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MATERIALS TRANSACTIONS Vol. 51 (2010), No. 3

ISIJ International
belloff
ONLINE ISSN: 1347-5320
PRINT ISSN: 1345-9678
Publisher: The Japan Institute of Metals and Materials

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MATERIALS TRANSACTIONS Vol. 51 (2010), No. 3

Role of Temperature Dependent Chemical Potential on Thermoelectric Power

Tsunehiro Takeuchi, Yasuhiro Toyama, Akio Yamamoto

pp. 421-427

DOI:

10.2320/matertrans.M2009349

Abstract

In this paper, the relation between chemical potential and thermoelectric power is investigated by using the linear response theory, possible models of electronic structure, the consequently obtained spectral conductivities, and high-resolution photoemission spectroscopy. We revealed that the effect of temperature dependent chemical potential on thermoelectric power S(T) is negligibly small when its magnitude is limited below 100 μV/K, but becomes nontrivial with increasing S(T). The validity of this argument we proposed on the basis of theoretical calculation was experimentally confirmed using the high-resolution photoemission spectra of the materials possessing a large magnitude in thermoelectric power.

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Role of Temperature Dependent Chemical Potential on Thermoelectric Power

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Kinetic Analysis of Crystallization Process in Amorphous Se90−xTe10Pbx Glasses

M. A. Abdel Rahim, A. Y. Abdel Latief, A. El-Korashy, M. A. Sabet

pp. 428-433

DOI:

10.2320/matertrans.MC200927

Abstract

The crystallization process of Se90−xTe10Pbx (where x=2.5, 5, 7.5 and 15 at%) glassy system was studied by differential thermal analysis (DTA) technique under non-isothermal conditions. The crystallization parameters were calculated using different kinetic models. The validity of the Johnson-Mehl-Avrami (JMA) model to describe the crystallization process for the studied compositions was discussed. The results showed that the two-parameter Sestak-Berggren (SB) is the most suitable for quantitative description of the crystallization process for the studied compositions. The results show more complicated crystallization process involving nucleation and growth. The increasing of the Pb content in the Se-Te-Pb system leads to a more complex and accelerated process. The crystalline phases were identified by using x-ray diffraction technique (XRD) and scanning electron microscopy (SEM).

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Kinetic Analysis of Crystallization Process in Amorphous Se90−xTe10Pbx Glasses

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Influence of Cold-Working and Subsequent Heat-Treatment on Young’s Modulus and Strength of Co-Ni-Cr-Mo Alloy

Takuma Otomo, Hiroaki Matsumoto, Naoyuki Nomura, Akihiko Chiba

pp. 434-441

DOI:

10.2320/matertrans.M2009327

Abstract

Changes in Young’s modulus of the Co-31 mass%Ni-19 mass%Cr-10 mass%Mo alloy (Co-Ni based alloy) with cold-swaging, combined with heat-treatment at temperatures from 673 to 1323 K, was investigated to enhance the Young’s modulus of Co-Ni based alloy. After cold-swaging, the Co-Ni based alloy, forming ⟨111⟩ fiber deformation texture, shows the Young’s modulus of 220 GPa. Furthermore, after ageing the cold-swaged alloy at temperatures from 673 to 1323 K, the Young’s modulus increased to 230 GPa, accompanied by a decrease in the internal fiction and an increase in the tensile strength. This suggests that the increment in Young’s modulus is caused by a moving of the vacancies to the dislocation cores and a continuous locking of the dislocations along their entire length with solute atoms (trough model). By annealing at 1323 K after cold swaging, Young’s modulus slightly increased to 236 GPa. On the other hand, the tensile strength decreases to almost the same value as that before cold swaging due to recrystallization. These results suggest that the Young’s modulus and the strength in the present alloy are simultaneously enhanced by the continuous dislocation locking during aging as well as the formation of ⟨111⟩ fiber deformation texture.

