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ONLINE ISSN: 1347-5320
PRINT ISSN: 1345-9678

MATERIALS TRANSACTIONS Vol. 42 (2001), No. 10

  • Thermodynamics of Micro-Alloying

    Taiji Nishizawa

    pp. 2027-2032

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    DOI:10.2320/matertrans.42.2027

    Abstract

    The functional role of micro-alloying elements in grain boundary migration, especially their influence on solute drag and particle pinning, are reexamined using very simple models. The solute drag phenomenon is analyzed in terms of the grain boundary dwell time and drag length of the solute, assuming a state of equilibrium boundary segregation. Effect of particle pinning is analyzed using a slightly modified Zener’s relation. The role of inverse pinning resulting from the anisotropy of AlN, first proposed by Taguchi and Sakakura in 1966 and utilized in the production of grain oriented Si-steel, is emphasized.

  • Disorder-L10 Transition Investigated by Phase Field Method with CVM Local Free Energy

    Munekazu Ohno, Tetsuo Mohri

    pp. 2033-2041

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    DOI:10.2320/matertrans.42.2033

    Abstract

    The ordering processes of nucleation-growth type and spinodal ordering type are examined using the Phase Field method (PFM) with the free energy formulated based on the Cluster Variation Method. The relaxation curves of Long Range Order parameter, ξ1, predicted by this approach are compared with those obtained by the Path Probability Method (PPM) in the homogeneous limit. Furthermore, it is shown that microstructural evolution process, which is described by time evolution of spatial distribution of ξ12, of spinodal ordering type is indistinguishable from the one of nucleation-growth type.

  • Thermal and Mechanical Properties of Cu-Based Cu-Zr-Ti-Y Bulk Glassy Alloys

    Tao Zhang, Kei Kurosaka, Akihisa Inoue

    pp. 2042-2045

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    DOI:10.2320/matertrans.42.2042

    Abstract

    A new Cu-based bulk glassy alloy with high tensile fracture strength above 2000 MPa was formed in a (Cu0.6Zr0.3Ti0.1)98Y2 alloy by copper mold casting. The maximum sample thickness for glass formation is 4 mm for Cu60Zr30Ti10 and increases to 5 mm for the 2%Y-containing alloy. The addition of 2%Y also causes an increase in the supercooled liquid region (ΔTx=Tx−Tg) from 36 to 50 K and in the reduced glass transition temperature (Tg⁄Tl) from 0.62 to 0.63. The increase in the glass-forming ability (GFA) is presumably due to the increase in ΔTx and Tg⁄Tl. The bulk glassy (Cu0.6Zr0.3Ti0.1)98Y2 alloy exhibits good mechanical properties, i.e., 1780 MPa for yield strength, 2030 MPa for tensile fracture strength, 2100 MPa for compressive fracture strength, 1.7% for elastic elongation and 1.5% for plastic elongation. The distinct plastic elongation indicates good ductile nature of the Cu-based bulk glassy alloy. The success of synthesizing the new Cu-based bulk glassy alloy with high GFA and good mechanical properties allows us to expect the extension of application fields as a new engineering material.

  • Microstructure and Magnetic Properties of Fe Nanoparticles Synthesized by Chemical Vapor Condensation

    Chul-Jin Choi, Xing-Long Dong, Byoung-Kee Kim

    pp. 2046-2049

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    DOI:10.2320/matertrans.42.2046

    Abstract

    Nano-sized Fe particles were synthesized by Chemical Vapor Condensation (CVC) using the precursor of iron pentacarbonyl (Fe(CO)5) as the source under a flowing helium atmosphere. The effect of CVC processing parameters on the formation of nanoparticles was studied. Microstructures and magnetic states were investigated systematically by means of XRD, HRTEM, DTA-TGA, Mössbauer spectroscopy and VSM . We synthesized the nanoparticles with nearly spherical shape, core-shell type structure and 5–13 nm in mean size by using liquid nitrogen cooling. Average particle size increased with increasing the decomposition temperature of the precursor. The magnetic states of Fe nanoparticles changed from ferromagnetism to superparamagnetism with the particle size and microstructure. The effect of particle size on the saturation magnetization and coercivity of nanoparticles were also discussed.

