Journal of the Japan Institute of Metals and Materials
Online ISSN : 1880-6880
Print ISSN : 0021-4876
ISSN-L : 0021-4876
Volume 68 , Issue 12
Showing 1-22 articles out of 22 articles from the selected issue
  • Kiyohito Ishida, Kozo Osamura, Ryosuke Kainuma, Hiroshi Okuda
    2004 Volume 68 Issue 12 Pages 965
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
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  • Tetsuo Mohri, Ying Chen
    2004 Volume 68 Issue 12 Pages 966-972
    Published: 2004
    Released: June 24, 2005
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    Cluster Expansion Method has been extensively employed for the first principles calculation of phase equilibria. The essential mathematical procedure is to calculate total energies for K ordered phases including pure elements, which forms K × 1 energy vector, and to operate K × K inversed matrix of correlation functions on the energy vector. The method is based on the orthogonality of the correlation functions in the thermodynamic configuration space and is versatile to various alloy systems. However, when one would like to obtain (K + 1)-st cluster interaction energy, it is not sufficient to add an arbitrary phase in the energy vector for which the total energy is to be calculated. This is because the elements of the inversed matrix of correlation functions are generally not preserved and, therefore, the net effect of the (K + 1)-st cluster interaction energy is obscured. In the present paper, algebraic aspects of the correlation functions are examined in detail and we propose some criterion to extract the net contribution of the (K + 1)-st cluster interaction energy. The criterion is applied to Fe-Pt system and the effects of 2nd nearest neighbor pair interaction and three body interaction energies on the transition temperature are discussed.
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  • Atsuto Seko, Shigeto R Nishitani, Isao Tanaka, Hirohiko Adachi
    2004 Volume 68 Issue 12 Pages 973-976
    Published: 2004
    Released: June 24, 2005
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    We developed the method to calculate free energy of precipitate nucleation. This method divides the free energy into the cluster energy and entropy terms. The former, consisting of the enthalpy of driving force and the interface energy, is precisely calculated by first-principles calculations. The latter, which is entropy loss from scattered atoms condensing into a cluster, is estimated by the ideal solution model. Model calculations have been performed for an Fe-Cu alloy, Ni added Fe-Cu alloy, and vacancy behavior around Cu clusters.
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  • Hideaki Sawada, Kazuto Kawakami, Masaaki Sugiyama
    2004 Volume 68 Issue 12 Pages 977-982
    Published: 2004
    Released: June 24, 2005
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    Interaction energy values between substitutional 3d transition metal elements and interstitial carbon atom in α-Fe is obtained by the first-principles calculation method. Calculated values of interaction energy are in good agreement with experimental values reported for those of Co, Ni and Cu elements, showing a repulsive interaction experimentally. On the other hand, the interaction energy for such elements as Ti, V, Cr and Mn is estimated to be a repulsive characteristics, although the attractive interaction between them and a carbon atom is experimentally obtained. The cause for this contradiction is discussed based on a different formation energy of carbide precipitation from the atomic pair interaction energy.
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  • Kazuhisa Shobu, Tatsuo Tabaru
    2004 Volume 68 Issue 12 Pages 983-987
    Published: 2004
    Released: June 24, 2005
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    Thermodynamic equilibrium calculation is sometimes difficult in a system when minor but important species are present, when only stoichiometric condensed phases are stable and the gas phase is absent, and when multiple minima are present in the Gibbs free energy of some non-ideal solution phases. New program is being developed to overcome these problems. The free-energy minimization method is implemented to determine thermodynamic equilibrium similarly to other conventional programs. However, the gas phase in equilibrium is assumed to be present even when the gas phase is unstable under the specified condition, similar to the equilibrium constant method. Chemical potentials of the system components are always determined uniquely by this additional condition, and the vapor pressure and composition can be calculated. Furthermore, an automatic routine that introduces multiple phases with different compositions and checks their stability is incorporated to detect possible phase-splitting in non-ideal solution phases.
