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Volume 59, Issue 8
Displaying 1-18 of 18 articles from this issue
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Hidehiro Yasuda, Hirotaro Mori1995 Volume 59 Issue 8 Pages 769-773
Published: 1995
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe structure and phase transformation in nanometer(nm)-sized Au-Pb alloy clusters have been studied in situ by means of transmission electron microscopy (TEM), in order to see the difference of phase equilibrium between a bulk material and the corresponding nm-sized cluster. When lead (or gold) atoms are vapor-deposited onto nm-sized gold (or lead) clusters kept at ambient temperature, spontaneous dissolution of the solute atoms into the clusters takes place and homogeneous Au-Pb alloy clusters are formed. The solid solubilities of lead and of gold in the Au-Pb solid solution clusters remarkably increase as compared to those in the corresponding bulk materials. A stable intermetallic compound formed preferentially in Pb-enriched Pb-Au alloy clusters is AuPb2 with a negative heat of formation. The phase transformation from Au-supersaturated Pb-Au solid solution clusters to single crystalline AuPb2 clusters takes place for a short period, and is similar to “martensitic” transformation.View full abstractDownload PDF (1086K) -
Masayoshi Nakaniwa, Koichi Sugimoto, Kiyoshi Kamei, Yasuhiko Nakamura, ...1995 Volume 59 Issue 8 Pages 774-779
Published: 1995
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSExperiments were carried out for Cu-xAl-5Ni-2Mn-1Ti shape memory alloys (x=11.45, 11.77, 11.88 mass%) in order to examine the effect of quenching rate on the transformation temperatures (Ms, Mf, As and Af). The quenching rate was varried from 5 to 1×104 K/s by changing the temperature of quenching media.
The transformation temperatures were determined by DSC measurements for all the samples quenched and are plotted as a function of quenching rate.
It was found that all the transformation temperatures decreased by about 10 K, when the quenching rate was increased 10 times as large as its initial value. The reason was explained by considering the degree of order in the beta-phase. The primary α- and γ2-phases do not precipitate even during air-cooling on quenching in the alloys with 11.77 and 11.88%Al, being close to the eutectoid composition. Therefore, no remarkable change in martensitic transformation temperature with reducing quenching rate was observed in these alloys. In other words, it can be concluded that these alloys are suitable for heat treatments in practice, where the specimens are cooled more slowly.View full abstractDownload PDF (484K) -
Yoshito Takemoto, Moritaka Hida, Akira Sakakibara1995 Volume 59 Issue 8 Pages 780-787
Published: 1995
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSTi-14 mass%Mo alloys aged for 1×106 s at 623 K were deformed by means of a tensile test at 300, 523, 623 and 723 K in Ar atmosphere or of rolling at room temperature in order to investigate the brittle fracture mechanism related to the ω phase. These deformed specimens were observed by optical and transmission electron microscopy. Both deformed structures consisted of many band-like products. In the products, very few ω particles could be found. Instead, zones having a structure different from ω, β and α phases existed. It was found that these zones possessed a body centered triclinic structure, which was newly named β″ on account of the structural similarity to the β phase. The β″ was transformed from ω by deformation. In the transformation process to β″, one ω variant changed into two types of β″; one was closely related to the β matrix, and the other had a {112}⟨111⟩ twin relation to the former. It is suggested that the band products act as a path of crack propagation prior to the brittle fracture in the aged Ti-Mo alloy.View full abstractDownload PDF (1858K) -
Hiroyuki Ogawa, Yoichi Nishino, Shigeru Asano1995 Volume 59 Issue 8 Pages 788-792
Published: 1995
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSMechanical responses of carbon-fiber-reinforced SiC ceramics before fracture were measured in the strain range below 2×10−3 by two experimental methods: mechanical hysteresis and internal friction. Load-deflection curves were obtained by the three-point bending deformation in loading-unloading cycles. A little permanent strain was found after the first cycle even in the range where fracture never occurred. A closed hysteresis loop was observed after several cycles and stabilized with a symmetrical shape after more than twenty cycles. Such a stabilized hysteresis loop is attributed to the steady-state microplastic deformation and may cause the amplitude-dependent internal friction.