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Influence of Cold-Working and Subsequent Heat-Treatment on Young’s Modulus and Strength of Co-Ni-Cr-Mo Alloy

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Coarsening of β′ Precipitates in an Isothermally-Aged Fe75-Ni10-Al15 Alloy

Orlando Soriano-Vargas, Maribel L. Saucedo-Muñoz, Victor M. Lopez-Hirata, Ana Ma. Paniagua-Mercado

pp. 442-446

DOI:

10.2320/matertrans.M2009332

Abstract

The coarsening process of the β′ precipitates was studied in an isothermally aged Fe75-Ni10-Al15 alloy. The aging treatments at 750, 850, and 920°C caused the precipitation of the β′ phase with the B2 type crystalline structure in a bcc ferritic matrix phase. As the aging progressed, the initial rounded shape changed to cuboids aligned in the ⟨100⟩ directions of the ferritic matrix, and finally to rectangular plates also aligned in the same direction. The coarsening process of the β′ phase was faster as the aging temperature increased. Nevertheless, the highest hardness and slowest overaging process took place during the aging at 920°C. This increase in hardness seems to be associated with the more rapid formation of the cuboid precipitates aligned in the ⟨100⟩ direction of the ferritic matrix.

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Coarsening of β′ Precipitates in an Isothermally-Aged Fe75-Ni10-Al15 Alloy

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Growth Behavior and Interfacial Character of Ir3Y Precipitates in the Ir2Y Lave Phase Matrix

N. Sekido, Y. Yamabe-Mitarai

pp. 447-454

DOI:

10.2320/matertrans.MBW200901

Abstract

A C15 Laves phase Ir2Y that forms in the Ir-Y binary system develops off-stoichiometry toward the Ir-rich composition at high temperatures, and its range of homogeneity becomes narrow with decreasing temperatures. One consequence of this solubility behavior is the formation of Ir3Y precipitates within the Ir2Y matrix of an Ir-30 mol%Y alloy. The orientation relationship between Ir3Y and Ir2Y has been identified as: (0001)Ir3Y||(111)Ir2Y and [2\\bar1\\bar10]Ir3Y||[\\bar110]Ir2Y. The similarity in the crystal structures of the two phases yields a plate-like Ir3Y precipitate showing a typical Widmanstätten structure. The growth of the precipitates has been suggested to follow the ledge mechanism. The interfacial character between the two phases has been identified in this study.

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Growth Behavior and Interfacial Character of Ir3Y Precipitates in the Ir2Y Lave Phase Matrix

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Atomic Arrangement of Interphase Boundary between Bainite and Austenite in Fe-Si-C Alloy

Kazuyuki Ogawa, Takahiro Sawaguchi, Setuo Kajiwara

pp. 455-462

DOI:

10.2320/matertrans.M2009394

Abstract

Atomic arrangement of bainite/austenite interface was examined by high resolution electron microscopy in a Fe-2Si-1.4C alloy. Lattice transition region with an intermediate lattice structure between two phases, which is a characteristic feature of shear-type deformation, was not observed either between upper bainite and austenite or between lower bainite and austenite. However, high density dislocations existed inside upper and lower bainites, which may be introduced as a result of lattice invariant shear deformation. Based on these experimental facts, the shear deformation assisted-diffusional transformation model was proposed for the bainitic transformation.

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Atomic Arrangement of Interphase Boundary between Bainite and Austenite in Fe-Si-C Alloy

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Order of Phase Transition on a Simple Cubic Lattice Determined by Cluster Variation Method

Naoya Kiyokane, Tetsuo Mohri

pp. 463-468

DOI:

10.2320/matertrans.MBW200904

Abstract

Detailed analyses of the free energy behavior near the order-disorder transition temperature on a simple cubic lattice are attempted by cluster variation method (CVM). The entropy is formulated within a cubic approximation of the CVM and two kinds of nearest neighbor pair interaction energies are assumed in the internal energy; one is independent of an atomic distance, r, and the other depends on r through Lennard-Jones type pair potential. In both cases, it is found that the order of the transition is of second order.

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Order of Phase Transition on a Simple Cubic Lattice Determined by Cluster Variation Method

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Kinetic Arrest of Martensitic Transformation in Ni33.0Co13.4Mn39.7Ga13.9 Metamagnetic Shape Memory Alloy

Xiao Xu, Wataru Ito, Rie Y. Umetsu, Keiichi Koyama, Ryosuke Kainuma, Kiyohito Ishida

pp. 469-471

DOI:

10.2320/matertrans.MBW200915

Abstract

Martensitic and magnetic properties of Ni33.0Co13.4Mn39.7Ga13.9 metamagnetic shape memory alloy were investigated. The kinetic arrest phenomenon was observed at about 120 K by thermomagnetization measurements, and magnetic field-induced transformation (MFIT) was also detected at various temperatures ranging from 4.2 to 300 K. By evaluation of the equilibrium magnetic fields and temperatures based on the transformation fields and temperatures, it was confirmed that the transformation entropy change below 120 K becomes almost zero, which results in the kinetic arrest phenomenon.

