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

MATERIALS TRANSACTIONS Vol. 43 (2002), No. 4

  • Low Temperature Swelling in Beta-SiC Associated with Point Defect Accumulation

    pp. 612-616

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    DOI:10.2320/matertrans.43.612

    An experimental technique to characterize irradiation-induced swelling, or isotropic volume expansion, through a combined utilization of medium-to-high energy accelerators and interferometric surface profilometry, was established. The technique was successfully applied to a characterization of swelling behavior in beta-silicon carbide arising from the accumulation of point defects at relatively low temperatures, i.e., 333–873 K, as a function of fluence level, displacement damage rate and irradiation temperature. Swelling rate and swelling at any given fluence level exhibited a negative dependence on irradiation temperature. The saturated low temperature swelling fell on the lower edge of neutron irradiated swelling data band. The influence of displacement damage rate appeared unremarkable. An additional study on the synergistic effect of atomic displacement damage and helium production revealed an enhancement of low temperature swelling in silicon carbide in the presence of helium.
  • Effect of Fiber Properties on Neutron Irradiated SiC/SiC Composites

    pp. 617-621

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    DOI:10.2320/matertrans.43.617

    The use of SiC/SiC composites for nuclear application has recently been considered because of intrinsic low activation and superior high temperature mechanical properties of SiC. The property of SiC fiber is a key issue in order to improve mechanical properties of SiC/SiC composites following irradiation. SiC/SiC composites with unidirectional fibers were fabricated by chemical vapor infiltration method. Low oxygen and highly crystalline fibers or just low oxygen fibers were used in the composites. The specimens were irradiated at Japan Material Testing Reactor and High Flux Isotope Reactor. The effects of neutron irradiation on mechanical properties were examined by three points flexural test. Microstructure and fracture behavior were observed by scanning electron microscopy before and after neutron irradiation. The SiC/SiC composites with a low oxygen content, near-stoichiometric atomic composition and highly crystalline SiC fibers showed the excellent stability to neutron irradiation. The mechanical property of this material did not degrade, even after neutron irradiation up to 10 dpa, while the other materials with non-highly crystalline SiC fibers degraded significantly.
  • Effects of Helium on Radiation Behavior in Low Activation Fe-Cr-Mn Alloys

    pp. 622-626

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    DOI:10.2320/matertrans.43.622

    In order to investigate the effects of helium on the microstructural evolution in Fe–Cr–Mn (W, V) alloy during three irradiation modes of electron beam, electron/He+-ion dual-beam and electron irradiation after helium pre-injection, in situ observations were carried out using a high voltage electron microscope connected with an ion accelerator. The interstitial-type dislocation loops and small voids were formed in the early stage of irradiation. The average void size was smaller and void number density was higher under irradiation condition by electrons after helium pre-injection and by dual-beam in comparison with the case of electron irradiation. Irradiation-induced grain boundary segregation of Cr and Mn was suppressed due to existence of helium. From these results it is suggested that helium strongly influences dislocation structural development and void nucleation during irradiation. The effect of interactions between helium and point defects is discussed.
  • Influence of Ion-Irradiation on Hardness Change in Type 304 Stainless Steel Weldment Containing Delta(δ) Ferrite

    pp. 627-632

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    DOI:10.2320/matertrans.43.627

