MATERIALS TRANSACTIONS
Online ISSN : 1347-5320
Print ISSN : 1345-9678
ISSN-L : 1345-9678
Volume 47 , Issue 4
Showing 1-50 articles out of 50 articles from the selected issue
  • Haruo Okahara, Miyoshi Ohara, Yorinobu Takigawa, Kenji Higashi
    2006 Volume 47 Issue 4 Pages 954-958
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    Grain sizes of die material and die surface coatings were examined with the achieving mass-production of magnesium alloys by advanced continuous press forming. The results showed that there is an optimum tungsten carbide grain size of 1 to 2 μm for press-forming AZ31 magnesium alloy in terms of surface roughness fluctuation. It was also shown that the adherence of the DLC coating was improved by implanting C ions into the tungsten carbide surface. 10,000 times square-cup drawings were successfully achieved at 543 K using C-ion implantation and a DLC coated die together with a newly developed heat-resistant lubricant.
    Download PDF (289K)
  • Shintaro Yoshimoto, Michiaki Yamasaki, Yoshihito Kawamura
    2006 Volume 47 Issue 4 Pages 959-965
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    The compositional dependence of mechanical properties and microstructural change of the extruded Mg-Zn-Y alloys has been investigated in the effort to develop a high strength Mg-Zn-Y alloy with long period ordered (LPO) structure. The extruded alloy Mg96Zn2Y2 exhibited a high yield strength of 390 MPa and elongation of 5% at room temperature, and of more than 300 MPa even at the elevated temperature of 473 K. The heat-treated ingot metallurgy (I/M) Mg-Zn-Y alloys containing very small amounts of yttrium and zinc are characterized by a lamellar phase constructed of 2H-Mg and 14H-LPO structures. Extrusion of the Mg-Zn-Y I/M alloys with LPO structure led to refinement of α-Mg grains and high dispersion of a hard lamellar phase consisting of torn-off 2H-Mg and bent LPO structures with random grain boundaries, resulting in strengthening of the alloys.
    Download PDF (411K)
  • Chui-Hung Chiu, Jian-Yih Wang, Horng-Yu Wu
    2006 Volume 47 Issue 4 Pages 966-970
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    A Mg–9%Li–1%Zn alloy was investigated by transmission electron microscopy and microdiffractometry. The alloy had a dual phase structure with dispersed particles of ZnO and MgO oxides. The Wurtzite structure of ZnO exhibited a good orientation with respect to the Mg matrix, but the MgO did not. The peak aging at a temperature of 100°C occurred at 10 h. At 50°C, the hardness reached the maximum value after an aging period of around 100 h. The appearance of the extra bump adjacent to the main peak of α(002) after aging at 50°C/100 h and 100°C/10 h, was thought to correspond to a precipitate phase or spinodal decomposition.
    Download PDF (283K)
  • Jian-Yih Wang, Tien-Chan Chang, Li-Zen Chang, Shyong Lee
    2006 Volume 47 Issue 4 Pages 971-976
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    The equal channel angular extrusion (ECAE) process is an innovative method to refine grain structure; however, it could be highly technical to perform to result in subsequent exotic mechanical properties. This study will demonstrate how easy or difficult of this operation. Yoshida et al. had applied the ECAE process on Mg-10%Li-1%Zn alloy to obtain a max. superplastic elongation of 421%. This paper tries to re-produce it with Mg-11%Li-1%Zn and Mg-9%Li-1%Zn alloys via the same ECAE process. For the 28 specimens having received 4 passes of ECAE, one of them shows a comparable but lesser elongation of 350% under selective temperature of 523 K and strain rate, 1×10−4 s−1, and the corresponding strain rate sensitivity exponent is 0.48. Furthermore, the ECAE process is imposed on three other Mg-Li-Zn alloys containing Al and Mn (Mg-9%Li-1%Zn-0.2%Mn, Mg-9%Li-1%Zn-1%Al-0.2%Mn and Mg-9%Li-3%Al-1%Zn-0.2%Mn), and this investigation is unprecedented. The original justification for this exploration is that Al and Mn addition may strengthen the α and β phases which are the sole micro-constituents of Mg-Li alloys when bearing Li content between 5% to 11%. Indeed, it is so at room temperature as determined by micro-hardness testing. However, high temperature tensile elongation is not benefited.
    Download PDF (432K)
  • Matthew S. Dargusch, Ketil Pettersen, Kazuhiro Nogita, Mark D. Nave, G ...
    2006 Volume 47 Issue 4 Pages 977-982
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    This paper investigates the relationship between mechanical properties and microstructure in high pressure die cast binary Mg-Al alloys. As-cast test bars produced using high pressure die casting have been tested in tension in order to determine the properties for castings produced using this technique. It has been shown that increasing aluminium levels results in increases in yield strength and a decrease in ductility for these alloys. Higher aluminium levels also result in a decrease in creep rate at 150°C. It has also been shown that an increase in aluminium levels results in an increase in the volume fraction of eutectic Mg17Al12 in the microstructure.
    Download PDF (388K)
  • Ritsuko Tsuzuki, Katsuyoshi Kondoh
    2006 Volume 47 Issue 4 Pages 983-988
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    The objective of this study is to develop a low-cost manufacturing process for recycling and circulating wasted glasses into a high added value product. Waste glass was used to synthesize Mg2Si and MgO by reaction with magnesium, and Mg2Si/MgO/Mg composites with high properties were produced. In the first stage of the study, the occurrence of solid-state synthesis between magnesium and wastes glasses was confirmed. The effect of repeated plastic working (RPW) on the refinement of grains and the composites was investigated. It was demonstrated that Mg2Si/MgO/Mg composites with excellent mechanical properties could be fabricated by RPW and hot extrusion using a mixture of magnesium powder and wasted glasses.
