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

MATERIALS TRANSACTIONS Vol. 53 (2012), No. 11

  • Establishment and Optimization of Angle Dispersive Neutron Diffraction Bulk Texture Measurement Environments

    pp. 1831-1836

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    DOI:10.2320/matertrans.MA201203

    Different from electron back-scattering diffraction and X-ray diffraction, neutron diffraction enables to directly measure the bulk texture because of the high penetrability and the large spot size of neutron beam and easily investigate the preferred orientation distributions of multiphase materials, coarse-grained materials and low symmetric materials including hexagonal metals, ceramics and rocks. In this paper, the texture measurement technical environments of two angle dispersive neutron diffractometers were established and optimized respectively, and their reliabilities were quantitatively examined through evaluating the bulk textures of a warm-pressed magnesium alloy and a multilayered multiphase steel sheet. It is found that the MUSASI-L neutron diffractometer with a single tube detector through selecting the proper collimation angle may achieve the similar texture evaluation reliability to the RESA-2 neutron diffractometer with one-dimensional position-sensitive detector, so that both of them are available to directly measure the bulk textures of various materials. In addition, the estimation of thermal neutron absorption shows that if a measurement error about 5–8% is acceptable, a cubic sample or a cylinder samples whose diameters is equal to its height may be employed to directly measure its bulk texture through completely bathing it in the well-collimated uniform neutron beam without doing the correction of neutron absorption anisotropy.
  • Application of Recrystallization Texture Evolution Model to Type 430 Stainless-Steel Strip Production

    pp. 1837-1846

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    DOI:10.2320/matertrans.MA201204

    The ridging phenomenon of type 430 stainless-steel originates from the texture due to crystal plasticity anisotropy. Thus, to predict the antiridging property, we must continuously analyze the hot-rolling, hot-rolling and annealing, cold-rolling, cold-rolling and annealing textures. However, it has been previously difficult to analyze the recrystallization texture. We thus developed a model to predict the recrystallization texture coupled with the Taylor rolling model. Furthermore, the ridging index was calculated in order to estimate the plasticity in type 430 stainless-steels. The plasticity prediction method was applied to type 430 stainless-steel strips rolled at a low temperature with a high reduction rate in an actual tandem hot strip mill.
  • Influence of Texture on Bendability of Cu–Ni–Si Alloys

    pp. 1847-1851

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    DOI:10.2320/matertrans.MA201205

    The influence of texture on the bendability in Cu–Ni–Si alloys was examined by using an age-hardened polycrystalline strip with various recrystallization textures. In multiple samples manufactured by adjusting conditions of rolling and heat treatment, the Cube orientation {100}<001>, the RD-rotated Cube orientation {012}<100>, the BR orientation {362}<853> and the R(S) orientation {231}<346>, which are the representative recrystallization textures of FCC metals, developed up to 40% in respective area fractions. The bendability was clearly dependent on texture. The sample that had a strongly developed Cube orientation showed the best bendability with respect to both the good and bad ways (GW, BW) in bending. In comparison, the samples in which the BR and the R orientations developed showed poor GW bendability. The sample having a comparably random orientation showed poor GW and BW bendability. The shape of the cracks generated by bending was linear, and these cracks developed in a direction about 40 degrees from the surface. Further, they developed along shear bands, and this result was confirmed by the EBSD measurement. Therefore, the cause of cracking resulting from bending was shear bands. The correlation between the good bendability and a low average Taylor factor was confirmed. More uniform deformation by crystalline slips through texture control was effective for restraining the shear bands, i.e., for obtaining excellent bendability.
  • Effect of Texture on 0°/180° Earing in Deep Drawing of Aluminum Alloy Sheets

    pp. 1852-1857

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    DOI:10.2320/matertrans.L-M2012825

    It is known in aluminum alloy sheets that two ears on a cup formed by deep drawing in 0 and 180° to the rolling direction may grow up by cold rolling. In the previous reports, Goss and RD rotated cube textures were fingered as the cause of the 0°/180° earing. But the growth process of the 0°/180° earing is not clear. In the present work, texture analysis has been carried out in cold rolling process with AA 6016 aluminum alloy sheets that have a strong cube texture through the thickness and weak Goss texture at the center layer. RD rotated cube texture is formed at the surface layer by cold rolling whereas cube texture at the center layer decreases rapidly. It is indicated that RD rotated cube texture at the surface layer and persisting Goss texture at the center layer cause high 0°/180° earing. These texture factors are discussed by a crystal plasticity finite element analysis. The calculated earing profiles derived by the finite element analysis show much the same patterns of experimental earing profiles.
  • Misorientation Change of the Grain Boundary in Pure Copper Bicrystals Subjected to One-Pass Equal-Channel Angular Pressing

    pp. 1858-1862

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    DOI:10.2320/matertrans.MA201213

    Grain boundaries can change their misorientation by absorbing lattice dislocations at relatively high temperature under moderate straining. The same phenomenon is believed to occur during severe plastic deformation down to room temperature leaving grain boundaries in the nonequilibrium state. Direct evidence of misorientation change of the grain boundary during severe plastic deformation was obtained in copper bicrystals subjected to equal-channel angular pressing (ECAP) for one pass. Marked dependence of misorientaion change on the initial orientation was revealed, and is associated with the unique slip patterns of ECAP, where the shear deformation is restricted to the narrow zone parallel to the intersecting plane of the two channels. The degree of change can be related to slip geometry in terms of grain boundary plane orientation.
  • Texture Evolution in Al–0.2 mass%Sc Alloy during ARB Process and Subsequent Annealing

    pp. 1863-1869

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    DOI:10.2320/matertrans.MA201223

