Fe content. The glassy alloys also have larger saturation magnetostriction constant (λs) than that of the conventional Fe-based amorphous alloys with the same Js. However, the glassy alloys tend to show relatively low coercivity (Hc) whereas λs is large. The theoretical analysis on the basis of domain-wall movement suggests that the low Hc originates from the much higher packing density of the glassy alloys than that of the conventional amorphous alloys, which realizes the low density of the quasi-dislocation dipole-type elastic stress sources or the low pinning force due to the elastic stress. The good combination of high glass-forming ability and good soft magnetic properties (especially low Hc) indicates the possibility of future development as new low loss material.
  • Electron Holography of Nanocrystalline Magnetic Materials

    pp. 2025-2034

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    DOI:10.2320/matertrans.44.2025

    Electron holography study on magnetic domain structures of nanocrystalline magnetic materials was overviewed mainly based on the experimental results recently obtained by the author and his colleagues. Electron holography system which was established by modifying a conventional analytical electron microscope, i.e., introducing a biprism and a special pole piece for magnetic domain observation shows the resolution of several nanometers under the magnetic field less than 1600 A/m at the specimen position. With this system, firstly magnetic domain structures of nanocrystalline soft magnetic materials Fe-Cu-Nb-Si-B with various heat treatments are clarified. Furthermore, by introducing the residual magnetic field of the objective lens in the thin film plane, magnetization process of the soft magnetic materials is observed. On the other hand, in nano-granular films Co-Zr-O, the dependence of both microstructures and magnetic domain structures on the composition is clarified in detail. It is found that the strength of the magnetic anisotropy field in the film directly depends on the magnetization distribution clarified by electron holography. Finally, in the nanocomposite magnets Nd-Fe-B, the detailed distribution of lines of magnetic flux at a nanometer scale is visualized. It is found that the distribution of lines of magnetic flux observed is directly related to the magnetic properties, such as coercivity and remanence. These results clearly demonstrate the usefulness and the potential of electron holography for the analysis of detailed magnetic domain structures of advanced magnetic materials such as nanocrystalline magnetic materials.
  • Atomic-Scale Characterization of Nanostructured Metallic Materials by HAADF/Z-contrast STEM

    pp. 2035-2041

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    DOI:10.2320/matertrans.44.2035

    We demonstrate that high-angle annular-dark-field scanning transmission electron microscopy (HAADF-STEM) with a finely-focused electron probe (∼0.15 nm) is very powerful technique to provide direct information on a local chemistry of nano-materials at atomic scale. This is due to an atomic-number (Z) sensitive nature of the HAADF contrast (Z-contrast). We describe the microstructures of some crystalline, quasicrystalline and amorphous metallic materials with focusing on their local chemical environments. Not only the chemical Z-contrast, HAADF-STEM possesses more substantial advantages compared to the conventional phase-contrast high-resolution imaging, so that it would be one of the most powerful methods for total characterization of nano-structured materials.
  • Local Atomic Structures of Amorphous Nd4.5Fe77B18.5 Alloys Formed under Different Cooling Rates and Their Relations to the Structures in the Early Stage of Crystallization

    pp. 2042-2047

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    DOI:10.2320/matertrans.44.2042

    A difference of amorphous structures of magnetic Nd4.5Fe77B18.5 alloys formed under two different cooling rates was investigated by means of electron microscopy, electron diffraction and X-ray diffraction techniques. In spite of no appreciable difference in the high resolution electron microscope images, an atomic structural difference especially in the B-centered polyhedral structures was found in these specimens in their as-formed states. The effect of the initial local structure difference on the process of primary crystallization in these alloys on annealing was discussed.
  • HRTEM Studies of nm-Size FePd Particles Embedded in MgO after Annealing over 920 K

    pp. 2048-2054

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    DOI:10.2320/matertrans.44.2048

    FePd particles were fabricated in MgO crystalline films by using an ultra-high vacuum (UHV) co-deposition method. As-deposited samples and samples annealed at 973 K and 1073 K were studied by high resolution electron microscopy (HRTEM). The as-deposited FePd particles were in a disordered fcc phase with a=0.3837 nm and have a certain epitaxial orientations i.e. [100] (001)FePd||[100] (001)MgO. The size of particles was about 2-3 nm and separated distance of particles was about 3-4 nm. After the as-deposited sample was annealed at 973 K for 24 hours, there were neither change in particle size and separated distance, nor phase transformation to take place from disordered fcc to L10 order structure. Only change was that lattice fringes in the FePd particles became more straight and regularly spaced than those of the as-deposited sample, and faults within the FePd particles became less than those of the as-deposited sample. After the as-deposited sample was annealed at 1073 K for 4 hours, the size of particles became almost about 3-4 nm and separated distance of particles was about 2-3 nm. Some coalescence took place among the particles. There was, however, no transformation to take place from disordered fcc to L10 order structure. The reason why L10 order structure of FePd can not be obtained at such higher annealing temperature than the transformation temperature for the bulk is suggested to be that the system energy of small particle was subjected to strain inside, which is caused by large lattice mismatch between FePd and MgO.
  • Microstructural and Chemical Characterisation of Metal Particles Nanostructures

    pp. 2055-2061

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    DOI:10.2320/matertrans.44.2055

