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

MATERIALS TRANSACTIONS Vol. 51 (2010), No. 4

  • Comments Concerning Some Features of Phase Diagrams and Phase Transformations

    pp. 583-596

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    DOI:10.2320/matertrans.M2010012

    Several interesting features in the study of stabilities of phases, and in phase transformations, are discussed. It is proposed that symmetry considerations related to the presence of magnetism in iron suggests that the respective phases, BCC alpha and FCC gamma, have in fact lower symmetries than cubic. A proposal is made that the symbol beta used in the past for the designation of the paramagnetic BCC iron should perhaps be returned as a feature in phase diagrams. The importance of the new concept of a ‘pseudogap’ in the electronic band structure, as a stabilizing electronic feature, is discussed in the light of the Hume-Rothery electron concentration rule. It is proposed that since the thermal activation is a major feature in the behavior of isothermal martensites, a more suitable designation for these types of phase transformations might be “thermally activated martensites”, or TAMs. Massive transformations are discussed briefly and it is emphasized that they present a specific example of an idiomorphic transformation process, not requiring the need for orientation relationships (ORs) between the parent and product phases.
  • Relationship between ⟨111⟩ Rotation Recrystallization Mechanism and Slip Bands with Compressive Strains during Tensile Deformation in Aluminum Single Crystals

    pp. 597-606

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    DOI:10.2320/matertrans.MG200905

    The ⟨111⟩ rotation recrystallization mechanism, that is the slip band intersection model, presents that a ⟨111⟩ rotation recrystallization nucleus is formed in an intersection part of two kinds of slip bands. The nucleus is obtained by the rotation of the deformed matrix around ⟨111⟩ axis normal to the common cross slip plane of these slip systems. Eight kinds of nuclei are composed of four ⟨111⟩ axes with clockwise and counterclockwise rotations. For these formations in tensile deformation, the operation of slip bands with compressive strain plays an important role. So the operation of twenty-four slip systems including plus and minus directions should be estimated. In tensile deformation, the recrystallization nuclei of ⟨001⟩, ⟨112⟩, ⟨111⟩, and Schmid factor m=0.5 with kink bands in aluminum single crystals have been estimated and compared with the experimental results, and good relations have been found between them in terms of the selection of kinds of nuclei and their frequency.
  • Characteristics of Strain-Induced Boundary Migration as Evaluated by the Crystal Rotation Axis Method in (001) [100] and (112) [11\\bar1] Aluminum Bicrystal Deformed by Plane-Strain Compression

    pp. 607-613

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    DOI:10.2320/matertrans.L-MG200952

    An aluminum bicrystal with (001) [100] and (112) [11\\bar1] orientation was deformed by plain-strain compression to a strain of 0.34. The types of slip systems responsible for producing crystal rotations relative to the initial orientations were clarified by the crystal rotation axis method. In the (001) [100] crystal, an affected zone developed along the grain boundary, which revealed a variety of slip systems in operation; the operation of some of these systems could be predicted from the Schmid factor while that of the remaining systems could not. The unpredictable slip systems were activated by the formation of cross slips. After annealing at 400°C for 30 s, recrystallization that occurred was characterized by strain-induced boundary migration. The recrystallized area had the same crystal orientation as that of the affected zone of the (001) [100] crystal. By using the crystal rotation axis method, it was determined that the affected zone was the origin of the strain-induced boundary migration.
  • Influence of Crystal Orientations on the Bendability of an Al-Mg-Si Alloy

    pp. 614-619

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    DOI:10.2320/matertrans.L-MG200951

    Aluminum alloy sheets are being increasingly used to reduce the weight of an automotive body. Al-Mg-Si alloys have been used because they have favorable properties for automotive bodies. One of the important requirements of these alloys is the ability to resist fracture while bending. In this study, the influence of crystal orientations on the bendability of an Al-Mg-Si alloy is investigated using single-crystal specimens from the viewpoint of the shear band formation. The bendability and the formation of shear bands are clearly dependent on the crystal orientation, and ⟨001⟩||ND-oriented specimens exhibit the highest bendability. The formation of denser shear bands is observed with a decrease in bendability. The shear bands behaved as the origin of the cracks and the propagation path. It is concluded that the inhibition of the formation of shear bands by controlling the orientations is very important to improve the bendability. Moreover, there exists a relation between the Taylor factor and the bendability because the bendability tended to decrease with an increase in the Taylor factor.
  • Deformation Microstructure and Texture in a Cold-Rolled Austenitic Steel with Low Stacking-Fault Energy

    pp. 620-624

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    DOI:10.2320/matertrans.MG200901

