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Volume 62, Issue 9
Displaying 1-13 of 13 articles from this issue
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Hiroyuki Hoshi, Kazuyoshi Takezawa, Kenzaburo Marukawa1998 Volume 62 Issue 9 Pages 783-789
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe ordered structure and its change by heat-treatments in the β phase (bcc structure) of an Ag-22.3 at%Zn-8.9 at%Al alloy were investigated by means of electron microscopy and electrical resistivity measurements. This alloy can be brought to the disordered state by quenching after heating to a little above the order-disorder transition temperature (about 340 K). The ordering in disordered specimens by aging at a temperature near room temperature proceeds in two stages. The first stage is the transition to C11b structure, whose unit cell is thrice as large as the unit cell of the bcc structure. This structure corresponds to a binary alloy of type A2B. The atomic composition of the present alloy suggests that Ag atoms should be arranged at A atomic sites and Zn or Al atoms at B sites. By prolonged aging, ordering moves to the second stage. The ordered structure in this stage, which we call C11b∗ structure, has the unit cell 3×3 times as large as the bcc unit cell, and it is composed of three kinds of atomic sites A, B, and C in the ratio of 6:2:1. It may be reasonable to assign Ag, Zn and Al atoms to A, B and C sites, respectively. Measurements of lattice parameters have shown that the transition to the C11b∗ structure accompanies a transformation strain. Regularly arranged twin plates, which have been observed in the C11b∗ phase, seem to accommodate the transformation strain. Disordered specimens transform martensitically by lowering the temperature to the vicinity of the liquid nitrogen temperature, but ordered ones do not transform.View full abstractDownload PDF (1015K) -
Katsumi Koyama, Goroh Itoh, Motohiro Kanno1998 Volume 62 Issue 9 Pages 790-795
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSHydrogen microprint technique with the aid of photographic effect was applied to pure aluminum and three types of titanium alloys to visualize the hydrogen atoms evolved during tensile deformation. Tensile specimens covered with a monolayer of photographic emulsion were deformed by about 5% at temperatures ranging from −180 to 82°C, subsequently developed and fixed under the safety light in a dark room. Silver grains indicating hydrogen emanation were revealed along coarse slip lines and some grain boundaries, and at second phase (constituent) particles. The density of silver grains was affected by the impurity hydrogen content of the specimen and by deformation temperature. Consequently it can be concluded that hydrogen atoms in the interior of the specimen are transported to the surface with a number of gliding dislocations at room temperature, and that grain boundary becomes a primary diffusion path at elevated temperatures. The newly developed technique with the aid of photographic effect has a higher sensitivity to hydrogen emanation than the conventional hydrogen microprint technique. Moreover, the present technique is by far simpler than tritium autoradiograhy and can be applied to a wide variety of metals and alloys which deform primarily by dislocation glide.View full abstractDownload PDF (1197K) -
Tetsuya Uda, Toru H. Okabe, Yoshio Waseda1998 Volume 62 Issue 9 Pages 796-802
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSInstead of the conventional metallic reductant, halide salt has been tested as a reductant for producing titanium powder directly from TiCl4. Using various thermodynamic data, DyCl2 was found to be suitable for the halidothermic reduction of TiCl4. When TiCl4 was fed into DyCl2 single salt or DyCl2 containing molten salts at 1073 K, fine titanium powder of several ten micron meters in diameter was obtained. In contrast to the sponge titanium produced by the conventional Kroll process, the present new process using halidothermic reduction appears to hold promise in reducing difficulties by making titanium powder without precipitation of sponge titanium on the metallic container. From the thermodynamic point of view, the resultant DyCl3 can be reduced to DyCl2 by magnesium. These particular features enable us to give possibility of the production of titanium powder directly from TiCl4 as well as the development of a new continuous titanium reduction process by adding reaction mediator in the Kroll process.View full abstractDownload PDF (977K) -
Hiroshi Fujiwara, Ryo Yonezawa, Kei Ameyama1998 Volume 62 Issue 9 Pages 803-811
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSCrystallography of α(HCP) phase precipitated in β(BCC) grains of a Ti-22 mass%V-4 mass%Al alloy has been studied using the Kikuchi patterns obtained by transmission electron microscopy. The relative orientation relationship between α precipitates and β matrix grains was determined by an analysis of the Kikuchi patterns taken from HCP and BCC phases. The analytical error was evaluated by the study of {1\bar101}hcp transformation twins in the martensite phase formed in a rapidly quenched commercially pure titanium specimen. Comparison of the experimental results obtained from the twins with the theoretical calculation has shown that the rotation angular error was less than 0.10°. The orientation relationship of intragranular α precipitates have a slight deviation from the exact Burgers orientation relationship. The average deviation angle was 0.68° for the parallel plane relationship, i.e., (0001)α⁄(110)β, and 0.61° for the parallel direction relationship, i.e., [2\bar1\bar10]α⁄[1\bar11]β. The grain boundary α precipitates were found to have the Potter orientation relationship rather than the Burgers orientation relationship with one of the adjacent β grains.View full abstractDownload PDF (3418K) -
