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Volume 61, Issue 5
Displaying 1-15 of 15 articles from this issue
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Eiji Taguchi, Naoto Sumida, Hiroshi Fujita1997 Volume 61 Issue 5 Pages 369-377
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSMicroscopic structures of aluminium-rich β′-NiAl thin foils annealed at 373-773 K have been studied by electron microscopy. The contrast of the bright field (BF) image shows a tweed pattern at the beginning stage of annealing and then turns gradually into a mottle pattern. The corresponding diffraction patterns of the [100] incidence are observed at a temperature below 573 K and 573-673K. The former pattern contains the ⟨110⟩ streaks connecting the fundamental spots and the diffuse intensity maxima at the halfway of the streaks. In the latter one, four extra spots appear at the distance, one sixth of |g110|, from all spots of β′-NiAl and the direction along the ⟨110⟩, streaks.
The characteristic in both the BF image contrast and the diffraction patterns suggests that the structure change in β′-NiAl by annealing occurs in the following two steps. The ordering of atom and constitutional vacancy occurs locally at the first step. In the new periodic structure, the Al and Ni sites of B2 type structure consist of Al, Al+Ni and Ni, Ni-vacancy respectively. At the second step, the structure of β′-NiAl separates partially into the Al-rich and Ni-rich phases (Ni2Al3; trigonal and Ni3Al2; L10 structure). Thin phase separation is closly related to the modulation of Ni-vacancy concentration caused by the formation of a local ordering structure at the first step.View full abstractDownload PDF (1804K) -
Akiyoshi Nomoto, Hiroshi Fukutomi1997 Volume 61 Issue 5 Pages 378-384
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSA process consisting of the high-temperature deformation in α single phase region followed by annealing and deformation in (α2+γ) region is examined, in order to control the alignment of the lamellar microstructure with the constituents of α2 and γ phases in the TiAl based alloys. The uniaxial compression in the α single phase region resulted in the formation of a fiber texture, though dynamic recrystallization occurred. The maximum pole density for the compression plane appeared about 35 degrees away from (0001) of the α2 phase. The heat treatment generated the lamellar microstructure reflecting the texture formed by the uniaxial deformation in the α single phase region. Work softening was observed at the deformation of the specimen with fully lamellar microstructure formed by deformation in the α single phase region and annealing in the two phase region. The work softening was attributed to the geometrical softening at the initial stage and dynamic recrystallization at the later stage of deformation. The deformation in the two-phase region brought about the rotation of the lamellae. The lamellar interface lied almost parallel to the compression plane after the deformation of about −0.8 in true strain.View full abstractDownload PDF (899K) -
Takashi Kimura, Haruo Doi, Kenki Hashimoto, Eiji Abe, Yukihiro Isoda1997 Volume 61 Issue 5 Pages 385-390
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe phase identification in the vicinity of the TiAl phase composition in the Ti-Al-Sb system has been carried out for the specimens heat-treated at 1373 K for 605 ks and at 1572 K for 57.6 ks by X-ray diffraction, electron probe microanalysis and differential thermal analysis. The compound phase (D8m lattice type) was found in the composition region of 63.0∼65.4 mol%Ti, 11.0∼17.1 mol%Al and 19.2∼25.5 mol%Sb, and was confirmed to be stable up to 1773 K. The three phases have been coexisting regions of the Ti3Al(α2)(DO19)+TiAl(γ)(L10)+Sb-rich(φ)(D8m) and the α-Ti(α)(A3)+γ+φ have been determined at 1373 K and 1573 K, respectively. The latter region is at higher Al-content than the former. The two phases region of γ+φ was found at 1373 and 1573 K. The solubility limits of Sb in the α2 and γ have been determined to be 0.7 and 0.4 mol%, respectively. The transformation temperature from α2 to α increases with addition of Sb. The coexistence of the φ and β phases have been confirmed in the Ti-rich corner at 1573 K in the Ti-Al-Sb ternary phase diagram.View full abstractDownload PDF (746K) -
Kazuhiko Adachi, Sumiyuki Tsubokawa, Takao Takeuchi, Hirowo G. Suzuki1997 Volume 61 Issue 5 Pages 391-396
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSA heavily deformed Cu-Cr in situ composite is quite promising as a material with high strength and high conductivity, while polycrystalline Cr itself is well known to be brittle at room temperature. In order to make clear why the Cr phase in the composite is ductile, texture formation of the Cr phase and the microstructural features are examined during cold rolling. The results are summarized as follows.
(1) The dendritic Cr phase in the as-cast Cu-Cr alloy is monocrystal with the ⟨110⟩ growth direction of dendrite.