    Deformation microstructure and texture in a cold-rolled austenitic steel 310S with low stacking fault energy (SFE) have been investigated by SEM and TEM. When 310S plates were rolled by 95% in thickness reduction, a remarkable development of the brass-type preferred orientation was confirmed by X-ray diffraction. SEM observations of the specimens with such texture exhibited a layered structure developed parallel to the rolling plane. TEM images demonstrated the inhomogeneity of highly deformed polycrystalline low SFE fcc metals. Dominant microstructure in 95% cold-rolled specimens is fine-grained structure caused by deformation twin and shear band formation (area (I)), but there exists small amount of areas without twin (area (II)). Dominant texture is the {110}⟨112⟩ brass-type in both areas (I) and (II), although {111}⟨112⟩ (twin-matrix lamellae), {110}⟨001⟩ (Goss), {112}⟨111⟩ (copper-type) are also observed in the area (I).
  • Influence of Microalloying Elements on Recrystallization Texture of Warm-Rolled Interstitial Free Steels

    pp. 625-634

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    DOI:10.2320/matertrans.MG200909

    The addition of microalloying elements such as Ti and Nb to increase the strength of deep drawing quality steels for automotive sheet products might affect the microstructure formed during the annealing after warm rolling in several ways. Firstly, the precipitates can exert a Zener’s pinning on growing recrystallized grain, which leads to a sluggish recrystallization kinetics. Secondly, the amount of microalloying elements control the amount of C, N, S, and P in solid solution, which indirectly affects the recrystallization texture obtained after annealing. In this sense, the work carried out with three different interstitial free (IF) and interstitial free high-strength (IFHS) steel grades allows us to conclude that the increase of microalloying additions delays recrystallization kinetics. Moreover, the abrupt texture change observed between as-rolled and annealed material indicates that the nucleation mechanism for recrystallization is more related to classical nucleation at deformed grain boundaries than subgrain rotation (continuous nucleation).
  • Effect of Microstructure before Cold Rolling on Texture and Formability of Duplex Stainless Steel Sheet

    pp. 635-643

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    DOI:10.2320/matertrans.MG200907

    The evolution of the microstructure and texture of type 329J4L duplex stainless steel (DSS) sheet during cold rolling and annealing were examined, and the effect of the initial microstructure before cold rolling on texture and formability was investigated. The texture of the α phase in the hot-rolled and annealed sheet had a strong α-fiber texture, and this was stable even in cold-rolled and annealed sheet. However, in the case of a coarse α grain caused by high-temperature annealing prior to cold rolling, the α-fiber texture and colony with ⟨100⟩||ND orientation in the α phase were reduced in cold-rolled and annealed sheet. This control of the α-fiber texture in the α phase in cold-rolled and annealed sheet improved the elongation, r-value, and ridging characteristics. These results showed that the texture and the formability of type 329J4L DSS cold-rolled and annealed sheet depended on the texture of the α phase and the initial α phase morphology before cold rolling.
  • Texture and Planar Anisotropy of r-Value in Duplex Stainless Steel Sheet

    pp. 644-651

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    DOI:10.2320/matertrans.MG200908

    The effect of cold-rolling reduction on texture and planar anisotropy of the r-value was investigated in type 329J4L duplex stainless steel (DSS) sheet, which has a two-phase ferrite (α) and austenite (γ) microstructure. In addition, the possibility of predicting the planar anisotropy of the r-value on the basis of the Taylor theory was investigated in consideration of the texture gradient through the thickness. An increase in cold-rolling reduction resulted in the improved average r-value and the strong directionality with a maximum value at the diagonal direction. The α phase had an extremely strong αbcc-fiber texture and the γ phase had β- and αfcc-fiber textures. The texture gradient in the thickness direction was more remarkable in the α phase than in the γ phase. The r-values calculated from the overall texture of the α phase using the relaxed constraints model with two relaxed shear strain constraints e13, e23 and a CRSS ratio of 1.1 for {112} and {011}⟨111⟩ glide systems were in quite good agreement with the experimental r-values. This suggested that slip deformation in the α matrix was dominant for type 329J4L DSS sheet. However, the difference between the experimental and calculated results was remarkable in the vicinity of the diagonal direction.
  • Crystallographic Texture Development and Its Effect on Corrosion Behavior of Pilgered Zirconium Alloy Tubes

    pp. 652-658

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    DOI:10.2320/matertrans.MG200911

    Crystallographic texture and corrosion of zirconium alloy tube with pilgering were studied. Average grain size of the cross-sectional surface of the tube was changed from 28 μm to 11 μm by 1st pilgering, and to 8 μm by 2nd pilgering. Aspect ratios of the elongated grains on longitudinal surface of as-received, 1st and 2nd pilgered tubes are 1, 6 and 12, respectively. Micro-hardnesses of the tubes are 172, 218 and 246 Hv for their cross sectional surfaces and 180, 233 and 252 Hv for their longitudinal surfaces, respectively. Pilgering results in increasing the (0001) basal and {10\\bar10} prismatic pole densities to TD (tangential direction) split type and AD (axial direction) concentration type, respectively. A preferred orientation is mainly formed by 1st pilgering. Further pilgering produces a texture of (\\bar12\\bar14)[10\\bar10] with a significant spread around [10\\bar10] parallel to AD. Corrosion potential and corrosion rate of the zirconium alloy tubes in dearated aqueous 5% NaCl solution (pH=6.3) at 20°C are in the range of −0.552∼−0.767 VSHE and 1.88×10−7∼12.02×10−7 A/cm2, respectively. Crystallographic anisotropy influences corrosion behavior of the zirconium alloy tubes. Pilgering results in reducing corrosion potential and increasing corrosion rate due to grain size refinement and increased dislocation density rather than crystallographic texture.
  • Electron Backscatter Diffraction Characterization of Microstructure Evolution of Electroplated Copper Film

    pp. 659-663

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    DOI:10.2320/matertrans.MG200910