Internal friction was measured in the fundamental mode of free-free resonant vibration as a function of strain amplitude. With increasing the amount of prestrain in the bending deformation, internal friction increased and became sensitive to the strain amplitude. The amplitude-dependent internal friction in the composites is considered to originate from fiber pull-out or microcrack propagation. The internal friction data were analyzed on the basis of the microplasticity theory and converted into the plastic strain expressed as a function of stress. Therefore, it becomes possible to non-destructively study the forerunning process of fracture of the fiber-reinforced ceramics.View full abstractDownload PDF (468K) -
Yasuhide Shindo, Tomoyuki Kobori, Katsumi Horiguchi, Eiichi Yamada, Hi ...1995 Volume 59 Issue 8 Pages 793-798
Published: 1995
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThis paper discusses fracture toughness and temperature rise for JJ1 austenitic stainless steel forged plate at liquid helium temperature for fusion reactor magnets of next generation. Elastic-plastic fracture toughness (JIC) testing was conducted in general accordance with ASTM standards E813-81 and E813-87, and unloading-compliance technique was applied using compact specimens 25.0 mm and 12.5 mm thick. Thermocouples were used to measure the temperature rise near the crack tip. The effects of specimen size and side-groove on the cryogenic fracture properties of this alloy are examined. Examination of the fracture surface of CT specimens by scanning electron microscopy showed ductile failure by microvoid coalescence. The effect of inclusion on fracture mechanics parameters (JQ, JIC) is also discussed using energy dispersive X-ray analyser.View full abstractDownload PDF (618K) -
Masao Morishita, Momonori Murase, Koichiro Koyama1995 Volume 59 Issue 8 Pages 799-805
Published: 1995
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe phase diagram of the LiCl-KCl-MgCl2 ternary system in low MgCl2 composition was determined by the hot thermo-couple method and the differential thermal analysis in order to find the molten salt electrolyte with a low melting temperature for deposition of magnesium on the zinc-plated steels. A ternary eutectic point, E, was found at 55 mol%LiCl-40 mol%KCl-5 mol%MgCl2 and 596 K which was 97 K lower than the melting point of zinc. Furthermore, a ternary peritecto-eutectic reaction was found at 9 mol%LiCl-63 mol%KCl-28 mol%MgCl2 and 675 K. Molten salt having the composition around the eutectic point, E, is expected to be a good candidate as the electrolytic bath for electrodeposition of magnesium on the zinc-plated steels.View full abstractDownload PDF (878K) -
Zhongda Yu, Kusuhiro Mukai1995 Volume 59 Issue 8 Pages 806-813
Published: 1995
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSA method to measure surface tension of a liquid was developed from the analyses of the observed static shape of meniscus formed along a vertical cylindrical rod which was dipped in the liquid in a cylindrical crucible. This method enables us to measure surface tension of the liquid in static state for the case where contact angle between the liquid and the rod is smaller than 90°.
Simultaneously, the density of the liquid can be also measured from the observed shape of a cylindrical crucible and that of the liquid above the crucible.
An apparatus for measuring the surface tension and density with this method was constructed, and it was confirmed to have a high precision and reliability for the measurements in the range from room temperature to 1673 K by using water and liquid B2O3.
By using the apparatus, the surface tension and density of FetO-SiO2-Al2O3 slags were precisely determined at 1673 K under an argon atmosphere in a strictly sealed chamber.
Thus, this method and apparatus can be widely used to measure precisely the surface tension and density of liquid oxides in the static state and controlled atmospheres.View full abstractDownload PDF (869K) -
Seiji Yokoyama, Katsuyoshi Saito, Naoto Ito, Masahiro Kawakami1995 Volume 59 Issue 8 Pages 814-820
Published: 1995
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSAs a fundamental study of evaporation rate of molten metal in cold gas stream, molten iron was evaporated in argon flow with the levitation melting method. In this experiment, an ultrafine particle was formed in vaporizing the molten iron. Therefore, the effects of temperature (2173∼2273 K) of the molten iron and gas flow rate (0.167∼2.50×10−4 m3·s−1 (STP) on the evaporation rate and the distribution of particle size were investigated.
Since a temperature gradient existed around levitated iron under the present experimental conditions, the evaporation rate was analyzed by the model that iron vapor was nucleated homogeneously in the boundary layer. Furthermore, the absorption of impurities in argon, such as oxygen, was also discussed because the content of oxygen in the levitated iron increased.
The results obtained were summarized as follows:
(1) The evaporation rate increased with increasing temperature and gas flow rate. The rate was well explained by the model.
