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

MATERIALS TRANSACTIONS Vol. 51 (2010), No. 7

  • Load Effects on Nanoindentation Behaviour and Microstructural Evolution of Single-Crystal Silicon

    pp. 1173-1177

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    DOI:10.2320/matertrans.M2010007

    Nanoindentation tests are performed on single-crystal silicon wafers using a Berkovich indenter and maximum indentation loads of 30 mN, 40 mN, and 70 mN. The microstructural evolutions of the indented specimens are examined using transmission electron microscopy and selected area diffraction techniques. The results show that the unloading curve of the specimen indented to a maximum load of 30 mN has a smooth profile, whereas those of the specimens indented to 40 mN or 70 mN have a pop-out feature. The hardness and Young’s modulus of the silicon specimens reduce with an increasing indentation load, and have values of 15.8 GPa and 182 GPa, respectively, under the highest indentation load of 70 mN. In addition, a strong correlation is observed between the indentation load and the microstructural change in the indentation affected area of the silicon specimens. Specifically, a completely amorphous phase is induced within the indentation zone in the specimen indented to a maximum load of 30 mN, whereas a mixed structure comprising amorphous phase and nanocrystalline phase is found in the indentation zones in the specimens loaded to 40 mN and 70 mN. The microstructural observations imply that the load-dependent nature of the unloading curves is related to the occurrence of different phase transformation mechanisms under different indentation loads.
  • Glassy Formability and Structural Variation of Zr50−xCu50Alx (x=0∼25) Alloys with Respect to Icosahedral Short-Range Ordering

    pp. 1178-1182

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    DOI:10.2320/matertrans.M2009363

    In this study, effects of Al addition on the glass-forming ability, phase evolution, and structural variation of Zr50−xCu50Alx (x=0∼25) alloys are investigated by means of X-ray diffraction and scanning electron microscopy. The phase type and structure of the Zr-Cu-Al alloys strongly depend on the Al content. The main phases of the Zr45Cu50Al5 alloy are CuZr and icosahedral phase when the casting size is between 5 mm and 10 mm, but change to CuZr + glassy phase when the casting diameter is decreased to 3 mm. The intensity and number of Bragg peaks corresponding to the icosahedral phase in the Zr45Cu50Al5 alloy decrease quickly as the cooling rate increases, and finally, only a diffuse peak is seen. These results suggest that there is strong correlation between the icosahedral phase and the glassy phase in the Zr-Cu-Al alloys during rapid solidification. The structure of the glassy phase in the Zr-Cu-Al alloys shows icosahedral short-range ordering. The icosahedron with five-fold symmetry is incompatible with lattice periodicity, which presents a barrier to crystallization and improves the glassy formability.
  • Influence on the Electro-Migration Resistance by Line Width and Average Grain Size along the Longitudinal Direction of Very Narrow Cu Wires

    pp. 1183-1187

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    DOI:10.2320/matertrans.M2009339

    The influence of microstructures of Cu wires on electromigration (EM) resistance has been investigated using Cu wires with various line widths from 50 to 280 nm and line heights of 300 nm or 500 nm. A strong line width dependence of median time to failure was observed as the EM resistance decreases substantially with narrowing of line widths from 280 nm to 50 nm. The activation energies for 50, 80, 100 and 140 nm widths were 0.61, 0.64, 0.68 and 0.71 eV. The EM resistance and activation energy of Cu wires could be represented as a function of the ratio of line length to average grain size, which corresponds to the number of grains along the longitudinal direction, and they both increased as this ratio decreased. The influence of this ratio was particularly significant when the line width was below 100 nm. These results indicate that coarsening of grain sizes in the current flow direction is mandatory to enhance EM resistance and lower resistivity for the very narrow Cu wires.
  • Effect of Nb on Transformation Kinetics and Mechanical Properties in Zr-Al-Ni-Cu Metallic Glasses

    pp. 1188-1193

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    DOI:10.2320/matertrans.M2010054

    The effect of Nb addition on the nucleation and grain growth behaviors has been investigated in the monolithic Zr65Al7.5Ni10Cu12.5Nb5 metallic glass. Nb has been well-known as an element for icosahedral quasicrystalline (QC) phase formation in the primary crystallization stage as well as for improving mechanical properties and corrosion resistance. The grain growth rate of the QC phase at near the crystallization temperature is 1.2×10−9 m/s, which is approximately 10 times smaller than that of the primary fcc Zr2Ni phase in the Zr65Al7.5Ni10Cu17.5 metallic glass. In contrast, nucleation rate increases drastically by Nb addition. It can be calculated as 1.2×1021/m3 s, which is approximately 105 times larger than that of the Zr65Al7.5Ni10Cu17.5 alloy. The results indicate that Nb is a very effective element for controlling grain growth and nucleation rates. Good plasticity is exhibited in the as-cast alloy, however, it is lost drastically even after the structural relaxation as well as the QC precipitation. Such significant change may be attributed to the local ordering and/or phase separating tendencies by a positive chemical affinity of the Zr-Nb pair.
  • Continuous Transition of Deformation Modes in Fe-30Mn-5Si-1Al Alloy

    pp. 1194-1199

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    DOI:10.2320/matertrans.M2010073