    Evolution of textures in the solution treated and aged Al–0.2Sc alloy heavily deformed by ARB process and subsequently annealed was investigated using pole figure and orientation distribution functions (ODF) that were determined by electron backscatter diffraction (EBSD) technique. Three kinds of starting materials were prepared before the ARB process: solution treated (ST) material, 300°C-aged material including fine Al3Sc precipitates, and 400°C-aged material having coarse Al3Sc precipitates. The results of deformation texture indicated that at early stage of ARB S {123} <634> orientation component developed and it changed to Copper {112} <111> and Taylor {4 4 11} <11 11 8> components at later ARB cycles in both ST-ARB and Aged-ARB specimens. However, in the Aged-ARB specimens after 5-cycle ARB process, Copper {112} <111> component decreased and Taylor {4 4 11} <11 11 8> component did not developed. Cube {100} <001> component strongly developed in the 400°C Aged-ARB specimen by annealing at high temperature, whereas Cube component did not develop in the ST-ARB and 300°C Aged-ARB specimen. Such a difference was understood as the effect of Al3Sc precipitates.
  • Texture Evolution in AZ80 Magnesium Alloy by the Plane Strain Compression Deformation at High Temperature

    pp. 1870-1875

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    DOI:10.2320/matertrans.L-M2012828

    The formation behavior of textures during high temperature plane strain compression deformation is experimentally studied on AZ80 magnesium alloy. Three kinds of specimens with different initial textures are prepared from the extruded bars having a <10\bar{1}0> fiber texture. Plane strain compression is conducted at 723 K, 5.0 × 10−2 s−1 and strains ranging from −0.4 to −1.0. New grains appeared after the deformation up to −0.4 in true strain. Initial texture gradually changes with increasing strain. After the deformation up to −1.0 in true strain, (0001)<10\bar{1}0>, {11\bar{2}0}<10\bar{1}0>, (0001)<11\bar{2}0> and {10\bar{1}0}<0001> appeared depending on the initial texture. (0001)<10\bar{1}0> and {11\bar{2}0}<10\bar{1}0> are formed irrespective of the initial texture. Simple crystallographic examination showed that all the texture components are orientations stable for the plane strain compression.
  • Texture and Corrosion Behavior of Thin Nickel Sheet Formed by Pulse Plating and Cold Rolling

    pp. 1876-1880

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    DOI:10.2320/matertrans.MA201224

    Thin nickel sheets were fabricated by electroforming, and cold rolled to improve their strength. The thin nickel sheets have very fine grains with a {001}<uv0> fiber texture. Cold rolling results in evolving a {001}<110> orientation and the formation of a weak {111}<uvw> fiber component. Micro-hardness of the nickel sheet on the surface normal to the normal direction (ND) was increased from 247.8 to 354.4 Hv by cold rolling with 87.5% reduction. The corrosion potential and corrosion rate of the nickel sheet in artificial sea water were in the ranges of −27 to −12 mVSCE and 4.2 × 10−7–1.8 × 10−6 A cm−2, respectively. The change in corrosion behavior with cold rolling on the surface normal to ND has little relation to crystallographic texture because of a stable {001} texture during rolling, unlike nickel bulk samples.
  • Formation and Evolution of Misoriented Grains in a-Plane Oriented Gallium Nitride Layers

    pp. 1881-1884

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    DOI:10.2320/matertrans.MA201221

    Annealed low-temperature GaN layers grown on r-plane sapphire substrates were examined by X-ray diffraction pole figure measurements. The GaN layers were mainly a-plane oriented, in which misoriented grains with four different orientations were detected. The c-axes of the misoriented grains are tilted from the surface normal by about 35°, which are along the bonds not parallel to the c-axis of the a-plane oriented layers. There was a difference among the peak intensities corresponding to the c-planes of the misoriented grains with the four different orientations. Considering the difference, the relative amount of misoriented grains with each orientation can be predicted. The evolution of the misoriented grains is expected to be controlled by the major polarity.
  • Structural Changes and Stability Switching by Indentation Simulation in Amorphous Metals

    pp. 1885-1891

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    DOI:10.2320/matertrans.M2012191

    We have attempted to reveal the deformation mechanism of amorphous metals by local lattice instability analysis, based on the positive definiteness of the atomic elastic stiffness coefficients, Bijα. In our previous study, changes in inhomogeneous structure are explained by the observation of the stability-switching or transition between detBijα > 0 and detBijα < 0. In this study, we have performed the indentation simulation on a binary amorphous metal, and discussed the inelastic deformation in the amorphous metal by Voronoi polyhedra analysis and the stability-switching of local lattice instability. The indentation simulation predicts that rearrangements of atoms occur not only on structures below the indentation point but also inside the amorphous metal structure. These structural changes produce a significant volume change in the Voronoi polyhedra, the stability-switching based on local lattice instability analysis, and a local volume reduction evaluated within scales of a few hundred atoms.
  • Hydrothermal Synthesis of Different Zinc Oxide Nanostructures: Growth, Structure and Gas Sensing Properties

    pp. 1892-1895

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    DOI:10.2320/matertrans.M2012203