    In order to achieve a full characterisation of metal particles nanostructures at the microstructural level, we show in this overview the use of different techniques: i) High resolution transmission electron microscopy (TEM) or energy filtered TEM (EFTEM) associated to energy dispersive X-Ray analysis (EDX) and electron energy loss spectroscopy (EELS). ii) A surface analysis technique like X-Ray photoelectron spectrocopy (XPS). iii) A technique sensitive to the local structure and chemical state like X-Ray absorption spectroscopy (XAS). Two systems will be described to illustrate this study:
    i) Nickel particles dispersed in an amorphous carbon matrix have been synthesized by a sonication method, and further heated at 773 K under Ar atmosphere. The as-prepared sample shows amorphous spherical particles (TEM) formed by Ni2+ highly dispersed in carbon (XPS, XAS). The heated sample shows spherical grains formed by nanocrystalline Ni particles embedded in an amorphous carbon matrix (HRTEM). Heterogeneities at micro- and nanoscopic scale have been determined by TEM/EELS and EFTEM. Quantification of the oxidation level for the heated sample was also determined by XAS. ii) Gold nanoparticles modified with neoglycoconjugates molecules have been prepared by a wet chemical method. Aggregates, isolated nanoparticles or two-dimensional self-organised nanostructures have been obtained by controlling the interaction forces between biological significant oligosaccharides. The EFTEM analysis has been used to demonstrate the role of divalent cations in the formation of the nanostructures.
  • Spin-Voltaic Effect and its Implications

    pp. 2062-2065

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    DOI:10.2320/matertrans.44.2062

    In an inhomogeneously doped magnetic semiconductor, an interplay between an equilibrium magnetization and injected nonequilibrium spin leads to the spin-voltaic effect–a spin analogue of the photo-voltaic effect. By reversing either the sign of the equilibrium magnetization or the direction of injected spin polarization it is possible to switch the direction of charge current in a closed circuit or, alternatively, to switch the sign of the induced open-circuit voltage. Properties of the spin-voltaic effect can be used to perform all-electrical measurements of spin relaxation time and injected spin polarization, as well as to design devices with large magnetoresistance and spin-controlled amplification.
  • Electrical and Optical Properties of Ultra-small Carbon Nanotubes Arrayed in Channels of Zeolite Single Crystals

    pp. 2066-2069

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    DOI:10.2320/matertrans.44.2066

    0.4 nm-sized single-walled carbon nanotubes (SWNTs) were produced by means of pyrolysing hydrocarbon molecules in 1 nm-sized channels of AlPO4-5 (AFI) single crystals. These small SWNTs are highly aligned and uniform in size. They behave as a good polarizer, having strong absorption for the light polarized parallel to the tube direction, and nearly transparent for the light polarized in perpendicular direction. The absorption bands are assigned to the dipole transitions between the van-Hove singularities. Resonant Raman scattering measurement confirmed these van-Hove singularity structures. Investigation of the magnetic and transport properties of these SWNTs revealed that at temperatures below 20 K, the 0.4 nm tubes exhibit superconducting behavior manifest as an anisotropic Meissner effect, with a superconducting gap and fluctuation supercurrent.
  • Microstructures of Cu-Ge Alloy Rods Pulled from a Hyperperitectic Melt by the Czochralski Method

    pp. 2070-2077

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    DOI:10.2320/matertrans.44.2070

    Cu-Ge alloy rods were pulled from a hyperperitectic melt at three kinds of pulling rates while the melt temperatures were lowered at controlled rates, respectively by the Czochralski method. The relationship between the pulling rate and the Ge concentration in the α phase that solidified first from the melt is approximated by the relation derived from the BPS expression for the effective distribution coefficient. A group of peritectic ζ grains is formed subsequent to the initial growth of α crystal in the rods pulled at some rates. Growth of the ζ grains is followed by growth of α phase, resulting in the formation of alternating structures of the primary α and the peritectic ζ which is accompanied by a simultaneous variation in rod thickness. This appears repeatedly at short intervals along the rod when it is pulled at a high rate. It is concluded that the alternating structures of α phase and peritectic ζ grains are formed by a peritectic solidification of Ge-rich melt at the cell boundary that develops on a constitutionally supercooled solid-liquid interface, and that their cessation is due to a decrease in Ge concentration of the liquid at the interface, with subsequent growth of the ζ phase.
  • Diffusion of niobium in α-iron

    pp. 2078-2083

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    DOI:10.2320/matertrans.44.2078