    Download PDF (570K)
  • Yasuo Ochi, Kiyotaka Masaki, Toru Hirasawa, Xiaorui Wu, Takashi Matsum ...
    2006 Volume 47 Issue 4 Pages 989-994
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    High cycle fatigue tests in rotating bending loading were carried out in extruded AZ31 magnesium alloys with two kinds of grain size (about 30 μm and about 50 μm). Effects of microstructure and grain size on fatigue behaviors such as fatigue strength, crack initiation and propagation behaviors were discussed. As the results, there were no clear difference in the fatigue strength, the crack initiation and propagation behaviors in the both alloys. There showed a clear bending point in the relation between crack propagation rate dadN and the stress intensity factor range ΔK at about ΔK=3 MPa\\sqrtm. The fatigue lives in the higher stress level were evaluated from the inclusion size and the relation of dadN−ΔK.
    Download PDF (370K)
  • Hidetoshi Somekawa, Toshiji Mukai
    2006 Volume 47 Issue 4 Pages 995-998
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    Examination of fracture toughness has been performed a commercial Mg-Zn-Zr alloy, ZK60, with fine strengthening particles. The commercial alloy was extruded at 633 K, and then heat treated at specific conditions. The microstructures were equi-axed grains, and average grain size and precipitate size were 11.6 μm and 50–150 nm, respectively. The yield strength and elongation-to-failure were 225 MPa and 17.0%. The plane-strain fracture toughness, KIC, was estimated to be 20.6 MPam1⁄2 in stretched zone analysis. From ductile fracture model, all the finer particles did not affect the void formation. The precipitates having a large diameter, more than 100 nm, were supposed to be the origin of void formation.
    Download PDF (205K)
  • Hiroyuki Watanabe, Masami Sugioka, Masao Fukusumi, Koichi Ishikawa, Mi ...
    2006 Volume 47 Issue 4 Pages 999-1007
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    The microstructures and mechanical properties of fullerene powder dispersed AZ91 magnesium alloy composites were examined. The AZ91 with 0, 1 and 5 mass% fullerene additions were produced by extruding a mixture of AZ91 machined chips and fullerene powder. The matrix grains of the extruded materials were equiaxed, and the size was ∼5 μm irrespective of the fullerene content. The agglomerated fullerene powder was aligned parallel to the extrusion direction in the composites. The addition of 1 mass% fullerene had little effect on the elastic moduli, tensile strength and ductility, whereas the addition of 5 mass% fullerene slightly decreased them. A comparison between the tensile properties of the present composites and those of AZ91 alloys processed by various methods was also made. The damping capacity increased steeply by the fullerene addition. The effectiveness of the fullerene addition for the enhancement of the damping capacity of metallic alloys was verified. A good combination of damping capacity, elastic moduli, strength and ductility was attained in the present composites.
    Download PDF (740K)
  • Tai Kumagai, Kisaburo Shimamura, Haruo Okahara, Yorinobu Takigawa, Ken ...
    2006 Volume 47 Issue 4 Pages 1008-1012
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    The tribological properties of hybrid process DLC (Diamond-like carbon) coating against magnesium alloy are examined in order to understand the basic friction and wear properties of DLC coatings against magnesium alloy and partially to simulate the drawing process in real transfer press line. The tests are conducted using simple ball or pin on disc system with various combination of uncoated/DLC-coated WC-Co (cemented carbide) and AZ31B specimen in room/elevated temperature and dry/lubricated environments. As the result, DLC coating has excellent tribological properties against AZ31B magnesium alloy at 250/260°C, which is the actual hot-working drawing condition of AZ31B sheet, in both dry and lubricated environment. DLC coating prevents possible adhesion between AZ31B and WC-Co at elevated temperature in less lubricated or nearly dry contact condition.
    Download PDF (396K)
  • Masaaki Hara, Kenji Matsuda, Wataru Yamauchi, Masaaki Sakaguchi, Toshi ...
    2006 Volume 47 Issue 4 Pages 1013-1019
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    The magnesium anodizing treatment described in this paper is an environmentally friendly treatment which excludes the use of chromates, fluorine compounds, and phosphates. An alkali bath, which mimics conditions necessary to form naturally occurring magnesium salts, was selected as an electrolytic bath. The components of the electrolytic bath were optimized, and the samples were evaluated by salt spray test. The results suggest that the anodizing treatment with the optimized conditions on the surface of magnesium alloys AZ91 can achieve a higher level of corrosion resistance than the traditional chemical conversion and anodizing treatments which use chromates, fluorine compounds, and phosphates.
    Download PDF (290K)
  • Chao-Sung Lin, Wei-Jen Li
    2006 Volume 47 Issue 4 Pages 1020-1025
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    Cerium conversion coatings are a potential alternative to chromium conversion coatings for improving the corrosion resistance of magnesium alloys. This study detailed the microstructure and corrosion resistance of cerium conversion coatings on AZ31 magnesium plates treated in 0.05 kmol m−3 cerium nitrate solution, with and without 0.25 kmol m−3 hydrogen peroxide. The results indicate that the corrosion resistance of the coating was related to the microstructure of the major overlay, and to the defects of the coating. The major overlay changed from a fibrous structure to a compact layer, as hydrogen peroxide was added to a cerium nitrate solution. Meanwhile, severely-damaged areas were observed on the coating formed in the presence of hydrogen peroxide. Although the compact coating displayed better corrosion resistance than its fibrous counterpart, both coatings were locally corroded during the polarization test.
    Download PDF (585K)
  • Takashi Yamaguchi, Tadashi Serikawa, Momoko Henmi, Hideki Oginuma, Kat ...
