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Volume 44, Issue 10
Displaying 1-13 of 13 articles from this issue
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Koichi Niihara, Atsushi Nakahira, Tohru Sekino, Yong-Ho Choa1997 Volume 44 Issue 10 Pages 887-896
Published: October 15, 1997
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSCeramic based nanocomposites can be divided into three categories: intragranular nanocomposite, intergranular nanocomposite and nano/nano composite. The intra- and intergranular nanocomposites, in which nano-sized particulates were dispersed within the matrix grains or at the grain boundaries respectively, were found to show the two to five times higher strength at room temperature than those of monolithic materials. The hardness, fracture toughness and fracture resistance for creep and fatigue at high temperatures as well as the thermal shock fracture resistance were also improved significantly in these nanocomposites. On the other hand, the new functions such as machinability and superplasticity were observed for the nano/nano composites. In this paper, the fabrication processes of these nanocomposites by sintering method, micro and nanostructure observation, improvements of mechanical properties were reviewed and the roles of the nano-sized dispersions were discussed. Finally, the new material design concept for multi-functional structural ceramics was given.View full abstractDownload PDF (9860K) -
Shuji Yazu1997 Volume 44 Issue 10 Pages 897-904
Published: October 15, 1997
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSThe development of new PcBN, PCD tool materials and the high pressure-high temperature technology of growing large diamond crystals are briefly reviewed. The topics covered are cBN-TiN based sintered material for cutting hardened steel, very fine grained sintered diamond material for fine cutting or fine wire drawing applications, the diamond growth process and conditions to grow large impurity-free crystals at a high growth rate using large seed crystals.View full abstractDownload PDF (3660K) -
Toshihiko Shigematsu1997 Volume 44 Issue 10 Pages 905-911
Published: October 15, 1997
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSThe author shows two examples of phase transformation in some oxide ceramics, which is caused by the reaction of oxide ceramics and a vapor phase. The first example is a tetragonal-to-monoclinic transformation in ZrO2-Y2O3 ceramics which takes place isothermally during low temperature aging in air, accompanying an weight increase. An absorption band at 3340 cm-1 appears in FT-IR DRIFT spectrum in association with the appearance of monoclinic phase in ZrO2-Y2O3 ceramics. The reaction between ZrO2-Y2O3 ceramics and H2O in air, and the diffusion of OH- ions in the powders must be essential for this phase transformation to take place. The second case is an oxidation and reduction of powdered ceramic superconductor YBa2Cu3Oy In the case of isothermal reduction using orthorhombic powders, the reduction is controlled by the removing rate of oxygen from the particle surface. On the other hand, in a case of isothermal oxidation of tetragonal powders, the orthorhombic phase exists as a skin surrounding the unreacted core of the tetragonal phase. The oxidation is recognized to be controlled by the moving rate of the interface between the tetragonal and orthorhombic phases.View full abstractDownload PDF (436K) -
Uichiro Mizutani1997 Volume 44 Issue 10 Pages 912-920
Published: October 15, 1997
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSAn amorphous alloy is defined as a solid with the lack of a long-range atomic order. The failure of the Bloch theorem is immediately deduced from this definition and can explain the possession of high electrical resistivities in amorphous alloys. However, studies of the local atomic structure of amorphous alloys have been extensively carried out since early 1980's and have led to the conclusion that certain short range order always develops in amorphous alloys. As its natural consequence, attention has been directed to its effect on various physical properties in the last decade. The discovery of quasicrystals in 1984 has certainly stimulated the research along this line, since quasicrystals are characterized by the absence of the translational symmetry but with the well-developed atomic order. In the present article, we demonstrate clearly how the short-range atomic structure affects the electron transport properties by analyzing the data associated with the metal-insulator transition for amorphous V-Si alloys. A unified picture for the electron transport mechanism for metallic solids, which include amorphous alloys, quasicrystals, approximants and crystals, is proposed.View full abstractDownload PDF (595K) -
Yoshihito Kawamura1997 Volume 44 Issue 10 Pages 921-929
Published: October 15, 1997
