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Volume 56, Issue 7
Displaying 1-19 of 19 articles from this issue
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Akira Nozue, Kenji Kasuga, Tomoo Watanabe, Tadatsune Okubo1992 Volume 56 Issue 7 Pages 735-740
Published: 1992
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSA transformation toughening method has been known to enhance fracture toughness for ceramics. In the present study, nearly the same type of method has been developed to increase the fracture toughness of a material. A near beta type of Ti alloy was utilized as a model of the transformation toughening. For its Ti alloy, specimens consist of fine alpha precipitates within the beta matrix, after solution-treated and aged. The present method is taken as follows: Specimens were cathodically charged at 303 K and then baked at 473∼673 K in a vacuum furnace in order to form hydrides only on alpha precipitates. Fracture toughness tests were carried out with CT specimens of 10 mm thickness. At almost the same strength levels, only the fracture toughness was increased up to about 20% mainly due to the transformation of the alpha phase to hydrides. The hydrides were confirmed by a transmission electron microscope and hydrogen content measurement. Therefore, the present method made it possible to increase the fracture toughness and to retain the high strength.View full abstractDownload PDF (1768K) -
Taiji Hoshiya, Shoji Den, Hiroei Ando1992 Volume 56 Issue 7 Pages 741-746
Published: 1992
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSDeformation behavior of Ti-Ni shape memory alloys at temperatures below 673 K and of those irradiated by neutrons and subsequently annealed at 473, 523 and 573 K, has been studied by tensile tests. From experimental results of the high temperature tensile test, work-hardening exponents of the irradiated specimens showed a maximum value near 523 K. It is presumed that the order-disoder transformation under irradiation is involved in this case, since that peak may be due to the strain-hardening associated with the ordering. The unusual tensile properties were restored by annealing at elevated temperatures above 523 K after irradiation. Irradiations at 520 K had almost no influences on those tensile properties. It is suggested that irradiation induced and thermally activated vacancies assist the thermal recovery through enhancement of the ordering processes.View full abstractDownload PDF (820K) -
Taiji Hoshiya, Shoji Den, Hiroshi Katsuta, Hiroei Ando1992 Volume 56 Issue 7 Pages 747-756
Published: 1992
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSTransformation characteristics and deformation behavior of hydrogenated Ti-50.5 at%Ni alloys, which were occluded in a low pressure range of hydrogen between 1.1 and 78.5 kPa, have been studied by electrical resistivity measurement, tensile test, X-ray diffraction analysis and microstructural observation.
Ms temperature of the Ti-Ni alloys decreased with an increase in hydrogen content. This corresponds to the stabilization of the parent phase during cooling, which was confirmed by X-ray diffraction: The suppression effect of hydrogen takes place on the martensitic transformation.
Critical stress for slip deformation of hydrogenated Ti-Ni alloys changed with hydrogen content and thus hydrogen had a major influence on deformation behavior of those alloys. With hydrogen contents above 0.032 mol%, hardening was distinguished from softening which was pronounced in the contents from 0 to 0.032 mol%H.
Hydrides were formed in hydrogen contents over 1.9 mol%. The hydride formation results in the reorientation in variants of the R phase and an increase in the lattice strains of the parent phase.View full abstractDownload PDF (1793K) -
Satoru Yamamoto, Atsushi Kirihata, Masataka Mizuno1992 Volume 56 Issue 7 Pages 757-763
Published: 1992
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe aim of this investigation is the clarification of the mechanism of age-softening and the influence of pre-treatments on this phenomenon in Al-Fe alloys. The main results are as follows. The combination of treatments: soaking at 673 K, hot-rolling at 673 K and annealing at 673 K as pre-treatments results in age-softening in Al-Fe alloys. It has been cleared by the measurement of specific resistivity that the amount of Fe dissolved into matrix is always limited below 0.01 mass%Fe in the age-softened specimens. Electron microscopic observation has clarified fine precipitates smaller than 1 μm and recrystallized structures in the age-softened specimens but no such precipitates nor recrystallized structures in the work-hardened specimens.