    Differences of high energy-ion induced microstructure of bcc δ-ferrite and fcc austenite matrix, and the effects of δ-ferrite on the Vickers micro-hardness (Hv) after irradiation were investigated for Type 304 stainless steel weldments containing two different δ-ferrite contents: ferrite number (FN) 5.5 and 8.5, respectively. Specimens were irradiated to 1.5 dpa with 8 MeV Fe+4 ions using a Tandem Vande-Graff accelerator (flux: 4.3×1010 ion/cm2·s, fluence: 0.83×1015 ion/cm2) at below 60°C. Calculations TRIM 95 showed that a peak damage appeared at 1.5 \\micron in depth with 0.7 \\micron full width at half maximum (FWHM). These results on irradiation-induced defects (IIDs) distribution were confirmed by TEM. Clear differences for the size and number density of IIDs as black dots (size: 5–10 nm) and loops were observed in both the austenitic matrix and δ-ferrite, where the size of IIDs was far larger in the fcc matrix than the bcc δ-ferrite. Hv test results showed that the irradiation hardening of δ-ferrite was about 1.5 times larger than the austenitic matrix. From microstructural observation the increase of the higher Vickers micro-hardness was explained.
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  • The Effect of 800 MeV Proton Irradiation on the Mechanical Properties of Tungsten

    pp. 633-637

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    DOI:10.2320/matertrans.43.633

    For the Accelerator Production of Tritium (APT) and the Accelerator Driven Transmutation Facility (ADTF), tungsten is being proposed as a target material to produce neutrons. Previous work has shown that the mechanical properties of tungsten are degraded from irradiation in a fission neutron flux but little work has been performed on the irradiation of tungsten in a high energy proton beam. In this study, tungsten rods were irradiated at the 800 MeV Los Alamos Neutron Science Center (LANSCE) proton accelerator for six months. To avoid corrosion during irradiation, the rods were slip fit with thin (0.25 mm thick) 304L stainless steel (SS) or (0.125 mm thick) annealed Alloy 718 tubing. After irradiation to a maximum dose in the tungsten of 23.3 dpa at Tirr=50–270°C, the clad rods were opened in the hot cells and the tungsten was removed. The tungsten was then sliced into short compression specimens (∼ 3 mm long). Hardness tests and compression tests were performed on the tungsten rods to assess the effect of irradiation on their mechanical properties. Results show an increase in hardness with dose and irradiation temperature and an increase in yield stress with dose.
  • Improvement of Corrosion Resistance and Structural Change in 304 Stainless Steel by means of Ion-Mixing

    pp. 638-640

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    DOI:10.2320/matertrans.43.638

    High-energy ion-beam mixing technique was applied for the surface modification of austenitic stainless steel, followed by electrochemical characterization and microstructural observation. The co-mixing of silicon and chromium resisted the passivation current to 1/1000 relative to the un-modified condition. The corrosion resistance improved remarkably. Microstructural observation revealed that the enhanced diffusion and induced amorphous structure introduced by the co-mixing of silicon and chromium, which played a very important role in the improvement of electrochemical behavior at surface.
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  • A Numerical Study on Composition Pattern Formation in Immiscible Alloys under Irradiation Condition

    pp. 641-645

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    DOI:10.2320/matertrans.43.641

    The kinetics of spontaneous composition pattern formation in a quenched alloys under irradiation is numerically studied by means of phenomenological Enrique-Bellon equation for the local concentration field. In the present model the irradiation effect is modeled as a ballistic mixing with an average distance of atomic relocation R and its frequency Γ. Several two-dimensional computer simulations show that the competitive mechanism between phase separation and irradiation-induced mixing might provide a novel way to stabilize and tune the steady-state nanostructures of phase separating materials in some region on (R, Γ) space.
  • Generation of Nanosized Structures on Ni and Fe Surfaces by Electron Irradiation

    pp. 646-649

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    DOI:10.2320/matertrans.43.646

    We report a new type of self-organized nanostructure for pure Ni and Fe thin foils irradiated with 400 keV electrons. Nanostructure develops at the electron exit surface of the foils. For Ni(001) irradiated along [001] direction at 105 K nanogrooves extend along [100] and [010] in the outer area of the beam, but the pattern differs from those near the beam center. For [011] irradiation, nanogrooves extend mainly along [100] direction and nanowires are finally formed. For Fe(111) irradiated along [111] at 300 K nanoholes are generated in the initial stage and then develop to a pattern of nanogrooves. The nanostructure is rather stable at temperatures lower than 823 K, although the evaporation from the specimen surface occurs.
  • Electron-Irradiation-Induced Amorphization in Mo/Si Nano-Multilayer Material

    pp. 650-653

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    DOI:10.2320/matertrans.43.650

