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

MATERIALS TRANSACTIONS Vol. 57 (2016), No. 3

  • Alloy Design Based on Molecular Orbital Method

    pp. 213-226

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    DOI:10.2320/matertrans.M2015418

    A molecular orbital approach to alloy design has recently made great progress. It is based on the electronic structure calculations by the DV-Xα cluster method, and new alloying parameters are obtained for the first time from the calculations. A theory for alloy design relevant to transition-metal based alloys have been developed using alloying parameters. For example, New PHACOMP has been developed in order to predict the formation of harmful and brittle phases (e.g., σ phase) in nickel-based superalloys. A universal relation has also been discovered between electron density minima and atomic (or ionic) radii in various materials from a series of molecular orbital calculations. Furthermore, another electronic approach is explained focusing on the energy expression of the chemical bond between atoms in hydrides and hydrocarbons. All the hydrides and hydrocarbons are located on an atomization energy diagram, despite the significant differences in the nature of the chemical bond among them. One of the applications of this approach is the catalyst design. The catalytic activities of metal oxides (e.g., Nb2O5) are evaluated quantitatively on the dehydrogenation reaction of magnesium hydride (MgH2), MgH2 → Mg + H2.
  • Effect of Solution Carbon and Nitrogen on the Microstructural Size and Crystallography of Lath Martensite in Fe–N and Fe–C Alloys

    pp. 227-232

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    DOI:10.2320/matertrans.MB201503

    Microstructures of lath martensite that contains bcc or bct martensite crystals in Fe–C alloys are known to depend on the carbon content of the alloys. The effect of nitrogen content on microstructure, however, has not yet been elucidated. This study elucidates the effects of carbon and nitrogen content on microstructures via local crystallographic analysis. We found that the packet sizes are similar when the nitrogen content in the alloys are the same as the carbon content, with the packet size decreasing with increasing carbon and nitrogen content. The block and sub-block thicknesses in low nitrogen lath martensite are smaller than those in low carbon lath martensite, whereas those in medium and high carbon and nitrogen lath martensites are similar. Martensite lath thickness and dislocation density in the Fe–N alloy laths are lower than those in the Fe–C alloys laths, and the distribution of misorientation angles between adjacent the blocks and sub-blocks in Fe–N alloys is similar to that in Fe–C alloys.
  • Compatibility at Junction Planes between Habit Plane Variants with Internal Twin in Ti-Ni-Pd Shape Memory Alloy

    pp. 233-240

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    DOI:10.2320/matertrans.MB201515

    The kinematic compatibility (KC) between habit plane variants (HPVs) was numerically analyzed and classified in Ti-25Ni-25Pd alloy. There are six distinct types of HPV pair that can satisfy the KC condition at averaged junction plane (JP) between twinned HPVs. By analyzing the KC condition between lattice correspondence variants (CVs) in the HPVs, it was found that there are three types of HPV pair in which all the CVs can be compatible due to the existence of the common rotation to keep the KC at all JPs simultaneously. On the other hand, it was found that the incompatibility inevitably remains in the morphologies known as spear (wedge), folk and herring-bone.
  • Enhancement of Shape Memory Properties through Precipitation Hardening in a Ti-Rich Ti-Ni-Pd High Temperature Shape Memory Alloy

    pp. 241-249

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    DOI:10.2320/matertrans.MB201516

    Effects of aging on martensitic transformation temperature, microstructure and shape memory characteristics were investigated for Ti50Ni20Pd30 and Ti52Ni18Pd30 alloys. There was no significant change in the microstructure and transformation temperature by aging, irrespective of aging temperature, in case of the Ti50Ni20Pd30 alloy. On the other hand, fine Ti2Pd type precipitates were formed upon aging in the Ti52Ni18Pd30 alloy within the aging temperature range of 673-1073 K. The transformation temperature of the Ti52Ni18Pd30 alloy was sensitively dependent on the aging temperature. The Ti2Pd type nanoscaled precipitates were found to be very effective in enhancing the high temperature dimensional stability during shape memory cycling. Excellent shape memory properties with a large recovery strain and a small plastic strain even at 500 MPa were observed in the Ti52Ni18Pd30 alloy solution treated and aged at lower temperatures of 673 and 773 K owing to the formation of fine and dense Ti2Pd type precipitates.
  • Antiphase Boundary-Like Structure of B19 Martensite in Ti-Ni-Pd Shape Memory Alloy

    pp. 250-256

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    DOI:10.2320/matertrans.MB201505

    The antiphase boundary (APB)-like structure of B19 martensite in the Ti-Ni-Pd alloy was investigated by means of conventional transmission electron microscopy and high-angle annular dark-field scanning transmission electron microscopy. Some APB-like structures with wide and curved contrast exhibited shifts along the (010)B19 and (001)B19 planes; that is, it exhibited facets composed of those planes at the atomic level. This atomic displacement reflects the atomic movement stemming from not only martensitic but also a kind of R-phase transformations.
  • The Effects of Aging on the Degree of Order in Cu-Al-Ni Shape Memory Alloys

    pp. 257-262

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    DOI:10.2320/matertrans.MB201511

    The fractions of Al atoms at three kinds of crystallographic sites were determined in a Cu-15.5Al-4.0Ni (mass%) alloy before and after aging using powder X-ray analysis in order to clarify the effect of aging on the martensite start temperature, Ms. The ordering between first nearest neighbors (the B2 ordering) was almost finished even just after quenching, but the ordering between second nearest neighbors (the L21 ordering) was incomplete. The B2 type ordering occurs in advance of the L21 ordering in Cu-Al-Ni alloys as well as in Cu-Al-Zn alloys. The degree of L21 order increases from 0.699 to 0.844 during aging at 200°C for an hour. The increase in Ms during the aging is attributed to the L21 ordering in Cu-Al-Ni alloys.
  • Effect of Alloying Element X on Transformation Strains and Phase Stabilities between α′′ and β Ti-Nb-X (X = Al, Sn, Zr, Ta) Ternary Alloys from First-Principles Calculations

    pp. 263-268

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    DOI:10.2320/matertrans.MB201509

