MATERIALS TRANSACTIONS
Online ISSN : 1347-5320
Print ISSN : 1345-9678
ISSN-L : 1345-9678
Volume 45 , Issue 7
Showing 51-88 articles out of 88 articles from the selected issue
  • Setsuo Takaki, Kazuhiro Fukunaga, Junaidi Syarif, Toshihiro Tsuchiyama
    2004 Volume 45 Issue 7 Pages 2245-2251
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    In martensitic steels, it is well known that a certain chemical driving force (about 180 MJ/m3) is required to start martensitic transformation (Ms), and additional driving force has to be charged further to complete the transformation (Mf). In the case of metastable austenitic steels with Ms temperature at around room temperature, however, only the chemical driving force needed to start martensitic transformation has been stored at room temperature. Hence, the state of austenite is very unstable thermally. It has already been known that such a metastable austenite undergoes a partial martensitic transformation during isothermal holding at room temperature or cooling to a low temperature. It is very convenient to investigate the behavior of martensitic transformation of austenite. In this study, the effect of austenite grain size on martensitic transformation is introduced from the viewpoint of microstructural analysis and thermo-dynamics. The steel used in this investigation is an Fe-16 mass%Cr-10 mass%Ni ternary alloy, which has Ms temperature at around room temperature. The grain size of this steel can be controlled from 0.8 μm to 80 μm using the technique of reversion of deformation induced martensite. In the material with coarse grain size (80 μm), about 18% of martensite was detected at room temperature and the amount of martensite was increased to 50% by the following subzero treatment to 77 K. However, martensite was hardly detected in the material with ultra fine grains (0.8 μm) even after the subzero treatment. It was found that such a stabilization occurs in the materials with the grain size below 10 μm and the stabilization was reasonably explained by considering the relation between austenite grain size and elastic strain energy which is required on the single variant martensitic transformation.
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  • Andrey Belyakov, Yoshikazu Sakai, Toru Hara, Yuuji Kimura, Kaneaki Tsu ...
    2004 Volume 45 Issue 7 Pages 2252-2258
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    The annealing behaviour of ultrafine grained steels containing nano-scale dispersed oxides was studied in a temperature range of 600—900°C by means of microstructural observations and hardness measurement. The starting materials with submicrocrystalline structures were developed by mechanical milling of Fe-Fe3O4 powders followed by consolidating bar rolling at 700°C. Depending on the initial oxygen content and the mechanical milling time, the fraction of dispersed oxides varied from 0.3 to 3.0 vol%. During the heating up to 800°C (i.e. within the ferrite region), the initial ultrafine grained microstructures were essentially stable against any discontinuous grain growth. The grain coarsening and the softening can be roughly expressed by power-law functions of annealing time. The main mechanism of microstructure evolution that operated during annealing is considered as a normal grain growth accompanied by recovery. The grain coarsening is characterized by a rather high value of the grain-growth exponent of about 20. The grain growth kinetics correlates with the oxide coarsening. The effect of dispersed oxides on the annealing behaviour of submicrocrystalline oxide bearing steels is discussed in some detail.
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  • Toshihiro Tsuchiyama, Yoshikazu Nakamura, Hideyuki Hidaka, Setsuo Taka ...
    2004 Volume 45 Issue 7 Pages 2259-2263
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    Ultrafine grained austenitic structure was obtained in 18Cr-9Ni stainless steel by thermomechanical treatment using reversion from deformation-induced martensite. The superplastic deformation behavior was investigated at 923 K for the steels containing various amounts of retained martensite particles in the initial structure before tensile testing. The retained martensite was effective for suppressing grain growth of austenite and necessary for the superplasticity although it was thermodinamically unstable phase and gradually decreased its volume fraction with superplastic deformation. Therefore, the superplastic elongation was strongly dependent on the initial volume fraction of the retained martensite. The total superplastic elongation was enlarged with increasing the initial amount of martensite, and the maximum elongation of about 270% was obtained when the volume fraction was controlled to be around 10 vol%. However, the increase in elongation was leveled off in the range above 15 vol% martensite. The effect of the retained martensite on the superplasticiy was discussed in connection with the changes in volume fraction of the martensite, austenite grain size and deformation mechanism.
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  • Nicholas Edward Hamilton, Michael Ferry
    2004 Volume 45 Issue 7 Pages 2264-2271
    Published: 2004
    Released: June 24, 2005
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    A sub-micron grained microstructure in an Al-0.2 mass% Sc alloy was produced by high strain deformation using Equal Channel Angular Pressing (ECAP). The alloy was solution treated prior to deformation, deformed by ECAP then aged at low temperature to produce a sub-micron grained microstructure with a large fraction of high angle grain boundaries (HAGB) decorated with fine Al3Sc particles. General grain stability and particle/grain boundary interactions were studied using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), focussed ion beam (FIB) microscopy and transmission electron microscopy (TEM). The fine-grained microstructure was found to be highly stable during annealing at temperatures up to 500°C due to Zener pinning from stable Al3Sc particles. The volume fraction, f, and average radius, r, of particles and their rate of coarsening were found to have a strong influence on grain growth. It was found that the limiting grain size, Rc, in the Al-Sc alloy may reasonably be predicted by the relation: Rc = 0.17r/f. This relation is known to be applicable for coarse-grained alloys (>1 μm) and indicates its validity for predicting the limiting grain size in sub-micron, particle-containing alloys.