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Kinetic Arrest of Martensitic Transformation in Ni33.0Co13.4Mn39.7Ga13.9 Metamagnetic Shape Memory Alloy

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Microstructure and Corrosion Properties of Mg-xSn-5Al-1Zn (x=0, 1, 5 and 9 mass%) Alloys

Kyung Chul Park, Byeong Ho Kim, Hisamichi Kimura, Yong Ho Park, Ik Min Park

pp. 472-476

DOI:

10.2320/matertrans.M2009308

Abstract

In the present work, the corrosion properties of Mg-xSn-5Al-1Zn (x=0, 1, 5 and 9 mass%) alloys have been investigated. Potentiodynamic polarization and immersion tests were carried out in 3.5% NaCl solution of pH 7.2 at room temperature to measure the corrosion properties of Mg-xSn-5Al-1Zn (x=0, 1, 5, and 9 mass%) alloys. Microstrucral analysis shows the Mg17Al12 and Mg2Sn phase were mainly precipitated along grain boundaries. With increase of the Sn contents, the volume fraction of the secondary phases, i.e. Mg17Al12 and Mg2Sn phase, was increased. The corrosion resistance of Mg-xSn-5Al-1Zn alloys was improved by the Sn addition. Especially, the AZ51-5 mass%Sn alloy characterized the superior corrosion resistance in the studied alloys. It seems that the presence of Sn stabilized the Mg(OH)2 layers on the surface of Mg alloys and the secondary phases effectively formed semi-continuous structures, resulting in a drastic improvement of corrosion resistance of the Mg alloys.

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Microstructure and Corrosion Properties of Mg-xSn-5Al-1Zn (x=0, 1, 5 and 9 mass%) Alloys

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Effect of Tool Materials on Dynamic Friction Characteristics and Microstructural Evolution at Elevated Temperature in Extruded AZ31 Magnesium Alloy

Li-Fu Chiang, Noriaki Nishioka, Jian-Yih Wang, Hiroyuki Hosokawa, Tokuteru Uesugi, Yorinobu Takigawa, Kenji Higashi

pp. 477-481

DOI:

10.2320/matertrans.MBW200914

Abstract

The effect of the coating materials of the tools on the dynamic friction characteristics and microstructural evolution with straining was investigated by the ring-typed compressive test at a temperature of 473 K and at a strain rate of 10−2 s−1 in the extruded AZ31 magnesium alloy with an average grain size of 15 μm. The values of the dynamically recrystallized grain size in the samples compressed up to about 45% by using the WC-Co tools with and without the DLC coating were 3.8 μm and 4.8 μm, respectively. The dominant deformation mechanism under all the testing condition for the present alloy was the climb-controlled dislocation creep. The dynamic friction coefficient, m value, for the sample compressed by the WC-Co tool was higher than that done by the DLC tool, even if though there was identical tendency in stress level. The integration degree of the grains within 10 degree from ⟨0001⟩ direction to compressive axis in the sample compressed by the WC-Co tool was larger than that done by the DLC tool. It was concluded that the higher m value could enhance an alignment of the planes perpendicular to the compressive direction to the basal plane even if under same testing condition.

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Effect of Tool Materials on Dynamic Friction Characteristics and Microstructural Evolution at Elevated Temperature in Extruded AZ31 Magnesium Alloy

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Calculations of Internal Oxidation Rate Equations and Boundary Conditions between Internal and External Oxidation in Silicon Containing Steels

Takashi Onishi, Shouhei Nakakubo, Mikako Takeda

pp. 482-487

DOI:

10.2320/matertrans.M2009256

Abstract

The rate constants for internal oxidation of Si containing steels (Fe-Si alloys) at 850°C were calculated in order to clarify the formation mechanism of fayalite scale, which can form as a “sub-scale” in Si containing steels. The diffusion coefficient of oxygen in the oxide layer, DO, and the oxygen concentration at specimen surface, NO(s), which are constituents of the internal oxidation rate constant, (2DONO(s)⁄NB(O)n), were calculated under various oxidation conditions, and the rate equation for the internal oxide layer was derived. Comparing the calculated and the measured values of (2DONO(s)⁄NB(O)n), we confirmed that the rate equation determined for the internal oxide layer was reasonable. The conditions at the boundary between internal to external oxidation of Si containing steels (Fe-Si alloys) at 850°C were also calculated by substituting the calculated values of DO and NO(s) at the boundary into the rate equation.

