All issues
Volume 64, Issue 8
Displaying 1-15 of 15 articles from this issue
- |<
- <
- 1
- >
- >|
-
Kenichi Nakajima, Hiromitsu Ino, Kohmei Halada2000 Volume 64 Issue 8 Pages 591-596
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSLCA (Life cycle assessment) is a tool to evaluate quantitatively the resource consumption, the environmental loads and impacts of a product throughout its life cycle. The purpose of the present work is to establish how to evaluate the effect of recycling of materials and how to predict the environmental loads of new materials by a prospective application of LCA. Beverage cans were chosen as an evaluating object for LCA in which the recycling rate of a material of a steel or aluminum can was changed. A fictitious process for a stainless steel can was also analyzed in order to search the feasibility of the new material for a beverage can. In the absence of recycling, the energy consumption and the CO2, SOx, NOx emissions for the aluminum can are much higher than those for the steel product. The recycling of materials changes the situation, because the environmental loads for the aluminum can are reduced much higher than those for the steel can. As for the stainless can, it was shown that the environmental loads for the system are comparable to the conventional beverage cans when the can is decreased in thickness and fully recycled. In conclusion, it is emphasized that the decrease in environmental loads can be achieved by the combination of the selection of recyclable materials and the development of production technology.View full abstractDownload PDF (584K) -
Tomoyuki Nishida, Hidekazu Sueyoshi2000 Volume 64 Issue 8 Pages 597-603
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSGraphite was bonded to Ni under a compressive stress range from 3 to 33 MPa in a vacuum over a temperature range from 973 to 1273 K using a RF-induction furnace. The influence of joining conditions on the bending strength of the graphite/Ni joint, and changes of microstructure and hardness near the joining interface of Ni, were investigated. Thermal stress induced in the joint was estimated with a finite element method. On the basis of these results the influence of thermal stress on the bending strength of the joint as examined.
Completion of the graphite/Ni joint depends on both the compressive stress and the joining temperature. Good solid state bonding becomes feasible under low compressive stress in case of higher joining temperatures. Axisymmetric thermoelastic finite element analysis suggests that maximum tensile thermal stress is induced at a distance of 0.64 mm from the joining interface on the surface of the graphite and is increased with increasing joining temperatures. The position of fracture in a bending test corresponds approximately to that of the maximum tensile thermal stress. A part of the thermal stress in practical joints is relaxed and less than that calculated by finite element method. The bending strength of the joint increases with decreasing residual tensile stress on the surface of graphite. Relaxation of maximum tensile thermal stress depends on the amount of carbon atoms which diffuse into Ni. This may be related to the changes in plasticity of Ni and graphite, that is, the changes in the amounts of C super-saturately dissolved in Ni and the point defects introduces in graphite.View full abstractDownload PDF (1308K) -
Kimitsugu Soki, Hisami Yumoto, Kazuo Akashi, Shigeru Ito, Tsutomu Seki ...2000 Volume 64 Issue 8 Pages 604-608
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSIn the case of H2 production via steam reforming of CH4, it is necessary to prepare a hydrogen-permselective membrane without pin-holes and cracks. The formation of metal hydride causes cracks in the membrane, resulting in hydrogen embrittlement. Hydrogen embrittlement was prevented by alloying the membrane with a metal such as Mo which does not form a hydride. Moreover, high H2 permeation is expected by the alloying. In general, a hydrogen permeable metal has a high melting point. As the alloying of high melting point metals is difficult, there have been few papers on an alloy membrane of high melting point.
In this study, a Nb hydrogen-permselective membrane was alloyed with Mo at 1.3 Pa of Ar gas pressure by Physical Vapor Deposition (PVD) method such as arc-ion plating (AIP). Two targets of Nb and Mo were used. Vegard’s law was observed in the Nb-Mo alloys.
