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

MATERIALS TRANSACTIONS Vol. 55 (2014), No. 10

  • Effect of Doping for Epitaxial (Ba1−xYbx)(Fe0.2Zr0.8)O3−δ Thin Films with Yb

    Ryoichi Shinoda, Norie Hirao, Yuji Baba, Akihiro Iwase, Toshiyuki Matsui

    pp. 1521-1524

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    DOI:10.2320/matertrans.M2014194

    Abstract

    We fabricated epitaxial (Ba1−xYbx)(Fe0.2Zr0.8)O3−δ (BYFZO) thin films and studied their structural and dielectric properties using synchrotron X-ray photoelectron spectroscopy. The 10%-Yb-substituted BYFZO samples had almost the same good insulation properties as the non-doped BFZO samples. Saturation magnetization occurred at 0.242 µB/f.u. It is believed that a large amount of Yb3+ substitution produced carrier electrons, leading to recombination of the charge balance. This resulted in an increase in the leakage current and a decrease in the saturation magnetization. The ferromagnetic nature of the x = 0.0 and x = 0.1 samples was believed to have super-exchange interactions because the samples showed good dielectric properties. Additionally, for the x = 0.1 samples, the magnetic moments of the Yb3+ ions added to the magnetization. Therefore, the maximum saturation magnetization occurred when the amount of Yb-substitution was x = 0.1.

  • Effects of Temperature and Strain Rate on Plastic Deformation of Ultrafine-Grained Copper Prepared by Equal-Channel Angular Pressing

    Satoshi Okubo, Hiroki Abe, Yoji Miyajima, Toshiyuki Fujii, Susumu Onaka, Masaharu Kato

    pp. 1525-1530

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    DOI:10.2320/matertrans.M2014172

    Abstract

    Ultrafine-grained (UFG) pure copper of 280 nm grain size was prepared by equal-channel angular pressing. Tensile tests, strain-rate change tests and temperature change tests were conducted on UFG Cu in the temperature range between 77 K and 373 K. As usual, tensile strength increased as temperature decreased and strain rate increased. The activation energy of deformation increased linearly with the increase in temperature. On the other hand, the activation volume first increased with the increase in temperature from 77 K to about 200 K while it decreased with temperature above 200 K. Therefore, the activation volume shows the maximum value of 180 b3 at about 200 K. These experimental results are discussed by considering two different thermally-activated deformation processes.

  • Peierls Barrier of Screw Dislocation in bcc Iron at Finite Temperature

    Hideki Mori

    pp. 1531-1535

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    DOI:10.2320/matertrans.M2014170

    Abstract

    The Peierls barrier of a screw dislocation in body-centered cubic iron at finite temperature is investigated by using the free energy gradient method. By using the empirical potential, the Peierls barrier is shown to decrease from 11.7 to 6.9 meV per unit length of the Burgers vector with temperature increasing from 0 to 300 K. The entropy term of the Peierls barrier is estimated to be 0.19 kB, and the change of free energy, which is an entropic effect, is found to strongly depend on the local atomic configuration.

  • Preparation of Iron Doped Hydroxyapatite Microsphere by Mist Process

    Mitsutaka Sato, Atsushi Nakahira

    pp. 1536-1539

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    DOI:10.2320/matertrans.Y-M2014830

    Abstract

    Hydroxyapaite and Fe doped hydroxyapatite microsphere were prepared by mist process using Ca(NO3)2, FeCl3 and (NH4)2HPO4 aqueous solutions, and the effects of the preparation condition and Fe doping on the crystal phase, microstructure and other properties were investigated. From XRD analysis, obtained powders were HAp in a single phase at the Ca/P ratio from 1.5 to 2.0, independent from preparation temperature and gas flow rate. In the case of the Ca/P ratio of 1.0, obtained powder was mixed phase of HAp and Ca2P2O7. The crystallinity of powders strongly depended on preparation temperature and flow rate of carrier gas and was enhanced with decreasing flow rate of argon and increasing preparation temperature. The SEM observation suggested that the obtained samples had a fine microsphere consisted of further smaller primary grains. The microsphere size of sample was about 1 µm, and size distribution was between 0.5 and 5 µm.

