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Volume 64, Issue 9
Displaying 1-27 of 27 articles from this issue
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Toshiyasu Nishimura, Akira Tahara, Toshiaki Kodama2000 Volume 64 Issue 9 Pages 699-702
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSRust formed on a 2.0 mass%Si-bearing steel was analyzed by EPMA, XPS and TEM after a wet/dry corrosion test using chloride solution. Si-enriched layer was found in the lower part of the rust on the Si-bearing steel, and Si was identified as being in an intermediate-oxide state, different to SiO2, by analyses of Si Kα and Kβ EPMA spectra, 2s and 2p XPS spectra. An Fe-Si binary potential-pH diagram shows that the formation of Fe2SiO4 is expected in the lower part of the rust. TEM observations confirm that Si is present in Fe3O4 in the Si2+ state, and thermodynamic calculation corresponds to the results obtained by EPMA and XPS.View full abstractDownload PDF (320K) -
Terukazu Honda, Masato Yamashita, Noriyuki Furuichi, Hitoshi Uchida2000 Volume 64 Issue 9 Pages 703-706
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe susceptibility of cold drawn pure copper to stress corrosion cracking (SCC) in an acetic acid solution depending on cold reduction and strain rate has been studied using the slow strain rate technique. The main crack of SCC propagated after the stress reached the maximum value. The higher reduction sample had a lower SCC susceptibility at the same strain rate. The lower strain rate led to a higher SCC susceptibility. These dependence of the SCC susceptibility, both on the cold reduction and on the strain rate, can be attributed to the growth behavior of the surface oxide film.View full abstractDownload PDF (393K) -
Akinori Sato, Masakatsu Hinai2000 Volume 64 Issue 9 Pages 707-710
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe damping capacity and magnetoelastic properties were investigated for 64 mass%Co-Fe and 68 mass%Co-Fe alloys. The alloys were heat-treated for 7.2 ks at 1123 K, and then cooled with and without magnetic field of 16 kA/m. Measurements of the logarithmic decrement (δ) and ΔE effect (ΔE⁄E0) were carried out using a cantilever method, and the magnetic hysteresis loop was measured using a direct current BH tracer. The δ and ΔE⁄E0 of alloys heat-treated without a magnetic field showed low values; the magnetic hysteresis loop exihibited a “bulge” in the low magnetic field range and the coercive force (Hc) value was relatively large. The δ and ΔE⁄E0 values of alloys heat-treated in a magnetic field were considerably higher; the magnetic hysteresis loop had a “normal” shape and the Hc value was small. This indicates a close relationship between the damping capacity and magnetoelastic properties of the alloys.View full abstractDownload PDF (305K) -
Masahiko Katagiri, Hidehiro Onodera2000 Volume 64 Issue 9 Pages 711-714
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSHydrogen-Induced Amorphization (HIA) has been focussed as a hopeful method to control the microstructure. We have investigated the microscopic mechanism of HIA on AB2 C15 Laves phase compounds using a molecular dynamics (MD) method. In our previous paper, we reported the softening phenomena of bulk modulus by hydrogenation. We found two softening mechanisms. The first is due to the volume expansion, originating from the non-linearity of the interatomic potentials; this also appears in non-HIA materials. The second is due to the atomic relaxations of A and B atoms, and is characteristic of HIA materials. In HIA materials of C15 Laves phase compounds, A atoms (A=rare earth) contract and B atoms (B=Fe, Co, Ni) are expanded compared to the pure crystals. It realizes the second softening mechanism. In this study, we calculate the elastic constants at finite temperature directly from the MD results by fluctuation formula. We observed the third mechanism due to the pressure-tensor fluctuation in addition to two mechanisms described above. The third is characteristic of HIA materials as well as the second. It can be considered that the softening of the bulk modulus due to these mechanisms is an indication of the increase of the elastic instabilities by hydrogenation.View full abstractDownload PDF (326K) -
Eiichi Kondoh2000 Volume 64 Issue 9 Pages 715-718
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSCu-1 mass%Ti thin films stacked on PMDA-ODA polyimide are studied in terms of the adhesion strength and film (111) texture. The presence of Ti is found to greatly increase the film adhesion strength and the development of (111) texture. This tendency is much enhanced when the polyimide surface is treated with oxygen-containing plasma prior to metallization. The results are discussed from a point of view of surface and interface energy minimization during the nucleation stage.View full abstractDownload PDF (263K) -