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  • Nobuhiro Tsuji, Susumu Okuno, Yuichiro Koizumi, Yoritoshi Minamino
    2004 Volume 45 Issue 7 Pages 2272-2281
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    A plain IF steel and a P-added IF steel having various ultrafine grain sizes from 0.24 to 11 μm were fabricated by the accumulative roll bonding (ARB) process followed by annealing. Dynamic fracture toughness of the ultrafine grained IF steels was investigated as a function of grain size by miniaturized Charpy impact test. The static strength of the IF steels significantly increased with decreasing the grain size, while the uniform elongation was limited in the ultrafine grained samples. A number of delamination appeared in the impact-tested specimens, especially in the ultrafine grained materials at low temperatures. It was concluded that the frequent delamination is not owing to insufficient roll-bonding in the ARB specimens but it is rather a characteristic feature of the ultrafine grained materials fabricated through heavy deformation. Because of the delamination, the absorbed energy in the impact test continuously decreased with decreasing the test temperature. On the other hand, an obvious change from the ductile fracture surface characterized by dimples into the brittle fracture surface mainly due to intergranular fracture was recognized at a certain low temperature. The ductile-brittle transition temperature determined from the microscopic fracture surfaces greatly decreased with decreasing the grain size, and finally no brittle fracture happened even at −190°C when the grain size was smaller than 5 μm or 2 μm in the plain IF steel or the P-added IF steel, respectively. It was concluded that the ultra-grain refinement is quite effective to improve the low-temperature toughness of ferritic steels and that it is possible to make phosphorus substantially harmless by grain refinement.
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  • Giuliano Angella, Paola Bassani, Ausonio Tuissi, Maurizio Vedani
    2004 Volume 45 Issue 7 Pages 2282-2287
    Published: 2004
    Released: June 24, 2005
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    A study was carried out on the aging behaviour of a solution treated 6082 aluminium alloy deformed by equal channel angular pressing up to six passes. Aging of the so obtained ultrafine alloy was studied by DSC and TEM analyses as well as by isothermal treatments at 130, 160 and 180°C. The results showed that the formation of metastable β″ and β′ precipitates were markedly anticipated and that the stable β phase was partially suppressed in the alloy processed to 4 and 6 passes, presumably due to anticipated precipitation of Si-rich particles. TEM analyses revealed that a transition in strengthening-precipitate structure occurred in the severely deformed alloy leading to a predominance of globular precipitates over the rod like phases typically found in the undeformed and aged samples. Tensile tests carried out on severely deformed and aged samples allowed to quantify the maximum strength achievable by the 6082 alloy after concurrent grain refinement and peak-hardness aging at 130°C.
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  • Naoya Machida, Masafumi Noda, Kunio Funami, Masaru Kobayashi
    2004 Volume 45 Issue 7 Pages 2288-2294
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    The current study was conducted to develop a Ti-6Al-4V alloy composite material with a fine structure with improved mechanical properties by precipitating TiC particles via reaction-sintering and, additionally, by incorporating the effects of hydrides formed by hydrogenation treatment, using powder to which Mo2C had been added. The effects of precipitated TiC particles, and the subsequent generation of hydrides by hydrogenation treatment, heavy-strain working, and recrystallization treatment on grain refinement during the forming process were studied by means of structural observations. Warm rolling and multi-axial alternate forging (MAF) were employed as the heavy-strain working methods. The base metal structure of the Ti-6Al-4V composite material prepared by hydrogenation treatment on the sintered body prepared by spark plasma sintering (SPS) contains particles with a grain size not greater than 1 μm, which become finer with increasing hydrogen content. The particle size of TiC formed by reaction sintering, however, is not changed by heavy-strain working after hydrogenation. Its room temperature tensile strength increases with the amount of TiC precipitation, and is higher than that of non-hydrogenated material.
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  • Eiichi Sato, Kenshi Kawabata, Koichi Kitazono, Kazuhiko Kuribayashi
    2004 Volume 45 Issue 7 Pages 2295-2303
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    Composite creep deformation was analyzed, based on a continuum plasticity representation of the matrix, in an ideal composite at high temperatures in the case of negligible interfacial diffusion and sliding. A general formula of the steady-state creep strain rate was derived for a composite consisting of an ellipsoidal rigid reinforcement and a creeping matrix with a stress exponent of one. A closed-form solution was then derived for a composite with a cylindrical reinforcement under pure shear deformation in a two-dimensional analysis. The resultant creep deformation satisfies the requirements of impotency, volume conservation and interfacial continuity. Traces of two types of edge dislocations were analytically drawn; they show that dislocations climb over the reinforcement, retaining no dislocations either in the matrix or at the interface. Also, two types of dislocations simultaneously climb up and down at any portion in the matrix through dislocation core shuffling without long-distance diffusion. Finally, it was concluded that plastically-accommodated creep is characterized by two types of dislocations that simultaneously climb over a reinforcement, generating a heterogeneous creep strain increment without long-distance diffusion.
