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Volume 64, Issue 2
Displaying 1-15 of 15 articles from this issue
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Han-Cheol Choe, Keum-Yeon Hwang, Kwan-Hyu Kim2000 Volume 64 Issue 2 Pages 79-84
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe surface characteristics and corrosion behavior of plasma nitrided austenitic stainless steel containing Mo has been investigated using a wear tester, a micro-hardness tester and potentiostat equipment. It was found that plasma nitriding at 823 K, compared with at 653 K, resulted in a thick nitrided layer, and consequently good wear resistance and hardness, as the nitriding time increased. Whereas for the Mo addition, wear resistance and hardness decreased. Intergranular corrosion(IGC) resistance improved significantly in the case of plasma nitrided SS containing 4.05 mass%Mo at 653 K because the nitrogen and Mo act synergistically to form a protective surface layer which is responsible for the aggressive SCN− ion. Plasma nitriding at 823 K decreased IGC resistance as the Mo content increased owing to retardation of the nucleation and growth of chromium carbide(Cr23C6) or nitride(CrN) in grain boundary.View full abstractDownload PDF (1968K) -
Katsuhiko Nonaka, Hideki Fujii, Hideo Nakajima2000 Volume 64 Issue 2 Pages 85-94
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSReaction diffusion in Ti/Al and Ti-5 mol%O/Al diffusion couples has been investigated by electron-probe microanalysis. Only one intermetallic compound TiAl3 was observed as an intermediate phase in a temperature range from 773 to 903 K in both the diffusion couples. Si, an impurity element in aluminum, was concentrated in TiAl3. The growth of the intermediate layer turned out to be diffusion limited.; the activation energy was estimated to be 237±15 kJ mol−1 and the temperature dependence of square of the rate constant, k2, for layer growth can be described with the following equation in the temperature range from 773 to 903 K in the Ti/Al diffusion couples.
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In the case of the oxygen doped diffusion couples, the layer growth of TiAl3 was significantly suppressed and the activation energy was 263±7 kJ mol−1 for temperatures from 773 to 873 K. The suppression is explained by aluminum oxide formed between aluminum and TiAl3. The Kirkendall marker was shifted toward the aluminum side, which suggests that diffusion of Al is faster than that of Ti in the intermediate phase.View full abstractDownload PDF (3027K) -
Kunimasa Takeshita, Yuhji Terakura2000 Volume 64 Issue 2 Pages 95-100
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSBending tests were performed using titanium joints brazed with aluminum filler metal. The influences of aluminum and Al3Ti layer thickness on the bending moment at joint fracture were investigated.
The bending moment at joint fracture reaches its maximum value of 1.1 N·m at an aluminum layer thickness of 14 μm, and decreases from 1 to 0.5 N·m as the aluminum layer thickness increases from 80 to 280 μm, regardless of the Al3Ti layer thickness. A small portion of the fracture surface of joints with relatively thin aluminum layers reveals that the ridges of the dimpled aluminum structure protruding above the surface, much more so than at the fracture surface of joints with relatively thick aluminum layers.