Toru Izumi, Xin Yao, Natsuro Hobara, Kazuomi Kakimoto, Katsuya Hasegaw ...2000 Volume 64 Issue 9 Pages 719-722
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSWe tried to apply NiO as a buffer layer for LPE (Liquid Phase Epitaxy) coated conductors. We confirmed the suppression effect to the reaction between NiO/Ni substrate and solution saturated with NiO. On the other hand, NiO addition to the solution was found to decrease the peritectic temperature of YBa2Cu3Oy (Y123) and increase the crystallization temperature of Ba-Cu-Ni-O compound. These phenomena made it difficult to grow Y123 crystals alone from the NiO saturated solution. We tried to grow Nd123 that has a higher peritectic temperature than Y123 on the MgO substrate, and confirmed that Nd123 could be grown stably from the NiO saturated solution. Because of low Tc value of the Nd123 crystals grown from the NiO saturated solution, we had to grow Y123 on it from the solution without NiO. The sample with this double LPE layer showed a Tc value of 90 K.View full abstractDownload PDF (290K) -
Keizo Kobayashi, Akihiro Matsumoto, Toshiyuki Nishio, Kimihiro Ozaki, ...2000 Volume 64 Issue 9 Pages 723-726
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSTi-35 at%Fe-5 at%B-5 at%Si alloy synthesized by a cold crucible levitation melting furnace was mechanically ground (MG) for 360 ks by using a planetary ball mill. The obtained powder consisted of an amorphous phase and a crystalline one. The amount of the amorphous phase in the MG powder increased as increasing milling time. The crystallization temperature of Ti-35 at%Fe-5 at%B-5 at%Si powder milled for 360 ks was 673 K.
The MG powder after milling for 360 ks was packed into a stainless steel pipe and set up in the chamber of a pulsed current sintering (PCS) machine. Continuously, the powder was consolidated at 573 K with a high pressure application of 1568 MPa using PCS process, accompanied with deformation of the pipe. An obtained compact had a thickness of 1 mm and contained only about 6 vol% pores. An exothermic reaction was observed at nearly 673 K for the DSC trace of the compact, which indicated the amorphous phase remained in the compact.View full abstractDownload PDF (602K) -
Natsuro Hobara, Kazuomi Kakimoto, Yuichi Nakamura, Teruo Izumi, Yuh Sh ...2000 Volume 64 Issue 9 Pages 727-730
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe fabrication process of RE123 system superconducting tape on Hastelloy substrates was developed using the liquid phase epitaxy (LPE) process. To prevent reactions between metal substrates and the Ba3Cu5Ox solution, we selected an MgO buffer layer for the solution saturated with MgO. The Hastelloy substrate was completely dissolved into the melt without addition of MgO. However, the Hastelloy substrate survived in the MgO saturated solution. The modified LPE process was developed which is the Y123 LPE growth using the Y123 layer saturated with MgO as the second buffer layer to prevent dissolution of the first MgO buffer layer into the melt. Using the MgO single crystal substrates, we got the YBa2Cu3Ox film on the YBa2(Cu, Mg)3Ox/MgO substrates. Finally, the YBa2(Cu, Mg)3O layer was grown on MgO/Hastelloy substrates from the solution saturated with MgO.View full abstractDownload PDF (508K) -
Hirofumi Inoue, Yoshichika Nagata, Masaaki Ishio, Takayuki Takasugi2000 Volume 64 Issue 9 Pages 731-734
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSA new process for producing Ti-Al intermetallic composites was developed. The process consisted of the repetitive roll-bonding for making a laminated Ti/Al sheet and the subsequent heat treatment promoting a solid phase reaction in the laminated Ti/Al sheet. In order to finally obtain two-phase intermetallics of TiAl and Ti3Al, the roll-bonding was first conducted by adjusting the thickness of Ti and Al sheets. The 55-layered sheet, which had an alternately stacked structure of Ti and Al with the surface layer of Ti, was prepared in this study. The heat treatment for reactive diffusion was composed of three stages: (1) the 1st heat treatment below a melting point of Al, (2) the 2nd heat treatment below the α to β transformation temperature of Ti and (3) the 3rd heat treatment for obtaining the two-phase intermetallics of TiAl and Ti3Al. It was found that the formation of voids due to interdiffusion took place mainly in the formation process of Al3Ti. An intermittent or continuous pressure such as hot rolling and compression is therefore required at the 1st stage to produce void-free materials. Depending on heating temperature at the 3rd stage, two different types of microstructures, that is, the macroscopically stacked layer structure and the fully lamellar microstructure of TiAl and Ti3Al were formed.View full abstractDownload PDF (890K) -
