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

MATERIALS TRANSACTIONS Vol. 54 (2013), No. 11

  • Enhanced Strength and Electrical Conductivity of Cu–8Fe Composite by Adding Trace Ag and P

    pp. 2075-2078

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    DOI:10.2320/matertrans.M2013260

    Cu–8Fe–0.5Ag–0.02P (mass%) in situ composites were fabricated by inductive melting and then the as-casted sample drew heavily at room temperature to refine the microstructure and optimize the mechanical and electrical properties. The microstructure evolution of the composite during drawing was investigated, while the tensile strengths and electrical conductivity of the as-drawn samples were measured. Comparing to Cu–8Fe composite, the tensile strength and electrical conductivity were enhanced largely by adding trace Ag and P. The results show that trace Ag refines the primary Fe dendrites and promotes the precipitation of secondary phase Fe particles. Trace P reacts with the solid solution Fe atoms and then facilitates ellipsoid Fe3P particles precipitation. The mechanical strength and electrical conductivity of Cu–8Fe–0.5Ag–0.02P were improved obviously, which is attributed to the combined effects of trace Ag and P.
  • Effect of Addition of Phosphate Powder on Unconfined Compressive Strength of Sand Cemented with Calcium Phosphate Compound

    pp. 2079-2084

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    DOI:10.2320/matertrans.M-M2013827

    For the purpose of improving a novel grout composed of a calcium phosphate compound (CPC-Chem), we have conducted an unconfined compressive strength (UCS) test on samples cemented with CPC-Chem and tricalcium phosphate (TCP) powder. The UCS of these test samples was significantly larger than the UCS of the non-additive test samples. The UCS reached the targeted value of over 100 kPa, and after 28 days of curing, reached a maximum of 261.4 kPa. Additionally, the pH of the samples cemented with CPC-Chem and TCP powder was weakly acidic. These results suggest that the novel geotechnical method using a combination of CPC-Chem and TCP powder has the potential to be used as a non-contaminating and recyclable application, as a biogrout that uses microbial activity and for ground improvement because it satisfies the strength requirements for practical use.
  • Effect of High-Density Electric Current on the Microstructure and Fatigue Crack Initiation of Stainless Steel

    pp. 2085-2092

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    DOI:10.2320/matertrans.M2013198

    To investigate the effect of high-density electric current on the delay of fatigue crack initiation, the dislocation structures before and after the application of electric current were investigated by transmission electron microscopy. Dislocation density was quantitatively characterized before and after the application of electric current to further understand the mechanics of the healing effect. Atomic force microscope results showed that the slips disappeared locally and the slip height decreased on the surface of the specimens. Furthermore, the delaying effect of the crack initiation due to the application of electric current was evaluated by the fatigue crack-initiation model in which the accumulation of the dislocation density was considered.
  • Effects of Stacking Fault Energy on Fundamental Deformation Modes in Single Crystalline Magnesium by Molecular Dynamics Simulations

    pp. 2093-2097

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    DOI:10.2320/matertrans.MAW201311

    In order to investigate effects of stacking fault energies (SFEs) on fundamental deformation modes of slips and deformation twinnings in magnesium, we carried out molecular dynamics simulations of shear deformations for the deformation modes with two kinds of many-body interatomic potentials. The SFEs of the basal and second-pyramidal planes are lower for a generalized embedded atom method (GEAM) potential than for an embedded atom method (EAM) potential. While the basal slip quite easily occurs and the prism dislocation is activated, the first-pyramidal slip and the second-pyramidal slip are hard to be operated. However, for the GEAM simulations, the second-pyramidal slip was activated due to reduction of the second-pyramidal SFE. Additionally, the reduction of the SFEs suppresses nucleation of the {10\bar{1}1} twin in the b2{10\bar{1}1} shearing direction. The relative order of the other fundamental deformation modes in the critical shear stress is qualitatively maintained despite the reduction of the SFEs.
  • TiC Coating on Titanium by Carbonization Reaction Using Spark Plasma Sintering

    pp. 2098-2101

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    DOI:10.2320/matertrans.L-M2013829

