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Volume 61, Issue 8
Displaying 1-18 of 18 articles from this issue
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Yuh Fukai, Yoshifumi Kurokawa, Hirokatsu Hiraoka1997 Volume 61 Issue 8 Pages 663-670
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSA theory is proposed for the formation of superabundant vacancies in metal-hydrogen alloys, amounting to 10∼20 at%, considering hydrogen effects to decrease the formation energy of a vacancy by cluster formation and the configurational entropy of the system at high hydrogen concentrations. A formula derived for the vacancy concentration is found to give excellent descriptions of experimental results on nickel-hydrogen and molybdenum-hydrogen alloys obtained under high hydrogen pressures. Some of the consequences of the superabundant vacancy formation are discussed including solubility enhancement, formation of defect structures and voids, and enhancement of metal-atom diffusion.View full abstractDownload PDF (836K) -
Saiji Matsuoka, Masahiko Morita, Osamu Furukimi, Takashi Obara1997 Volume 61 Issue 8 Pages 671-677
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe application of an EBSD technique in an SEM reveals a new approach to analyze a morphology of low carbon steel rolled in the nonrecrystallized austenite region. The bainitic ferrite structure has a grain size of 5 to 20 microns and a strong {332}⟨113⟩ and {311}⟨011⟩ transformation texture is developed as observed by the conventional measuring method. (1) The grain observed in the etched steel with conventional microscopy is defined as a region where a misorientation between adjacent points is within 1°, surrounded by boundaries having a misorientation over 2° by means of EBSD. In this steel, some of the grain boundaries include subboundaries having a misorientation from 2 to 5°. (2) Orientation colonies, which consist of some grains having a misorientation between adjacent grains within 15°, are observed with EBSD. These colonies are flat-elliptical in shape corresponding to a deformed austenite grain before transformation, resulting in the transformation from deformed one austenite grain to some ferrite grains with variant selection. (3) The orientation colony is divided into some regions which consist of a few grains having a misorientation between adjacent grains within 5°, resulting in the transformation from divided austenite grain to some ferrite grains with the same variant or close variants of the K-S relation. (4) In an orientation colony, each grain has a misorientation within 15°, leading to the transformation from austenite to ferrite with a close variant of the K-S relation. (5) These experimental results suggest that a bainite transformation might have proceeded in such a way that the Bain strain or shear strain corresponding to the Bain strain as first occurred and the variant selection is controlled by this strain.View full abstractDownload PDF (912K) -
Yukiharu Suzuki, Tetsuya Suzuki, Tokuzou Tsujimoto1997 Volume 61 Issue 8 Pages 678-683
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSDiscontinuous coarsening reaction have been used to obtain the microstructure of fine-grained lamellae in a Ti-46 mol%Al alloy, which is expected to improve ductility at room temperature. The process was very simple because the structure change was performed only by aging subsequent to quenching. The refinement mechanism was investigated by optical and scanning electron microscopy.
The nuclei of discontinuous coarsening reaction were coarsely spaced lamellae which were generated at grain boundaries and inside grains of finely spaced lamellae. The nucleation of coarsely spaced lamellae during aging increased with increasing cooling rates from the liquid phase and the alpha single phase. When the aging temperature was below 1473 K, the discontinuous coarsening reaction occurred preferentially and the microstructure was refined. The refinement by this process was achieved via the following steps: (1) nucleation of coarsely spaced lamellae, (2) changing the growth direction and (3) suppression of the grain growth. Thermal stability of the fine-grained microstructure obtained by this process was quite high.View full abstractDownload PDF (1479K) -
Yukiharu Suzuki, Tetsuya Suzuki, Tokuzou Tsujimoto1997 Volume 61 Issue 8 Pages 684-689
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSMechanical properties of a Ti-46 mol%Al alloy with full lamellae refined using a discontinuous coarsening reaction have been examined by a compression test in a range of RT∼1273 K and a tensile test at both RT and 1073 K. Also, the effects of lamellar grain size, lamellar grain boundary and lamellar morphology on the deformation behavior have been investigated.