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  • Yasuo Fujinaga
    2004 Volume 68 Issue 12 Pages 988-991
    Published: 2004
    Released: June 24, 2005
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    The eutectic temperatures of the In-Zn, Ag-Pb and Al-Sn binary systems under high pressures are predicted by applying an experimental equation given by Fujinaga. The eutectic temperatures are determined experimentally by means of the measurements of electrical resistance against temperature. The predicted values for the Ag-Pb and Al-Sn systems are approximately in agreement with the experimental results. But the predicted values for the In-Zn system are considerably different from the experimental results. Although there are exceptional case, the experimental equation can be applied for most of the binary systems.
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  • Jun Sato, Katsunari Oikawa, Ryosuke Kainuma, Kiyohito Ishida
    2004 Volume 68 Issue 12 Pages 992-1001
    Published: 2004
    Released: June 24, 2005
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    Phase equilibria of solid phases in the Co-W system have been investigated by using two-phase alloys and diffusion couple technique. In addition, systematic studies of magnetic and martensitic transitions have been conducted by using Differential Scanning Calorimeter (DSC), Vibrating Sample Magnetometer (VSM) and dilatometric measurement. Two-phase separation into ferromagnetic αCo and paramagnetic αCo was confirmed in the Co-rich side. The Curie temperature and saturation magnetization decrease with increasing W content and those disappear at around 25 at%W. Furthermore, thermodynamic assessment by using CALPHAD approach has been performed. A set of thermodynamic values for describing the Gibbs energy of Co-W system yields a good agreement with experimental phase diagram. The calculation of metastable magnetically induced phase separation along the Curie temperature is also presented.
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  • Tatsuya Tokunaga, Hiroshi Ohtani, Mitsuhiro Hasebe
    2004 Volume 68 Issue 12 Pages 1002-1007
    Published: 2004
    Released: June 24, 2005
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    The amorphous-forming ability of Ni-Si-B ternary alloys has been evaluated by coupling the Davies-Uhlmann kinetic approach with the CALPHAD method. For the computation, the time-temperature-transformation (TTT) diagram, which gives the time necessary for the formation of the detectable amount of crystal during transformation, was obtained at a finite temperature. The critical cooling rate for amorphization could be defined as the minimum cooling speed that does not intersect the TTT curve and, hence, these critical cooling rates enable us to evaluate the glass-forming ability of Ni-Si-B ternary alloys. The driving force for the crystallization of the crystalline phase was derived, on the basis of the thermodynamic functions of each phase formulated by the present study. The calculated results showed good agreement with the experimental data on the compositional range of amorphization in this alloy system. According to our calculations, at a given alloy composition, it was found that the phase other than the primary crystalline phase controls amorphization. This finding is closely related to the smaller entropy of fusion for the phase that controls amorphization versus that of the primary crystalline phase.
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  • Toshiyuki Koyama, Hidehiro Onodera
    2004 Volume 68 Issue 12 Pages 1008-1012
    Published: 2004
    Released: June 24, 2005
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    The FePt nano-particle structure has been considered to be a candidate for the next generation of high-density recording media due to its large magnetocrystalline anisotropy. The large magnetocrystalline anisotropy originates in L10 ordered structure of the FePt phase. However, it has been reported in recent investigation that disordering takes place when the FePt particle size is smaller than a critical size for ordering. In this study, the ordering of FePt nano-particle is modeled using the phase-field method, and the size dependence on the ordering of FePt nano-particle is analyzed based on this model. As a result, the disordering in the FePt particle proceeded rapidly when the particle size is less than the critical size for ordering. This phenomenon is due to an increase of the volume fraction of the disordered region at the vicinity of particle surface, when the particle size decreases.
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  • Masayuki Omichi, Masahide Sato, Tatsuya Tokunaga, Hiroshi Ohtani, Mits ...
    2004 Volume 68 Issue 12 Pages 1013-1019
    Published: 2004
    Released: June 24, 2005
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    Various cladding materials consisting of plain carbon steels with lower carbon concentrations and alloy steels with higher carbon concentrations have been considered to analyze the behavior of interdiffusion across the interface theoretically. The combination of the plain carbon steel and the alloy steel for the cladding was selected to make the chemical potential of carbon greater in the plain carbon steel than in the alloy steel. For the selection, the phase diagrams were computed with Thermo-Calc. The theoretical analysis was carried out using DICTRA that is the software developed at the Royal Institute of Technology in Sweden. The analysis indicates that the up-hill diffusion of carbon spontaneously occurs from the plain carbon steel to the alloy steel during annealing at elevated temperatures. For example, the cladding material composed of a plain carbon steel with a concentration of 0.046 mass%C and a 18Cr-8Ni stainless steel with a concentration of 0.06 mass%C exhibits such an up-hill diffusion at 1200 K, resulting in precipitation of Cr23C6 at the cladding interface.
