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

MATERIALS TRANSACTIONS Vol. 58 (2017), No. 11

  • Magnetic-Field-Induced Acceleration of Phase Formation in τ-Mn-Al

    pp. 1511-1518

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    DOI:10.2320/matertrans.MAW201709

    The phase formation of ferromagnetic L10-MnAl (τ-phase) was accelerated by annealing in magnetic field. With in-field annealing at 623 K, the magnetization of the τ-phase annealed at 15 T was a maximum of 72.2 A・m2/kg at 1.5 T, which is over 4 times larger than that annealed without an external magnetic field for the same annealing time. On the other hand, the transformation from τ-phase to β-phase was suppressed under magnetic field. The obtained bulk sample did not show magnetic anisotropy because of the ε-τ solid-state transformation. Obtained results suggested that magnetic field induced acceleration of transformation was due to the gain of Zeeman energy, which increases the driving force of the ε-τ transformation.
  • Influence of Electron Beam Irradiation on Surface Roughness of Commercially AISI 5140 Steel

    pp. 1519-1523

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    DOI:10.2320/matertrans.M2017093

    In this study, a commercially AISI 5140 steel with two different levels of initial surface state (initial high-roughness (IHR) and initial low-roughness (ILR)) was surface-treated by large-area pulsed electron beam irradiation (LPEBI). Surface morphology in 2D and 3D of the two types of samples after LPEBI treatment was characterized. The results show that the surface roughness of IHR samples decreases clearly with increasing LPEBI pulse numbers, while an opposite trend is found in the ILR samples. It is considered that the final surface roughness is influenced by surface remelting and formation of crater-like structures (CLSs) in local regions. For the IHR samples with amounts of mechanical scratches, the remelting plays the leading role, owing to the high surface energy which provides extra driving force for remelting during LPEBI. In contrast, such extra driving force is less due to the relatively flat surface of the ILR samples, instead remelting the surface suffers from the formation of CLSs in localized region. Compared to the formation of localized CLSs, the surface remelting is beneficial to surface roughness of the LPEBI processed samples.
  • The Effect of Annealing Atmosphere on the Evolution Behavior of Inhibitors in Thin-Gauge Grain-Oriented Silicon Steel

    pp. 1524-1531

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    DOI:10.2320/matertrans.M2017114

    In this paper, 0.18 mm thin-gauge S-type steels with MnS and N-type steels with AlN as main inhibitors, respectively, were fabricated using three different final annealing systems. Moreover, the evolution behavior of the MnS and AlN [(Al, Si)N] particles and grain orientation were investigated. Number density and mean diameter of second-phase particles were statistically determined by field-emission scanning electron microscopy. Results indicated that evolution of MnS and AlN would be suppressed with increased N2 content during annealing. The onset ripening temperature of MnS was lower than that of AlN particle, which caused secondary recrystallization in the S-type samples at lower temperature compared with that of the N-type samples. Moreover, for the N-type steel fabricated by nitriding method, the effective inhibitor was (Al, Si)N formed by the decomposition of (Al, Mn, Si)N. The decomposition of (Al, Mn, Si)N particles and coarsening of (Al, Si)N inhibitors were strongly inhibited and delayed with increased N2 content in annealing atmosphere. In conclusion, N2/H2 ratio of annealing atmosphere could be an effective control parameter to enhance the inhibition ability and delay secondary recrystallization onset in forming sharp Goss texture.
  • Self-Piercing Riveting of Metal Foam Sandwich Structures

    pp. 1532-1537

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    DOI:10.2320/matertrans.M2017187

    Metal foam sandwich structures are widely used in construction and transportation fields because of their good acoustic performance, high thermal stability, lightweight, and high stiffness. This paper deals with join-ability of self-piercing riveted metal foam sandwich structures. Self-piercing riveting tests were performed on AA5052 aluminium alloy sandwich structures embedded with different metal foams. Tensile-shear tests were conducted to characterize the mechanical properties of different self-piercing riveted metal foam sandwich structures. The results illustrate that the connection of metal foam sandwich structures can be effectively realised with the self-piercing riveting technique. The joints exhibit good forming quality and mechanical performance. For metal foam sandwich joints, the sandwich structures embedded with nickel foam exhibits the best mechanical properties. The failure modes of the self-piercing riveted sandwich structures were observed at the separation of the lower sheets and rivet.
  • Effects of Additives on the Surface Roughness and Throwing Power of Copper Deposited from Electrorefining Solutions

    pp. 1538-1545

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    DOI:10.2320/matertrans.M2017215

