All issues
Volume 58, Issue 12
Displaying 1-18 of 18 articles from this issue
- |<
- <
- 1
- >
- >|
-
Hiromi Miura, Taku Sakai1994 Volume 58 Issue 12 Pages 1349-1354
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSHigh-temperature deformation and fracture behavior of Cu-SiO2 bicrystals with different misorientation angles of 8° and 30°, and SiO2 volume fractions of 0.43% and 1.7% were studied. Though typical intermediate-temperature embrittlement was observed in all the bicrystals, their deformation and fracture behavior depended strongly on the misorientation angle and the volume fraction. The elongation to fracture decreased and the temperature range of low ductility became wider with increase in misorientation angle. The strength increased with increasing volume fraction. Although the elongation to fracture in the 8° bicrystal decreased with increasing SiO2 volume fraction, the elongation to fracture in the 30° bicrystal was almost constant independent of SiO2 volume fraction. These differences in deformation and fracture behavior were reasonably understood by considering the dependence of grain-boundary sliding and stress relaxation on the grain-boundary character.View full abstractDownload PDF (1450K) -
Fukuji Inoko, Kazuyuki Kawakami, Dong Cheng Zhang, Toshiyuki Hirano, K ...1994 Volume 58 Issue 12 Pages 1355-1363
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSBehaviour and mechanisms of recrystallization at grain boundaries were investigated on stoichiometric Ni3Al which was unidirectionally solidified by a floating zone method. Two specimens were deformed in tension to the two strains of about 0,17 and 0.28, and then were annealed at 1173 K for 3.6×103 s and 7.2×103 s, respectively. Recrystallized grains were formed by two kinds of mechanisms preferentially along the grain boundaries. The strain induced boundary migration (SIBM) mechanism can operated where dislocations with edge components impinged and piled up against the grain boundary. The other is the ⟨111⟩ rotation mechanism along the grain boundary where dislocations with screw components impinged and piled up. These results are similar to those in aluminum and copper, especially copper bicrystals.View full abstractDownload PDF (1760K) -
Tomoshi Takahashi, Akihiro Takahashi, Hideki Araki, Toshiki Tanaka, Yo ...1994 Volume 58 Issue 12 Pages 1364-1371
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe interdiffusion coefficients in the α fcc phase of Al-Cu-Mg alloys have been determined under pressures from 0.101 to 3000 MPa in the temperature range from 793 to 853 K. The direct and indirect interdiffusion coefficients are positive. The diffusion coefficients decrease with increasing pressure. The activation energies for interdiffusion and impurity diffusion increase with pressure. The ratios of the activation volumes to the molar volume of aluminum are between 1.01 and 1.08. It is concluded that the diffusion of copper and magnesium in the Al-Cu-Mg alloy occurs predominantly by the monovacancy mechanism.View full abstractDownload PDF (900K) -
Moritaka Hida1994 Volume 58 Issue 12 Pages 1372-1379
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe so-called mechanical agitation allows a material system the effective restraint and relaxation which cause some mechanically stimulated reactions (MSR), e.g. mechanical alloying, and it draws the system in a certain dissipative structure. From the common phenomena in the various experimental results belonging to MSR, it can be pointed out that the gradient of plastic strain is a reasonable variable (xr) as that of the thermodynamic intensive variables, in order to express the dissipative function related to the rate of excess entropy production. According to the idea a simple function taking in the thermal activation process is proposed as the evolutional equation (dxr⁄dt) for the non-equilibrium state accomplished by the chemical reaction (r). The hierarchy of phase transformation composed by MSR in the system is qualitatively discussed while considering the behavior of the steady state solution.View full abstractDownload PDF (1609K) -
Kenichi Takai, Jun’ichi Seki, Goro Yamauchi, Yoshikazu Homma1994 Volume 58 Issue 12 Pages 1380-1385
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSHydrogen and deuterium trapping sites in high-strength steels have been observed by secondary ion mass spectrometry (SIMS). High-strength steels with 1400 MPa tensile strength are loaded and dipped in D2O and 20% NH4SCN solution at 323 K to occlude hydrogen and deuterium. As a result, the depth profiles by SIMS show the presence of deuterium means hydrogen trapping site occluded during delayed fracture test. Secondary ion-image analysis by SIMS has made possible to observe hydrogen and deuterium trapping sites in high-strength steels. Hydrogen tends to accumulate at grain boundaries, in segregation bands, and in inclusions. Line scans by SIMS show that the concentration of hydrogen is 7.8 times as high at grain boundaries as in the matrix, 5.0 times as high in the segregation bands, and 11 times as high in the inclusions. Hydrogen trapping sites at grain boundaries can be observed by measuring after the delayed fracture test as soon as possible.View full abstractDownload PDF (603K) -
Susumu Ikeno, Hideki Murase, Kenji Matsuda, Hiroshi Anada, Shizuo Tada ...1994 Volume 58 Issue 12 Pages 1386-1392
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSAged-hardened Al-1 mass%Mg2Si-0.4 mass%Si alloys were deformed by a tensile testing machine and changes in surface topographies near grain boundaries with deformation were examined by Scanning Tunneling Microscopy (STM).