Takanori Nakazawa, Shunichi Suzuki, Yoshihiko Tanaka, Hajime Komatsu1998 Volume 62 Issue 9 Pages 812-819
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSIn order to investigate the controlling factors in grain boundary sensitization of type 304 stainless steels during welding, grain boundary corrosion and carbide precipitation were examined using optical and transmission electron microscopy after thermal or thermomechanical cycles. Thermomechanical treatment, which simulated high temperature dynamic strain during welding, enhanced carbide precipitation on the grain boundary and sensitization of SUS304 steel. This behavior occurred only when the maximum temperature was below the solution temperature of the carbide. Straining in heating was more effective for sensitization and carbide precipitation than that in cooling. High temperature dynamic strain was more effective for sensitization and carbide precipitation than cold working before thermal treatment. Thermomechanical treatment sensitized SUS304L steel as well, while the degrees of grain boundary corrosion and carbide precipitation were lower than those in SUS304 steel. Grain boundary migration was observed only in SUS304L steel after thermomechanical cycles when the maximum temperature was below the solution temperature of the carbide. Ratio of sensitization increased with increasing grain size.View full abstractDownload PDF (2348K) -
Nagayoshi Suzuki, Hirotsugu Ogi, Masahiko Hirao1998 Volume 62 Issue 9 Pages 820-826
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSChanges in ultrasonic velocity and attenuation were studied by noncontact and continuous measurement method for polycrystalline pure copper during deformation. This measurement, involving two ultrasonic waves at the same time, has been made possible by electromagnetic acoustic resonance (EMAR). Use of an electromagnetic acoustic transducer (EMAT) can isolate the attenuation within the plate specimens. The method relies on the Lorentz force mechanism to couple the EMAT and the specimen surfaces and then eliminates the extra losses, which otherwise occur in the use of the piezoelectric transducers. Ultrasonic velocity and attenuation changes are interpreted in terms of the dislocation behavior and the acoustoelastic effect. The changes in dislocation density and loop length can be analyzed using dislocation damping theory. Pure third-order elastic canstants, which are free from the velocity change due to the dislocation movement, can also be derived and compared with the existing experiments.View full abstractDownload PDF (652K) -
Kenji Matsuda, Tokimasa Kawabata, Tsutomu Naoi, Yasuhiro Uetani, Seich ...1998 Volume 62 Issue 9 Pages 827-833
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe behavior of two step aging in an Al-1.0 mass%Mg2Si-0.4 mass%Si alloy was investigated by high resolution transmission electron microscopy (HRTEM) together with hardness, electrical resistivity measurements. A number of primary G.P. zones with the diameter of about 1nm were observed in the specimen aged at 293 K for 60 ks. Both the mono- and multi-layer G.P. zones were detected in the specimen aged at 343 K for 60 ks. On the contrary, almost no G.P. zones were formed in the specimen aged at 423 K for 60 ks. Instead, a number of random type precipitates were observed. The aging at 473 K produced precipitates in the following sequences:
the random type→parallelogram type→β″ phase→TYPE-B→TYPE-A(→ partially TYPE-C).
The maximum hardness (HVmax) of the specimen aged at 473 K after pre-aging at 293 K for 60 ks indicates a negative effect, i.e. the HVmax of the two step aged specimen is lower than that of the specimen only aged at 473 K. The HVmax of the specimen aged at 473 K after pre-aging at higher temperatures than 343 K shows a positive effect, i.e. the HVmax of the two step aged specimen is higher than that of the specimen only aged at 473 K. In the specimen pre-aged at 423 K which exhibits a positive effect, a number of the random type precipitates are formed. On the other hand, in the specimen pre-aged at 293 K, which exhibits a negative effect, a number of the β″ phase are formed. It is concluded that the random type precipitates produced at 423 K pre-aging are stable at the 473 K final aging, while the primary G.P. zones produced after pre-aging at 293 K become unstable at the 473 K final aging due to dissolution into the matrix, resulting in the heterogeneous precipitation of the β″ phase.View full abstractDownload PDF (1875K) -
Masakazu Kobayashi, Yoshimasa Takayama, Tatsumi Tozawa, Hajime Kato1998 Volume 62 Issue 9 Pages 834-843
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSSimulation of grain growth towards the microstructural image data base has been performed by the Monte Carlo technique proposed by Exxon’s group. In the present simulation, dependence of grain boundary energy on crystallographic misorientation, which is expressed in the same way as the vector method (one of the ODF analysis methods) is taken into consideration in order to describe actual microstructures. For the evolution of the simulated microstructure, more realistic feature and migration of grain boundary are observed with an increase in the number of neighboring shell ks for calculating the interactive energy. Grain growth exponents n in the microstructures with ks≥3 are about 0.4∼0.5. Grains surrounded with low energy boundaries grow preferentially. Further, it is found that the low energy grain boundaries do not always decrease in length during grain growth, while the high energy grain boundaries decrease gradually.View full abstractDownload PDF (979K) -