    The microstructure evolution of electroplated copper films was characterized by electron backscatter diffraction (EBSD). Special care was taken during the preparation of the cross-sectional specimens and microstructure analysis to obtain reliable results. The film exhibited a columnar grain structure with a large fraction of twin boundaries. Annealing induced normal grain growth and caused many of the general high-angle grain boundaries to be replaced by twin boundaries, possibly by annealing twinning.
  • Molecular Dynamics Simulation of Grain Growth of Cu Film —Effects of Adhesion Strength between Substrate and Cu Atoms—

    pp. 664-669

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    DOI:10.2320/matertrans.MG200903

    The growth process of Cu polycrystal films on Si, Ti, W and Ru substrate during isothermal annealing was studied by the molecular dynamics method. We focused on the influence of the adhesion strength between substrate and Cu on crystallinity and orientational order of the film. After structural relaxation at low temperature (50 K), the movements of individual Cu atoms were calculated for different annealing temperatures using the molecular dynamics method. The crystallinity and orientational order of the film were examined by 2D-Fourier transformation of the atomic structure. We found that the system with strong adhesion strength between substrate and Cu showed higher crystallinity and orientational order for (111) oriented Cu film.
  • Irradiation Induced Localized Amorphization in Mo-Re Alloy Films

    pp. 670-674

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    DOI:10.2320/matertrans.M2009306

    To investigate the irradiation properties of Mo-Re alloy of low Re content (atm%: 0%∼8.4%), Mo-Re alloy films were irradiated by 200 keV xenon ions at the dose of 5×1015 ions/cm2. Different irradiation effects were observed on the samples of different Re content. While the sample of pure Mo remained the same after irradiation, obvious localized amorphization phenomenon took place in the sample with Re content of 8.4%. So it is possible that Mo-Re alloy with low Re content might break down for the irradiation induced amorphization process. The formation mechanism of amorphous regions was then discussed by irradiation experiments at ion dose from 1×1015 to 5×1015 ions/cm2, by which the amorphization process developing from lattice damages to amorphous clusters, and finally to amorphous regions, was connected with the increase of irradiation dose step by step.
  • Diagnostic Structures for Interatomic Potentials

    pp. 675-678

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    DOI:10.2320/matertrans.M2009418

    We design special structures for testing interatomic potentials. These are highly symmetric structures for which the simple mathematical forms of interatomic potentials result in artificial relations between atomic force components. Here, pair-potentials and embedded-atom method (EAM) potentials are considered and we quantify the extent to which these relations are violated by ab-initio calculations. From such analysis we deduce more generally the suitability of using such potentials to reproduce atomic forces and hence their suitability in describing atomic dynamics.
  • Two-Stage Martensitic Transformation in Thermal-Cycled Ti40.5Ni49.5Hf10 Shape Memory Alloy

    pp. 679-684

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    DOI:10.2320/matertrans.M2009235

    Thermal-cycled Ti40.5Ni49.5Hf10 alloy exhibits B2↔B19′ martensitic transformation and two DSC transformation peaks appear after 10 thermal cycles. Transformation temperatures rapidly decrease during the early cycles. XRD tests reveal that both transformation peaks are associated with B2↔B19′ transformation. TEM observations indicate that as-homogenized B19′ martensite mainly consists of internal ⟨011⟩M type II twins. However, they are gradually replaced by internal (001)M compound twins with increasing the thermal cycles. This feature accounts for these two transformation peaks are associated with B2↔B19′ transformation with two different internal twinning modes. The microstructural evolution of B19′ martensite is ascribed to the dislocations induced by thermal-cycling as they can promote the formation of thin internal (001)M compound twins.
  • Springback Characteristics of Magnesium Alloy Sheet AZ31B in Draw-Bending

    pp. 685-693

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    DOI:10.2320/matertrans.P-M2010803

    In this study, we carried out a two-dimensional draw-bending test on an AZ31B magnesium alloy sheet at various forming temperatures and blank holding forces, and the springback characteristics of the Mg alloy sheet were systematically examined. The amount of springback decreased with increasing temperature and blank holding force. The decrease in the amount of springback caused by the increase in temperature was much larger than that caused by the increase in blank holding force, which indicated that increasing temperature was much more effective for decreasing the amount of springback than increasing blank holding force. The amount of springback became negligible at 200°C and above. This result was attributable to the following factors: (a) flow stress decreased rapidly as temperature increased, (b) reverse bending on the sidewall arose at 150°C and above, and (c) fine grains due to dynamic recrystallization were formed at 200°C and above. Microstructure evolution during the draw-bending test was also observed with particular focus on twinning, and its effects on springback characteristics were studied in detail.
  • Influence of Surface Treatments on Fatigue Strength of Ti6Al4V Alloy

    pp. 694-698

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    DOI:10.2320/matertrans.MA200901