The bending moment at joint fracture is calculated using a finite element method of analysis, which considers ductile failure within the aluminum layer of the joint. The calculated results generally agree with experiment.View full abstractDownload PDF (2040K) -
Narihito Nakagawa, Yoshiharu Waku, Takumi Wakamoto, Hideki Ohtsubo, Ka ...2000 Volume 64 Issue 2 Pages 101-107
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSIn order to develop stable composite materials in an air atmosphere above 1773 K, unidirectionally solidified Al2O3/Er3Al5O12 eutectic composites were fabricated by using the Bridgman-type equipment at the Japan Ultra-high Temperature Materials Research Center. Composites with dimensions of 40 mm in diameter by 70 mm in length consisted of single-crystal-like Al2O3 and single-crystal Er3Al5O12 without colonies or pores. The flexural strength of the composite is temperature independent from room temperature up to 2073 K (just below its melting point of about 2130 K). It was found also that the microstructure of the present composite has excellent thermal stability at 1973 K in an air atmosphere. The above superior high-temperature characteristics are due to a microstructure consisting of three-dimensionally continuous and complexly entangled single-crystal-like Al2O3 and single-crystal Er3Al5O12 phases, the formation of interfaces with no amorphous phases and comparatively good coherence.View full abstractDownload PDF (3327K) -
Hiroyuki Horimura, Kenji Okamoto, Akihisa Inoue2000 Volume 64 Issue 2 Pages 108-114
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe utilization of crystallization reaction of an amorphous phase is a useful method for the formation of nanocrystalline structure. However, degassing and extrusion processes at elevated temperatures are necessary for the consolidation of the rapidly solidified powders. Consequently, the thermal history must be taken into consideration in the control of the structure and characteristics of the consolidated alloys. In this paper we examined the structure and mechanical properties of as-quenched amorphous and annealed nanocrystalline states of Al-Fe-Y alloys with high crystallization temperatures. The Fe and Y contents are located near the low solute concentration range of the amorphous phase region. The structure of the as-quenched alloys is composed of amorphous, amorphous+fcc-Al and fcc-Al solid solution and the grain size of the Al phase is about 5 nm. The annealing of the Al90Fe5Y5 amorphous alloy causes an increase of hardness and a decrease of fracture strain. The maximum hardness was obtained after annealing for 3.6 ks at 573 K. With further increase of annealing temperature to 623 and 673 K, the structure changes to Al+intermetallic compounds, accompanied by a rapid decrease in hardness. The embrittlement of the annealed samples having hardness above 200 is suppressed by Al enrichment. The crystallization process for this alloy is similar to that for the Al90Fe5Y5 alloy. The grain size of the crystallized phases is about 100 nm after annealing at 673 K. It is therefore concluded that the Al92Fe5Y3(at%) alloy is an appropriate composition for the production of nanocrystalline Al-based alloys with high elevated temperature strength.View full abstractDownload PDF (2475K) -
Seiya Yanagita, Toshimasa Yoshiie, Hiromitsu Ino2000 Volume 64 Issue 2 Pages 115-124
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSWe performed a model calculation of damage rate dependence on defect structures and mechanical property changes in Fe-Cu model alloy. The model was based on the rate theory, and focused on the nucleation and growth of point defect clusters and Cu clusters. The effect of irradiation cascade was introduced as the direct formation of small point defect clusters in cascade. We assumed that the production rate of irradiation cascade was proportional to that of Frenkel pairs. We also took into account the instability of small point defect clusters caused by thermal dissociation. We assumed that interstitials, vacancies and copper atoms were the mobile defects. From the result of this model calculation, we estimated the yield stress change in Fe-Cu model alloy using Orowan and Russel-Brown models. The concentrations of interstitial and vacancy clusters increased with increasing the damage rate, whereas their average radii decreased. On the other hand, both of the concentration and the average radius of copper clusters increased with decreasing the damage rate. This dependence is caused by the difference in the number of jumps of vacancies before annihilation since copper atoms migrate by vacancy mechanism. The major factor of yield stress change varies depending on the damage rate. At the lower damage rate, the change is caused by the copper clusters, and at the higher damage rate, it is by the defect clusters. In the Russel-Brown model, the transition region appears around P=10−8 dpa/s. This transition region falls between the irradiation conditions of power and test reactors. Hence, the effect of damage rate should be carefully considered when one interpretes results of accelerated irradiation tests.View full abstractDownload PDF (1647K) -
Rongguang Wang, Masahiko Kato, Keijiro Nakasa2000 Volume 64 Issue 2 Pages 125-133
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSN2+ ions were implanted into specimens of commercially supplied pure titanium at 1.5 MeV with different doses ranging from 5×1020 to 2×1021 ions per m2, and the oxidation behavior of specimens was investigated in air and water vapor at 823 K and 1073 K.