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  • Takako Yamashita, Naoyuki Sano, Chi Zhang, Masato Enomoto, Yasuharu Sh ...
    2004 Volume 68 Issue 12 Pages 1020-1025
    Published: 2004
    Released: June 24, 2005
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    The effects of prestraining on the Cu precipitation and hardening were studied in an Fe-1.5 mass%Cu alloy. The specimens showed considerable precipitation hardening only at temperatures higher than 500°C without prestraining, while the 10% prestrained specimens exhibited an appreciable amount of hardening at temperatures as low as 300°C. To investigate the mechanism for hardening due to prestraining, the precipitation of Cu particles in bcc Fe matrix is simulated using Langer-Schwartz theory (modified by Kampmann and Wagner). The Cahn-Hilliard non-classical theory was employed to calculate the nucleation activation energy of nucleation of bcc Cu particles or nano-clusters. The influence of excess vacancies and dislocations introduced during prestraining on the Cu precipitation was considered, and simulated results were compared with experimental observation by 3D-APFIM and TEM. The increase in hardness above 500°C with and without prestraining may be attributed to the Cu precipitation in the matrix. A small, but significant amount of increase in hardness of prestrained specimens aged at a temperature as low as 300°C is likely to be due to Cu precipitation on dislocations. It is also possible that excess vacancies accelerate the diffusion and thus, the kinetics of Cu precipitation both in the matrix and at dislocations.
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  • Hiroshi Okuda, Shojiro Ochiai
    2004 Volume 68 Issue 12 Pages 1026-1030
    Published: 2004
    Released: June 24, 2005
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    Effects of grain boundary precipitation on the microstructural development near the precipitation-free zone (PFZ) have been examined by a Monte Carlo simulation with a semi grand canonical boundary condition. When the solute depletion at grain boundaries and the precipitation in the grains occur concomitantly, the average size of precipitates inside the grain is almost constant up to the PFZ boundary. The width of the PFZ is of the same order in magnitude as the average distance between the precipitates inside the grain. In contrast, when the grain boundary precipitation occurs during quenching, the average size of the precipitates changes gradually at the PFZ boundary. A parabolic growth law for PFZ width does not apply to the case.
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  • Jae Sik Yoon, In Sung Bae, Hyeoung Ho Park, Shoji Goto, Byung Il Kim
    2004 Volume 68 Issue 12 Pages 1031-1038
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    In the conventional metallothermic reduction (MR) process for obtaining tantalum powder in batch-type operation, it is difficult to control morphology and location of tantalum deposits. On the other hand, an electronically mediated reaction (EMR) process is capable to overcome these difficulties and has a merit of continuous process, but it has the defect that the reduction yield is poor. MR-EMR combination process is a method that is able to overcome demerits of MR and EMR process. In this study, an MR-EMR combination process has been applied to the production of tantalum powder by sodium reduction of K2TaF7. In the MR-EMR combination process, the total charge passed through external circuit and average particle size (FSSS) were increased with increasing reduction temperature. The proportion of fine particle (-325 mesh) was decreased with increasing reduction temperature. The tantalum yield was improved from 65 to 74% with increasing reduction temperature. Considering the charge, impurities, morphology, particle size and yield, an reduction temperature of 1123 K was found to be optimum temperature for MR-EMR combination process.
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  • Shin-ichi Yamaura, Yoichiro Shimpo, Hitoshi Okouchi, Motonori Nishida, ...