Both the steps at grain boundaries and the slidings of grain boundary parallel to the specimen surface increased with the amount of deformation. In many cases, such steps and slidings were generated independently at grain boundaries. In a few cases, they were observed simultaneously at three adjacent grain boundaries.
When either a step or a sliding occurred at a grain boundary, a fold was yielded at the triple point. The only exception that the fold formation at the triple point is not yielded, was the following cases where the steps were generated simultaneously in the same direction at two adjacent grain boundaries.
When deformation bands with surface undulation like stairs impinged on a grain boundary, the anomalous amount of displacement were observed at the grain boundary. This was due to the superimposition of an intrinsic grain boundary step and the undulation of deformation bands.View full abstractDownload PDF (966K) -
Hiroshi Tsuda, Manabu Enoki, Teruo Kishi1994 Volume 58 Issue 12 Pages 1393-1400
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSIt is well known that the reinforcing fibers used in ceramic matrix composites have a wide strength distribution so that the continuous fiber breaking occurs during tensile loading. The fracture process analyses have been rarely reported although the ultimate strength prediction theories in which the fiber strength scatter is considered have been proposed. In the present study, the Nicalon SiC fiber-reinforced Pyrex composites with various fiber coating thicknesses were used as test materials. The extracted fiber tensile tests as well as the composite tensile tests were performed. The fracture process of these composites was theoretically analyzed using probabilistic fracture models. As a result, the measured ultimate strength agreed well with the predicted ultimate strength from the model considering only bridging mechanism. The influences of the fiber strength scatter on the toughening mechanisms were also analyzed. The bridging mechanism proved to dominate the toughening of fiber-reinforced ceramic composites.View full abstractDownload PDF (1335K) -
Koichiro Koyama, Tomohiro Harada1994 Volume 58 Issue 12 Pages 1401-1407
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe phase relationships in the Fe-Mo-O system in the solid state, which are necessary to determine thermodynamic quantities of the Fe-Mo and Fe-Mo-O systems by the electromotive force method using an oxide solid electrolyte, were determined by X-ray diffraction analysis and electromotive force measurements in the temperature range from 1173 to 1473 K. The αFe(Mo)-Fe3Mo2-Fe2Mo3O8 three phase equilibrium at low temperatures changes to the αFe(Mo)-Fe3Mo2-Fe2MoO4 three phase equilibrium at 1230 K ± 4 K. FeMoO3 does not exist at around 1273 K. At 1173 K, the FeMoO4-Fe2Mo3O12-MoO3 three phase equilibrium is incorrect, and the FeMoO4-Fe2Mo3O12-MoO2 three phase equilibrium is correct.View full abstractDownload PDF (772K) -
Shinji Hirai, Hiroshi G. Katayama, Hideo Kanisawa1994 Volume 58 Issue 12 Pages 1408-1413
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSIn order to inprove the corrosion resistance to chloride-containing aqueous solution of steel for concrete reinforcement, an attempt were made to form a low Al alloyed layer on steel surface by the powder packing method using a mixture of Al2O3 and Mg powders. The surface Al concentration and the thickness of alloyed layer increased with the increase of the treating temperature and time and Mg content in the powder mixture. In the case of the powder mixture containing SiO2, the surface Al concentration and the thickness of the alloyed layer decreased with the increase of SiO2 content. On the other hand, the surface Si concentration increased with SiO2 content up to 5 mass%SiO2 and then decreased. The anodic polarization tests showed a corrosion potential of −430 mV, a current density for maintaining the passive state of approximately 7 μA·cm−2, and a pitting potential of +600 mV for the specimen having the surface composition of about 10 mass%Al. The corrosion potential increased and the pitting potential declined when the surface Al concentration was increased or decreased. In the case of a low Al-Si alloyed layer containing 4.8 mass%Al and 1.8 mass%Si, the pitting potential was almost the same as that of the low-Al alloyed layer, but the current density for maintaining the passive state was remarkably lower. In tensile and bending tests, it was found that an alloyed layer having the surface composition of about 10 mass%Al did not degrade the mechanical properties of the parent material and that it had excellent adhesion with the parent material. An alloyed layer could be formed even by heating specimen in no contact with the powder mixture. From this fact, it is concluded that Al2O and SiO vapors produced in the powder mixture is reduced by Mg vapor on the surface of the specimen, forming the alloyed layer.View full abstractDownload PDF (1885K) -
Hidehiko Kamide, Kenji Fujitsuka, Yuichi Tanaka1994 Volume 58 Issue 12 Pages 1414-1419
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSMeasurement of dissolution rates of prestrained austenite and α′ martensite of 304 stainless steel was done to study a role of carbon during plastic deformation in stress corrosion cracking.