    Diffusion coefficient of 95Nb in α-iron has been determined in the temperature range between 823 and 1163 K by use of a serial sputter-microsectioning technique. The diffusion coefficient of niobium is about two times as large as the self-diffusion coefficient in α-iron. The temperature dependence of the diffusion coefficient, D, in the whole temperature range of α-iron across the Curie temperature (TC=1043 K) can be expressed by D=(1.40−1.05+4.17)×10−1exp\\big[−\\frac(299.7±12.7 kJmol−1)[1+(0.061±0.007)s2]RT\\big] m2s−1 where s is the ratio of the spontaneous magnetization at T K to that at 0 K. The factor 0.061 in the equation is smaller than 0.156 for the self-diffusion, showing that the magnetic effect on the diffusion of niobium in α-iron is smaller than that on the self-diffusion. The activation energy 299.7 kJmol−1 for niobium diffusion in the paramagnetic iron is much higher than 250.6 kJmol−1 for the self-diffusion. Atomic size effect is predominant in the activation energies for the diffusion of transition metal solutes in the paramagnetic α-iron.
  • Ni-Based Refractory Bulk Amorphous Alloys with High Thermal Stability

    pp. 2084-2087

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    DOI:10.2320/matertrans.44.2084

    Enhancement of thermal stability and glass forming ability in Ni60Nb40−xTax (x=0, 3, 5, 10, 20 at%) alloys has been investigated. The crystallization temperature increases from 660°C in binary Ni60Nb40 amorphous phase to 721°C in Ni60Nb20Ta20 amorphous phase. The fully amorphous rod with diameter of 2 mm is fabricated in Ni60Nb30Ta10 alloy by an injection casting method. The compressive failure strength of the Ni60Nb30Ta10 bulk amorphous alloy is 3346 MPa.
  • Development of Machinable High-Strength Copper-Based Alloys by Sulfide Dispersion

    pp. 2088-2093

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    DOI:10.2320/matertrans.44.2088

    Studies on the properties of Cu-S-Ti and Cu-S-Zr alloys containing 0.8-1.6 at% S, and 0.4-2.7 at% Ti or Zr were carried out. Titanium and zirconium formed (Ti, Cu)S and (Cu, Zr)2S, respectively, which were uniformly dispersed. Age-hardening phenomena were observed in the alloys having the composition ratio of Ti/S>1 or Zr/S>1, which indicates that the soluble titanium and zirconium in the Cu-matrix after formation of sulfide result in age-hardening. (Ti, Cu)S and (Cu, Zr)2S were found to be the effective inclusions for improving the machinability. The Cu-S-Ti and Cu-S-Zr alloys developed by sulfide dispersion are very promising as a new type of copper-based alloys having high strength, high electrical conductivity and good machinability.
  • Characterization of Melt-Spun NdFeB Magnets Prepared by Explosive Compaction

    pp. 2094-2098

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    DOI:10.2320/matertrans.44.2094

    Explosive compaction processing is applied to prepare NdFeB magnets with melt-spun powders. It is found that shock consolidation processing could result in the magnetic properties, compressed strength and density of NdFeB bulk better than that of the conventional resin-bonded magnet. Scanning electron microscope (SEM) observation shows the melted areas and a mass of the micro-cracks in the close-packed particles resulted from the shock wave. The small Nd2Fe14B grains less than 100 nm, existing inside the powder particle without appreciable change of the original grain size, are revealed using the field emission scanning electron microscope (FE-SEM). The corresponding magnetic structure consisting of the very fine magnetic domains is also revealed with magnetic force microscopy (MFM). The results indicate that not only the microstructure but also the magnetic domain structure of the original powder are kept after explosive compaction. Although there are many micro-cracks in particles, the excellent magnetic properties are still obtained because the magnetic domain structure is so fine that seems not to be affected by the micro-cracks. The compression strength is also 40% higher than that of the polymer-bonded NdFeB magnet for its increased density.
  • Gold Recovery from Nickel Catalyzed Ammonium Thiosulfate Solution by Strongly Basic Anion Exchange Resin

    pp. 2099-2107

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    DOI:10.2320/matertrans.44.2099

    Copper catalyzed ammonium thiosulfate leaching process has been proposed as an alternative gold extraction process to cyanidation. In order to recover gold from the ammonium thiosulfate solution, ion exchange process has been proposed as a gold recovery method using strongly basic anion exchange resin. However, the co-adsorption of copper along with gold causes difficulty in separating gold and copper at the gold elution stage. Our previous study has demonstrated that nickel catalyzed ammonium thiosulfate solution for gold extraction has the advantage of reducing thiosulfate consumption. In this study, the results also demonstrated the advantage of gold recovery from the nickel catalyzed ammonium thiosulfate solution by strongly basic anion exchange resin. The optimal gold loading conditions on a 1 g/dm3 strongly base anion exchange resin (wet base value) are investigated in several ion concentrations and 95 kg-Au/t-resin has been obtained. The alternative gold eluant was investigated as the gold loaded resin cannot be eluted by conventional hydrochloric acid. Results showed that the elution efficiency was in the order of OH < Cl << NO3 < Br << I < ClO4. The maximum gold recovery by using 2.5 mol/dm3 ClO4 was around 98% with the stripped resin assayed as 0.2 kg/t Au. The feasibility of resin recycling has demonstrated that there was no deterioration in gold adsorption and desorption for four cycles.
  • Surface Tension and Wettability of Liquid Fe-16 mass%Cr-S Alloy with Alumina

    pp. 2108-2113

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    DOI:10.2320/matertrans.44.2108