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  • Yong-Jai Kwon, Ichinori Shigematsu, Naobumi Saito
    2004 Volume 45 Issue 7 Pages 2304-2311
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    Ultra-fine grained specimens of 1050 Al alloy were produced by friction stir process (FSP), and also the influence of the tool rotation speed on the microstructure and mechanical properties was experimentally investigated. FSP was performed with only a single pass at tool rotation speeds ranging from 560 to 1840 min−1. For 1350 min−1 and below, the hardness within friction stir processed zone (FZ) was higher on the advancing side than on the retreating side. However, around the FZ, no heat affected zone in which the hardness drops was formed. For 1840 min−1, the hardness distribution was roughly uniform within the FZ. The average hardness of the FZ was isotropic and was increased by 37% compared with the cold-rolled 1050 Al alloy (starting material) with decreasing the tool rotation speed, i.e. with decreasing the grain size. During tensile deformation, the friction stir processed materials with grain sizes of 2 μm and below exhibited an abrupt stress drop phenomenon at very early stage, which was not accompanied by a further stress increase resulting from strain strengthening. On the contrary, grain sizes of 2∼3 μm provided strain strengthening after a small stress drop. For grain sizes of 3∼4 μm, stress reached a maximum value with strain strengthening after a continuous transition from elastic to plastic deformation with no abrupt stress drop. When the grain size was below 3 μm, there was no severe loss of total elongation because of a large local elongation after the stress drop. The total elongation increased with the grain size. The tensile strength was inversely dependent on the grain size and increased remarkably to even about 46% greater than that of the starting material. Therefore, it is evident that FSP is very effective in enhancing hardness and tensile strength of materials through grain refinement.
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  • Felipe Hernandez-Santiago, Nicolas Cayetano-Castro, Victor M. Lopez-Hi ...
    2004 Volume 45 Issue 7 Pages 2312-2315
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    The precipitation kinetics in a Cu-4 mass% Ti alloy was studied using SEM, TEM, XRD and Vickers hardness. A Cu-4 mass% Ti alloy was prepared, homogenized, solution treated and then aged at 673, 773 and 873 K for times between 0.6 to 720 ks. The XRD and TEM results indicated that the phase decomposition occurred by spinodal decomposition during the early stages of aging. The growth kinetics of composition modulation wavelength is very slow at the early stages of aging. The precipitation of metaestable β′ (Cu4Ti) preceded to that of the equilibrium phase β phase (Cu3Ti), which formed through cellular precipitation. The coarsening process of β′ phase followed the LSW theory for diffusion-controlled growth. The activation energy for this coarsening process was determined to be about 190 ± 10 kJ·mol−1. The discontinuous precipitation of β phase has an activation energy of about 207 kJ·mol−1 and an exponent time of about one. The highest hardness and fastest transformation kinetics occurred at aging temperatures of 673 and 873 K, respectively.
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  • Yoshimasa Takayama, Jerzy A. Szpunar
    2004 Volume 45 Issue 7 Pages 2316-2325
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    The relation between the stored energy and the Taylor factor (TF) has been investigated using the SEM/EBSP analysis in an Al-Mg-Mn alloy sheet worked by the continuous cyclic bending (CCB). The analysis reveals that the stored energy is high for the high TF region, whereas a significant increase of the stored energy with the decrease of the Taylor factor appears in the vicinity of the minimum TF value of 2. This observation is discussed using the Schmid factor calculated. Further, the local strain accommodation during deformation is analyzed for grains of different orientations. The stored energy is derived from the calculation based on the kernel average misorientation (KAM).
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  • Akira Taniyama, Masahiro Arai, Toru Takayama, Masugu Sato
    2004 Volume 45 Issue 7 Pages 2326-2331
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    In-situ observation was performed with X-ray diffraction technique using synchrotron radiation to reveal growth behavior of the Fe-Zn intermetallic compounds, the ζ and δ1 phases, at the initial stage of galvannealing process. The galvanized sample and electroplated sample were used in the observation. The diffraction peak profiles were successfully obtained at intervals of 1 second with heating the sample, and the growth of the Fe-Zn intermetallic compounds was observed dynamically. In the galvanized sample including a small amount of aluminum in the coating, there was an incubation period of 7 seconds before the δ1 phase started to grow. The thickness estimated with the peak intensity of the δ1 phase increased in proportion to the square root of heating time when the incubation period was taken into account. In the electroplated sample including no aluminum in the coating, the thickness of ζ phase increased in proportion to the square root of heating time. The δ1 phase started to grow as soon as the ζ phase occupied the entire coating. The thickness of the δ1 phase also increased in proportion to the square root of heating time. These results suggest that that the growth behavior of the δ1 phase at the initial stage of galvannealing is dominated by the interdiffusion between Fe and Zn, neither by interfacial reaction nor by autocatalytic reaction whether the coating contains aluminum or not.
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  • Yongzhong Zhan, Guoding Zhang, Yinghong Zhuang
    2004 Volume 45 Issue 7 Pages 2332-2338
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    The effects of applied load, sliding velocity and SiC volume fraction on the transitional behavior between mild and severe wear in SiC particulate reinforced copper matrix composites were studied under dry sliding wear condition. Increasing SiC fraction or decreasing sliding velocity delays the occurrence of severe wear up to higher transition load. Mechanically mixed layer (MML), which is markedly harder than that of the bulk material, is absent in the post-transition regime. The coverage rate of MML is affected by applied load and sliding velocity. SiC particulates act as load-bearing components and lessen the frictional deformation extent in the subsurface region. In the pre-transition regime, microcrack propagation induced detachment of MML and subsurface material are the primary wear mechanism. In the severe wear process, thermally activated subsurface deformation plays a significant role in the tear of surface layer from the substrate material.