    2004 Volume 68 Issue 12 Pages 1039-1042
    Published: 2004
    Released: June 24, 2005
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    The (Ni0.6Nb0.4)45Zr50X5(X = Al, Co, Cu, P, Pd, Si, Sn, Ta or Ti) alloy ribbons were produced by the melt-spinning technique. All ribbon specimens were confirmed to have a single amorphous phase by XRD analysis. The crystallization temperature of the melt-spun (Ni0.6Nb0.4)45Zr50X5(X = Al, P, Pd, Si or Sn) amorphous alloys are higher than that of the (Ni0.6Nb0.4)50Zr50 amorphous alloy (727 K). Although the hydrogen permeability of the (Ni0.6Nb0.4)45Zr50X5(X = Si, Sn, Ta or Ti) amorphous alloys could not be measured due to severe embrittlement during the permeation test, the (Ni0.6Nb0.4)45Zr50X5(X = Al, Co, Cu, P or Pd) amorphous alloys had high ductility which was enough to measure the permeability. The hydrogen permeabilities of the (Ni0.6Nb0.4)45Zr50Co5 and the (Ni0.6Nb0.4)45Zr50Cu5 amorphous alloys were 2.46 × 10-8 and 2.34 × 10-8[mol·m-1·s-1·Pa-1/2] at 673 K, respectively. The (Ni0.6Nb0.4)45Zr50P5 amorphous alloy possesses the lowest permeability of 1.36 × 10-8[mol·m-1·s-1·Pa-1/2] at 673 K among the alloys where the permeability was measured. The reduction of the permeability in the (Ni0.6Nb0.4)45Zr50P5 amorphous alloy is thought to be due to the preferential formation of Zr-P atomic pairs which may suppress the hydrogen solubility and hydrogen diffusivity in the alloy. Since the heat of mixing for Zr-P atomic pairs is negatively larger than that for other pairs such as Ni-P and Nb-P. It is concluded that the Ni-Nb-Zr-X (X = Co or Cu) amorphous alloys have high potential to hydrogen permeable membranes.
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  • Keitaro Horikawa, Kenichi Yoshida
    2004 Volume 68 Issue 12 Pages 1043-1046
    Published: 2004
    Released: June 24, 2005
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    Hydrogen distribution in high-purity-based polycrystalline Al-5%Mg alloys prepared by changing the melting atmosphere was visualized by means of hydrogen microprint technique with electron backscattering pattern analysis after a tensile deformation at room temperature. The number of hydrogen atoms observed as silver particles on the slip lines was increased when the applied strain was increased. Hydrogen atom observed on the slip lines was totally increased when the melting atmosphere of the alloys was changed from argon to air. Hydrogen atom was observed at both slip lines and special grain boundaries when an air-melted specimen was deformed. It was shown that hydrogen atom accumulation at grain boundaries varied with the misorientation of grains and the angle to the tensile direction.
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  • Masayuki Mizumoto, Yujiro Kaneko, Akio Kagawa
    2004 Volume 68 Issue 12 Pages 1047-1052
    Published: 2004
    Released: June 24, 2005
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    Process parameters to control the microstructure of fiber reinforced metal matrix composite (FRMMC) fabricated by the low pressure infiltration process (LPI process) have been investigated. The mixed particles consisted of SiC and pure aluminum particles in various volume fraction were employed to control volume fraction and distribution of fibers in FRMMC. The Al-12 mass%Cu alloy melt was forced to infiltrate into the preform by applying a certain pressure on the melt surface. The optimum ratio of SiC particles in the mixed particles was 50 mass% to fabricate the FRMMC without any casting defects and a segregation of fibers due to preferential flow. The experimentally determined critical pressures required for the infiltration of the alloy melt into the preform were in good agreement with the theoretical ones, where an effective fiber volume fraction was considered. The volume fraction and distribution of reinforcement fibers was able to be controlled accurately by using the mixed particles having the same size with the fiber spacing calculated from the model where the reinforcement fibers distribute homogeneously in the composite. The coefficient of thermal expansion of both the 20 vol% and 30 vol%SiCf/Al-Cu composites was hardly changed during thermal cycling, suggesting that the strong bonding at the reinforcements/matrix interface was achieved in FRMMC specimens fabricated by LPI process.
