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Volume 62, Issue 8
Displaying 1-12 of 12 articles from this issue
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Motoi Hara, Michio Inoue, Tokiko Nakagawa1998 Volume 62 Issue 8 Pages 691-700
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe effect of trace of NaCl vapor on oxidation of Ti-6 mass%Al-4 mass%V alloy at 923 to 1073 K was investigated by measurement of mass change of specimens, observation and analysis of scales formed on the specimens. In O2 atmospheres containing NaCl vapor, the alloy was oxidized acceleratedly. An increase in concentration of NaCl vapor increased the oxidation rate of the alloy. Such an accelerated oxidation occurred at the temperatures above 973 K. Scales formed on the alloy after the accelerated oxidation consisted of rutile-TiO2. For a scale formed in O2 with 123.0 vol ppm NaCl vapor, V2O5 was observed in the vicinity of the scale/metal interface. These scales were porous, and contained voids. On the basis of the experimental results and a thermodynamical equilibrium discussion, a mechanism that NaCl vapor induced the formation of molten V2O5 to cause accelerated oxidation of the alloy was presented.View full abstractDownload PDF (3278K) -
Haruki Yamane, Juro Mita, Masanobu Kobayashi1998 Volume 62 Issue 8 Pages 701-707
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSA sensor element material for a new sensitive magnetic sensor was developed by a NiO spin-valve film. The magnetic sensor is composed of a multilayered structure that includes the spin-valve element and a bias current line. High sensitivity is obtained by using only the (rising or falling) edge of the magnetoresistive (MR) loop. An AC bias magnetic field induced by a square-wave bias current (plus or minus) is applied to the spin-valve element. The bias magnetic field is set to be slightly smaller than the rising field. The resistance of the spin-valve element is constant, if an external magnetic field is not applied. The output signal synchronizes with the input bias current, if the bias field is made to cross the rising edge of the MR loop by applying an external magnetic field. The spin-valve film: [NiO/NiFeCo/Cu/NiFeCo] exhibits the appropriate properties for the sensor element, such as a MR ratio of 5.1%, a sensing field of 0.2 kA/m, a driving field of 1.4 kA/m, an element destroying field of 32 kA/m and a high corrosion resistance. Moreover, the spin-valve element, patterned to a microscopic size, exhibits a step-shaped MR loop in which a free-layer magnetization switches like a single domain. The magnetic sensor using this spin-valve film detects an external field change of 0.04 kA/m.View full abstractDownload PDF (1471K) -
Yoji Mine, Shinji Ando, Hideki Tonda, Kazuki Takashima, Yakichi Higo1998 Volume 62 Issue 8 Pages 708-717
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe fatigue crack growth behavior of α-titanium single crystals has been investigated in laboratory air at room temperature. Six types of CT specimens A, B, C, D, E and F with different notch orientations were prepared. The notch plane and direction in the A-specimen were (1\bar210) and [10\bar10], and those in the B-specimen were (01\bar10) and [2\bar1\bar10], respectively. The notch plane of the C-specimen was (01\bar10) and that of the D-specimen was (1\bar210), and the notch direction of both the C- and the D-specimens was [0001]. In the E- and the F-specimens, the notch plane was (0001), and the notch directions were [10\bar10] and [2\bar1\bar10], respectively. The crack in the A- and the B-specimens propagates parallel to (01\bar10) [2\bar1\bar10]. Therefore, the crack is deduced to extend by alternating shear on two intersecting prismatic slip systems at the crack tip. The crack in the C- and the D-specimens propagates close to the basal plane which is perpendicular to the notch directions. This indicates that the fatigue crack is difficult to grow along [0001] compared with parallel to the basal plane. In the E- and the F-specimens, the crack propagates roughly parallel to the basal plane and the traces which correspond to {10\bar12} twin systems are found near the crack plane. Ridges parallel to ⟨10\bar10⟩, and traces and bands due to {10\bar12} twinning are observed on the fatigue surfaces. These results suggest that the crack growth might occur plausibly by the activation of micro-twins. A definite crystallographic dependence of fatigue crack growth behavior in α-titanium is obtained.View full abstractDownload PDF (5608K) -
Kenji Matsuda, Tomoo Yoshida, Tomomi Wada, Megumi Yoshida, Yasuhiro Ue ...1998 Volume 62 Issue 8 Pages 718-726
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe precipitation sequence and the behavior of two-step aging in the Al-1.0 mass%Mg2Si-0.4 mass%Mg (excess Mg alloy) alloy was investigated by hardness and electrical resistivity measurements, and high resolution transmission electron microscopy (HRTEM).
In the excess Mg alloy at the early stage of aging at 473 K, two types of precipitates were observed as reported previously. First, the random type precipitates which indicate the non-periodic arrangement of bright dots in its HRTEM image; Second, the parallelogram-type precipitates which indicate a parallelogram arrangement of bright dots in its HRTEM image. A number of the parallelogram-type precipitates appeared near the maximum value of the hardness (HVmax). In the over-aged condition, many β′ phase appeared and, especially, the parallelogram type precipitates having interior angles near 60° also were observed.
