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

MATERIALS TRANSACTIONS Vol. 42 (2001), No. 3

  • Relationship between Deformation and Recrystallization in Σ3 Isoaxial Aluminum Bicrystal Deformed in Tension along the <011> Axis

    pp. 381-384

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    DOI:10.2320/matertrans.42.381

    Deformation and recrystallization behaviors were examined using a Σ3 isoaxial aluminum bicrystal specimen deformed in tension along the ⟨011⟩ axis. At a tensile strain of 20%, an inhomogeneously deformed structure was developed near the GB . The recrystallization at the GB was dominated by the strain-induced grain boundary migration (SIBM). The strong edge components of piled-up dislocations contributed the occurrence of the SIBM, whereas the screw dislocations moved into the GB from both component crystals were considered to pass through or canceled each other in the GB, because of the special orientational and geometric conditions in the crystals.
  • Characterization of the Strain-amplitude and Frequency Dependent Damping Capacity in the M2052 Alloy

    pp. 385-388

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    DOI:10.2320/matertrans.42.385

    In order to reveal the damping behavior of M2052 alloy dependent on the strain-amplitude and frequency, a centrally excited beam sample was used in free-decaying and frequency sweeping damping measurement. The decaying oscillations and the resonant peaks were obtained directly by the surface strain of the sample. Frequency sweeping was conducted at the strain-amplitudes of 1×10−5∼1×10−4, and frequencies between 50 and 4000 Hz. The loss factor results were described in a contour map as the function of both strain-amplitude and frequency. Logarithmic decrement and loss factor were also obtained from the free-decaying oscillations at the first resonant frequency and different strain-amplitudes. The damping capacity of the alloy at larger strain-amplitudes could be also affected by the damping mode.
  • Small Specimen Test Technology for Evaluation of Fatigue Properties of Fusion Structural Materials

    pp. 389-392

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    DOI:10.2320/matertrans.42.389

    Fatigue tests of ferritic/martensitic steels for fusion reactor application were carried out at room temperature using mini-sized and full-sized hourglass type fatigue specimens, as the basic study of small specimen testing techniques, which are indispensable for the effective use of the limited volumes of material testing reactor and proposed intense neutron sources. The FIB micro-sampling technique was applied to make the cross sectional thin foil specimen from the fatigue crack tip nearby the fractured surface. Effects of specimen size on fatigue properties, such as lifetime, plastic strain range and stress range, were not significant in the specimens used. TEM examination around the crack tip revealed original martensitic lath structure had changed to polygonization-like-structure and fatigue crack had been initiated along pre-austenite grain boundary.
  • Eutectic Growth Mode in Strontium, Antimony and Phosphorus Modified Hypoeutectic Al-Si Foundry Alloys

    pp. 393-396

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    DOI:10.2320/matertrans.42.393

    The effect of strontium (Sr), antimony (Sb) and phosphorus (P) on nucleation and growth mode of the eutectic in hypoeutectic Al–10 mass%Si alloys has been investigated by electron back-scattering diffraction (EBSD) mapping. Specimens were prepared from a hypoeutectic Al–10 mass%Si base alloy, adding different levels of strontium, antimony and phosphorus for modification of eutectic silicon. By comparing the orientation of the aluminium in the eutectic to that of the surrounding primary aluminium dendrites, the solidification mode of the eutectic could be determined. The results of these studies show that the eutectic nucleation mode, and subsequent growth mode, is strongly dependent on additive elements. The EBSD mapping results indicate that the eutectic grew from the primary phase in unmodified and phosphorus-containing alloys. When the eutectic was modified by strontium or antimony, eutectic grains nucleated and grew separately from the primary dendrites.
  • C and Si Impurity Atoms on a GaAs(001) Surface

    pp. 397-398

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    DOI:10.2320/matertrans.42.397

    Ab initio pseudopotential calculations of C and Si impurity atoms on an As-terminated GaAs(001) surface have been performed. First, the C atom is found to stay near a midpoint between the As atoms on the surface and the Si atom a cation site. Secondly, we find that the C atom is more strongly bound to the GaAs surface than the Si atom. Geometrically as well as energetically, the C atom is more difficult to remove from the GaAs surface. The present results agree with an experimental fact that in contrast with the case of Si, eliminating the C impurity through the surface requires thermal etching at such a high temperature of 750°C.
  • Observation of Hydrogen Distribution in V35Cr40Ti25 Alloy by Tritium Radioluminography

    pp. 399-402

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    DOI:10.2320/matertrans.42.399