After the cyclic H2 absorption/desorption test in 1×105 Pa H2, the formation of Nb hydride was confirmed in the Nb membrane, but metal hydride was not observed in the Nb-Mo alloy membrane. It was estimated from the lattice strain that the Nb-10 at%Mo alloy showed the highest H2 permeation.View full abstractDownload PDF (833K) -
Keiichiro Oh-ishi, Hideki Kumamoto, Zenji Horita, Minoru Nemoto2000 Volume 64 Issue 8 Pages 609-615
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSHardness and microstructural variations during aging of Ti-Al-Cr ternary L10- and L12-phase alloys have been investigated in terms of hardness measurements and transmission electron microscopy. Both the L10 and L12 phase alloys harden by aging at 973 K after solution annealing at higher temperatures. The amount of age hardening of the L12 phase alloy is larger than that of the L10 phase alloy. The phase separation between L10 and L12 phase have not been observed by aging at 973 K. But Al2Ti was formed in each matrix alloy during aging. The crystal structure of the Al2Ti phase is a Ga2Zr type in the L10 and a Ga2Hf type in the L12 phase, respectively. At the beginning of aging the fine coherent cuboidal Al2Ti-phase are formed in the L10 phase. By further aging, two variants of Al2Ti precipitates grow along the two {110} habit planes. On the other hand, in the L12 phase, the Al2Ti phase forms on the {100} planes of the L12 matrix lattice. After prolonged aging the precipitates are rearranged along a preferential direction of the matrix lattice and form a domain consisting of only one variant. It is suggested that the precipitation of Al2Ti in each matrix alloy occurs to form a morphology which efficiently relaxes the elastic strain between precipitate and matrix lattices.View full abstractDownload PDF (905K) -
Rongguang Wang, Masahiko Kato, Keijiro Nakasa2000 Volume 64 Issue 8 Pages 616-624
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSCommercially supplied pure titanium was N2+ ion implanted at 1.5 MeV with different doses ranging from 0.5×1021 to 2×1021 ions per m2 and with an implantation current density of 0.050 or 0.075 A/m2. The morphology of the implanted surface and the deformation properties of the layer before and after aging were examined using an atomic force microscope, an X-ray diffraction apparatus and an ultra-micro hardness tester. When the implantation current density was 0.050 A/m2 and the implantation dose was larger than 1×1021 ions per m2, titanium nitrides precipitated and grew along certain crystal planes, whereas when the implantation current density was 0.075 A/m2 the titanium nitrides were uniformly precipitated below the surface. By aging at 473 K, the growth and combination of the nitrides as well as new precipitation of nitrides occurred. The arithmetic mean roughness Ra of the implanted surface increased with increasing implantation dose and decreased with increasing aging time. The deformation resistance of the surface layer measured by means of the ultra-micro hardness tester increased as a result of ion implantation and aging at an early indentation stage of 0.2∼0.4 μm, which also suggested the precipitation of nitrides just below the surface.View full abstractDownload PDF (1609K) -
Guofeng Zhang, Masao Morishita, Koichiro Koyama2000 Volume 64 Issue 8 Pages 625-631
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe effect of addition of Cr on the corrosion resistance of a Ni-NiMo2B2 two-phase alloy in 6%HNO3 aqueous solution was examined by measuring the mass loss, the corrosion potential and the anode polarization curve, and also by metallography. When the content of Cr in the alloy was 15 mass%, Cr was distributed evenly to the both phases of the Ni matrix and boride NiMo2B2, and consequently the chemical composition of Ni matrix became Ni-15 mass%Mo-15 mass%Cr while the boride phase changed from the orthorhombic boride NiMo2B2 to the tetragonal boride (Ni, Mo, Cr)3B2. The corrosion resistance of the Cr-containing Ni-(Ni, Mo, Cr)3B2 two-phase alloy in the 6%HNO3 aquoeus solution was about 10 times superior to the Ni-(Ni, Mo, Cr)3B2 two-phase alloy which does not contain chromium. The corrosion of the Cr-free Ni-NiMo2B2 two-phase alloy proceeded by a mechanism in which the Ni matrix worked as the anode while the boride NiMo2B2 phase worked as the cathode. On the other hand, in the Cr-containing Ni-(Ni, Mo, Cr)3B2 two-phase alloy, the Ni matrix became passivated, and as a result, its corrosion potential became more noble than that of the boride (Ni, Mo, Cr)3B2. Consequently, the corrosion of the Ni-(Ni, Mo, Cr)3B2 two-phase alloy proceeded through the preferential corrosion of the boride (Ni, Mo, Cr)3B2. Furthermore, the corrosion current density of the boride (Ni, Mo, Cr)3B2 was found to be as small as about 0.2 A· m−2 from the polarization curve. Also, the difference in the corrosion potential between the Cr-containing Ni matrix and (Ni, Mo, Cr)3B2 was 60 mV smaller than that between the Ni matrix and NiMo2B2 in the Ni-NiMo2B2 two-phase alloy. Therefore, the driving force for the local cell corrosion of the Cr-containing alloy was reduced by the addition of Cr. That is to say, the lower corrosion current density of the boride (Ni, Mo, Cr)3B2 and the smaller corrosion potential difference improved remarkably the corrosion resistance of the Ni-(Ni, Mo, Cr)3B2 two-phase alloy.View full abstractDownload PDF (1179K) -
Masanori Seki, Hiroki Yamamoto, Makoto Nojiri, Keisuke Uenishi, Kojiro ...2000 Volume 64 Issue 8 Pages 632-640
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSTi-Ni shape memory alloy (NT-L) was brazed to SUS304 by using BAg-8, BAg-8+0.5%Ni and BAg-8+3.0%Ni filler metals. The joint strength and reaction layer formation were investigated.