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSThe closed powder metallurgy processing system for the production and consolidation of rapidly soldified powders has been developed in Institute for Materials Research, Tohoku University. The sequent steps can be carried out in a vacuum or argon gas atmosphere containing oxygen and moisture of 0.5 ppm without exposing the powder to air, The superiorities of the closed process were: 1) improvement of the strength and ductility of compacts, 2) reduction of the working degree of consolidation and enlargement of the dimensions of compacts, 3) abbreviation of the degassing process or lowering of the degassing temperature, 4) reduction of the thermal history, 5) widening of the consolidation conditions, 6) safety production and consolidation of reactive powders. The synthesize of nanocrystalline aluminum alloys by crystallization of amorphous phase was exemplified as developments of advanced materials using the closed P/M processing system. The nanocrystalline Al-Ni-Ln-(Co, Ti, Zr) (Ln: lantanide metal) alloys had high strength at room and elevated temperatures, high Young's modulus, high wear resistance, low thermal expansion etc.View full abstractDownload PDF (4450K) -
Hideaki Tsuru, Takeo Nakagawa, Yoshiharu Inaba1997 Volume 44 Issue 10 Pages 930-935
Published: October 15, 1997
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSPowder metallurgy (P/M) is a unique process suitable for a mass-production of near-net-shaped products and for a special alloy composition a conventional molten process can't prepare. In order to utilize these advantages for P/M products, it is important to manufacture a green part highly accurate, uniform in density and completely defect-free. Although hydraulic and mechanical presses have been used for a powder compaction so far, in recent years an expanding area of application for a P/M part has raised a need for a novel powder compacting press which brings a break-through towards a complicated P/M product with high quality. Due to the structural limitation in tool motion and control, a conventional press has a difficulty to solve many of technological problems such as green density distribution and cracking. Since 1987, by applying the high-output servo motor and CNC (Computerized Numerical Control) technology, authors have developed a fully motor-driven powder compacting press, and a variety of experiments and analyses on powder compacting process have been carried out. The study has revealed that a CNC powder compacting press brings an important clue for P/M products with high quality, by indicating the pressing process, the compacting phenomena and a property of a green part in a quantitative manner.View full abstractDownload PDF (5613K) -
Shouichi Ochiai1997 Volume 44 Issue 10 Pages 939-944
Published: October 15, 1997
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSThe Ni3Al intermetallic alloys with the composition of Ni-25mol%Al were produced by powder metallurgical method using elemental powders of nickel and aluminum. After blending starting powders, sintering was performed by hot press process. Some sintered alloys were heat treated for homogenization. Influence of the microstructural change caused by the heat treatment on the mechanical properties for compacts was investigated. Although the mean grain diameter of as-sintered alloys was about 32μm, finer microstructures with the diameter of less than 7μm were achieved by homogenization heat treatment, Alloys were found to be composed of single Ni3Al phase and the degree of long range order increased with homogenization time. As-hot pressed alloy revealed the flow stress at room temperature of about 300MPa, whereas the homogenized alloy showed that of about 700MPa. Flow stress was analyzed by decomposing it to σG, σH and σp, which were the stress components concerning Peierls force, positive temperature dependence of flow stress, and grain diameter respectively. The Hall Petch parameter, ky, was about 1.3 at room temperature and had the tendency to decrease with temperature.View full abstractDownload PDF (2414K) -
Takekazu Nagae, Masaru Yokota, Masateru Nose1997 Volume 44 Issue 10 Pages 945-950
Published: October 15, 1997
Released on J-STAGE: December 04, 2009
JOURNAL FREE ACCESSSpark plasma sintering (SPS) method has been applied for the consolidation and sintering of argon gas atomized powder of Al-25mass%Si-3.5%Fe-3.5%Ni-1%Mg alloy. Through this experiments, firstly, we investigated the sintering process of SPS method for Al alloy powder by means of optical microscopy, scanning electron microscopy and X-ray diffraction. Secondly, we investigated the mechanical properties of near-net-shape formed AI alloy powder by SPS method. Results obtained were as follows:
(1) At the sintering process of SPS, the sample temperature rose faster and it was kept 10 K higher than the temperature of die. After shut off the electric power, sample temperature goes down faster than that of die.
(2) At the very early step of SPS process, each particle of Al alloy gather to dense by slipping and deformation. When sample temperature is up to 650-660 K, necking of particles is formed.