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  • Woei-Shyan Lee, Tai-Nong Sun
    2004 Volume 45 Issue 7 Pages 2339-2345
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    This paper studies the dynamic plastic flow behaviour, fracture characteristics, and microstructural evolution of Inconel 690 alloy under impact loading conditions. Compressive impact tests are performed using the compressive split-Hopkinson bar at strain rates ranging from 2.3 × 103 to 8.3 × 103 s−1 at room temperature. The effects of strain rate on the dynamic flow response, work hardening characteristics, strain rate sensitivity, and thermal activation volume are evaluated. A constitutive law based on the Zerilli-Armstrong model is proposed to describe the impact flow behaviour. The relationships between flow stress, dislocation, and twinning are analyzed and discussed in relation to the loading conditions. The evolutions of the dislocation and twinning substructures are investigated using transmission electron microscopy. Damage initiation and the fracture mechanisms are evaluated by scanning electron microscopy. The flow stress-strain response is shown to be significantly dependent on the strain rate, which not only causes obvious changes of the work hardening rate, strain rate sensitivity, and activation volume, but also influences the dislocation tangling and deformation twin substructures. The results indicate that the catastrophic failure at high strain rates results from the formation of localized shear bands. Finally, it is shown that the proposed constitutive law provides accurate predictions of the stress-strain relationship.
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  • Zan Bian, Jamil Ahmad, Wei Zhang, Akihisa Inoue
    2004 Volume 45 Issue 7 Pages 2346-2350
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    An in situ formed (Cu0.6Zr0.25Ti0.15)93Nb7 bulk metallic glass (BMG) composite was prepared successfully. The ductile Nb-rich crystalline phase with a dendritic structure disperses homogeneously in the BMG matrix. The mean size of the dendritic Nb phase is about 5∼10 μm. For Cu-Zr-Ti-Nb glassy ribbons, the additions of Nb element cause the glass transition and crystallization onset temperature to shift to much higher values, and improve the thermal stability of the glassy phase. For the in situ formed (Cu0.6Zr0.25Ti0.15)93Nb7 bulk metallic glass composites, its glass transition temperature and crystallization onset temperature is almost the same as those of the Nb-free Cu60Zr25Ti15 BMG, implying that almost all the added Nb element precipitates from the melt upon cooling. The (Cu0.6Zr0.25Ti0.15)93Nb7 BMG composite also presents a good combination of excellent mechanical properties. The compressive fracture strength and fracture elongation are 2130 MPa and 6.4%, respectively. The increase in elongation results from the homogeneous dispersion of the ductile and dendritic Nb-rich crystalline phase in the BMG matrix.
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  • Tatsuro Morita, Yusuke Iwasaki, Kazuhiro Kawasaki
    2004 Volume 45 Issue 7 Pages 2351-2356
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    The effects of a surface-layer whose Young's modulus is lower than that of the substrate on the fatigue strength were studied. Pure iron plates possessing pure titanium layers on the both sides were prepared as a model material. The formation of the titanium layer remarkably improved the fatigue strength of pure iron. In addition to the fatigue test, we made a calculation of the image stress which acts on a dislocation due to the discontinuity of the elastic constants at the surface and interface. As a result, it was found that the absolute value of image stress in the vicinity of the surface becomes smaller as the elastic modulus of the surface-layer is decreased. From the results of the above experiment and calculation, it was thought that the improvement of the fatigue strength with the formation of the titanium layer was caused by the reduction in the remote applied stress and image stress acting on dislocations near the surface.
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  • Kusuhiro Mukai, Feng Xiao, Kiyoshi Nogi, Zushu Li
    2004 Volume 45 Issue 7 Pages 2357-2363
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    A modified pycnometric method has been developed to obtain the accurate density value of liquid nickel and Ni-Cr alloy in the liquid and solid-liquid coexistence states. The density of liquid nickel decreases linearly with increasing temperature in the range from the melting point to 1873 K. The density at the melting point and the volume thermal expansion coefficient of liquid nickel are 7.91 Mg·m−3 and 1.87 × 10−4 K−1, respectively. The density of Ni-Cr alloys in the liquid and solid-liquid coexistence states was found to decrease linearly with increasing temperature and chromium concentration in the alloy. The temperature coefficient of density of Ni-Cr alloys was found to change at the liquidus temperature. The absolute value of temperature coefficient of density in the solid-liquid coexistence state is larger than that of the liquid alloy.
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  • Man-Seung Lee, Kyoung-Ju Lee, Young-Joo Oh
    2004 Volume 45 Issue 7 Pages 2364-2368
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    We have conducted solvent extraction experiments of FeCl3 in HCl solution with Alamine336 as an extractant. Solvent extraction reaction depended on the ratio of initial concentration of Alamine336 to FeCl3. When the concentration of Alamine336 was in excess to that of FeCl3, the extractant reacted as a dimer. When the initial concentration ratio of Alamine336 to FeCl3 was below three, ferric chloride was extracted by monomeric extractant. The equilibrium constants of solvent extraction were determined by applying ionic equilibria to the experimental data. These ionic equilibria consisted of chemical equilibria, mass and charge balance equations. The activity coefficients of solutes in aqueous phase were calculated by using Bromley equation. The predicted distribution coefficients of iron agreed well with those measured.