Further, the lowering of recrystallization temperature has been confirmed by the experiments of isochronal annealing of specimens. Thus, the mechanism of age-softening in Al-Fe alloys is as follows: The pre-treatments are necessary for the complete precipitation of dissolved Fe which results in the lowering of recrystallization temperature. The age-softening occurs due to the recovery and recrystallization of the worked specimens at room temperature. The preexisting second phase (Al3Fe) in the as-cast state accelerates the precipitation of dissolved Fe. The physical meanings of each step of pre-treatments are as follows:
673 K: the temperature suitable for the complete precipitation of dissolved Fe in Al.
soaking: homogenizing of structure of segregated cast alloys which results in the easiness of following hot-rolling.
hot-rolling: acceleration of precipitation of dissolved Fe.
annealing: complete precipitation of remaining dissolved Fe.View full abstractDownload PDF (1918K) -
Kensuke Kageyama, Manabu Enoki, Teruo Kishi1992 Volume 56 Issue 7 Pages 764-769
Published: 1992
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSNumerical simulation of the shape and width of the transformed zone and R-curve behavior in partially stabilized zirconia was carried out. The toughening mechanism by transformation has been theoretically studied by McMeeking et al. However, the result by their model is not coincident with the experimental data in Ce-TZP by Yu et al. because they assumed that the transformation volume fraction is low and the stress field is generated only from the main crack tip. In this paper, we assume that the stress filed is generated from both main crack tip and transformed particles, and that the transformation distribution is discontinuous by each particle. As a result, we have two formation processes of the transformed zone. In the case of the low transformation volume fraction, the R-curve behavior agrees with the analysis by McMeeking et al. and the width of the transformed zone with crack extension is almost constant. In the case of the high fraction, however, the transformed zone extends and elongates along the crack tip, and the shape changes and the width of the transformed zone extends discontinuously. It demonstrates a step-like R-curve behavior.View full abstractDownload PDF (914K) -
Yasuo Kogo, Yutaka Kagawa, Hiroshi Hatta1992 Volume 56 Issue 7 Pages 770-778
Published: 1992
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe fracture toughness of CeO2 stabilized ZrO2 (CeO2-ZrO2) has been measured under mode I, mode II and their mixed-mode conditions. The conventional single-edge-notched bending (SENB) test was carried out to obtain the mode I fracture toughness. The anti-symmetric four-point bending (AS4PB) test, which is the modified SENB test, was adopted for the mixed-mode and mode II fracture toughness tests. The obtained stress intensity factors at unstable fracture were discussed with the phase transformation behavior of ZrO2 and the phase-transformation toughening mechanism.
The results showed the maximum principal stress criterion and the non-coplanar strain energy release rate criterion is applicable to the KI-KII fracture curve. Under the mode II loading condition, the KIIC/KIC value of CeO2-ZrO2 was 0.6, which was lower than those of non-transforming brittle materials. The low KIC/KIIC value is attributed to the shielding effect by the transformation which is effective only on the mode I stress intensity.View full abstractDownload PDF (2359K) -
Shigeaki Sugino, Takashi Hori, Hisato Hagiwara1992 Volume 56 Issue 7 Pages 779-784
Published: 1992
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe activities of Zn in dilute solution with molten Au and Au-Cu alloy have been measured by the use of an isopiestic method at 1423 K, and the first and second order interaction parameters between Zn and Cu in molten Au have been determined.
Additions of Cu to Au-Zn binary alloy increase the activity of Zn. The activities of Zn in the Au-Cu-Zn ternary molten alloys are well expressed by Wagner’s relation taken into account the second order terms, in the composition range NZn+NCu≤0.10. It has been demonstrated that the quadratic formalism proposed by Darken is valid for this system in the composition range, NCu≤0.08 and NZn<0.07.