    In the Mo–Si system, there are three typical intermetallic compounds. In order to get insight into the phase stability under irradiation, interface structure and non-equilibrium phase formation in multilayer materials with several nanometers scale were investigated by means of high-voltage electron microscope. The initial structure was composed of crystalline Mo and amorphous Si layers, and transition layer existed at the interfaces. The thickness of transition layers is thicker at the Mo-on-Si than at the Si-on-Mo interface. While those structures were basically stable after thermal annealing up to 773 K, two types of amorphous layers developed during electron irradiation at room temperature: one is an amorphous-Si layer and the other is a Mo–Si mixing layer. And the radiation-induced amorphization was accompanied by anomalous shrinkage in the thickness of layers. It is suggested that those phenomena are related to non-equilibrium phase formation and biased diffusion process during irradiation.
  • Self-Diffusion of 22Na and 137Cs in Simulated Nuclear Waste Glass

    pp. 654-659

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    DOI:10.2320/matertrans.43.654

    The knowledge of self-diffusion of various elements is important for understanding and elucidating the long-term dissolution of the nuclear waste glass. The self-diffusion coefficients of Na and Cs in P0798 simulated nuclear waste glass have been measured by an ion beam sputter-sectioning technique using the radioactive isotopes 22Na and 137Cs. The temperature dependence of the diffusion coefficients in each temperature range in P0798 glass below the glass transition temperature Tg can be expressed by the following equations: (428–574 K):D_Na-belowT_g&=2.7×10^-6exp(-113 ± 4 kJ·mol^-1/RT)m^2·s^-1
    (713–758 K):D_Cs-belowT_g&=7.1×10^-5exp(-241 ± 10 kJ·mol^-1/RT)m^2·s^-1The diffusion coefficient of 22Na was about ten orders of magnitude larger than that of 137Cs at 573 K. The large difference in the diffusion coefficients is explained in terms of the ion size effect, the mixed-alkali effect and lower concentration of Cs compared with Na in P0798 glass.
  • Effects of Metastable Phase Formation on the Magnetic Properties of Pr4.5Fe77B18.5 Amorphous Ribbons

    pp. 660-666

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    DOI:10.2320/matertrans.43.660

    The effects of isothermal annealing on the magnetic properties of Pr4.5Fe77B18.5 amorphous ribbons have been investigated. Two separate reactions increasing coercive force (Hc) were recognized during the progress of annealing. In the first reaction, hard magnetic Pr2Fe14B particles with nanoscale diameters precipitated in the vicinity of Fe3B and Pr2Fe23B3 particles. The precipitation of fine Pr2Fe14B particles increased Hc largely but reduced saturation magnetization (Ms) significantly. In the second reaction, the Pr2Fe23B3 particles decomposed into Pr2Fe14B particles containing very fine α-Fe particles within them. This resulted in the second increase in Hc due to both the volume fraction increase of Pr2Fe14B particles and the exchange-coupling interaction between the Pr2Fe14B grains and α-Fe particles within them. This phenomenon was observed originally in the present study. In the final stages of annealing, both Hc and Ms were decreased substantially by the decomposition of Pr2Fe14B into PrFe4B4 particle in addition to the coarsening of α-Fe particles.
  • Synthesis of Fe-Cu Nanoparticles by Mechanochemical Processing Using a Ball Mill

    pp. 667-673

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    DOI:10.2320/matertrans.43.667