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Calculations of Internal Oxidation Rate Equations and Boundary Conditions between Internal and External Oxidation in Silicon Containing Steels

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Effects of Graphite, SiO2, and Fe2O3 on the Crushing Strength of Direct Reduced Iron from the Carbothermic Reduction of Residual Materials

Hsin-Chien Chuang, Weng-Sing Hwang, Shih-Hsien Liu

pp. 488-495

DOI:

10.2320/matertrans.M2009299

Abstract

The effects of various additives (Fe2O3, SiO2, graphite) on the crushing strength of direct reduced iron (DRI) were investigated. Using a mixture of various residual materials produced in a steel plant, the chemical composition was altered using various additives. The mixture was then agglomerated into a cylindrical pellet and reduced at 1250°C for 15 min. The DRI was then tested for its crushing strength. It was found that adding graphite resulted in more carbon remaining in the DRI. Although the metallization degree of DRI was increased, the crushing strength of DRI decreased due to the presence of discontinuous carbon granules in DRI. Adding SiO2 caused the slag basicity (the ratio between CaO and SiO2) to decrease. The addition of Fe2O3 consumed the carbon content in the pellet, reducing the metallization degree of DRI. The softening and melting temperatures of slag were adjusted by changing the slag basicity and FeO content. A proper amount of Fe2O3 or SiO2 addition increased the crushing strength of DRI due to the softening of slag. Excessive Fe2O3 or SiO2 resulted in the melting of slag, which decreases crushing strength.

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Effects of Graphite, SiO2, and Fe2O3 on the Crushing Strength of Direct Reduced Iron from the Carbothermic Reduction of Residual Materials

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Effect of Conditions of Unidirectional Solidification on Microstructure and Pore Morphology of Al-Mg-Si Alloys

Tae Bum Kim, Shinsuke Suzuki, Hideo Nakajima

pp. 496-502

DOI:

10.2320/matertrans.M2009333

Abstract

Aluminum and Al-Mg-Si alloy ingots with pores were fabricated by unidirectional solidification through thermal decomposition of Ca(OH)2 powders. The porosity of aluminum and Al-Mg-Si alloy were 10–17% and 0.1–2%, respectively. While the pores with 250–400 μm diameter were observed in a grain or across several grains in the aluminum ingots, smaller pores with 50–300 μm were observed in an eutectic region between primary α dendrites in the Al-Mg-Si ingots. In the alloys with Mg(0.25–0.5 mass%) and Si(0.2–0.4 mass%), the unidirectional pores were aligned between columnar dendrites grown in the unidirectional solidification. With higher Mg and Si contents, the equiaxed dendrite zones with spherical pores were observed in a region with low temperature gradient. The results of thermal analysis showed that constitutional supercooling, which causes equiaxed dendrites, tends to occur with increase in Mg and Si contents and with low temperature gradient at the solid-liquid interface. Under this condition, spherical pores were evolved, because the surrounding α-dendrites solidified isotropically. Therefore, it is concluded that the pore growth direction is affected by morphology of dendrites.

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Effect of Conditions of Unidirectional Solidification on Microstructure and Pore Morphology of Al-Mg-Si Alloys

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Titanium Doped ITO Thin Films Produced by Sputtering Method

Leandro Voisin, Makoto Ohtsuka, Takashi Nakamura

pp. 503-509

DOI:

10.2320/matertrans.MBW200907

Abstract

Indium-tin-oxide (ITO) thin films, typically produced by In2O3-10 mass%SnO2 target, are widely used for the elaboration of optoelectronics devices such as liquid crystal displays (LCD), flat panel displays (FPD), plasma displays, touch panels, etc., and they are required to satisfied specific optoelectronical properties such as, low volume resistivity and high transmittance.
Due to the current high cost and limited supply of indium, titanium was investigated as dopant element for the production of ITO thin films. Two sputtering method were carried out; a combinatorial method where an In2O3-10 mass%SnO2 and a Ti targets were simultaneously sputtered and then a co-sputtering method where, in addition to the previous targets, an In2O3-50 mass%SnO2 and a TiO2 targets were also sputtered.
Effects of the oxygen flow and heat treatment temperature on the optoelectronical properties of ITO thin films doped with Ti, as metal and dioxide, were investigated and the results were discussed on the basis of crystallization for bixbyte structure of In2O3. The obtained results indicate that the use of Ti as dopant element during the production of ITO thin films by sputtering method will be promising.