    Deformation modes at various stages of plastic deformation have been investigated at the same location in an Fe-30Mn-5Si-1Al (mass%) alloy specimen, which exhibits a good shape memory effect associated with the FCC(γ)→HCP(ε) martensitic transformation and a relatively high ductility caused by deformation twinning. The surface relief caused by the γ→ε martensitic transformation, deformation twinning and slip band formation has been analyzed by measuring the surface tilt angles corresponding to each deformation mode by atomic force microscopy. Although the ε-martensitic transformation is the dominant deformation mode at an early deformation stage, a part of the ε-martensite plates changes to deformation twins with increasing tensile strain. Slip deformation also occurs inside the same region under excessive strain. A continuous transition of these deformation modes occurs in other grains as well in the same order: ε martensite → deformation twins → slip bands.
  • Method of Evaluating Workability in Cold Pilgering of Zirconium Alloy Tube

    pp. 1200-1205

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    DOI:10.2320/matertrans.P-M2010812

    The workability in the cold pilgering of a zirconium alloy tube was investigated. In this study, a compression test was proposed as a method of evaluating cold workability. Compression test results showed the effects of heat treatment in the fabrication process and the texture of the tube on the cold workability of a Zircaloy-4 tube shell. Cold pilgering test results ascertained that the reduction in the height of the circumferential-direction specimen of the tube shell at the crack initiation in the compression test was a good measure of cold workability. The numerical analysis results of cold pilgering proved the validity of the compression test as a method of evaluating cold workability.
  • The Effect of Boron/Antimony on the Brittle-to-Ductile Transition in Silicon Single Crystals

    pp. 1206-1209

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    DOI:10.2320/matertrans.M2010048

    The brittle-to-ductile transition (BDT) in boron or antimony doped Czochralski (CZ) silicon single crystals was investigated by three-point bending. The temperature dependence of the apparent fracture toughness was measured in three different crosshead speeds, indicating that the BDT temperature in boron doped silicon is the same as that in non-doped one while the BDT temperature in antimony doped silicon is lower than that in non-doped one. The activation energy was obtained from the deformation rate dependence of the BDT temperature, suggesting that the dislocation velocity in boron doped silicon is the same as that in non-doped while the dislocation velocity in antimony doped is larger than that in non-doped one.
  • Friction Coefficient in Hot Compression of Cylindrical Sample

    pp. 1210-1215

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    DOI:10.2320/matertrans.M2010056

    In order to analyze the evolution behavior of friction coefficients during large strain hot forging processes, compression tests were carried out on IHS38MSV hypoeutectoid steel samples at a stroke rate of 1.2 mm/s and temperatures ranging from 1073 to 1473 K. The simulation results of the geometrical change in the sample during the compression process obtained by using various friction coefficients were compared with experimental results in order to verify the validity of the “instantaneous friction coefficient”. The results showed that the friction coefficient was a constant at lower strain level, and the instantaneous friction coefficient, ms, showed an approximately exponential relationship at higher strain level. The simulation results obtained by using ms showed better results as compared to those obtained by using average friction coefficients (mc and ma). It was also found from the simulation results that at a certain strain level, the variation of friction coefficient did not have a strong effect on the shape of deformed sample; however, the radius of the top surface of the sample, Rt, changed greatly due to friction.
  • Adiabatic Shearing Localisation in High Strain Rate Deformation of Al-Sc Alloy

    pp. 1216-1221

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    DOI:10.2320/matertrans.M2010053

    Aluminium-scandium (Al-Sc) alloy is subjected to shear deformation at high strain rates ranging from 3.0×105 s−1 to 6.2×105 s−1 using a compressive-type split-Hopkinson pressure bar (SHPB). The effects of the strain rate on the shear stress, adiabatic shear band characteristics, and fracture features of the Al-Sc alloy are systematically examined. The results show that both the shear stress and the strain rate sensitivity increase with an increasing strain rate. In addition, it is shown that an adiabatic shear band is formed within the deformed specimens for all values of the strain rate. As the strain rate is increased, the width of the shear band decreases, but the microhardness increases. Moreover, the distortion angle and the magnitude of the local shear strain near the shear band both increase with an increasing strain rate. At a strain rate of 3.0×105 s−1, the fracture surface is characterised by multiple transgranular clearage fractures. However, for strain rates greater than 4.4×105 s−1, the fracture surface has a transgranular dimple-like characteristic, and thus it is inferred that the ductility of the Al-Sc alloy improves with an increasing strain rate.
  • The Equilibrium Relation of Immiscibility in an Fe-Cu-B System at 1873 K

    pp. 1222-1226

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    DOI:10.2320/matertrans.M2009415