The HVmax in the excess Mg alloy aged at 473 K after pre-aging at 293 K for 6 ks was lower than that aged at only 473 K and this was a typical negative effect. The microstructure in this aging condition was coarse and there were a number of the random type precipitates with coarse β′ phase and cube-shaped phase. HVmax in the excess Mg alloy aged at 473 K after pre-aging at 343 and 423 K for 6 ks were higher than that only aged at 473 K and this was a typical positive effect. The microstructure in this aging condition was fine and there were a lot of the multilayer G.P. zones and the random type precipitates. These precipitates existed in the specimen just after pre aging at temperaturos higher than 343 K.View full abstractDownload PDF (6523K) -
Takao Takeuchi, Yoshihiro Nemoto, Hiroshi Maeda, Kikuo Itoh, Kiyoshi I ...1998 Volume 62 Issue 8 Pages 727-734
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe V3Si multifilamentary superconductor, which can be fabricated by controlling the diffusion reaction between V and Cu-Si solid-solution alloy, is promising as a new A15-type multifilamentary conductor for ac use, since it is possible to leave appropriately a normal-conducting V5Si3 layer as a high-resistivity barrier around V3Si filaments. In the present study, the flux pinning mechanism and the ac loss characteristics are investigated in correlation with metallurgical microstructure. Angular dependence of flux pinning force with respect to the field direction, for a flattened conductor, was well fitted to the proposed model in which two kinds of ellipsoidal-microstructure are mutually perpendicular and act as pining centers, respectively. We could thereby confirm that both the grain boundary and the superconducting(S)/normal conducting(N) interface act as the pinning centers. Elemental pinning force of the SN interface is 2∼3 times larger than that of grain boundaries. It was revealed that the V5Si3 layer is effective in suppressing the proximity coupling between filaments and hence to reduce the hysteresis loss.View full abstractDownload PDF (1728K) -
Hideo Awaji, Toshiya Kato1998 Volume 62 Issue 8 Pages 735-741
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe Griffith energy criterion for brittle fracture is extended to mode II and combined mode I-II fracture by postulating that crack extension occurs when the maximum energy release rate in non-coplanar crack extension is equal to the fracture energy rate required for the mode II or the combined mode crack extension. The fracture energy rate is considered to be proportional to the critical magnitude of the area of a frontal process zone at a crack tip for brittle materials. The area of the frontal process zone is simply assessed here from the area enclosed in the iso-stress contours of both the maximum principal stress and the maximum shear stress around a crack tip. The anticipated ratio of mode II and mode I fracture toughness, KIIC⁄KIC, is 1.20. The value of the ratio, KIIC⁄KIC, is also estimated experimentally for float glass using a disk test. The result shows that the value of KIIC⁄KIC is 1.28 which agrees quite well with the anticipated one.View full abstractDownload PDF (1055K) -
Katsumi Koyama, Goroh Itoh, Motohiro Kanno1998 Volume 62 Issue 8 Pages 742-747
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSSilver decoration technique was applied to high purity aluminum specimens with two impurity hydrogen levels to visualize the hydrogen atoms evolved from the specimen during tensile deformation. The specimens were deformed by about 5% in the silver decoration solution of K[Ag(CN)2]. A number of needle-shaped deposits indicating hydrogen evolution were revealed along coarse slip lines produced by the deformation. The deposits were identified by AES not as metallic silver but as AgCN crystals. The amount of the deposits was affected significantly by the impurity hydrogen content of the specimen and by pH and temperature of the silver decoration solution, but not markedly by K[Ag(CN)2] concentration in the solution. This new method using silver decoration technique is a relatively simple and valuable tool for the study of hydrogen embrittlement of metals and alloys.View full abstractDownload PDF (2560K) -
Satoru Ishihara, Norio Furushiro, Shigenori Hori1998 Volume 62 Issue 8 Pages 748-753
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSHigh-temperature deformation behavior of high-purity polycrystalline alumina (the mean grain size is about 6 μm) prepared with no additive was investigated. In the testing temperature range from 1400 to 1600°C, ductile deformation is obtained at a low strain rate. The ultimate compression stress in each test is decreased with the testing temperature and increased with the strain rate. The strain rate sensitivity is about 0.6 and the apparent activation energy is almost consistent with that of grain boundary diffusion of aluminum ion in the ductile deformation. Stress-enhanced grain growth and nucleation of cavities at grain boundary triple points were observed during the ductile deformation. The increase in area fraction of the cavity is proportional to the strain. It can be speculated that the cavities nucleate and growth at the triple point by nonaccommodated grain boundary sliding.View full abstractDownload PDF (1470K) -
Yoshitaka Adachi, Akira Seki1998 Volume 62 Issue 8 Pages 754-760