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Titanium Doped ITO Thin Films Produced by Sputtering Method

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Mechanical and Thermal Properties of Vapor-Grown Carbon Fiber Reinforced Aluminum Matrix Composites by Plasma Sintering

Zhe-Feng Xu, Yong-Bum Choi, Kazuhiro Matsugi, Dong-Chun Li, Gen Sasaki

pp. 510-515

DOI:

10.2320/matertrans.MBW200918

Abstract

Vapor-grown carbon fiber (VGCF) reinforced aluminum matrix composites were fabricated by plasma sintering method, and their mechanical and thermal properties were investigated. The aluminum powders with average diameters of 1 μm, 3 μm and 30 μm were chosen as the matrix. The monolithic aluminum blocks were also fabricated by plasma sintering method in order to comparing with the composites. As decreasing the aluminum powder size, VGCFs became to disperse more uniformly in composites. Compared with the monolithic aluminum block, Vickers hardness of the composites was enhanced remarkably. For 1 μm aluminum powders, the increment rate of Vickers hardness of the composites to monolithic aluminum was as high as 78.3%. While the tensile strength of the composites was lower than that of the monolithic aluminum. In contrast, the coefficient of thermal expansion of composites with 1 μm or 3 μm and 30 μm aluminum powders were decreased and increased, respectively, compared with the aluminium blocks with their powder. The thermal conductivity of the composites also increased compared with that of the monolithic aluminum blocks, but was not dependent on the size of aluminum powders.

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Mechanical and Thermal Properties of Vapor-Grown Carbon Fiber Reinforced Aluminum Matrix Composites by Plasma Sintering

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Estimation of Kinetic Parameters for Combustion Synthesis of FeAl Intermetallic Compound by Dipping Experiment of Fe Wire into Al Melt

Atsushi Hibino

pp. 516-524

DOI:

10.2320/matertrans.M2009319

Abstract

The formation reaction rate of Fe-Al intermetallic compounds was examined by dipping experiment of Fe wire into Al melt in the temperature range between 973 K and 1373 K, to determine the kinetic parameters of combustion synthesis of FeAl. A piece of Fe wire and Al powder were put into an alumina crucible, and vacuum-sealed in a quartz tube. The tube was held in an electric furnace to promote the compound formation reaction. A microstructure observation and SEM-EDX analysis of the dipped Fe wire were performed. It was found that the compound formation reaction occurred at the interface between the molten Al and the Fe wire, and a cylindrical Fe2Al5 layer was formed in the wire. The thickness of the formed layer depended on the holding time and the dipping temperature. The reaction process has been similar to the combustion synthesis of FeAl intermetallic compound. Therefore, the kinetic parameters could be determined by the dipping experiment. The experimental data have been analyzed using a cylindrical model which took into account the diffusion process of Al in the Fe2Al5 compound layer and chemical reaction process on the interface between Fe2Al5 and Fe. The diffusion coefficient, DAl and the reaction rate constant, kc were estimated. The curves were calculated by using the obtained kinetic parameters and were in satisfactory agreement with the experimental values. & log_10D_Al/m2·s−1=-1887/T-8.369
& log_10k_c/mol·m−2·s−1=-3177/T+1.839

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Estimation of Kinetic Parameters for Combustion Synthesis of FeAl Intermetallic Compound by Dipping Experiment of Fe Wire into Al Melt

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Shape Memory Response in Ni40Co10Mn33Al17 Polycrystalline Alloy

Wataru Ito, Burak Basaran, Rie Y. Umetsu, Ibrahim Karaman, Ryosuke Kainuma, Kiyohito Ishida

pp. 525-528

DOI:

10.2320/matertrans.MBW200903

Abstract

Shape memory response of the polycrystalline Ni40Co10Mn33Al17 alloy were investigated. In the isobaric thermal cycling experiments, the measured transformation strain levels increased with increasing stress reaching about 3.6% under 200 MPa. The slope of the stress vs. transformation temperature diagram, constructed using the data from these experiments, almost coincided with the predicted one obtained using the Clausius-Clapeyron equation, and experimental entropy data and transformation strain. Perfect pseudoelasticity was observed up to 405 K during compressive straining up to 2.5%.