    We report the nanostructures and gas-sensing properties of Zinc oxide nanosheets prepared by hydrothermal method. In particular, needle-like Zinc oxide was also prepared for comparison. The morphology and structural properties were investigated using X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). Subsequent gas-sensing measurement between Zinc oxide nanosheets and Zinc oxide nanoaciculars indicated that the nanosheets exhibited higher gas response to ethanol. The enhanced gas sensing properties of Zinc oxide nanosheets suggests that governing the shape and the surface structure of nano Zinc oxide is a significant approach for developing high performance gas sensors.
  • Analysis for Kinetics of Ferrite Growth due to Isothermal Decarburization of Austenite in the Binary Fe–C System

    pp. 1896-1904

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    DOI:10.2320/matertrans.M2012161

    If a binary Fe–C alloy with a single-phase microstructure of the austenitic γ phase is isothermally annealed in an appropriate decarburization atmosphere, a layer of the ferritic α phase is formed on the surface of the γ phase and gradually grows into the γ phase. The kinetics for the growth of the α layer during the decarburization was quantitatively analyzed using a diffusion model at annealing temperatures between 1011 and 1185 K. In the analysis, the diffusion coefficient of C in each phase is considered independent of the chemical composition. According to the model, the square of the thickness l of the α layer is proportional to the annealing time t as described by the relationship l2 = Kt. This relationship is called the parabolic relationship. As the initial concentration xγ0 of C in the γ phase increases from the minimum value to the maximum value for the γ single-phase region at each annealing temperature T, the parabolic coefficient K monotonically decreases from the maximum value Kdmax to the minimum value Kdmin. As T decreases, Kdmax decreases, but Kdmin increases. However, both Kdmax and Kdmin vary depending on T in a complicated manner. Thus, an Arrhenius equation is not applicable even to the temperature dependence of Kdmax in the whole annealing temperature range. At a constant value of xγ0, K monotonically decreases with increasing value of T. This means that the growth of the α layer takes place faster at lower annealing temperatures than at higher annealing temperatures. Such temperature dependence of the kinetics coincides well with experimental observations.
  • Impact of Strain Rate on Thermomechanical Coupling Effects in TiNi SMA Subjected to Compression

    pp. 1905-1909

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    DOI:10.2320/matertrans.M2012212

    In this study, the thermomechanical coupling effects accompanying stress-induced martensitic transformation in TiNi shape memory alloy subjected to compression test were investigated. The mechanical characteristics were elaborated and the temperature changes related to the exothermic martensitic forward transformation and the endothermic reverse one were measured in a contactless manner by a fast and sensitive infrared camera. The obtained temperature changes of the specimen depend on the strain rate applied. At higher strain rate, greater temperature changes were observed, because the heat flow to the surroundings was lower and the process was closer to adiabatic conditions. The temperature changes of the shape memory alloy significantly influence its stress–strain characteristics. Moreover, the energy dissipated during a compression cycle was calculated for various strain rates. The study revealed that both the loading work and recoverable strain energy increase with increasing strain rate, while the dissipated energy fraction decreases.
  • Characterization of the Microstructure Evolution and Microsegregation in a Ni-Based Superalloy under Super-High Thermal Gradient Directional Solidification

    pp. 1910-1914

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    DOI:10.2320/matertrans.M2012173

    The microstructure evolution and microsegregation behavior of alloying elements in a Ni-based superalloy at a series of growth rates under super-high thermal gradient directional solidification were quantitatively characterized. Both microstructure and dendritic segregation are functions of growth rate. The high growth rate solidification leads to refinement in primary (λ1) and secondary (λ2) dendrite arm, decreased size of γ/γ′ eutectics and γ′ phase, as well as reduced microsegregation degree of alloying elements. Also with the growth rate increased, the morphology of γ′ precipitates changes from irregular shape to a cuboidal one. The electron probe microanalysis (EPMA) reveals that Cr, Mo and γ′ forming elements (Al, Ta and Nb) all partition to interdendritic region, while W and Re both preferably segregate to dendrite core. Thus at fast growth rates (or high cooling rates), finer dendrites, uniformly coherently cuboidal γ′ precipitates and decreased segregation favorable to the performance of superalloys are obtained. These quantitative results provide a basis for the establishment of cast and heat treatment process.
  • Microstructural Evolution during Austenitization and Quenching of a 5% Cr Work Roll

    pp. 1915-1921

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    DOI:10.2320/matertrans.M2012238

    The effects of a slow heating rate and a long austenitizing time with various cooling rates on the carbide dissolution and phase transformations of a 5% Cr work roll steel was investigated based on actual austenitization and quenching conditions and a large roll size using transmission and scanning electron microscopy, dilatometry, and thermodynamic calculations. When the roll temperature reached the austenitization temperature of 1173 K, the dissolution of pre-existing carbides was nearly complete due to the slow heating rate of 100 K/h, indicating that the austenite matrix had an equilibrium chemical composition at 1173 K before quenching. After quenching at cooling rates ranging from 0.1 to 3.0 K·s−1 along the radial direction of the roll, the core of the roll contained ferrite, pearlite, bainite and undissolved carbides, while the surface consisted of martensite and undissolved carbides.
  • Microstructural Development and Coarsening Behavior of γ′ Precipitates in Co–Ni–Al–W-Base ODS Alloys

    pp. 1922-1928

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    DOI:10.2320/matertrans.M2012093