    Hard TiC coating layer is formed on commercially pure titanium by heat treatment in a spark plasma sintering (SPS) mold filled with graphite powder. In case of heat treatment at 1243 K for 3600 s, the obtained thickness of the coating layer is about 10 µm and almost uniform. This coating itself consists of TiC and graphite, and there is no titanium oxide detected by X-ray diffractometer (XRD). Vickers hardness tests have revealed that the hardness of titanium coating is 1600 HV, which is much higher than that of the titanium substrate (130 HV). The hard TiC coating on titanium is considered to be advantageous when applied to load bearing parts of hard tissue replacements. The growth behavior of TiC is parabolic with an activation energy of 218.6 kJ/mol. This value is close to the activation energy of carbon diffusion in TiC. Therefore, the growth rate of TiC is rate-controlled by inward diffusion of carbon in the TiC phase.
  • Fabrication of Porous Al–Cu Alloys with Aligned Unidirectional Pores by Dipping Pipes in Melt and Semi-Solid Slurry

    pp. 2102-2108

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    DOI:10.2320/matertrans.L-M2013828

    Aligned seven pure aluminum pipes with internal diameter of 3 mm and wall thickness of 0.5 mm were dipped into Al–4 mass% Cu melt and semi-solid slurry. The specimen was cooled and solidified after holding times 0, 15 and 30 s. The pipes were bonded to the base metal with maintaining the shape of pipes by using the semi-solid base metal. An increase in solid fraction of the base metal is effective to avoid thermal damage of the pipes. Penetration of Cu into the pipe was found by EPMA analyses. Diffusion of Cu from the base metal to grain boundary of pipes decreases the liquidus temperature of α phase in the vicinity of the grain boundary of the pipes. As a result, the α phase melted partly and the pipes were bonded to the pipes with the base metal metallurgically. Porous Al–Cu alloys with aligned unidirectional pores with porosity of 26% are fabricated by this method.
  • Influence of Casting Conditions on Initially Solidified Structures Formed during Permanent-Mold Casting of Zn–Al and Al–Cu Alloys

    pp. 2109-2118

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    DOI:10.2320/matertrans.M2013160

    Molten Zn–2.54 mass% Al (the Zn–2Al) and Al–2.35 mass% Cu (the Al–2Cu) alloys were poured on the copper chill block to obtain initially solidified structures on the bottom of the specimen. The Zn–2Al alloy poured on the chill block polished with emery paper formed discs that protruded about 1 µm from the bottom of the alloy specimen, as the case of the Al–2Cu alloy. From the discs, predendrites that forms a cellular structure extended radially, and then dendrites grew outside the predendrites in the preferred orientation. The solute content had a local maximum at the center of the disc, which suggests that the solidification began from undercooled liquid. The orientation of the discs formed on the bottom of the Zn–2Al ally specimen was [0 0 0 1] direction, but the discs formed on the bottom of the Al–2Cu alloy specimen did not show a specific orientation. With increasing surface roughness of the polished chill block, the disc diameter increased but the areal number density of discs decreased. Furthermore, with increasing pouring temperature, the disc diameter and the areal number density of discs both increased. For a buffed chill block, however, no disc appeared for the Zn–2Al alloy specimen but fine dendrites appeared on the bottom. In contrast, large discs formed on the bottom of the Al–2Cu alloy. In particular, when the molten Al–2Cu alloy was poured at 800°C or higher on the buffed chill block, two types of discs appeared on the bottom: normal discs of 20 to 30 µm in diameter, and very large discs (superdiscs) of 100 to 200 µm in diameter. Following these results, the formation process of the initially solidified structure is discussed.
  • Intergranular Segregation in the Pressure Vessel Steel of a Commercial Nuclear Reactor Studied by Atom Probe Tomography

    pp. 2119-2124

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    DOI:10.2320/matertrans.M2013133

    Solute/impurity segregation and precipitation at grain boundaries (GBs) in a nuclear reactor pressure vessel (RPV) steel were investigated using laser-assisted atom probe tomography (APT): RPV surveillance test specimens irradiated in a commercial nuclear reactor to neutron doses of 0.83 × 1019 n·cm−2 (low-dose) and 5.1 × 1019 n·cm−2 (high-dose), corresponding to in-service exposure of ∼5 and ∼30 years, respectively. The segregation of C, P and Mo was found on GBs after the low-dose irradiation. The segregation of Si and Mn as well as C, P and Mo was observed after the high-dose irradiation. The monolayer coverage of P is estimated to be less than a suggested level for intergranular embrittlement. The segregation of C, P and Mo was also observed along parallel array of dislocation lines in small-angle grain boundaries. However, no segregation of Si and Mn was detected there. Copper-nano precipitates (CNPs) were observed on the GBs, along the dislocation lines and in the matrix. The sizes and the solute-impurity enrichment in these CNPs are compared.
  • Effects of Electrostatic Discharge Stress on Electrical Properties of Bidirectional TVS Zener Diode with Abrupt Junctions

    pp. 2125-2130

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    DOI:10.2320/matertrans.M2013144