    The effect of alloying element X (X = Al, Sn, Zr, Ta) on the transformation strains and phase stabilities of Ti-12.5 at%Nb and Ti-25 at%Nb alloys was investigated. The principle strain, η2, was calculated as a function of the X concentration. The value of η2 of Ti-12.5 at%Nb-6.25 at%Zr was larger than that of Ti-12.5 at%Nb-6.25 at%Ta. This is consistent with the experimental results. The difference of solution energy, Δ Hsolα ” - β, was also calculated. The value of Δ Hsolα ” - β increased with the addition of Al, Sn, Zr, and Ta to Ti-12.5 at% Nb-6.25 at%X alloys. We found a good linear correlation between the experimental values for the decrease of the martensitic transformation start temperature (Ms), dMs/dc, and the calculated values of Δ Hsolα ” - β. The effect of the alloying element on the shape-memory properties of Ti-Nb-based alloys were evaluated from the first-principles calculations.
  • Martensitic Transformations and Superelastic Behavior at Low Temperatures in Ti50−xNi40+xCu10 Shape Memory Alloys

    pp. 269-277

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    DOI:10.2320/matertrans.MB201504

    In the present study, Ni content dependence of martensitic transformation behavior in Ti50−xNi40+xCu10 alloys (x = 0.0–3.0) was investigated, and then the superelastic behavior of a x = 2.4 alloy was examined at low temperatures. The Ti50−xNi40+xCu10 alloys are in B2 single-phase up to x = 2.4 at 1373 K. The B2/B19 and B19/B19′ transformation temperatures decrease with increasing x and the lowest martensitic transformation starting temperature of 125 K was detected. In the alloys with Ni compositions over x = 1.4, a pre-martensitic “intermediate” phase was detected by thermoanalysis measurements. While the middle eigenvalue λ2 is close to 1.0, which was found to be independent of the Ni content, the thermal hysteresis, Thys increases with increasing Ni content. This is explained by the drastic decrease in transformation entropy change. Although starting to drastically increase at temperatures below 100 K, the temperature dependence of stress hysteresis in compression testing is basically smaller than that in Ti48.2Ni51.8 binary alloy.
  • Mechanical Properties of the R-Phase and the Commensurate Phase under [111] Tensile Stress in Iron-Doped Titanium-Nickel Alloys

    pp. 278-282

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    DOI:10.2320/matertrans.MB201518

    We have studied deformation behavior of two kinds of iron-doped Ti-Ni shape memory alloys under tensile stress applied in the [111] direction. One is Ti-46Ni-4Fe (at%) alloy which transforms to the R-phase and the other is Ti-44Ni-6Fe (at%) alloy which transforms to the commensurate phase (C-phase) in the cooling process. The stress-strain curve measured in the R-phase region shows a residual strain due to rearrangement of variants while that measured in the C-phase shows a pseudoelastic behavior characteristic to stress-induced martensitic transformations. The strain-temperature curve measured under constant stress shows an obvious transformation strain associated with the transformation to the R-phase, while a bend point appears associated with the transformation to the C-phase.
  • Design Concept and Applications of Fe–Mn–Si-Based Alloys—from Shape-Memory to Seismic Response Control

    pp. 283-293

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    DOI:10.2320/matertrans.MB201510

    Fe–Mn–Si-based alloys exhibit a shape-memory effect associated with deformation-induced γ → ε martensitic transformation and its reversion. The γ → ε martensitic transformation also enhances mechanical properties, such as strength, hardness, wear-resistance and low-cycle fatigue lives of the alloys. In this article, we review fundamental researches on transformation behavior, microstructural and crystallographic characteristics, and functional and mechanical properties of the Fe–Mn–Si-based alloys, and introduce various examples of their practical applications. A special emphasis is placed on their new application as architectural seismic dampers, which were developed based on a new finding of the passive two-way martensitic transformations under cyclic tensile-compressive loading.
  • Preparation of Ag-Cu Composite Nanoparticles by the Submerged Arc Discharge Method in Aqueous Media

    pp. 294-301

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    DOI:10.2320/matertrans.M2015288

    For this study, electrical discharge machining (EDM) and the submerged arc discharge method (SADM) were used to melt a silver-copper composite metal in deionized water through concentrated arc energy in order to produce metal fluids containing nano- and submicron particles. The fabrication process did not require additional chemicals, and was simple and efficient. The critical processing parameters for EDM were the discharge voltage and current as well as the on-off duration for pulse discharge; the sample concentration could be controlled under appropriate conditions. The experimental results revealed that, through electronic system design and manufacturing (ESDM), silver-copper composite metal particles could be achieved at a nano to submicron level. In addition, the results obtained varied according to differences in the on-off duration regarding pulse discharge. In this study, when the discharging parameter (Ton-Toff) was at 30 : 50, nanocomposite fluids with an optimal concentration and small particles were obtained. The application of EADM could enable the mass production of composite metal fluids or particles at low cost and high efficiency. Employing EADM for the fabrication of composite metal fluids or particles warrants research attention, and the process itself can be developed further.
  • Ligand-Driven Spin-Crossover Behavior of FeII Molecules

    pp. 302-304

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    DOI:10.2320/matertrans.M2015368

    In order to explore a way to tailor thermal hysteresis behavior of spin-crossover (SCO) complexes, a series of seven FeII(LX2) complexes with different ligand configurations has been designed or reconstructed. These FeII(LX2) complexes differ in axial ligands X = Py, CNPY, NC5H4CH3, NC5H4OCH3, NC5H4Cl, X = NC5H4Br, and Him. Geometric structure, electronic structure, and magnetic properties of FeII(LX2) complexes have been investigated using density-functional theory with full geometry optimization. Our calculated results show that the spin-state electrostatic-energy difference (ΔU) of these FeII SCO complexes can be tailored by adjusting the pKa constant of axial ligands X. The increase of ΔU of these FeII SCO complexes from −12.18 eV to 6.64 eV results from the increase of pKa constant of axial ligands X from 1.10 to 7.00. The role of axial ligands X in determining SCO behavior of FeII SCO complexes has been revealed. In addition, our previous study (N. A. Tuan: J. Appl. Phys. 111 (2012) 07D101) demonstrated that thermal hysteresis of spin-crossover increased with the ΔU of FeII SCO complexes. These results would give some hints into how thermal hysteresis can be tailored in FeII SCO complexes.
  • Improvement of Low-Temperature Impact Value of Sandwich-Structural (CFRP/ABS/CFRP) Laminate Plies by Homogeneous Low-Energy Electron Beam Irradiation (HLEBI)

    pp. 305-311

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    DOI:10.2320/matertrans.M2015332