    Hydrogen distribution in a V35Cr40Ti25 alloy with a BCC structure has been quantitatively examined to obtain a mapping image of hydrogen by tritium radioluminography. It has been found that the hydrogen concentration has been varied depending on the position on the surface of the specimen. The hydrogen distribution has been compared with the mapping images of constituent elements observed by the wavelength dispersive X-ray spectrometry. In the heat affected region which contacted with water-cooled copper hearth during the arc-melting, hydrogen concentration has correlated with the distribution of titanium, that is, hydrogen concentration is higher at the titanium enriched region. Whereas, at the slowly solidified and rapidly solidified regions, there is no relation between hydrogen distribution and the constituent elements. In this region, hydrogen distribution depends on the morphology of the interdendritic segregation of titanium.
  • Oxidation Mechanism of Ultra Thin TiN Films Prepared by an Advanced Ion-plating Method

    pp. 403-406

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    DOI:10.2320/matertrans.42.403

    We deposited ultra thin TiN films with thickness as small as 5–40 nm using an advanced ion-plating (AIP) methods. The films showed a slight resistivity increase in air. In this paper, we investigated the mechanism of the resistivity increase by using x-ray photoelectron spectroscopy (XPS) measurements. We found that the TiN film after 1000-hour exposure to air was the mixture of TiN, intermediative TiOxNy and TiO2. We thus supposed that the resistivity increase was mainly due to high-resistivity oxidized species. We concluded that the structural change proceeded in two steps in the ultra thin TiN film: TiOxNy compounds were formed uniformly over the entire region of the film prior to the TiO2 formation.
  • Interfacial Segregation of Early Transition Metals in Nickel Aluminide

    pp. 407-410

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    DOI:10.2320/matertrans.42.407

    Segregation behavior of Ti, V, and Hf impurities at antiphase boundaries (APBs) in Ni3Al is computed and related to the site preference. The effect of relaxation of atomic positions is considered. Using a relationship between site preference and segregation behavior, the effect of other transition metals on APBs is predicted.
  • Ion-Plating Deposition of MgO Thin Films

    pp. 411-413

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    DOI:10.2320/matertrans.42.411

    We developed an advanced ion-plating (AIP) method and deposited MgO thin films for protective layer in plasma display panel (PDP) with it. The preferred orientation of the films was dependent on deposition conditions; oxygen content and substrate temperature. The film was mainly (111) oriented with a small amount of randomly oriented textures. Fine columnar structures grew vertically from the substrate interface with sharp apexes at the film surface. It was supposed that the film structure could be improved a great deal for PDP applications by our AIP.
  • Forging Characteristics of AZ31 Mg Alloy

    pp. 414-417

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    DOI:10.2320/matertrans.42.414

    Characteristics of open die forging in an AZ31 Mg alloy and a relation between microstructure and mechanical properties of the forged alloy have been investigated for an as-received specimen and an extruded specimen, where the as-received specimen consisted of both elongated coarse grains and equiaxed small grains, and the extruded specimen consisted of only equiaxed small grains. Each specimen was forged at 323 to 673 K . In addition, tensile tests of the forged specimens were carried out at room temperature and the microstructure was observed using an optical microscope. In the forging tests, the specimens could be forged from 18 mm to 2.5 mm in thickness at forging temperatures of more than 423 K . In particular, the specimen could be forged without surface cracks when the grains were refined by extrusion prior to forging. However, for the as-received specimen, some cracks were observed at the edge of the specimens forged at less than 573 K . Therefore, it is suggested that the microstructure of the pre-forged specimens needs to be homogeneous, in order to attain a good surface quality, when forging is carried out at temperatures less than 573 K . The grain size of the forged specimens decreased with decreasing forging temperature. It should be noted that a very small grain size of about 3 \\micron was attained by forging at 473 K . The tensile strength and the 0.2% proof stress of the forged specimens increased with decreasing forging temperature due to grain refinement by forging.
  • Effects of Grain Size and Temperature on Environmental Embrittlement of Ni3(Si, Ti) Alloy

    pp. 418-421

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    DOI:10.2320/matertrans.42.418