Tatsuya Ohmi, Kazuhiko Kirihara, Masayuki Kudoh2000 Volume 64 Issue 9 Pages 735-738
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSA modified centrifugal combustion synthesis process has been developed that enables precisely casting synthesized materials and simultaneously joining them to a dissimilar metal. The material to be synthesized was a Ni-25 mol%Al alloy and that to be bonded was a stainless steel, an ultra-low carbon steel, pure nickel or a Ni-25 mol%Al alloy. The base material to be bonded; a graphite mold; and a green compact of reactants consisting of Al, Ni and NiO were set in a centrifugal caster. When the combustion synthesis reaction was induced in the centrifugal force field, synthesized molten Ni-Al alloy flew into the mold and collided with the base material. This process was successfully applied in joining the synthesized Ni-Al alloy and various base materials. Centrifugal force was also confirmed to assist the molten Ni-Al alloy fill the mold cavity and adhere to the surface of the base materials.View full abstractDownload PDF (639K) -
Takeshi Houga, Akihiro Yamada, Yuji Ueda2000 Volume 64 Issue 9 Pages 739-742
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSA pulse electrodeposition technique using a pulse generator circuit has been utilized to produce multilayer films with control on an atomic scale. The pulse generator was designed to control the deposition time within the range of 0.1 ms. The magnetoresistance ratio for the multilayer film controlled on an atomic scale had a maximum value of about 9.5% at the stacking number of 110. The temperature dependence of magnetization for the films with thin layers shows superparamagnetic behavior.View full abstractDownload PDF (341K) -
Toshinori Chuto, Takuya Nagasaka, Takeo Muroga, Manabu Satou, Katsunor ...2000 Volume 64 Issue 9 Pages 743-746
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThree alloys of V-4Cr-4Ti type containing Si, Al and Y were fabricated by 2.5 kg scale levitation melting in this study. Workability and recrystallization behavior of the alloys were studied in order to establish the fabrication method of high-purity large ingot of V-Cr-Ti-Si-Al-Y type alloys, especially reducing interstitial impurity levels. Oxygen contents decreased with increasing yttrium contents and were kept below 180 mass ppm over wide region in the ingots. Nitrogen contents in the V-Cr-Ti-Y-Si-Al type alloys were only 100 mass ppm, which were as low as that in the starting materials. Only the V-4Cr-4Ti-0.1Y, Si, Al alloy could be cold-rolled at as-melted condition. Because large yttrium inclusions were observed in the alloys containing 0.5 mass%Y, it is necessary to optimize yttrium contents to avoid large inclusions and to obtain good workability.View full abstractDownload PDF (643K) -
Masahiro Nagae, Jun Takada, Yoshito Takemoto, Yutaka Hiraoka, Tetsuo Y ...2000 Volume 64 Issue 9 Pages 747-750
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe control of microstructure and recrystallization temperature in the internally nitrided dilute Mo-Ti alloys was studied through a novel three-step nitriding process at 900 to 1600°C in N2 gas, in order to develop highly ductile Mo alloys having a heavily deformed microstructure near the specimen surface. Primary internal nitriding process below the recrystallization temperature of the present alloys at around 1000°C brings uniform dispersion of superfine Ti-nitride precipitates in the Mo matrix where the deformation microstructure remains. These superfine precipitates decompose and disappear after heating at 1200°C in a vacuum. However, after secondary nitriding at 1500°C in a nitrogen atmosphere, those particles grew up to be stick-shaped particles with a length of 50 to 120 nm without the recrystallization of Mo matrix within about 130 μm from the specimen surface. The depth of the region where the recrystallization of Mo matrix was suppressed was greatly dependent upon the secondary nitriding temperature. The third nitriding was conducted at 1500 or 1600°C. For the specimen nitrided at 1600°C, the recrystallization temperature in a vacuum was elevated above 1600°C.View full abstractDownload PDF (852K) -
Masahiro Nagae, Jun Takada, Yutaka Hiraoka, Yoshito Takemoto, Tetsuo Y ...2000 Volume 64 Issue 9 Pages 751-754