    Experimental results show applying homogeneous low-energy electron beam irradiation (HLEBI) treatment of 0.30 MGy to both sides of sandwich structural CFRP/ABS/CFRP composite constructed of an ABS core between two thin plies of carbon cross textile fiber/epoxy CFRP apparently increased Charpy impact values, auc at all fracture probabilities, Pf at temperatures of 77, 200 and 300 K, within the low temperature range of aircraft operation and below the minimum of reusable launch vehicle operation in space reported as 116 K. At median-Pf = 0.50 auc was increased 98% from 11.4 to 22.5 kJ m−2 at low temperature of 77 K, while the HLEBI increased auc at Pf = 0.50 221% and 25% at 200 and 300 K, respectively. Although the lowest statistical impact value calculated by the 3-parameter Weibull equation, as at Pf = 0 (as) was reduced in the 200 K samples, as was improved for the 77 and 300 K samples. The lower as for the 200 K samples is probably the result of high scatter in the data although the auc was remarkably improved at all experimental Pf. In general, the auc increased with test temperature. Optical observation shows the HLEBI appears to increase the auc by preventing brittle shattering of the ABS core in the 77 and 200 K samples, and increasing core ductility in the 300 K samples. Within the outer single CFRP plies the HLEBI strengthens by generating dangling bonds in the epoxy matrix as micro-compressive forces increasing adhesion to the fibers by terminated atoms by Coulomb attractive force. Since calculated HLEBI penetration depth, Dth into the sample was less (119 µm) than the 265 µm CFRP ply thickness, it is possible the strengthened plies carried the load protecting the ABS core. It is also possible the highly conductive carbon fibers transferred charge to the ABS core, generating dangling bonds and/or polarizing the ABS polymer strengthening the ABS itself preventing shattering.
  • Atomic Arrangement and Magnetic Order in Mn2RuZ (Z = Sn, Si)

    pp. 312-315

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    DOI:10.2320/matertrans.M2015358

    Recently, new compounds Mn2RuSn and Mn2RuSi were synthesized and their crystal structures were studied by X-ray diffraction measurements. This measurement indicates that they have a Heusler-like cubic structure, but the details have been unclear so far. To clarify their atomic arrangement and magnetic order, we carried out first-principles total-energy calculations for several different atomic arrangements, together with ferrimagnetic and ferromagnetic ordering. The comparison among total energies indicates that the most stable structure is a ferrimagnetic Hg2CuTi one in both Mn2RuSn and Mn2RuSi. We also found that the compound Mn2RuSi with the Hg2CuTi structure could be a half-metallic ferrimagnet.
  • Magnetic and Structural Properties of Metamagnetic MnCo0.92Fe0.08Ge Compound

    pp. 316-320

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    DOI:10.2320/matertrans.M2015382

    The magnetic and structural properties of ferromagnetic MnCo0.92Fe0.08Ge were investigated by magnetization and X-ray powder diffraction measurements in magnetic fields up to 5 T. The compound showed first-order transition between the paramagnetic and ferromagnetic state with a thermal hysteresis of approximately 24 K, which was accompanied by the martensitic transformation from the hexagonal Ni2In-type structure to the orthorhombic TiNiSi-type structure in the vicinity of 275 K. The cell volume expanded by 4.1% during the martensitic transformation. The magnetic moment of MnCo0.92Fe0.08Ge was estimated to be 111 Am2 kg−1 (3.7 μB/f.u.) at 10 K. The compound showed both metamagnetic transition and magnetic field-induced martensitic transformation.
  • Suppressed Hydrogen (H) Solubility in Body Centered Cubic Vanadium (V) by Alloying with Molybdenum (Mo), Chromium (Cr), Iron (Fe) or Cobalt (Co) Appreciated in Terms of Statistical Thermodynamics

    pp. 321-328

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    DOI:10.2320/matertrans.M2015415

    Equilibrium isothermal pressure-composition relationships reported for H solubility in body centered cubic (bcc) V1−yMyHx (M = Cr, Mo, Fe or Co) by Suzuki et al. recently on this journal were analyzed with statistical thermodynamics under a priori assumption of constant H-H interatomic interaction energy E(H-H) within homogeneity composition range of bcc V1−yMyHx phase at arbitrary temperature T. Results of the present statistical thermodynamic analysis showed that detected H solubility suppression for the examined V1−yMyHx was consistently interpreted in terms of decrease of available number θ for occupation by H atoms per metal atom in the V1−yMy lattice from θ = 0.55 determined for bcc VHx in the earlier work of the author. The extent Q of stabilization of H atoms in the V1−yMy lattice through formation of H-V and H-M bonds was one of principal parameters determined by the statistical thermodynamic analysis. It was intriguing to note that Q(V1−yMyHx) with M = Fe and Co became less negative than Q(VHx) in pure bcc VHx implying that the extent of stabilization of H atoms in V1−yMy lattice with M = Fe or Co increased with reference to that in pure VHx in spite of decreased θ from that (0.55) in VHx. On the other hand, Q(V1−yMyHx) with M = Cr and Mo became less negative (that is decreased stability of H) than Q(VHx) corresponding straightforwardly to the detected decrease of θ value from that in VHx. Noting the promoted H permeability reported for V1−yFey membrane by Suzuki et al., search for alloying element M that induced H solubility drop form that in the bcc V but with effect of enhancing stability of H in the V1−yMy lattice was concluded to be a pragmatic guideline for the screening of alloying constituent towards development of V-based H permeation membrane material.
  • Effects of Solute Fe, Zn and Mg on Recrystallization in Aluminum

    pp. 329-334

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    DOI:10.2320/matertrans.MBW201515