In the case of BAg-8, Fe and Cr from SUS304 diffused to NT-L, and Ti from NT-L diffused to SUS304, which caused the formation of (Fe, Ni)2Ti and (Fe, Ni)Ti reaction layers at the bondline. This layer was not formed at the bondline of the similar material joints. Obvious reaction layer was not formed at relatively low brazing temperature. In such conditions, the joint strength was increased with higher brazing temperature or longer holding time. Once the Fe-Ti based reaction layers were formed, joint strength reached to maximum about 275 MPa that was less than 50% of based metal strength, and was not affected by brazing condition. Fracture occurred around reaction layers consisted of Fe-Ti intermetallic compounds.
In the case of Ni added BAg-8 filler, diffusion of Ti and Fe was surppressed, resulting in no Fe-Ti intermetalliic compounds formation at the bondline. In the NT-L side, Ni in filler metal diffused to NT-L/filler interface to form Ni3Ti layer. In the SUS304 side, fcc solid solution was formed, and any intermetallic compounds were not formed. Fracture occurred along the boundary between Ni3Ti layer and NiTi base metal. Due to the absence of brittle Fe-Ti based compound layers, joint strength increased to about 400 MPaView full abstractDownload PDF (1147K) -
Hidemichi Fujiwara, Tatsuo Sato, Akihiko Kamio2000 Volume 64 Issue 8 Pages 641-650
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSDuring cold rolling and annealing process in precipitating hardened copper alloys, the changes in microstructure, which decide the electrical or mechanical properties, were mainly brought about by the recrystallization of the matrix and the formation of precipitates in the matrix. To design the optimum process condition, it is necessary to analyze the characteristics of the change in microstructure and properties systematically in various copper alloy systems. The changes in microstructure and properties in Cu-Fe, Cu-Cr and Cu-Ni-Si system alloys were observed experimentally during cold rolling and annealing treatments after solution or pre-aging treatments. The hardenability by the precipitation became larger in order of increasing misfit energy, Cu-Fe, Cu-Cr, Cu-Ni-Si system alloy. The suppression effect of recrystallization is dominant in the condition of the pre-aging at 773 K in Cu-Cr alloy, and at 973 K in Cu-Fe and Cu-Ni-Si alloys. During the recrystallized grain boundary migration, the effect of interface structure changes between the precipitate and matrix was analyzed, based on the boundary pinning theory proposed by Ashby. It seems that misfit energy change in Cu-Ni-Si alloy, and the chemical energy change by interface structural change of precipitates in Cu-Fe, reduced the boundary pinning energies that affect the rate of recrystallization.View full abstractDownload PDF (1496K) -
Takahisa Ohtsuji, Tomohiro Akiyama, Jun-ichiro Yagi2000 Volume 64 Issue 8 Pages 651-655
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSMagnesium-based alloys, Mg-Fe and Mg-Co, in particular, are very attractive as covalent or ionic hydrides for their large hydrogen storage capacity; 5.5 and 4.5 mass%, respectively. In a previous study, we produced pure Mg-X(X=Fe, Co) hydride successfully by combustion synthesis for the first time. However, in order to establish an industrial process, elucidation of the reaction mechanism for synthesizing the hydrides are needed. The aim of this study is to investigate the intermediate products during the combustion synthesis by using differential scanning calorimeter and X-ray diffraction analysis.