    A bidirectional transient voltage suppressor (TVS) Zener diode was fabricated with abrupt junctions using the low-temperature epitaxy process. The effects of various electrostatic discharge (ESD) stresses on the electrical properties are demonstrated, such as the current–voltage (IV) and 1/f noise power spectral density (PSD). Very sharp and uniform bidirectional multi-junctions result in good symmetric IV behavior over a wide range of operating temperatures of 300–450 K. The differential resistance in the breakdown region is only 0.2 Ω, and the reverse leakage current density is completely suppressed to 1.5 × 10−4 A/m2. The thermal activation energy obtained from the Arrhenius plot is nearly equal to half the band gap of Si, indicating that the reverse leakage current is dominated by thermal generation at the depletion edges for the entire reverse bias regions. The manufacture bidirectional TVS devices exhibit excellent ESD robustness, regardless of the stress conditions of the human body model and electrical fast transient. However, a ±4.5 kV machine model and ±13 kV IEC61000-4-2 stresses led to severe damage of the epitaxially grown junction, resulting in rapid increases in both the reverse leakage current and 1/f noise PSD.
  • Effects of Ti Addition into Core Alloy on Forming and Brazing Characteristics of 4343/3003/4343 Aluminum Alloy Clad Sheets

    pp. 2131-2138

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    DOI:10.2320/matertrans.M2013213

    The effects of Ti addition into a 3003 core alloy on the cold press forming and brazing properties of 4343/3003/4343 aluminum clad sheets were investigated. 3003 alloys with various Ti addition levels (0, 0.02 and 0.16 mass%) were prepared by adding with an Al–10 mass%Ti master alloy; these alloys were then fabricated into three-layer clad sheets by a roll-bonding process. The addition of a small amount of Ti into the 3003 core alloy at the initial casting stage had a large effect on the grain structure and microstructure of the core layer (after stress relief annealing) and the filler layer (after brazing), as well as on the grain structure in the as-cast state. The cold-forming characteristics of the clad sheets strongly depended on the recrystallization and grain growth behavior of the 3003 core layer during stress relief annealing at different Ti addition levels. Moreover, Ti addition increased the press formability of the clad sheets at room temperature by twofold or more. A coarse microstructure of the resolidified filler layer due to slow cooling during the brazing process was observed to cause intergranular cracking in the filler layer of the clad sheets. For this reason, significant Ti migration from the core layer to the clad layer improved the brazing strength of the clad sheets, refining the microstructure of the resolidified filler layer. Further, sagging resistance during the brazing process was also improved upon increasing the Ti level.
  • Vacuum Ultraviolet Irradiation Treatment for Reducing Gold–Gold Bonding Temperature

    pp. 2139-2143

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    DOI:10.2320/matertrans.MF201313

    Low-temperature Au–Au bonding was achieved under vacuum ultraviolet irradiation in the presence of oxygen gas (VUV/O3). The Au surfaces obtained after the VUV/O3 treatment were analyzed by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) measurements. The results indicate that the amount of carbon-based contaminants was dramatically decreased and that there was no serious damage to Au surfaces caused by the VUV/O3 treatment. The Au–Au bonding temperature was successfully reduced to 150°C after the VUV/O3 treatment. The average shear strength was approximately 56 MPa, and cross-sectional scanning electron microscopy (SEM) images of the bonded samples confirmed the absence of voids and cracks. Therefore, VUV/O3 treatment is highly effective for achieving low-temperature Au–Au bonding.
  • Influence of Welding Currents on Microstructure and Microhardness of Ni45 Alloy Reinforced with Spherical Tungsten Carbides (40 mass%) by Plasma Transferred Arc Welding

    pp. 2144-2150

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    DOI:10.2320/matertrans.M2013263