    The effects of grain size and temperature on environmental embrittlement of an L12-type Ni3(Si, Ti) ordered alloy were investigated as a function of strain rate by tensile tests and scanning electron microscope fractography. Irrespective of grain size and temperature, ductile-brittle transition (DBT) occurred when the strain rate decreased. Corresponding to the DBT, fracture surfaces changed from transgranular to intergranular fracture. DBT of a coarse-grained material occurred in a higher strain rate region than that of a fine-grained material. DBT of materials deformed at 423 K occurred in a lower strain rate region than that of materials deformed at room temperature. In a very low strain rate region, an anomalous increase of tensile elongation was observed for a fine-grained material deformed at 423 K.
  • Calculation of Short-Range-Order Diffuse Intensity for a Two Dimensional Square Lattice within Cluster Variation Method

    pp. 422-424

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    DOI:10.2320/matertrans.42.422

    The Cluster Variation Method (CVM) within the square approximation is employed to calculate Short-Range-Order diffuse intensity spectrum for a binary alloy in a two dimensional square lattice. The peak intensity at 1:1 stoichiometric composition is attained at (kx,ky)=(0.5,0.5) in the k-space. The instability temperature determined by the calculation of the Short-Range-Order diffuse intensity coincides with the phase boundary, indicating that the transition is of second-order. The integrated intensity in a Brillouin zone is also calculated to examine the level of the approximation
  • Molecular Dynamics Simulation of Temperature Dependence of Dislocation Behavior in fcc Ni Single Crystal under Tensile Condition

    pp. 425-428

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    DOI:10.2320/matertrans.42.425

    A molecular dynamics (MD) simulation of plastic deformation under a uniaxial tensile strain condition for fcc Ni single crystals is performed in order to clarify the temperature dependence of the edge dislocation behavior. Simulations are performed for the temperature range from 77 to 1200 K using Finnis-Sinclair-type potentials. An edge dislocation first forms at the surface and propagates inside of the crystal on the {111} planes in the ⟨112⟩ direction. The temperature dependence of the simulated Young’s modulus is quite similar to the experimental results. The transverse sound velocity is estimated from the simulated elastic constants at each temperature. Below 600 K, the dislocation speed reaches up to 70% of the transverse sound velocity. The dislocation speed decreases with increasing temperature linearly above 600 K . Dislocations at elevated temperature propagate under lower stress than at room temperature. The extrapolated dislocation speed becomes zero at 1200 K . At this temperature, no dislocations are observed in the present simulation system. The temperature dependence of macroscopic deformation behavior and the possibility of the existence of supersonic dislocations are discussed.
  • Strain Dependence of Solute Atom Energy in Aluminum-Rich Alloys

    pp. 429-431

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    DOI:10.2320/matertrans.42.429

    The dependence of the solute atom energy on the homogeneous strain is derived by expanding the energy of the binary alloy to the second order in the solute concentration and the homogeneous strain components. The energy change is found to be proportional to the solute induced stress. An ab-initio method is then applied to calculate the solute induced stress for Cu, Fe, Li, Mg, Mn, Si, and Zn solute atoms in aluminum.
  • All-Electron Mixed-Basis Calculation to Optimize Structures of Vanadium Clusters

    pp. 432-434

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    DOI:10.2320/matertrans.42.432

    As a powerful ab initio method for systems with transition metal elements, all-electron mixed-basis approach which uses both plane waves and atomic orbitals as basis functions is tested to optimize structures of vanadium clusters. A good agreement with several previous calculations is obtained for V2 and V4.
  • Evaluation of Microplastic Flow Stress in Copper Alloys from Amplitude-Dependent Internal Friction

    pp. 435-438

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    DOI:10.2320/matertrans.42.435

    Stress-strain relations are evaluated from amplitude-dependent internal friction in polycrystalline solid solution copper alloys. The flow stress in microplastic strain range much below the yield point is examined for eight kinds of specimens, prepared by alloying commercial-grade pure copper with 0.3 at% solute atoms (aluminum, silicon, nickel, gallium, germanium, indium, tin and gold). Internal friction is measured at room temperature under atmospheric pressure using the free-decay method of flexural resonant vibration with both free ends around 600 Hz. The flow stress of Cu–Sn alloys required to cause the plastic strain of 1×10−9 is about 440 times larger than that of pure Cu, while that of Cu–Ni alloys only 6 times larger. Thus the flow stress evaluated from amplitude-dependent internal friction reflects sensitively the change of solute elements. The flow stress is examined in terms of the misfit parameters between solute and solvent atoms proposed by Fleischer, and it is shown that the flow stress in microplastic strain range is controlled by the elastic interactions between screw dislocations and solute atoms in solid solution copper alloys.
  • A Monte Carlo Simulation on the Process of Cluster Deposition

    pp. 439-442

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    DOI:10.2320/matertrans.42.439