Activity coefficient of Zn at infinite dilution of Zn in Au-Cu binary solvent varies with NAu⁄NCu smoothly, and seems to be qualitatively in accordance with the prediction from the equation formulated by Richardson.View full abstractDownload PDF (705K) -
Toshio Shimoo, Ken-ichi Kakimoto, Kiyohito Okamura1992 Volume 56 Issue 7 Pages 785-793
Published: 1992
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe pyrolysis of Si-Ti-C-O amorphous fiber (Tyranno fiber) coated with oxide film was investigated at temperatures between 1573 and 1773 K. After the oxide film was formed around the fiber in an O2 gas stream, the atmosphere gas was changed from O2 to Ar. During this heat treatment, the mass change of the fiber was measured by means of a thermobalance. The heat-treated fiber was examined with X-ray diffraction, SEM and TEM observation.
At 1773 K, the fiber coated with the oxide film pyrolyzed completely, and the growth and coarsening of β-SiC crystal was observed. At the temperatures lower than 1723 K, the size of β-SiC crystallite, to which the amorphous fiber was crystallized before it was coated with the oxide film in the O2 gas stream, remained unchanged in the Ar gas stream. The tensile strength of this fiber was from 1/5 to 1/4 as large as that of the original fiber.
If adequate control is provided in the formation of the oxide film, the high-temperature strength of Tyranno fiber can be improved.View full abstractDownload PDF (3412K) -
1992 Volume 56 Issue 7 Pages 793
Published: 1992
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSPlease see pdf. Wrong:X=ΔW/{W0⋅(MSiO2+0.02MTiO2)/(MSi+0.02MTi+1.40MC+0.64MO)} Right:X=ΔW/[W0⋅{(MSiO2+0.02MTiO2)-(MSi+0.02MTi+1.40MC+0.64MO)}/(MSi+0.02MTi+1.40MC+0.64MO)]View full abstractDownload PDF (25K) -
Effect of Molybdenum Content on the Corrosion of 9Cr Ferritic Steels in a Flowing Sodium EnvironmentIsao Mutoh, Tadashi Suzuki1992 Volume 56 Issue 7 Pages 794-801
Published: 1992
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSIn a previous paper the sodium compatibility of high purity (5∼15) Cr-1Mo-0.1C ferritic steels had been studied in order to know the effects of chromium content and the influence of sodium velocity, using a sodium loop constructed of Type 316 stainless steel. Molybdenum has been considered to be one of the alloying elements having higher corrosion resistance to sodium. In the present work, the compatibility of high purity 9Cr-(0∼6)Mo with and without 0.1C ferritic steels in a high velocity sodium environment has been studied to know the effects of molybdenum content. The sodium conditions used were 873 and 923 K, 1∼2 mass ppm oxygen, and 4.0 m/s in velocity. Since the compositions of ferritic steels were close to those in quasi-equilibrium in the sodium loop (as to the contents of Fe, Cr and Ni; Fe-∼6Cr-<1Ni at 923 K and Fe-∼7Cr-<1Ni at 873 K) and the chromium contents were a little higher than those in quasi-equilibrium, the corrosion loss was relatively small with the dissolution of small amounts of chromium and the slight deposition of nickel. Both corrosion loss and decarburization of the steels were decreased by the addition of up to ∼1 mass% molybdenum, but they were scarecely decreased by a further addition of molybdenum. Also, tensile tests of sheet specimens of the ferritic steels before and after exposure to sodium showed almost no beneficial effects of more than ∼1 mass% molybdenum additions. Thus, ∼1 mass% molybdenum additions are considered to be most favorable to the high purity 9Cr ferritic steels as other benefits such as strengthening of the steels by formation of intermetallic compounds composed of molybdenum, iron and other metallic elements.View full abstractDownload PDF (2498K) -
Yukinori Ono, Tsutomu Takechi, Noriko Murai, Keisaku Ogi1992 Volume 56 Issue 7 Pages 802-809
Published: 1992
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe partition coefficients of chromium and carbon to primary austenite were determined on Fe-Cr-C ternary alloys containing 1.1 to 3.6 mass%C and 1.5 to 25.5 mass%Cr. The specimens were held for 3.6 ks just below the liquidus temperature, and the mixtures of liquid and solid were quenched onto a copper chill plate. Chromium and carbon contents of primary austenite (CSCr, CSC) and those of quenched liquid (CLCr, CLC) were analyzed with EPMA, and the partition coefficients (kCr and kC) were evaluated as CSCr/CLCr and CSC/CLC. To avoid the influence of contamination in EPMA analysis, the C content was measured on the fresh surface of the specimen moving at a constant rate of 60 μm/min.