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  • The Effect of Surface Machining on the High-Temperature Oxidation of a Single Crystal Ni-Based Superalloy

    Nairong Sun, Lanting Zhang, Zhigang Li, Feng Sun, Xianping Dong, Aidang Shan

    pp. 1540-1546

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    DOI:10.2320/matertrans.M2014077

    Abstract

    Single crystal samples were subjected to different surface compressive finishing conditions on [001] oriented surfaces. The initial surface residual compressive stresses were determined to be 901, 635 and 0 MPa, respectively. Isothermal oxidation in ambient atmosphere at 1573 and 1273 K resulted in a reduction of oxide scale thickness and a change of primary oxides from nickel oxide to alumina on deformed surface. Such result can be attributed to the increased diffusivity of aluminum beneath the deformed surface at high temperatures.

  • Nano Structure and Electrochemical Behavior of the Rust Formed on Ni Bearing Steel after Exposure Tests in a Tropical Indian Environment

    T. Nishimura, N. Rajendran

    pp. 1547-1552

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    DOI:10.2320/matertrans.M2014200

    Abstract

    Exposure tests were performed on low alloy steels in a tropical environment, and the structure and electrochemical behavior of the rust were analyzed by TEM (Transmission Electron Microscopy) and EIS (Electrochemical Impedance Spectroscopy). In the exposure test, chloride ion from the sea was found to be the dominant cause of the corrosion of the steels, while the effects of temperature and humidity were not particularly significant. The Ni bearing steel exhibited lower corrosion weight loss as compared to the carbon steel (SM), and had excellent corrosion resistance. EIS measurements on exposure test samples were performed to determine the rust resistance (Rrust) and corrosion reaction resistance (Rt) of low alloy steels. The Rrust and Rt of Ni bearing steel were much larger than those of SM after an extended exposure test. Raman spectroscopy showed that the rust on Ni bearing steel was mainly composed of nano-size α-FeOOH and spinel oxides. TEM showed that nano-scale complex iron oxides containing Ni2+ were formed in the rust on the Ni bearing steel. It was found that the Ni bearing steel formed nano-scale iron complex oxides containing Ni in the rust, which increased Rrust and Rt, and suppressed the corrosion by chloride ions in the tropical environment.

  • In-Situ Monitoring of Oxide Ion Induced Breakdown in Amorphous Tantalum Oxide Thin Film Using Acoustic Emission Measurement

    Takashi Tsuchiya, Kaita Ito, Shogo Miyoshi, Manabu Enoki, Shu Yamaguchi

    pp. 1553-1556

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    DOI:10.2320/matertrans.M2014198

    Abstract

    An acoustic emission (AE) measurement was employed under DC bias applied condition to investigate breakdown behavior of highly resistive tantalum oxide thin film induced by redox reaction of oxide ion and its resultant generation of oxygen gas. Above dc bias of 14 V, AE event with strong components around 400 kHz and below 100 kHz was detected only once just after the bias was applied. On the other hand, a number of AE events were intermittently observed at 20 V, where the resistivity of the film drastically dropped. The behavior indicates oxygen gas was generated at the bottom electrode interface and released due to forming of a blister as large as several hundreds of micrometers.

  • Mechanical Properties and Tool Life of Friction-Stir-Welded DP590 Using the Si3N4 Tool

    Young-Gon Kim, In-Ju Kim, Ji-Sun Kim, Jae-Hyun Park

    pp. 1557-1563

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    DOI:10.2320/matertrans.M2014159

    Abstract

    Early studies have been conducted on the friction stir welding of steel, tungsten (W), molybdenum (Mo), tungsten carbide, and the like for the production of tools, but the tool materials were significantly worn out and deformed while they were being joined. So far, the polycrystalline cubic boron nitride (PCBN) tool, which is very strong at high temperatures and is wear-resistant, has performed relatively well, but the improvement of its productivity is limited by its high manufacturing cost. In this study, 1.4 mm-thick DP590 steel was subjected to FSW using the ceramic material of a Si3N4 tool. The main process parameters of the butt joint at rotation speeds of 600–1,000 rpm and traveling speeds of 180–300 mm/min were determined through the bead-on-plate experiment. Also, the tensile strength, hardness, and Charpy impact properties of each FSW joint were evaluated, the full extent of the wear was measured and the tool life of the PCBN tool that was about four times as costly to produce was compared with the maximum joint length to determine the durability of the tool.