    Fe–Cu nanoparticles were synthesized by mechanochemical processing, which utilizes the reaction of FeCl3 and CuCl2 with Na during ball milling. Morphologies, structures and magnetic properties of the synthesized nanoparticles were investigated. The crystallite size and mean particle size of the washed nanoparticles after 84 h milling were approximately 9 nm and 50 nm, respectively. During ball milling, the crystallite size remained constant at approximately 14 nm, while the particle size increased. The elemental mapping images of Fe and Cu by imaging filter revealed that the synthesized nanoparticles were a solid solution of the Fe–Cu system. It was seen that numerous hexagonal plates of Fe(OH)2 exist in the washed nanoparticles. The plates had a few nm in thickness and a few hundreds nm in diameter. The coercivity of the synthesized Fe–Cu nanoparticles after 48 h milling was as high as 33.5 kA/m. This is because the particle is close to the critical size for a single magnetic domain of α-Fe.
  • Formation of Anomalous Defect Structure on GaSb Surface by Low Temperature Sn Ion-Implantation

    pp. 674-680

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    DOI:10.2320/matertrans.43.674

    Defect formation in (100) GaSb by 60 keV Sn+ ion-implantation at 150–153 K is investigated using cross-sectional TEM, SEM and EDX. An anomalous structure consisting of many cells, which looks like a honey comb, was formed on the surface implanted with 8.9×1018 ions/m2. The diameter and the depth of a cell were about 50 nm and 220–250 nm respectively. The thickness of the walls partitioning the cells was about 10 nm. The upper part of the partitioning wall is amorphous and rich in Ga, while the lower part shows crystalline structure. A heavily strained region of 50 nm thickness, corresponding to the maximum depth of the projected Sn ions, was observed under the cells. This defect structure is compared with similar defects which have been observed in ion-implanted GaSb. The defect formation mechanism is discussed, and an explanation based on movement of the implantation induced point defects is proposed. It is assumed that hills and hollows are formed in the early stage of implantation. The point defects created on the hills do not contribute to the development of the defect structure, because they annihilate almost completely by the recombination of vacancy and interstitial and by the movement to the near surface sink. However, under the hollows, vacancies which escaped recombination remain, and the interstitial atoms, which are highly mobile at low temperatures, migrate far from there to aggregate under the hills. The hollows become deeper by the movement of the remaining vacancies to the surface, and the hills develop into the walls by the migration of the interstitial atoms from the surrounding hollows.
  • Structure and Transport Properties of (Bi1-xSbx)2Te3 Thermoelectric Materials Prepared by Mechanical Alloying and Pulse Discharge Sintering

    pp. 681-687

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    DOI:10.2320/matertrans.43.681

    Mechanical alloying followed by pulse discharge sintering (MA-PDS) has been employed to develop the bulk (Bi1−xSbx)2Te3 thermoelectric materials with various Sb alloying contents. Substitutional solid solutions of (Bi1−xSbx)2Te3 are formed in the whole Sb content range by MA-PDS process. The sintered compacts are dense and have refined microstructures. Systematic investigations on the electrical, thermal and thermoelectric properties reveal that the transport properties of the obtained (Bi1−xSbx)2Te3 samples are quite sensitive to the Sb alloying content. At room temperature, the samples with x<0.57 exhibit n-type semi-conduction. However, at x>0.57, the samples become p-type. The pure constituents of Bi2Te3 and Sb2Te3 as well as the Sb-poor, n-type samples exhibit the room-temperature figure of merit of the order of 1.0×10−3 K−1. High values of figure of merit have been obtained in the Sb-rich, p-type samples. The maximum value of 3.35×10−3 K−1 is attained at x=0.80, which corresponds to the carrier concentration and Hall mobility of 1.95×1019 cm−3 and 207 cm2/Vs, respectively.
  • Phase Equilibria in Nb-W-rich Zone of the Nb-W-Si Ternary System

    pp. 688-693

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    DOI:10.2320/matertrans.43.688