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  • Masaaki Yamamura, Takao Yamaguchi, Imao Nagasaka, Setsuro Hiraoka
    2004 Volume 68 Issue 12 Pages 1053-1059
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    The relation between the thickness of the other material on the base metal surface and the spectral emissivity hasn't yet been clarified.
    The authors choose SUS304 as the base metal and examined as follows. Gold is evaporated on the SUS304, whose wavelength dependency of spectral emissivity in the visible region and neighboring (0.38∼0.90 μm) is totally different. As the result, the spectral emissivity changes from the value of SUS304's emissivity as the layer thickness increases from 0 μm. When the layer thickness reaches to 0.05∼0.07 μm, the emissivity gradually shows asymptotic convergence to the emissive value of the gold. Generally the spectral Emissivity depends on gold layer thickness. However, the spectral emissivity is constant (0.40) at the wavelength 0.53 μm, which is independent of the layer thickness and shows that is a fixed point. The above result (fixed point) does not comply if it is applied to optical dispassion formula of linear analysis. It means the relation of spectral emissivity between a layer thickness and a wavelength is not always linear.
    This study considers the spectral emissivity of evaporated gold layer, where the emissivity depends on layer thickness, is analyzed by the nonlinear dispersion model of optical interference phenomenon. The wavelength dependency can be explained by nonlinear behavior of free electron model and analyzed the data calculated from nonlinear dispersion formula, which can justify the fixed point.
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  • Takema Teratani, Hideaki Yamano, Noriyuki Mifune, Kazumi Tani, Yoshio ...
    2004 Volume 68 Issue 12 Pages 1060-1067
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    A MCrAlY alloy bond coat is widely used in thermal barrier coating (TBC) systems to protect substrates from high-temperature oxidizing environments. However, failure of the ceramic top coat can occur due to a thermally grown oxide (TGO) layer that grows at the interface between the bond coat and the top coat. Local stresses are produced by multiple oxides that grow separately at the interface. It seems that the multiple oxides may originate in the rapid oxidation of unmelted MCrAlY particles attached to the bond coat during spraying. Thus, it has become an important issue to control the growth behavior of TGOs.
    In the present study, the effect of chromate treatment was investigated. Prior to top coat deposition, a thin film of Cr2O3 was formed on the bond coat surface. High-temperature oxidation tests were carried out using samples coated both with and without chromate pretreatment, and the oxidation rates were determined by inspection of cross sections. Similar oxidation tests were carried out using MCrAlY powder material assumed to be unmelted particles. Chromate-treated bond coat showed outstanding oxidation resistance in comparison with bond coat without chromate pretreatment. In the case of pretreated MCrAlY powder, only the surfaces of particles were oxidized, even under conditions in which most particles without pretreatment were fully oxidized. This outcome is thought to result from the preferential formation of an oxidation-resistant Al2O3 layer in the early stage of oxidation. Calculations that take into account the oxidation of particles in the top coat indicate the generation of sufficient internal tensile stress to cause local fracture of the top coat. Because of its simplicity and applicability to complicated shapes, the chromate treatment is quite useful as a countermeasure against bond-coat oxidation and local fracture of the top coat near the interface.
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  • Yuji Imashimizu, Jirô Watanabé
    2004 Volume 68 Issue 12 Pages 1068-1075
    Published: 2004
    Released: June 24, 2005
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    In order to know about the Czochralski growth of peritectic system, Cu-Ge alloy rods were pulled from a hyperperitectic melt at three kinds of pulling rates while the melt temperatures were lowered at controlled rates, respectively. The germanium distribution and the microstructures of the pulled rods were investigated.
    The relationship between the pulling rate and the Ge concentration in the α phase that grew first from the melt is approximated by a relation derived from the BPS expression for the effective distribution coefficient. A group of peritectic ζ grains is formed subsequent to the initial growth of α crystal in the rods pulled at some rates. Growth of the ζ grains is followed by growth of α phase, resulting in the formation of alternating structures of the primary α and the peritectic ζ which is accompanied by a simultaneous variation in rod thickness. This appears repeatedly at short intervals along the rod when it is pulled at a high rate. It is concluded that the alternating structures of α phase and peritectic ζ grains are formed by a peritectic solidification of Ge-rich melt at the cell boundary that develops on a constitutionally supercooled solid-liquid interface, and that their cessation is due to a decrease in Ge concentration of the liquid at the interface with subsequent growth of the ζ phase.