    The equilibrium relation of the phase separation in the Fe-Cu-B system is investigated at 1873 K for potential use in the separation of copper from iron in steel scrap recycling. Liquid immiscibility is confirmed even at low boron content in iron, [mass%B](in Fe)=0.006. By combining the Taylor series equation proposed by Wagner and that of the quadratic formalism proposed by Darken, the thermodynamic interaction parameters of copper for boron in molten iron, which can be applied with precision over the wide concentration range, are derived. The first and the second order interaction parameters of copper for boron in molten iron at 1873 K are:
    εCuB=−ρCuCu,B=12.1(±0.6),ρCuB=−18.9(±11.0) (NB(in Fe)<0.34)
    eCuB=0.254(±0.014),rCuB=−0.032(±0.014) ([mass%B](in Fe)<8.9)
    Moreover, the immiscibility range in the Fe-Cu-B system is also investigated by applying a symmetrical and regular solution model.
  • Control of Si Crystal Growth during Solidification of Si-Al Melt

    pp. 1227-1230

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    DOI:10.2320/matertrans.M2010001

    The growth of Si crystals from a Si-55.3 at%Al melts was investigated with the aim of developing a new Si refining process for SOG-Si production. Si crystals were grown by directional solidification of the Si-Al alloy. The temperature at the bottom of the sample was controlled from 1273 K (the alloy’s liquidus temperature) to 1173 K. Bulk Si crystals were successfully obtained in this study, and the crystal growth was found to be controlled by the diffusion of Si in the melt. By controlling the crystal growth conditions, the Al content of the Si crystals could be decreased to the level of the solid solubility of Al in Si; furthermore, other impurity elements could be efficiently removed by this refining method.
  • Thermally Activated Cr2O3+x for Elimination of Volatile Organic Compounds

    pp. 1231-1236

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    DOI:10.2320/matertrans.M2010085

    We have previously shown that oxide semiconductors (for example, TiO2, NiO, etc.) exhibit significant catalytic effects when heated at about 350–500°C. This is due to the formation of a vast number of highly oxidative holes at high temperatures. Then, we applied the present finding for complete removal of volatile organic compounds (VOCs). In the present investigation, we focused on Cr2O3+x (0<x<1) in an attempt to lower the operation temperature of VOC decomposition. We present here how the low-temperature operation proceeds with Cr2O3+x and also elucidate why Cr2O3+x is colored green, on the basis of the temperature dependences of electrical conductivity and Seebeck potential of Cr2O3+x. The green color of Cr2O3+x is found to arise from Cr vacancies in Cr2O3+x, and the vacancies are responsible for the formation of a narrow conduction band or a deep acceptor level, resulting in the low-temperature operation of VOC decomposition.
  • Hexagonally Ordered Ni Nanocone Array; Controlling the Aspect Ratio

    pp. 1237-1241

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    DOI:10.2320/matertrans.M2010071

    Hexagonally ordered Ni nanocones and films possessing a cone geometry were produced using anodization and metal plating techniques. The conical porous anodic alumina (PAA) film was produced using a process of repeated applications of anodization and pore-widening steps, applying the two steps alternately. The structures on the PAA films were a hexagonally ordered array with an interval of 100 nm. An intended height of 100–500 nm of the conical pores were produced by tuning the fabrication conditions of the PAA film. The Ni nanocones were produced by electroless deposition onto the conical PAA film. The Ni films with a nanocone topography were produced by detaching the deposited layer. These nanostructures were produced using wet-process techniques of anodization, electroless and electrochemical deposition.
  • Analysis for Kinetics of Austenite Growth due to Isothermal Carburization of Ferrite

    pp. 1242-1248

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    DOI:10.2320/matertrans.M2010075