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  • Manabu Iguchi, Yasushi Sasaki, Nobuharu Kawabata, Toshikatsu Iwasaki
    2004 Volume 45 Issue 7 Pages 2369-2376
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    Effective mixing of a cylindrical bath is of crucial for wastewater treatment. Measurements were carried out on the mixing time in a cylindrical bath agitated simultaneously by bottom gas injection and side liquid injection. Air was injected into the bath through a centered single-hole bottom nozzle. Water was injected into the bath through a single-hole nozzle attached to the side wall of the vessel, drained from a pipe installed at the opposite bottom corner, and injected again with a small pump. The mixing time due to simultaneous gas and water injection, Tm3, was satisfactorily correlated by the following empirical equation.
    1/Tm3 = 1/Tm1 + 1/Tm2
    where Tm1 and Tm2 are the mixing time values for water injection alone and gas injection alone, respectively. This relationship means that mixing by gas injection and that of liquid injection proceed in parallel with each other.
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  • Akira Takara, Yukio Nishikawa, Hiroyuki Watanabe, Hidetoshi Somekawa, ...
    2004 Volume 45 Issue 7 Pages 2377-2382
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    Plastic formability in the secondary processing of an AZ31 magnesium alloy was investigated using fine-grained and relatively coarse-grained materials, respectively. To produce components for mobile electric appliances, boss formability was examined at a relatively low temperature of 523 K. The boss with a height of 14 mm was successfully formed in fine-grained material under a nominal forming pressure of 582 MPa in 5 s. Analysis of the boss forming revealed that the forming occurred under the high-strain-rate superplastic condition. The grain size in the boss region was slightly coarsened, probably as a result of strain-induced grain growth, which is a widespread property of superplastic flow. On the other hand, even in the coarse-grained material, a relatively high boss height of 5 mm was obtained under the same forming condition. After the boss forming, grain refinement was observed in the coarse-grained material. It was suggested that the coarse-grained materials exhibited relatively high formability because of dynamic recrystallization. It was concluded that plastic forming concomitant with grain growth was more effective than that concomitant with grain refinement in AZ31 magnesium alloy. An empirical equation to perform plastic forming under the condition concomitant with grain growth was developed.
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  • Hidemi Kato, Dmitri V. Louzguine, Akihisa Inoue, Hyoung Seop Kim, Ho-S ...
    2004 Volume 45 Issue 7 Pages 2383-2388
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    Nonlinear viscoelasticity influenced by an in situ nanocrystallization under constant load compression at the glass transition temperature, Tg, is investigated with a Cu60Zr30Ti10 (at %) bulk metallic glass (BMG). The experimental curves showed the characteristics, softening and subsequent recovering phenomena which have been observed in a ‘stable’ Zr-based BMG and also hardening through whole deformation process due to the in situ nanoprecipitation in the glass matrix. These characteristics are fairly reproduced by the fictive stress model extended by the Johnson-Mehl-Avrami (JMA) equation and mixture rule for respectively expressing influences of the Newtonian viscosity and of Young's modulus and critical stress on volume fraction of the nanoprecipitates.
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  • Koichi Kitazono, Seiji Nishizawa, Eiichi Sato, Tetsuichi Motegi
    2004 Volume 45 Issue 7 Pages 2389-2394
    Published: 2004
    Released: June 24, 2005
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    Closed-cell Al-Si alloy foam was produced from two bulk alloy strips. Preform sheet containing titanium hydride (TiH2) particles was first manufactured through accumulative roll-bonding (ARB) processing. Large ARB cycle number was effective to achieve uniform distribution of the TiH2 particles in the Al-Si matrix. Following high temperature foaming tests revealed that high porosity and small pore size can be obtained from the preform prepared through large cycle number. These results indicate that a suitable ARB processing condition enables to optimize the cell microstructure of the metal foams.
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  • Ramanujam Rajagopal, Yalamanchili Krishna Rao
    2004 Volume 45 Issue 7 Pages 2395-2402
    Published: 2004
    Released: June 24, 2005
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    The vapor-phase homoepitaxy of monocrystalline silicon by reduction of chlorosilanes is modeled using a novel approach. With digital computer calculation, the growth rate of silicon is predicted under ambient pressure (1.0 atm or 101.325 kPa) in the high-temperature regime 1200—1600 K, where silicon growth is expected to be mass-transport limited. This study considers four different initial stoichiometries, namely, 0.1% SiH4 + 0.4% HCl + H2, 0.1% SiCl4 + H2, 0.5% SiCl4 + H2, and 0.2% SiHCl3 + H2 in the Si-Cl-H system in order to make comparisons between the predicted and the experimentally determined growth rates. By combining the iterative equilibrium constant method with the Stefan-Maxwell relations for diffusion in a multi-component gas-phase, the respective molar fluxes of nine gaseous species that include SiCl4, SiHCl3, SiH2Cl2, SiH3Cl, SiH4, SiCl2, SiCl, SiCl3, and Si(g) were computed for steady-state condition; and the data on fluxes enabled the determination of the net silicon flux to the surface of the substrate. The computed rates were compared to the measured deposition rates of silicon.