    Cluster deposition process is expected to open a new scheme for thin-film formation process, which realizes better physico-chemical properties than by conventional processes. We simulate the variants of morphologies of thin films fabricated by the cluster deposition, since it is important to investigate the properties of the thin film. In this paper, a Monte Carlo method is applied to describe the motion of clusters and monomers. The present numerical simulation is performed on a three-dimensional lattice. Some growth morphologies are obtained, and the relationship between the resultant morphologies and the parameters used in the simulation such as deposition rate and size of the clusters are examined.
  • High-Pressure Synthesis of Hydrides of Ca-TM Systems (TM=Mn, Fe, Co and Ni)

    pp. 443-445

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    DOI:10.2320/matertrans.42.443

    New hydrides of Ca–TM–H systems (TM=Mn, Fe, Co and Ni) have been explored by using a high-pressure technique. The high-pressure of up to 5 GPa was yielded by cubic-anvil-type apparatus. All the samples of Ca–TM–H systems (TM=Mn, Fe and Co) prepared at 1073 K under 5 GPa were found to be mixtures of the raw materials. However, for the Ca–Ni–H system, a new hydride with a chemical composition of CaH2–33 at%Ni was prepared at 1223 K under 5 GPa. The color of the hydride was reddish brown. As an additional hydrogen source was used during the synthesis, the color changed into black. The new hydride prepared with additional hydrogen was found to have the CsCl-type structure. The lattice parameter was a=0.35542(2) nm.
  • Electromagnetic Microwave Absorption Properties of a Fine Structure Formed from the Sm2Fe17 Compound after Disproportionation in Air or Nitrogen

    pp. 446-449

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    DOI:10.2320/matertrans.42.446

    It was reported in our previous papers that the disproportionation reaction of the Sm2Fe17 compound in hydrogen can be used to prepare fine, soft-magnetic powders for use in electromagnetic wave absorbers. In this study, the microstructure and electromagnetic wave absorption properties in the GHz frequency range of Sm2Fe17 powders, disproportionated in air or nitrogen atmospheres, were investigated. A fine α-Fe structure, of sub-micron order size, is formed from the Sm2Fe17 compound after disproportionation in either air or nitrogen. In the case of disproportionation in air, the powder treated at 423–573 K was in a α-Fe/SmO two-phase state. While in the case of disproportionation in nitrogen, the powder treated at 923 K showed α-Fe/SmN two-phase state; this powder then had to be heated at 423–523 K in air in order to oxidize the SmN phase. Epoxy-resin composite samples were made from these powders, and their electromagnetic wave absorption properties were measured. It was found that the sample disproportionated at 923 K for 2 hours in a nitrogen gas flow, milled for 30 minutes and oxidized at 523 K for 2 hours in air, exhibited the best absorption properties. The R.L. value was under −20 dB in the frequency range 1.2 to 2.3 GHz, when the absorber thickness was between 7.2 to 4.2 mm. Therefore, compared with a carbonyl-iron/resin composite (which had the same Fe content), the absorber was 30% thinner.
  • A Dilatometric Study of the Martensitic Transformation of Zirconia Containing 1.82.0 mol% Yttria

    pp. 450-452

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    DOI:10.2320/matertrans.42.450

    The martensitic transformation during a continuous cooling was monitored by the dilatometric and HT-XRD method for the samples of zirconia containing 1.8∼2.0 mol%Y2O3. The alloys exhibited distinctly different Ms (martensite start temperature) for the surface and bulk martensite when the cooling rate was relatively low. From the dilatometric data, the thickness of the surface martensite was estimated to be about 90 \\micron. With increasing cooling rate, the Ms tended to decrease and the transformation was eventually completely suppressed, in agreement with the isothermal nature of the transformation suggested earlier.
  • Cage Structure Development in Furan-Resin-Derived Carbon

    pp. 453-456

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    DOI:10.2320/matertrans.42.453