(2) The ultrafine particles were of α-Fe and Fe3O4. Its mean particle size was ca. 50 nm and unaffected by the experimental conditions.
(3) Since the iron vapor and/or condensed particle reacted with the impurities in the boundary layer, the partial pressure of oxygen on the levitated iron had a tendency to decrease with increasing evaporation rate.View full abstractDownload PDF (664K) -
Hidehiko Kamide, Kenji Fujitsuka1995 Volume 59 Issue 8 Pages 821-826
Published: 1995
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe relationship between the exposed area and the dissolution depth of α′ martensite of type 304 stainless steel was studied to clarify the dependence of stress corrosion cracking susceptibility of 304 stainless steel on the NaCl concentration of 2.5 kmol/m3 H2SO4 solutions.
The time to failure of 20% prestrained specimen showed the highest SCC susceptibility at the NaCl concentration of 0.4 kmol/m3. The number of cracks and the crack depth decreased with increasing NaCl concentration.
The dissolution tests of α′ martensite induced by sub-zero treatment in liquid nitrogen were conducted in 2.5 kmol/m3 H2SO4-(0.4∼2.0) kmol/m3 NaCl solution at Ecorr+50 mV (vs SCE). The exposed area of α′ martensite was measured by an image analysis computer and its dissolution depth was measured by using the focus of an optical microscope. The dissolution depth increased linearly with the logarithm of the exposed area at each NaCl concentration. The critical exposed area for corrosion initiation was estimated from this linearity by extrapolating to the dissolution depth of zero. This area decreased with decreasing NaCl concentration and at the concentration of 0.4 kmol/m3 after 14.4 ks was smaller than the exposed area of strain induced α′ martensite. This behaviour was dependent upon corrosion resistance of the steel in each solution.
The results show that SCC crack in this system initiates when the critical exposed area of α′ martensite which depends upon the chemical composition of both the steel and the solution is smaller than the exposed area of strain induced α′ martensite.View full abstractDownload PDF (669K) -
Masayuki Itagaki, Tatsuo Suzuki, Kunihiro Watanabe1995 Volume 59 Issue 8 Pages 827-832
Published: 1995
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe kinetics of transpassive dissolution of the Mo electrode has been investigated using electrochemical impedance spectroscopy (EIS). Nyquist plots of impedance responses conrresponding to transpassive dissolution of Mo in aqueous alkaline solutions (pH10∼12) show a capacitive loop at −0.4V∼−0.1V vs. SSE and an apparent Warburg impedance above 0 V. A theoretical model is proposed that takes into account the electrochemical reaction at the metal/electrolyte interface and the diffusion of dissolved Mo (VI) ions. The comparison of the theoretical electrochemical impedance with experimental data leads to the conclusion that not only electroshemical reaction at the interface but also diffusion process of dissolved species determine the total reaction rate above 0 V. The surface concentration of Mo (VI) ions calculated by the present theoretical model is more than 102 mol/m3, when the diffusion process influences the electrochemical impedance responses and polarization curves.View full abstractDownload PDF (524K) -
Keizo Hosoya, Katsuhisa Sugimoto1995 Volume 59 Issue 8 Pages 833-839
Published: 1995
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSSurface films on iron formed in methanol solutions containing various amounts of water with or without 0.1 kmol/m3 LiClO4 have been analyzed by in-situ ellipsometry and ex-situ XPS. It was found that surface films having refractive indices n2 and absorption coefficients k2 in the range of 1.8∼2.2 and 0.25∼0.3, respectively, are formed on iron at potentials of the passive state. The values of n2 and k2 for passive films on iron obtained in the methanol are smaller than those of passive films formed in aqueous solutions. The refractive index n2 of the surface film on iron in the methanol became larger with increasing water or dissolved oxygen content. In the deaerated methanol with the water content less than 0.07%, a surface film having a refractive index of 1.7 was formed on iron, and XPS spectrum of this film showed a spectrum which was similar to that obtained from iron methoxide Fe(OCH3)3 powder. By the addition of water or oxygen into methanol and also by anodic polarization, the surface film changed from an iron methoxide to an iron hydroxide or oxide. The above mentioned increase of refractive index is considered to be due to the oxidation from a ferrous methoxide to a ferric hydroxide or oxide. Therefore, the passivation of iron in methanol is thought to be brought about by the oxidation of the ferrous methoxide by water or dissolved oxygen.View full abstractDownload PDF (674K) -
Noboru Akao, Eiji Shimizu, Katsuhisa Sugimoto1995 Volume 59 Issue 8 Pages 840-845
Published: 1995
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSCorrosion behavior of sputter-deposited TbFeCo magneto-optical recording films with protection coating has been studied in an aqueous solution. Specimens having Si3N4 (0∼234 nm)/Tb0.33Fe0.48Co0.19 (74 nm)/glass structure were prepared and an immersion corrosion test and an electrochemical impedance measurement of the specimens were performed in 1.0 kmol·m−3 Na2SO4 of pH6.30.