    A diffusion model was used to analyze mathematically the kinetics for isothermal carburization of pure iron at annealing temperatures between 1011 K and 1185 K. Under such carburization conditions, the austenitic γ phase is produced as a layer on the surface of the ferritic α phase. In the analysis, the diffusion coefficient of carbon in each phase is considered independent of the composition. According to the model, the square of the thickness of the γ phase is proportional to the annealing time. Such a relationship is called the parabolic relationship. The parabolic coefficient is a monotonically increasing function of the annealing temperature and the concentration of carbon on the surface of the γ phase. However, the dependence of the parabolic coefficient on the carbon concentration is less remarkable at higher annealing temperatures than at lower annealing temperatures. The parabolic coefficient varies depending on the annealing temperature in a complicated manner, even if the activity of carbon in the carburization atmosphere remains constant. Thus, the temperature dependence of the parabolic coefficient cannot be described by an Arrhenius equation in the whole annealing temperature range.
  • Investigation on Dynamic Friction Properties of Extruded AZ31 Magnesium Alloy Using by Ring Upsetting Method

    pp. 1249-1254

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    DOI:10.2320/matertrans.P-M2010811

    The dynamic friction properties of the extruded AZ31 magnesium alloy of the grain size of 20 μm were investigated by ring upsetting method test at 523, 548 and 573 K at strain rate of 1.0×10−2 s−1, where all the initial testing conditions were the climb-controlled dislocation creep. The MoS2 lubricant maintained lower dynamically friction coefficient (m value) than the oil lubricant. The difference in m values between machined surface and polished surface was unclear. The m values for WC-Co and diamond like carbon (DLC) tools were similar in MoS2 lubricant. The m values for DLC tool were lower than those for the WC-Co tool in the oil lubricant. The extruded direction influenced to the friction properties. The aspect ratio of the inner diameter on 90° to extruded direction after testing was almost isotropic; on the other hand, the anisotropy occurred on 0° and 45°. The extent of anisotropy at 548 K was the highest, although the lower temperature, the higher the critical shear stress of non-basal plane. The condition at 523 K, where the fine grain sizes less than 3 μm could be obtained by dynamic recrystallization during deformation, is suitable temperature to make superplasticity at the given strain rate.
  • Determination of the Cyclic-Tension Fatigue of Extruded Pure Magnesium Using Multiple Ultrasonic Waves

    pp. 1255-1263

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    DOI:10.2320/matertrans.M2009432

    Three acoustic techniques, namely longitudinal wave reflection, vertically-polarized shear wave (SV) reflection, and horizontally polarized shear wave (SH) transmission methods, were used to assess the cyclic-tension fatigue of an extruded pure magnesium. The acoustic velocities were measured by the reflection methods, and found to decrease considerably at the beginning of the fatigue. This suggests that void defects formed at grain boundaries (Coble creep). Decrease in the elastic moduli and increase in the internal frictions revealed decrease in the mechanical and increase in the viscoelastic properties during the fatigue progress, respectively. For SH transmission method, acoustic parameters such as propagation time, amplitude and logarithmic damping ratio were strongly affected by detouring of acoustic waves, accompanied by variation in the residual stress caused by acoustoelasticity, in comparison with the reflection methods. These acoustic results were determined using OM, SEM, Vickers hardness tester, surface roughness tester and XRD.
  • Effect of Repeated Tempering on Hardness and Retained Austenite of High Chromium Cast Iron Containing Molybdenum

    pp. 1264-1271

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    DOI:10.2320/matertrans.M2010018

    Two series of hypoeutectic high chromium cast iron specimens containing 16 mass% Cr and 26 mass% Cr with and without Mo were prepared to study the variation of hardness and volume fraction of retained austenite (Vγ) during repeated tempering. In the as-hardened state, the hardness did not change in the 16 mass% Cr cast irons, but it increased gradually in the 26 mass% Cr cast irons as their Mo content increased. The Vγ rose gradually with an increase in the Mo content of both series of cast iron specimens. In the tempered state, the hardness decreased and then increased with a successive number of tempering cycles. In other words, a secondary hardening was evident due to the precipitation of secondary carbides in the austenite and the transformation of destabilized austenite into martensite during cooling. The hardness increased with rising tempering temperature. The Vγ decreased gradually with repeated tempering and increasing tempering temperature. The maximum tempered hardness (HTmax) was obtained at 723–798 K after triple tempering. The HTmax increased proportionally with a rise in Mo content in both the 16 and 26 mass% Cr cast irons. The highest values of HTmax were 900 HV30 in 16 mass% Cr and 950 HV30 in 26 mass% Cr cast irons, respectively.
  • Crack Monitoring during Plasma Spraying of Ceramic Coatings by Non-Contact Acoustic Emission Method

    pp. 1272-1276

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    DOI:10.2320/matertrans.M2010004