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSInternally nitrided dilute Mo-Ti alloys having a heavily deformed microstructure near the specimen surface were prepared by a novel two-step nitriding process at 1173 to 1773 K in N2 gas. For the nitrided specimens, three-point bend tests were performed at temperatures from 77 to 298 K in order to investigate the effect of microstructure control by internal nitriding on the ductile-brittle transition temperature (DBTT) of the alloy. Yield strength obtained at 243 K of the specimen maintaining the deformed microstructure by the two-step nitriding was about 1.7 times as much as recrystallized specimen. The specimen subjected to the two-step nitriding was bent more than 90 degree at 243 K, whereas recrystallized specimen was fractured after showing a slight ductility at 243 K. DBTT of the specimen subjected to the two-step nitriding and recrystallized specimen was about 153 K and 203 K, respectively. These results indicate that multi-step internal nitriding is very effective to the improvement in the embrittlement by the recrystallization of molybdenum alloys.View full abstractDownload PDF (599K) -
Tsuyoshi Arakawa, Yukiyoshi Aramaki2000 Volume 64 Issue 9 Pages 755-758
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSCrystalline powders of Si and Ln (Ln=Sm, Nd, Gd, Tb, Dy, Er) in the composition ratio Si : Ln=2 : 1 were mechanically alloyed in an inert atmosphere using a laboratory ball mill. The progress of the mechanical alloying was identified by X-ray diffraction. The amorphization reaction between Si and Ln proceeded according to a second-order formula. The sequence of the rate of amorphization reaction for the Si-Ln system was Sm>Gd>Tb>Nd≥Dy>Er. The reaction rate was affected by the crystal structure of Ln. In the case of Gd, Tb, Dy and Er having the same structure (hexagonal closed packed), the reaction rate was correlated to the volume ratio (VLn⁄VSi). In the Sm-Si system, which had the fastest MA rate, Sm has a unique structure in which triangular planes of Sm atoms overlap fourfold and would be easily attacked by Si atoms. In Nd-Si system, the rate would be affected by the structure of double hexagonal closed packed of Nd. The crystallization of Si-Ln was studied by means of X-ray diffraction, differential thermal analysis and electrical resistivity measurement.View full abstractDownload PDF (282K) -
Analysis of Instability at Solid-Liquid Interface from Molar Flux Balance in Diffuse Interface LayerShigeo Kotake2000 Volume 64 Issue 9 Pages 759-762
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSBy assuming a balance in molar flux at a diffuse interface layer between a solid and liquid with thickness δ, we explain the interfacial instability in the directional solidification of alloys. The state of constitutional undercooling is equivalent to the directional change in the molar flux at the interface, ji. We compared the interfacial instability criterion from the present model with that from Mullins-Sekerka’s theory. From the flux balance between ji and the interfacial diffusion (jd), we deduced the thickness of the interface, which shows good agreement with experimental results. Since an empirical relation of interfacial energy per mole, γm=RTfδ, was analytically explained, the flux balance can provide new models for capillary-effected phenomena, where R is the gas constant and Ti is the temperature at the solid and liquid interface.View full abstractDownload PDF (391K) -
Hideyuki Saitoh, Hirofumi Homma, Toshihei Misawa, Takuya Tamura, Takah ...2000 Volume 64 Issue 9 Pages 763-766
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSTritium radioluminography has been applied to V-Zr-Ti-Ni protium absorption alloys with the two-phase structure of BCC phase and Laves phase to examine the behavior of protium. The specimens were V77.8Zr6Ti8.8Ni7.4 and V54.5Zr18.25Ti11.25Ni16, the ratio of the BCC phase to the Laves phase in them being 4 : 1 and 1 : 1, respectively.
In the range of lower hydrogen content as hydride never formed, hydrogen concentration in the Laves phase is observed to be higher than in the BCC phase by tritium radioluminography. The protium concentration in the BCC phase and Laves phase in the alloy has been determined to be 70 mass ppm and 1300 mass ppm, respectively. It has been found that the preferential path for the protium penetration into the alloy is not the BCC phase but the Laves phase. In the range of higher hydrogen content as hydride formed, the amount of absorbed hydrogen has increased when the ratio of BCC phase to Laves phase increases, by the PCT measurement. It has been found that the main hydrogen storaging phase is BCC phase.