    In this paper the solidification behavior and phase stability in Nb–W–Si alloys near the Nb–W binary are described. A partial liquidus surface projection of the Nb–W–Si system is constructed based on the observations of microstructure evolution during solidification. Microstructural and microchemical evidences prove the existence of the following eutectic and peritectic reactions: L→β(Nb, W)5Si3+Nbss;L+β(Nb, W)5Si3→(Nb(W))3Si; L→(Nb(W))3Si+Nbss. One invariant point for reaction of L+β(Nb, W)5Si3→(Nb(W))3Si+Nbss is determined near composition Nb–16Si–3W. Moreover, phase stabilities at 1773 K in these alloys are briefly described by identifying the constituent phases after prolonged annealing treatment.
  • Mössbauer Spectroscopic Study of Rust Formed on a Weathering Steel and a Mild Steel Exposed for a Long Term in an Industrial Environment

    pp. 694-703

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    DOI:10.2320/matertrans.43.694

    The rusts formed on mild steel (15-year exposure) and weathering steel (32-year exposure) exposed to an industrial environment have been characterized by means of X-ray diffraction technique and 57Fe Mössbauer spectroscopy. By using an X-ray diffraction method, it is suggested that the rusts formed on both steels consist of the crystalline α-FeOOH, γ-FeOOH and an X-ray amorphous phase, which gives no peak to X-ray diffraction pattern. The amount of the X-ray amorphous phase exceeds 50% of the total amount of the rust. The 57Fe Mössbauer spectra observed at 10 K indicate that the rust contains only α-FeOOH, γ-FeOOH and Fe3−δO4 (γ-Fe2O3) for mild steel, and only α-FeOOH and γ-FeOOH for weathering steel. The X-ray amorphous substance in the rust layer formed on mild steel possesses the structures of mainly α-FeOOH showing superparamagnetism owing to its small particle size, and Fe3−δO4 (γ-Fe2O3). They are contained both in the inner rust layer and in the outer rust layer. The X-ray amorphous phase in the rust layer formed on weathering steel is mainly α-FeOOH.
  • Exohedral Bonding Nature of Si Atom on the Ba@Si28 Cluster; Ab Initio Study

    pp. 704-707

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    DOI:10.2320/matertrans.43.704

    First-principle electronic structure is studied for the Si28 and Ba@Si28 clusters, which are components of the clusters in silicon clathrate II. We obtain the geometrically optimized relaxed cage structures of the clusters and the exohedral binding nature of single Si atom on the Ba@Si28 clusters. The hollow Si28 cluster relaxes into the Si24 like cluster in the clathrate I having four exohedral Si atoms outside the hexagon in the Si24 cluster. The hexagons on the Ba@Si28 cluster are deformed into a chair type with relaxation. The exohedral Si atom is the most stable at the edge center near the top that meets three pentagons. We have found for the first time that the exohedral Si atom forms the three-center covalent bond between the two caged Si atoms.
  • New Bulk Glassy Ni-Based Alloys with High Strength of 3000 MPa

    pp. 708-711

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    DOI:10.2320/matertrans.43.708

    New Ni-based bulk glassy alloys with high strength and good ductility were synthesized for the first time in Ni–Nb–Ti–Zr base system by the mold-clamp or copper mold casting method. The bulk glassy Ni53Nb20Ti10Zr8Co6Cu3 alloy has a rod shape with diameters up to 3 mm or a sheet shape with thickness up to 1 mm. The glass transition temperature (Tg) and the supercooled liquid region defined by the difference between Tg and crystallization temperature (Tx), ΔTx(=TxTg) are 846 and 51 K, respectively, and no distinct change in Tg, Tx and ΔTx with sample diameter is seen. The Ni-based alloy is located in the vicinity of eutectic composition and has a high reduced glass transition temperature (TgTm) of 0.67. The Ni-based bulk glassy alloy also exhibits good mechanical properties, i.e., tensile fracture strength of 2700 MPa, tensile fracture elongation of 2.1%, compressive fracture strength of 3010 MPa and compressive fracture elongation of 2.4%. It is noticed that the tensile fracture strength is the highest among all bulk glassy alloys developed up to date. The success of synthesizing the new Ni-based bulk glassy alloy with good mechanical properties is promising for future uses as a new type of high strength material.
  • Characterization of Directionally Solidified B4C-TiB2 Composites Prepared by a Floating Zone Method

    pp. 712-720

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    DOI:10.2320/matertrans.43.712