  • Tensile Strength of Al/ABS-CFRP Joint Reinforced by Nickel Coated Carbon Fiber Cloth

    Kazuma Shiraishi, Shigehito Inui, Sho Ishii, Yoshihito Matsumura, Yoshitake Nishi

    pp. 1564-1567

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    DOI:10.2320/matertrans.M2013424

    Abstract

    A new method with extremely large friction force by broad interface of carbon fiber (CF:6 µm-diameter) cloth coated by nickel (Ni) to control Al4C3 formation rate and to enhance the ability of fiber rapping by molten Al have been suggested for a joint (Al/cloth/ABS-CFRP) of carbon fiber reinforced ABS polymer (ABS-CFRP) and aluminum (Al). The new joint part was strengthened by impregnated nickel-coated carbon fiber cloth. The Al/cloth/ABS-CFRP joint exhibited the high values of the initial and maximum elasticity ((dσ/dε)i and (dσ/dε)m), as well as the tensile strength (σb) of Al/cloth/ABS-CFRP (8.38 MPa), which was 5.3 and 16.1 times higher than that of Al/Glue/ABS and Al/ABS, respectively. Based on the XRD analysis and EPMA observation, aluminum carbide could not be detected. Consequently, the new joint method by using carbon fiber cloth remarkably enhanced the safety level with lightweight and high resistance to fracture of airplane.

  • Microstructural Evolution of As-Cast 3.5%NiCrMoV Steel Containing Centimeter-Scale Grain Structure during Reheating and Plastic Deformation

    Wen Long Zhao, Qing Xian Ma

    pp. 1568-1574

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    DOI:10.2320/matertrans.M2014080

    Abstract

    Given the importance of microstructure on the mechanical properties of heavy forgings, the typical microstructure of as-cast 3.5%NiCrMoV steel was confirmed through the dissection of a 380 ton ingot as centimeter-scale grains. Subsequent investigation into the change of this grain structure during forging determined that temperature plays a predominant role in not only breaking up centimeter-scale grains into equiaxed grains, but also controlling the extent to which equiaxed grains are refined. This means that a fine grain structure with an average grain size of less than 60 µm is formed at 900 and 1000°C, whereas coarse grains are usually retained at 1100 and 1200°C. Moreover, at higher temperatures such as 1200°C, centimeter-scale dendrites are completely crushed by a reduction ratio greater than 30%. Grain size homogeneity is improved by dynamic recrystallization (DRX) at a reduction ratio of 10%, but these grains exhibit anisotropy when the reduction ratio is increased to 40%. Microstructural evolution was also found to be influenced by grain growth during reheating, with a significant increase in grain size not observed between 1000 and 1150°C, but grain coarsening occurring at 950°C. Taking into account the complexity and duality of this microstructural evolution, it is concluded that the deformation parameters and reheating conditions of heavy forgings need to be carefully controlled to ensure an appropriate microstructure is formed.

  • The Effects of Fe2P and Fe3P Intermediate Equilibrium Phases on Glass-Forming Ability of Fe76Si9B10P5 Bulk Metallic Glass

    Akira Takeuchi, Akihiro Makino

    pp. 1575-1581

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    DOI:10.2320/matertrans.M2014148

    Abstract

    The glass-forming ability (GFA) of an Fe76Si9B10P5 bulk metallic glass (BMG) was evaluated thermodynamically with commercial software, Thermo-Calc, with Fe-base database, TCFE7 by utilizing its best ability to deal with equilibrium phases. The Fe76Si9B10P5 BMG was selected because it is the simplest Fe-rich BMG belonging to Fe-metalloid type with the greatest sample dimensions. A possible reason for the presence of intermediate equilibrium phases to degrade GFA of the Fe76Si9B10P5 was discussed. The results revealed that the Fe76Si9B10P5 BMG is characterized by near eutectic composition in the Fe-rich Fe-Si-B-P quaternary system and by the simultaneous presence of Fe3P and absence of Fe2B phases in equilibrium at a range below the solidus- to the glass-transition temperatures. The analysis of Fe76(Si,B,P)24 alloys for equilibrium phases revealed that the Fe2P phase can degrade GFA of the Fe76Si9B10P5 BMG.