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  • Hiroshi Kato, Tomoyuki Suzuki, Yoshiharu Annou, Kensuke Kageyama
    2004 Volume 45 Issue 7 Pages 2403-2409
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    Aluminum alloy die-cast plates (ADC 12) were subjected to ultrasonic measurement to obtain a relation between the intensity distribution of the ultrasonic wave and positions of cold flakes appearing in the plate for developing a nondestructive method to detect cold flakes in the die-casts. Die-cast plates of 170 mm in length, 50 mm in width and 6.8 mm in thickness were produced with wider gates to introduce larger cold flakes in the plate. Then the ultrasonic measurement was carried out with the immersion method by using a probe generating a longitudinal wave of 20 MHz in frequency. Intensity distributions of the ultrasonic wave were obtained from the surface to the bottom. The cross section analysis was carried out to examine the distribution of the cold flake. From the cross section analysis, three types of cold flakes were observed: the type A with a straight boundary of initial solidification with oxide thin layer, the type B with a straight boundary without oxide layer, and the type C of an irregular and wavy boundary without oxide layer. In the case of the type C, the oxide layer was thought to be out of the observed section. The ultrasonic wave was slightly reflected from the front and rear boundaries between the cold flake and the matrix, and it was found that the position and the thickness of the cold flake can be detected by ultrasonic measurement.
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  • Akihiro Yamazaki, Junichi Kaneko, Makoto Sugamata
    2004 Volume 45 Issue 7 Pages 2410-2416
    Published: 2004
    Released: June 24, 2005
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    Mg-Al alloy powder was mechanically alloyed (MA) by addition of metal silicides (TiSi2, CrSi2 and WSi2), using a planetary ball mill under an Ar atmosphere. The MA powders were consolidated via vacuum hot pressing and hot extrusion. Solid state reactions in the MA powders and extruded materials were examined by XRD and TEM. Mechanical properties were evaluated by hardness and compression tests. In all alloy systems, in situ formation of Mg2Si and metal silicides with lower Si content than the added silicides occurred by solid state reaction during MA and subsequent heating processes. All of the as-extruded materials with fine dispersoids and fine matrix grain structures exhibited high hardness and specific proof strength. The as-extruded material of the Mg-Al-TiSi2 system showed the highest hardness of 141 HV, 0.2% compressive proof stress of 657 MPa and specific proof stress of 337 MPa/(Mg/m3) at room temperature.
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  • Yung K. Choi, Michelle Salvia
    2004 Volume 45 Issue 7 Pages 2417-2421
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    Growing attention has been given in the last years to the development of smart materials and structures. Among them, composite materials play evidently a leading role. In fact, it is relatively easy, taking in account their processing techniques, to embed in the structural material itself some sensors, processors and actuators at a mesoscopic scale. Shape memory alloys (SMA) are particularly fitted as actuators because they can be easily drawn into thin wires and incorporated in polymeric and metallic matrices or in classical fibre epoxy laminate structure. To test the influence of the materials and processing conditions on the actuation properties of adaptive hybrid composites four sets of asymmetric composite systems based on a glass epoxy laminate with embedded wires of a shape memory Ti-Ni-Cu alloy were processed. The SMA wires in One Way Shape Memory Effect (OWSME) or (Two Way Shape Memory Effect TWSME) conditions were incorporated as far as possible away from the neutral plan. These asymmetric hybrid laminate beams were tested in clamp-free conditions. With the actuators heated by Joule effect undergoing a reversible martensite to austenite transformation, the reversible bending was induced due to the recovery strain in relation with the shape memory effect. The most important deflection of the composite was obtained for the material, processed with embedded wires in TWSME conditions. Nevertheless, for samples just prestrained for the OWSME, a self-training effect occurred in relation to the reverse polarised austenite to martensite transformation, during cooling after actuation. In order to follow the phase transitions in the embedded SMA wires, resistance measurements have been performed during actuation. Describing the macroscopic behaviour in the frame of the unidirectional approach de Liang and Rogers and using metallurgical parameters defined from a Clausius-Clapeyron diagram, a description of the temperature-deflection curves can be obtained. Nevertheless some parameters have to be mastered in order to process real structural parts.
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  • Kyoungkeun Yoo, Keiko Sasaki, Naoki Hiroyoshi, Masami Tsunekawa
    2004 Volume 45 Issue 7 Pages 2422-2428
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    The optimum conditions for Mn2+ removal from acid mine drainage was studied by a SRB (sulfate reducing bacteria) bioreactor. Chemical experiments with Na2S as a S2− source were conducted to investigate the effects of pH, coexisting metal ions, and the components in a growth medium for SRB on MnS formation from Mn2+ solutions. The amount of Mn removed from the Mn2+ solutions decreased with decreasing pH. The Zn2+ or Fe2+ coexisting in the solutions consumed S2− by forming ZnS or FeS, and this inhibited Mn removal. Sodium citrate, a component of the growth medium for SRB, formed a complex with Mn2+ and suppressed MnS formation. Biological experiments using the SRB reactor were carried out at 37°C and it was confirmed that the Mn2+ concentration decreased to less than 10 g·m−3 from 100 g·m−3 at neutral pHs (pH 5—7) after 100 hours when other metal ions and sodium citrate were absent. The formed precipitate was identified to be metastable γ-MnS with a band gap of about 3.8 eV by XRD, XRF, and UV-VIS.
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  • Kyoungkeun Yoo, Keiko Sasaki, Naoki Hiroyoshi, Masami Tsunekawa, Tsuyo ...
    2004 Volume 45 Issue 7 Pages 2429-2434
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    In the design of sulfate reducing bacteria (SRB) bioreactors to remove metal ions from acid mine drainage, the tolerance of bacteria to metal ions is an important factor. The present study investigated the effects of Mn2+ concentration on the growth and Mn removal activity of SRB in mediums containing 100∼600 g·m−3 Mn2+. The Mn2+ adsorbed on SRB cells and weakened the ability of bacterial sulfate reduction. However, the suppressive effect of Mn2+ on SRB growth can be disregarded, and 200 g·m−3 of Mn2+ in solution was removed, satisfying the requirement of the maximum contaminant level (MCL) of environmental water quality in Japan.