  • Cube Texture Development in an Al-Mg-Mn Alloy Sheet Worked by Continuous Cyclic Bending

    Yoshimasa Takayama, Jerzy A. Szpunar, Hyo-Tae Jeong

    pp. 2050-2058

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    DOI:10.2320/matertrans.42.2050

    Abstract

    Changes in texture after the continuous cyclic bending (CCB) and the subsequent annealing in sheets of an Al–4.7 mass%Mg–0.7 mass%Mn alloy have been investigated. The CCB was recently proposed as a straining technique that generates a high strain on the surface and a much lower strain in the central layer of the sheet. The Cube texture in the surface layer is sharpened remarkably during the CCB process and the annealing that follows. The 50 CCB passes lead to a sharper texture in all layers of the sheet. After annealing, marked development of the Cube component is observed in the surface layer. On the other hand, for the 20 pass-CCBent sample, the Cube texture appears only after annealing in a salt bath, while this texture is not observed after annealing both in Ar and in air. The mechanism of texture formation and the effect of processing on the sharpening of Cube texture is discussed based on results obtained from the electron backscatter diffraction pattern (EBSP) analysis and from the in-situ measurement of X-ray peak intensity during heating.

  • Glass-Forming Ability, Crystallized Structure and Magnetic Properties of Fe67Co9.5Nd3Dy0.5B20 Glassy Alloy with Large Supercooled Liquid Region

    Wei Zhang, Mitsuhide Matsusita, Chunfei Li, Hisamichi Kimura, Akihisa Inoue

    pp. 2059-2063

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    DOI:10.2320/matertrans.42.2059

    Abstract

    The glass-forming ability, thermal stability and magnetic properties have been investigated for a Fe67Co9.5Nd3Dy0.5B20 glassy alloy with a large supercooled liquid region of 48 K prepared by the melt-spinning technique. The glassy phase is formed in the wide sheet thickness range from 20 to 250 \\micron. The glass transition temperature (Tg), crystallization temperature (Tx), supercooled liquid region (ΔTx=Tx−Tg) and heat of crystallization (ΔHc) remain almost unchanged in the thickness range below 250 \\micron, and then the ΔHc gradually decreases with further increasing sheet thickness. The crystallized nanocomposite structure consists of Fe3B, α-Fe, Nd2Fe14B and remaining glassy phase, and their average grain sizes are about 25 nm annealed at 903 K for 420 s. The remanence (Br), coercivity (iHc), and maximum energy product (BH)max are 1.26 T, 235 kA/m, and 104 kJ/m3, respectively, for the sheet of 250 \\micron in thickness annealed at 903 K for 420 s. The hard magnetic properties remain almost unchanged in the thickness range below 250 \\micron, and decrease gradually in the sheets with thicknesses above 250 \\micron.

  • Vibration-Fracture Resistance of Sn-Pb and Sn-Ag Eutectic Solders

    Chuang-Ming Chuang, Truan-Sheng Lui, Li-Hui Chen, Tsuey-Mei Yin

    pp. 2064-2070

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    DOI:10.2320/matertrans.42.2064

    Abstract

    A striated deformation feature can be observed in Sn–Pb eutectic solder with higher Sn content or a coarse Sn-rich phase after the solder is subjected to a vibration test. This deformation feature may accelerate the life deterioration of Sn–Pb solder under vibration. A similar feature can be observed in lead-free Sn–3.5 mass%Ag eutectic solder. A very little crack can be observed around the deformation areas of an Sn–3.5 mass%Ag sample, and that is the main reason it possesses a lower crack growth rate than Sn–Pb solder. A comparison of the deflection vs. cyclic number (D-N) curves of Sn–Pb and Sn–Ag solders under an identical vibration push force or identical initial defection amplitude demonstrates that Sn–3.5 mass%Ag solder possesses better vibration fracture resistance than Sn–Pb solders. In the case of an identical vibration push force, the initial deflection amplitude of Sn–3.5 mass%Ag solder is significantly smaller than that of Sn–Pb solder, and it may improve the solder’s vibration fracture resistance.