Yasuhisa Yamamoto, Kenki Hashimoto, Takasi Kimura, Hideaki Moriya, Min ...1998 Volume 62 Issue 9 Pages 844-852
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSThe phase, structure and compositions of Al-Mn-Ti-X(X=Zr, V, Ag, Ga) alloys were studied by X-ray diffraction and Electron Probe Microanalysis(EPMA). The solubility of X(X=Zr, V, Ag, Ga) element into the L12-type {(AlMn)3Ti}(1−n)Xn trialuminide at 1450 K was varied from 6.8 mol% of Zr to 12.9 mol% of Ga. It was found that the resultant quaternary alloys had the region of the single phase of the L12-type {(AlMn)3Ti}(1−n)Xn trialuminides for all additional elements. Its single phase region was shown in the quaternary phase diagram of Al-Mn-Ti-X alloys. When the Zr, V or Ga was added into the L12-type (AlMn)3Ti trialuminide, they occupied the Al- and Ti-sublattice in the L12 crystal. The lattice parameter of the resultant quaternary trialuminide was smaller than that of the ternary counterparts. On the other hand, the Ag occupied the Al-sublattice in the L12-type (AlMn)3Ti trialuminides when it was added into the L12 crystal. Its lattice parameter of the resultant quaternary trialuminide was larger than that of the ternary counterparts. The variation of lattice parameter of the L12-type {(AlMn)3Ti}(1−n)Xn trialuminide can be explained by the atomic size effect.View full abstractDownload PDF (1173K) -
Satoru Yamamoto, Teruo Tanabe, Hisayoshi Kobayashi1998 Volume 62 Issue 9 Pages 853-860
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSIn the present work, the cohesive energy and energy fluctuation of metal cluster have been calculated by the extended Hückel method. On the other hand, the Vickers hardness of Al and Cu with or without additional elements has been measured at high temperatures. The stability of metals and alloys at high temperatures has been discussed by comparing the calculated results of the cohesive energy and the energy fluctuation with the measured hardness values. The main results of the present work are described as follows:
(1) The addition of elements such as Mn, Ce and La to pure Al, and the addition of Y, Cr and Ce to pure Cu decreases the energy fluctuation and increases the cohesive energy of metal cluster at high temperatures. On the other hand, these elements increase the Vickers hardness of Al or Cu at high temperatures.
(2) Both the cohesive energy and the energy fluctuation are physical quantities to show a measure of stability, and especially the energy fluctuation is more suitable for the discussion of the stability of metals and alloys at high temperatures.View full abstractDownload PDF (690K) -
Hiroshi Hatta, Emi Sudo, Yasuo Kogo, Ichiro Shiota1998 Volume 62 Issue 9 Pages 861-867
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSSiC coated C/C composites were formed by the processing route of the Si melt impregnation method, SMIM, under various temperature. The oxidation behavior and strength of the coated C/C composites made by the SMIM were then examined to clarify advantages of this method. From the viewpoint of oxidation resistance, the SiC coating formed by the optimal condition of the SMIM is shown to be superior to the conventional CVD methods. It is especially true when the heat treatment temperature of the SMIM is low, i.e., just above the melting temperature of Si. Underlying mechanisms of this superior oxidation resistance were explained in terms of the variation of the coating thickness and coating crack opening. By the SMIM treatment the interlaminar shear strength was also improved remarkably but the bending strength was found to be degraded noticiably. It was suggested to be rather difficult to relieve the bending strength degradation by changing the SMIM treatment condition.View full abstractDownload PDF (1136K) -
Yasunori Harada, Masanobu Ohmori, Hironori Ando, Hidenori Matsui, Tomo ...1998 Volume 62 Issue 9 Pages 868-875
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSChromium-nickel sintered compacts containing 50 and 80 mass%Cr were tried to improve their mechanical properties by means of a thermo-mechanical treatment, i.e., repeated rolling and annealing. Specimens from the as-sintered compacts showed no ductility at room temperature and small ductility at temperatures higher than 1000 K because of poor alloying of nickel with chromium. Tensile properties of the sheets repeatedly rolled with the intermediate annealing at 1173 K were very similar to those of the as-sintered specimen. While the sheets rolled with the annealing at 1573 K were excellently improved in their strength and ductility due to the considerable interdiffusion of chromium and nickel. The intermediate temperature embrittlement, that is, the ductility minimum well observed around 1000 K in a chromium-nickel alloy appeared also in the sheets rolled with the annealing at 1573 K.View full abstractDownload PDF (1700K) -
1998 Volume 62 Issue 9 Pages 876
Published: 1998
Released on J-STAGE: April 24, 2008
JOURNAL FREE ACCESSPlease see Errata PDF Wrong:ΔdL, t Right:dL, tView full abstractDownload PDF (35K)
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