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  • Jin-Kook Yoon, Kyung-Hwan Lee, Gyeung-Ho Kim, Jun-Hyun Han, Jung-Mann ...
    2004 Volume 45 Issue 7 Pages 2435-2442
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    The low-temperature cyclic oxidation resistance of MoSi2/19.3 vol% SiC nanocomposite coating formed on a Mo substrate in air at 500°C was investigated and compared with that of the monolithic MoSi2 coating using field emission-scanning electron microscopy (SEM) and cross-sectional transmission electron microscopy (XTEM). The nanocomposite coating was produced by a prior carburizing process followed by chemical vapor deposition of Si on a Mo substrate. While the accelerated oxidation behavior was observed for the monolithic MoSi2 coating after the incubation time of about 454 cycles, no pest oxidation was observed in the nanocomposite coating. The excellent low-temperature cyclic oxidation resistance of nanocomposite coating resulted from the deceleration of further inward diffusion of oxygen by formation of relatively dense SiO2 and Mo9O26 composite oxide scale through the preferential oxidation of SiC particles followed by oxidation of MoSi2 phase.
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  • Hee Young Kim, Satoru Hashimoto, Jae Il Kim, Hideki Hosoda, Shuichi Mi ...
    2004 Volume 45 Issue 7 Pages 2443-2448
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    Mechanical properties and shape memory behavior of Ti-(20—29)at%Nb alloys were investigated in order to develop Ni-free biomedical shape memory alloys. The Ti-Nb alloys were fabricated by arc melting method. The ingots were cold-rolled with a reduction up to 95% in thickness and then solution treated at 1173 K for 1.8 ks. The martensitic transformation temperature decreased by 43 K per 1 at% increase of Nb content. The shape memory effect and superelastic behavior were observed at room temperature in the Ti-(22—25)at%Nb alloys and Ti-(25.5—27)at%Nb alloys, respectively. A small enthalpy of the martensitic transformation and a large difference between Ms and Mf were observed in the Ti-Nb alloys compared to Ti-Ni shape memory alloys. The maximum recovered strain of 3% was obtained at room temperature in solution treated Ti-(25−27)at%Nb alloys. The heat treatment at 573 K for 3.6 ks stabilized superelastic behavior of Ti-Nb alloys by increasing the critical stress for slip.
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  • Yen-Huei Hon, Jian-Yih Wang, Yung-Ning Pan
    2004 Volume 45 Issue 7 Pages 2449-2455
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    Effects of iron (1 mass%) and hafnium (1—7 mass%) on the microstructure and mechanical properties of Ti-30Nb base alloys were investigated in this study. Experimental results indicate that the addition of 1 mass% Fe to the Ti-30Nb alloy transforms the original α + β + ω structure into a single β phase structure. Accompanying the structure change, both the tensile strength and 0.2% proof stress were reduced by some 15%, while the elastic modulus was reduced from 80 GPa to 68 GPa. Regarding the effect of Hf, precipitation of sporadic ω phase in the otherwise complete β phase structure can be detected when hafnium is added. An addition of just 1 mass% Hf to the Ti-30Nb-1Fe alloy increases the tensile strength and 0.2% proof stress by 32% and 27%, respectively, while slightly decreasing the elastic modulus by some 10%. The Ti-30Nb-1Fe-1Hf alloy has relatively high strength (∼914 MPa T.S.), reasonable ductility (∼10% El), and an elastic modulus of around 62 GPa. Consequently, the ratio of 0.2% proof stress to elastic modulus increases moderately. The ratio of 0.2% proof stress to elastic modulus of Ti-30Nb-1Fe-1Hf was found to be 1.39 × 10−2, which was around 1.8 times higher than Ti-6Al-4V (0.78 × 10−2), and around 3.5 times higher than c.p.Ti (0.4 × 10−2). Hafnium content exceeding 1 mass% gives no further improvement in the ratio of 0.2% proof stress to elastic modulus. From the results obtained here, Ti-30Nb-1Fe-1Hf alloy has excellent potential for orthopedic implant applications.
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  • Pingguang Xu, Fuxing Yin, Kotobu Nagai
    2004 Volume 45 Issue 7 Pages 2456-2462
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    The compact strip production (CSP) technology composed of thin slab casting and direct hot rolling has attracted much attention due to its apparent cost advantage. In this paper, the microstructural and textural variations in the through-thickness direction and their effects on the plastic anisotropy gradient in a thin-slab-cast low-carbon steel are investigated by optical metallography (OM), orientation imaging microscopy (OIM), transmission electron microscopy (TEM) and quantitative X-ray texture analysis. The thin steel slab shows a relatively uniform strength-ductility balance with the exception of the surface and center layers. The textures in all the through-thickness layers are composed of relatively strong {111} ‹uvw› and weak {001} ‹uvw› components which reach their maximum intensities in the middle layer near S = 0.4 and in the center layer, respectively (S is the normalized distance from the slab center to the specific layer and S to the slab surface is 1.0). The γ-fiber oriented ferrite exhibits a roof-shape tendency of the average grain size variation in the through-thickness direction. The lower carbon content in the surface layer is responsible for the better normal anisotropy (rm value) even with the weakest {111} ‹uvw› component. In spite of the relatively strong {111} ‹uvw› component intensity in the center layer, the lowest rm value is related to the solidified shrinkage cavities and the large MnS inclusions.