    The Ni45 alloy reinforced with spherical tungsten carbides powder was deposited on the surface of 304 L stainless steel by plasma transferred arc welding (PTAW). To determine the microstructure and microhardness of the coating with different currents, X-ray diffraction, an optical microscope, a scanning electron microscope, an electron microprobe and a hardness tester were all employed. The experimental results indicated that the microstructure of the coatings consisted mainly of different morphological strengthening phases and tungsten carbides distributed in γ-Ni matrix. Uniformly dispersed tungsten carbides were mostly in their original shape. Welding currents had strong effects on dilution with the base material and also on the formation of transition zones where the tungsten carbides were completely melted near the interface. In addition, lower currents resulted in transverse cracks along the fringe of the tungsten carbides. Concerning hardness it was found that higher currents contributed to lowering the hardness of the coating because of the intermixing of Fe in the hardfacing, the dissolution of the tungsten and the re-precipitation of the secondary carbides in the matrix. However, with higher currents, the hardness in the transition zone was greater than that with lower ones, which was the result of the predominant effect of melted tungsten carbides.
  • Rapid Synthesis and Consolidation of a Nanostructured Mg0.6Al0.8Ti1.6O5 Compound by Pulsed Current Activated Heating

    pp. 2151-2154

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    DOI:10.2320/matertrans.M2013255

    Nanocrystalline materials have received much attention as advanced engineering materials with improved physical and mechanical properties. Attention has been directed to the application of nanomaterials as they possess high strength, high hardness and excellent ductility and toughness. A one-step synthesis and consolidation of nanostructured Mg0.6Al0.8Ti1.6O5 was achieved by pulsed current activated heating using the stoichometric mixture of MgO, Al2O3 and TiO2 powders. Before sintering, the powder mixture was high-energy ball milled for 10 h. From the milled nanopowder mixture, a highly dense nanostructured Mg0.6Al0.8Ti1.6O5 compound could be obtained within one minute under the simultaneous application of 80 MPa pressure and an pulsed current. The advantage of this process is that it allows an instant densification to the near theoretical density while sustaining the nanosized microstructure of raw powders. The sintering behavior, microstructure and mechanical properties of Mg0.6Al0.8Ti1.6O5 were evaluated.
  • Mechanochemical Synthesis and Rapid Consolidation of Nanostructured (Ti,Al,V)C by Pulsed Current Activated Heating and Its Mechanical Properties

    pp. 2155-2158

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    DOI:10.2320/matertrans.M2013252

    Solid-solution nanocrystalline powder, (Ti,Al,V)C, was prepared by the high-energy milling of Ti–Al–V alloys with graphite. The (Ti,Al,V)C was formed during the milling process of Ti–Al–V alloys + graphite and the synthetic procedures were investigated in terms of the phase evolution from XRD data. The rapid sintering of nanostructured (Ti,Al,V)C hard materials in a short time was investigated with pulsed current activated heating sintering process. The advantage of this process is that it allows very quick densification to near theoretical density and inhibits grain growth in nanostructured materials. A dense nanostructured (Ti,Al,V)C hard material with a relative density of up to 96% was produced with simultaneous application of 80 MPa pressure and a pulsed current of 2000 A within 2 min. Microstructure and mechanical properties of binderless (Ti,Al,V)C were investigated.
  • Cactus-Like SnO2 Nanostructures Grown by Thermal Evaporation Technique

    pp. 2159-2161

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    DOI:10.2320/matertrans.M2013240

    SnO2 nanostructures with cactus-like morphology were synthesized by thermal evaporation of Sn powder. Any catalyst and substrate were not used for the formation of SnO2 nanostructures. X-ray diffraction result showed that the SnO2 nanostructures had rutile crystallographic structure. Scanning electron microscopy study revealed that the cactus-like SnO2 nanostructure consisted of main microrod stem and many branched nanowires. The secondary growth of SnO2 nanowire branches occurred on the primary main SnO2 microrods. Vapor–solid growth mechanism was proposed for the growth of the SnO2 nanostructures because no catalytic particles were found at the tips of the nanowires. A strong visible emission peak at 530 nm was observed in the cathodoluminescence spectrum taken from the cactus-like SnO2 nanostructures at room temperature.
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  • Fused Line Study of 17-4PH Stainless Steel Deposited with Co-Based Alloy

    pp. 2162-2165

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    DOI:10.2320/matertrans.M2013243

    To improve the surface performance, precipitation hardening martensitic stainless steel 17-4PH is deposited with Co-based alloy stellite12 by plasma-transferred arc welding (PTAW). The microstructure and microhardness of the fused line between base metal and coating were characterized by optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM) and hardness tester. The results show that the interface between weld coating and base metal is favorable without pore and crack. The microstructure of the fused line is composed of martensite and austenite, without precipitates.

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