    Directionally solidified B4C–TiB2 composites were prepared by a Floating Zone method. TiB2 phases in a rod shape were continuously connected in the B4C matrix. The c-axes of TiB2 and B4C phases were perpendicular and tilted 22° to the growth direction, respectively. The (101) and (1\\bar20) planes of the B4C were in parallel to the (001) and (100) planes of TiB2, respectively. The electrical conductivity of the composite parallel to the growth direction (σ||) was greater than monolithic B4C by a factor of 100 to 1000. The thermal conductivity of the composite parallel to the growth direction (κ||) was about one and a half times as high as that of B4C. The anisotropy of electrical and thermal conductivity were basically explained by a mixing law using the values of B4C and TiB2. The microhardness of the composite was almost the same as that of B4C. The electric discharge machining of the composite was possible owing to the enhancement of electrical conductivity.
  • Solid-liquid Interface Energy of Metals at Melting Point and Undercooled State

    pp. 721-726

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    DOI:10.2320/matertrans.43.721

    By investigating the effects of the configurational entropy, the vibrational entropy and the bonding strength of solid-liquid atoms on the structure of solid-liquid interface, a model for the interface energy of rough solid-liquid interface has been developed. From present model, the non-dimensional solid-liquid interface energies for metals at melting point are predicted to be 0.66–0.73, which are almost equal to the experimental result (0.66–0.75) obtained from grain boundary method. The solid-liquid interface energy decreases with increasing undercooling. At the maximum undercoolings that metals have reached, the non-dimensional solid-liquid interface energies predicted from present model are equal to 0.52–0.56. They are near to the experimental results (0.49–0.57) obtained from nucleation undercooling method. The predicted results of solid-liquid interface energy for metals from present model are in very good agreement with the experimentally measured results at melting point and undercooled state.
  • Non-Destructive Evaluation of Fatigue Damage in Type 316 Stainless Steel Using Positron Annihilation Lineshape Analysis

    pp. 727-734

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    DOI:10.2320/matertrans.43.727

    We applied positron annihilation lineshape analysis for non-destructive evaluation of fatigue stored in type 316 stainless steel, mainly used in primary water lines of pressurized water reactors (PWR). Using 68Ge as a positron source, an energy spread of annihilation gamma ray peaks from stainless steel specimens was measured. After preparing stress- and strain-controlled fatigue specimens, we investigated the relation between fatigue life and a non-destructive parameter of lineshape analysis defined as the S-parameter and compared the microstructure of the fatigue specimens with the S-parameter. As a result, there was good correlation between the S-parameter and fatigue life; the S-parameter increased with dislocation density monotonically. The relation between the S-parameter and fatigue life in stress-controlled fatigue differed from that in strain-controlled fatigue. The S-parameter increased faster in early stage of the latter than in the former. In stress-controlled fatigue, the change in the S-parameter did not depend on stress amplitude in the range of ratio to yield stress under 0.9. In the strain-controlled fatigue, the change in the S-parameter did not depend on strain amplitude in the range from 0.25 to 0.31%. However, when stress amplitude or strain amplitude became higher, the change in the S-parameter increased largely in the early stage of the fatigue life. We demonstrated systematic data to evaluate the fatigue damage in type 316 stainless steel.
  • Processing of a Continuous Ceramic Fiber/Iron Alloy Composite

    pp. 735-740

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    DOI:10.2320/matertrans.43.735