(2) Each Cr dendrite in the Cu matrix deforms by primary slip probably under the hydrostatic compression stress, and thus the {001} ⟨110⟩ rolling texture, being typical of bcc monocrystal metals, is formed by the deformation.
(3) Cr fibers do not exhibit extensive areas with virtually tangled dislocations, which may be responsible for keeping the ductility of the Cr phase even in the heavily deformed composite (up to rolling strain η=4.51).
(4) With increasing η, the Cu matrix spacing decreases faster than that of Cr. However detachment of the Cu matrix from the Cr fiber is not confirmed during cold rolling, with microstructural observations. Thus, the discrepancy between Cu and Cr spacing suggests that plastic flow occurs in the Cu matrix and Cr deformation is promoted under the hydrostatic compression stress.View full abstractDownload PDF (952K) -
Kazuhiko Adachi, Sumiyuki Tsubokawa, Takao Takeuchi, Hirowo G. Suzuki1997 Volume 61 Issue 5 Pages 397-403
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSA heavily deformed Cu-Cr in situ composite is quite promising as a material with high strength and high conductivity. In order to make clear the strengthening mechanism of the Cu-Cr in-situ composite, the Cu-15 mass%Cr composite wire, fabricated by the conventional process from the ingot, was investigated in terms of the variation of microstructure, hardness and tensile strength with increasing drawing strain. The results are summarized as follows.
(1) The thickness and spacing of Cr phase decrease exponentially with increasing drawing strain.
(2) The hardness and tensile strength increase proportionally with increasing drawing strain. High tensile strength of 906 MPa is attained at a maximum drawing strain of η=6.87.
(3)It is understood that the tensile strength involves the additional component due to the work hardening of the Cu matrix on the basic component due to microstructural fineness, obeying the Hall-Petch relationship with the decrease in Cr phase spacing.View full abstractDownload PDF (1153K) -
Akira Nozue, Ryoko Kuwahara, Ikko Mori, Tadatsune Okubo1997 Volume 61 Issue 5 Pages 404-408
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSA double solution treatment has been developed to increase the tearing modulus and to reduce the variation of crack growth resistance on the R curve. Its microstructure consists of tempered martensite and relatively fine and many quasi-circular platelike α phases. A crack stops, blunts and deflects in front of the quasi-circular platelike α phase nearly perpendicular to the crack extension, which results in a high tearing modulus. In the case of the quasi-circular platelike α phase nearly parallel to the crack extension, a crack propagates through the boundary. This crack growth behavior has been confirmed mainly with in-situ observation of the crack growth during loading. A fractal analysis has been carried out on the cross-section morphology of the fracture surface to correlate the tearing modulus. A good relationship has been found between the tearing modulus and the fractal dimension.View full abstractDownload PDF (925K) -
Zhengming Sun, Isamu Yamamoto, Toshiro Kobayashi, Kazuhisa Shibue1997 Volume 61 Issue 5 Pages 409-415
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSTensile tests of a γ-base Ti-45 at%Al-1.6 at%Mn intermetallic compound with duplex microstructure prepared by a reactive sintering method were carried out at strain rates ranging from 3.5×10−4 s−1 to 3.2×102 s−1 using a servohydraulic high rate testing machine. Both the ultimate tensile strength (UTS) and the 0.2% proof stress (YS) were found to increase with increasing testing strain rate. The strain rate sensitivities of UTS and YS were found to have an identical value of 1.2×10−2. The tensile elongation, around 1.5% in value, also showed a slight positive dependence on the strain rate. The experimental study on the microstructure before and after the tensile test was performed by both transmission electron microscopy and scanning electron microscopy. It was demonstrated that the predominant deformation mechanism both in the equiaxed γ grains and in the lamellar laths is caused by the deformation twinning, although the observed dislocations in the deformation twin variants may also contribute to the mechanical behavior. It is believed that the low strain rate sensitivity of the mechanical properties in the tested material stemmed from the twinning mechanism, which operates at high strain rates. It was demonstrated that though the deformation twins may easily propagate across the twin boundary in the γ grains, the process becomes difficult when the grain boundaries are encountered. The stress concentration is likely to result in leading to the crack initiation at the grain boundaries and finally introducing intergranular cracking. On the other hand, in the lamellar region, the deformation twins, normally perpendicular to the lamellar laths, were found to propagate frequently across the γ inter-variant interfaces, whilst the stress concentration at the γ⁄α2 interfaces was introduced. The microstructure observation was found to be consistent with the fractography.View full abstractDownload PDF (2079K) -