The corrosion morphology of the specimens in the solution was pitting, which started from pinhole defects in Si3N4 protection films. The morphology changed with the thickness of the protection films. The selective dissolution behavior of alloying elements in TbFeCo films into the test solution also changed with the thickness of the protection films.
Electrochemical impedance diagrams changed with the progress of pitting corrosion on the specimens. After an analysis using an electrical equivalent circuit of the corroding system, the values for the charge transfer resistance and the relaxation coefficient were found to decrease with the growth of pitting corrosion.View full abstractDownload PDF (610K) -
Takehiro Dan, Kohmei Halada, Yuji Muramatsu1995 Volume 59 Issue 8 Pages 846-850
Published: 1995
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSBoth profile fitting and curvature plotting methods have previously been submitted as new image processing techniques in the sessile drop method by the authors. The purpose of this research is to elucidate the characteristics and the applicable limits of these data processing methods (including the traditional Bashforth and Adams method) and in turn submit a guide to their choice. Both theoretical sessile-drop profile as a solution of Laplace equation and sessile drop profile from the present experiment are processed by the above methods. As a result, the precision and the optimal applicable range of these methods are discussed.
The results obtained are as follows. (1) Under the present processing conditions, the precision of the profile determination is estimated to be ±1.3 μm. This value is comparable to that obtained with an optical projecting magnifier which is usually used in the traditional Bashforth and Adams method. (2) The error in the data processing through the use of the profile fitting method is determined to be less than 0.1%, independent of the number of profile data points (more than 130 points). (3) The precision of the presumed β-value, which was defined by Bashforth and Adams, by the curvature plotting method is dependent on the number of profile data points definitely. However, the curvature plotting method is optimal in order to inspect a local little change in the sessile drop profile. (4) The traditional Bashforth and Adams method is very simple and requires only a few measuring points. However, it is apparent that the confirmation of fitting of an experimental profile with a recalculated profile from the obtained β-value is indispensable. (5) The surface tension of an Au20 at%-Ag80 at% alloy at 1375.15 K in Ar-7 vol%H2 atmosphere was determined to be 914.0 mN/m. This value was in good agreement with the reference data.View full abstractDownload PDF (731K) -
Saburou Ohtani, Masanori Watanabe, Nobuya Iwamoto1995 Volume 59 Issue 8 Pages 851-856
Published: 1995
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSTo solve the problems such as shallow and nonuniform distribution of implanted atoms, implantations with a low acceleration voltage ranging from 200 to 2000 V into Fe, Fe-9 at%Ti and Fe-19 at%Ti evaporated thin films held at the temperatures ranging from 270°C to 400°C were conducted. The effects of substrate temperatures, the implantation energies and current densities on the depth profiles of implanted nitrogen atoms were examined using secondary ion mass spectroscopy. Binding energies of N 1 s electron and crystal structures of the implanted layers were also examined using X-ray photoelectron spectroscopy and X-ray diffraction, respectively. When the substrates were kept at 300∼400°C, the redistribution due to the diffusion effect of the implanted nitrogen atoms was observed even when the energy as low as 1000 eV was used. Although the nitrogen atoms implanted in the Fe thin films showed nonuniform distribution, almost homogeneous and deep distributions of the nitrogen atoms were obtained in the case of the Fe-9 at%Ti thin films. This can be attributed thermodynamically to the preferential binding between titanium and nitrogen atoms. It was, however, recognized that the depth profiles of the nitrogen atoms implanted into the Fe-19 at%Ti thin films became shallower than those into the Fe-9 at%Ti thin films. It can be considered that the reason why the diffusing movement of the implanted atoms occurred at a lower temperature than that of ion-nitriding treatment is due to nonnecessity of the nitride formation at the substrate surface by forcing direct implantation of nitrogen atoms into surface layers.View full abstractDownload PDF (499K) -
Motonori Tamura, Naoki Okumura1995 Volume 59 Issue 8 Pages 857-861
Published: 1995