The mass gain of the specimen increases with increasing holding time and it is much larger in water vapor than in air. The mass gain of the implanted specimen is less than that of unimplanted specimen in both environments, and the amount of oxidation decreases with increasing implantation doses. According to X-ray diffraction analysis, TiH2 is detected in the substrate after oxidation in water vapor. The X-ray analysis and the microscopic observation of cross section indicate that the oxidation in water vapor occurs from the interface between the oxidation film and the substrate by the inner transfer of water vapor. The reason for the reduction of oxidation by N2+ ion implantation can be that the Ti2N or TiN precipitates decrease the effective surface area for oxide formation and the soluted nitrogen atoms prevent the ingress of oxygen atoms into the surface region.View full abstractDownload PDF (3107K) -
Songji Li, Hisami Yumoto, Michio Shimotomai2000 Volume 64 Issue 2 Pages 134-140
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSTo design advanced steel, it is important that the mechanical properties of the cementite phase are studied. However, few papers on these properties have been published. For those that have been published, the samples were cementite embedded in steels or extracted from steels by electrolysis.
The purpose of this paper is to prepare a thick cementite film without the oxide, and to study the temperature dependence of the hardness in detail.
A single phase cementite film, 3 μm thick, was prepared by the electron-shower PVD method. The composition of the film was Fe : C : O=76 : 24 : 0. The Vickers hardness of the cementite was 1140 at room temperature and decreased to half at 400°C. The hardness of composite film of Fe and cementite is explained by the law of mixture. The cementite film was oxidized above 400°C in atmosphere, but was very stable at room temperature.View full abstractDownload PDF (2054K) -
Junichi Kaneko, Makoto Sugamata, Masahiro Numa, Yasuhisa Nishikawa, Hi ...2000 Volume 64 Issue 2 Pages 141-147
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSWith the purpose of evaluating texture hardening in magnesium alloys, the crystallographic texture and mechanical properties at room and elevated temperatures of extruded bars and rolled sheets were studied. Cast ingots were used as the reference materials, since they exhibited nearly isotropic orientation distribution. Formability of AZ31 sheet was evaluated at room and elevated temperatures by the Erichsen test, conical cup test and forming limit diagram. Strong texture is observed in magnesium wrought materials in which the basal plane is oriented parallel to the extrusion or rolling direction. As a result, tensile strength of magnesium wrought materials increased by 15 to 20% due to texture hardening at room temperature. The AZ31 alloy sheet is highly anisotropic at room temperature with high γ-value above 4, resulting that forming limits in biaxial tension are much lower than those in uniaxial tension. However, this anisotropy decreases with increasing forming temperature and no texture hardening is found at 473 K. In this respect, formability of magnesium alloys sheets in terms of Erichsen and conical cup values is remarkably poor at room temperature but appreciably improves with increasing temperature. Sheet forming of magnesium alloys is practically possible only at the high temperature range where plastic anisotropy disappears.View full abstractDownload PDF (1785K) -
Toshiyasu Nishimura, Akira Tahara, Toshiaki Kodama2000 Volume 64 Issue 2 Pages 148-153
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe iron rust phase has been analyzed by using EPMA, TEM and alternating current (AC) impedance methods after wet/dry corrosion test using 0.5 mass%NaCl solution. The steel containing 0.8 mass%Al showed higher corrosion resistance than carbon steel in the test.
Aluminum was identified in the spinel oxide of inner rust of Al-bearing steel by TEM and EPMA, which is confirmed by thermodynamic calculation.