    Co–Ni–Al–W-base alloy, strengthened by nanosized oxide and γ′ precipitate is a novel type of high-temperature structural material. The microstructural evolution of the alloys during heat treatment was investigated, and the γ–γ′ misfit and the coarsening kinetics of γ′ precipitate were discussed. The alloys consisted of γ/γ′ two-phase region, discontinuously formed area and several secondary phases (AlxCo, Co3W and Co7W6). An increase in the solution temperature and Ni contents favored the precipitation of γ′ phase due to the enhanced solid solubility of Al and W in cobalt matrix. The ordered arrangement of near cuboidal γ′ precipitates was observed, and the γ–γ′ misfit was calculated to be 0.57%. The coarsening kinetics of γ′ precipitates conformed to the L-S-W model. The Arrhenius analysis yielded the activation energy of 188 KJ·mol−1.
  • Electrical Resistivity and Morphology of Sn1−x/Six Core–Shell Cluster Network Prepared by a Plasma-Gas-Condensation Cluster Source

    pp. 1929-1932

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    DOI:10.2320/matertrans.M2012232

    Sn1−x/Six cluster assembled films have been prepared by a plasma-gas-condensation cluster beam deposition apparatus. Transmission electron microscope images indicate that individual clusters have core–shell morphology, where Sn cores are covered by Si shells. Temperature dependence of electrical resistivity exhibits a metallic behavior and a superconducting transition at low temperature for 0 < x < 0.20, while a semiconductor-type behavior and no superconductivity down to 2 K for x > 0.29. These results indicate that the cluster network and/or core–shell morphology Sn1−x/Six cluster assembled films changes with x.
  • Mechanical Properties of TiB2–Al3Ti and TiB2–(Al,Ni)3Ti Composites

    pp. 1933-1937

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    DOI:10.2320/matertrans.M2012248

    Composites of TiB2-tetragonal Al3Ti and TiB2-cubic (Al,Ni)3Ti have been fabricated using spark plasma sintering method at the temperature between 1173 and 1573 K. When TiB2–(Al,Ni)3Ti specimens were sintered between 1273 and 1373 K, (Al,Ni)3Ti filled in space between TiB2 grains and dense samples were obtained. On the other hand, when TiB2–(Al,Ni)3Ti specimens were sintered at above 1473 K, (Al,Ni)3Ti evaporated and monolithic TiB2 were obtained. A similar results have been obtained for the TiB2–Al3Ti composites. The highest bending strength of TiB2–(Al,Ni)3Ti specimens were 660 MPa obtained for TiB2–30 mass%(Al,Ni)3Ti sintered at 1373 K. The highest bending strength of TiB2–Al3Ti composites were 610 MPa obtained for TiB2–30 mass%Al3Ti sintered at 1473 K. The Vickers hardness of TiB2–(Al,Ni)3Ti composites increased as the sintering temperature increased and the maximum value of 2100 Hv were obtained by the sintering at 1573 K.
  • Effects of Fine Particle Bombarding on Surface Characteristics and Fatigue Strength of Commercial Pure Titanium

    pp. 1938-1945

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    DOI:10.2320/matertrans.M2012226

    This study investigated the effects of fine particle bombarding (FPB) on the surface characteristics and fatigue strength of commercial pure titanium. For comparison, conventional shot peening (SP) was also performed. The surface microstructure was nano-crystallized by FPB and SP. The grain size of nano-crystals reduced with decreasing particle diameter or increasing air pressure for accelerating particles. The surface hardness and compressive residual stress markedly increased by FPB. The surface layers were uniformly generated along the surface, and effectively suppressed the initiation of fatigue cracks. As a result, the fatigue strength greatly increased. Since the surface layers acted as a barrier to subsurface cracks, its improvement ratio was closely related to the surface characteristics.
  • Electrodeposition Behavior of a Zn–Ni Alloy in an Alkaline Zincate Solution

    pp. 1946-1951

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    DOI:10.2320/matertrans.M2012241

    Electrodeposition behavior of Zn–Ni alloys was investigated at current densities of 10–500 A·m−2 and a charge of 5 × 104 C·m−2 in an unagitated zincate solution containing triethanolamine, which forms a stable complex with Ni2+ ions at 308 K. At low current densities, the Zn–Ni alloy exhibited normal codeposition, wherein electrochemically more noble Ni deposited preferentially, while at high current densities, it exhibited anomalous codeposition, wherein less noble Zn deposited preferentially. Ni deposition and H2 evolution were significantly suppressed in the region of anomalous codeposition at higher current densities, showing the formation of an inhibitor for deposition, which results from Zn2+ ions in the cathode layer. In contrast, in the region of normal codeposition at lower current densities, the underpotential deposition of Zn apparently occurred with Ni. Because Zn–Ni alloys are composed of a stable intermetallic compound of Ni5Zn21, the activity coefficient of Zn in the deposit appears to decrease remarkably.
  • Effects of Tool Geometry on Hardened Layer of Friction Stir Processed Cast Iron

    pp. 1952-1955

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    DOI:10.2320/matertrans.F-M2012824

    The authors clarified that various cast irons can be hardened by friction stir processing (FSP) in a previous study. However, the high applied tool load was indispensable for obtaining the hardened layer. In this study, the effect of the tool geometry on the applied tool load was investigated for forming the hardened layer by the FSP with a lower applied tool load. As a result, the applied tool load could be reduced by 36% using a concave tool.
  • Surface Hydrophilicity and Osteoconductivity of Anodized Ti in Aqueous Solutions with Various Solute Ions

    pp. 1956-1961

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    DOI:10.2320/matertrans.M2012082