    2006 Volume 47 Issue 4 Pages 1026-1030
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    Magnesium silicide (Mg2Si) bulky materials are useful to improve the surface function of light metals such as magnesium or aluminum alloys, due to its superior corrosion resistance to the conventional stainless steel, and its high mechanical properties.
    In this study, Mg2Si thin film coated on AZ31 magnesium alloys by using a high frequency sputtering method, was examined. A neutral salt spray test to evaluate the corrosion resistance indicated that AZ31 substrate with Mg2Si coating was hardly damaged after 240 h. On the other hand, the non-treated one was corroded in only 1 h. Concerning wear resistance under the oil lubricant test, a friction coefficient of the AZ31 alloy with Mg2Si film is remarkably stable in employing S35C steel as a counter specimen. No sticking between both specimens was detected. In the combination of AZ31 alloy disc and S35C pin specimens, seizure and sticking phenomena occurred and the μ value suddenly increased. Accordingly, Mg2Si coating technology is a suitable surface modification process to improve corrosion and wear resistance of magnesium alloys.
    Download PDF (278K)
  • Yusuke Nakaura, Akira Watanabe, Koichi Ohori
    2006 Volume 47 Issue 4 Pages 1031-1039
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    Effects of Ca alone and Ca/Sr composite additions on microstructures, die castability, mechanical properties and creep properties of the Mg-Al based alloys are investigated for the purpose of the development of new Mg-Al-Ca-Sr alloy for automotive powertrain applications. Ca addition of more than about 1% to AM50 alloy significantly improves creep resistance but also enhance casting crack tendency. By the addition of approximately 0.2%Sr, such casting cracks are significantly suppressed, and besides creep resistance and mechanical properties increase. The improvement of creep resistance by Sr addition seems to be attributed to the suppression of grain boundary sliding due to the creation of thermally stable Al-Sr compound along the grain boundary and the suppression of discontinuous precipitation of β-Mg17Al12 phase.
    Download PDF (591K)
  • Yasumasa Chino, Tetsuji Hoshika, Mamoru Mabuchi
    2006 Volume 47 Issue 4 Pages 1040-1046
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    Machined chips of a magnesium ally were repeatedly recycled by hot extrusion at 673 K, and mechanical and corrosion properties of the recycled specimens were investigated. At room temperature, the recycled specimen with a high repeated number showed high 0.2% yield stress and high tensile strength but low elongation at room temperature. The main strengthening mechanism of the repeatedly recycled specimen was grain refinement strengthening. Inhomogeneous distribution of oxide contaminants adversely affected the elongation. At elevated temperature, the recycled specimen showed low strength and low elongation as the recycling was repeated. The recycled specimen by a single extrusion exhibited a superior corrosion resistance to the reference specimens. On the other hand, the repeatedly recycled specimen showed poor corrosion properties even though a large amount of oxides is contaminated. The deteriorated corrosion properties are caused by the excessive iron contamination which promotes pitting sites resulting from localized galvanic corrosion sites.
    Download PDF (675K)
  • Jian-Yih Wang, Ying-Nan Lin, Tien-Chan Chang, Shyong Lee
    2006 Volume 47 Issue 4 Pages 1047-1051
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    The commonly used die-cast magnesium alloy AZ91D in chip form bearing different environmental corrosive conditions was compacted, and then extruded in order to assess the feasibility of recycling in solid-state. This recycled material showed no inferior mechanical properties than its un-chipped counterpart. It was also aging hardenable just as the original bulk material. Metallurgical investigation of the processed material showed a eutectic-like microstructure in the specimens receiving solution treatment followed by aging. This phenomenon is considered as the same as isothermal transformation in the eutectoid steel.
    Download PDF (443K)
  • Yijing Wang, Tatsuhiko Aizawa, Chikashi Nishimura
    2006 Volume 47 Issue 4 Pages 1052-1057
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    Mg–Co system is employed to investigate the solid-state reactivity of Mg2Co from the elemental powder mixture of magnesium and cobalt and to describe the hydrogenation and de-hydrogenation processes of Mg2Co. Mg2Co is successfully solid-state synthesized as a non-equilibrium phase compound by the bulk mechanical alloying. This solid-state reactivity is controlled by the repeated plastic flow of ductile elements in the powder mixture. This non-equilibrium phase, Mg2Co is stable up to 833 K. Its hydrogenation and de-hydrogenation processes are described by DSC, PCT and XRD. These processes take place in multi-step with strong dependency on the holding temperature. Hydrogenation process from Mg2Co is composed of two steps to Mg2CoH5 and dehydrogenation from Mg2CoH5, one step to Mg2Co, at 633 K. Maximum hydrogen absorption capacity at 633 K is still limited to 2.03 mass% since hydrogenation and de-hydrogenation steps, working at higher temperature, are never activated without chemical modification to original Mg2Co.
    Download PDF (509K)
  • Tatsuhiko Aizawa, Renbo Song, Atsushi Yamamoto
    2006 Volume 47 Issue 4 Pages 1058-1065
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    Profound understanding and survey of magnesium base intermetallic compounds is hindered by various difficulties in their processing and fabrication. Solid-state synthesis via the bulk mechanical alloying (BMA) is free from contaminations and segregation through high reactivity of elemental constituents against crucibles or vials. Magnesium–tin system is employed to demonstrate the solid-state reactivity to Mg2Sn from the elemental powder mixture. This process is characterized by the gradual solid-state reaction to Mg2Sn with processing time. Since the blended mixture of magnesium and tin with the initial molar ratio of Mg66.7%Sn33.3%, is repeatedly strained via BMA in the controlled conditions, the solid-state reaction advances monotonically with refinement of interparticle distance between magnesium and tin. Ternary semi-conductive compounds, Mg2Si1−xSnx for 0≤x≤1, are also synthesized by this process. Thermoelectric properties of this ternary alloy are investigated to discuss the effect of tin content on the band-gap, the thermal conductivity, the Seebeck coefficient and the figure-of-merit. In addition, these data are compared to the previously reported results by using melt and solidified samples in order to describe the common features in the solid-solution type thermoelectric compounds. Furthermore, p–n transition behavior is also reported in this ternary alloy system.