    Titanium alloys do not exhibit good seizure toughness. In general, a surface treatment must be applied if the component is subjected to sliding contact. For surface hardening, it is well known that oxygen and nitrogen treatments can be used because they are easily available, inexpensive elements. However, these treatments cause the fatigue strength to decrease which is a problem.
    The reason for the fatigue strength decrease due to oxygen diffusion treatment is residual tensile stress on the surface. Shot peening is an effective technique to improve the fatigue strength of oxygen diffusion treated titanium. This report details the effects on fatigue strength due to surface treatments such as notch and shot peening.
  • Tensile Deformation and Failure Behavior of Open Cell Nickel and Copper Foams

    pp. 699-706

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    DOI:10.2320/matertrans.M2009383

    Tensile deformation and failure behavior at room temperature of the open cell nickel and copper foams with high porosity (≈96%) fabricated with the slurry foaming process at Mitsubishi Materials Corporation, Japan, was studied. In-situ observation of the deformation and failure behavior was conducted with a digital microscope. Stress-strain curves were measured, in which a non-contact extensometer was employed to detect the strain of the samples accurately. Electric resistance was measured to monitor the damage evolution. Finite element stress analysis was conducted to calculate the morphological change of cells with applied strain and the stress distribution in cells. It was revealed that the deformation and failure progressed through the following four stages; stage I characterized by the elastic deformation, stage II by plastic deformation, stage III by the co-occurrence of plastic deformation and cumulative failure of struts and stage IV by the chain reaction of strut failure nearly in a limited cross-section, respectively. Also it was found that the distribution of failure strain of struts in stage III, measured from the serrations in the stress-strain curve, could be described by the Weibull distribution, with which the transition from stage II to III was identified. Also, the result of the statistical analysis suggested that the average failure strain of the struts in the foam is much higher than the strain at ultimate stress of the foam.
  • Order-Disorder Transformation in Fe50Co50 Particles Synthesized by Polyol Process

    pp. 707-711

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    DOI:10.2320/matertrans.M2009251

    X-ray diffraction applied anomalous dispersion effect was used for characterizing the order-disorder transformation in Fe50Co50 fine particles synthesized by polyol process. The long range order parameter was estimated from the superlattice peak intensities in the diffraction pattern of particles annealed in the temperature range between 20 and 800°C. The results showed that fine particles of as-synthesized Fe-Co have a disordered structure at room temperature, while the ordered structure is present, to a great extent, in Fe-Co bulk alloys. The fine particles of the disordered alloy were transformed to the ordered state by annealing up to about 450°C. The magnetic properties of the Fe-Co alloy fine particles annealed at different temperatures were also investigated using a vibrating sample magnetometer, in which magnetic fields of up to 15 kOe were applied to samples at room temperature. The saturation magnetization of the as-synthesized particles increased with annealing temperature. This may be attributed to transformation from disordered to ordered structure, along with sintering.
  • Electrodeposition of Sn–Ag Alloys and Evaluation of Connection Reliability for Automotive Connectors

    pp. 712-719

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    DOI:10.2320/matertrans.M2009425

    Electrodeposition behavior of Sn–Ag alloys was investigated at current density 1–1000 A·m−2 in both sulfate and pyrophosphate-iodide solutions at 298 K, and the contact resistance of Sn–Ag alloys deposited on a Cu connector was evaluated. In both solutions, Ag behaved as a more noble metal than Sn, showing regular codeposition. The difference in deposition potential between Ag and Sn was 0.4 V in the pyrophosphate-iodide solution and 0.2 V in a sulfate solution containing thiourea as a complexing agent for Ag+ ions. The deposits obtained from a pyrophosphate-iodide solution consisted of blocks of a few microns in size, while those from a sulfate solution exhibited grains smaller than 1 μm. The deposits containing Ag less than 45 mass% were composed of an Ag3Sn intermetallic compound and Sn. This is in accordance with the equilibrium phase diagram of the binary Ag–Sn system. The contact resistance of deposited Sn–Ag alloys, after heating at 433 K for 120 h, was slightly smaller at Ag content below 45 mass% than that of reflow Sn plating. The connection reliability of connectors after abrasion was better in deposited films of Sn–Ag alloys than in those with reflow Sn plating.
  • Formation of Ni Aluminide Containing Hf by Simultaneous Electrodeposition of Al and Hf and Cyclic-Oxidation Resistance

    pp. 720-726

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    DOI:10.2320/matertrans.M2009323