    Surface hydrophilicity is considered to have a strong influence on the biological reactions of bone substituting materials. However, the relationship between hydrophilicity and osteoconductivity has not been discussed quantitatively. In this study, Ti substrates were coated with TiO2 having different water contact angles, using anodizing in aqueous solutions containing different types of solute ion, and the quantitative relationship between hydrophilicity and osteoconductivity was investigated.
    All of the anodized coatings were anatase-type TiO2 with a fine surface roughness. Most of the solute ions were included in the coatings, but they did not influence the hydrophilicity of the anodized coatings. However, the surface hydrophilicity of the anodized coatings depended on the pH of the aqueous solution. The amount of hard tissue formed on TiO2-coated specimens (denoted as RB-I) depended on the water contact angle on their surface. For water contact angle between 20 (deg.) and 55 (deg.), the value of RB-I increased as water contact angle decreased. On the other hand, for water contact angle between 55 (deg.) and 70 (deg.), the value of RB-I increased as water contact angle increased.
  • Correlation between Microstructure and Magnetic Properties in Sm2Fe17N3 Magnet Prepared by Pulsed Current Sintering

    pp. 1962-1966

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    DOI:10.2320/matertrans.M2012169

    The consolidation of Sm2Fe17N3 powder was examined by pulsed current sintering below its decomposition temperature. Although decomposition of the powder was not observed, its coercivity decreased dramatically. Annealed powder was observed by transmission electron microscopy in order to clarify the mechanism for the reduction in the coercivity. In powder annealed at 673 K, a thin nanostructured layer was formed around the Sm2Fe17N3 particles. The crystal structure of this thin layer had a crystallographic symmetry higher than that of the Sm2Fe17N3 structure. This higher symmetry layer appeared to have a smaller magnetic anisotropic energy, allowing it to act as a nucleation site for a reverse magnetic domain, when a reverse magnetic field is applied to the magnetized powder. Therefore, the coercivity of the powder decreased below its decomposition temperature. Irregular growth of the thin layer was observed in powder annealed above the decomposition temperature, and the grown region was confirmed to be an iron phase.
  • Evaluation of the Microstructural Contribution to the Coercivity of Fine-Grained Nd–Fe–B Sintered Magnets

    pp. 1967-1971

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    DOI:10.2320/matertrans.MAW201207

    The relationship between coercivity and the microstructural parameters α and Neff for grain refined Nd–Fe–B sintered magnets was examined. The parameter α describes the effect of grain misalignment and a decrease in the magnetocrystalline anisotropy of the Nd2Fe14B grains on the coercivity. The parameter Neff describes the influence of the demagnetizing field on the coercivity. These parameters were evaluated for Nd–Fe–B sintered magnets with three different grain sizes and the same composition. Neff decreased with grain refinement, while α varied only slightly with grain size. This implies that the decrease in the demagnetizing field increased the coercivity through grain refinement. Grain shape and asperity were then evaluated by the aspect ratio, angle of the grain to the direction of magnetization, and reverse circularity. Although the aspect ratio and angle of the grains were not related to the changes in Neff, variation of the average reverse circularity corresponded to the changes in Neff with grain refinement. Therefore, improving the asperity should increase the coercivity through grain refinement.
  • Electric Current-Induced Liquation Features of Cast Pure Tin

    pp. 1972-1975

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    DOI:10.2320/matertrans.M2012162

    Electric current-induced liquation feature of cast pure β-tin under alternating current (AC) was investigated in this study. According to the experimental results, the initial fusion emerges from grain interior. Since the fusion paths traverse the grain boundaries preferentially in a high-angle manner, their track inside a grain tends to be curved and thus longer than the grain size. Continued electrification leads fusion paths to form network-like interconnected fusion structure with most triple junctions residing within grain interior. Lateral thickening of the interconnected fusion paths leads to final failure. The result that the network-like fusion structure is rather equiaxed can eliminate the effect of crystal anisotropy on the fusion behavior if it exists.
  • Reduction in Lattice Thermal Conductivity of InSb by Formation of the ZnIn18GeSb20 Alloy

    pp. 1976-1980

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    DOI:10.2320/matertrans.M2012176

    InSb is known to be a good candidate as a thermoelectric (TE) material owing to its high carrier mobility and narrow band gap of around 0.18 eV. However, a high ZT value has not been achieved in InSb because of its high lattice thermal conductivity (κlat). In order to reduce the κlat of InSb, In3+ ions in InSb were partly replaced by Zn2+ and Ge4+ ions to form the ZnIn18GeSb20 alloy. Polycrystalline samples of ZnIn18GeSb20 were prepared by a powder metallurgy process combining mechanical alloying and hot pressing followed by water quenching or slow cooling. The TE properties of the quenched and slow-cooled samples were examined over the temperature range of room temperature to 723 K. The κlat values of the quenched and slow-cooled samples at room temperature were 2.70 and 2.83 W m−1 K−1, respectively. These values were approximately 6 times lower than that of InSb, presumably due to grain refinement through MA and effective alloy scattering from the multi-component system. The present study confirmed that the relatively large secondary phase would played an important role for the decreased the thermal conductivity in the Zn–In–Ge–Sb system unlike the AgPbmSbTem+2 (LAST-m) system, in which nano-sized Ag–Sb inclusion are embedded in the PbTe matrix.
  • Effect of Al Addition on Superelastic Properties of Aged Ti–Nb–Zr–Al Quaternary Alloys

    pp. 1981-1985

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    DOI:10.2320/matertrans.M2012184

    The effect of Al content on superelastic properties of Ti75−xNb15Zr10Alx (x = 0–6 at%) quaternary β Ti alloys were investigated. And the effects of baking for coating or plating on superelastic properties were also studied. The alloys containing 3 and 4 at% of Al clearly exhibited superelastic behavior after aging at 453 and 553 K, which are appropriate temperatures for industrial coating and plating, respectively. Ti72Nb15Zr10Al3 alloy exhibited the largest recovery strain of 2.5% due to superelastic behavior even after industrial coating and plating. In this quaternary alloy system, strange non-monotonical change of superelastic behavior as a function of Al content was also found.
  • Precipitation of Cerium Sulfate Converted from Cerium Oxide in Sulfuric Acid Solutions and the Conversion Kinetics

    pp. 1986-1991

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    DOI:10.2320/matertrans.M-M2012826