    Download PDF (418K)
  • Kentaro Yamada, Yoshiyuki Okubo, Masashi Shiono, Hidetsuna Watanabe, S ...
    2006 Volume 47 Issue 4 Pages 1066-1070
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    The effects of zinc addition on microstructure evolution and mechanical properties of Mg-Gd-Y-(-Zr) based alloys are investigated in details using OM, TEM, Vickers hardness tests and tensile tests. Specific line-shaped structure is formed inside of matrix grain in the as-cast specimen. This structure is dissolved after a solution-treatment at 773 K. Instead of it, in the 0.3–1Zn alloy, the 14H LPSO structure is observed at grain boundaries of Mg matrix phases after the solution heat treatment. Metastable β′ phase is formed during subsequent aging treatment at 498 K. The 14H LPSO structure is stable and remained even after the aging treatment. These structure and phase coexist at the peak-aged condition in the microstructure. In cast- specimens, 0.2% proof stress and tensile strength slightly decreases with an addition of zinc up to 0.75 mol% and rapidly decreases over 1 mol% zinc addition. On the contrary, in rolled-specimens, addition of 0.3–1 mol% zinc improves mechanical properties in both strength and ductility significantly. It is found that the UTSs reach more than 400 MPa in the 0.3–1Zn alloys. This characteristic effect is considered to be the contribution of LPSO structure and its specific orientation relationship with matrix phase.
    Download PDF (442K)
  • Shinji Fukumoto, Soshi Tanaka, Toshitsugu Ono, Harushige Tsubakino, To ...
    2006 Volume 47 Issue 4 Pages 1071-1076
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    Microstructural development of friction welded AZ31 alloy was studied. The microstructures near weld interface consist of mainly three regions that are recrystallized fine-grain, mixed-grain and twin regions. The most impressive microstructural feature is grain refinement. Fine grains whose size was approximately 2 μm were produced at the weld interface due to a hot heavy working, resulting in the increase of micro-Vickers hardness. New fine grains were born at the shear bands that were introduced during the friction and upset processes. The grain size depended on the welding condition, especially the upset pressure. The smaller grains were obtained with higher upset pressure and shorter friction time. Although Hall–Petch relation was basically realized in friction welded AZ31, it is necessary to consider the effect of work hardening.
    Download PDF (834K)
  • Masato Tsujikawa, Yukiko Abe, S. W. Chung, Sachio Oki, Kenji Higashi, ...
    2006 Volume 47 Issue 4 Pages 1077-1081
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    The feasibility of friction stir welding (FSW) for cold worked Mg-14 mass%Li-1 mass%Al alloy was investigated. The alloy melted and cast into ingots under pressurized argon gas atmosphere. Slabs prepared from homogenized ingots, then cold-rolled up to 0.5 mm thickness. The density of this alloy is 1.326 g/cm3 and its ultimate tensile strength is from 180 to 294 MPa according to the reduction ratio of rolling. The cold rolled plates of 2 mm thickness were butted and jointed by FSW with various tool rotation and traveling speeds. It was found that the sound joints can be made at specific conditions apart from that of AZ31 alloy. Measurement of cross sectional hardness profile revealed slight higher hardness of stir zone than that of work-hardened base metal. The hcp peaks clearly appeared at XRD profiles from stir zones.
    Download PDF (373K)
  • Kenichiro Suetsugu, Akio Furusawa, Masato Tanaka, Hiroaki Takano, Hide ...
    2006 Volume 47 Issue 4 Pages 1082-1089
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    A method for designing lead-free solder was studied using the liquidus temperature of a 2-component eutectic solder in order to develop a high temperature lead-free solder. In this work, tests were done to obtain a targeted liquidus temperature of a 4-component lead-free solder based on the weight percentage of two sets of 2-component eutectic solders. This 2-component eutectic solder was assumed to be thermodynamically stable in itself. The weight percentages of five respective types of Bi–Cu, Ag–Cu etc. eutectic solders were varied and the design temperature was predicted and compared against the measured liquidus temperature. In doing this, it was learned that the measured apparent liquidus temperatures were liniear with respect to the design temperatures. Similar studies were conducted into a medium temperature material of Sn–Ag–Cu and a low temperature material of Sn–Bi–Ag. The measured temperatures of these solders also corresponded to the design temperatures.
    Download PDF (211K)
  • Tomoaki Akabane, Yasushi Sasajima, Jin Onuki
    2006 Volume 47 Issue 4 Pages 1090-1097
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    By the molecular dynamics method, a computer simulation of a scratch test with a nanometer scale was performed. The specimen was composed of 1008 silicon atoms with a diamond single-crystal structure. The indentor was assumed to be a perfect rigid body, and the Morse potential was utilized as the interaction between the indentor and a silicon atom. Two types of potential, i.e., Stillinger-Weber and Tersoff potentials, were examined as the interaction between silicon atoms. The present simulation clarified that the standard deviation of the friction constant increased with decreasing scratch depth and became maximum when the indentor just began to scratch the specimen surface at critical load. The friction coefficient, indentation hardness and scratch hardness at critical load were estimated to be 1.2–1.6, 80–90 GPa and 8.5–9.4 GPa, respectively.