    Furan-resin is one of the thermosetting resins. Carbons synthesized from thermosetting resins are generally grouped into non-graphitizable carbons. We investigated the microstructures of furan-resin-derived carbon under high-temperature heat treatments in detail by transmission electron microscopy. The carbons heat-treated at 1773 K or lower temperatures exhibited amorphous structure. The carbon heat-treated at 2073 K revealed a cage structure composed of several wavy graphene layers. The specimens heat-treated at higher temperatures exhibited a more developed cage structure, as evidenced by the number of stacked layers and the periodicity. In the case of 3273 K, about 10 graphene layers formed the cage structure and the cage periodicity was approximately 6 nm.
  • Preparation of Thick Functionally Graded Layers of Ceramics by Surface Modification of Tantalum and Titanium Using High Temperature Plasma Processing

    pp. 457-459

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    DOI:10.2320/matertrans.42.457

    Surfaces of metals, such as Ta and Ti, have been changed successfully to a new type of ceramic layers having the compositional gradient by means of the plasma processing at high temperature above 900°C. Surfaces of Ta and Ti were transformed to thick layers of ceramics, i.e. TiC, TiN, TaC or TaN components, respectively, by carburizing or nitriding. Resultantly, a Vicker’s hardness of each modified sample surface remarkably increased over 3000 kg/mm2. The density of carbides or nitrides in the modified layer and at the interface was measured to decrease with depth. The width of interface was wide about 7 \\micron, in the case of TiC . Additionally, the irradiation of 20 MeV-electron beam to samples as the pretreatment before the plasma processing was effective to increase the thickness of modified layer.
  • Combustion Synthesis of Aluminum Nitride From Dross

    pp. 460-463

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    DOI:10.2320/matertrans.42.460

    For effective use of aluminum dross and development of cost-effective refractory with high thermal conductivity, the combustion synthesis of aluminum nitride was experimentally studied, in which effect of metallic aluminum concentration of a raw material and nitrogen pressure on ignition was mainly examined by using a newly-designed equipment. Once one end of powder mixture of aluminum and alumina was ignited at nitrogen atmosphere, combustion wave of exothermic reaction (Al+0.5N2=AlN) propagated to another end of the powder successfully. With decreasing the aluminum concentration and the nitrogen pressure, the propagating rate decreased. In decreasing the concentration and/or the pressure extremely, it was quite difficult to ignite it. Relationship between nitrogen pressure and aluminum concentration for the possible combustion synthesis of aluminum nitride was expressed in the diagram. This map appealed that aluminum dross can be a raw material of the combustion synthesis for producing aluminum nitride industrially by controlling the conditions.
  • Stoichiometry Splitting of β Phase in Ni-Al-Mn, Ni-Al-Co and Ni-Al-Fe Ternary Systems

    pp. 464-470

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    DOI:10.2320/matertrans.42.464

    The stoichiometry of the ternary β phase in the Ni–Al–Mn, Ni–Al–Co and Ni–Al–Fe systems has been studied through the measurements of hardness and lattice parameter. It is shown that two stoichiometry lines are observed in the β phase region of the Ni–Al–Mn ternary system. The first stoichiometry line is located on the composition line connecting NiAl and MnAl, whereas the second stoichiometry line is located on the composition line connecting NiAl and NiMn. In the Ni–Al–Co ternary system, there is a single stoichiometry line, which starts from NiAl and terminates at CoAl. In the Ni–Al–Fe system, there are also two stoichiometry lines. One starts from NiAl and ends at FeAl, and the other directs toward from NiAl to the Fe corner. The stoichiometry line of the ternary β phase in the Ni–Al–X system is either a single or a plural type, which is basically determined by the relative magnitudes of the Ni–X, Al–X and Ni–Al bonding forces. The concentration dependence of solid solution strengthening or defect strengthening is greatly varied depending on ternary elements in the β phase in the Ni–Al–Mn, Ni–Al–Co and Ni–Al–Fe ternary systems.
  • Viscosity of Liquid Fe-Cu-Si Alloy Formed in New Melting Process for Domestic Waste Incineration Residue

    pp. 471-477

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    DOI:10.2320/matertrans.42.471