    The conversion of cerium (IV) oxide into cerium (IV) sulfate in sulfuric acid solutions was studied in a batch-type glass reactor under atmospheric pressure. The effects of agitation speed, acid concentration, reaction temperature, initial amount of cerium (IV) oxide per sulfuric acid solutions (C/S), and particle size on the conversion process were investigated. All experiments were carried out in the range of 8–14 mol/dm3 for sulfuric acid concentration, 105–135°C for reaction temperature, 0.04–0.28 mol/dm3 for C/S, and 2.5–112.5 µm for average particle size. The conversion process involves the dissolution of cerium (IV) oxide and the precipitation of cerium (IV) sulfate. Cerium (IV) oxide reacted with sulfuric acid very slowly and then dissolved cerium (IV) in a saturated condition directly formed cerium (IV) sulfate indicating that the conversion rate was controlled by the dissolution rate of cerium (IV) oxide. Increases in sulfuric acid concentration and reaction temperature increased the dissolution rate, whereas increase in particle size decreased it. However, the C/S had no effect on the dissolution rate. In terms of the yield of precipitated cerium (IV) sulfate after reaction equilibrium, increases in sulfuric acid concentration and C/S increased the yield. However, the particle size and the reaction temperature had no effect on the yield of precipitated cerium (IV) sulfate. The kinetics of cerium (IV) oxide dissolution, under various conditions of sulfuric acid concentration, reaction temperature, C/S, and particle size, was interpreted by a shrinking core model with chemical reaction. The variation of rate constant upon dissolution with temperature obeyed the Arrhenius equation with an activation energy of 123 kJ/mol.
  • Conversion Kinetics of Cerium Oxide into Sodium Cerium Sulfate in Na2SO4–H2SO4–H2O Solutions

    pp. 1992-1996

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    DOI:10.2320/matertrans.M-M2012827

    The conversion of cerium oxide (CeO2) into sodium cerium sulfate (NaCe(SO4)2·H2O) in Na2SO4–H2SO4–H2O solutions was studied at elevated temperatures using a batch-type glass reactor under atmospheric pressure. Sodium sulfate (Na2SO4) concentration, sulfuric acid (H2SO4) concentration and reaction temperature were chosen as dependent variables, and the effects of these three variables on the conversion of cerium oxide into sodium cerium sulfate in Na2SO4–H2SO4–H2O solutions were investigated. The conversion includes two chemical reactions: cerium oxide dissolution and sodium cerium sulfate synthesis. The experimental data showed that increases of sodium sulfate concentration and sulfuric acid concentration decreased the conversion rate, whereas the conversion rate increased with increasing reaction temperature. The conversion kinetics of cerium oxide into sodium cerium sulfate for these three variables was analyzed and the fitted equation to the experimental data was determined. The variations of rate constant in dissolution and synthesis with temperature obeyed the Arrhenius equation with activation energies of 120 and 200 kJ/mol, respectively. In addition, the rate constant of cerium oxide dissolution was a function of the sodium sulfate concentration and sulfuric acid concentration at N−0.3 and C6.5, respectively, and for sodium cerium oxide synthesis at N−0.2 and C−4.3.
  • Quantitative Evaluation of the Abrasion Rate in Attrition Washing on Lead Contaminated Soil from Shooting Ranges

    pp. 1997-2003

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    DOI:10.2320/matertrans.M2012240

    The effects of attrition on sandy and silty Pb-contaminated soil from shooting ranges were quantitatively investigated. The abrasion rate could be quantitatively evaluated using a population balance model from the size distribution of soil particles before and after attrition in an intensive mixer. The maximum abrasion rate was 0.047 µm/s in the first stage of attrition (1 min of grinding), and then declined between 2 and 4 min of grinding. The two samples had similar maximum abrasion rates, but the decline in the abrasion rate was larger in the silty soil, which would have a thinner soft layer on the surface of the soil particles, than the sandy soil. The incremental change in the mass fraction of Pb in the <20 µm particle size fraction increased proportionally with the abrasion thickness from the surface of the soil particles. Although the Japanese regulatory standard for the Pb concentration in soil (150 mg/kg) was not met for either sample, the Japanese regulatory standard for the concentration of leached Pb (0.01 mg/L) was met for silty soil after attrition. Sequential extraction using Tessier’s procedure for the >20 µm size fraction before and after attrition showed the attrition was more effective for the oxides or organic-bound species and carbonate species of Pb chemical forms.
  • Structural Modification of Chalcopyrite Ore for Enhanced Copper Recovery

    pp. 2004-2010

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    DOI:10.2320/matertrans.M2012128

    Malanjkhand copper project, Madhya Pradesh, India, generates a lot of lean sulphidic ores containing chalcopyrite (∼0.3% of copper) with traces of oxidized, semi-oxidized and secondary sulfides. EPMA analysis shows that the granitic rock samples have plagioclase feldspar, orthoclase feldspar and quartz as major constituents within which the ore minerals are sparsely distributed. Due to the complex structure and low solubility of the sulphide-bearing granitic rock, the dissolution of copper from the hard matrix is difficult. The present study deals with change in crystallographic and chemical nature of the mineral system present in the host rock. In an attempt to increase copper recovery, the ore was subjected to heating at 600°C under normal atmospheric conditions. This heat treatment resulted in enhanced copper recovery, up to 98% within 60 days of progressive leaching.
  • Characteristics of Resistance Spot Welding for 1 GPa Grade Twin Induced Plasticity Steel

    pp. 2011-2018

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    DOI:10.2320/matertrans.M2012167