    In this work, the effects of solute Fe, Zn, and Mg on the suppression of recrystallization in Al are studied. The materials are Al-22.2 atomic parts per million (at ppm) Fe, Al-53.6 at ppm Fe, Al-0.1 at% Mg, Al-1.1 at% Mg, Al-0.1 at% Zn, and Al-3.0 at% Zn. All were synthesized using high-purity starting materials. The amount of impurities other than the additional elements is less than a few ppm. The variation in the Vickers hardness with annealing time after isothermal annealing treatments at various temperatures is measured. The results of the isothermal annealing treatments are discussed in terms of the Johnson–Mehl–Avrami–Kolmogorov (JMAK) equation. The effect of the suppression of recrystallization per concentration unit is highest for Fe, less so for Mg, and least for Zn. The values of the apparent activation energy for recrystallization are calculated as: 139, 146, 63, 66, 47.7, and 67 kJ/mol for Al-22.2 at ppm Fe, Al-53.6 at ppm Fe, Al-0.1 at% Mg, Al-1.1 at% Mg, Al-0.1 at% Zn, and Al-3.0 at% Zn, respectively. The values of the apparent activation energy for recrystallization are close to the values of the activation energy for grain boundary diffusion in the same alloy systems.
  • Geometry Effects in Four-Point Bending Test for Thin Sheet Studied by Finite Element Simulation

    pp. 335-343

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    DOI:10.2320/matertrans.M2015178

    Some experimental geometry parameters of four-point bending tests, such as span ratio and support radius, obtained from experience, likely lead systematic errors into the final results. In this paper, some typical geometry effects of four-point bending tests for thin sheet are investigated by employing finite element analysis (FEA). In order to assure the reasonability and accuracy of the FEA results, the standard tensile tests and four-point bending tests are carried out by commercial instruments. Based on the simulation results, it is noted that the stress distribution between the inner supports and outer supports is different with the variation of span ratio. The maximum wedging stress is located near the inner supports. According to the study, the optimum value of the span ratio is suggested to be around 1/3 at plastic stage. In addition, the effects of support radius and contact roughness are also discussed to make a beneficial reference for designing four-point bending experiments and devices.
  • Mechanical Properties and Dislocation Substructure of 6061-T6 Aluminum Alloy Impacted at Cryogenic Temperatures

    pp. 344-350

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    DOI:10.2320/matertrans.M2015170

    The mechanical properties and dislocation substructure of 6061-T6 aluminum alloy deformed at temperatures of 0°C, −100°C and −196°C and strain rates of 1000 s−1, 3000 s−1 and 5000 s−1 are investigated using a compressive split-Hopkinson pressure bar. It is found that the flow stress and strain rate sensitivity increase with increasing strain rate, but decrease with increasing temperature. In addition, the work hardening rate decreases with increasing strain rate and temperature. The flow stress corresponding to a true strain of 0.6 is modelled using a power law expression with an activation energy of 1.7 kJ/mol and an average strain rate sensitivity of 0.154. The dislocation density increases with increasing strain rate and decreasing temperature, and leads to a greater flow stress. A greater multiplication and tangling of the dislocations occurs at higher strain rates and lower temperatures. The flow stress and square root of the dislocation density are linearly related via the Bailey-Hirsch type relation σ = σ0 + α1Gb√ρ , where α1 has a value of 0.46 for the current 6061-T6 aluminum alloy.
  • Damping Characteristics of the Inherent and Intrinsic Internal Friction of Ti50Ni50−xFex (x = 2, 3, and 4) Shape Memory Alloys

    pp. 351-356

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    DOI:10.2320/matertrans.M2015425

    Ti50Ni50−xFex shape memory alloys (SMAs) have higher inherent and intrinsic internal friction peaks during R → B19′ transformation ((IFPT + IFI)R→19′) than during B2 → R transformation ((IFPT + IFI)B2→R). The reasons are that the former has the larger transformation strain and the abundant movable twin boundaries appearing in both R-phase and transformed B19′ martensite. Ti50Ni50−xFex SMAs also exhibit higher (IFPT + IFI)R→19′ peaks than annealed Ti50Ni50 SMA after cold-rolling because the latter needs dislocations to be introduced to form R-phase, but the former does not. For Ti50Ni48Fe2 SMA, the tan δ values of the (IFPT + IFI)B2→R and (IFPT + IFI)R→B19′ peaks and that of IFI in the R-phase regime decrease after the dehydrogenation treatment at 600°C for 6 h in a vacuum furnace, due to pinning of the twin boundaries by hydrogen atoms. However, the hydrogen pinning effect is small for IFI in B2 phase and B19′ martensite. Ti50Ni50−xFex SMAs with x = 2 and 3 at% have quite good (IFPT + IFI)R→19′ tan δ values (> 0.035), but their low transformation temperatures may restrict their use in practical high-damping applications.
  • A Novel Process for the Production of Gold Micrometer-Sized Particles from Secondary Sources

    pp. 357-361

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    DOI:10.2320/matertrans.M2015266

    A novel method for the production of gold micrometer-sized particles from secondary sources is presented. The method consists of the leaching of gold using dimethyl sulfoxide (DMSO, (CH3)2SO) solutions containing copper chloride (CuCl2) followed by the precipitation of gold with hydrochloric acid (HCl). Gold was dissolved in a DMSO solution with 0.1–0.2 M CuCl2 and 0–0.3 M sodium chloride (NaCl) at 343 K. The precipitation of dissolved gold was performed by the addition of HCl, during which the effects of the concentration of the Cl ion was investigated. It was found that the initial gold dissolution rate in DMSO solutions with CuCl2 was up to 14.8 mg cm−2 h−1, which was larger than the rates obtained with other leaching methods, but smaller than the author’s previous research using copper bromide (CuBr2) and potassium bromide (KBr). A gold recovery efficiency of up to 92.6% was obtained by precipitation with HCl solution. We obtained “raspberry-like” or “confeito-like” gold microspheres under the condition of less than 1.5 M of Cl ion and over 0.013 M of dissolved gold. Our results demonstrated that a circulating system for gold leaching and recovery and production of functional material could be developed, which would offer a number of advantages, including eco-friendliness, easy operation, low costs, and minimization of chemical sludge production.
  • Hardness and Wear Properties of Ti-Mo-C-N Film

    pp. 362-367

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    DOI:10.2320/matertrans.M2015383