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSDiffusion induced recrystallization(DIR) has been studied by zincification of pure iron as well as interstitial free steel with particular attention on the local misorientation in grains caused by DIR. A change in microstructure was investigated as a function of annealing temperature from 723 K up to 963 K. Misorientation was measured using Electron Back Scattering Diffraction (EBSD) technique. Fine grains of ferrite nucleate on the surface of substrates considerably in the couples annealed at a higher temperature such as 963 K and complete a fine-grained surface layer. Boundaries between the fine grains are regarded as high angle boundaries since they are micro-etched strongly with the eventual formation of grooves along them. In contrast to the fine grains formed at a higher temperature, sub-grains form at a lower temperature such as 723 K and boundaries between sub-grains are regarded as low angle boundaries. The sum of local misorientation along a particular scanning direction, however, depends on the direction. The largest variation of misorientation in the original grains in which sub-grains caused by DIR exist is often observed along the scanning direction which terminates with high angle boundaries of original grains at least on one of its ends, while a smaller variation in misorientation is obtained along the direction which terminates with Σ or low angle boundaries on both ends. A possible interpretation of DIR is developed that the largest variation of misorientation leads high angle boundaries to be formed with the eventual formation of fine grains with high angle boundaries.View full abstractDownload PDF (3619K) -
Masahiko Kato, Hisaoki Sasano, Kazuhiro Honma, Toshiyuki Suzuki1998 Volume 62 Issue 8 Pages 761-765
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSInterdiffusion in single-phase NiAl was investigated using a vapor-solid diffusion couple in the temperature range between 1072 and 1572 K. Aluminum was diffused by a chemical transportation technique in which aluminum chloride was used as the carrier gas and consequently NiAl of high aluminum composition was formed on the surface of the NiAl substrate of low aluminum composition. The results obtained showed that interdiffusion coefficients at the temperatures above 1367 K are almost the same as already reported. However, it was found that the interdiffusion coefficients in the composition range around the stoichiometric NiAl at the temperatures between 1072 and 1324 K are extraordinarily small. Particularly, below 1123 K at which little is known, the composition dependence of the diffusion coefficients showed a completely different tendency from that at higher temperatures. The composition range became wider as the temperature decreased. Based on these experimental results, the possibility that a miscibility gap exists in a certain composition range of NiAl phase is discussed.View full abstractDownload PDF (1547K) -
Ken-ichiroh Igashira, Koji Nishio, Haruki Hino, Shozo Okazaki1998 Volume 62 Issue 8 Pages 766-773
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSSi-Ti-C-OF/SiC composites were fabricated by the polymer-impregnation pyrolysis (PIP) process. Before the PIP process, the fibers were coated with thin CVD-SiC or thin resin derived carbon. The composite with uncoated fibers was also prepared by the same PIP process for comparison. SEM and TEM observations and TEM-EDX analysis were performed to characterize the interfaces between fiber and matrix of three kinds of composites. The turbostratic carbon layer with a thickness of 20-200 nm was recognized between the fiber and the CVD-SiC layer in the composite with the CVDed-SiC fiber. Mechanical properties of three kinds of composites were compared by the tensile test, the 4 point bending test, and the Chevron notched beam bending test at room temperature. The composites with the surface treated fiber were much higher in strength and toughness than those with the untreated fiber. Especially for the composite with the CVD-SiC fiber, the tensile strength was 400 MPa, the flexure strength was 640 MPa, and the fracture toughness was 22 MPa·m1⁄2.View full abstractDownload PDF (4590K) -
Setsuo Aso, Shoji Goto, Yoshinari Komatsu1998 Volume 62 Issue 8 Pages 774-782
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSSlurry erosion rate (WS) generally depends on the slurry flow rate in a power law as follows,
(This article is not displayable. Please see full text pdf.)
\ oindentwhere k is a constant, V is a slurry flow rate and n is an exponent. The n-value usually falls between 2 to 3 for metals, although there are some observation which exist outside this range. Consequently, there is no clear definite value assigned to the n exponent. The reason for this may be the difference in the mechanism of attack caused by the simultaneous and synergistic interaction between erosion and corrosion. This being so, it seems useful to separate the action of slurry erosion into those factors, namely one dominated by erosion, another dominated by corrosion and the third being synergistic interaction between erosion and corrosion. This holds true even in multi-phase alloy like high-chromium white irons.
Fe-(15, 25)%Cr-C-B alloys are modified high-chromium white irons that contain boron ranging from 0.5 to 2.5 mass%. These alloys possess a good slurry erosion resistance compared to that of an ordinary type of high-chromium white iron. The reason for this is the presence of boron. The addition of boron tend to produce hard boride and/or borocarbide. It also prevent the formation of pearlite.
A slurry flow rate with the range of 4.5 to 10.3 m/s was used. The low slurry flow rate region was corrosion-dominated while the high slurry flow rate region was erosion-dominated. The experiments also indicate a n-value range of 3.3 to 4.9 when a tap water slurry is used. Whereas for a seawater slurry, a range of 0.4 to 3.2 was observed. Therefore, the change in n-value may mainly be attributed to the degree of corrosiveness of the slurry. Fe-(15, 25)%Cr-C-B alloys possessed a good slurry erosion resistance compared with both SUS430 and SUS304 stainless steels in tap water slurry. Moreover, Fe-25%Cr-C-B alloys possess an excellent slurry erosion resistance even in the slurries containing sea water and 40 vol% sand.View full abstractDownload PDF (2736K)
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