    The surface tension and wettability of liquid Fe-16 mass%Cr-S alloy with alumina substrate at 1823 K and the temperature dependence of surface tension of liquid Fe-16 mass% Cr-S alloy in the temperature range of 1808-1883 K were measured using the sessile drop technique. The surface tension and contact angle of liquid Fe-16 mass%Cr-S alloys with alumina substrate decreased markedly with increasing sulphur concentration in the alloys. The variation of surface tension of liquid Fe-16 mass% Cr-S alloys with sulphur activity can be described by the following equation: σ1g=1640−182ln(1+157aS) (mass% O=0.0037-0.0075, mass% S ≤ 0.195) (mN/m). The interfacial tension between liquid Fe-16 mass% Cr-S alloys and alumina substrate, calculated using Young’s equation, can be expressed by the following equation: σs1=2170−220ln(1+237aS) (mass% O=0.0037-0.0075, mass% S ≤ 0.195) (mN/m). The work of adhesion between liquid Fe-16 mass% Cr-S alloys and alumina had a tendency to increase with increasing sulphur concentration. The temperature coefficient of surface tension, dσ⁄dT, for Fe-16 mass% Cr-S system in the temperature range of 1808-1883 K increased with increasing sulphur concentration, and changed from negative to positive value when the sulphur concentration exceeded 20 mass ppm.
  • Anodically Deposited Mn-Mo-Fe Oxide Anodes for Oxygen Evolution in Hot Seawater Electrolysis

    pp. 2114-2123

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    DOI:10.2320/matertrans.44.2114

    In order to avoid chlorine evolution on the anode in hot seawater electrolysis, the oxygen evolution anodes were tailored. γ-MnO2-type Mn1−xyMoxFeyO2+x−0.5y anodes consisting of Mn4+, Mo6+ and Fe3+ were prepared by anodic deposition. The anodes with the 100% oxygen evolution efficiency in the electrolysis of 0.5 kmol m−3 NaCl at pH 12, 353 K and a current density of 1000 Am−2 were prepared in solutions consisting of 0.003 kmol m−3 Na2MoO4, 0.1 kmol m−3 Fe(NH4)(SO4)2 and 0.2 kmol m−3 or higher concentrations of MnSO4 at pH 0.33-0.5, 363 K and a current density of 600 Am−2. In the outside of this range, generally because of lower deposition efficiency, the electrode surface was not completely covered with anodically deposited oxides with a consequent lower oxygen evolution efficiency.
  • Photobleaching of Methylene Blue Aqueous Solution Sensitized by Composite Powders of Titanium Oxide with SrTiO3, BaTiO3, and CaTiO3

    pp. 2124-2129

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    DOI:10.2320/matertrans.44.2124

    We have examined photocatalytic reactions sensitized by composite particles consisting of titanium oxide, and perovskite-type titanate containing alkaline earth elements. The photocatalytic activities of perovskite-type oxides SrTiO3, BaTiO3, and CaTiO3 are fairly weaker than that of anatase-type titanium dioxide TiO2; however, in photobleaching of methylene blue under irradiation with Xe discharge light, the composite particles with TiO2 exerted photocatalytic activity several times that of TiO2 alone. Especially, the composite powder containing 30 mass% SrTiO3 exhibited the highest photocatalytic activity. The results imply the flow of photogenerated electrons and holes through the heterogeneous junctions in the composite particles. The photocatalytic activity of the composite powder was decreased when the SrTiO3 was doped with Ga and Y, presumably because of recombination of the photogenerated charges via oxygen vacancies created by the doping.
  • Liquidus Surface of FeO-Fe2O3-SiO2-CaO Slags at Constant CO2/CO Ratios

    pp. 2130-2135

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    DOI:10.2320/matertrans.44.2130

    Liquidus surface of FeO-Fe2O3-SiO2-CaO slags is an important parameter in various smelting and converting processes. It helps not only to optimize the slag chemistry of current processes and their fluxing strategies but also to determine the availability of new slags for more advanced technologies. In our previous publications, the liquidus surface of some multicomponent iron oxide slags has been quantified at several constant oxygen potentials and the effect of the latter, ignored until that moment, was quantified along with the effect of some minor components. In this work, the liquidus surface of some iron oxide slags is quantified at constant CO2/CO ratios. This is a new convenient way for the quantitative description of the slag liquidus surface and the effect of several fluxes, especially in those processes, such as slag solidification, where oxygen potential changes continuously. This type of diagram also describes more dynamically the effect of oxygen potential, clarifies the relation between CO2/CO ratio and oxygen potential in terms of the liquidus surface (not widely understood by metallurgists today) and reduces the gap between laboratory work and industrial experience.
  • Liquidus Surface of “Lime Ferrite” Slags at Intermediate Oxygen Potentials

    pp. 2136-2140

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    DOI:10.2320/matertrans.44.2136