    The hardness and wear properties of Ti-Mo-C-N films were investigated by nanoindentation and ball-on-disc measurements, respectively. Ti-Mo-C-N films were deposited onto a stainless steel substrate by a reactive RF magnetron sputtering in the mixture of argon (7.5 ccm) and nitrogen (0–6.0 ccm) gases using Ti25Mo25C50 target. Ti-Mo-C film deposited without nitrogen gas flow showed a hardness of 34.8 GPa. The hardness drastically decreased with increasing nitrogen gas flow rate (fN2) and reached to a minimum hardness of 16.4 GPa at fN2 = 2.0 ccm. Contrarily, at over fN2 = 3.0 ccm, the hardness drastically increased with increasing fN2 and reached a maximal value of 32 GPa, and then slightly decreased again with further increase of fN2. It was found by TEM observation that the drastic decrease in hardness is caused by the formation of nanocrystalline microstructure, while the increase in hardness is due to the microstructural change from nanocrystalline to columnar structure. The friction coefficient decreased with increasing fN2 and the film deposited at fN2 = 5.0 ccm showed a minimum value of 0.27. The simple oxidation test in air indicated that lubricious MoO3 is easy to be formed in the film deposited at a high fN2, which should cause the reduction of friction coefficient.
  • High Adhesive Force between Laminated Sheets of Titanium and Polyurethane Improved by Homogeneous Low Energy Electron Beam Irradiation Prior to Hot-Press

    pp. 368-372

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    DOI:10.2320/matertrans.MBW201513

    2-layer Titanium/Polyurethane (Ti/PU) laminated sheets were prepared by a new adhesion method, a double-step treatment consisting of applying low dose (≦ 0.43 MGy) homogeneous low energy electron beam irradiation (HLEBI) prior to hot-press under 5 MPa and 413 K. Although the weak hot-press adhesion of the Ti/PU was observed without HLEBI, the new adhesion raised the bonding forces as evidenced by the mean adhesive forces of peeling resistance (oFp). Based on the 3-parameter Weibull equation, the lowest oFp value at peeling probability (Pp) of zero (Fs) could be estimated. An increasing trend in Fs occurred by the double-step treatment applying HLEBI up to 0.22 MGy reaching a maximum at 123 Nm−1, improving the safety level without radiation damage. XPS (X-Ray Photoelectron Spectroscopy) observations of the peeled 0.22 MGy irradiated Ti revealed generation of a TiO2 peak at 530.6 eV possibly explaining the increased adhesion. The residual PU deposition is apparently found to be retained on the Ti sheet by inter-matrix fracture of PU further into the thickness. This can be explained by the adhesion force between Ti/PU being stronger than the cohesive force of PU polymer itself.
  • Effects of Homogeneous Low Energy Electron Beam Irradiation (HLEBI) on Adhesive Force of Peeling Resistance of Laminated Sheet with Polyethylene (PE) and Austenitic 18-8 Stainless Steels

    pp. 373-378

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    DOI:10.2320/matertrans.MBW201509

    2-layer laminated sheets (PE/18-8) with Polyethylene (PE) and austenitic 18-8 stainless steels (18-8) were prepared by a new adhesion method, a double-step treatment consisting of applying low dose (≦0.43 MGy) homogeneous low energy electron beam irradiation (HLEBI) prior to hot-press under 5 MPa and 343 K. Although the weak hot-press adhesion of the PE/18-8 was observed without HLEBI, the new adhesion raised the bonding forces as evidenced by the mean adhesive forces of peeling resistance (oFp). Based on the 3-parameter Weibull equation, the lowest oFp value at peeling probability (Pp) of zero (Fs) could be estimated. An increasing trend in Fs occurred by the double-step treatment applying HLEBI up to 0.30 MGy reaching a maximum at 0.85 N m−1, improving the safety level without radiation damage. When HLEBI cut the chemical bonds in PE polymer and generated terminated atoms with dangling bonds, they probably induced the chemical bonding. Therefore, increasing adhesion force between the laminated sheets could be explained.
  • Effects of Number of Graphite Nodules on Fatigue Limit and Fracture Origins in Heavy Section Spheroidal Graphite Cast Iron

    pp. 379-384

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    DOI:10.2320/matertrans.F-M2015841

    The purpose of this study is to investigate the effects of number of graphite nodules on fatigue limit and fracture origins in spheroidal graphite cast iron where carbon content and the number of graphite nodules are changed. As specimens, spheroidal graphite cast irons with 3.0, 3.2, 3.4, 3.6 and 3.8 mass% carbon content were produced respectively. Matrix was conducted pearlite (PDI) and ausferrite (ADI) by heat treatment (normalizing and austempering). The mean diameter of the graphite nodule decreases as the carbon content increases, and the number of graphite nodules per unit area increases. No differences were observed in tensile strength as a result of variations in the number of graphite nodules. The rotating bending fatigue test was conformed to JIS (Japanese Industrial Standards). Load frequency was 47 rpm, number of cycle to discontinue test was 1.0 × 107 cycles, and the specimen used was the 1 type of 8.00 mm in diameter. All the fracture surfaces were observed with a scanning electron microscope. The relationship between the characteristics of fatigue strength and the size of fracture origins (defect size) was investigated.
    No differences were observed in fatigue limit as a result of variations in the number of graphite nodules. Fracture origins were micro-shrinkage, unspheroidizing graphite nodule and aggregate graphite nodules. The percentage of fracture origin of aggregate graphite nodules was increased by cluster of the graphite nodules. The reason of this phenomenon was due to the decrease of the graphite nodules spacing. The mean defect size in each sample was constant irrespective of the change of number of graphite nodules, which was good agreement with the results of the fatigue limit.
  • Mechanical Properties and Deposition Mechanism of Cold-Sprayed CoNiCrAlY/YSZ Cermet

    pp. 385-391

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    DOI:10.2320/matertrans.T-M2016802