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  • Yu-Hua Song, Truan-Sheng Lui, Li-Hui Chen
    2004 Volume 45 Issue 7 Pages 2463-2470
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    Ferritic spheroidal graphite cast irons generally exhibit intergranular fracturing even if the specimens are strengthened by silicon in solid solution when tested under wet conditions. The maximum area fraction of intergranular fracture is closely related to the microstructural feature and ambient aqueous environment that caused the deterioration in vibration fracture resistance. In spite of the increasing silicon content, experimental evidence confirms the overall D-N curves can be generalized into three characteristic regions. Intergranular cracks initiated in the vicinity of the nodular graphite; the existence of nodular graphite acting as porosity should be considered as a dominant microstructural factor on the initiation of intergranular fractures. It should be noted that the intergranular cracks can be prevented, resulting in better vibration fracture resistance, when a specimen is covered with oil film. Based on experimental results, when the silicon content is increased, the vibration fracture resistance in general will be improved for all specimens whether they are tested in oil mist, air or aqueous environments. In particular, when the deflection amplitude is fixed, the vibration fracture resistance can be significantly raised for a high silicon sample (4.4Si).
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  • Fanxiong Cheng, Chuanhai Jiang, Jiansheng Wu
    2004 Volume 45 Issue 7 Pages 2471-2473
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    Crystallization and phase transformation of amorphous Co0.33Si0.67 thin films prepared by radio frequency magnetron sputtering using CoSi2 alloy target were researched by X-ray diffraction in situ. The results showed that CoSi formed firstly at 250°C and some of the films were still amorphous. The residual amorphous films transformed to CoSi2 at 300°C, CoSi and CoSi2 remained stable at 350—500°C and CoSi transformed to CoSi2 when the temperature was elevated further. The first phase that precipitated from the amorphous Co-Si films was decided by the effective heat of formation of phases and the short-range structure of amorphous films.
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  • Eun Soo Park, Won Tae Kim, Do Hyang Kim
    2004 Volume 45 Issue 7 Pages 2474-2477
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    The effect of partial substitution of Y for Gd on the glass forming ability of Mg65Cu15Ag10Y10 alloy has been studied using X-ray diffraction and differential thermal calorimetry. Partial substitution of Y by Gd improves the glass forming ability. The Mg65Cu15Ag10Y2Gd8 alloy shows the highest glass forming ability among the alloys investigated, enabling the fabrication of bulk metallic glass with the diameter of 9 mm by conventional Cu-mold casting method in air atmosphere. The compressive fracture strength and fracture elongation of the Mg65Cu15Ag10Y2Gd8 bulk metallic glass are 956 MPa and 1.6% respectively.
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  • Toshimasa Wadayama, Terumasa Yamashita, Ryoji Tanimura, Takanori Sato, ...
    2004 Volume 45 Issue 7 Pages 2478-2481
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    Infrared reflection absorption spectroscopy (IRRAS) and reflection high-energy electron diffraction (RHEED) have been applied to in-situ observations of fcc-Fe epitaxial growth on Cu(100) at room temperature under very low carbon monoxide (CO) pressures. Extended layer-by-layer growth of fcc-Fe is observed at a CO pressure of 2.7 × 10−8 Pa. Nevertheless, no adsorbed CO was detected on the growing film surface. The layer-by-layer growth is hampered severely at a CO pressure higher than 1.3 × 10−7 Pa. A small band that is attributable to CO adsorption appears in the IRRAS spectra taken in the early stages of deposition at 1.3 × 10−6 Pa. These observations indicate that the dissociation of adsorbed CO on the growing film surface plays an important role in the promotion of the layer-by-layer film growth of fcc-Fe.
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  • Akira Taniyama, Masahiro Arai
    2004 Volume 45 Issue 7 Pages 2482-2485
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    The variation of aluminum content at the interface between the zinc coating and the steel substrate, which corresponds to the quantity of the Fe-Al interface layer, with dipping time in a molten zinc bath was measured quantitatively with inductively coupled plasma optical emission spectrometry. Comparing the aluminum content between the sample dipped in the Zn-0.14 mass%Al bath and that dipped in the Zn-0.18 mass%Al bath, it was found that the Fe-Al interface layer disappeared with linear relationship with dipping time in the Zn-0.14 mass%Al bath. This suggests that the disappearance behavior of the Fe-Al interface layer was dominated by an interface reaction.
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  • Apiwat Muttamara, Yasushi Fukuzawa, Naotake Mohri, Takayuki Tani
    2004 Volume 45 Issue 7 Pages 2486-2488
    Published: 2004
    Released: June 24, 2005
    JOURNALS FREE ACCESS
    Precise machining technologies of advanced insulating ceramics are demanded in many industrial fields. Normally Electric Discharge Machining (EDM) utilizes for electrical conductive materials. Recently, insulating materials have been succeeded to machine with the assisting electrode method (AEM) that was proposed by authors. Some ceramics were still recognized as hard materials. Especially the high purity oxide ceramics of Al2O3 are difficult to machine for this method. Moreover single crystal Al2O3 of sapphire (99.99%) is recognized as the hard machining material for the EDM method. In this paper, EDM of crystallographic planes on 3 different sapphires were carried out. The effects of the crystal orientation were discussed on the machining properties of sapphires.
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