    Processing of a continuous ceramic fiber/iron alloy composite by powder metallurgy was investigated. The preparation of continuous ceramic fiber/iron alloy composite is feasible by hot isostatic pressing of a laminate of iron alloy powder sheets, prepared from a doctor blade method, and continuous ceramic fiber sheets. It is necessary to choose suitable temperature and pressure which enable iron alloy to penetrate into ceramic yarn through the small openings between the fibers. The continuous ceramic fiber/iron alloy composite in which fibers are uniformly dispersed can be produced by choosing an appropriate combination of the thickness of iron alloy powder sheet and the number of continuous ceramic fiber sheet.
  • Quantitative Research on Color of Cu-Mn-Zn Alloys

    pp. 741-744

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    DOI:10.2320/matertrans.43.741

    In this paper, the color characteristics of ternary Cu–Mn–Zn alloys are investigated quantitatively and systematically. Using CIE LAB color system, the color parameters such as L, a and b, which were measured by a spectrophotometer, are used to describe the surface color of the forty-six experimental alloys. By the computer technique of data processing and graph editing, a set of the colorful color-composition diagrams of Cu–Mn–Zn alloys are established. The relationship between the chromaticity parameters and the composition is illustrated clearly. A series of equations are derived to correlate color parameters with the alloy compositions. As a result, the color of ternary Cu–Mn–Zn alloys can be calculated and estimated quantitatively.
  • Effect of Mold Material and Binder on Metal-Mold Interfacial Reaction for Investment Castings of Titanium Alloys

    pp. 745-750

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    DOI:10.2320/matertrans.43.745

    The aim of the present paper is to investigate the combined effect of mold material and binder for investment casting of titanium and titanium alloys. A plasma arc melting furnace was used for melting titanium alloy, and the interfacial reaction of titanium castings was determined by optical microscope, SEM, EDS analysis and hardness profile. The mold materials examined were ZrO2, Al2O3, CaZrO3 and CaO. Machined graphite mold was examined for comparison. The result shows that the titanium castings produced using ZrO2 and Al2O3 mold had a clear reaction whereas a negligible reaction occurred in the castings in CaO, CaZrO3 and graphite molds. CaZrO3 is regarded as a promising mold material for titanium castings from the viewpoints of thermal stability against molten titanium alloy, sufficient mold handling strength and slurry viscosity control.
  • Effect of Surface Finishes on Ball Shear Strength in BGA Joints with Sn-3.5 mass%Ag Solder

    pp. 751-756

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    DOI:10.2320/matertrans.43.751

    The present study is aimed at the assessment on the reliability of solder ball attachment to the bond pads of BGA substrate with various plating schemes. The reliability of solder ball attachment is characterized by mechanical ball shear tests. In addition to the ball shear tests, SEM is performed to inspect the cross-section and the fracture surface of the tested specimens for failure analysis. The aging was conducted in convection ovens in air at 343, 393, 423 and 443 K respectively for times ranging 8.64×104 to 864×104 s. Without regard to the deposited layer, the shear strength of BGA joints decreased with the increasing temperature and time. After isothermal aging, the fracture surface shows various characteristics depending on aging temperature and time, and the types of BGA pad.
  • Effect of Equal Channel Angular Pressing on the Distribution of Reinforcements in the Discontinuous Metal Matrix Composites

    pp. 757-761

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    DOI:10.2320/matertrans.43.757

    The 6061 Al–10 vol% SiCw composites were prepared by powder metallurgy with the powders having the different sizes, i.e. <30 \\micron and 30 \\micron<. The composites were subjected to equal channel angular pressing (ECAP) under various conditions and the microstuctural changes during ECAP were examined. A special focus was made on the effect of ECAP conditions on the distribution of SiC whiskers. The present investigation was aimed at exploring the feasibility of ECAP as a post working process for manufacturing the discontinuous metal matrix composites. The microstructural examination and the microhardness measurement of the ECAPed samples suggested that the optimum combination of the uniform microstructure and enhanced mechanical properties would be obtained by (a) using the powders having the smaller size, (b) decreasing ECAP temperature, and (c) repeating ECAP.
  • Growth Condition and X-ray Analysis of Single Al64Cu23Fe13 Icosahedral Quasicrystal by the Czochralski Method

    pp. 762-765

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    DOI:10.2320/matertrans.43.762