    The properties of agglomerated and sintered powders of the cermet of yttria-stabilized zirconia (YSZ)/CoNiCrAlY and coatings thereof were investigated. Three multimodal cermet powders were prepared with different compositions (75% CoNiCrAlY:25% YSZ; 50% CoNiCrAlY:50% YSZ; and 25% CoNiCrAlY:75% YSZ) for deposition by a cold-spraying process. Each of the cermet powders was successfully deposited onto a bond-coated substrate by the cold-spray process with low kinetic energy. Each feedstock powder ensured a homogeneous distribution of YSZ powders in the coating layer. The microstructural characterization and phase analysis of the feedstock powders and the as-sprayed coatings were obtained by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). In the XRD and EDX results, the YSZ content in the coating increased with the increase of YSZ content in the powder blend. Against conventional expectations, the deposition efficiency and hardness of the as-sprayed coatings were improved by low gas pressure. In particular, the as-sprayed coatings with more than 50 mass% YSZ showed decreased cracks in the coating layer. To understand these results, the cermet particles were coated onto Al substrates by cold-spraying. Then, the particles were cut open to observe the bonded cross-sectional surface by focused ion beam (FIB) analysis.
  • Fabrication of Reliable Joints of Alumina Ceramics by Microwave-Assisted Reactive Brazing Technique

    pp. 392-396

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    DOI:10.2320/matertrans.M2015350

    Microwave-assisted reactive brazing technique was utilized for joining of alumina ceramics at 950°C and 1050°C for 20 min in argon atmosphere using TICUSIL (68.8Ag-26.7Cu–4.5Ti in mass%) paste as the braze alloy. Conventional heating technique was also employed for comparison purpose only. The microwave and conventionally brazed joints were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis and Vickers microhardness measurement. X-ray diffraction data showed that the Ti-based compounds were formed at the substrate-filler alloy interfaces of the microwave and conventionally brazed joints. Scanning electron microscopy exhibited the formation of thicker reaction region in the case of joints microwave brazed at higher temperature. Energy dispersive X-ray analysis determined the elemental compositions across the joint cross-section. Vickers microhardness measurements indicated more reliable performance of the joints microwave brazed at lower temperature. Hermiticity of the microwave and conventionally brazed joints was evaluated by Helium leak test and found to be acceptable for actual applications.
  • Frequency Dependence of the Defect Sensitivity of Guided Wave Testing for Efficient Defect Detection at Pipe Elbows

    pp. 397-403

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    DOI:10.2320/matertrans.M2015319

    Guided wave testing offers an efficient screening method for thinning of pipe walls because of its long inspection range and its ability to inspect pipes with limited access. However, the existence of an elbow in pipes makes the interpretation of echo signals difficult. The present study investigates the sensitivity of defect detection when guided wave testing is applied to detect a defect at a pipe elbow. To examine the defect sensitivity when a defect exists at different locations on an elbow, an artificial defect was produced at one of 12 different locations on the outer surface of the elbow of each aluminum alloy piping specimen. The defect signals were observed as the defect depth was gradually increased at each defect location to obtain the defect sensitivity. The transmitted guided wave frequency was in turn set to 30 kHz, 40 kHz, and 50 kHz. At 30 kHz, high sensitivity values were obtained at the intrados of the elbows, whereas at 40 kHz and 50 kHz, high sensitivity values were obtained at their extrados. This paper also shows the results of computer simulations that used the same configuration as that used in the experiments to analyze the propagation behavior of guided waves passing through the elbow. In addition to the experimental results, the simulation results indicate that the defect-sensitive locations are controlled by the guided wave frequency. Thus, proper selection of the excitation frequency for guided wave testing enables efficient defect detection at pipe elbows.
  • Effect of Process Parameters on Purification of Aluminium Alloys by Backward Extrusion Process under a Semisolid Condition

    pp. 404-409

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    DOI:10.2320/matertrans.M2015381

    Although the recycling of aluminium has many environmental and economic benefits, the accumulation of impurities is a problem in the case of repeated recycling. In this study, the purification of A7075 wrought aluminium alloy and ADC12 based hypereutectic aluminium alloy was conducted by the backward extrusion process under a semisolid condition. The effect of process parameters such as the semisolid temperature and backward extrusion ratio was investigated. From the results of optical microscopic imaging, scanning electron microscopy (SEM) and energy-dispersive X-Ray spectroscopy (EDS) analysis, it was confirmed that the percentage of purified aluminium, the distribution of aluminium and the yield of the purified part for A7075 alloy were significantly affected by the semisolid temperature and extrusion ratio. For ADC12 based hypereutectic aluminium alloy, it was found that the silicon flakes still remained even in the unextruded part after the purification process.
  • Effect of Casting Parameters on the Microstructure and Mechanical Properties of ADC10 Alloys Using a Semisolid Die Casting and Heat Treating Process

    pp. 410-416

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    DOI:10.2320/matertrans.M2015406

    The effect of casting parameters on the microstructure and mechanical properties during semisolid die casting using commercial ADC10 alloys was studied. Fine and uniform globular microstructures were produced using optimized casting conditions, where low pouring temperatures of 878 K (605°C) and pre-heating of the slurry-making container temperatures up to 523 K (250°C) resulted in better microstructural control. To obtain the conditions for high quality slurries within a mass production system, the microstructural characteristics of slurries produced with various cooling rates were analyzed. Cooling rates between 0.1°C/s and 0.9°C/s were found to result in comparatively good microstructural characteristics, which corresponded to form factors of 0.75 or greater and α-Al particles less than 65 µm in the slurries. The hardness and tensile strength were evaluated for T6 heat-treated semisolid die cast products and compared with the properties of high-pressure die cast specimens. Transmission electron microcopy (TEM) and electron probe micro-analysis (EMPA) were also used to identify and verify the precipitated secondary phases and the solute distribution.
  • Internal Activation of Thermoplastic Polypropylene GFRTP Composite by Homogeneous Low Energy Electron Beam Irradiation (HLEBI) of the Interlayered Glass Fiber Chopped Strand Mats (GF-CSM) Prior to Assembly

    pp. 417-422

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    DOI:10.2320/matertrans.MBW201510