Isao Saeki, Hidetaka Konno, Ryusaburo Furuichi, Tsuneo Nakamura, Katsu ...1997 Volume 61 Issue 5 Pages 416-423
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSInitial oxidation of type 430 stainless steels with 0.09 and 0.9 mass%Mn was studied at 1073-1273 K. For the steel with 0.09 mass%Mn, oxide growth took place ununiformly compared with the steel with 0.9 mass%Mn, resulting in rougher surface with oxidation time. The Cr concentration at the oxide surface on the steel with 0.09 mass%Mn, which is analyzed by X-ray photoelectron spectroscopy, increased and the Fe concentration decreased with temperature, whereas for the steel with 0.9 mass%Mn, the temperature dependence of surface concentrations of Cr, Fe and Mn was not simple. This complicated compositional change at the oxide surface was explained by the γ transformation phenomenon of the substrate metal. The oxides formed were of the corundum and spinel type oxides and the amount of the latter was found to be related to the Mn and Cr contents at the oxide surface.View full abstractDownload PDF (1577K) -
Naoki Yasumaru1997 Volume 61 Issue 5 Pages 424-429
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe surface nitrided layer of austenitic stainless steels ion-nitrided at a relatively low temperature of about 623 K was investigated in order to elucidate the nature of an f.c.t. nitride YN formed in this layer with high corrosion resistance and high hardness of about Hv 1500. In this layer, only YN nitride was produced and X-ray diffraction peaks of chromium nitride were not detected. The surface nitrogen concentration was found to increase with the nitriding time from about 6 to about 9.5 mass%. Furthermore, the concentration profile of nitrogen in this layer showed a monotonous decrease from the maximum value at the surface to the minimum value of about 6 mass% at the nitriding front. The tetragonal crystal structure of YN phase was recognized to be derived from the f.c.c. cell of γ′-Fe4N by an expansion in the a direction and a contraction in the c direction, according to the location of the nitrogen atoms on the centers of the four c axes.
YN nitride was formed only in the low-temperature ion-nitrided layer of austenitic stainless steels of Fe-Cr-Ni, but not formed in the austenitic steels of Fe-high Ni or Fe-high Mn and in the ferritic stainless steels of Fe-Cr.View full abstractDownload PDF (932K) -
Takashi Goto, Takuya Sasaki, Toshio Hirai1997 Volume 61 Issue 5 Pages 430-436
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSPractical heat-resisting alloys such as stainless steel 304, Inconel 625 and Incoloy 825 showed a significant mass loss (active corrosion) and a mass gain (passive corrosion), respectively, at a low and a high oxygen partial pressure in a bromine-containing atmosphere around 1000 K. The transition oxygen partial pressures from the active to passive corrosion for these alloys were about 0.05 to 0.2 kPa at 1073 K. This result was almost in agreement with the thermodynamic calculations by an optimization method. The addition of water vapor (PH2O=1.17 kPa) at 1073 K and PO2=0.063 kPa caused the change from the active to passive corrosion for stainless steel 304 but not for Inconel 625. This behavior was also explained with the thermodynamic calculations.View full abstractDownload PDF (513K) -
Hiromitsu Takeuchi, Yoshiki Tsunekawa, Masahiro Okumiya1997 Volume 61 Issue 5 Pages 437-443
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe electrolyte jet containing ceramic particles not only greatly accelerates the deposition rate of the Ni-P matrix but also allows the volume fraction of particles and the phosphorus content in the deposit to be controlled by changing the jet velocity. Because of the forced nickel ion supply by the electrolyte jet, the deposition rate of the matrix becomes faster as far as the rate determining process is mass transfer. The volume fraction of Al2O3 particles is higher than that of SiC particles in the deposit when the jet velocity is high. The reverse takes place when it is slow. More nickel ions are adsorbed on Al2O3 particles with a larger specific surface, so that it is hard for Al2O3 particles to agglomerate in the electrolyte as compared with SiC particles. The phosphorus content in the matrix increases with jet velocity. The crystalline grain of the matrix becomes finer due to the hindered crystal growth of nickel by adsorbed phosphorus atoms.View full abstractDownload PDF (1027K) -
Kazuo Kameda, Katsunori Yamaguchi, Toshiko Kon1997 Volume 61 Issue 5 Pages 444-448
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe activities of indium in liquid In-Pb-Ag and In-Bi-Sb alloys have been determined by the emf measurement using a zirconia electrolyte at 1012∼1263 K and 886∼1179 K for fifteen different compositions of the two alloy systems, respectively. Combining the binary data on In-Pb and In-Ag alloys in the In-Pb-Ag system, and In-Bi and In-Sb alloys in the In-Bi-Sb system the isoactivity curves at 1100 and 1200 K, 1000 and 1100 K were obtained in the whole composition ranges, respectively. There seem no published data to be compared with.View full abstractDownload PDF (444K) -