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Shape Memory Response in Ni40Co10Mn33Al17 Polycrystalline Alloy

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Bioactivity of a Ni-Free Ti-Based Metallic Glass

F. X. Qin, K. Wada, X. J. Yang, X. M. Wang, M. Yoshimura, K. Asami, A. Inoue

pp. 529-534

DOI:

10.2320/matertrans.MBW200910

Abstract

In this study, a bone-like apatite layer was formed on a Ni-free Ti-based metallic glass. A two-step treatment method, i.e., hydrothermal-electrochemical treatment followed by pre-calcification treatment, was developed to prepare a bioactive surface on the Ti-based metallic glass. The results reveal that the combination of electrochemical-hydrothermal and pre-calcification treatments can accelerate nucleation and improve growth rate of apatite on Ti-based metallic glass in simulated body fluid (Hanks’ solution). The reasons why the two-step treatment accelerates the nucleation and growth of apatite were also discussed.

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Bioactivity of a Ni-Free Ti-Based Metallic Glass

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Detection of Neodymium-Rich Phase for Development of Coercivity in Neodymium-Iron-Boron-Based Alloys with Submicron-Sized Grains Using Positron Lifetime Spectroscopy

Takeshi Nishiuchi, Masaki Nakamura, Satoshi Hirosawa, Masataka Mizuno, Hideki Araki, Yasuharu Shirai

pp. 535-541

DOI:

10.2320/matertrans.M2009342

Abstract

In order to evaluate the relationship between positron lifetime and microstructure, which contributes to the development of coercivity in hydrogenation-disproportionation-desorption-recombination (HDDR)-processed Nd-Fe-B-based alloys, detailed studies of positron lifetime spectroscopy were performed on HDDR-processed Nd-Fe-B-based alloys during desorption-recombination (DR) treatment. After the onset of coercivity, the change in positron lifetime closely corresponded to the change in intrinsic coercivity (HcJ) with the progress of DR treatment. This result can be explained in terms of the grain size of the recombined Nd2Fe14B phases and the diffusion length of positrons, which annihilate in the matrix before reaching the grain boundary. Furthermore, positron lifetime spectroscopy was able to detect small changes in the grain boundary region very sensitively compared with thermal desorption spectroscopy (TDS) and X-ray diffraction (XRD). These changes in the grain boundary region caused the onset of coercivity attributed to the formation of Nd-rich intergranular phases. These results indicate that formation of a small amount of the Nd-rich intergranular phase during the DR process, which could be detected by positron lifetime spectroscopy, contributes to the onset of coercivity, even if NdHx phases remain.

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Detection of Neodymium-Rich Phase for Development of Coercivity in Neodymium-Iron-Boron-Based Alloys with Submicron-Sized Grains Using Positron Lifetime Spectroscopy

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Effects of Tool Rotating Rate and Pass Number on Pore Structure of A6061 Porous Aluminum Fabricated by Using Friction Stir Processing

Takao Utsunomiya, Ken-ichi Tamura, Yoshihiko Hangai, Osamu Kuwazuru, Nobuhiro Yoshikawa

pp. 542-547

DOI:

10.2320/matertrans.MBW200916

Abstract

As a new fabrication method of porous aluminum with the advantages of high productivity and low manufacturing cost, the authors proposed a fabrication method called the “FSP route precursor method”. FSP (friction stir processing) is a solid-state process involving the generation of friction heat and intense plastic flow simply by inserting a rotating tool and allowing it to traverse through the aluminum alloy matrix. In this method, the precursor is manufactured by mixing a blowing agent powder and a stabilization agent powder into the aluminum alloy matrix using the intense stirring action of FSP. Then, porous aluminum can be obtained by foaming the precursor under suitable conditions. In this study, aluminum alloy 6061 (A6061) plates are used as a starting material and porous aluminum is fabricated by applying the procedure of multipass FSP. The effects of the tool rotating rate and the number of passes on the porosity and pore structure of A6061 porous aluminum are investigated. To obtain porous aluminum with high porosity and high quality (i.e., a uniform pore size distribution and highly spherical pores), the tool rotating rate should be approximately from 1000 to 2200 rpm when the rotating tool traverses the matrix four times and the foaming conditions (holding temperature and holding time when the blowing agent is foamed) are optimized. The porous aluminum obtained has a porosity of 70%, and the average equivalent diameter of pores is approximately from 1.5 to 2 mm.