    Download PDF (295K)
  • Takeshi Nakajima, Mahoto Takeda, Takao Endo
    2006 Volume 47 Issue 4 Pages 1098-1104
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    Growth of precipitates during creep was investigated of a commercial magnesium alloy AZ80. TEM observations in this study confirmed that the cube of the average particle size changed roughly with creep time at grip parts and the growth rate was greater at the gauge part than at the grip part of crept specimens. The cube of the average particle size changed roughly with creep time at grip parts. This suggests that the coarsening of particles at grip part obeyed the Ostwald ripening theory in which the growth rate was assumed to be controlled by the lattice diffusion. In order to make clear the factors affecting the growth rate of precipitates at gauge part, interrupted creep tests were carried out. The present analysis of the experimental results showed that the effect of strain on the particle growth was more important than that of stress. The influence of concurrent straining on the particle growth is also discussed in terms of traveling dislocations with solute atmospheres.
    Download PDF (212K)
  • Takeshi Nagase, Akimasa Yokoyama, Yukichi Umakoshi
    2006 Volume 47 Issue 4 Pages 1105-1114
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    The microstructure in rapidly-solidified Fe70−xCuxZr10B20 (x=0, 10, 20, 30, 35, 60 and 70) alloy ribbons prepared by single-roller melt-spinning method was examined. In spite of the positive heat of mixing in Fe–Cu atom pair, metallic glass was formed in Fe–Cu–Zr–B ribbons. F.c.c.–Cu nano crystalline globules dispersed in Fe–Zr–B based metallic glass was formed in Fe60Cu10Zr10B20 and Fe50Cu20Zr10B20 alloys. Size of the globules in nano-emulsion structure increased with increasing Cu concentration. In Fe35Cu35Zr10B20 and Fe10Cu60Zr10B20 alloys, an entangled marble-like duplex structure composed of Fe-rich and Cu-rich crystalline phases was formed. Zr and B additions in Fe–Cu based alloys cause the formation of metallic glass and unique solidification structures in rapidly solidified melt-spun ribbons.
    Download PDF (1885K)
  • Keesam Shin, Junghoon Yoo, Sungwook Joo, Takahiro Mori, Daisuke Shindo ...
    2006 Volume 47 Issue 4 Pages 1115-1120
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    Ordering of In and Ga in In0.53Ga0.47As films grown at 573 K, 673 K, and 773 K by molecular beam epitaxy was investigated by electron diffraction pattern analysis using a transmission electron microscope equipped with an Ω-filter and imaging plates. In addition, high-resolution electron microscopy on the specimens and fast Fourier transformation analyses were performed to identify the short-range ordering. In the EDPs obtained from the specimen grown at 573 K, the diffuse scattering corresponding to short-range ordering was observed only when the film was investigated at [\\bar110] beam incidence, whereas for the specimens grown at 673 and 773 K, diffuse scattering was observed only at [110] beam incidence. The ordering of 573 K specimen has a triple period and those of 673 K and 773 K have a double period. Through the processing of the HREM images and comparison of calculated and observed diffuse-scattering distribution, models of short-range ordered structures were proposed on the basis of the triple-A type ordering at the specimen grown at the 573 K and the CuPt-B type ordering at the specimen grown at 773 K.
    Download PDF (504K)
  • Eiichi Sato, Tomoyasu Yamada, Hisamune Tanaka, Itaru Jimbo
    2006 Volume 47 Issue 4 Pages 1121-1126
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    The creep behavior at an ambient temperature of typical h.c.p., b.c.c. and f.c.c. metals and alloys of annealed states were surveyed. Cubic metals and alloys demonstrated negligible creep strain under all stress ranges. In contrast, h.c.p. metals and alloys demonstrated significant creep behavior. In particular, Ti–6Al–4V alloy and CP–Ti metal showed accumulated large creep strains. The difference among metals and alloys were negligible, for Mg and Zr. After being cold rolled, Ti–6Al–4V alloy and CP–Ti metal showed less significant creep behavior.
    Download PDF (609K)
  • Shuhei Osaki, Hideki Kondo, Katsuyuki Kinoshita
    2006 Volume 47 Issue 4 Pages 1127-1134
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    For underaged Al-Mg-Si alloys with excess Si, No. 5(Al-0.7 mass%Mg-1.1 mass%Si) and No. C5 with 0.2 mass%Cr addition, SSRT tests have been carried out to reveal the contribution of hydrogen embrittlement (HE) to SCC processes at strain rate 6.9×10−7 s−1 under three environments; \\ding172dry nitrogen gas, \\ding173wet air with 90% relative humidity and \\ding174an acid sodium chloride (ISO) solution. Under env.\\ding173, alloy No. 5 with coarse grains shows a decrease in elongation comparing with that under the inert env.\\ding172, while alloy No. C5 with finer gains exhibits rather an increase. The small areas of intergranular(IG)- and transgranular(TG)-facets both with a feature of wavy slips are observed in contact with the free-surface of the specimens, respectively, which are regarded as an evidence of hydrogen-enhanced localized plasticity. Under env.\\ding174, alloy No. 5 shows a high susceptibility to SCC, while alloy No. C5 exhibits a low one improved through Cr addition. On SCC fracture surface of alloy No. 5, three modes of IG one with crystallographic pits, IG another with fine ledges and TG one with an appearance of quasi-cleavage are presented, which indicates that the mechanism of plastic deformation localization induced by anodic dissolution plays a dominant role in the SCC. Even though HE is involved in the SCC process, the effect is estimated to remain small.