The compression properties at RT were improved by refinement of the lamellar grain. Up to 1073 K, the strength was not decreased because the area of the serrated grain boundary which was considered to improve the high-temperature strength was increased by the refinement. The deformation mechanism of coarsely-spaced lamellae was similar to that of finely-spaced lamellae.View full abstractDownload PDF (1223K) -
Yoshiharu Shimada, Shigeru Asano, Makoto Usui1997 Volume 61 Issue 8 Pages 690-695
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSIn austenitic stainless steels, an internal friction peak caused by dissolved hydrogen has been found and attributed to a Snoek-type relaxation of hydrogen atom complexes in the FCC lattice. However, much of the structure of the complexes remains unknown because no precise data are available on the dependence of relaxation strength on hydrogen concentration in austenitic stainless steels. On the other hand, Fe-35%Ni Invar alloy is known to form a similar internal friction peak with more sufficient relaxation strength even by the gas equilibration method of hydrogen charging. The hydrogen peak of internal friction is confirmed in the Fe-35%Ni alloy containing 30∼320 at ppm hydrogen. The peak position is around 250 K at about 700 Hz. The peak height increases monotonously with increasing hydrogen concentration but shows a complicated tendency when plotted against hydrogen concentration. However, the peak height appears to increase parabolically with low hydrogen concentrations from 0 to 100 at ppm. This fact suggests that hydrogen atom pairs are most likely to contribute as the corresponding complexes to the hydrogen peak of internal friction in FCC iron alloys.View full abstractDownload PDF (516K) -
Yoji Shibutani, Jun-ichi Toryu, Yoshihiro Tomita1997 Volume 61 Issue 8 Pages 696-701
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSA stress-induced phase transformation phenomenon is one of the hierarchical mechanical behaviors in which atomistic rearrangements are simultaneously and dually reflected to macroscopic strength of material. It has so far been recognized as one of the bifurcation problems in the fields of thermodynamics and continuum mechanics. Softening of phonon dispersion curves has also been acknowledged as precedence of transformation as well. Movements of atoms in an α-iron under uniaxial tension are first traced by the molecular dynamics (MD) simulations on the assumption of a constant applied stress ensemble proposed by Parrinello & Rahman. Stress dependency of phonon dispresion curves obtained from the deformed lattice structures are then examined. Bifurcation conditions derived from positive definiteness of strain energy in the whole deformed matters are, at the same time, investigated using analytical elastic constants defined from only an atomic configuration and the force constants which are the second derivative of an employed interatomic potential. It is found that softening of phonon dispersion curves, especially the long-wavelength acoustic branch, could correspond to the macroscopic bifurcation conditions over the scale.View full abstractDownload PDF (507K) -
Yoshinori Murata, Yutaka Shimamura, Takayuki Ishida, Masahiko Morinaga1997 Volume 61 Issue 8 Pages 702-709
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe oxidation behavior of Ti-50 mol%Al and Fe-40 mol%Al at high temperatures and at low oxygen partial pressures was investigated mainly by means of X-ray photoelectron spectroscopy and scanning electron microscopy.
The layer structure consisting of the outer TiO2 layer and the inner TiO and Al2O3 mixed layer was formed on the surface in the early stage of oxidation of TiAl in air. The existence of TiO was manifested in the oxide products of TiAl. At low oxygen partial pressures, the stacking of such layers was no longer present, but instead there was the mixture of Ti-oxides and Al2O3 on the surface, without forming any protective Al2O3 layer against oxidation. The grain size of the oxides formed on TiAl increased with increasing temperature and with decreasing oxygen partial pressure.
The layer structure consisting of the outer Fe2O3 layer and the inner Fe3O4 and Al2O3 layer was formed in the early stage of oxidation of FeAl in air. In this case, the inner Al2O3 layer acted to be a protection layer against the oxidation. On the other hand, only Al2O3 was observed on the surface of FeAl oxidized at low partial oxygen pressures and high temperatures except 1473 K. At 1473 K, a little Fe3O4 was also observed on the Al2O3 layer. The oxide morphology in FeAl did not change with the oxidation conditions so largely as that in TiAl.View full abstractDownload PDF (942K) -
Yoshinori Murata, Yutaka Shimamura, Takayuki Ishida, Masahiko Morinaga1997 Volume 61 Issue 8 Pages 710-714
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe growth of oxides formed on Ti-50 mol%Al and Fe-40 mol%Al was investigated at high temperatures and low oxygen partial pressures.