  • Effect of Annealing on Magnetic Properties of Ultrafine Jet-Milled Nd-Fe-B Powders

    Michihide Nakamura, Masashi Matsuura, Nobuki Tezuka, Satoshi Sugimoto, Yasuhiro Une, Hirokazu Kubo, Masato Sagawa

    pp. 1582-1586

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    DOI:10.2320/matertrans.MAW201402

    Abstract

    This paper reports the effects of annealing on the magnetic properties of ultrafine Nd-Fe-B powders with an average particle size of 0.67 µm. The powder was fabricated from hydrogenation–disproportionation–desorption–recombination (HDDR)-treated Nd-Fe-B alloys by hydrogen decrepitation and helium jet milling. The coercivity of the ultrafine powders was slightly increased by annealing below 500°C, and was drastically increased by annealing above 600°C. These two stepwise increases in coercivity were attributed to hydrogen desorption and formation of a liquid Nd-rich phase. In addition, after annealing below 500°C, the coercivity (μ0Hc) of the ultrafine powder was higher than that of the conventional powder, which was prepared from a strip-cast Nd-Fe-B alloy power with a particle size of 1.12 µm, because of a decrease in particle size. In contrast, after annealing above 600°C, the μ0Hc of the ultrafine powder was smaller than that of the conventional powder. The rare earth element content (Nd + Pr) was lower in the ultrafine powders than in the conventional powder. These results indicate that the rare earth element content was insufficient in the ultrafine powders.

  • Shear Strength of Adhesive Lamination Joint of Aluminum and CFRP Sheets Treated by Homogeneous Low Energy Electron Beam Irradiation Prior to Lamination Assembly and Hot-Press

    Takumi Okada, Masae Kanda, Michael C. Faudree, Yoshitake Nishi

    pp. 1587-1590

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    DOI:10.2320/matertrans.MAW201419

    Abstract

    Adhesive 2-layer lamination joint of aluminum/carbon fiber reinforced epoxy polymer (Al/CFRP) were prepared by a new adhesion method, a double-step treatment consisting of applying low dose (= 0.22 MGy) of homogeneous low energy electron beam irradiation (HLEBI) to the CFRP and Al prior to lamination assembly and hot-press in vacuum below 1 Pa for 2 h at 403 K. No fasteners or external adhesives were applied: the cured epoxy enhanced by the HLEBI acts as the adhesive to the Al. The new treatment apparently boosted shear strength (τ) of the Al/CFRP 45% at low shear strength probability (Ps = 0.06) at 0.22 MGy. XPS (X-ray photoelectron spectrometry) measurements detected carbon on the shear fractured Al interface indicating the residual epoxy adhered well to the Al by the HLEBI. This is probably a result of adhesion force of Al/CFRP being made stronger than the cohesive force of epoxy polymer in the CFRP itself. When HLEBI cuts the chemical bonds and generates active terminated atoms with dangling bonds in epoxy polymer, the nonbonding electrons probably induced the chemical bonding and intermolecular coulomb attractive forces at the interface. Hence, the increased adhesion force in the Al/CFRP joint can be explained.

  • Computer Simulations on Barkhausen Effects and Magnetizations in Fe Nano-Structure Systems

    Shuji Obata

    pp. 1591-1598

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    DOI:10.2320/matertrans.M2014161

    Abstract

    The magnetization processes in regular lattice Fe nano-systems are investigated by means of the numerical simulations based on classical magnetic dipole moment interactions. The domain energies are calculated from moment-moment interactions over whole systems using large scale computing resources. The results directly show basic magnetization phenomena. The Barkhausen effects are represented with magnetization steps in external field changes of ΔH, which are composed of jumps ΔMB and terraces ΔHB.