    Atmospheric plasma spraying (APS) is an effective process to make ceramic coatings. However, several types of cracks are inherently present in the coatings and among them, delamination cracks within the coatings or at the interface with the underlying layer are believed to reduce their durability and reliability. In this study, non-contact laser acoustic emission (AE) method and original AE measurement system successfully detected the cracks during APS in real time, which was very difficult because of noise from the APS system. AE waveform was sampled and recorded continuously during the testing time. AE events due to delamination cracks were successfully detected from noisy waveform by this system. Influences of the scanning speed and the power of the plasma jet to the delamination were also confirmed.
  • Effect of TiB Whiskers Orientation on Mechanical Properties in an In Situ TiB/Ti-1100 Composite

    pp. 1277-1280

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    DOI:10.2320/matertrans.M2010014

    In this paper, Ti-1100 composite reinforced with TiB whiskers was fabricated using in situ technologies. Mechanical properties of the composite with randomly oriented and aligned TiB reinforcements are evaluated by tensile tests at 923 K, and the failure process of the composite is observed by SEM. Strengthening efficiency of the differently oriented reinforcement is calculated. The failure mechanism and strengthening efficiency of the TiB whiskers during tensile tests are investigated. The effect of the orientation of TiB whiskers on the failure mechanism and strengthening efficiency for the investigated composite is also discussed.
  • Microstructures of Zr-Added Co-Cr-Mo Alloy Compacts Fabricated with a Metal Injection Molding Process and Their Metal Release in 1 mass% Lactic Acid

    pp. 1281-1287

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    DOI:10.2320/matertrans.M2010040

    The microstructures of Zr-added Co-29Cr-6Mo alloy compacts fabricated with a metal injection molding (MIM) process and their metal release from the compacts immersed in 1% lactic acid were investigated for medical applications. The relationship between the microstructure and amount of Co released from the compacts is discussed phenomenologically. The relative density of the Co-29Cr-6Mo compacts increased when Zr was added to the powder with amounts of 0.03 and 0.1 mass% and sintered in Ar or N2. The amounts of Co released from the compacts containing 0.03 and 0.1 mass% Zr sintered in Ar or N2 were smaller than those from the other compacts. Therefore, the addition of Zr to the Co-29Cr-6Mo powders enhanced the sintering of the compacts and decreased the porosity in the resultant products, leading to the suppression of the Co release from the compacts. When the Zr-added Co-29Cr-6Mo alloy powders were sintered in N2, the relative density of the compacts was smaller than that of those sintered in Ar. The powders were nitrided during sintering in N2, and the nitrides disturbed the densification during sintering. In addition, a lamellar structure was formed in the Co-29Cr-6Mo and Co-29Cr-6Mo-0.5Zr compacts. The amount of Co released from these compacts was larger than that released from the other compacts because local corrosion occurred at the interface between the different phases in these compacts during immersion in 1% lactic acid. In the MIM process, a small addition of Zr (less than 0.1 mass%) to the Co-29Cr-6Mo alloy is effective for densification during sintering and suppression of the Co release from the compacts.
  • Four-Dimensional Annihilation Behaviors of Micro Pores during Surface Cold Working

    pp. 1288-1295

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    DOI:10.2320/matertrans.M2010069

    The annihilation behavior of micro pores in an aluminum alloy casting during surface cold working was continuously observed using the synchrotron radiation microtomography. To analyze micro pore annihilation behavior, the displacement of artificially dispersed particles was measured and thereby local strain distributions were mapped in high-density. A peening treatment annihilated most of the micro pores with a diameter of over 10 μm in the upper part of the specimen that could initiate fatigue cracks. The annihilation behavior of the micro pores could be understood as a function of effective strain locally accumulated around them, and not as a function of local hydrostatic strain. The effective strain varied significantly, with some large pores remaining where local effective plastic strain was relatively low. The complete annihilation of large pores in the surface layer suggests that the application of sufficiently long surface cold working is effective in improving the high-cycle fatigue properties.
  • Change of Mechanical Property and Fracture Mode of Molybdenum by Carbon Addition

    pp. 1296-1301

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    DOI:10.2320/matertrans.M2009377