In the early stage oxidation of TiAl, Al2O3 with equiaxed crystal grains was first formed on the surface and then Ti-oxides were formed in the intergrains. The Ti-oxides grew more rapidly than the Al2O3 did with oxidation time. This phenomenon implies that the oxidation resistance of TiAl does not maintain but decreases when the oxidation progresses for a long time at any oxygen partial pressures.
In FeAl, a protective Al2O3 layer against oxidation was formed in the early stage of oxidation even at a low oxygen partial pressure. This Al2O3 layer was thin and stable for a long term. However, small cracks were sometimes observed in the Al2O3 layer, and they seemed to be formed owing to a large difference in the thermal expansion coefficient between FeAl and Al2O3. Therefore, the protecitve Al2O3 layer on FeAl may be broken away when it undergoes any thermal cyclic oxidation.View full abstractDownload PDF (799K) -
Masaaki Kohno, Kazuhide Ishii, Yukio Usui, Susumu Satoh1997 Volume 61 Issue 8 Pages 715-720
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe effect of pre-annealing on the oxidation behavior of Fe-20 mass%Cr-5 mass%Al alloys containing up to 0.11 mass%La was examined by a cyclic oxidation test at 1423 K in air. SIMS and chemical analysis were carried out for thin oxide layers formed by pre-annealing and Al2O3 scales formed by oxidation. The oxidation rate of La-added Fe-20%Cr-5%Al alloys was decreased markedly by hydrogen annealing, while that of La-free alloy was not changed. La enrichment was found in both the thin oxide layer formed on the alloy annealed in hydrogen and the Al2O3 scale formed on that alloy. It is concluded that La enrichment in the oxide film formed during hydrogen annealing suppresses the inward diffusion of oxygen through the Al2O3 scale, resulting in a decrease in the oxidation rate.View full abstractDownload PDF (577K) -
Masato Yamashita, Hiroo Nagano1997 Volume 61 Issue 8 Pages 721-726
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSCorrosion potential and corrosion rate of a low-alloy steel covered with a thin solution layer have been examined mainly in air using the Kelvin probe apparatus and a pressure sensor. Corrosion potential, Ecorr(V vs SHE), and corrosion rate, icorr (A·m−2), increase with decreasing thickness of the solution layer, h, in the thickness range between 200×10−6 m and 10×10−6 m, as follows:
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\ oindentThese observed changes of Ecorr and icorr are attributed to the varied oxygen reduction rate with h which corresponds to the thickness of the oxygen diffusion layer. When h becomes lower than 10×10−6 m, the corrosion product formed on the steel surface suppresses steel dissolution; so that icorr decreases and Ecorr stays at a certain value. At h of 0.1×10−6 m, the Ecorr jump-up was observed. This might be because the solution is no longer in the form of a thin layer but in the form of fine droplets; if this is the case then Ecorr reflects a mixed potential of corrosion potential under solution droplet and work function of the water adsorbed steel surface. Ecorr measurements in nitrogen supports the above understanding of the results obtained in air.View full abstractDownload PDF (654K) -
Kiyoshi Mizuuchic, Kiyoshi Yamauchi, Kenichi Hamada, Kanryu Inoue, Min ...1997 Volume 61 Issue 8 Pages 727-735
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSTi-Pd-Ni-W SMA fiber/Titanium matrix composites were produced by sheath-rolling. A thirty μm thick homogeneous reaction layer was formed in the vicinity of the interface between the fiber and the matrix. The interfacial layer between fiber and matrix consists of three different intermetallic compounds. Young’s modulous of the fiber increased with increasing temperature above the As point. The yield strength of the composites increased with increasing temperature above the Af point. This increase of yield strength would be due to residual compressive stress by fiber’s shape memory effect. Ductile fracture patterns were observed on the fracture surface of the interfacial layer between the fiber and the matrix. This interfacial layer would be effective for stress conductivity.View full abstractDownload PDF (1311K) -
Hidekazu Sueyoshi, Nobuyuki Fukuda, Tomoyuki Nishida1997 Volume 61 Issue 8 Pages 736-743
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSGraphite was bonded to S45C steel by using RF-induction furnace, and bending strength, microstructure and carbon distribution of graphite/S45C steel joint were investigated. Thermal stress produced in the joint was estimated with an X-ray stress analysis and a finite element method. On the basis of these results the influence of thermal stress on bending strength of the joint was examined in connection with the diffusion of carbon atoms.