    Download PDF (560K)
  • Feng-cang Ma, Wei-jie Lu, Ji-ning Qin, Di Zhang
    2006 Volume 47 Issue 4 Pages 1135-1139
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    In the present work, samples which were added various contents of C into Ti-1100 alloy were prepared, and in situ 5 vol% TiC/Ti-1100 composite was prepared. The microstructure of samples after hot–forging was examined using optical microscopy (OM). Mechanical properties of the samples were tested by tensile tests at ambient temperature and 873 K, respectively. Fractography of the composite was performed by scanning electron microscope (SEM). It was found that C element increases strength of Ti-1100 alloy obviously. But the strengthening mechanism of C in the composite was different at ambient temperature and 873 K. Compared to monolithic Ti-1100 alloy, the increase in strength at ambient temperature mainly results from solute C element in matrix, but at 873 K, the increase in strength also results from TiC particles.
    Download PDF (444K)
  • Yao-Chih Chuang, Shih-Chin Lee, Hsin-Chih Lin
    2006 Volume 47 Issue 4 Pages 1140-1144
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    The microstructure and wear resistance of a laser surface alloyed Al-Mg-Si with Co alloy powder were investigated. The experimental results indicate that a porosity-free zone can be generated but some cracks appear after laser surface alloying (LSA). In this investigation, two regions, A (surface region) and B (bottom region), are observed in the pool. Al9Co2 particles with a network structure are present in region A and block-like Al13Co4 particles are distributed in region B. The hardness of the LSA specimens is three to nine times higher than that of the Al-matrix. The high hardness of LSA specimens cause them to exhibit excellent sliding wear performance so they have a lower friction coefficient and wear rate. Notably, the critical temperature of the sliding wear resistance of the LSA specimen exceeds that of the Al-matrix by approximately 50 K.
    Download PDF (420K)
  • Osamu Takeda, Toru H. Okabe
    2006 Volume 47 Issue 4 Pages 1145-1154
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    The possibility of a high-speed and (semi-)continuous titanium production process by the magnesiothermic reduction of titanium subchloride—titanium dichloride (TiCl2) and/or titanium trichloride (TiCl3)—is discussed. When the TiCl3 feed material and magnesium reductant charged into a titanium reaction container were heated at a rate of 0.056 K/s (3.3 K/min) in an argon atmosphere, the temperature of the container rapidly increased above 973 K, and the magnesiothermic reduction of TiCl3 proceeded at a high speed. After the reduction, the reaction product magnesium chloride (MgCl2) and the excess magnesium were removed by leaching or vacuum distillation. An efficient separation process of MgCl2 from titanium metal by a combination of draining and vacuum distillation was also investigated. Under a suitable condition, titanium with 99.5% purity was efficiently obtained. The titanium reaction container showed no signs of damage, thus proving its suitability for the magnesiothermic reduction of TiCl3.
    Download PDF (561K)
  • Keiko Sasaki, Takashi Sakimoto, Mai Endo, Hidetaka Konno
    2006 Volume 47 Issue 4 Pages 1155-1162
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    Morphological characterization of jarosite groups formed from Fe(III) biologically oxidized with different numbers of Acidithiobacillus ferrooxidans was conducted using FE-SEM. The higher population of A. ferrooxidans resulted in more distinct jarosite mineral shape, and stronger Raman intensities for potassium jarosite, ammoniojarosite and argentojarosite. The morphology of the jarosites might be dependent on iron-oxidizing activity of A. ferrooxidans.
    The technique was applied to identify jarosite compounds formed during microbially mediated dissolution of arsenopyrite by A. ferrooxidans. It is difficult to identify this jarosite compound by X-ray diffraction and Raman spectroscopy because amounts are typically low and the crystallization is poor in minerals formed by microbially mediated oxidation. However, FE-SEM image provided helpful information for identification of jarosite compounds.
    The results suggest that morphology would provide useful information for identification and history of jarosite minerals as geochemical samples.
    Download PDF (611K)
  • In-Joon Son, Hiroaki Nakano, Satoshi Oue, Shigeo Kobayashi, Hisaaki Fu ...
    2006 Volume 47 Issue 4 Pages 1163-1169
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    The effect of equal-channel angular pressing (ECAP) on the pitting corrosion resistance of Al and Al-Mg alloy was investigated by means of polarization curves in solutions containing 300 ppm of Cl and by surface analysis. The potentials for pitting corrosion of Al and Al-Mg alloy were clearly shifted in the noble direction by the ECAP process, indicating that this process improves resistance to pitting corrosion. SEM observations revealed that pitting corrosion occurred near impurity precipitates and that the size of the impurity precipitated decreased as a result of the ECAP process. The time-dependence of corrosion potential and the polarization resistance determined using the AC impedance technique suggest that the ECAP process increases the rate of formation of Al oxide films. The improvement in pitting corrosion resistance of Al and Al-Mg alloy by ECAP appears to be attributable to a decrease in the size of impurity precipitates and an increase in the rate of formation of Al oxide films.
    Download PDF (509K)
  • Motofumi Ohki, Tatsuya Ishibashi, Jun Kinoshita
    2006 Volume 47 Issue 4 Pages 1170-1177
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    Thermal Barrier Coatings (TBCs) are developed as a method for increasing the operation gas temperature of gas turbines for electric power stations, and recently they are applied to 1500°C class gas turbines. On the other hand, they have been reported that the repetition of thermal stress caused by a difference in the thermal expansion coefficient between thermal barrier ceramic layer and metallic layer in TBCs promotes coating damage. Therefore, understanding the accurate value of top-coat (TC) Young’s modulus that can estimate the extent of generated thermal stress is necessary to ensure material reliability. However, because TBCs are formed as a composite material of combined thin layer coatings, the essential problem that TBCs can’t apply to general materials estimation experiment is obvious.