    “Lime ferrite” slag with limited silica content has proven to be a valuable choice in the modern processes of copper smelting and converting due to several advantages that this slag offers compared to classical silicate slags. Nevertheless the liquidus surface of this slag has been experimentally measured only at low oxygen potentials such as in equilibrium with iron or near it and in air. Although most of the smelting and converting processes that use this slag occur at intermediate oxygen potentials, the liquidus surface of this slag is not known at these conditions and the effect of oxygen potential and silica has not been correctly understood. This has brought some confusion in literature as well as in the industrial practice. In this work the liquidus surface of the calcium ferrite slags has been quantified by the means of a new thermophysicochemical model and a new type of liquidus surface diagrams which are very convenient for any industrial process that uses calcium ferrite slags. These diagrams can be easily used to select the lowest liquidus temperature of calcium ferrite slags at a minimum cost and can help design several fluxing strategies in copper smelting and converting processes. The effect of the oxygen potential and silica is also quantified and important industrially related conclusions are drawn.
  • Fabrication and Mechanical Properties of Mg65Cu15Ag5Pd5Gd10 Bulk Metallic Glass

    pp. 2141-2144

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    DOI:10.2320/matertrans.44.2141

    The effect of partial substitution of Cu for Ag and Pd on the glass forming ability of Mg65Cu25Gd10 alloy has been studied. Mg65Cu15Ag5Pd5Gd10 bulk metallic glass with diameter of at least 10 mm can successfully be fabricated by conventional Cu-mold casting method in air atmosphere. The critical cooling rate for glass formation is estimated to be ∼0.7 K/s. The compressive fracture strength and fracture elongation of the Mg65Cu15Ag5Pd5Gd10 bulk metallic glass are 817 MPa and 1.6% respectively.
  • Effect of Raw Material Characteristics on the Carbothermal Reduction of Titanium Dioxide

    pp. 2145-2150

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    DOI:10.2320/matertrans.44.2145

    In the present study, the focus is on the effect of the particle characteristics of titanium dioxide powder in the carbothermal reduction of the titanium dioxide/carbon system. Four types of titanium dioxide powders with various phase structures and mean particle sizes were mixed with carbon black. These mixtures were heat treated under a flowing argon atmosphere. The changes in the phase structure and thermal gravity of the mixtures during heat treatment were analyzed using XRD and TG-DTA. Titanium dioxide powders with 100% anatase phase structure exhibit a higher titanium carbide (TiC) formation ability than the titanium dioxide powders with the mixed phase structure of the anatase and rutile phase structures. It was concluded that the phase structure of the titanium dioxide plays a more important role than the particle size on the carbothermal reduction of the titanium dioxide/carbon system.
  • Long-Period Hexagonal Structures in Melt-Spun Mg97Ln2Zn1 (Ln=Lanthanide Metal) Alloys

    pp. 2151-2156

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    DOI:10.2320/matertrans.44.2151

    Novel long-period hexagonal structures with six and fourteen layered atomic configurations were formed in melt-spun Mg97Ln2Zn1 (Ln=Y, Gd and Sm) ternary alloys annealed at 573 K for 1.2-3.6 ks and in an as-spun Mg97Y2Zn1 alloy, respectively. The Mg-based alloys containing La or Ce as the Ln element have a mixed structure of hcp Mg and compound phases and no long-period hexagonal structure is formed in the as-spun and annealed states. There is a clear formation tendency of the novel long-period structure to increase with a decrease in the precipitation tendency of the intermetallic compound, an increase in the atomic size ratio of Ln/Mg and an enhancement of the formation tendency of Mg-based reinforced solid solution. The formation of the novel long-period structure is interpreted to result from the necessity of relaxation of strains caused by the reinforced solid solution of Ln and Zn elements into the Mg phase. In addition, the enrichment of Y and Zn elements was observed at the misfit sites of the atomic array in the fourteen layered hexagonal structure of the as-spun Mg97Y2Zn1 alloy. The atomic level segregation of Y and Zn elements is also thought to be the origin for the high stability of the long-period structure. The two types of long-period hexagonal structures found in the Mg-Ln-Zn alloys are important as a new mechanism for future development of high-strength Mg-based alloy.
  • Effect of Silicon on Grain Refinement of Aluminum Produced by Electrolysis

    pp. 2157-2162

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    DOI:10.2320/matertrans.44.2157