    A new melting system is being developed to solve the problems in the treatment of ash from municipal waste incinerators. The viscosity of liquid Fe–Cu–Si ternary melt has been measured in the present work by the oscillation crucible technique in the temperature range from 1523 to 1673 K in order to obtain the basic information on the fluidity of the typical alloy system generated in the ash melting furnace. The relation between the viscosity of Fe–Cu–Si ternary alloys and 1⁄T can be expressed by Arrhenius-type formula in the temperature range from 1523 to 1673 K . Viscosity of the alloy is in the range of 5 to 7 mPa·s in the composition range of 0∼5 mass%Cu and 10∼20 mass%Si at 1723 K . These values are approximately double of that in pure Cu melt at 1723 K . From the result obtained, the appropriate condition is discussed for the operation of the melting furnace for ash from municipal solid waste incinerator.
  • Effect of Al on the Corrosion Behavior of Low Alloy Steels in Wet/Dry Environment

    pp. 478-483

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    DOI:10.2320/matertrans.42.478

    The iron rust phase has been analyzed by using EPMA, TEM and alternating current (AC) impedance methods after wet/dry corrosion tests using 0.5 mass%NaCl solution. The steel containing 0.8 mass%Al showed higher corrosion resistance than carbon steel in the test. Aluminum was identified in the spinel oxide of inner rust of Al-bearing steel by TEM and EPMA, which is confirmed by thermodynamic calculation (Pourbaix analysis). By AC impedance it is demonstrated that the resistance of the rust (Rrust) corresponds to the structural factor of the rust of steels. The Rrust value of Al-bearing steel increases after the continuous formation of inner rust, which implies that Al takes part in the conversion of spinels into fine structure that prevents the penetration of Cl-ions.
  • Effects of Titanium Addition on the Microstructure and Mechanical Behavior of Iron Aluminide Fe3Al

    pp. 484-490

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    DOI:10.2320/matertrans.42.484

    The microstructure, mechanical properties and deformation behavior of four Fe3Al-based alloys containing 0, 5, 10 or 15 at%Ti were investigated. With the addition of Ti, the coarse-grained microstructure of Fe3Al was refined and the degree of D03 ordering was decreased. Poor bending ductility and a change of fracture mode from cleavage to mixture of intergranular and cleavage were observed in Ti-added alloys. It was shown that the Ti addition decreased the room temperature yield strength, but increased the yield strength at elevated temperatures. Anomalous temperature dependence of yield strength was observed in all the alloys, and the peak strength was shifted to higher temperatures with increasing Ti content. The Ti addition was also revealed to decrease the strain rate sensitivity and activation energy for high temperature deformation. Finally, hot working conditions for the Ti-added Fe3Al alloys were proposed by taking the stress-strain response, strain rate sensitivity and deformation microstructure into account.
  • Characteristics of Spray-Dried WC-17 mass%Co Composite Powder Part 1: Effect of Heating

    pp. 491-495

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    DOI:10.2320/matertrans.42.491

    In this study, WC–17 mass%Co composite powder for HVOF (High Velocity Oxy-Fuel)-thermal spray was fabricated by the spray-drying method and the effect of heating temperature (850°C, 1000°C, 1150°C, 1300°C) on the microstructure, particle size distribution, flowability and phases was investigated. The as-spray dried powder had a spherical morphology and the particle size distribution, mean particle size, and flowability were 20.6–51.7 \\micron, 27.2 \\micron, and 3.8 g/s, respectively. The agglomerated powder became dense by heating. After heating at 1300°C, the particle size distribution and mean particle size were decreased to 6.9–37.9 \\micron and 17.8 \\micron, respectively. And the flowability was improved to 8.7 g/s. Accordingly, investigating the effect of heating temperature on particle size distribution, mean particle size, flowability, and microstructure of spray-dried WC–17 mass%Co powder, we found that the optimum heating temperature of spray-dried WC–17 mass%Co powder for HVOF-thermal spray powder ranged from 1150 to 1300°C. And during the heating, Co6W6C and Co3W3C phases were produced and the critical temperature transforming Co6W6C into Co3W3C phases was 1150°C.
  • Mode of Boron Solubility in Ferrous Alloys

    pp. 496-501

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    DOI:10.2320/matertrans.42.496