    We have studied the estimation of TC Young’s modulus by using indentation hardness tests. In the former paper, we reported that the calculated TC Young’s modulus for TBCs specimens depends on the indentation load. Therefore, we first discuss such dependency in the present paper. As a result, we clearly show that the reason for the load dependency of the calculated TC Young’s modulus below 147 N of indentation load is the effect of under-coat (UC) and calculating TC Young’s modulus by using this procedure can eliminate the UC effect until an indentation load of 9.8 N. In addition, we examine the fracture behavior of TC following the indentation process and discuss the reason why does calculated TC Young’s modulus decrease above 147 N.
    We also discuss the influence of TC anisotropy on calculated TC Young’s modulus, and then we confirm that the influence of TC anisotropy rarely appears using this procedure.
    Download PDF (861K)
  • Kwang-jin Lee, Shinji Kumai
    2006 Volume 47 Issue 4 Pages 1178-1185
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    Lap joining of the low carbon steel (SPCC: Steel Plate Cold-rolled C) and aluminum alloy 6111-T4 plates was carried out using a defocused YAG laser beam. Precise TEM and TEM-EDX analyses were performed for the intermetallic compound (IMC) layer formed at the welding interface of the lap joint, which was fabricated under the following conditions: (laser power: 3.0 kW, defocus distance: 20 mm, laser traveling speed: 2.17×10−2 ms−1). The IMC layer consisted of very fine granular crystals. The fine IMC crystals with about 500 nm in diameter formed at the interface between IMC layer and solidified A6111 region. In contrast, IMC crystal grains at the central region of the layer were relatively large and the average size was 1 μm. Both TEM-EDX and electron diffraction pattern analyses confirmed that the former is Al13Fe4 and the latter is Al5Fe2. The greater part of the IMC layer was occupied by Al5Fe2 in the present welding condition. Another ultra fine IMC grains were observed at the interface between the SPCC and IMC layer. The electron diffraction pattern analysis revealed that they were FeAl, Fe3Al and Al6Fe.
    Download PDF (334K)
  • Ya-Yun Chou, Hung-Ju Chang, Jer-Haur Kuo, Weng-Sing Hwang
    2006 Volume 47 Issue 4 Pages 1186-1192
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    A three-dimensional computer aided analysis system has been developed in this study based on fluid dynamics to simulate the shape evolution of solder joints during the reflow process.
    The solution of velocity and pressure fields is based on SOLA (SOLution Algorithm) scheme, and the method to construct the interface and the transportation of volume fractions of liquid in the cells are coupled with PLIC (Piecewise Linear Interface Calculation) and VOF (Volume of Fluid) technologies. In order to consider the effect of surface tension on a fluid surface, the CSF (Continuum Surface Force) model is employed.
    The simulated results are compared with experimental measurements and good consistency is observed. Furthermore, the simulated results can reveal the evolution of the molten solder from its initial state to the equilibrium state. It is also capable of analyzing the overflow conditions when the amount of solder deposit is too much to be constrained in the solder pad, which is not achievable by the energy-based technique such as Surface Evolver.
    Download PDF (243K)
  • Wen-Jun Li, Rong Tu, Takashi Goto
    2006 Volume 47 Issue 4 Pages 1193-1197
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    TiC-TiB2-SiC composites were synthesized by arc-melting using TiC, TiB2 and SiC powders as starting materials in Ar atmosphere. TiC-TiB2-SiC system was a ternary eutectic, whose eutectic composition was 34TiC-22TiB2-44SiC (mol%). The TiC-TiB2-SiC eutectic composite showed a lamellar texture, where lamellar SiC grains paralleled to lamellar TiC grains. TiB2 grains had an angle of about 30 to 60° with lamellar SiC and TiC grains. The hardness of TiC-TiB2-SiC eutectic composite was 25.5 GPa at the load of 1.96 N and increased with increasing TiC content. The electrical conductivity of the eutectic composite was 2.81×103 Sm−1 at the room temperature and decreased with increasing temperature. The thermal conductivity of the eutectic composite was 25 to 60 WK−1 m−1 at the room temperature and decreased with increasing temperature. The electrical conductivity of TiC-TiB2-SiC ternary composites decreased with increasing SiC content, and the thermal conductivity decreased with increasing TiC content.
    Download PDF (374K)
  • Kyeong Ho Baik
    2006 Volume 47 Issue 4 Pages 1198-1203
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    Ti-Al-V preforms were manufactured by low pressure plasma spraying (LPPS) from two different sizes of Ti-6Al-4V feedstock powders, and subsequently consolidated by vacuum hot pressing (VHP). During LPPS, a loss of alloying elements and an incorporation of [H] and [O] occurred, which were much significant for a smaller feedstock powder. Subsequent VHP completely removed [H] content, whereas a considerable amount of [O] remained. The microstructure of LPPS deposits comprised a splat-quenched lamellar structure, incorporating unmelted particles. The each splat contained α′ martensite plates and Ti hydrides which provided heterogeneous nucleation sites for recrystallization during subsequent VHP, transforming into an equiaxed α grain structure. The tensile properties of LPPS/VHP Ti-Al-V alloy were primarily affected by [O] content. An increase in [O] content up to 0.35 mass% increased tensile strength, but dramatically decreased ductility. Further [O] incorporation formed a large fraction of embrittled α-phase, resulting in a significant decrease in both tensile strength and ductility.
    Download PDF (1075K)
  • Kazuya Shimoda, Nobuhiko Eiza, Joon-Soo Park, Tatsuya Hinoki, Akira Ko ...