    To elucidate the synergistic effects of gelatin, thiourea, and chloride ions on the surface roughness, throwing power, and polarization curves for Cu deposition from electrorefining solutions, Cu electrodeposition was performed at a current density of 200 A·m−2 and a charge of 5 × 105 C·m−2 in an unagitated sulfate solution containing 0.708 mol·dm−3 of CuSO4 and 2.04 mol·dm−3 of H2SO4 at a temperature of 60℃. In solutions containing all three additives (gelatin, thiourea, and chloride ions), the surface roughness of deposited Cu decreased with increasing thiourea and gelatin concentrations and decreasing chloride ions concentration. On the other hand, the throwing power of deposited Cu improved with decreasing thiourea concentration and increasing gelatin concentration in solutions containing all three additives. The throwing power of deposited Cu was significantly improved in solutions containing both gelatin and chloride ions. The polarization resistance dE/di for Cu deposition increased in solutions containing both gelatin and chloride ions, resulting in an improvement in the throwing power of Cu deposition. As small amounts of thiourea have a depolarization effect on Cu deposition, a smoothing effect is expected to result from the promotion of deposition at recesses. This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 81 (2017) 358–365.
  • Kinetic Investigation into the Formation of Titanium Nitride from Titanium Dioxide by Carbonitrization

    pp. 1546-1554

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    DOI:10.2320/matertrans.MAW201711

    The production of titanium nitride by direct reaction of nitrogen and titanium oxide requires unrealistic conditions such as a high nitrogen partial pressure and quite low oxygen partial pressure. In contrast, titanium nitride can be prepared experimentally by carbonitrization with commercial grade nitrogen gas. However, because carbonitrization is a gas-solid reaction, a high reaction rate is not expected. I carried out a kinetic investigation into the carbonitrization reaction to clarify the titanium nitride formation mechanism. To achieve this, I used simultaneous thermal gravimetric and differential thermal analysis (TG-DTA). The ratio of carbonitrization to other reactions, such as the combustion of carbon, was determined using reaction enthalpies from a thermodynamic literature. Using kinetic analysis, the net carbonitrization reaction was found to comprise a series of consecutive reactions, and the order of the reaction was determined to be n = 0.1 to 0.5. That is, the reaction of titanium nitride formation is controlled by diffusion processes, as indicated by the dimension of “n,” and is dependent on the previous combustion process, the combustion of carbon.
  • Effect of Age-Hardening to Metal Structure and Tribology Characteristics of Lead-Free Bismuth Bronze Casting Containing Sulfur

    pp. 1555-1561

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    DOI:10.2320/matertrans.F-M2017831

    The age-hardening behavior and low friction characteristics of Cu-Sn-Bi alloy with 1.5 mass% nickel and 0.3 mass% sulfur (PBX alloy) have been investigated. The PBX alloy showed age-hardening when aged at the temperature range of 623 K to 743 K for over 0.6 ks after solution treatment at α+γ stable temperature. Peak hardness was obtained by aging at 673 K. After aging at the temperature range of 573 K to 743 K, the supersaturated solid solution part changed into eutectoid structure in which fine δ precipitated. The age-hardening of the PBX alloy showed a two-step hardening. The first step began within 0.6 ks and then hardness increased slowly with aging time. Aged at 673 K, the eutectoid matrix changed into a pine needle-shaped structure. The structure is a mixed structure of a bainitic structure and quasi-martensite having mid-rib structures in several places. Aged at 743 K, the macro crystal grain size did not change in 3.6 ks, but aging over 14.4 ks caused macro crystal grain refinement. The dynamic friction coefficient of the PBX alloy in an oil bath of 333 K was smaller than that of JIS CAC603 alloy due to the eutectoid structure of the α phase and fine δ phase. This Paper was Originally Published in Japanese in J. JFS. 87 (2015) 861–867.
  • Strain Behavior of JIS ADC12 Alloy Die Castings during Heat Treatment and Its Mechanism

    pp. 1562-1570

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    DOI:10.2320/matertrans.F-M2017832