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  • Nobuhito Sakaguchi, Mitsuo Niinomi, Toshikazu Akahori, Junji Takeda, H ...
    2004 Volume 68 Issue 12 Pages 1076-1082
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    Effect of Ta content on mechanical properties of Ti-30Nb-XTa-5Zr alloys and effect of Zr content on mechanical properties of Ti-30Nb-10Ta-XZr alloys were investigated. Ti-30Nb-10Ta-5Zr, which is the simplified compositional alloy of Ti-29Nb-13Ta-4.6Zr developed for biomedical applications, has been selected as the basic alloy composition. Tensile tests and elastic modulus measurements and microstructural observations were carried out on those alloys.
    Microstructures of Ti-30Nb-XTa-5Zr alloys containing Ta less than 10 mass% show the mixture of β and ω phases. Microstructures of Ti-30Nb-XTa-5Zr alloys containing 10 mass%Ta or greater than 10 mass%Ta show single β phase.
    The tensile strength and elongation of Ti-30Nb-XTa-5Zr alloy show a great change with changing Ta content. The threshold of Ta content for the changing exists between 5 mass% and 10 mass%Ta. The tensile properties of Ti-30Nb-10Ta-XZr alloys are affected by the change of deformation mechanism of β phase.
    The tensile strength of Ti-30Nb-10Ta-XZr alloys increases with increasing Zr content. The elongation of these alloys decreases with increasing Zr content. The tendency of tensile properties of Ti-30Nb-10Ta-XZr alloys is also caused by the change in deformation mechanism of β phase.
    From the point of view of stress-strain curves obtained by tensile tests and variation of elastic modulus with changing Zr content, Zr found to act as β stabilizer in Ti-Nb-Ta-Zr system alloy.
    Ti-30Nb-5Ta-5Zr, Ti-30Nb-10Ta and Ti-30Nb-10Ta-3Zr have relatively lower elastic moduli and greater elongation. Thus, these three Ti-Nb-Ta-Zr system alloys have potential to be used for biomedical applications.
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  • Kiyoshi Mizuuchi, Kanryu Inoue, Masami Sugioka, Masao Itami, Masakazu ...
    2004 Volume 68 Issue 12 Pages 1083-1085
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    Boron fiber reinforced Ti matrix composites were fabricated by a pulsed current hot pressing (PCHP) process at various holding temperatures between 973 K and 1273 K at pressure of 32 MPa for 600 s. Well bonding between the fiber and matrix was obtained by the PCHP at 1073 K. When fabricated at the holding temperature higher than 1173 K, a TiB2 layer was formed along the interface between the fiber and the matrix, and the crystallization of boron in the vicinity of tungsten core in the fiber occurred. The thickness of TiB2 layer formed and the crystallized boron increased with increasing the holding temperature. Tensile tests were carried out at room temperature for the composites fabricated by the PCHP at 1073 K. The yield stress of the composites containing 17.2 vol% boron fiber was attained at 706 MPa. This value was about 80% of the yield stress calculated by the force equilibrium equation of a composite along with the fiber axis direction.
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  • Tetsuyoshi Suzuki, Alexei Vinogradov, Satoshi Hashimoto
    2004 Volume 68 Issue 12 Pages 1086-1088
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    Equal Channel Angular Pressing (ECAP) is one of the effective plastic working processes to achieve metals strengthening. In the present study, the strengthening of Au, Au-25Ag and Au-12.5Ag-12.5Cu (in mass%) by ECAP is examined. The rectangle-shaped working billets were pressed repeatedly with both 0° rotation (route A) and 90° rotation (route Bc) between successive pressings, up to four passes corresponding to equivalent strain of ε = 4.6. These samples were then subjected to Vickers hardness and tensile tests. The hardness measurements revealed that, in Au up to four passes, Vickers hardness values of the samples produced by route Bc and route A were Hv117 and Hv98, respectively. Vickers hardness value and the tensile strength of Au-Ag-Cu alloy aged after ECAP are estimated to be of Hv345 and of 1.1 GPa.
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