    Commercially available specimens of pure molybdenum were immersed in a graphite-filled Ta container and heated at a relatively low temperature of 1373 and 1473 K for 1.2 to 18.0 ks. Changes in the yield and maximum strength were evaluated by a three-point bending test at a temperature between room temperature and liquid-nitrogen temperature. Then two parameters, critical stress (apparent intergranular fracture strength) and critical temperature (DBTT), were determined. Finally, the fracture mode was examined using SEM and the apparent transgranular fracture strength was estimated from the relationship between the critical stress and the fracture mode.
    Results are summarized as follows.
    (1) Both the critical stress and the critical temperature changed drastically with carbon addition and exhibited a peak value under optimum conditions: 1373 K–3.6 ks and 1473 K–1.2 ks.
    (2) The fracture mode changed from intergranular to transgranular after carbon addition.
    (3) The change in the critical stress as a function of the increase in carbon content in this work almost agrees with that in the previous work of Hiraoka et al.
    (4) The apparent transgranular fracture strength was unchanged (about 990 MPa) after carbon addition of 10 mass ppm or less. This value is almost equal with that before carbon addition. The apparent transgranular fracture strength was lowered after excess carbon addition.
  • Magnetization Process in Sm2Fe17N3 Fine Powders Studied Using Lorentz Microscopy and Electron Holography

    pp. 1302-1307

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    DOI:10.2320/matertrans.M2010081

    The magnetization process for Sm2Fe17N3 fine powders was studied by Lorentz microscopy and electron holography. In ex situ observations under the external magnetic field produced by an electromagnet, the change of the domain wall position was observed by Lorentz microscopy, while the drastic change in the distribution of lines of magnetic flux outside the fine powders was clarified by electron holography. Through in situ observations with a piezodriving holder with localized magnetic field produced by a sharp magnetic needle, the shift of domain walls was observed in real time by Lorentz microscopy. Finally, on the basis of Lorentz microscopy observations, the magnetization process of Sm2Fe17N3 fine powders was briefly discussed taking into account a hysteresis loop.
  • Effect of Pulsed Magnetic Field on Spark Plasma Sintering of Iron-Based Powders

    pp. 1308-1312

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    DOI:10.2320/matertrans.M2010057

    Iron-based powders were sintered by spark plasma sintering coupled with different pulsed magnetic field strength ranging from 0 to 3.93 MA·m−1. The effects of pulsed magnetic field on the sintering behavior of the powders as well as the microstructure and mechanical properties of sintered alloys were investigated. The results showed that the sintering temperature field on the cross section of sample was more uniform via coupling a pulsed magnetic field. The density, hardness and bending strength of the alloy sintered by coupling an appropriate pulsed magnetic field, arose to 7.75 g·cm−3, 55 HRC and 1235 MPa, respectively. There was no remarkable change of sintered density with a further increase of pulsed magnetic field strength, while the hardness and bending strength of sintered alloys adversely decreased. The roles of pulsed magnetic field coupled with electric field are explained to accelerate the diffusion and reaction of alloying elements by raising sintering temperature, facilitate powders rearrangement, intensify sparking among powders, improve the growth of sintering neck and the formation of new sintering neck, and reduce the sintering temperature gradient on cross section.
  • Kinetics of the Volatilization Removal of Zinc from Manganese Dust

    pp. 1313-1318

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    DOI:10.2320/matertrans.M2010108

    Manganese dust which contains significant amounts of manganese, zinc and potassium is collected from the off-gas during manufacturing ferromanganese and silicomanganese alloys at Dongbu Metal Company in Korea. The removal of zinc and potassium from the manganese dust is very important in the process for recycling the dust back into the ferromanganese smelting furnace. This is because the potential accumulation of zinc and potassium in the smelting furnace can cause irregularities in the operation of the smelting furnace. In this study, the reduction-volatilization reaction of the zinc oxide contained in the manganese dust with carbon was examined at reaction temperatures between 923 and 1323 K in nitrogen atmosphere using a thermogravimetric method. The results of experiments on the kinetics of the reaction are presented in this paper. Experimentally, the rate of this reaction was demonstrated by the removal of 99% zinc in 20 min at 1198 K under a carbon addition amount of 9 mass%. The reduction-volatilization reaction started at above 973 K and proceeded very fast at above 1023 K. Furthermore, manganese and iron oxides in the dust was partially reduced during the reaction. The shrinking-core model for a surface chemical reaction control was found to be useful in describing the reduction-volatilization reaction rate, which had an activation energy of 173 kJ/mol (41.3 kcal/mol).
  • Effect of Welding Parameters on Weld Formation and Mechanical Properties in Dissimilar Al Alloy Joints by FSW

    pp. 1319-1325

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    DOI:10.2320/matertrans.M2010032

    The dissimilar Al alloys, 5052 and 5J32, were joined by friction stir welding (FSW) technique under several welding conditions, including material arrangement. The tool rotation speeds were 1000 and 1500 rpm, and the welding speeds were varied within the range from 100 to 400 mm/min. At a tool rotation speed of 1000 rpm, all joints with the 5052 on the advancing side exhibited better properties than those with the opposite arrangement. When the 5J32 was placed on the advancing side, defect-free welds were obtained under all welding conditions. However, when the 5J32 was placed on the retreating side with a rotation speed of 1500 rpm, some defects were detected below the top surface of the retreating side. Furthermore, fractographs of the defects indicated an evidence of liquation cracking during FSW. The experimental results showed that the weld formation and mechanical properties depended upon the material arrangement as well as the conventional welding parameters.
  • Microstructure and Gas-Sensing Property of Titania-Added ZnSnO3

    pp. 1326-1329

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    DOI:10.2320/matertrans.M2010017