  • Electron Density Distribution in Amorphous Se Determined by Reverse Monte Carlo Simulation Coupled with Anomalous X-ray Scattering Data

    Masatoshi Saito, Yoshio Waseda

    pp. 2071-2074

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    DOI:10.2320/matertrans.42.2071

    Abstract

    The ion-electron structure factor estimated from the anomalous X-ray scattering measurements near the Se K absorption edge has been used in the reverse Monte Carlo (RMC) simulation for determining the valence electron density distribution in amorphous Se. The results clearly indicate that the origin of particular valence electron distribution for Se can be explained by two non-bonding electrons and two bonding electrons.

  • Experimental Study on Diffusion Bonding in Pure Magnesium

    Hidetoshi Somekawa, Hiroyuki Hosokawa, Hiroyuki Watanabe, Kenji Higashi

    pp. 2075-2079

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    DOI:10.2320/matertrans.42.2075

    Abstract

    Applicability of diffusion bonding was examined on pure magnesium rolled sheet with an initial grain size of 85 \\micron. The diffusion bonding tests were carried out in air at the pressure range from 2 to 20 MPa and at the temperature range from 573 to 673 K and for the times up to 72 h. Before diffusion bonding, the surfaces to be bonded were blasted to make rugged. The post-bonded mechanical properties were estimated by the compression lap shear test, and the microstructure after bonding were also observed by the microscopy in order to achieve the optimal process for diffusion bonding. The maximum of lap shear strength was 0.888 at a bonding pressure of 20 MPa and a bonding temperature of 673 K, with a bonding time of 1 hour. In high ratio of lap shear strengths, the bond line was not identified by optical microscopy, and surface fracture after compression lap shear test was also fully ductile failure. The present results revealed that there is a possibility to fabricate magnesium products using diffusion bonding technique.

  • Effects of Prestrainning on the Impact Response and Twinning Structure of 304L Stainless Steel

    Woei-Shyan Lee, Chi-Feng Lin

    pp. 2080-2086

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    DOI:10.2320/matertrans.42.2080

    Abstract

    An investigation has been made into the effects of prestraining on the impact response and twinning structure of 304L stainless steel by means of a split Hopkinson bar and TEM metallography. Annealed 304L stainless steel was pre-deformed at prestrains of 0.15 and 0.3 using a Saginomiya 100 metal forming machine, providing specimens with different microstructural parameters and mechanical properties. Cylindrical specimens were machined from the pre-deformed material and tested at room temperature at strain rates of 10−3, 8×102, 2.3×103 and 4.8×103 s−1, with the true strains varying from 0.1 to 0.3. The results indicate that the overall stress-strain response was strongly dependent on applied strain rate and prestrain level. Flow stress increased with strain and strain rate for each prestrain condition. The higher prestrain specimen was generally stronger because of the different initial microstructure and degree of work hardening. Strain-rate sensitivity and activation volume varied with prestrain and work hardening stress (σ−σy). Increased prestrain and work hardening stress resulted in increased strain-rate sensitivity, but the inverse was observed for activation volume. TEM thin foil observation revealed deformation twinning was operative in 304L stainless steel over a broad strain and strain rate range, and can combine with prestrain effects for different work hardening characteristics and impact strength enhancement. Twin density was observed to increase with prestrain and work hardening stress.

  • Improvement of Crashworthiness in Ultra Lightweight Metallic Foam by Heat-Treatment for Microstructural Modification of Base Material

    Hidetaka Kanahashi, Toshiji Mukai, Yasuo Yamada, Koji Shimojima, Mamoru Mabuchi, Tatsuhiko Aizawa, Kenji Higashi

    pp. 2087-2092

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    DOI:10.2320/matertrans.42.2087

    Abstract

    It is very important to understand the strain rate dependence of the plateau stress or the impact energy for the applications to a suitable design of automotive components. Limited data are, however, available for the mechanical response of metallic foams under dynamic loading in comparison with polymer foams. In this study, the mechanical response and absorbed energy of an open-celled SG91A aluminum foam with the low relative density of 0.03–0.065 is evaluated at a dynamic strain rate in ∼ 103 s−1 order in compression by the split Hopkinson pressure bar apparatus. In order to investigate the effect of microstructure in the solid material, solution treatment and aging are performed and then examined at the same dynamic strain rate. As a result, mechanical strength and absorption energy for as-received and heat treated SG91A aluminum foams showed the strain rate dependence. This dependency was clearly decreased by the heat treatment. This mechanical response directly affects the energy absorption: the strain rate dependence of absorption energy is weakened with enhancing the ductility in solid materials by the heat treatment. Therefore, it is possible to control the absorption energy of the metallic foam by the modification of its microstructure, which affects the ductility in the solid material.