  • Two-Dimensional Observation of Grain Boundary Sliding of ODS Ferritic Steel in High Temperature Tension

    Hiroshi Masuda, Satoshi Taniguchi, Eiichi Sato, Yoshito Sugino, Shigeharu Ukai

    pp. 1599-1605

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    DOI:10.2320/matertrans.M2014115

    Abstract

    High-temperature tensile deformation was performed using ODS ferritic steel, which has grain structure largely elongated and aligned in one direction, in the direction perpendicular to the grain axis. In the superplastic region II, two-dimensional grain boundary sliding (GBS) was achieved, in which the material did not shrink in the grain-axis direction and grain-boundary steps appeared only in the surface perpendicular to the grain axis. In this condition, a classical grain switching event was observed. Using kernel average misorientation maps drawn with SEM/EBSD, dominant deformation mechanisms and accommodation processes for GBS were examined in the different regions. Cooperative grain boundary sliding, in which only some of grain boundaries slide, was also observed.

  • Effects of O2 and N2 Flow Rate on the Electrical Properties of Fe-O-N Thin Films

    Yukiko Ogawa, Daisuke Ando, Yuji Sutou, Junichi Koike

    pp. 1606-1610

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    DOI:10.2320/matertrans.M2014089

    Abstract

    We report the dependence of electrical properties of Fe-O-N thin films on the deposition condition as well as on O2 and N2 gas flow rate. Fe-O-N films were deposited by reactive sputtering using O2 and N2 as reactive gas. The electrical resistivity of Fe-O-N films increased with increasing O2 and N2 gas flow rate. The resistivity increase with the O2 flow rate was due to structure change from a mixed phase of metallic Fe+Fe3O4, to a mixed phase of FeO+α-Fe2O3, and to a single phase of α-Fe2O3, as evidenced by XPS analysis of Fe 2p core excitation peaks. Meanwhile, the resistivity increase with the N2 flow rate was due to structure change from a metallic Fe, to a mixed phase of metallic Fe+Fe3O4, and to a single phase of Fe3O4.

  • The Kinetics of Isothermal Hydrogen Reduction of Nanocrystalline Fe2O3 Powder

    Geon-Yong Lee, Joon-Phil Choi, Jun-Il Song, Sung-Soo Jung, Jai-Sung Lee

    pp. 1611-1617

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    DOI:10.2320/matertrans.M2014182

    Abstract

    The kinetics of reduction of nanocrystalline Fe2O3 powder with hydrogen was investigated in the temperature range from 573 K to 813 K. A comparison between the reduction rates of the nanocrystalline powder (20–50 nm) and those of the conventional powder (200–400 nm) showed no discernible difference despite a substantially larger specific surface area of the former. Since observations under the scanning electron microscope revealed that the nanocrystalline powder forms large agglomerates, the kinetic results were theoretically tested for the possibility that the reduction of the powder was inhibited by intra-agglomerate pore diffusion. Alternatively, a potential influence of water vapor remaining in the packed powder bed is discussed. Activation energies of 47.2 and 51.5 kJ/mol were obtained for the reduction of the nanocrystalline and the as-received powder, respectively. These values show fair agreement with those obtained by previous studies.

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  • Corrosion Behavior of Superalloys in a LiCl-Li2O Molten Salt

    Jong-Ho Lim, Woo-Jin Jung

    pp. 1618-1622

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    DOI:10.2320/matertrans.M2013262

    Abstract

    A study on the corrosion behavior of Inconel alloys and Incoloy 800H in a molten salt of LiCl-Li2O was investigated at 650°C for 24–312 hours in an oxidation atmosphere. The order of the corrosion rate was Inconel 600 < Inconel 601 < Incoloy800H < Inconel 690. Inconel 600 showed the best performance suggesting that the content of Fe, Cr and Ni are the important factor for corrosion resistance in hot molten salt under an oxidation conditions. The corrosion products of Inconel 600 and Inconel 601 were Cr2O3 and NiFe2O4. In case of Inconel 690, a single layer of Cr2O3 was formed in the early stage of corrosion and an outer layer of NiFe2O4 and inner layer of Cr2O3 were formed with an increase of corrosion time. In case of Incoloy 800H, Cr2O3 and FeCr2O4 were observed. Most of the outer scale of the alloys was observed to be spalled from the results of the SEM analysis and the unspalled scale which adhered to the substrate was composed of three layers. The outer layer, the middle one, and the inner one were Fe, Cr, and Ni-rich, respectively. Inconel 600 showed localized corrosion behavior and Inconel 601, 690 and Incoloy 800H showed uniform corrosion behavior. Ni improves the corrosion resistance and too much Cr and/or Fe content deteriorates the corrosion resistance.