    A Ni aluminide layer containing Hf was formed on a Ni specimen by the simultaneous electrodeposition of Al and Hf using a molten-salt bath. Al and Hf were only slightly electrodeposited and an electrodeposited layer was not formed when the simultaneous electrodeposition of Al and Hf was tried using molten NaCl-KCl containing 3.5 mol%AlF3 and 3.5 mol%HfF4. On the other hand, an electrodeposited layer consisting of Ni2Al3 and NiAl3 layers, for which the Al3Hf particles were formed on the surface region, was formed, when the simultaneous electrodeposition of Al and Hf was carried out using the molten NaCl-KCl containing 3.5 mol% AlF3 and 0.05 mol% HfF4. The cyclic-oxidation resistance of the Ni specimens covered by the Ni aluminide layer containing the Al3Hf particles was evaluated in air at 1423 K. The sample covered with the Ni aluminide containing the Al3Hf particles, which was formed using the melt containing 3.5 mol%AlF3 and 0.05 mol%HfF4, showed a high cyclic-oxidation resistance. On this sample after the oxidation test, an adhesive scale having a spiked shape, which consisted of Al2O3 as the outer layer and HfO2 as the inner layer, was formed.
  • Kinetics of Methane Hydrate Formation Catalyzed by Iron Oxide and Carbon under Intense Stirring Conditions

    pp. 727-734

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    DOI:10.2320/matertrans.M2009369

    As an active surface can be a nucleation site for some reactions, the possibility of iron and carbon acting as a catalyst for methane hydrate formation has been examined in the previous study. If iron oxide and carbon can be used as a catalyst, they would have a low environmental influence and a relatively low cost. It has previously been shown that carbon and iron oxide can be used as a catalyst under weak stirring conditions. In the present study, experiments involving intense stirring were conducted for the establishment of the basis for a high production system.
    The proposed reaction model consisted of the mass transfers of CH4 in the liquid films both at the gas-liquid and the liquid-solid interfaces and the diffusion in liquid water, and a chemical reaction at the liquid-solid interface. The kinetic analysis was performed using the model and the following results were obtained.
    The reaction was a mixed control between the mass transfer and the chemical reaction at 277 K, which was closed to the maximum temperature of methane hydrate formation thermodynamically. While in the lower temperature region lower than 275 K, the mass transfer including the diffusion of CH4 and the apparent mass transfers in the liquid films, ks′ was dominant.
    The addition of catalysts (hematite, graphite and its mixture) had acceleration effects on hydrate formation, but to varying degrees. The catalyst “Mix” (mixture of hematite and graphite) had the largest effect on hydrate formation over the whole stirring range. From the results of kinetic analysis, the existence of catalyst had a relatively large influence on the chemical reaction of the formation of methane hydrate.
  • Properties of Cold Work Tool Steel Shot Peened by 1200 HV-Class Fe-Cr-B Gas Atomized Powder as Shot Peening Media

    pp. 735-739

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    DOI:10.2320/matertrans.MBW200922

    Shot peening is widely used for automobile parts such as springs and gears to improve fatigue strength. In general, high hardness media is required for shot peening to targets with high hardness. Recently, shot peening to various tool steels such as cold and hot tool steels and high speed tool steel has been investigated and is used in some applications, and improvements in fatigue strength and die life by the increase of compressive residual stress and hardness at their shot peened surface have been reported.
    In this study, the properties of cold work tool steel shot peened by Fe-8%Cr-6.5%B (mass%) gas atomized powder (FeCrB powder) with 1200 HV-class Vickers hardness and long life as shot peening media were examined. Quenched and tempered JIS-SKD11 followed by shot peening by FeCrB and high speed steel powder sieved between 45 and 125 μm was used.
    Vickers hardness and compressive residual stress of the shot peened JIS-SKD11 surface by FeCrB powder were higher than these by high speed steel powder. As a result, JIS-SKD11 shot peened by FeCrB powder showed excellent fatigue property, Charpy impact value and wear resistance property.
  • Alloy Design of Ti Alloys Using Ubiquitous Alloying Elements and Characteristics of Their Levitation-Melted Alloys

    pp. 740-748

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    DOI:10.2320/matertrans.F-M2010801

    The α+β type Ti-5.5Al-2Fe and β type Ti-2.5Fe-2Mn-2Zr alloys have been theoretically designed, for the modification of Ti-6Al-4V and the achievement of the high tensile strength more than 1000 MPa at the solution treatment state, respectively, using ubiquitous alloying elements in order to establish the strategic method for suppressing utilization of rare metals. The utilization of the cold crucible levitation melting (CCLM) is very useful for the production of ingots, because titanium is very chemically reactive at high temperature. The experimental alloys with high purity and without contaminations from a crucible were prepared, and the homogeneous melt was also achieved by the diffusion mixing effect of CCLM. The microstructure, phase stability, strength, corrosion-resistance and workable properties of the design Ti-5.5Al-2Fe alloy, were comparable to those of Ti-6Al-4V. In contrast, the solution heat treated Ti-2.5Fe-2Mn-2Zr alloy showed the tensile strength of 1200 MPa, and the 1.3 times increase in the specific strength compared with Ti-15Mo-5Zr-3Al. The alloy design can be successfully carried out even using ubiquitous alloying elements by the d-electrons concept, which leads to the establishment of one method for the strategic utilization of rare metals.
  • Texture Randomization of AZ31 Magnesium Alloy Sheets for Improving the Cold Formability by a Combination of Rolling and High-Temperature Annealing

    pp. 749-755

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    DOI:10.2320/matertrans.L-M2010802