    The influence of various silicon contents on the grain refinement and crystal morphology of pure aluminum and the Al-based alloy with low titanium content produced by electrolysis is comparatively investigated. The nucleation behavior and crystal morphology are studied with SEM and the nucleants are detected by EDS. The Al-based alloy shows better grain refinement response to silicon content, especially to high silicon content. The α-Al crystal morphology remains fine equi-axed structure even though silicon content of the Al-based alloy increases to 5%. This better grain refinement should be attributed to the potential nucleants. All the nucleants might be in the type of TiAl3 or Ti(Al1−X, SiX)3, but the atomic fraction of silicon, X, might increase with increase in silicon content of the alloy. The increases of macro-grain grade and micro-grain size with silicon content might be attributed more to the change of phase structure than to the change of α-Al crystal morphology.
  • Shear Strength in Solder Bump Joints for High Reliability Photodiode Packages

    pp. 2163-2168

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    DOI:10.2320/matertrans.44.2163

    The shear strength and fracture surfaces of Sn-Pb bump and Au stud bump for photodiode packages after isothermal aging testing were studied experimentally. Al/Au stud bumps and Cu/Sn-37 mass%Pb solders were adopted, and aged at 373 K and 423 K for up to 900 hours to analyze the effect of intermetallic compound (IMC). The shear strength decreased with aging time. The diffraction patterns of Cu6Sn5, scallop-shaped IMCs, and planar-shape Cu3Sn were observed by transmission electron microscopy (TEM). The formation of Kirkendall voids with the growth of IMCs at the solder was found to be a possible mechanism for shear strength reduction. IMCs between Au stud bumps and Al pads were identified as AlAu2.
  • Mold Filling Analysis in Lost Foam Casting Process for Aluminum Alloys and Its Experimental Validation

    pp. 2169-2174

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    DOI:10.2320/matertrans.44.2169

    A mathematical model is developed in this study to simulate the filling pattern in lost foam casting and validated by comparing the simulated results to the experimental measurements. A special treatment is devised to handle the unique problem of back-pressure generated due to the evaporation of polystyrene during filling in lost foam casting. Experiments are also conducted with thermocouples embedded in the pattern of lost foam casting. With the measured temperature data, filling pattern can be derived. The mathematical model is then tested on several lost foam castings, where experimental measurements are also conducted. As the simulated filling patterns are compared with the experimental measurements, good agreement is observed.
  • Improvement of Board Level Reliability for μBGA Solder Joints Using Underfill

    pp. 2175-2179

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    DOI:10.2320/matertrans.44.2175

    The underfilling μBGA as an alternative to direct chip attachment for high density packaging technologies have been developed. This paper discusses the thermomechanical and metallurgical effects of underfill material and the resulting improvement in board level reliability for underfilled μBGA assemblies. Finite element analysis (FEA) models were developed to predict the thermal fatigue life of the solder joints during thermal cycling tests for μBGA assemblies without and with underfill material. FEA predicted that the stress concentrated in the solder at the crevice between the solder ball and upper substrate was approximately 60 percent of the stress without underfill. Subsequently, the predicted fatigue life was as much as 10 times higher for the underfilled assemblies. The thermal fatigue failure of μBGA solder joints was also investigated experimentally using thermal cycle testing with subsequent solder joint analysis by scanning electron microscope (SEM) and energy dispersive X-ray (EDX). The experiments revealed that solder joint failure was caused by propagation of cracks that initiated in the solder at the upper interface between the solder ball and copper pad. The fatigue life of the underfilled assemblies was about 8 times that of the assemblies without underfill. The results showed that the underfill material can play an important role in improving board level reliability for μBGA solder joints in harsh environments.
  • Magnetocrystalline Anisotropy in a Single-Variant Co-Ni-Al Ferromagnetic Shape Memory Alloy

    pp. 2180-2183

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    DOI:10.2320/matertrans.44.2180

    The single-variant state and the magnetocrystalline anisotropy in a single crystal Co41Ni32Al27 ferromagnetic shape memory alloy (FSMA) have been investigated. After applying compressive stress, the single-variant state was confirmed by optical micrograph and linear thermal expansion measurements. In the heating process for the single-variant martensite phase, the shrinkage of about 7% takes place at the reverse transformation temperature. From the magnetization curves along the c-, a-axes and the [110]M directions in the single-variant state, the c-axis is determined to be the hard axis and the magnetocrystalline anisotropy constant in the single crystal Co41Ni32Al27 β′ martensite phase is evaluated to be 3.2×105 J/m3 at 5 K.
  • Magnetic Evaluation of Microstructures and Strength of Eutectoid Steel

    pp. 2184-2190

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    DOI:10.2320/matertrans.44.2184

    Microstructures and strength of variously heat treated eutectoid steel were evaluated by magnetic property measurements. Isothermal transformation, continuous cooling or spheroidization heat treatment was performed to produce various microstructures. Microstructural parameters (phase, pearlite interlamellar spacing), mechanical properties (fracture strength) and magnetic parameters (coercivity, remanence, hysteresis loss, saturation magnetization) were measured to investigate the relationships among these parameters. Coercivity and remanence were observed to be high in order of martensite, pearlite and ferrite phase. The linear decrease of coercivity and remanence with the interlamellar spacing and the linear increase of those with fracture strength of pearlitic eutectoid steel were found. Coercivity and remanence were suggested as potential magnetic parameters for discriminating phases and quantitatively assessing the pearlite interlamellar spacing as well as strength of eutectoid steel.
  • Environmental Loads of Process Scrap by using I/O table for Life Cycle Inventory

    pp. 2191-2196

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    DOI:10.2320/matertrans.44.2191