  • Microstructure and Mechanical Properties of Cobalt-Based Alloys Strengthened with Tantalum Carbide Powder via Vacuum Sintering and HIP Treatments

    Shih-Hsien Chang, Chien-Chung Chen

    pp. 1623-1629

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    DOI:10.2320/matertrans.M2014044

    Abstract

    In this study, different amounts of TaC powders (0, 10, 15 and 20 mass%) were mixed and added to the cobalt-based alloy powders. The composite powders were sintered at 1260, 1270, 1280 and 1290°C, respectively, for 1 h. The experimental results showed that adding 10 mass% TaC and sintering at 1270°C for 1 h was the optimal process, resulting a high TRS value of 1160 MPa and uniform carbides precipitations. From the microstructural observations, it was cleared that M6C carbides precipitated in the matrix of the Co-based alloys (0% TaC) after vacuum sintering. However, the more uniform precipitations of M6C, M23C6 and MC (M = Ta) carbides precipitated in the matrix and grain boundaries of the Co-based alloys after vacuum sintering. Furthermore, in the HIP treatment (1250°C/125 MPa/100 min) of 0% and 10% TaC sintered composite materials, it was proved that the closed pores were effectively eliminated and mechanical properties significantly improved. The highest hardness (HRA 79.3) and TRS (1720 MPa) were obtained by adding 10% TaC powders, which were sintered at 1270°C for 1 h, followed by HIP treatment.

  • Microstructure and Magnetic Property of Sm2Fe17 Nanopowder Synthesized by Modified Reduction-Diffusion Process

    Joon-Chul Yun, Su-Min Yoon, Geon-Yong Lee, Joon-Phil Choi, Jai-Sung Lee

    pp. 1630-1633

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    DOI:10.2320/matertrans.M2014152

    Abstract

    A modified reduction-diffusion (MRD) process at low temperature was performed on the microstructure and magnetic property of a base alloy nanopowder of Sm2Fe17 for high performance Sm2Fe17N3 magnetic materials. The Sm2Fe17 nanopowder with a particle size distribution of 100–500 nm was synthesized by MRD process at 700°C. The measurement of magnetic property revealed that the Sm2Fe17 nanopowders had a saturation magnetization (Ms) of 128 A·m2/kg and a high coercivity (Hc) of 91.8 kA/m. It is expected that the magnetic property of Sm2Fe17 nanopowder provides a superior base alloy material for fabricating high performance Sm2Fe17N3 magnetic materials by subsequent nitriding treatment.

  • Magnetic Susceptibility of Zr-Cu Binary Alloys

    Seung-Pyo Hong, Yeong-Mu Ko, Chung-Seok Kim

    pp. 1634-1636

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    DOI:10.2320/matertrans.M2014222

    Abstract

    The objective of this study is to investigate the magnetic susceptibility of Zr-Cu binary alloys for their potential use as biomaterials with nullifying magnetic properties for magnetic resonance imaging diagnosis. The Zr-Cu binary alloys were prepared using the arc-melting process with zirconium strips and oxygen-free copper. This binary alloy has two dominant phases consisting of α-Zr and CuZr2 intermetallic phase. The magnetic susceptibility of the Zr-Cu binary alloys was extremely low, approximately 10−7; this level is approximately one order less than that of pure Zr and other commercialized metallic biomaterials. Consequently, Zr-Cu binary alloys have the potential to be used as biomaterials with low magnetic property.

  • Editor’s Announcement

    pp. 1637-1637

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    DOI:10.2320/matertrans.EAM2014601

  • © 2014 The Japan Institute of Metals and Materials

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