    A new process of internal activation of glass fiber reinforced thermoplastic polymer (GFRTP) of Polypropylene (PP) was achieved by homogeneous low energy electron beam irradiation (HLEBI) to the interlayered glass fiber chopped strand mats (GF-CSM) prior to assembly. Panels were fabricated by hot-press consisting of 5 HELBI-treated GF-CSMs between 6 untreated PP sheets. HLEBI improved the Charpy impact value (auc) of the internally activated GFRTP. HLEBI from 0.22 to 0.86 MGy mostly improved the auc at each accumulative probability of fracture (Pf). Based on the 3-parameter Weibull equation, the auc value was defined as the statistically lowest impact value, as estimated as the auc at Pf = zero. The highest as values at more than 87 kJ/m2 were found for GFRTP irradiated at 0.65 MGy which appears to be at or near the optimum HLEBI dose. Strengthening the adhesion force at the extremely broad surface area of the fibers increased interfacial friction force to prevent fiber pull out, fiber/matrix debonding and crack generation in the hard to adhere PP matrix GFRTP, resulting in increasing auc of GFRTP with glass fiber surface-activated by HLEBI.
  • Investigation of New Ammonia Synthesis Process Utilizing Vanadium-Based Hydrogen Permeable Alloy Membrane

    pp. 423-427

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    DOI:10.2320/matertrans.MBW201507

    The possibility of a new ammonia synthesis process has been investigated by utilizing V-based alloy membrane under moderate temperature and pressure conditions. Three membrane samples with different coating conditions of Pd-Ag alloy on the outlet side surface have been tested. It is found that the deposition of Pd-Ag alloy on the outlet side surface is needed for V-based alloy membrane for hydrogen permeation at 623 K. While keeping the hydrogen permeation condition, nitrogen gas is flowed to the outlet side surface of the membrane samples, and the reaction gas is bubbled into distilled water to detect ammonia formation by using Nessler’s reagent. Ammonia is not synthesized for the membrane sample coated thickly with Pd-Ag alloy on the outlet side surface, indicating that Pd-Ag alloy does not have a dissociation ability of nitrogen molecule. In contrast, ammonia is formed for the membrane sample coated in a grid pattern with Pd-Ag alloy on the outlet side surface. In this case, both V-based alloy and Pd-Ag alloy coexist on the outlet surface, and hydrogen atoms permeating through the membrane and nitrogen atoms dissociated on the surface of V-based alloy probably react with each other to form ammonia.
  • Microbially Induced Sand Cementation Method Using Pararhodobacter sp. Strain SO1, Inspired by Beachrock Formation Mechanism

    pp. 428-437

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    DOI:10.2320/matertrans.M-M2015842

    To develop an alternative ground improvement technique in coastal areas based on bio-stimulation, we investigated sand cementation using bacteria that have been shown to enhance beachrock formation. We conducted cementation tests using Pararhodobacter sp. strain SO1, a local ureolytic bacteria originating from the sand near beachrock in Okinawa, Japan. Specifically, we attempted to cement sand specimens to unconfined compressive strength (UCS) of several MPa and establish the influence of several test conditions (curing temperature, injection interval of cementation solution, Ca2+ concentration and sodium malate concentration in the cementation solution, and test period) on the UCS. Column specimens were cemented up to UCS of 10 MPa after 28 days under the conditions (curing temperature; 30°C, injection interval; 1 day, Ca2+ concentrations in cementation solution; 0.3 M). Multiple regression analysis showed that the relevant conditions for UCS were test period, D (days), and Ca2+ concentration of the cementation solution, Cca (M). The prediction formula for UCS, qud (MPa), was experimentally determined to be qud = 48.3Cca + 0.456D − 19.51. Overall, the results of this study will contribute to the application of a new technique for coastal sand improvement and bio-stimulation.
  • Novel Numerical Simulation of the Stereological Bias of Binary Particles

    pp. 438-444

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    DOI:10.2320/matertrans.M-M2016801

    Stereological correction, which corrects an overestimation of the degree of liberation of minerals in a two-dimensional measurement, has not been adequately established, despite its importance in the evaluation of not only the crushed product but also the efficiency of comminution and sorting in the mining process. A unique numerical method was conducted using Discrete Element Method in order to investigate the relationship between the two-dimensional information obtained by cross-sectional measurement and three-dimensional practical information. First, spherical particles of a certain-sized dispersion were packed in a sampling cell. Following this, phases with a lognormally distributed volume fraction, which was designated by a median MD and standard deviation SD, were placed between the particles. Finally, the serial cross-sectional information was analyzed in the height direction, and the following fundamental results were obtained: 1) the area fraction of the cross-sectional circles distributed around the practical volumetric fraction and 2) the degree of liberation was overestimated by the two-dimensional cross-sectional measurement. A series of parametric studies was then conducted on the phases using various MD and SD values, and a correlation between the two-dimensionally measured and three-dimensional actual parameters was obtained. In using this correlation, the volumetric distribution of the phase, together with its degree of liberation (which is usually difficult to measure directly), was estimated with parameters obtained by cross-sectional measurement, such as optical microscopy, QEM*SEM, and MLA. This was based on the assumption that all the particles include a single spherical phase with a lognormally distributed volume.
  • Effects of Doping Elements in β-FeSi2 Prepared Utilizing Cast Iron Scrap Chips

    pp. 445-451

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    DOI:10.2320/matertrans.M2015357