The dissolution rate of solution treated austenite of 18Cr-11Ni stainless steel was not affected by carbon contents but that of α′ martensite was decreased with increasing carbon content in a 2.5 kmol/m3 H2SO4-0.4 kmol/m3 NaCl solution. But the dissolution rate of prestrained austenite increased with increasing dislocation density and the dissolution rate of high carbon austenite showed a lower value than that of low carbon austenite at high dislocation density sites. In addition, the dissolution rate of α′ martensite existed on the extended line of the relationship between the dissolution rate and the dislocation density of austenite. Therefore, the preferential dissolution of α′ martensite is attributed to the high density of dislocations. On the other hand, EPMA linear analysis showed that Ni and Cr concentration were not changed but carbon was enriched on the surface of α′ martensite which held high dislocation density after the corrosion test.
It is thought that carbon is enriched at the region of high dislocation density and it depresses the dissolution rates of high prestrained austenite and α′ martensite, and, therefore, the decrease of dissolution rates with carbon enrichment at slip steps or crack tips is one of the factors to decrease the stress corrosion cracking susceptibility.View full abstractDownload PDF (559K) -
Motoi Hara, Tokiko Nakagawa, Yoshiyuki Sato, Kunihiko Yamaguchi, Yutak ...1994 Volume 58 Issue 12 Pages 1420-1428
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe photopotential vs. time curves and photoelectric polarization curves of copper oxide films formed by high temperature oxidation were measured in Na2SO4 solutions of various pHs. Particular attention was given to the difference in these curves between CuO(outer)/Cu2O(inner) film and Cu2O single film. The signs of photopotentials for the CuO/Cu2O films were independent of solution pH, and were positive. On the contrary, those of the Cu2O film varied, depending on the pH region of the solution, that is, the signs observed in the solutions at pH2∼5 were positive, whereas those at pH5∼12 were negative. A relatively large photocurrent of the CuO/Cu2O film was observed as a cathodic current, while the anodic photocurrent of the film was hardly observable. In contrast, both anodic and cathodic photocurrents were observed for the Cu2O film. It was found that in the solutions of pH2∼12, flat-band potentials of the CuO/Cu2O films were higher than those of the Cu2O films. It was observed for both oxide films that the relative height between the flat-band potential and the rest potential determines the sign of photopotential. Such a difference in photoelectrochemical behavior between the two films was explained in terms of the energy-band model in the vicinity of the oxide surface.View full abstractDownload PDF (1047K) -
Tetsuo Yano, Toshihiko Ooie, Masafumi Yoneda, Munehide Katsumura1994 Volume 58 Issue 12 Pages 1429-1435
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSMo films were deposited by an excimer laser ablation method under different conditions of laser fluences and target-substrate distances. Their surface morphology was observed with scanning electron microscopy (SEM). We also examined the adhesion of Mo films deposited on the substrate with an ion beam preirradiation. Spectroscopy of Mo plume was carried out. The main results obtained are as follows.
(1)The adhesion of the Mo films is improved by ion beam irradiation which removes thin surface layer on a substrate.