Magnesium and iron or cobalt powders that are well mixed, and then compressed, are slowly heated up to 850 K. These are cooled down to room temperature under hydrogen pressure of 7.0 MPa. The heat of reaction is monitored by DSC and intermediate products at the specified temperature are identified by XRD.
As a result, magnesium absorbs hydrogen partially in the initial stage of heating, and then releasing it with the increase in temperature. This is common phenomenon for both systems. At high temperatures, Mg-Co and Mg-Fe systems showed different behavior. In the Mg-Co system, Mg3CoH5 and Mg2CoH5 are produced, dehydrided and reproduced, while no hydrogen absorption was found in the Mg-Fe system.
It is supposed that the hydrides were synthesized directly from the mixture of metallic powders because no intermetallic compound was observed in both systems. Mg2FeH6, Mg3CoH5 and Mg2CoH5 were finally obtained by heating up and cooling down in hydrogen atmosphere. These results revealed the reaction mechanism for synthesizing Mg-X(X=Fe, Co) hydrogen storage alloy.View full abstractDownload PDF (419K) -
Takahisa Ohtsuji, Tomohiro Akiyama, Jun-ichiro Yagi2000 Volume 64 Issue 8 Pages 656-661
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSMetallic hydrides of Mg-Fe and Mg-Co systems are quite attractive as a hydrogen storage alloy for their large storage capacity; 5.5 mass% in Mg2FeH6 and 4.5 mass% in Mg2CoH5. However, the production of Mg2Fe and Mg2Co alloys before hydriding has been difficult due to their unstable phases.
The purpose of this study is to directly produce the metallic hydrides of Mg-Fe and Mg-Co using the hydriding combustion synthesis. With this method, the pre-production process of intermetallic compounds can be eliminated. Well-mixed and compressed metallic powders are heated in hydrogen atmosphere and then the chemical compositions of the products are identified by X-ray diffraction analysis.
As a result, pure metallic hydrides are successfully obtained by controlling hydrogen pressure, heating and compressing conditions. These results also give a possibility for an innovative production process of Mg2FeH6 and Mg2CoH5.View full abstractDownload PDF (711K) -
Toshio Oishi, Atsushi Hirata, Hitoshi Ishida, Katsutoshi Ono2000 Volume 64 Issue 8 Pages 662-668
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSAs a fundamental study to prepare copper based Cu-Cr and Cu-Zr alloys without any inclusions, the solubilities of chromium and zirconium in liquid copper in equilibrium with C-Cr3C2, Cr3C2-Cr7C3 or C-ZrC were determined, respectively.
Cu-Cr alloys containing higher Cr concentrations than those expected from the present preparatory experiments were melted in a graphite crucible in an argon atmosphere at temperatures 1573-1873 K. The excess Cr reacted with carbon to form Cr3C2 and solubilities of Cr in the liquid copper in equilibrium with C-Cr3C2 were determined;
(This article is not displayable. Please see full text pdf.)
The solubilities of Cr in the liquid copper under coexistence with Cr3C2 and Cr7C3 were also determined using alloys containing higher or lower Cr concentrations than those expected from the preparatory experiments. The alloys were melted in BN crucibles with Cr3C2 or Cr7C3 in an argon atmosphere at temperatures 1523-1673 K. The solubilities of Cr in liquid copper in equilibrium with Cr3C2-Cr7C3 are given by
(This article is not displayable. Please see full text pdf.)
Cu-Zr alloys containing 30∼780 mass ppm Zr were melted in a graphite crucible with ZrC in an argon atmosphere at temperatures 1623-1823 K. The solibilities of Zr in liquid copper in equilibrium with C-ZrC are expressed as
(This article is not displayable. Please see full text pdf.)