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSSeveral effects of energetic ions on formation of Ti-C-N films were observed. Mass spectroscopic analysis showed that Ti+, ions were major ions in the process of ion plating activated by arc discharge. This suggested Ti-C-N formed on the surface of substrates by a reaction of Ti+, N2 and C2H2. Adhesion of films at low temperature (200°C) ion plating was improved more than twice by ion impact at the early stage of deposition. The ion impact induced high density defects, as were observed at the interface of substrates in width of 0.05 μm. High values of film hardness were obtained by ion plating. The grain size of the hard film deposited by ion plating was 10 times smaller than that by vacuum evaporation. The grain size could be affected by the number of nucleation sites on the substrates created by ion bombardment. Effects of energetic ions on the film formation such as re-evaporation of adsorbed atoms, migration, nucleation, chemisorption reaction, and densification in the early states of deposition were discussed.View full abstractDownload PDF (682K) -
Toshiya Kinoshita1995 Volume 59 Issue 8 Pages 862-868
Published: 1995
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe relationship between fracture toughness and bending strength in Si3N4 ceramics was studied. Three-point bending tests were carried out. The fracture toughness was estimated by the single edge precracked beam method. Grain morphology was observed using transmission microscopy.
The fracture toughness increased with grain growth. The strength increased with fracture toughness up to KIC=7 MPam0.5 and decreased in spite of increasing fracture toughness over 7 MPam0.5.
The linear elastic fracture mechanics is not applicable to small cracks in ceramics. Because of this, the effective crack size for fracture is not equal to the original equivalent crack length. In order to elucidate the fracture toughness-strength relation, the effective crack size must be estimated. In the previous work, the tendency in the crack size-strength relation was explained by adding a material-dependent constant to the original equivalent crack length. But this constant was not related to the physical process of fracture and was calculated according to the experimental results. In this study, the effective crack size of fracture origin was estimated experimentally and the fracture toughness-strength relation was investigated using the effective crack size.
The increase in strength up to 7 MPam0.5 resulted from a constant effective crack size. The decrease in strength over 7 MPam0.5 was due to both the increase in fracture toughness by the R-curve behavior and the increase in effective crack size.View full abstractDownload PDF (1675K) -
Takehiro Ishizuka, Yoriko Ohta, Kenji Wakashima1995 Volume 59 Issue 8 Pages 869-877
Published: 1995
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSIn an effort to obtain a reasonable fracture criterion necessary for a micromechanics-based approach to the design of ceramic-metal “functionally graded materials,” disk-bending tests have been carried out for a series of zirconia (PSZ: ZrO2-2 mol%Y2O3) particle-reinforced nickel (Ni) matrix composites fabricated by hot-press consolidation of PSZ-Ni powder mixtures with several different compositions (0, 20, 40, 60, 80 and 100 vol% PSZ). Disk-shaped samples of typical dimensions 20 mm dia.×1 mm are radially “four-point” bent at room temperature; it is thereby found that the samples containing PSZ over 40 vol% fracture by radial cracking under equibiaxial loading. The convex-face tensile strains at fracture of these samples are determined by assuming a simple geometry of spherical bending; the corresponding fracture stresses in PSZ particles are calculated with a micromechanics-based method which takes account of the plasticity of the Ni matrix. The results are analyzed on the basis of a fracture-mechanics criterion in terms of the energy release rate for a penny-shaped crack under multiaxial loading. An equivalent normal stress σneq is then defined as σneq=\sqrtσn2+τ2⁄(1−0.5ν)2, where σn and τ are the normal and shear stresses acting on the crack surface and ν is Poission’s ratio. It is found that fracture occurs when the maximum value of σneq in PSZ particles reaches a constant level. Scanning electron microscopic observations give evidence of this particle cracking-controlled fracture.View full abstractDownload PDF (1632K) -
Hisashi Mori, Manabu Enoki, Nobuo Takeda, Teruo Kishi1995 Volume 59 Issue 8 Pages 878-879
Published: 1995
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSDownload PDF (196K)
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