    We report the microstructure and gas-sensing property of TiO2-loaded ZnSnO3 prepared by three different addition methods. We find that the loading of TiO2 enables a significant improvement of sensor response and selectivity to ethanol and that the wet process, which is defined as the introduction of TiO2 gel to ZnSnO3 precipitants, is most efficient to enhance the gas-sensing behaviors. Microscopically, surface characterizations suggest that the improved sensing properties for the TiO2-loaded ZnSnO3 can be attributed qualitatively to its large specific surface area and porous morphology. A gas adsorption model based on surface physics is proposed to discuss further the mechanism behind the sensing property enhancement. This study may open up an avenue for effectively tuning gas-sensing character of ZnSnO3, which is important for modifying functionality of other sensing materials.
  • Chlorine Occupancy Dependence of Crystal Structure of Pure β-Phase of Iron-Oxyhydroxide

    pp. 1330-1339

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    DOI:10.2320/matertrans.M2010086

    Crystal structure of β-phase of iron-oxyhydroxide (Akaganeite) with different chlorine occupancy was studied by X-ray diffraction with Rietveld analysis. The structure depends on chlorine occupancy, u in tunnel sites of the phase. The crystal system was assigned to monoclinic (I2/m) throughout u range whereas the lattice and structure parameters changed with u. The chemical formula was estimated to be Fe83+O162−H8+2u+Cl2u(H2O)2w (0.25≤u≤0.56 and w\\simeq0.2) where w denotes fraction of water molecules in tunnel sites. A sample with u=0.44 showed the highest crystal symmetry throughout the u range. The u-dependence of some structural parameters was discussed from the view point of oxygen displacements.
  • Surface Characteristics, Optical and Electrical Properties on Sol-Gel Synthesized Sn-Doped ZnO Thin Film

    pp. 1340-1345

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    DOI:10.2320/matertrans.M2009378

    Un-doped ZnO and Sn-doped ZnO (SZO) thin films were synthesized using the sol-gel method. The surface morphology of the SZO films showed a large amount of crystallization. Doping with tin dopants not only reduced the surface roughness of the film, but also repaired defects in the pore structure. Notably, the SZO film with a crystallization temperature of 650°C possessed better crystallization and fewer defects when tin dopants were added. XPS analysis confirmed the presence of O-Sn4+ phases proving the contribution of tin doping on the electrical conductivity of the SZO films. With regards the PL spectra, luminescence in the Zn2SnO4 phase was observed and affected the red-shifted of broad visible emission. In addition, the 9 at% Sn doped ZnO (S9ZO) film showed excellent optical transmittance, however the transmittance improved further when the trace of tin dopants (0.4 at%) and 2 at% In were doped in ZnO matrix (I2S0.4ZO).
  • The Effect of Cerium on Microstructures and Mechanical Properties of Mg-4Al-2Sn-1Ca Alloy

    pp. 1346-1349

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    DOI:10.2320/matertrans.M2010042

    The development of new creep resistant magnesium alloys has become a major research focus. This study examined the microstructure and creep properties of Mg-4.0 mass%Al-2.0 mass% Sn-1.0 mass%Ca alloys containing Ce. The results showed that Ce could improve dramatically the tensile strength and ductility of the alloy at room temperature and increase the creep resistance at elevated temperatures significantly. With a trace amount of Ce, the morphology changed from a coarse CaMgSn phase to a refined shape and the microstructure of the alloy was remarkably refined.
  • A Novel Cyclic Process Involving Zinc for Separating Silver from Lead-Free Solder Residue

    pp. 1350-1353

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    DOI:10.2320/matertrans.M2010128

    In recent years, the major issue posed by the recycling of tin-lead and lead-free solder residues is to recycle effectively lead-free solder residues because large volume of lead-free solder residues has been generated from electric and electronic industry as the environmental regulation becomes to be strictly in Europe. In general, the lead-free solder residues are generated from the step to affix components to printed circuit boards, which contains 2–4% of silver and 90–93% of tin. In this study, a novel cyclic process to separate silver from the lead-free solder residues using a metal solvent has been developed. The process uses zinc as a metal solvent which selectively forms intermetallic compounds with silver, followed by the volatilization separation step to recover zinc which can be reused as the metal solvent. Based on the results obtained, up to 90% of the silver in a lead-free solder residue was calculated to be separated into the dross phase through the sixth silver separation stage using the proposed process. This paper is only concerned with the results for the separation of silver from a lead-free solder residue using zinc as a metal solvent.
  • Visualization of Hydrogen on Ti-6Al-4V Using Hydrogen Microscope

    pp. 1354-1356

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    DOI:10.2320/matertrans.M2009410