    This study investigated the strain variation of JIS ADC12 aluminum alloy die castings by heat treatment and its relation with the strain arising from the precipitation of silicon, copper, and magnesium so that the most effective measures can be adopted to ensure dimensional precision in various service environments.Expansion strain of over 0.1% was produced in JIS ADC12 aluminum alloy die castings by heat treatment, which resulted in a simultaneous decrease in the half-width angles of the X-ray diffraction (XRD) peaks of the aluminum phase in the die castings. Moreover silicon, copper, and magnesium concentrated zones appeared in the aluminum phase after heat treatment. Thus, the decrease in the half-width angles can be regarded as a result of the improved crystallinity of the aluminum phase because of the relaxation of the lattice strain by the precipitation of silicon, copper, and magnesium. Hence, the strain variation in the ADC12 alloy die castings due to the heat treatment can be attributed to the precipitation of silicon, copper, and magnesium from the supersaturated aluminum phase. For quantitative verification of the above relation, growth attributable to the precipitation of silicon, copper, and magnesium from the aluminum phase and the transformation of the precipitated metastable Cu-Al compounds was estimated theoretically and compared with the measured strain variation caused by the heat treatment of the ADC12 alloy die castings. The results confirmed that the strain variation of the ADC12 alloy die castings by heat treatment corresponds well to the growth resulting from the precipitation of silicon, copper, and magnesium from the aluminum phase and the transformation of the precipitated metastable Cu-Al compounds. The results also revealed that silicon, copper, and magnesium precipitated at the early stage of heat treatment and that silicon precipitation contributed the most to the growth. The precipitated metastable Cu-Al compound, θ”, transformed into another metastable compound, θ’, and finally into the stable compound, θ, thereby resulting in expansion and contraction growth. This Paper was Originally Published in Japanese in J. JFS. 89 (2017) 111–118.
  • Thermodynamics and Kinetics of Direct Synthesis of Solar Grade Silicon from Metallurgical Silicon Wafer by Liquid Phase Migration in Solid Silicon

    pp. 1571-1580

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    DOI:10.2320/matertrans.M2017202

    We propose a process for the direct synthesis of solar grade Si from a metallurgical Si wafer focusing on the fact that its microstructure is composed of almost pure Si grains and grain boundaries enriched with impurities. Principally, heating a metallurgical grade Si wafer above its eutectic temperature and applying a temperature gradient allows the grain boundaries to be melted and causes them to migrate to the high-temperature direction. The liquid phases are finally terminated at the end surface, resulting in the upgrading of the Si and making it more favorable for solar cells. In the present paper, to determine the purification effect during the liquid phase migration process, thermodynamic assessment was performed using CALPHAD method. Liquid phase migration experiments were also conducted using synthetic MG-Si (Si-Fe alloy) to determine the reaction time for the process. A maximum migration velocity of 8.17 × 10−7 m/s was obtained at 1623 K, which allows the migration process to be accomplished within 3 min for a 150-μm wafer.
  • Characteristics and Properties of Ti-8Mo-6Cr Alloys with Added NbC Powders through the Vacuum Sintering Process at Various Temperatures

    pp. 1581-1586

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    DOI:10.2320/matertrans.M2017128

    In this study, three different powders are mixed and used to produce Ti-8Mo-6Cr-xNbC alloys of three different proportions: Ti-8Mo-6Cr-1NbC, Ti-8Mo-6Cr-3NbC and Ti-8Mo-6Cr-5NbC. The Ti-8Mo-6Cr-xNbC alloys simultaneously undergo a vacuum sintering process at temperatures of 1250, 1275 and 1300℃, respectively. The experimental results show that the lowest apparent porosity (0.1%) and highest hardness (66.5 HRA) of the Ti-8Mo-6Cr-1NbC alloys are acquired after sintering at 1300℃ for 1 h. However, the transverse rupture strength (TRS) values of the Ti-8Mo-6Cr-1NbC alloys sintered at 1300℃ display an obvious decrease as a result of the grain-coarsening phenomenon. Due to the TiC precipitates, grain refinement and a lower porosity appear in the 1250℃-sintered Ti-8Mo-6Cr-1NbC alloys, with the TRS showing an obvious increase (as compared with Ti-8Mo-6Cr, the TRS value increases from 1333 to 1532 MPa). These alloys also have the lowest corrosion current (Icorr was 1.47 × 10−5 A·cm−2) and highest polarization resistance (RP was 3.61 × 103 Ω·cm2) in 1M H2SO4 solutions. These results confirm that the Ti-8Mo-6Cr-1NbC alloys sintered at 1250℃ possess the suitable mechanical properties and optimal corrosion resistance.
  • Compressive Behavior of Open-Cell Titanium Foams with Different Unit Cell Geometries