    To improve the cold formability of AZ31 magnesium alloy sheets, we investigate texture control by rolling and annealing. The texture ideal for forming close to random orientation was obtained by annealing at 773 K before and after isothermal rolling at 298–573 K. For the randomizing process, such a high temperature in pre-annealing was essential, whereas a slightly lower temperature was acceptable for final annealing, assuming a sufficiently long annealing time. The randomized sheet could be obtained in a wide range of rolling temperatures and reductions. It could also be produced easily with a standard mill without roll heating. The microstructure of the randomized sheet consisted of relatively homogeneous grains 25–30 μm large on average. In a 90 degree V-bending test, a well randomized sheet could be bent without cracking with a minimum bending radius per thickness Rt=1.4, which was about half of that in commercial AZ31D-O sheets, in spite of manganese content of over 0.6%.
  • Aluminum-4 mass%Copper/Alumina Composites Produced from Aluminum Copper and Rice Husk Ash Silica Powders by Powder Forging

    pp. 756-761

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    DOI:10.2320/matertrans.M2009429

    This research demonstrated simple but effective process to produce Al-4 mass%Cu/Al2O3 composites, by powder metallurgy method. The starting powders were aluminum, copper, and rice husk ash silica. Processing was by sintering at 650°C for 3.6 ks, hot forging of sintered billet at 600°C under 660 MPa pressure, followed by heat treatment. Hot forging of sintered billet induced plastic deformation of the matrix as well as fractured the porous silica, thus created ultimate contact between the two phases. The following heat treatment produced alumina, which was the reinforcement phase, by chemical reaction between fractured rice husk ash silica and aluminum matrix. The fabricated composite contained γ- and κ-alumina, and elemental silicon in matrix of aluminum solid solution. Addition of copper facilitated sintering by formation of liquid phase, as well as yielding a matrix material which can be strengthened by precipitation hardening. Maximum hardness obtained was 44 HRA, for composite material using 15 vol% rice hush ash silica. Peak hardness of the matrix was in range of 130–136 HV, after aging for 28.8 to 43.2 ks.
  • Corrosion Resistance of Dental Ti-Ag Alloys in NaCl Solution

    pp. 762-766

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    DOI:10.2320/matertrans.M2009355

    The purpose of this study was to evaluate the corrosion resistance of experimental dental Ti-Ag alloys in 0.9% NaCl solution. Open-circuit potential (OCP) measurement and elution tests of the alloys with 5–30% Ag were performed. The amounts of both Ti and Ag ions released from the alloys with Ag≤20% were below the detection limit. A very small amount of Ti ions was released from some of the 22.5% Ag specimens and some of the 25% Ag specimens. The time for the Ti-Ag alloys with 5–25% Ag to become the stable potential was earlier than that for titanium, and the OCP of the alloys was higher than that of titanium. These results indicated that the corrosion resistance of the alloys with 5–25% Ag was equivalent to that of titanium. On the other hand, it was suggested that the precipitation of TiAg deteriorated the corrosion resistance of Ti-Ag alloys because TiAg dissolved preferentially in the NaCl solution. Ti-Ag alloys with 5–25% Ag can be used not only as dental restorative materials but also as dental implant materials.
  • Room Temperature Thermoelectric Properties of Epitaxially Grown Si-Ge Thin Films on SOI Substrates

    pp. 767-770

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    DOI:10.2320/matertrans.M2009318

    Thermoelectric properties of epitaxially grown SiGe based thin films prepared by ion beam sputtering technique were investigated. Although carrier concentration was considered to be the highest in B doped SiGe sample, it showed the highest thermoelectric power of ∼1 mVK−1 corresponding to the three times larger value than bulk SiGe. On the other hand, the electrical resistivity decreased by increasing the growth temperature due to the impurity activation and crystallization. As a result, SiGeB epitaxial films prepared at growth temperatures of more than 773 K showed twice larger power factor than bulk SiGe at 300 K. Moreover, the thermoelectric power was found to decrease and resistivity to increase in the polycrystalline phase, concluding that the improvement of thermoelectric performances was achieved by introducing the epitaxially grown phase.
  • Conductivity Percolation on a Square Lattice with Core-Shell Particles

    pp. 771-774

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    DOI:10.2320/matertrans.M2009329