  • Corrosion Behavior of Glass Coated Hastelloy-XR in Boiling Sulfuric Acid

    Rong Tu, Takashi Goto, Lidong Chen, Toshio Hirai, Lianmeng Zhang

    pp. 2093-2097

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    DOI:10.2320/matertrans.42.2093

    Abstract

    Hastelloy-XR alloy was coated with glasses to improve the corrosion resistance in boiling sulfuric acid for application in thermochemical hydrogen production process. Pre-oxidation of Hastelloy-XR alloy enabled one to produce well-adhered glass coating. The glass composition with the highest corrosion resistance was 48SiO2–8B2O3–6Al2O3–11CaO–25BaO–2ZnO . The glass-coated Hastelloy-XR alloy showed almost no mass change in boiling sulfuric acid of 40 to 80% aqueous solution at 408 to 503 K after 43 ks.

  • Formation of Primary Silicon during Cooling and Solidification of Al-20%Si Alloy

    William John Kyffin, William Mark Rainforth, Howard Jones

    pp. 2098-2101

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    DOI:10.2320/matertrans.42.2098

    Abstract

    The relationship between the cooling curve and formation of primary silicon from the melt has been investigated for Al–20%Si alloy in the uninoculated state and when prior-treated with a phosphorus-bearing inoculant. The results suggest that coarse branched silicon forms from an uninoculated melt at sub-liquidus temperatures well above the primary silicon arrest temperature and that increasingly effective inoculation both reduces intensity of the arrest and shifts it to higher temperature eventually eliminating it completely in favour of a sharp reduction in slope of the cooling curve at or just below the liquidus temperature. It is proposed that this could be used as a simple diagnostic test for efficiency of refinement of primary silicon by inoculant additions under specified conditions.

  • Crystallisation and Phase Decomposition Processes in Pr4.5Fe77B18.5 Amorphous Ribbon

    Yun-Chul Jung, Yasuya Ohmori, Kiyomichi Nakai, Satoshi Hirosawa, Hirokazu Kanekiyo

    pp. 2102-2111

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    DOI:10.2320/matertrans.42.2102

    Abstract

    The isothermal crystallisation processes and the decomposition behaviours of the crystallised phases in Pr4.5Fe77B18.5 amorphous ribbons prepared by a melt quench technique have been investigated by means of differential thermal analysis, X-ray diffraction, and high resolution transmission electron microscopy, and the following results were obtained. The phase initially crystallised is Fe3B and the crystallisation of Pr2Fe23B3 particles occurs immediately after the Fe3B formation. This is probably due to the fact that Fe3B/amorphous interphase boundaries provide potent nucleation sites for Pr2Fe23B3 particles in view of chemistry in the vicinity of Fe3B particles and the structure of the interfaces. Then, fine hard magnetic Pr2Fe14B particles nucleate at Fe3B interfaces directly. In the following processes, Pr2Fe14B and Pr2Fe23B3 particles grow by the coalescence of fine particles. In the later annealing stages, Pr2Fe23B3 particles decompose into Pr2Fe14B networks involving spherical α-Fe particles in a eutectoid-like mode. At the final stage of annealing these Pr2Fe14B networks transform in-situ into those of PrFe4B4.