kCr decreased from 0.80 to 0.53 mainly with the increase in carbon content of the alloy, while kC decreased from 0.38 to 0.25 with the increase in chromium content. The content of Si from 0.19 to 0.25 mass% dissolved into liquid from the crucible (46 mass%Al2O3, 50 mass%SiO2) little influenced both kCr and kC.View full abstractDownload PDF (1238K) -
Yuichi Nakamura, Teruo Izumi, Yuh Shiohara, Shoji Tanaka1992 Volume 56 Issue 7 Pages 810-818
Published: 1992
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe unidirectional solidification by a zone melt method was performed in order to clarify the solidification mechanism of YBa2Cu3Ox (123) superconducting oxides. The continuous growth of 123 crystals were obtained under the growth rate less than 3 mm/h. A sharp faceted interface of 123 crystals was observed in the sample grown at 1 mm/h and the volume of the 211 phase decreased drastically from liquid into 123 crystal across the interface. From these results, we concluded that the necessary solute for peritectic reaction (211+liq.→123) is provided through a liquid. Based on this idea, we considered the driving forces for diffusion in liquid between the 211 particle and the growing interface, and developed a unidirectional solidification model. From this growth model, we can predict the balanced velocity of 123 growth and the distributions of 211 particles trapped in 123 crystal, and this model is in good agreement with the experimental results.View full abstractDownload PDF (1697K) -
Jun Su Kim, Junichi Kaneko, Makoto Sugamata1992 Volume 56 Issue 7 Pages 819-827
Published: 1992
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSBoth cast and extruded composites of SiC whisker reinforced AZ91 magensium and 2324 aluminum alloys were fabricated by high pressure infiltration of the alloy melt and hot extrusion of the composite ingot. Deformation behavior at elevated temperatures was investigated by tensil tests under various conditions. The extruded composites of SiCW/AZ91 and SiCW/2324 showed higher tensile strength than each matrix alloy at temperatures below 573 K. On the contrary, tensile strength of the extruded composites was lower than that of each matrix alloy at temperatures above 573 K. The cast composites of SiCW/AZ91 showed, however, higher tensile strength than the matrix alloy at all the tested temperatures. The strain rate exponent (m-value) of the cast composites was lower than that of the matrix alloy, whereas the m-value of extruded composites was higher than that of the matrix alloy. The highest tensile elongation of SiCW/AZ91 extruded composites was about 100% at 703 K under an initial strain rate of 5×10−2s−1. Lower tensile strength, higher elongation and higher m-value of extruded composites were attributed to their very fine grain structures in which grain boundary sliding preferentially occurred at elevated temperatures.View full abstractDownload PDF (2072K) -
Tai-Whan Lim, Koji Hayashi1992 Volume 56 Issue 7 Pages 828-832
Published: 1992
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe pore microstructures in both the incompletely densified sintered compact of carbonyl iron powder near the interface of the diffusion couple of the sintered compact/Mo or Nb plate, etc., and the completely densified sintered compact of oxide-reduced iron powder (containing the oxide particles and no pores) into which carbon was diffused by heating in CH4 atmosphere, were investigated in order to verify the present authors’ hypothesis that the incomplete or complete densification of iron fine powder sintered compact mainly depends on whether the equilibrium pressure (PCO) of CO gas which is generated by the reduction reaction of the oxide with impurity carbon and is trapped in closed pores, is higher or lower than the surface stress, i. e., the driving force for pore shrinkage.