    Particles made by coating an insulating core with a thin layer (shell) of conducting materials, called core-shell particles, are recently proposed to realize materials with particular nano-scale structures. Such structures work as a “porous media” of electric current, and its modified characteristics may be useful to improve some materials, for example the transparent conducting films.
    In this report, the basic feasibility of this idea is tested in the framework of the percolation model and the random register network model. The observed critical behavior and critical exponents of conductivity are also discussed, for the first time for 2D situations with core-shell particles.
  • Removal of Magnesium from Aluminum Scrap by Compound-Separation Method Using Shirasu as an Additive

    pp. 775-780

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    DOI:10.2320/matertrans.MBW200919

    The removal of magnesium from the molten aluminum scrap containing magnesium was examined by compound-separation method. As an additive, three types of Shirasu (a natural resource in South Kyushu, Japan) with different particle sizes were used. The addition of Shirasu to the molten aluminum scrap at 1023 K resulted in the formation of MgAl2O4 and MgO by the reactions among SiO2 and Al2O3 in Shirasu and magnesium in the molten scrap. It was feasible to remove magnesium by separating these reaction products as dross. Assuming that all the Shirasu reacted with magnesium in the molten scrap, the amount of removed magnesium, which was calculated from these reactions, was in agreement with the measured one. In the addition of flaky Shirasu with a small particle size, the amount of removed magnesium increased linearly with agitation time after Shirasu addition. This is because the over-all reaction is mainly controlled by a surface-controlled reaction. In the addition of granular Shirasu with a large particle size, the increase in magnesium removal was parabolic. This is because the over-all reaction is mainly by a diffusion-controlled reaction.
  • Reassessment of Liquid/Solid Equilibrium in Ni-Rich Side of Ni-Nb and Ni-Ti Systems

    pp. 781-786

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    DOI:10.2320/matertrans.M2009351

    The liquidus and solidus for the Ni-rich side of the Ni-Nb and Ni-Ti systems on a region of Ni-Nb and Ni-Ti systems of <10 mass% Nb or Ti were measured in order to establish the phase equilibria between the liquid and fcc phases. The thermodynamic parameters for both systems were reassessed based on the experimental data. The calculated liquidus and solidus agree well with the measured values of Ni-base superalloys as well as the present binary data.
  • Bonding Quality of Copper-Nickel Fine Clad Metal Prepared by Surface Activated Bonding

    pp. 787-792

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    DOI:10.2320/matertrans.M2009354

    The effects of surface roughness and heat treatment on the bonding quality of surface-activated bonding (SAB)-treated copper-nickel fine clad metals were investigated. An increase in the surface roughness of the copper layer decreased the peel strength after cladding, indicating that increases in the surface roughness decreased the contact area between the clad materials in the SAB cladding process, unlike conventional cold rolling that induces high deformation. In addition, the peel strength of the clad metals increased up to 7.3 N/mm with decreasing surface roughness of the copper layer after heat treatment. The change in the total sheet resistance of the copper-nickel clad metal with the heat treatment depended on the balance between a decrease in the sheet resistance due to the reduction of dislocation and the increase in the heat treatment temperature, and an increase in the sheet resistance due to the diffusion of nickel in the copper direction.
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  • In-Situ Transmission Electron Microscopy Investigation of the Interfacial Reaction between Er and SiO2 Films

    pp. 793-798

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    DOI:10.2320/matertrans.M2009371

    We fabricated metal-oxide-semiconductor (MOS) devices with a high-k Er-silicate gate dielectric, and demonstrated their electrical performance. The increase in the rapid thermal annealing (RTA) temperature leads to a reduction of the equivalent oxide thickness (EOT), which is attributed in par to the thickness evolution of Er-silicate film and to the chemical bonding change from an Si-rich to an Er-rich silicate. The in-situ investigation of the interfacial reaction between the Er and SiO2 film using a high-voltage electron microscopy (HVEM) revealed a linear relationship between the squared thickness of Er-silicate layer and in-situ annealing time, indicating that the Er-silicate growth is a diffusion-controlled process. The parabolic growth constants of the Er-silicate film were calculated to be 2.3×10−16 and 9.3×10−16 cm2/s for in-situ annealing temperatures of 350 and 450°C, respectively.
  • Effect of Carbon Addition on the Microstructural Evolution and Mechanical Properties in Hypo-Eutectic Fe-Zr(-Nb) Alloys

    pp. 799-802

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    DOI:10.2320/matertrans.M2009386

    The effect of carbon addition on the microstructure and mechanical properties of Fe-Zr and Fe-Zr-Nb ultrafine eutectic-dendrite composites has been investigated. Addition of carbon leads to the formation of iron solid solution strengthened by carbon interstitials and carbide particles encapsulated by α-Fe dendrites preferentially nucleated on the carbides. Consequently, the ultrafine eutectic Fe-5Zr-5Nb-0.3C (mass%) alloy exhibits high compressive strength (∼1.2 GPa) and large plastic strain (∼24%). The present study suggests another effective way to enhance the mechanical properties of Fe-based nano-eutectic alloys.
  • Ultrasonic Evaluation of the Quality of A356.2 Alloy by Fluxing Treatment

    pp. 803-809

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    DOI:10.2320/matertrans.M2009416