(2)Smooth surface of Mo films without droplet is successfully formed under the conditions of laser fluences of less than 0.25 MJ/m2, target-substrate distances of longer than 40 mm, and with a target rotation.
(3)Mo films with a b.c.c. structure show the (110) preferred orientation of ⟨110⟩.
(4)Mo plume generated by laser ablation is in an excited state containing Mo+.View full abstractDownload PDF (2159K) -
Toshio Yamauchi, Yoshinori Nishida1994 Volume 58 Issue 12 Pages 1436-1443
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSIn order to make the infiltration mechanism clear, pressure changes and ram speeds were measured when SiC whisker reinforced JIS-AC8A (Al-12%Si-1%Cu-1%Mg-1%Ni) alloy composites were fabricated by squeeze casting. The deformation of SiC whiskers preforms occurred due to compressive stress during infiltration by the aluminum alloy. To analyze the correlation between applied pressure and the location of infiltration front in the preform, the hardness along the infiltration direction in the composite was measured and the distribution of SiC whisker volume fraction was calculated by the distribution of hardness.
A theoretical expression including solidification is derived to describe the fluid flow in the preform during the infiltration on the assumption that the pressure on the preform surface starts to rise from zero and when the applied pressure exceeds the compressive strength of preform, deformation starts. The starting point of deformation of preform and the distribution of volume fraction in the composites can be calculated by the theory.View full abstractDownload PDF (1827K) -
Nobuyuki Mori, Keisaku Ogi1994 Volume 58 Issue 12 Pages 1444-1453
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe growth mechanism of 123 crystals is investigated to explain how the 123 (YBa2Cu3O7−x) columnar crystal grows with a facet interface from liquid+211 (Y2BaCuO5) through a peritectic reaction with solute diffusion in liquid. The following relation is conducted between 123 growth rate (R) and undercooling (ΔTpc=Ti−Tp, Ti: interface temperature, Tp: peritectic temperature) by the analysis of kinetics for 123 crystal growth, which occurs by sequential three primitive processes: (1) growth of the 123 phase, (2) melting of the 211 phase, (3) diffusion of solute in liquid.
R=(Ca⁄η)·{(ML·ΔTpc+ΔCrc)⁄(Tp⁄mL123+Cf·Tp⁄mL211)}2, where Ca is a constant, η is the viscosity, ML=1⁄mL123−1⁄mL211, mL123 and mL211 are the gradients of liquidus of 123 and 211, ΔCrc is the change in equilibrium solute concentration caused by surface energy of 211 particles at the 123 freezing front, Cf is a constant. This relation agrees well with the experimental results.
The following approximate relation is also obtained between the maximum radius (r) of 211 particles which melts in the diffusion layer and the distance (Xd) from the 123 freezing front.
r=(2Γ⁄mL211)⁄[{Cb·Xd⁄(Tp−ΔTpc)}·{(ML·ΔTpc+ΔCrc)⁄(Tp⁄mL123+Cf·Tp⁄mL211)}2+ΔCrc], where Cb is a constant, Γ is the Gibbs-Thomson coefficient.
The transition of 123 crystals from the columnar to equiaxed structure is successfully simulated by using the above R-ΔTpc relation and the experimental result on undercooling (ΔTp) for the nucleation of 123 crystals.View full abstractDownload PDF (1410K) -
Kikyung Song, Toshifumi Kikuchi, Makoto Yoshida, Hideo Nakae1994 Volume 58 Issue 12 Pages 1454-1459
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSA new technique for the measurement of the interfacial energy between an Al-Si eutectic melt and solid Si was proposed, based on the equilibrium dihedral angle at the Si grain boundary. Pure Si having one right angled grain boundary at the surface was used as for the solid sample. And as for the liquid sample, pure Al and Al containing 0.16 mass%Sr were adopted.
A liquid sample was placed on the Si and heated in a vacuum. Just after melting of the liquid sample, the temperature of the sample was cooled to 853 K rapidly and held for 5 h. From the grain boundary grooves, we measured the dihedral angles and calculated the interfacial energy between the Al-Si eutectic melt and solid Si. The dihedral angle changed from 79.6±5.1° to 63.2±4.7° with the addition of Sr. We confirmed that the decreasing rate in interfacial energy was more than 10% with the addition of Sr. This result supports the interfacial energy theory for the modification mechanism in Al-Si alloys.View full abstractDownload PDF (1692K) -
Kunimasa Takeshita1994 Volume 58 Issue 12 Pages 1460-1466
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSAluminum-iron alloys with Fe contents of 1.8, 2.4, 3.9, 5.1, 6.2, 7.7 mol% were rapidly solidified to foils with about 50 μm thickness and 6 mm width by the planar flow casting method.