Toshio Suzuki, Takeshi Sato1997 Volume 61 Issue 5 Pages 449-455
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSMinimal spanning tree has been applied to the analysis for spatial point distribution pattern of microstructures. The technical remarks on the analysis have been examined by using generated model patterns of square lattice, triangle lattice square inhibition and triangle inhibition models. The number of sample points is an important factor for comparing the patterns of the specimen microstructures with the model patterns and it should be in the same range of numbers for the models and microstructures. Both angular distributions of edges and power spectrum of Fourier transform images of pattern data give useful information for identifying the type of spatial patterns of the microstructure. The array of primary dendrite arms in the uni-directionally solidified nickel-based superalloy samples has been analyzed using the minimal spanning tree. It is shown that the spatial distribution of primary dendrite arms is neither regular nor periodic and is dominated by the square inhibition rule which prohibits primary arms to coexist within a certain distance. The change in the regularity of dendrite array with the growth conditions is quantitatively described from the obtained data.View full abstractDownload PDF (792K) -
Jicai Feng, Masaaki Naka, Julius C. Schuster1997 Volume 61 Issue 5 Pages 456-461
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSSiC was bonded to SiC using Ta foils at temperatures from 1673 to 1773 K for 3.6∼144 ks in vacuum. The reaction phase and microstructure formed at the an interfaces between SiC and Ta were investigated. At the initial stage, an hexagonal Ta2C phase is formed at the Ta side of the reaction zone, and the hexagonal Ta5Si3Cx phase at the interface SiC/Ta2C. At a longer bonding time, Ta and Ta2C were consumed and the cubic TaC, hexagonal TaSi2 and Ta5Si3Cx phase were detected in the reaction zone.
The reaction layer grew with the joining time following the parabolic law, and the activation energy for the growth was 266 kJ/mol.
At a constant bonding temperature of 1773 K, the strength of the SiC joint showed a maximum at the bonding time of 28.8 ks. The brittle single phase of TaSi2 decreases the strength of the SiC joint.View full abstractDownload PDF (740K) -
Yoshimitsu Okazaki, Emiko Nishimura, Sethumadhavan Rao, Tetsuya Tateis ...1997 Volume 61 Issue 5 Pages 462-469
Published: 1997
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe cytocompatibility of new Ti alloys not containing Al and V such as Ti-15%Zr-4%Nb-4%Ta-0.2%Pd-0.05%N-0.2%O and Ti-15%Sn-4%Nb-2Ta-0.2%Pd-0.2%O was investigated by comparing with that of pure Ti grade 2 and Ti-6%Al-4%V ELI (Extra Low Interstitial) alloys. The relative growth ratio for the medium extraction of Al, containing only few V ions (less than 0.03 ppm) was very low as compared to that of V-free Al extraction. However, mixed powder extraction such as Ti+Zr+Nb+Ta and Ti+Sn+Nb+Ta had evidently no effect on the relative growth ratio of the L929 cells. The relative growth ratios of both the L929 and MC3T3-E1 cells for the new Ti alloys were almost equal to unity and were slightly higher than pure Ti grade 2 and Ti-6%Al-4%V ELI alloys. Also, the influences of extracting conditions with Eagle’s minimum essential medium (Eagle’s MEM) solution for the L929 cells and ultra pure water for the MC3T3-E1 cells on the relative growth ratio of the cells were examined. Further, wear tests were conducted using the new Ti alloys, pure Ti grade 2 and Ti-6%Al-4%V ELI alloy disks against apatite ceramics and alloy pins in Eagle’s MEM solution. The relative growth ratios of the L929 and MC3T3-E1 cells were estimated using these wear test solutions. The relative growth ratio of the L929 cells were almost equal to unity for the new Ti alloys and pure Ti grade 2 against an apatite ceramics pin up to 105 wear cycles. However, the relative growth ratios of the L929 and MC3T3-E1 cells sharply decreased in the Ti-6%Al-4%V ELI disk against the apatite ceramics pin from 3×104 wear cycles. It was observed that the pH of the Eagle’s MEM solution gradually increased as the number of wear cycles increased in all the cases of alloy disks against the apatite ceramics pin, Also, the V ion concentration increased as the number of wear cycles increased. A similar result was obtained for the MC3T3-E1 cells. Further, the relationship between metallic concentration in the medium extracted with Ti, Al, V, Zr, Sn, Nb, Ta, and Pd powders and the relative growth ratios of the L929 and MC3T3-E1 cells were evaluated. A similar dependence of the concentration of vanadium ions and the relative growth ratios of the L929 and MC3T3-E1 cells were seen as in the case of wear tests.View full abstractDownload PDF (908K)
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