The results obtained were as follows: (1) The closed pores in the carbonyl iron sintered compact did not disappear by diffusing-in of the elements like Mo which has no ability to decrease PCO, and did disappear by that of the elements like Nb which has ability to decrease PCO. (2) The diffusing-in of carbon into the oxide-reduced iron sintered compact resulted in the formation of pores around the oxide particles near the surface of the compact. (3) The above results as well as the results and considerations in the present authors’ previous report could be said to all support the above hypothesis.View full abstractDownload PDF (1651K) -
Hiroshi Kimura, Wha.-Nam, Myung, Shinichi Kobayashi, Masayoshi Suzuki, ...1992 Volume 56 Issue 7 Pages 833-841
Published: 1992
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSA novel HIP processing of mechanically alloyed(MA) amorphous powder is developed, based on the densification via viscous flow mechanism, with which it is possible to obtain a fully dense amorphous compact of large scale. This study describes the evaluation of viscous flow in a thermal mechanical analyzer (TMA) and the optimization of HIP variables, time, temperature, pressure and heating rate for a nearly full densification of MA amorphous Co79.5Nb15Zr5.5 powder.
The pre-compacted compressive sample of amorphous Co79.5Nb15Zr5.5 shows a drastic plastic displacement after thermal shrinkage in a constant heating rate experiment far below the temperature at the onset of crystallization(Tx). An analysis of the TMA curve for a porous amorphous compact permits us to derive the displacement rate and the viscosity. The temperature dependence of the newtonian viscosity(η) is fairly well expressed by an Arrhenius typed relation of η=η0 exp (221 kJ·mol−1/kT) within the range of the experiment in this study. The well-defined glass temperature(Tg) shows a constancy for heating rates above 1.7×10−1 K·s−1, but a great increase due to structural relaxation below 8.3×10−2 K·s−1.
HIP cmpaction of MA amorphous powder in vacuumed can in a temperature range, Tg<T<Tx under a pressure of 196 MPa makes it possible to obtain a high density amorphous product with a diameter of 24 mm at the nearly maximum in our laboratory HIP apparatus. An increase in holding time and/or temperature leads to an increase in relative density of the amorphous HIP compact, approaching to theoretical one. These increases are in good agreement with a HIP map which is constructed based on newtonian viscous flow mechanism with an Arrhenius equation with an increased η0 for MA amorphous powder subjected to extensive structural relaxation.
The compressive strength(σF) for the amorphous HIP compact of Co79.5Nb15Zr5.5 greatly increases with decreasing porosity(Po). A power law of compressive strength is derived as σF=BP−0.5o.View full abstractDownload PDF (1779K) -
Yasushi Fukuzawa, Sigeru Nagasawa, Yo Kojima, Hiroshi Sakuta, Kazusige ...1992 Volume 56 Issue 7 Pages 842-848
Published: 1992
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSAs metal-ceramics jointed materials are processed at elevated temperatures, thermal residual stresses are generated on the bonding interface during the cooling process. The discrepancy of thermal expansion coefficients between metals and ceramics causes a large residual stress on the ceramic side interface and the overall ceramics strength decreases at a edge of the bonding interface as a results of residual stress concentration effects. In order to make a high strength joint, the thermal peak residual stress has to be reduced and its distribution is expected to be uniform. Effects of three types of interface shapes, flat, convex and concave on the bonding strength are investigated in this study. An electrical conductive TiB2-base ceramic is reshaped using an electrical conductive discharge machine (EDM) with a nickel electrode. The ceramic is then jointed with the electrode using a monel sheet as an insert material by the diffusion bonding heat process. To study the detailed residual stress levels and their distribution around the interface, tensile tests are conducted. A 2-dimensional finite element method (FEM) analysis based on an elasto-plastic condition of these shaped joints is also carried out. From experimental observations, the FEM analysis results imply that the crack propagation behavior is associated with the residual stress levels and their distributions. The results also show that in all cases the largest tensile stress level is present around the outside periphery of the interface, and the distribution of the principal stress is affected by the shape of the interface.View full abstractDownload PDF (1311K) -