Austenite phase contributes greatly to solid-state bonding of graphite/steel system. Therefore good diffusion bonding becomes feasible when joining temperature exceeds eutectoid transformation temperature A1. Axisymmetric thermoelastic finite element analysis suggests that the increase in carbon content near the interface of S45C steel has no influence on maximum tensile stress induced on the surface of graphite. Bending strength of the joint increases with decreasing residual stress on the surface of graphite. Relaxation of thermal stress is increased to a maximum when the amount of carbon atoms which diffuse into S45C steel comes to an optimum value. Lattice defects introduced with the Kirkendall effect seem to be pertinent to stress relief.View full abstractDownload PDF (938K) -
Osamu Ohashi, Yuichiro Asano1997 Volume 61 Issue 8 Pages 744-749
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe relationship between changes in surface composition heating in a vacuum and subsequent bonding phenomena was studied using an ultrahigh vacuum diffusion bonding equipment with Auger spectroscopy. A variety of materials were used such as titanium, copper and SUS304 stainless steel. These materials could be joined to produce good bonds once oxides and contaminants based on oxygen and carbon were removed from the surface. Heat treatment in vacuum was found to cause surface oxide dissociation due to the dissolution of oxygen into the base metal and oxide reduction by carbon. However, Auger analysis of the surface revealed the formation of a sulfur-rich monolayer. It is thought that sulfur (in the bulk material) segregates to the surface and forms this sulfur-rich layer. The layer has the effect of preventing the adsorption of impurity elements such as oxygen and carbon which interfere with the joining process, but also lowers the bonding temperature. This is because the bonding temperature is determined by the temperature at which surface oxides dissociate and since the sulfur-rich layer dissociates at lower temperature than surface oxides based on oxygen, lower bonding temperatures can be employed.
Therefore, a new, lower temperature diffusion bonding process has been developed. Unlike the conventional bonding process where the joints region is heated after the bonding surfaces are brought into contact, in this method specimens are treated in vacuum prior to bonding.View full abstractDownload PDF (816K) -
Fumiyoshi Kirino, Shigekazu Ohotomo, Nagatsugu Koiso1997 Volume 61 Issue 8 Pages 750-758
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe influence of the composition and preparation conditions on the corrosion resistance and the crystal structure of Fe-Hf-N soft magnetic thin films is studied to obtain a soft magnetic material with Bs over 1.5 T. The best corrosion resistance was obtained for the Fe-Hf-N film, deposited in sputtering gas with 8 vol%N2. In this case, the grain sizes of the Fe crystals in the film are small, which is supposed to be the main cause of the good corrosion resistance. The films prepared using sputtering gas containing 12 vol%N2 are susceptible to corrosion, due to the excessive growth of the Hf-N grainss. The films prepared with higher RF power show a larger Fe 110 peak in X-ray diffraction, while they get weaker against corrosion. The films prepared at higher sputtering gas pressure show larger Fe and Hf-N grains, while their corrosion resistance remains unchanged. The change in the annealing temperature between 773 and 863 K does not influence the crystal structure nor the corrosion resistance of the films. After optimization of the composition and preparation conditions, a film was obtained with Bs=1.5 T, Hc=48 A/m, λs=3×10−6 and μ=2000(at 1 MHz) at the composition of Fe70.5Hf11.0N18.5 after annealing at 823 K.View full abstractDownload PDF (1023K) -
Soshu Kirihara, Yo Tomota, Tokuzou Tsujimoto1997 Volume 61 Issue 8 Pages 759-764