    X-ray and neutron diffractometry and inelastic neutron scattering studies on a set of cast ferritic iron-chromium alloys containing boron indicate that the dissolved boron is present interstitially rather than substitutionally within the α-Fe,Cr matrix. Inelastic neutron scattering spectra of the alloys may be interpreted in terms of the phonon dispersion curves for α-Fe. These spectra show small shifts in the frequencies of particular phonons, indicative of lattice disruption by the presence of interstitial atoms. These results were subsequently confirmed by internal friction measurements.
  • Is Ductilization of Intermetallics by Nanostructure Processing a Possibility?

    pp. 502-508

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    DOI:10.2320/matertrans.42.502

    Nanocrystalline materials with a grain size of ≤100 nm are expected to be strong and hard and at the same time exhibit improved ductility/fabricability in comparison to their coarse-grained counterparts. Even though this has been shown to be possible in some nanocrystalline ceramic materials, there have been concerns on the validity of these results because of inadequate densification of the samples. It has also been suggested that achievement of nanostructures may not be desirable to ductilize the intermetallics. This article presents an overview of the fracture behavior of materials as a function of grain size, and shows that based on the observations that the strain-rate sensitivity and fracture toughness of nanostructured materials are higher than in their coarse-grained counterparts, achievement of nanocrystallinity in materials (including intermetallics) can lead to improved ductility and hence is a profitable route to investigate.
  • The Structure of an Al-Ni-Co Decagonal Quasicrystal Studied by Atomic-Scale Electron Microscopic Observations

    pp. 509-513

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    DOI:10.2320/matertrans.42.509

    The structure of an Al–Ni–Co decagonal phase, which was found as a highly-ordered decagonal quasicrystal in an Al72Ni20Co8 alloy, has been studied by atomic-scale observations of high-resolution electron microscopy (HREM) and high-angle annular detector dark-field scanning transmission electron microscopy (HAADF-STEM). It has been found that a large columnar cluster of atoms with a decagonal section of about 3.2 nm in diameter exists as a basic structural unit. A structural model of the cluster is proposed from HREM and HAADF-STEM images.
  • Thermodynamic Activity of Ga in Ni3Ga

    pp. 514-519

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    DOI:10.2320/matertrans.42.514

    Thermodynamic activity of Ga in the L12-ordered intermetallic phase Ni3Ga has been determined by measuring the electromotive force of a galvanic cell with zirconia solid-electrolyte, Ni–Ga, Ga_2O_3|ZrO_2 (+ Y_2O_3) | Ga, Ga_2O_3in the temperature range between 1050 and 1300 K for six compositions. The activity of Ga varies with composition most steeply at the stoichiometric composition (25 mol%Ga), the dependence being more pronounced at low temperatures. By applying a thermodynamic model based on the Bragg-Williams approximation (Ikeda et al.: Acta Mater. 46 (1998) 6605–6613), the effective pair interaction energy between Ni and Ga atoms has been determined to be 9.75±0.19 kJ/mol. The thermodynamic factor in chemical diffusion in the L12 phase has been derived from the composition dependence of the thermodynamic activity.
  • Fluxless Wetting Properties of the UBM-Coated Si-Wafer to Pb-Free Solders under Different Atmosphere

    pp. 520-527

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    DOI:10.2320/matertrans.42.520

    The wetting balance method was used to estimate the fluxless wetting properties of UBM (Under Bump Metallurgy)-coated Si-wafer to binary lead-free solders (SnAg, SnSb, SnBi, SnIn, SnZn). The wetting property estimation of UBM-coated Si-wafer was possible with new wettability indices from the wetting curves of one side-coated specimens; Fmin, Fs, and ts. Au/Cu/Cr UBM is better than Au/Ni/Ti UBM from the point of wetting time. At general reflow process temperature, the wettability of high melting point solders (SnSb, SnAg) is better than that of low melting point ones (SnBi, SnIn). The nitrogen atmosphere was more effective for improvement in fluxless wettability than in fluxed wettability. The contact angle of one side-coated Si-plate to solder can be calculated from the force balance equation by measuring the static state force and the tilt angle.
  • Formation of Ti-Zr(Hf)-Ni-Cu Amorphous Alloys and Quasicrystal Precipitation upon Annealing

    pp. 528-531

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    DOI:10.2320/matertrans.42.528