    New method of environmental load estimation for scraps and by-products production in Life cycle inventory (LCI) based on Input-Output table (I/O table) has been developed. And a new description method of I/O table with scraps and by-products sections for the estimation is developed. In this study, both scraps and by-products are regarded as products, and are dealt with as an independent section in I/O table, respectively. By means of this method, the energy consumption and CO2 emission of process-scrap steel production are estimated as an example study. And a weighted average value of energy consumption and that of CO2 emission with consideration to the monetary amounts of production of process-scrap steel were calculated by using the estimated data, respectively. Moreover, a reliability of the estimated data is analyzed. And LCI of converter steel and EAF steel are done in order to evaluate an influence by differences of data. As a result, when the value of a process scrap was assumed to be zero, the energy consumption rates of zero against the maximum is estimated 0.5% for the converter steel, and 20.4% for the EAF steel, respectively. Therefore, in case of converter, it is possible to treat the environmental load of a process scrap for nothing in approximation.
  • Effect of Austempering Duration on Erosion Wear Resistance of ADI by Al2O3 Particle

    pp. 2197-2206

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    DOI:10.2320/matertrans.44.2197

    Effect of the duration of austempering on particle erosion wear resistance of ADI was studied. In short duration (Stage I) region, a fair amount of martensite phase can be recognized, and hence deterioration of erosion wear resistance. In initial Stage II, the austempering region (0.5 hr duration) is free of carbide. If prolonged the austempering duration, the retained austenite amount tend to decrease and hence carbide formation. Even if slightly increase of carbide amount that still can play an important role on debasing wear resistance, resulted from the alternation of erosion behavior. Erosion-induced phase transformation of retained austenite also can be determined that is generality transformed to ε-carbide.
  • Formation of Crystallographically Aligned BiMn Grains by Semi-solid Processing of Rapidly Solidified Bi-Mn Alloys under a Magnetic Field

    pp. 2207-2212

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    DOI:10.2320/matertrans.44.2207

    Alignment of the BiMn grains during solidification under a magnetic field was examined for Bi-Mn alloys (20,30,40 and 50 at%Mn). During the conventional peritectic solidification, the BiMn grains produced through the peritectic reaction did not align because of difficulties of the grain rotation. Rapid solidification produced the finely distributed BiMn grains in the Bi-rich matrix or the Bi-BiMn eutectic structure at off-eutectic compositions. Heating the rapidly solidified structure resulted in the semi-solid state even for Bi-50 at%Mn alloy, in which no semi-solid state containing BiMn phase in equilibrium. The BiMn grains suspended in the semi-solid state rotated in the favorable direction. Growth of the BiMn grains following the rotation achieved c-axes alignment of the BiMn grains. The semi-solid state, which is controlled by the initial microstructure obtained by the rapid solidification, is significantly useful for the magnetic alignment.
  • Strain Rate Effect on Dynamic Nucleation at Triple Junctions in a Copper Tricrystal

    pp. 2213-2219

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    DOI:10.2320/matertrans.44.2213

    Effect of strain rate on dynamic recrystallization (DRX) at triple junction (TJ) in a copper tricrystal was investigated in tension during high-temperature deformation at 873 K. DRX nucleation appeared preferentially at the TJ at around a strain about 2/3 of the peak strain and became easier with decreasing strain rate. The preferential DRX nucleation observed at TJ seemed to have close relationship with occurrence of grain-boundary sliding (GBS). That is, easier occurrence of GBS at lower strain rate can cause more severe stress and deformation concentration at TJ, followed by operation of stimulated DRX nucleation at TJ. The effect of grain boundary misorientation composing the TJ on DRX nucleation at the TJ and its mechanism is also discussed in detail.
  • Thermal Stability and Mechanical Properties of Cu-Based Bulk Glassy Alloys in Cu50(Zr1-xHfx)45Al5 System

    pp. 2220-2223

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    DOI:10.2320/matertrans.44.2220

    The thermal stability, crystallization and mechanical properties of the Cu50(Zr1−xHfx)45Al5 (x=0 to 1) bulk glassy alloys have been investigated. The glass transition temperature (Tg), crystallization temperature (Tx), liquidus temperature (Tl) and the supercooled liquid region ΔTx (=TxTg) increase with increasing Hf content. The reduced glass transition temperature (TgTl) is in the range from 0.603 to 0.615. The Vicker’s hardness (Hv), Young’s modulus (E) and compressive fracture strength (σc,f) of the bulk glassy alloys increase linearly with increasing Hf content and reach the maximum values of 627, 121 GPa and 2262 MPa, respectively, for Cu50Hf45Al5. A different crystallization behavior is observed for Cu50Zr45Al5 and Cu50Hf45Al5 glassy alloys. The final crystallization phases are Cu10Zr7 for the former alloy, and Cu10Hf7 and CuHf2 for the latter alloy.
  • Formation of Ductile Cu-Based Bulk Metallic Glass Matrix Composite by Ta Addition

    pp. 2224-2227

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    DOI:10.2320/matertrans.44.2224