Microstructural changes across the thickness of foils were investigated as a function of Fe content in aluminum. All the foils examined exhibit two zones: zone A on the substrate side of the foil with a slight etching response and zone B on the air side of the foil with a strong one. The foils with Fe contents of 5∼6 mol% have a maximum area fraction of zone A, the value of which is about 80% of the cross-sectional area of the foil. As for the foils with Fe contents of up to 6.2 mol%, the zone A region reveals the microstructure of a fine α-Al cell whose spacing is about 100 nm, while the zone B region reveals that of a coarse α-Al dendritic cell whose spacing is about 350∼1000 nm depending on Fe content. The zone A region of the foil with a Fe content of 7.7 mol% reveals the microstructure of a fine lamellar eutectic whose spacing is about 100 nm and the zone B region consists of primary spherical compounds surrounded by a coarser lamellar eutectic. It is found in all the foils regardless of Fe content that the spacings at the transition regions from zone A to zone B are approximately constant around a value of 220 nm which corresponds to the limit of resolution of a microscope used.
On the basis of the calculation of a solidification problem considering the kinetics of constrained cellular growth of α-Al, the origin of the microstructural change from a fine cell to a coarse dendritic cell is interpreted as a sudden drop in the heat transfer coefficient at the foil-substrate interface. Values of the heat transfer coefficient and of the initial undercooling at the onset of solidification are estimated through most suitably fitting the calculated results to the experimental ones.View full abstractDownload PDF (851K) -
Biing Hwa Yan, Der Chun Tsai1994 Volume 58 Issue 12 Pages 1467-1472
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSIn order to reveal the electrical discharge machining characteristics of electrical conductive alumina based ceramics, a series of EDM tests are carried out. The following main results are obtained. (1) The surface roughness of ceramics machined with negative polarity is larger than that with positive polarity. (2) When machining ceramics with small current, compared with positive polarity, the material removal rate of negative polarity is larger and the electrode wear ratio is smaller. But when machining with large current, the relation is reversed. (3) When machining with short pulse and negative polarity, the recast layer is thinner and almost no crack is observed because of the impact force caused between the workpiece and electrode is larger than positive polarity. (4) Compared with normal EDM, material removal rate machined with orbital motion of an electrode is higher, but the surface roughness and the electrode wear ratio are worse. But when the orbital distance of an electrode increases, the surface roughness and the electrode wear ratio are improved remarkably.View full abstractDownload PDF (1312K) -
Kazutoshi Toda, Tsuyoshi Mikami, Teruo Hoshino1994 Volume 58 Issue 12 Pages 1473-1478
Published: 1994
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSA typical damage of bearings used in contaminated lubricants is caused by increasing of shearing stress at dents due to harder wearing particles in the lubricants.
In this study, SUJ2 steel was used as the test material in which the amount of retained austenite and hardness were changed under various heat treatments. Rolling fatigue tests were repeated by the use of specimens having sharp dents intruded by a Vickers indenter. From the results of the rolling fatigue tests, the effect of the retained austenite on the fatigue life was investigated, considering the work hardening of the dent ridge.
The main results were obtained as follows.
(1) Retained austenite changed into martensite under rolling load and induced work hardening of the ridge, and then further shape changes of the ridges were virtually prevented.
(2) As the dent with ridge caused the flaking of the rolling surface that occurred under shearing stress, the optimizing amount of retained austenite must be found for rolling fatigue life.
(3) The upper amount of retained austenite was 20∼30 vol%, judging from the surface hardness, work hardening, life range and toughness.
Based on the present results, the taper roller bearings which were controlled 20∼25 vol% retained austenite in the surface layer (10 μm depth from surface) and the surface hardness of 800∼860 HV were made. These bearings showed 11.3 times longer life than the conventional ones in contaminated oil. It was proved that the retained austenite had a significant effect on the formation and elimination of these ridges.View full abstractDownload PDF (791K)
- |<
- <
- 1
- >
- >|