An extraordinal phenomenon has been observed for the time dependence of hydrogen concentration by the radioluminography. That is, the hydrogen concentration in the BCC region decreases for a few days after hydrogen charging and then changes to increse, while the hydrogen concentration in other region decreases successively.View full abstractDownload PDF (622K) -
Kazuhiko Noda, Toshiyasu Nishimura, Hiroyuki Masuda, Toshiaki Kodama2000 Volume 64 Issue 9 Pages 767-770
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSLow-alloy steel foils of 20 μm thick were corroded under a cyclic wet-and-dry condition simulating highly corrosive coastal environment. Compositions of Fe-1 mass%Co, Fe-3 mass%Co, Fe-3 mass%Ni and Fe-0.8 mass%Al were selected as testing materials because they were thought to be basic alloys of weathering steels for the use in coastal environments. The steel foils were entirely transformed into rust to form rust membranes by processing more than 20 wet-and-dry cycles. The rust membranes were carefully attached to a dual-compartment cell for the measurement of membrane potential. Membrane potential generated by the difference in ionic diffusion rates of K+ and Cl− ions was measured as a function of concentration difference of KCI between solutions in the compartments separated by the membrane. The membrane potential thus measured was proved to be effective in evaluating the performance of rust formed on steel surface. The rust layer formed on the steels of Fe-3%Ni and Fe-1%W showed anion selectivity, while the rust on Fe-1%Co, Fe-3%Co, and Fe-0.8%Al steels, revealed cation selectivity. The addition of Co and Al to the steel decreases the corrosion rate because penetration of chloride ions into the rust is inhibited by the cation selective permeability of rust. The addition of Ni and W is known to be effective in decreasing corrosion rate of steel, despite their anion selective nature in rust. Alternative mechanisms other than ion selectivity are required for the elucidation of inhibition by Ni and W.View full abstractDownload PDF (434K) -
Keun-Soo Kim, Toshitada Shimozaki, Takahisa Okino, Chan-Gyu Lee2000 Volume 64 Issue 9 Pages 771-775
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSReactive diffusion of the Co-Si binary system has been studied by using bulk diffusion couples consisting of a 99.98% and 99.997%Co plate and a ⟨100⟩ oriented Si wafer in the temperature range from 973 K to 1273 K. The experimental results were compared with the previous results obtained by using Co thin film/bulk Si and bulk Co/bulk Si diffusion couples. In these bulk diffusion couples, 3 kinds of Co silicides (Co2Si, CoSi, CoSi2) were formed. All of them grew according to the parabolic law. The interdiffusion coefficients of CoSi in the bulk diffusion couples almost coincide with the values for thin film diffusion couples. However, the values of interdiffusion coefficients of Co2Si for the bulk diffusion couples and thin film diffusion couples do not agree with each other. If the first crystalline phase is Co2Si in Co/Si diffusion couples, the reason for the difference in interdiffusion coefficients between the thin film and bulk samples can be explained by the fast diffusion such as grain boundary diffusion in the thin film diffusion couples.View full abstractDownload PDF (446K) -
Shinji Itoh, Hitoshi Yamaguchi, Toshiyuki Hobo, Takeshi Kobayashi2000 Volume 64 Issue 9 Pages 776-780
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe analyses of silver and palladium brazing filler metals by means of the glow discharge mass spectrometry (GDMS) have been studied. A double focusing glow discharge mass spectrometer, Fisons Instruments (UK) VG 9000, was used. As it was difficult to obtain an adequate commercial silver brazing filler metals, which contained all analytes under investigation, multi-component silver-based alloys were prepared in a graphite crucible by using a high-frequency induction furnace. Chemical compositions of those alloys were obtained by the JIS analytical method. Spectral interference due to argide ions of main constituent Cu and Zn was solved by selecting suitable isotopic species in the range from m⁄z102 to m⁄z124, depending on the major and minor constituents of sample. The relative sensitivity factor (RSF) of each analyte was evaluated from the analytical values of ten reference materials. The analytical results of a practical sheet sample (Ag-32Cu-10Pd, thickness; 500 μm) showed good agreement with results obtained by X-ray fluorescence spectrometry based on the fundamental parameter method and by chemical analysis. The analytical precision of proposed method, defined as RSD, was within 1% for major element and within 20% for trace impurity.View full abstractDownload PDF (474K) -