    For the last few decades, formability and weldability of steels have been intensively investigated to increase the productivity and the safety in automotive companies. Recently, steel which has both high ductility and high tensile strength is required to reduce vehicle weight. Twin induced plasticity (TWIP) steel has high tensile strength as well as improved ductility and is applicable to automobiles. Since, TWIP steel is an austenitic alloy which contains high content of Mn, it would have different resistance spot welding characteristics comparing with dual phase (DP) steel. In this work, TWIP steel, the newly developed steel, was introduced. To identify the resistance spot welding characteristics of 1 GPa grade TWIP steel, the experiments for both DP and TWIP steels were conducted. Resistance and power signals were measured to analyze the welding characteristics. The suitable welding ranges were also obtained with the lobe diagrams for these steels. In order to analyze the weld, shear tension and hardness tests, and a microstructure analysis were conducted. Both steels show a different microstructure in base metal, heat affected zone, and nugget. Because of the different microstructures between the two steels, the two steels showed different hardness distribution and tensile shear strength in the weld. Also, the differences in dynamic resistance signal, welding power signal, and welding heat input are shown between the two steels. These distinctions in microstructure and welding process characteristics caused the difference in suitable welding range. As well, this study provides guidelines to the application of DP and TWIP steels in resistance spot welding for vehicle manufacturing process.
  • Investigation of Strain and Thin Film Relaxation in GexSi1−x/Si Strained-Layer Superlattice by Dark-Field Electron Holography

    pp. 2019-2022

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    DOI:10.2320/matertrans.M2012138

    Elastic strain plays an important role in modifying physical properties such as the mobility of charge carriers in semiconductors. Strain analyses reveal that the reduction of the total strain and the elastic strain could be as large as 30 and 65%, respectively in a very thin transmission electron microscopy (TEM) specimen. The strain and thin film relaxation in a cross-sectional transmission electron microscopy (XTEM) specimen of GeSi/Si strained-layer superlattice has been investigated by dark-field electron holography with a large holographic field of view (FOV) to 150 nm achieved by moving the specimen down below the front-focal plane of the objective lens in free lens control mode.
  • Optimization of Laser Processing in the Fabrication of Stents

    pp. 2023-2027

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    DOI:10.2320/matertrans.M2012188

    Stents are commonly inserted into coronary arteries for treating cardiovascular diseases. Nonetheless, the process of manufacturing metal stents is challenging owing to the geometric design, the optimization of machining methods and the materials involved. Fiber lasers were used as the laser cutting technology for cutting stents. The experiment revealed the importance of precise technical parameters, including the lens’ focal length, focus position, pulse frequency, cutting speed and pulse width. These parameters strongly influence the kerfs width and the quality of the cutting seam surface. Our results indicate that the width of the kerfs increases with an increase in the pulse frequency and pulse width, whereas it decreases or shows minimal change at higher cutting speeds. The surface roughness for stent laser cutting was Ra 43.5 nm, which essentially meets the design requirement for further performance evaluation. Finally, high-quality cutting of a 316LVM stainless steel vascular stent was achieved.
  • Creep Characterization in Advanced Heat-Resistant Steel Using Ultrasonic Nonlinearity Technique

    pp. 2028-2033

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    DOI:10.2320/matertrans.M2012146

    The creep of heat-resistant steel (12Cr–3.45W alloy) is experimentally characterized to estimate damages using a nonlinear ultrasonic technique. The finite amplitude method has been used to measure the ultrasonic nonlinearity parameter in all creep damaged specimens by through transmitted longitudinal wave. The microstructure showed significant changes in precipitate size and dislocation density during creep. The normalized ultrasonic nonlinearity decreases significantly in stage I and decreases monotonously in stage II and stage III. However, the ultrasonic nonlinearity increase due to the formation of creep voids in the vicinity of the creep failure region. The correlation between the microstructural changes and ultrasonic nonlinearity is discussed.
  • Recovery of Rhenium and Molybdenum from Molybdenite Roasting Dust Leaching Solution by Ion Exchange Resins

    pp. 2034-2037

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    DOI:10.2320/matertrans.M2012208

    Ion exchange separation of rhenium using Purolite A-170 and Purolite A-172 was carried out from the dust leach solution of molybdenite concentrate. Different parameters such as effect of contact time, equilibrium pH, and solid liquid ratio were investigated. The optimum absorption condition for Purolite A-172 resin was determined, and the absorption efficiency of Re and Mo were obtained to be about 90 and 0%, respectively. From results, it was evident that, the performance of Purolite A-172 resin was more effective than Purolite A-170 resin, towards the selective recovery of Re from the molybdenite dust leach solution.
  • Recovery of Molybdenum and Rhenium Using Selective Precipitation Method from Molybdenite Roasting Dust in Alkali Leaching Solution

    pp. 2038-2042

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    DOI:10.2320/matertrans.M2012209