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Effects of Tool Rotating Rate and Pass Number on Pore Structure of A6061 Porous Aluminum Fabricated by Using Friction Stir Processing

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Nondestructive Observation of Pore Structures of A1050 Porous Aluminum Fabricated by Friction Stir Processing

Yoshihiko Hangai, Yuichiro Ozeki, Shigehiro Kawano, Takao Utsunomiya, Osamu Kuwazuru, Makoto Hasegawa, Shinji Koyama, Nobuhiro Yoshikawa

pp. 548-552

DOI:

10.2320/matertrans.MBW200921

Abstract

In the automotive industry, porous aluminum is expected to be used as a new functional material because of its light weight, high energy absorption and high sound-insulating property. Recently, a new processing route for fabricating the porous aluminum precursor, which utilizes friction stir processing (FSP), has been developed. It is expected that, by applying the FSP route precursor method, the cost-effective fabrication of porous aluminum with high productivity can be realized. In this study, two different types of A1050 porous aluminum were fabricated from two different sizes of precursor by the FSP route precursor method. The two types of porous aluminum fabricated using small and large precursors are hereafter referred to “FSP-S porous aluminum” and “FSP-L porous aluminum”, respectively. The pore structures of FSP-S porous aluminum, FSP-L porous aluminum and also commercially available porous aluminum (ALPORAS, fabricated by Shinko Wire Co., Ltd.) were nondestructively observed by X-ray computed tomography (X-ray CT). From the nondestructive observation of pore structures, it was shown that a large number of pores of smaller area and volume were distributed in porous aluminum fabricated by the FSP route precursor method compared with the pores in ALPORAS. However, there was little difference in the circularity of pores between porous aluminum fabricated by the FSP route and ALPORAS, and there was little dependence of the pore structure on the precursor size for porous aluminum fabricated by the FSP route. This result indicates the potential of the FSP route for fabricating larger porous aluminum samples.

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Nondestructive Observation of Pore Structures of A1050 Porous Aluminum Fabricated by Friction Stir Processing

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Structural Flexibility of a Pd40Ni40Si5P15 Bulk Metallic Glass

N. Chen, D. V. Louzguine-Luzgin, G. Q. Xie, Y. C. Wang, K. F. Yao, A. Inoue

pp. 553-556

DOI:

10.2320/matertrans.M2009274

Abstract

We report that clearly different microstructures were obtained corresponding to different parts in a Pd40Ni40Si5P15 glassy rod, showing a nature of structural flexibility of a glass. Such a structural difference was believed to have the origin in the different cooling rate induced by the solidification in succession of the molten alloy during the casting. Upon this difference in the microstructure, the samples show very different deformation behaviors.

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Structural Flexibility of a Pd40Ni40Si5P15 Bulk Metallic Glass

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Room-Temperature Ferromagnetism in Cobalt and Aluminum Co-Doping Tin Dioxide Diluted Magnetic Semiconductors

Xingzhi Ning, XiaoFang Liu, Ronghai Yu, Ji Shi, Yoshio Nakamura

pp. 557-560

DOI:

10.2320/matertrans.M2009373

Abstract

Sn0.897Co0.10Al0.003O2 diluted magnetic semiconductor films were grown on (100) silicon substrate by magnetron sputtering and then annealed at 300°C and 500°C for 1.5 h, respectively. Room temperature ferromagnetism was observed for the as-deposited film. The saturation magnetization (Ms) decreases as annealing temperature increases, and the value of Ms for the films annealed at 500°C is about half of the value for the as-deposited films. The electrical resistivity of Sn0.897Co0.10Al0.003O2 drops in a range of 106 to 10Ω·m with increasing the annealing temperature. The XRD and HRTEM investigation illustrates that no impurity phase and Co clusters exist in the films, indicating the ferromagnetism of the films is intrinsic. The F-center-mediated exchange model is adopted to explain the room-temperature ferromagnetism of the films.

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Room-Temperature Ferromagnetism in Cobalt and Aluminum Co-Doping Tin Dioxide Diluted Magnetic Semiconductors

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Phase Stability of Bi2(V1−xMEx)O5.5+δ (ME=Li and Ag, x=0.05 and 0.1)

Yu-ki Taninouchi, Tetsuya Uda, Tetsu Ichitsubo, Yasuhiro Awakura, Eiichiro Matsubara

pp. 561-566

DOI:

10.2320/matertrans.M2009348

Abstract

The phase transition of high oxide-ion conductor Bi2(V1−xMEx)O5.5+δ (ME=Li and Ag, x=0.05 and 0.1) and its long-term phase stability against thermal decomposition have been studied. The transition behavior was determined by differential scanning calorimetry (DSC) as well as high-temperature X-ray diffraction (HT-XRD) analysis. The observed thermal and structural changes during temperature scans reveal the temperature dependence of electrical conductivity. Li- and Ag-doping do not sufficiently suppress thermal decomposition at intermediate temperatures between 400 and 600°C. In particular, partial decomposition was detected in Bi2(V0.9Ag0.1)O5.3 during a temperature scan by HT-XRD analysis, which explains the distinct change in electrical conductivity. We have generated pseudo-binary phase diagrams for Bi2(V1−xMEx)O5.5+δ based on the X-ray diffraction analysis of powders annealed for 200 h and differential thermal analysis. The thermodynamically stable region of Bi2(V1−xMEx)O5.5+δ is not sufficiently expanded by Li- and Ag-doping. At around 500°C, Bi2(V1−xMEx)O5.5+δ is metastable, although it shows the highest oxide-ion conductivity among solid oxides.

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Phase Stability of Bi2(V1−xMEx)O5.5+δ (ME=Li and Ag, x=0.05 and 0.1)

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Influence of Flat Cavity Formation on Stress vs. Strain and Strain-Rate Relations of Superplastic Deformation in 3Y-TZP

Yoshinobu Motohashi, Vasyl Ryukhtin, Takaaki Sakuma, Jan Saroun

pp. 567-573

DOI:

10.2320/matertrans.M2009381

Abstract

During superplastic deformation (SPD) of tetragonal zirconia polycrystals containing 3 mol% yttria (3Y-TZP) at high strain-rates, a number of crack-like flat cavities having very narrow gaps lying along grain boundaries mostly normal to the tensile axis are produced in addition to conventional cavities. In order to see when (from which strain point) the flat cavities get started to form, the tensile deformation of the 3Y-TZP was interrupted at different strain points including a yield point, and then a small angle neutron scattering (SANS) technique was applied to examine the existence of the flat cavities. It was found that no flat cavities were produced at the yield point but they got started to form soon after the yielding, i.e., after a superplastic flow began. The formation of the flat cavities can decrease the cross-sectional area of the specimen, resulting in a decrease in the flow stress apparently. It is therefore recommended that the formation of the flat cavities should be taken into consideration for an accurate evaluation of the flow stress in SPD at high strain-rate deformations.

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Influence of Flat Cavity Formation on Stress vs. Strain and Strain-Rate Relations of Superplastic Deformation in 3Y-TZP

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First-Principles Calculations of the Specific Heats of Cubic Carbides and Nitrides

Satoshi Iikubo, Hiroshi Ohtani, Mitsuhiro Hasebe

pp. 574-577

DOI:

10.2320/matertrans.MBW200913

Abstract

Calculated specific heats of several carbides and nitrides with a B1 structure have been compared with those of experimental data up to 3000 K. The specific heats at constant pressure are calculated with the quasiharmonic approximation, using phonon dispersions calculated from direct method, and pseudopotential plane-wave method. The calculated results of HfC, TaC, TiC, ZrC, and ZrN are in excellent agreement with the experimental data up to 3000 K. For NbC, TiN, and VC, the calculated results are also in excellent agreement with the experimental data up to 2000 K, while they show an excessive rise over the experimental data above 2000 K. The deviation of the calculation from the experiment at high temperature is caused by instability of the B1 structure or anharmonic effect.

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First-Principles Calculations of the Specific Heats of Cubic Carbides and Nitrides

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Densification of TiO2 Nanopowders by Magnetic Pulsed Compaction

H. S. Kim, J. G. Lee, C. K. Rhee, U. H. Joo, S. J. Hong

pp. 578-581

DOI:

10.2320/matertrans.M2009324

Abstract

In this study, sintered bodies of TiO2 nanopowders were fabricated by the combined application of magnetic pulsed compaction (MPC) and subsequent sintering and then, their density and shrinkage were investigated. The optimum mixing conditions of polyvinyl alcohol, water, and TiO2 nanopowder for compaction were found to be 2–3 mass% PVA, 15–20 mass% water, and 70–85 mass% of TiO2 powder in the sintered bulks. High pressure and rapid compaction using magnetic pulsed compaction (MPC) enhanced the density with the increasing MPC pressure up to 0.7 GPa and significantly reduced the shrinkage rate (about 15% in this case) of the sintered bulks compared to the general process (about 18%).

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Densification of TiO2 Nanopowders by Magnetic Pulsed Compaction

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