Takeshi Suemitsu, Kozi Nishio, Seiji Motojima2000 Volume 64 Issue 9 Pages 781-786
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSPyrolytic carbon films were prepared by chemical vapor deposition on Si-Ti-C-O ceramic fiber, using argon or hydrogen as dilute gas with methane gas. The effects of argon or hydrogen gas on the deposition process were investigated in terms of the temperatures and the duration of the incubation period preceding the formation of the film. When argon was used as the dilute gas, carbon films were formed in the temperature range between 1350 K and 1550 K, but when hydrogen was used, there was no deposition at temperatures below 1450 K. The activation energy for carbon film formation was 110 kJ/mol. The duration of the incubation period was about 1 ks. The incubation time might have been delayed because residual hydrogen from the hydrogen-cleaning pretreatment hindered the film formation process and the surface conditions of the films had changed.View full abstractDownload PDF (852K) -
Kazutaka Fujita, Akihisa Inoue, Tao Zhang2000 Volume 64 Issue 9 Pages 787-792
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSA nanocrystalline(NC) bulk glass Zr55Al10Cu30Ni5(at%) which contains nano-scale crystals embedded uniformly in a glassy matrix has both high tensile strength of 1.7 GPa and high ductility. It is therefore expected to find practical application in machines and structures. The fatigue crack propagation behavior of the NC bulk glass was examined. The threshold stress intensity factor range ΔKth was about 0.9 MPa\sqrtm, and the fatigue fracture toughness Kfc was about 13 MPa\sqrtm. Fatigue crack propagation rate da⁄dn was approximately proportional to ΔK2. No significant difference in da⁄dn between the NC glassy alloy and single phase amorphous alloys in literature was seen when they are compared on the basis of ΔK divided by Young’s modulus E. The da⁄dn values were nearly the same as those for steels with the same tensile strength level. The da⁄dn values were larger than those for low strength steels, Al alloys and Ti alloys in the low da⁄dn range. When compared with the effective stress intensity factor range ΔKeff divided by E, the da⁄dn values for crystalline alloys were almost coincident with those under different stress ratios for the NC glassy alloy. This indicates that the da⁄dn values for the NC glassy alloy can be estimated on the basis of the da⁄dn data for crystalline alloys.View full abstractDownload PDF (764K) -
Katuo Saitou2000 Volume 64 Issue 9 Pages 793-797
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSUltrafine nickel particles (UFPs) were produced using an Ar-H2 plasma jet generated by an insulated constrictor plasma torch, and the effects of plasma gas flow rate and hydrogen content on the proportion of UFPs produced were investigated. Since hydrogen supply from the cathode causes erosion of a copper anode, two different methods were proposed to prevent erosion of the anode: use of an anode with a tungsten pipe insert in the nozzle and supply of hydrogen from a feed ring installed under the anode.
The proportion of UFPs produced decreased with increasing plasma gas flow rate. This decrease is due to the reduction in residence time of powders present in the plasma. The proportion of UFPs produced increased with increasing hydrogen content. This is because the recombination energy of dissociation and ionization were added to the plasma. However for a relatively high hydrogen content, the proportion of UFPs saturated or decreased because a melt drop adhesion occurred in the nozzle. Further examination to find more effective powder heating methods and to prevent the melt drop adhesion is required in order to increase the proportion of UFPs.View full abstractDownload PDF (434K) -
Katuo Saitou2000 Volume 64 Issue 9 Pages 798-802
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSImprovements to the anode of an insulated constrictor plasma torch were carried out in order to increase the proportion of ultrafine particles (UFPs) produced by means of the plasma jet method. Nickel UFPs were produced using the improved anode to examine its effects. The improved anode is a unified type consisting of the electrode and feeding ports for powders and hydrogen. Two types of improved anode with different feeding port positions were made, and the effect of the relative position of feeding port to nozzle length on the proportion of UFPs produced was examined. In addition, the geometry of the nozzle exit was modified in order to prevent melt drop adhesion.