Hitoshi Nakamura, Masahiro Kitada1992 Volume 56 Issue 7 Pages 849-853
Published: 1992
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe purpose of this work is to establish the effect of induced and shape magnetic anisotropy on the magnetoresistive response curve (MRRC) of permalloy thin film sensors. The films were deposited by electron beam system, and the sensors were prepared using photolithography. The dimensions of the sensor were 300 μm long, 20 μm wide and 0.05 μm thick. The direction of the induced anisotropy was tilted through θ=0°∼90° to shape anisotropy (along sensor’s length). The MRRC was measured under 50 Hz AC field (H=8 kA/m) applied in the sensor’s width. The results are as follows. Discontinuous MRRC with the Barkhausen noise was obtained in the sensors with θ≥10° and the maximum noise was attained at θ=90°. However, continuous MRRC without noise was obtained in the sensor with θ=0°∼5°. The bitter figure, after the AC erasure along sensor’s width, showed a single domain at θ=0° and hence revealing clear domain structure with increasing θ. Domain wall migration caused by the DC magnetic field was observed in the sensor with θ≥10°. From these facts it might be said that induced anisotropy contributes to nucleation of the reversed domains which nucleate easily as θ increases. The Barkhausen noise is due to the abrupt expansion of reversed domain. However, the θ dependence of the effective anisotropy direction, α, calculated by a coherent rotation model agrees fairly well with that of the additional AC field direction to the sensor’s width direction, Δφ0, which minimizes the Barkhausen noise. This result strongly suggests that the effective anisotropy experimentally obtained is in the direction of Δφ0 from the sensor’s length direction, and that the continuous parts of MRRC are due to the coherent rotation based on the effective anisotropy. The maximum value of Δφ0=3° corresponds to θ=40°∼50°. Thus, the effective anisotropy might be attributable to the shape anisotropy.View full abstractDownload PDF (833K) -
Kazuhide Ishii, Tatsuo Kawasaki1992 Volume 56 Issue 7 Pages 854-862
Published: 1992
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSThe oxidation behavior of Fe-20∼25Cr-5Al alloys of 50 and 500 μm thicknesses and containing up to 0.09%La or up to 0.06%Ce was examined in an isothermal oxidation test at 1423 and 1473 K in air. Mass gain measurements were made, and an investigation of the oxide layer by scanning electron microscopy, X-ray diffraction, electron probe microanalysis, and chemical analysis was carried out after the test.
The oxidation process proceeds in three stages in the 50 μm foil. In the first stage, an Al2O3 layer grows governed by the parabolic rate law, which is the same as the rate law for thicker specimens. In the second stage, a Cr2O3 layer grows between the Al2O3 layer and the substrate bulk after the exhaustion of the Al in the bulk. The kinetic behavior of the oxidation of the Cr2O3 layer follows the linear oxidation law, and the linear rate constant is proportional to the parabolic rate constant in the first stage. In the third stage, Fe in the bulk begins to oxidize after the Cr content of the bulk falls below a critical value as a result of Cr oxidation. The oxidation of Fe then leads to “Breakaway” oxidation.
The addition of La decreases the growth rate of the Cr2O3 layer by reducing the growth rate of the Al2O3 layer and improves the oxidation resistance of the Cr2O3 layer. The duration of the second stage is thereby extended, and the La-containing foil exhibits good oxidation resistance.
The addition of Ce, in contrast, increases the growth rate of the Cr2O3 layer by accelerating the growth of the Al2O3 layer and thus leads to quick “Breakaway” oxidation.View full abstractDownload PDF (1581K) -
Seiichi Iwata, Yuzuru Ohji, Akitoshi Ishizaka1992 Volume 56 Issue 7 Pages 863-864
Published: 1992
Released on J-STAGE: April 04, 2008
JOURNAL FREE ACCESSDownload PDF (290K)
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