    A study has been conducted for the separate recovery of molybdenum and rhenium from alkali leaching solution of molybdenite roasting dust by a selective precipitation method. Two kinds of synthetic alkali leaching solutions were employed and more than 85% of molybdenum was recovered as a precipitate in the experimental conditions of 243.15 K, pH 2.2, 200 rpm of agitation speed, 7,200 s of reaction time, and 1.5 of equivalence ratio between NH4OH and NaOH for NaOH leaching solution. Regarding NH4OH leaching solution, the optimal conditions for the formation of molybdenum precipitate were found to be 243.15 K, pH 2.5, 100 rpm of agitation speed, and 18,000 s of reaction time. The precipitation efficiency of molybdenum was higher than 99% in these conditions and molybdenum was observed to be precipitated as ammonium molybdate. Contrary to the precipitating behavior of molybdenum, rhenium was precipitated very little in the given conditions, which suggested a possibility for the selective recovery of molybdenum and rhenium.
  • Effect of Flame Spray Distance on the Adhesive Characteristics of Ni–20 mass%Cr Layers on SCM415 Substrates

    pp. 2043-2048

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    DOI:10.2320/matertrans.M2012217

    In this work, experimental results on the morphology and adhesive characteristics of flame-sprayed Ni–20 mass%Cr coating layers deposited on preheated SCM415 surfaces are presented. The flame spray distance was varied from 100 to 200 mm so as to investigate the change in the adhesive strength of the deposited layers. Commercially available Ni–20 mass%Cr particles with a mean diameter of 45 µm were employed in the experiments, and computational fluid dynamics (CFD) simulations using a commercial code (FLUENT) were conducted so as to estimate the temperature and velocity distributions of continuous and discrete phases before impact on the substrate. From FE-SEM images of the deposited layers, it was observed that, as the flame spray distance decreased, the metal particle morphology exhibited a splash-like pattern and a short, stretched shape. Such morphological characteristics were induced by the higher particle momentum associated with very high gas velocities. In addition, as the flame spray distance decreased, the adhesive strength between the deposited layer and the substrate increased due to the stronger momentum of the molten metal particles.
  • The Effects of Crystallization on Mechanical Mechanism and Residual Stress of Sputtered Ag Thin Films

    pp. 2049-2055

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    DOI:10.2320/matertrans.M2012199

    Silver film is widely used in optoelectronic and semiconductor industries, but its stress problem has not been verified. Sputtered Ag films of different thicknesses were used to investigate the effect of the crystallization on their solidification residual stress and electrical properties. From XRD data (2θ > 90°), an increase the thickness of the Ag film from 30 to 400 nm, not only raised the index of crystallization, but also obtained a lower resistivity. However, the peak (331) had a dissolution tendency due to the residual stress. The grain size of Ag films with greater thickness had grown because of the longer sputtering duration. Due to variations in the crystallized texture, the 30 and 110 nm films showed no sign of elasticity under nano-indentation testing. Under low-energy XRD (30 kV-20 µA), the 30 nm film not only had more residual stress, but also formed a new plane of diffraction at 104.2° of 2θ and the actual compressive stress value was 14.94 MPa. After an electrical current induced crystallization (EIC) test, the resistivity and residual stress of Ag film were improved.
  • Synthesis and Characterization of Iron Oxide Nanoparticles Prepared by Electrical Explosion of Fe Wire in Ar–O2 Gas Mixtures

    pp. 2056-2059

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    DOI:10.2320/matertrans.M2012186

    Iron oxide nanoparticles were prepared using a wire explosion method. Pure Fe wire was exploded in Ar–5%O2, Ar–10%O2 and Ar–30%O2 gas mixtures. The variation in the oxygen partial pressure in the explosion chamber resulted in a full spectrum of iron oxide nanoparticles, the sizes of which ranged from 10 to 200 nm. The phases in the explosion products were augmented in the order FeO → magnetite (Fe3O4) → maghemite (γ-Fe2O3) → hematite (α-Fe2O3) as the oxygen partial pressure was increased. Among the oxide phases, magnetite (Fe3O4) and maghemite (γ-Fe2O3) were the major phases, and the identification and relative quantification of both phases was possible through a step-scan and peak deconvolution routine. The presence of the magnetite-maghemite phase mixture was also substantiated by a field-emission transmission electron microscopy (FE-TEM) study on individual particles. The average particle size and phase ratio (maghemite/magnetite) decreased with increasing oxygen partial pressure.
  • Strength Anisotropy of NITE-SiC/SiC Composite by Various Failure Modes

    pp. 2060-2063

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    DOI:10.2320/matertrans.M2012182

    SiC/SiC composite is a candidate material for demonstration fusion power reactor (DEMO). To identify the inherent anisotropy of composites, it requires predicting axial/off-axial mechanical properties by various failure modes. This study evaluated failure behavior of SiC/SiC composites by various mode tests such as tensile, Inter-laminar shear and Trans-thickness tensile modes. To provide strength anisotropy maps and discussed a method to predict this trend analytically. The identification of various fabric orientations from strength anisotropy maps clearly indicate that the composites failed by the mixed modes. The strength anisotropy can be described satisfactorily.
  • Microstructure and Damping Capacity of Mg2Si/Mg–Al–Si–(Bi) Composites

    pp. 2064-2066

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    DOI:10.2320/matertrans.M2012255

    Influences of Bi addition on microstructures and damping capacities of Mg2Si/Mg–Al–Si–(Bi) composites have been investigated. The Bi addition is beneficial to modify Mg2Si phase from coarse Chinese script shape to fine polygonal shape. Even though the Bi-containing alloy has modified polygonal Mg2Si compounds, its damping capacity shows similar level with that of the Bi-free alloy. This would be attributed to the increased solute concentration related to high solubility of Bi in Mg, which eventually offsets the damping increment in response to Mg2Si modification.

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