The proportion of UFPs produced using the improved anode was greater than the fraction produced using an unimproved anode. The position of feeding ports did not greatly affect the proportion of UFPs produced although an appropriate feeding port position relative to the nozzle length may exist which improves the proportion of UFPs produced. The cause of the melt drop adhesion was found to be the cold hydrogen which was added to the argon plasma. The melt drop adhesion was formed by cold hydrogen flowing along the inner-wall of the nozzle.View full abstractDownload PDF (431K) -
Hideo Numata2000 Volume 64 Issue 9 Pages 803-811
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSMetal hydride (MH) formation in a Ti-47 mol%Al (47Al) alloy with the γ+α2 lamellar structure through electrochemical treatment in sulfuric acid has been studied by X-ray diffractometry (XRD), thermal desorption spectrometry (TDS) combined with quadrupole mass spectrometry (QMS) and SEM.
It has been shown for the γ phase that cathodic polarization (CP) makes only one type of MH having a tetragonal structure (MHTET) of about 10 μm thick at the reaction surface. An addition of anodic polarization (AP) after CP makes another type of MH having a hexagonal structure (MHHEX) of 1-2 μm thick along the reaction surface. On the other hand, MH with HCP structure (MHHCP) is formed in the α2 phase by either CP or CP+AP. Each hydride gives an individual peak in TDS and QMS curves. The peaks of MHTET, MHHEX and MHHCP are located at around 200, 400, 600°C, respectively. Heating in vacuum to the temperature above each peak decomposes the hydride corresponding to the peak.
The preferential dissolution of Al atom from the γ phase of 47Al alloy by anodic reaction makes compositional change and lattice defects near the reaction surface, and it is considered that MHHEX is formed by movement of hydrogen atoms to the defects. The fact that the formation of two types of MH in the γ phase of 47Al alloy by CP+AP is strongly suggests the possibility that two kinds of MH are formed in the γ single phase alloy.View full abstractDownload PDF (1295K) -
Ryoichi Monzen, Hideyuki Shigehara, Kazuhisa Kita2000 Volume 64 Issue 9 Pages 812-817
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe misorientation dependence of discontinuous precipitation (DP) for [001] symmetric tilt and twist boundaries in Cu-0.75 mass%Be alloy bicrystals has been systematically investigated in a temperature range from 523 to 698 K. A grain boundary migrates at a constant rate during DP under an isothermal condition, maintaining a constant interlamellar spacing. The interlamellar spacing increases with temperature. The formation and growth of DP cells at twist boundaries are suppressed, compared with those at symmetric tilt boundaries. For the two types of grain boundary, the incubation period to initiate DP and cell growth rate at a boundary show a good correlation with the energy of the boundary. The formation and growth of cells are easier at higher-energy boundaries. The grain-boundary diffusion data have been determined through the kinetic analysis of DP using several models. Although the activation energy Qb of boundary diffusion varies with the models, the values of Qb are smaller than the activation energy of volume diffusion of Be in Cu. For the two types of boundary, a close correlation is found between the diffusivity and the energy of boundaries. A lower-energy boundary has a lower diffusivity with a larger activation energy and a larger pre-exponential factor.View full abstractDownload PDF (757K) -
Mitsuyoshi Shimaoka, Itsuo Ohnaka2000 Volume 64 Issue 9 Pages 818-824
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe application of electromagnetic force to the In-Rotating-Liquid-Spinning process has been tried in order to produce short fibers and improve the cross-sectional roundness and dimensional uniformity of the continuous fiber. The electromagnetic force was generated by applying a direct current to the molten alloy jet that passed through the static magnetic field formed by two Nd-Fe-B permanent magnets facing each other in parallel. Both molten Cu-Be and Sn-Pb-Bi alloy jets were easily cut into short fibers by the periodical and impulsive electromagnetic force. The minimum length of the fibers was about 40 mm in the case of Sn-Pb-Bi alloy. Molten aluminum jet, which tends to flow along the rotating coolant surface, sunk into the coolant through the electromagnetic force applied in the radial direction of rotating drum. Applying the electromagnetic force in the axial direction of the drum to the molten Sn-Pb alloy jet increased the cross-sectional roundness of the fiber from about 0.3 to 0.6. A Co-Cu-Be alloy fiber having magnetism below the magnetic transformation point was cut into short length by magnetic force during passing through the magnetic field. The mean length of the obtained fibers changed depending on the distance from the nozzle tip to the magnet. The calculated jet orbits of Sn-Pb and Cu-Be alloy under the electromagnetic force in the radial direction of drum, agreed approximately with observed ones in the distance of about 30 mm from the nozzle exit. The application of the electromagnetic force was proved effective for the production of continuous fibers with better uniformity and for producing short fibers.View full abstractDownload PDF (802K)
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