    Growth conditions for the preparation of a single Al64Cu23Fe13 icosahedral (I-) quasicrystal with excellent quasicrystallinity were examined using the Czochralski method. The appreciation of the quasicrystallinity of the grown single quasicrystal was performed by X-ray structural analysis. The full widths at half-maximum (FWHM) of the Bragg reflections along 2-, 3- and 5-fold symmetry directions have no Q|| and Q dependence. Where the Q|| and Q mean the phason momentum and real scattering vector. Furthermore, peak shifts from ideal Bragg positions were not observed. These means that the grown Al64Cu23Fe13 quasicrystal by the Czochralski method has perfect I-phase structure.
  • Soft Magnetic Bulk Glassy Fe-B-Si-Nb Alloys with High Saturation Magnetization above 1.5 T

    pp. 766-769

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    DOI:10.2320/matertrans.43.766

    New Fe-based bulk glassy alloys were synthesized in the (Fe0.75B0.15Si0.10)100−xNbx system by copper mould casting. The maximum diameter of the bulk glassy alloy rod was 0.5 mm at 1 at%Nb, 1.0 mm at 2 at%Nb and 1.5 mm at 4 at%Nb. No glass transition is observed at 0 at%Nb, but the addition of Nb causes the appearance of glass transition before crystallization. The glass transition temperature (Tg) and crystallization temperature (Tx) of the bulk glassy rods were 815 K and 858 K, respectively, for the 1 at%Nb alloy, and 835 K and 885 K, respectively, for the 4 at%Nb alloy. The reduced glass transition temperature (TgTl) defined by the ratio of Tg to the liquidus temperature (Tl) was measured as 0.56 at 1 at%Nb, 0.57 at 2 at%Nb and 0.61 at 4 at%Nb. There is a tendency for Tg, ΔTx (=TxTg) and TgTl to increase with increasing Nb content. The effect of Nb addition can be interpreted in the framework of the three component rules for the formation of bulk glassy alloys and the stabilization of supercooled liquid. The Fe–B–Si alloy satisfies the three component rules by the addition of Nb. The bulk glassy alloy rods exhibited good soft magnetic properties, i.e., high saturation magnetization (Is) of 1.47 to 1.51 T, low coercive force (Hc) of 2.9 to 3.7 A/m and Curie temperature of 593 to 684 K. The high Is and low Hc, as well as the formation of bulk glassy alloys in the simple alloy system are promising as a new type of soft magnetic bulk alloy.
  • New V45Zr20Ni20Cu10Al2.5Pd2.5 Glassy Alloy Powder with Wide Supercooled Liquid Region

    pp. 770-772

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    DOI:10.2320/matertrans.43.770

    New multicomponent V-based glassy alloy powder has been synthesized by mechanical alloying a mixture of elemental V45Zr20Ni20Cu10Al2.5Pd2.5 powder at room temperature, using a low energy ball mill. The glassy powder of the end-product (720 ks) in which its glass transition temperature (Tg) lies at a rather high temperature (745 K), crystallizes through two sharp exothermic reactions at 843 K and 919 K, respectively. The total enthalpy change of crystallization (ΔHx) is −1.78 kJ/mol. The supercooled liquid region before crystallization, ΔTx of the synthesized glassy powder shows a high value (98 K) for a metallic glassy system. The reduced glass transition temperature (ratio between Tg and liquidus temperatures, Tl (TgTl)) was found to be 0.52.

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