  • Suzuki Segregation and Dislocation Locking in Supersaturated Co-Ni-Based Alloy

    Akihiko Chiba, Mok Soon Kim

    pp. 2112-2116

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    DOI:10.2320/matertrans.42.2112

    Abstract

    The stress relaxation experiment has been performed at temperatures ranging from room temperature to 1073 K to study changes in motion and structure of the dislocations induced into the Co–Ni-based alloy. The resultant zero rate of stress relaxation at room temperature can be assumed to be due to the immobilization of the induced dislocations originating from an elastic interaction between dislocation cores and solute atoms. At elevated temperatures where the dynamic strain aging (DSA) occurs, the zero rate of the stress relaxation at an initial stage can be attributed to the dislocation locking effect caused by the Suzuki segregation. The stress relaxation at the DSA temperature range occurs by the sole movement of leading partial dislocations, resulting in wide dislocation dissociations. At exceeding the DSA temperature range, the dislocation locking effect caused by the Suzuki segregation fades away and the two partial dislocations simultaneously glide by viscous motion, resulting in the lack of the observed wide dislocation dissociation. The phase diagram calculation and microstructure observations reveal that the present alloy SPRON 510 is a supersaturated solid solution and that the occurrence of the Suzuki segregation is strongly associated with the degree of the supersaturation of the solid solution.

  • Development of a Closed Cell Aluminum Alloy Foam with Enhancement of the Compressive Strength

    Tetsuji Miyoshi, Shigeta Hara, Toshiji Mukai, Kenji Higashi

    pp. 2118-2123

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    DOI:10.2320/matertrans.42.2118

    Abstract

    There is a great demand for more weight reduction in aluminum foams for fuel economy in the automotive and aerospace fields. The enhancement of compressive strength in a close-celled aluminum can be achieved by the selection of matrix material or modification of the cellular structure without increasing relative density. A commercial closed-cell aluminum (ALPORAS®) is made by adding foaming agent into a molten alloy. In this study, the matrix aluminum was strengthened by adding 5%Zn and 1%Mg without an increase in weight. The compressive strength of the present foam is found to be approximately twice as high as that of the conventional foam (ALPORAS®).

  • Production of Undercooled Melt by Heating the Metastable Al2O3-YAP Eutectic Structure

    Hideyuki Yasuda, Yoshiki Mizutani, Itsuo Ohnaka, Akira Sugiyama, Yoshiharu Waku

    pp. 2124-2130

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    DOI:10.2320/matertrans.42.2124

    Abstract

    This paper demonstrates the undercooled melt formation from the metastable eutectic structure by heating procedures in the Al2O3-YAG system. Phase transformation during heating/cooling procedures is detected by optical DTA equipment. Firstly, the Al2O3-YAP metastable eutectic structure is obtained by solidification after heating the melt above 2273 K . The undercooled melt formation is confirmed when the Al2O3-YAP metastable eutectic structure composed of crystalline phases is heated up to temperatures above the metastable eutectic temperature for the equilibrium eutectic composition (18.5 mol%Y2O3) and the metastable eutectic composition (23.5 mol%Y2O3). The undercooled melt formation is immediately followed by the solidification in the Al2O3-YAG equilibrium path for the 18.5 mol%Y2O3 specimens. For the 23.5 mol%Y2O3 specimens, the obtained undercooled melt is kept even for as long as 3600 s without solidification. Furthermore, the fine and uniform Al2O3-YAG eutectic structure is obtained when the melting and the solidification simultaneously occur. The solidification with the exothermic heat beside the melting with the endothermic heat has a great advantage for heat release of the latent heat. Consequently, the high growth rate leads to the fine eutectic structure in the off-eutectic composition.

  • Energy-Filtered Image of Surface Blisters by Grazing Incidence Electron Microscopy

    Sin Igarashi, Shunsuke Muto, Tetsuo Tanabe, Tadashi Maruyama

    pp. 2131-2132

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    DOI:10.2320/matertrans.42.2131

    Abstract

    We have examined fine structure of surface blisters formed by D+ or He+ irradiation onto mono-crystalline silicon by grazing incidence electron microscopy (GIEM), using an energy-filtering transmission electron microscope (EFTEM). Mapping of the projected thickness clearly visualized the structural difference of the blister skins formed by D+ and He+ irradiation respectively. A He distribution image of the He-blister was also successfully obtained.