    In this work, the thermoelectric properties of p- and n-type β-FeSi2, prepared utilizing cast iron scrap chips, have been characterized by measuring the Seebeck coefficient, electrical conductivity and thermal conductivity at temperatures ranging from room temperatures to 800°C. In a previous study, the upgrade recycling of cast iron scrap chips into β-FeSi2 thermoelectric materials was proposed as an eco-friendly and cost-effective production process. By doping with different substitution concentrations of Co, Mn and Al, the conduction type and properties of β-FeSi2 can be modified and improved using cast iron scrap chips as a starting material. The effects of the doping elements are discussed for preparing β-FeSi2 utilizing cast iron scrap chips. Cast iron scrap chips could be preferable as a starting material to replace pure Fe for n- and p-type β-FeSi2 thermoelectric materials. An optimum composition for n-type β-FeSi2 0.94C.I.-0.06Co-1.86Si shows that the largest ZT value of 0.22 occurs at 700°C, whereas for p-type β-FeSi2 0.92C.I.-0.08Mn-1.86Si, the largest ZT value of 0.17 occurs at 800°C.
  • Gas Separation Properties of the Dense Polymer — Zeolite Powder Composite Membranes

    pp. 452-456

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    DOI:10.2320/matertrans.M2015387

    The natural balance in the Earth’s atmosphere is significantly influenced by the human emission of the combustion products, mainly carbon dioxide. Therefore, strong efforts are directed in the direction of the reduction of that emission. The solution might be searched in the direction of the construction of the membrane that would be highly transparent to the carbon dioxide, but not transparent to the other gases commonly present in the waste gases (oxygen, nitrogen, hydrogen, methane). One of the feasible designs for this purpose is dense, non-porous membranes, with zeolite particles dispersed in the polymer matrix. Zeolite particles should increase the solubility of the carbon dioxide, and thus enhance its permeability. In this paper, the possibility of application of polyether-b-amide (with 60% of PEG) as a polymer matrix was tested. For the inorganic component, four different zeolite types with three different pore geometries were tested. The influence of the additive which was added in order to provide good contact between the highly polar and charged zeolite inorganic particle, and hydrophobic polymer chains was also tested.
  • Planar Bonded Magnets with 52% Enhanced Stray Magnetic Flux Density and the Same Polarity at Both Surfaces via Homopolar Magnetization

    pp. 457-460

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    DOI:10.2320/matertrans.MBW201506

    An optimized homopolar magnetizing fixture consisting of four magnetic pole pieces was developed with the aim of achieving a focused magnetic flux on the surfaces of Nd-Fe-B alloy-based permanent magnets, and thus enhancing the magnetic flux density. In this fixture, only the transverse pieces involved coils providing the same magnetic poles in response to a pulsed current. Rectangular anisotropic and isotropic bonded magnets as well as sintered magnets, having dimensions of 6 mm × 12 mm × 24 mm or 6 mm × 12 mm × 16 mm, were magnetized to multipoles using a prototype fixture in conjunction with a pulsed power source. As a result, the magnetic flux density perpendicular to the surface (Bz) was increased by 52% relative to that of conventional simple magnets containing the same volume of magnetic compound, with the front and back surfaces magnetized to opposite polarities. In addition, the Bz polarities of both the front and back sides of the magnet were determined to correspond to N-poles. The distribution pattern of Bz led us to conclude that the enhanced Bz and the equal polarity on both sides can both be attributed to the cusp field resulting from the flux generated by the transverse coils of the magnetizing fixture.
  • Effects of Si on Microstructures and High Temperature Properties of Beta Stabilized TiAl Alloy

    pp. 461-465

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    DOI:10.2320/matertrans.M2015355

    The effects of Si addition on microstructures, high temperature compressive properties and creep properties of the β-stabilized Ti-45Al-3Fe-2Mo alloy have been studied in this work. The results show that the Si addition decreases the volume fraction of β phase and precipitates particulate Ti5Si3 phase. At the same time, the Si addition improves the high temperature strength of the Ti-45Al-3Fe-2Mo alloy for about 200 MPa at 800°C and decreases the creep strain for about 35% at 800°C under an applied stress of 150 MPa. The decrease in volume fraction of β phase and precipitation of Ti5Si3 particles are believed to be the dominant mechanisms for the improvement of the high temperature properties of the Si-doped TiAl alloy.
  • Board Level Drop Reliability of Epoxy-Containing Sn-58 mass% Bi Solder Joints with Various Surface Finishes

    pp. 466-471

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    DOI:10.2320/matertrans.M2015260

    Board-level drop reliability testing under JEDEC (Joint Electron Device Engineering Council) drop conditions was conducted for low-temperature Sn-58 mass%Bi solder joints. The effects of surface finish and the number of reflow processes (one, three, or five) on the drop reliability of the Sn-58Bi joints were evaluated. Three types of surface finishes were used including electroless nickel immersion gold (ENIG), electroless nickel electroless palladium immersion gold (ENEPIG), and organic solderability preservatives (OSP). We successfully fabricated six types of drop test specimens with various surface finishes and bonding materials, and then performed the board-level drop tests. The board-level drop reliability was improved when using the composite Sn-58Bi solder with epoxy as compared to Sn-58Bi solder without epoxy. In addition, the reliability of the Sn-58Bi epoxy solder/OSP joint was better than both the ENIG and ENEPIG surface finishes. When the number of reflow processes increased, the drop reliability showed two different behaviors; specifically, the reliability of the ENIG and ENEPIG surface finishes decreased while the OSP surface finish improved. The existence of epoxy in the solder paste improved the drop reliability of the solder joints. After drop testing, cracks propagated differently with different surface finishes, namely between Ni3Sn4 IMCs and the Ni-P layer for the ENIG surface finish, between Ni3Sn4 IMCs and the solder bulk for the ENEPIG surface finish, and within the solder bulk for the OSP surface finish. These data show that, when it is necessary to perform repeated reflow processes for electronic components, solder joints with an OSP surface finish provide better drop test reliability results.
  • Micro-Scale Cyclic Bending Response of NiTi Shape Memory Alloy

    pp. 472-475

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    DOI:10.2320/matertrans.M2015423

    Fatigue performance of micro-scale pseudoelastic nickel-titanium (NiTi) wires was investigated under cyclic bending loading. The current findings demonstrated that the change from macroscopic to microscopic scale promotes the formation of the B19′ phase and significantly hinders stabilization of the R-phase.

Article Access Ranking

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