    pp. 1587-1592

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    DOI:10.2320/matertrans.L-M2017834

    Mechanical properties of open-cell titanium foams with different cell geometries (truncated octahedron and rhombic dodecahedron cells) were examined through compressive tests. These foams were manufactured through the electron beam melting (EBM) process. The compressive behavior depends on the porosity, cell geometry and the cell orientation. Titanium foams with truncated octahedron cells showed high strength compared to those of rhombic dodecahedron cells. This is due to the short cell edges in truncated octahedron cells. In addition, the parallel and oblique cell edges against the compression direction are effective to increase the compressive strength. Macroscopic shear bands caused by ordered cell geometry were observed in some titanium foams.
  • Microstructural Evolution of Sn-58Bi/Cu Joints through Minor Zn Alloying Substrate during Electromigration

    pp. 1593-1600

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    DOI:10.2320/matertrans.M2017162

    Minor Zn was alloyed into Cu substrate to improve the electromigration reliability of Sn-58Bi/Cu solder joints in this paper. Electromigration behavior of Sn-58Bi/Cu and Sn-58Bi/Cu-4.89Zn was studied with the current density of 1.0 × 104 A/cm2 from the microstructural evolution on the surface morphologies and the interior interfacial structure. In case of the surface morphologies in Sn-58Bi joints, the existence of Zn in Cu substrate effectively postponed the formation of Sn hillocks of whiskers at the anode side and the depletions/voids at the cathode side. From the observation of interior interfacial structure, Cu-Zn substrate obviously depressed Bi segregation and the growth of Bi-rich layer at the anode interface. Because Zn atoms were migrated from the anode to the cathode while Bi atoms were migrated from the cathode to the anode during electromigration, Zn atoms would fill the vacancies left behind by the migration of Bi atoms. The electromigration resistance of Sn-58Bi solder joints was correspondingly improved by Zn alloyed into Cu substrate. the calculated DZ* of Bi atoms in the Cu and Cu-4.89Zn substrate is 3.69 × 10−11 cm2/s and 1.76 × 10−11 cm2/s, which also illustrates there exists a slower diffusion rate for Bi atoms in Sn-58Bi solder joint with Cu-Zn substrate.
  • Thermoelectric Properties of Ce3Te4 under High Pressure: First-Principles Calculation

    pp. 1601-1605

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    DOI:10.2320/matertrans.M2017204

    Based on the first-principles calculation and Mahan-Sofo's theory, we calculated the electronic structure and the thermoelectric figure of merit of Ce3Te4 under different pressures. The peak of DOS for Ce3Te4 shows the form of Dirac delta function around Fermi level. When the pressure is 1.1 GPa, the height of DOS peak is higher than those under other pressures, and the full width at half maximum is the narrowest. The thermoelectric figure of merit of Ce3Te4 under 1.1 GPa, 1.3 GPa, and 2.5 GPa pressure is the highest, which is just below 14.0. This illustrates that the appropriate pressure could change the electronic structure of Ce3Te4, and improves the thermoelectric properties of Ce3Te4.
  • Enhanced Tensile Strength of Titanium/Polycarbonate Joint Connected by Electron Beam Activated Cross-Weave Carbon Fiber Cloth Insert

    pp. 1606-1615

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    DOI:10.2320/matertrans.M2017012