  • Improved Hydrogen Storage Capacity of Ti60Zr15Ni15Cu10 Amorphous Alloy

    Xinquan Guo, Liqun Ma, Akihisa Inoue

    pp. 2133-2135

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    DOI:10.2320/matertrans.42.2133

    Abstract

    The hydrogen absorption property of a Ti60Zr15Ni15Cu10 amorphous alloy is presented. The maximum hydrogen concentration of the amorphous alloy was 1.41H⁄M at room temperature. The hydrogen absorption at lower temperatures with higher H2 pressures favored higher H/M ratios for the amorphous alloy without any crystalline hydride growth. The structures of the as-quenched and hydrogenated samples were investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The absorption was accompanied by expansion of interatomic spacing in the amorphous structure. The hydrogen storage ability of the Ti60Zr15Ni15Cu10 amorphous alloy was found to be better than that of the related crystalline phase in this system.

  • Bulk Glassy Co43Fe20Ta5.5B31.5 Alloy with High Glass-Forming Ability and Good Soft Magnetic Properties

    Baolong Shen, Hisato Koshiba, Akihisa Inoue, Hisamichi Kimura, Takao Mizushima

    pp. 2136-2139

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    DOI:10.2320/matertrans.42.2136

    Abstract

    A new Co-based bulk glassy alloy Co43Fe20Ta5.5B31.5 exhibiting a large supercooled liquid region before crystallization and good soft magnetic properties was synthesized by the copper mold casting method. The glass transition temperature (Tg) is 910 K and the supercooled liquid region (ΔTx) reaches 70 K . The high thermal stability of the supercooled liquid enabled us to produce bulk glassy alloys with diameters up to 2 mm. These bulk glassy alloys exhibit good soft magnetic properties, i.e., saturation magnetization of 0.5 T, very low coercivity of 0.9 A/m and very high permeability of 40000 at 1 kHz. It is noticed that the diameter of 2 mm is the largest value for Co-based bulk glassy alloys reported up to now. The success of forming the large-scale size Co-based bulk glassy alloy with high thermal stability of supercooled liquid and good soft magnetic properties is encouraging for future uses of bulk amorphous soft magnetic materials.

  • Hydrogen Assisted Intergranular Crack Propagation during Environmental Embrittlement in an Al-Zn-Mg-Cu Alloy

    Shigeru Kuramoto, Jun Okahana, Motohiro Kanno

    pp. 2140-2143

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    DOI:10.2320/matertrans.42.2140

    Abstract

    Hydrogen absorbed from the test environment was detected experimentally from an Al–4.9%Zn–2.2%Mg–1.3%Cu alloy deformed in laboratory air, which is a direct evidence of hydrogen embrittlement. The alloy exhibited grain boundary embrittlement when deformed at a strain rate of 10−7 s−1 in laboratory air and hydrogen behavior was studied using deuterium as a tracer of hydrogen. The direct detection of hydrogen supports the idea that gradual propagation of intergranular crack at sufficiently low strain rate may enable continuous absorption and accumulation of hydrogen in the stress field near the crack tip and eventually embrittle the material.

  • High Strength Mg-Zn-Y Alloy Containing Quasicrystalline Particles

    D. H. Bae, S. H. Kim, W. T. Kim, D. H. Kim

    pp. 2144-2147

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    DOI:10.2320/matertrans.42.2144

    Abstract

    A new magnesium alloy strengthened by icosahedral quasicrystalline particles and precipitates was developed by thermomechanical processes for an as-cast Mg-rich Mg95Zn4.3Y0.7 alloy. Quasicrystalline particles of 0.5–2 \\micron in size were distributed in the α-Mg matrix by the hot-rolling process, and nanoscale quasicrystals were also precipitated throughout the α-Mg grains during this thermomechanical process. The alloy exhibits high strengths and large elongations at room and elevated temperatures. High strength observed in the alloy is mainly due to the strengthening effect of large number of quasicrystals, where the volume fraction of quasicrystals is around 9%. The quasicrystalline phase is found to be in equilibrium with the α-Mg phase and stable against coarsening under deformation up to near the melting temperature of the eutectic. The stable quasicrystalline particle/matrix interface with a low interfacial energy can provide the improved mechanical properties of the alloy.
  • © 2001 The Japan Institute of Metals and Materials

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