Carbon and oxygen solubilities of both Cu-Cr and Cu-Zr alloys were also obtained and discussed.View full abstractDownload PDF (593K) -
Kenichi Takai, Akira Nozue2000 Volume 64 Issue 8 Pages 669-676
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSHydrogen occlusion behavior of eutectoid steel fabricated by isothermal transformation treatment and cold-drawing treatment has been evaluated by thermal desorption analysis (TDA). Specimens containing different shape cementite were produced under various isothermal transformation temperatures and also under cold-drawing at 85%. The amount of hydrogen occluded in the specimens dipped in 20 mass%NH4SCN solution was measured by using TDA. TDA analysis showed that the hydrogen evolution rate of the isothermally transformed specimens has only one peak, while that of the cold-drawn specimens has two peaks. The cementite shapes can change the hydrogen occlusion behavior in the specimens. The cold-drawn specimens containing longer cementite increase hydrogen released at higher temperature. This hydrogen does not cause delayed fracture. From transmission electron microscopy and TDA, it was suggested the higher temperature peak corresponds to hydrogen released from trapping sites such as interfacial dislocations between ferrite and cementite, and/or the cementite polycrystal interface formed by cold-drawing.View full abstractDownload PDF (1539K) -
Manabu Matsubara, Toshihiko Iwasaki, Shuji Hanada2000 Volume 64 Issue 8 Pages 677-683
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSIn order to increase the adhesive strength between Al2O3 coating and Nb-Al substrate and to relax the thermal stress in the coating, functionally graded material (FGM) coatings were synthesized by low pressure plasma spraying. Using Nb-Al alloy powder prepared by a hydriding and dehydriding process, plasma spraying conditions were optimized. Vickers hardness test and thermal shock test by laser irradiation were performed to characterize the FGM coatings.
Although the powder prepared by the hydriding and dehydriding process has a flaky shape with a wide variety of sizes, continuous powder supply to a plasma torch is achieved using sieved powder having sizes of 37 to 74 μm. The optimized conditions for plasma spraying are as follows; the preheating temperature of Nb-Al alloy substrate is 773 K, the chamber pressure is 6.7×103 Pa in Ar, and the spraying distance is 150 mm. It is found that the volume fraction of Al2O3 in the sprayed coating is about 1/5 as much as that of Nb-Al when the same amount of Al2O3 and Nb-Al powders are injected in the plasma torch. By controlling the amount of supplied powders under the optimized spraying conditions, Al2O3/Nb-Al FGM coatings are successfully synthesized. Vickers hardness test indicates that no crack is introduced at an interface between substrate and coating, and also between Nb-Al and Al2O3 in the coating. Thermal shock test by laser irradiation shows that no spalling occurs at an interface between substrate and coating when 100%Nb-Al is sprayed for undercoating on the substrate. Moreover, it is demonstrated that Nb-Al layer in the FGM coating is resistant to a crack propagation.View full abstractDownload PDF (2783K) -
Young Jo Park, Manabu Enoki, Tadatomo Suga, Teruo Kishi2000 Volume 64 Issue 8 Pages 684-690
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe generation of interfacial defects is an unavoidable problem in the room temperature bonding. For an application of this technology, it is important to elucidate the effect of interfacial defects on fracture behavior. Fracture mechanism and criterion were investigated using the Al/Sapphire joint known for easy control of bondability. The findings of this paper are summarized as follows. (1) Bondability at peripheral region appeared to be superior to that of central region, which was caused by higher compressive stress during the bonding. (2) The results showed clearly that the growth of interfacial defects is the dominant factor for the crack propagation and the location of fracture origin showed good agreement with the prediction made by the observation of as-bonded interface and by the calculation of stress field using FEM simulation. (3) A critical stress intensity factor for the growth of interfacial defect was also estimated by the analysis of FEM calculation and experimental observation.View full abstractDownload PDF (2448K) -
Young Jo Park, Manabu Enoki, Tadatomo Suga, Teruo Kishi2000 Volume 64 Issue 8 Pages 691-697
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSSurface activated room temperature bonding (SAB) has been proposed as a new process which can overcome many problems caused by traditional high temperature bonding. For an application of this technology, it is expected to elucidate mechanical properties and fracture behavior under the environment where it is supposed to be used. In this study, tensile tests were conducted for a Al/Sapphire joint cyclic heat treated to 400°C. That brought about increase of bonding strength, which provides SAB process with good outlook for application. We pursued an analysis including residual stress by combination of FEM calculation and experimental observations. The findings of this research are summarized as follows. Softening of bulk Al due to heat treatment increased the bonding strength by decreasing stress concentration, but the ultimate tensile strength of the joint remained constant. Specimens held at high temperature for a long time showed shrinkage of interfacial defects, which resulted in the increase of bonding strength. On the other hand, it became clear that relaxation of residual stress as well as bulk softening is a contributing factor for the increase in bonding strength for the specimens held at high temperature for a short time.View full abstractDownload PDF (2327K)
- |<
- <
- 1
- >
- >|