By AC impedance it is demonstrated that the resistance of the rust (Rrust) corresponds to the structural factor of the rust of steels. The Rrust value of Al-bearing steel increases after the continuous formation of inner rust, which implies that Al takes part in the conversion of spinels into fine structure that prevents from the penetration of Cl ion.View full abstractDownload PDF (1278K) -
Andreas Leithe-Jasper, Helmuth Klesnar, Peter Rogl, Masao Komai, Ken-i ...2000 Volume 64 Issue 2 Pages 154-162
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSPhase equilibrium relations in the M(M=Mo, W)-Fe-B ternaries were determined in isothermal sections at 1323 K based on X-ray powder diffraction and quantitative EPM-analyses (Mo, Fe, B) on argon arc-melted or reaction-sintered alloys, which were subjected to long term annealing. The investigation confirmed the existence of three ternary compounds in the Mo-Fe-B ternary at 1323 K and established their range of formation: stoichiometric Mo2FeB2(ordered U3Si2-type), Mo1−xFexB(CrB-type, 0.13≤x≤0.18) from 6 to 9 at%Fe at a stoichiometric boron content of 50 at%, Mo1+xFe2−xB4(Ta3B4-type, −0.08≤x≤0.76) at rather Fe-rich concentrations from 13 to 25 at%Mo at a stoichiometric boron content of 57 at%. In the system W-Fe-B two ternary compounds were found to exist in accordance to the literature: WFeB (TiNiSi-type) and W2FeB2(W2CoB2-type). No indication of ternary tungsten compounds with B contents higher than 40 at% was found. For both systems metastable Fe3B with the Ti3P-type was stabilised by the substitution of Mo or W for Fe. In both phases M0.2Fe2.8B is stable only in a limited temperature region 1353<T<1383 K.View full abstractDownload PDF (1854K) -
Hiroaki Otsuka, Masaaki Sugiyama, Ikuo Itoh2000 Volume 64 Issue 2 Pages 163-169
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe influence of aging time on the size and quantity of Ti precipitates in the NbTi layers of NbTi/Nb/Cu superconducting multilayer sheets and on the critical current density (Jc) was studied. Ti precipitates with a length of about 250 nm and a thickness of about 100 nm had been already precipitated at the grain boundaries after the aging at 623 K for 8 h. The orientation relationships between these large precipitates and the NbTi matrix were (0001)α\varparallel(1\bar10)β and [11\bar20]α\varparallel[111]β . When aging time exceeded 336 h, an other fine precipitate with a length of about 50 nm and a thickness of about 3 nm appeared in the matrix. The volume fraction and sizes of the large precipitates increased with increasing aging time, but they did not serve effectively as the pinning points of fluxons. The practically useful Jc could not be obtained until the fine precipitates began to precipitate after aging longer than 336 h.View full abstractDownload PDF (2867K) -
Hiroaki Nakamura, Youichi Ogawa, Akira Kasahara, Toshiaki Kodama2000 Volume 64 Issue 2 Pages 170-173
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSTo obtain highly ionic conductor of sulfides, a solid solution of 95CaS-5Na2S was prepared by sintering the powder mixture of CaS with the NaCl type structure and Na2S with the anti-fluorite structure.
Two concentration cells using the solid solution as solid electolyte were constructed as follows.
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The reversibility of the measured emf, was assured.
The electromotive forces of the concentraion cells were measured over the temperature range 670 to 1120 K. Because the measured values for the concentration cells coincided closely with the theoretical values from the Nernst equation, it is concluded that the ionic transference number of the solid solution, 95CaS-5Na2S, is unity.View full abstractDownload PDF (731K) -
Tetsuji Noda, Hiroshi Suzuki, John L. Lyman, Brian E. Newnam2000 Volume 64 Issue 2 Pages 174-175
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSFree electron laser (FEL) was irradiated to Si2F6 at 1000, 800 and 400 cm−1 bands, respectively, where the infrared absorption occurs. The isotope ratios of 28Si, 29Si and 30Si in the SiF4 products were measured as a function of wavenumber of the laser using an IR spectrometer. Obvious concentration of 29Si and 30Si was detected at all absorption bands. Especially it was the first time to observe the isotopical selective decomposition of Si2F6 at 800 and 400 cm−1 bands. The enrichment of 30Si at the 1000 cm−1 band was rather lower than that by pulse CO2 laser. The main reason was considered due to collisions among gas molecules during the longer pulse of the FEL compared to that of the CO2 laser.View full abstractDownload PDF (353K) -
2000 Volume 64 Issue 2 Pages 176
Published: 2000
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSPlease see Errata PDF Wrong:77 K Right:131 KView full abstractDownload PDF (27K)
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