    The two-dimensional distribution of hydrogen on Ti-6Al-4V gives very important information on the environmental embrittlement mechanism. The scanning-electron-stimulated desorption ion microscope, the so-called hydrogen microscope, can be used to visualize hydrogen on solid surfaces. In this study, we attempt to visualize hydrogen on Ti-6Al-4V alloy using a hydrogen microscope. As a result, the hydrogen distribution on the Ti-6Al-4V surface was clearly observed.
  • Kinetic Arrest of Martensitic Transformation in NiCoMnAl Metamagnetic Shape Memory Alloy

    pp. 1357-1360

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    DOI:10.2320/matertrans.M2010098

    Magnetic properties and martensitic transformation behaviors of NiCoMnAl metamagnetic shape memory alloys were investigated. The kinetic arrest phenomenon was observed at about 40 K during thermomagnetization measurements. At temperatures ranging from 4.2 to 200 K, magnetic field-induced reverse transformation was confirmed by a pulse magnetometer with a magnetic field up to 45 T. By plotting the equilibrium magnetic fields against the measured temperature, the transformation entropy change was calculated by using the Clausius-Clapeyron equation. The transformation entropy change was found to become zero below 40 K, which can explain the appearance of the kinetic arrest phenomenon.
  • VOC Decomposition System Based upon Heater-Integrated Catalyst Units Using NiO or Cr2O3

    pp. 1361-1363

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    DOI:10.2320/matertrans.M2010105

    We have previously shown that oxide semiconductors (TiO2, NiO, Cr2O3, etc.) exhibit remarkable catalytic effects when heated at high temperatures of about 350–500°C and that the effect has been interpreted in terms of the formation of a large number of highly oxidative holes caused by thermal excitation of semiconductors. This prompted us to utilize this technology for complete removal of volatile organic compounds (VOCs). In the present investigation, we aim at constructing a compact device for practical implementation composed of four-stacked “heater/honeycomb” units. Each unit comprises a spiral Ni-Cr heater as well as a honeycomb plate coated with powdered NiO or Cr2O3. Decomposition experiment was carried out in the range from room temperature to 500°C, using 10000 ppm toluene as the VOC at a flow rate of 10 l/min. As a result, the toluene decomposition was found to begin at about 100°C and was completed (i.e., 0 ppm) at about 300°C, showing an excellent decomposition characteristic in both NiO and Cr2O3.
  • Bauschinger Effect on Springback of Clad Sheet Metals in Draw Bending

    pp. 1364-1366

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    DOI:10.2320/matertrans.M2010058

    For clad sheet metals, springback behavior is directly related to the elastic-plastic properties such as Young’s modulus, the yield strength, workhardening and the Bauschinger effect of each metal layer. The aim of this study is to understand the springback characteristics of the clad sheet metals in draw bending based on the accurate FE simulation corresponding to experimental data on stainless-steel clad aluminum sheets. In the discussion, the special emphasis is placed on the influence of the Bauschinger effect. For that purpose, in the simulation, two types of material models, one is the classical isotropic hardening model (no Bauschinger effect included) and the other Yoshida-Uemori kinematic hardening model which describes the Bauschinger effect of materials properly, were used and these numerical results were compared.
  • The Effect of Sodium Silicate as pH Modifier and Depressant in the Froth Flotation of Molybdenite Ores

    pp. 1367-1369

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    DOI:10.2320/matertrans.M2009397

    In flotation of porphyry molybdenite ores or copper-molybdenite ores using oil collector, a molybdenite (MoS2) concentrate has mainly been separated by combination of sodium silicate (Na2SiO3) and lime (CaO) at about pH 9–11. In this research, the role of sodium silicate and the effect of collector (kerosene) in flotation of Dong-won molybdenite ores from Korea have been observed. It was confirmed that sodium silicate could adjust the pH of pulp to 11. Furthermore, flotation efficiency using sodium silicate was better more than that using lime in the alkaline conditions (pH 9.5–11). It was demonstrated that sodium silicate could be used not only as pH modifier but also as depressant/dispersant of slime. Also Mo grade of 54.1% and recovery of 92.5% were successfully obtained at 75 g/t kerosene and 1.25 kg/t Na2SiO3 (pH 10).

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