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSTo produce a Ti/Ti3Sn FGM, pure Ti and intermetallic compound Ti3Sn blocks were bonded by using an eutectic reaction. The eutectic bonded part formed between the Ti and the Ti3Sn blocks is composed of βTi which transforms to αTi during cooling and Ti3Sn with a gradual change in the amount of each constituent. The microstructure of this bonded part can be controlled precisely by changing a cooling rate or by annealing, or both. When these FGMs with controlled microstructure was repeatedly heated and cooled between 673 and 1473 K, neither cracks nor defects could be observed by in-situ optical microscopic observation.View full abstractDownload PDF (1076K) -
Toru Hinomura, Saburo Nasu, Hirokazu Kanekiyo, Minoru Uehara, Satoshi ...1997 Volume 61 Issue 8 Pages 765-773
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSBy means of 57Fe Mössbauer spectroscopy, X-ray diffraction and magnetization measurements, the magnetic properties and phase compositions of Cr-added Nd-Fe-B nanocrystalline composite magnets, Nd4.5(Fe1−xCrx)77B18.5(x=0, 0.013, 0.039, 0.065, 0.130, 0.260), have been investigated as a function of the Cr concentration. With increasing Cr content, the coercivity of the specimen increases, but the remanence decreases. In all the specimens, hard magnetic Nd2Fe14B crystallizes and its amount increases with increasing Cr concentration. Such an increase in the amount of the hard magnetic compound results in an increase of coercivity. The amount and kind of the soft magnetic phase formed varies with the Cr content. The specimen with low Cr content consists of both Nd2Fe14B and Fe3B. On the other hand, the specimen which contains a large amount of Cr consists of Nd2Fe14B-(Fe2B, α-Fe) nanocrystalline composite. From the Mössbauer measurements, it is found that the hyperfine magnetic fields of both Nd2Fe14B and α-Fe in the specimens are almost independent of the Cr content. The hyperfine magnetic field of the Fe-B compound decreases as a function of the Cr content, and consequently Fe2B in Nd4.5(Fe0.74Cr0.26)77B18.5 contains a large amount of Cr and becomes non-magnetic at room temperature. These results suggest that the Cr atoms mainly exist in the Fe-B compound, not in the Nd2Fe14B and α-Fe compounds, and reduce the magnetization and the Curie temperature of the Fe-B compound. Moreover, the total amount of the soft magnetic phases decreases with increasing Cr content. These are the origins of the decrease in remanence of Nd-Fe-B-Cr nanocrystalline composite magnets.View full abstractDownload PDF (1143K) -
Makoto Ohtsuka, Terukazu Yamauchi, Kimio Itagaki1997 Volume 61 Issue 8 Pages 774-780
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSAs a fundamental study of AB2-type Laves phase alloys for use of the Ni/MH rechargeable battery, the relationship between the structure and the hydrogen-absorption properties was investigated for the annealed Zr(Ni1−xMnx)2 and ZrNinMny (n=1.0, 1.1, 1.2, 1.3 and 1.4) alloys. For the Zr(Ni1−xMnx)2 alloys, a secondary phase with a low Mn content existed along with a main C15-type Laves phase, whose volume fraction decreased with increasing Mn content. It was clarified that the hydrogen storage capacity increased with decreasing volume fraction of the secondary phase. On the other hand, the capacity of the alloys with the single C15-type Laves phase decreased with increasing Mn content. A clear relationship was found between the hydrogen-absorption properties and the lattice parameter of C15-type Laves phase, which decreased with increasing Mn content. The hydrogen storage capacity increased with increasing unit cell volume, while the desorption pressure of hydrogen decreased. It was suggested that ZrNi1.3Mn1.1 alloy was the potential alloys investigated for the rechargeable battery.View full abstractDownload PDF (1364K) -
Takayuki Mamiya, Yoshihito Ogasawara, Shinji Sato, Toshio Suzuki, Akir ...1997 Volume 61 Issue 8 Pages 781-782
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSDownload PDF (226K)
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