    A new titanium (Ti)/polycarbonate (PC) joint [Ti/EBCF/PC] internally connected by homogeneous low potential electron beam irradiation (HLEBI) activated cross-weave carbon fiber (6 μm in diameter) cloth insert taking advantage of broad CF surface area had been developed. Applying HLEBI dose in the range of 0.043 to 0.43 MGy to the bare CF half-length prior to dipping in the thermoplastic PC molten resin enhanced ultimate tensile strength (σb) of Ti/EBCF/PC over that without HLEBI [Ti/CF/PC]. The 0.30 MGy dose appeared to be near the optimum resulting in σb of 20.7 MPa, an increase of 3.0, 3.9 and 21.1 times higher than that of Ti/CF/PC, with glue only [Ti/Glue/PC], and with spontaneous adhesion without glue [Ti/PC], at 7.00, 5.30, and 0.98 MPa, respectively. Moreover, regardless of HLEBI treatment, introduction of the CF insert into the joint prevented abrupt brittle fracture compared to the Ti/PC joint. The corrected ultimate tensile strength (cσb) defined as that of the 60 vol% CF-containing PC cross section portion calculated by rule of mixtures was also raised by the 0.30 MGy HLEBI to cσb = 195 MPa (Ti/EBCF/CFRPC); 6.89 and 31.7 times higher than that of Ti/CF/CFRPC and Ti/PC at 28.3 MPa and 6.16 MPa, respectively. The HLEBI probably enhanced the ability to adhere the CFs to difficult to adhere thermoplastic PC to generate the tremendously large friction force, with the aim of raising the safety level of lightweight material with high resistance to fracture for airplanes and automobiles.
  • Effects of Measurement Conditions on Ignition Temperature of Magnesium Alloys

    pp. 1616-1623

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    DOI:10.2320/matertrans.L-M2017833

    The effects of process parameters such as air flow rate, heating rate, sample surface area per volume (specific surface area), and sample compositions on the ignition temperature of magnesium alloys, both with and without calcium, were investigated by using differential thermal analysis. For magnesium alloys without calcium, increases in the heating rate, air flow rate, and specific surface area all contributed to a decrease in the ignition temperature, while an increase in the aluminum concentration promoted an increase in the ignition temperature at least under the present experimental conditions used in the present study. For magnesium alloys with calcium, adding 2 mass% calcium contributed to a significant increase in the ignition temperature. The effects of the flow rate, specific surface area and aluminum concentration on the ignition temperature qualitatively led to the same tendencies in magnesium alloys both with and without calcium. For the air flow rate, however, the opposite trend was observed. In the present study, the ignition temperatures obtained were much higher than those described in the literature, most likely because of the large differences in the specific surface area. This Paper was Originally Published in Japanese in J. JILM 66 (2016) 273–279.
  • Effect of Solidification Cooling Rate on Mechanical Properties and Microstructure of Al-Si-Mn-Mg Alloy

    pp. 1624-1627

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    DOI:10.2320/matertrans.M2017170

    Al-Si-Mn-Mg alloy, AA365 (Silafont-36), has been recently developed for automotive parts produced by the high-pressure die-casting process. During the die-casting process, differences in section thickness cause uneven cooling, which results in different mechanical properties and cause the build-up of residual stresses and defects in the part. In the present study, we have attempted to identify the microstructural changes of α-aluminum dendritic phase and eutectic region, and the mechanical property changes in AA365 alloy at different cooling rates during solidification. The alloy cooled at 9000 K/min (water quenching) acquired a secondary dendrite arm spacing (SDAS) of 3.4 µm and contained over 75% of dendritic α-aluminum phase, whereas the alloy having a cooling rate of 77 K/min (air cooling) showed 12 µm SDAS and 65.5% of α-aluminum phase. The ultimate tensile stress and the elongation of AA365 cooled at 9000 K/min went up to 262.3 MPa and 4.4%, respectively, when compared with the alloy cooled at 77 K/min, which had 192.3 MPa tensile strength and an elongation of 2.9%. The water quenching increases the hardness of dendritic α-aluminum phase by about 130% compared to that of the air-cooling, and it was confirmed that the fast cooling rate could increase the solubility of the elements that can be dissolved in the α-aluminum phase. The hardness of the alloy increased with an increase in the cooling rate during solidification due to uniform and fine size of the silicon bearing intermetallic phases in the eutectic region, caused by fast solidification.

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