    Ti60Zr15Ni15Cu10 and Ti60Hf15Ni15Cu10 amorphous alloys were prepared and the crystallization process was studied. These alloys crystallize through multiple step exothermic reactions, of which the low-temperature one corresponds to the precipitation of an icosahedral quasicrystalline phase (I-phase). The particle size of the precipitated I-phase is approximately 20 nm for the two alloys. Further annealing of the alloys at higher temperatures leads to the decomposition of the I-phase to other stable crystalline phases, implying that the present I-phase is in a metastable state. It is speculated that icosahedral atomic clusters exist in the amorphous phase, which causes high nucleation rate of the I-phase in the initial crystallization stage.
  • Microstructure of Partially Remelted Thixoformable Mg-Ni Alloys

    pp. 532-535

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    DOI:10.2320/matertrans.42.532

    The aim of this paper is to develop a thixoformable model alloy, Mg–Ni alloy of binary eutectic system with no range of solid solubility and to report the experimental results concerning the microstructural evolution of the alloys in the reheated semisolid state. Mg–Ni alloys of various nickel compositions were produced in the form of cylindrical billets by Rotation-Cylinder method. The results showed that the appropriate thixotropic structure, the globular solid phase with less liquid droplets entrapped inside the solid, could be obtained by the normal solidification and simple reheating procedures. Of more important feature of the thixoformable Mg–Ni alloy is that the size of the solid globules and the fraction liquid were mainly dependent on nickel composition, therefore could be controllable.
  • Prediction of Temperature Rise in Equal Channel Angular Pressing

    pp. 536-538

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    DOI:10.2320/matertrans.42.536

    In order to investigate the temperature rise of the workpiece during equal channel angular pressing (ECAP), a lumped heat transfer analysis was made. The main deforming zone was taken as the analysis domain. The temperature rise due to the work of plastic deformation and the frictional heat was considered. An equation for the temperature rise during the ECAP process was derived. The temperature increment increases with the strength of the material, the ram speed and the channel angle, and decreases as the density, the heat capacity and the die corner angle increase. The model was applied to Al and Al alloys with different ultimate tensile strengths. The calculated temperature rise is in good agreement with published experimental results.
  • Evaluation of Thermal Stability of Mold Materials for Magnesium
    Investment Casting

    pp. 539-542

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    DOI:10.2320/matertrans.42.539

    The relative thermal stability of mold materials against AZ91D magnesium alloy melt was evaluated. Special attention has been paid to obtain the applicable investment casting condition for conventionally used ZrSiO4 and Al2O3 molds, to develop a stable CaZrO3 mold, and to evaluate the reaction of AZ91D magnesium alloy melt with a thermodynamically stable CaO mold. The results showed that the castings in the ZrSiO4, Al2O3, and CaO molds had clear reaction zones when the mold temperature was over 673 K, but below it no reaction occurred except for the CaO mold. The relative thermal stability of the molds examined can be graded in the order of increasing thermal stability in the following sequence; CaO→ZrSiO4→Al2O3→CaZrO3. Although the CaZrO3 mold is promising for magnesium investment casting, it is worth noting that the colloidal silica bonded ZrSiO4 and Al2O3 molds could be used, provided that careful melting and casting environments were taken into consideration.
  • Preparation of Bulk Glassy Mg65Y10Cu15Ag5Pd5 Alloy of 12 mm in Diameter by Water Quenching

    pp. 543-545

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    DOI:10.2320/matertrans.42.543

    Cylindrical glassy alloys with diameters up to 12 mm were prepared for a Mg65Y10Cu15Ag5Pd5 with a high reduced glass transition temperature (TgTm) of 0.62 by water quenching the molten alloy in the iron tube. Neither cavities nor voids are seen over the whole inner region and no contrast revealing a crystalline phase is seen over the transverse cross section. The glass transition temperature (Tg), crystallization temperature (Tx), the temperature interval of the supercooled liquid region (ΔTx=TxTg) and the melting temperature (Tm) are measured to be 436, 468, 32 and 706 K, respectively, for the Mg65Y10Cu15Ag5Pd5 alloy with a diameter of 12 mm. The simultaneous addition of Ag and Pd to Mg–Y–Cu system causes an increase in the TgTm, leading to an increase in the glass forming ability. It is thus concluded that the application of the water quenching process with the iron tube to the Mg-based glassy alloys is useful for the formation of the bulk glassy alloys.

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