(3) Tensile strength of SPSed compacts is 235 N/mm2, however, this value is increased up to 285 N/mm2 by heat treatment.View full abstractDownload PDF (3457K) -
Magnetic Properties of Nd-Fe-B Magnets Sintered Using Granulated Powders by Spray Drying Method (IV)Yoshihisa Kishimoto, Osamu Yamashita1997 Volume 44 Issue 10 Pages 951-957
Published: October 15, 1997
Released on J-STAGE: December 04, 2009
JOURNAL FREE ACCESSNd-Fe-B alloy powder was granulated by a spray drying method using organic binder consisted of polyvinylalcohol or cellulose ethers, in order to improve the powder flowability during feeding and compacting. The compressing behavior of Nd-Fe-B granulated powders was investigated. In the case of granulated powders, the relation between compressing stress and powder bulk density was expressed by two straight lines containing one bending point, and the compressing stress on this point was defined as the average destruction strength(ADS). The ADS was closely related with the tensile strength of organic binder. By means of controlling the tensile strength of binder by changing its composition or polymer/plasticizer ratio, the ADS could be designed easily. In the case that the ADS was less than about 0.1N/mm2, the powder flowability of granulated powder was improved with increasing the ADS, whereas in the case of more than about 0.1N/mm2, it showed almost constant value. The magnetic characteristics (remanences and maximum energy product) of sintered magnets using granulated powders were improved proportionally with decreasing the ADS, which was independent of any kinds of polymers and binder composition. These facts mean that the degree of the magnetic orientation of primary particles in granulated powders under a magnetic field can be determined simply by the ADS.View full abstractDownload PDF (2582K) -
Yasuki Miyakoshi, Kohji Takazawa, Kohsuke Tagashira, Shuichi Kamota, H ...1997 Volume 44 Issue 10 Pages 958-962
Published: October 15, 1997
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSNew bonding method of cemented carbide tip and carbon steel with WC-(20-60mass%)Co alloy powder as thermal stress relaxation layer was proposed by authors. These joints were frequently fractured near the interface between sintered WC-Co alloy and steel. In this study, microstructure and strength of sintered bonding area between WC-40mass%Co alloy powder and 0.23-0.96mass%aC steels have been investigated. It is recognized that the reaction layer including tl phase of Co3W3C and Fe3W3C particles are formed inside the sintered WC-40mass%Co alloy near the interface. The thickness of reaction layer decreased with the increase in carbon content of steels and is zero for carbon content of 0.55mass% or more. Four-point bending strength, which is increased with the increase in C content of steels, is approximately 1.3GPa for 0.96mass%C. The strength is strongly affected by the existence of η phase.View full abstractDownload PDF (4930K) -
Chihiro Kawai, Takashi Matsuura, Jin-Joo Park, Masashi Yoshimura, Akir ...1997 Volume 44 Issue 10 Pages 963-969
Published: October 15, 1997
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSAmorphous Si3N4/TiO2 compacted bodies were heated at 1490°C, for 1 to 10 hr under N2 pressures of 0.92 and 1000 atm, and the effect of N2 pressure on the resulting grain refining was investigated, to clarify the role of TiO2 in the grain-refined mechanism. Thermodynamic calculation performed prior to experiments indicated that high N2 pressure inhibited the formation of SiO gas and new formation of Si3N4 by its re-nitridation. Crystallized phases after heating were α-Si3N4, Si2N2O and TiN. Although both N2 pressures formed the fine grains having a diameter of about 30 nm, high pressure accelerated the grain refining and crystallization of amorphous Si3N4 to a-Si3N4. From these results, the fine grains were considered to be formed not through re-nitridation of SiO gas but through crystallization of amorphous Si3N4.View full abstractDownload PDF (4796K) -
Takehisa Ohno1997 Volume 44 Issue 10 Pages 970-973
Published: October 15, 1997
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSCu-C60 composite nanoparticles were prepared by the condensation of C60 vapor onto flying Cu nanoparticles which were produced in advance by a gas-evaporation technique. The structural and morphological observation of these nanoparticles was carried out by means of a transmission electron microscope. It was found that the particle is composed of a Cu sphere with C60 crystallites sticking to a part of the sphere. The morphology means that not C60 vapor but C60 clusters condense onto Cu nanoparticles and the wetting between the Cu nanoparticles and C60 clusters is poor.View full abstractDownload PDF (2919K) -
Hisakazu Tomino, Hiroshi Watanabe, Yoshihito Kondo1997 Volume 44 Issue 10 Pages 974-979
Published: October 15, 1997
Released on J-STAGE: December 04, 2009
JOURNAL FREE ACCESSIn spark sintering copper powder and alumina one with a graphite and insulated dies under a constant pressure and a constant electric current, electric voltage between electrodes and temperature distributions of die, punch and specimen were measured. And, we considered effect of the electric current paths on the spark sintering.
In the first case of sintering the copper powder with the graphite die, during initial electricity, almost all the electric current went through the specimen. During sequential electricity, the electric current went through both the graphite die and the specimen. Therefore, fluctuation of temperature distribution in the specimen was decreased as the discharged time was spent.
In the second case of sintering the copper powder with the insulated die, the electric current went through the graphite punch and the specimen. The fluctuation of temperature distribution in the specimen was larger than that of the case which the graphite die was used, for the specimen was not heated by the graphite die.
In the third case of sintering of alumina powder with the graphite die, the electric current went through the graphite punch and the graphite die. Therefore, the temperature distribution of both the graphite mold and the specimen was considerably different from that of the case of the copper powder with the graphite die.View full abstractDownload PDF (412K)
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