    Aluminum alloys are often contaminated with non-metallic inclusion particles that react easily with oxygen or moisture, oxidizing to form oxide films. These inclusions and oxides can lead to the formation of porosity as well as significantly reduce the corrosion resistance and mechanical properties of aluminum alloy castings. Fluxing treatment is one of the conventional methods for removing inclusions and oxides from the melt to enhance the quality of aluminum alloy castings.
    In this study, we use four covering fluxes in fluxing treatments and investigate the quality of A356.2 alloy. The percentage of porosity is an accepted way to quantitatively evaluate the quality of aluminum alloy castings. In this study, the relative porosity, as represented by the percentage of porosity in A356.2 alloy is evaluated. Nondestructive ultrasonic techniques are adopted to investigate the relative porosity of A356.2 alloy samples produced by the various flux treatments. The relationship between the relative porosity and ultrasonic characteristics, including the ultrasonic velocity and the attenuation coefficient, are determined and compared, and the pore formation and oxide film distribution in the alloy are also discussed.
  • Effects of Rhenium on Microstructure and Phase Stability of MAR-M247 Ni-Base Fine-Grain Superalloy

    pp. 810-817

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    DOI:10.2320/matertrans.M2009331

    The effects of Re additions on the microstructure and phase stability of the cast fine-grain Mar-M247 superalloy were investigated in this study. The results showed that the grain sizes of the alloys with 0, 3, and 4.5 mass% Re content were 90, 60, and 50 μm, respectively. The primary γ′ phase became finer and more cuboidal as Re content increased. The addition of 3 mass% Re caused strip-like MC carbides within the grain to degenerate into discontinuous M23C6 carbides and initiated the formation of a deleterious topological closed-packed (TCP) phase within the grain interior. The addition of 4.5 mass% Re promoted phase instabilities that led to the precipitation of large amounts of needle-like P phase in the grain interior, attributable to Re and W segregation. This study found that 3 mass% Re was a critical addition to maintain optimal microstructure and phase stability, and improved the ultimate tensile strength and the yield strength at room temperature and 760°C. However, the addition of 4.5 mass% Re obviously resulted in a decrease in tensile properties at room temperature and 760°C.
  • Enhancement of Stretch Formability at Room Temperature by Addition of Ca in Mg-Zn Alloy

    pp. 818-821

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    DOI:10.2320/matertrans.M2009385

    The stretch formability of a rolled Mg-1.5Zn-0.1Ca alloy sheet was investigated at room temperature. The Mg alloy showed a large Erichsen value of 8.2. This is due to a reduction in intensity of basal plane texture and a spreading of the basal poles towards the transverse direction. It is suggested that solid solution of Ca atoms into Mg plays a critical role in the unique texture formation. Activation of non-basal slips by dilute Ca addition was hypothesized to be related to the unique texture formation.
  • The Pressure-Assisted Master Sintering Surface of Metallic Powder Mixture

    pp. 822-825

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    DOI:10.2320/matertrans.M2009303

    The use of master sintering curve (MSC) is an effective method to predict densification during sintering or hot pressing. Empirical models of MSC in early studies were developed using a single kind of powder or a major powder with a little amount of sintering additives. For the present study, the powder mixture consisting of 6 different metallic materials was used to see whether the concept of MSC can be applicable to the hot pressing of metallic powder mixture. Three data sets having different heating rates merged onto a single curve when the density was plotted as a logarithmic function of Θ as well as the best estimation of the activation energy was found, where Θ is the integral of temperature function over time. It was found that the density versus Θ profile can be used to predict the final density of metallic powder mixture at a given pressure regardless of heating history. The study was also extended to a range of pressures from 31.4 to 88.3 MPa to generate the pressure-assisted master sintering surface (PMSS).
  • Synthesis and Mechanical Properties of New Cu-Based Cu-Zr-Al Glassy Alloys with Critical Diameters up to Centimeter Order

    pp. 826-829

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    DOI:10.2320/matertrans.MBW200928

    A new Cu-based Cu-Zr-Al glassy alloy has been found to exhibit very high glass-forming ability, wide supercooled liquid region and high fracture strength. The addition of Al to a binary eutectic Cu55Zr45 alloy significantly increases the stabilization of supercooled liquid as well as glass-forming ability in Cu55−xZr45Alx (x=0 to 10) alloy series. The largest supercooled liquid region of 80 K, reduced glass transition temperature of 0.60 and γ value of 0.417 are simultaneously obtained for a ternary eutectic Cu47Zr45Al8 alloy, which can fabricate fully glassy sample with critical diameters up to 15 mm by copper mold casting. The bulk glassy alloy also exhibits high compressive fracture strength of over 1900 MPa and the high Young’s modulus above 100 GPa.

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