    The Effect of the Ta addition on the fabrication of the ductile phase reinforced Cu-Zr-Ti bulk metallic glass (BMG) matrix composite was investigated. A composite microstructure consisted of μm-scale Ta-rich solid solution particles distributed in the BMG matrix was successfully obtained by injection casting of the (Cu60Zr30Ti10)95Ta5 alloy into a copper mold. Ta-rich solid solution particles were observed to form first in the liquid melt during solidification, while the remaining melt solidified into the amorphous phase at lower temperature. The monolithic Cu60Zr30Ti10 BMG shows a compressive strength of 2080 MPa and a fracture strain of 3.3%, while the (Cu60Zr30Ti10)95Ta5 BMG matrix composite shows compressive strength of 2320 MPa and, in particular, a significantly improved plastic strain to failure of about 14.5%. The remarkable ductility improvement in the (Cu60Zr30Ti10)95Ta5 composite could be explained by the presence of the highly ductile Ta-rich particles.
  • Fabrication, Thermal Stability and Mechanical Properties of Porous Bulk Glassy Pd-Cu-Ni-P Alloys

    pp. 2228-2231

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    DOI:10.2320/matertrans.44.2228

    Porous Pd42.5Cu30Ni7.5P20 glassy alloy rods with diameters of 7 and 10 mm and a length of about 20 mm were produced by water quenching the mixture of Pd42.5Cu30Ni7.5P20 liquid and solid salt phases at a volume fraction ratio of 7 to 9, followed by leaching treatment into water to eliminate the salt phase. The pores had a polyhedral shape with sizes of 125 to 250 μm. The densities were 3.3 and 4.2 Mg/m3 and their pore fractions were evaluated as 65 and 55% for the 7 mm and 10 mm rods, respectively. The thickness of the cell walls was in the range of 50 to 250 μm. No crystalline phase was observed in the outer surface region as well as in the cell wall region. The glass transition temperature and crystallization temperature of the porous alloy rods were 578 and 679 K, respectively, in agreement with those of the pore-free alloy. Final rupture was not recognized for the porous alloys subjected to the uniaxial compressive test. The porous alloy exhibited lower Young’s modulus, lower yield strength, much higher absorption energy, being significantly different from those for the pore-free glassy alloy rod. The unique mechanical characteristics combined with high absorption energy ability indicate the possibility of future uses as a new type of structural and functional materials.
  • Giant Magnetoimpedance and Local Inhomogeneity in Manganite La0.65Ba0.35MnO3

    pp. 2232-2234

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    DOI:10.2320/matertrans.44.2232

    The magnetoimpedance and local inhomogeneity of the manganite La0.65Ba0.35MnO3 were investigated in the temperature range from 98 to 289 K. A metal – insulator transition peak occurs in the temperature dependence of impedance for the manganite La0.65Ba0.35MnO3. Under application of a dc magnetic field, the metal – insulator transition temperature TMI derived from the ac transport shifts to a higher temperature. The local inhomogeneity within the sample can be revealed through the application of ac currents with different frequencies. The ac frequency dependence of impedance for the manganite La0.65Ba0.35MnO3 is found to vary with temperature. The peak value of the magnetoimpedance ΔZZ0 can reach −26.3% at 100 kHz under a field H=3.98×105 A/m. The impedance of the manganites can be influenced by magnetic fields through permeability and resistivity.
  • Hardness and Fracture Toughness of Alumina-Doped Tetragonal Zirconia with Different Yttria Contents

    pp. 2235-2238

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    DOI:10.2320/matertrans.44.2235

    The 0.75 to 3.0 mol% Y2O3-stabilized tetragonal ZrO2 (Y-TZP) and Al2O3/Y-TZP fine-grained ceramics with 0.2 to 0.7 mass% of alumina were produced by a colloidal technique and low-temperature sintering. Trace alumina addition enhanced the densification of Y-TZP. The influence of the resulting density, microstructure, the yttria-stabilizer and the alumina content on the hardness and toughness were studied. The bulk 2.7Y-TZP ceramic with an average grain size of 110 nm reached a hardness of 13.6 GPa and fracture toughness of 11.2 MPa·m1⁄2. Y-TZP ceramics with a reduced yttria-stabilizer content were found to reach a fracture toughness of 13.8 MPa·m1⁄2 (2Y-TZP), and 14.5 MPa·m1⁄2 (1.5Y-TZP). A nano-grained alumina dispersed zirconia with 3 mol% Y2O3 with an average grain size of 97 nm was obtained, and the hardness increased to 16.8 GPa. Y-TZP/alumina ceramics with a 0.35 mass% Al2O3 were found to reach a fracture toughness of 15.7 MPa·m1⁄2 (2Y) and 15.3 MPa·m1⁄2 (1.5Y).

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