    2006 Volume 47 Issue 4 Pages 1204-1208
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    Dense SiC ceramics fabricated by NITE process (NITE-SiC), using SiC nano-powder, were subjected to exposure tests from 1000 to 1800°C in an argon-oxygen gas mixture with an oxygen partial pressure of 0.1 Pa. The thermal stability of NITE-SiC was examined through mass change, 3-point bending test, XRD analysis and TEM/SEM observation. The NITE-SiC presented excellent bending strength (above 800 MPa) up to ∼1800°C while the conventional liquid-phase sintered SiC ceramics (LPS-SiC), using SiC sub-micron powder, indicated severe degradation at 1300°C due to volatilization and softening of amorphous grain boundary phase. The in situ 3-point bending test at 1300°C was carried out to evaluate in-service fracture behavior, where excellent improvements in bending strength, elastic modulus and fracture behavior were confirmed, compared with the conventional LPS-SiC. These are interpreted by the modification with reduction and crystallization of grain boundary phase (Y3Al5O12). The decomposition of Y3Al5O12 were caused by the reactions with CO gas on the surface of NITE-SiC exposed at 1800°C, but the severe degradation was not identified in strength.
    Download PDF (319K)
  • Yosuke Horiuchi, Tomonari Inamura, Hee Young Kim, Syuichi Miyazaki, Ke ...
    2006 Volume 47 Issue 4 Pages 1209-1213
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    The effect of 3d-transition-metal alloying on the phase constitution of Ti-18 mol%Nb based shape memory alloys was investigated by X-ray diffraction analysis (XRD) at room temperature. The baseline binary Ti-18 mol%Nb alloy (called Binary) and ternary Ti-18 mol%Nb-3 mol%X alloys (X=V, Cr, Mn, Fe, Co and Ni, called 3X) were fabricated by Ar arc-melting method, followed by homogenization at 1273 K for 3.6 ks. These alloys were cold-rolled with 30% and 98% reduction in thickness. Some specimens from 98% cold rolled material were solution treated at 1273 K for 1.8 ks and quenched in water. It was found that the phase present in the solution-treated and quenched Binary and 3V was α″ martensite phase and that of the other alloys was β phase. No other phase or ordering was confirmed in these baseline and 3X alloys. The lattice parameter of β phase showed a good correlation with the Goldschmidt atom radius of the ternary alloying metals. It was confirmed that (1) almost same type of deformation texture was formed in β phase materials regardless of the alloying metals but that (2) the development of recrystallization texture was suggested to be different depending on the alloying metals.
    Download PDF (193K)
  • Kenji Matsuda, Tomoaki Saeki, Katsuhiko Nishimura, Susumu Ikeno, Yukin ...
    2006 Volume 47 Issue 4 Pages 1214-1220
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    Superconductive MgB2/Al composite material with low and high volume fractions of particles were fabricated by our special pre-packing technique and 3-dimensional penetration casting method. The composite material showed homogeneous distribution of MgB2 particles in the Al-matrix with neither any aggregation of particles nor defects such as cracks or cavities. The critical temperature of superconducting transition (TC) was determined by electrical resistivity and magnetization to be about 37–39 K. Specific heat measurements further supported these TC findings. The Meissner effect was also verified in the liquid He, in which a piece of the composite floated above a permanent magnet. The thermal conductivity of the MgB2/Al composite material was about 25 W/K·m at 30 K, a value much higher than those found for NbTi or Nb3Sn superconducting wires normally used in practice, which are 0.5 and 0.2 W/K·m at 10 K, respectively. A billet of the superconducting material was successfully hot-extruded, forming a rod. The same as the billet sample, the rod showed an onset TC of electrical resistivity of 39 K.
    Download PDF (704K)
  • Hidekazu Sueyoshi, Harunori Odo, Shinji Mizokuchi, Shigeru Abe, Kazuya ...
    2006 Volume 47 Issue 4 Pages 1221-1226
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    The consumption of a soldering iron by Pb-free solder is examined and the kinetic analysis of the reaction between the solder and the soldering iron is discussed. The consumption of the soldering iron increases with prolonged contact time between the solder and the soldering iron. No thick reaction layer is detected at the solder/soldering iron interface at the position where fused solder is removed by compressed air cleaning. However, at the position where fused solder remains, a thick reaction layer is formed. In particular, a thick FeSn2 reaction layer is observed when fused solder sticks on the surface of the soldering iron for a long time. On the basis of the reaction kinetics, the growth rate of the reaction layer is demonstrated to be controlled by iron diffusion through the reaction layer. The mechanism of soldering iron consumption by Pb-free solder is as that a ∼30 nm-thick layer is formed during one soldering process and then flaked off from the surface of the soldering iron during compressed air cleaning.
    Download PDF (337K)
  • Yong Bum Choi, Kazuhiro Matsugi, Gen Sasaki, Kazushi Arita, Osamu Yana ...
    2006 Volume 47 Issue 4 Pages 1227-1231
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    A metal-fiber-reinforced aluminum alloy composite was fabricated through low-pressure casting and its optimum process conditions were determined. The direct finite difference method (DFDM) based on Darcy’s law was used to calculate the pressure distribution inside the preform, and then the porosity inside the composite fabricated through low-pressure casting at 0.4–0.8 MPa was estimated. The relationship between the porosity and the pressure distribution inside the preform was also estimated. The porosity of the composites fabricated under the applied pressures of 0.4 MPa, 0.6 MPa, 0.7 MPa and 0.8 MPa was estimated to be 0.11%, 0.04%, 0.07% and 0%, respectively, at the pressure acceleration time of 1 s. Hence, the composite without pores was fabricated under the pressure of 0.8 MPa in applied pressure.
    Download PDF (358K)
  • Chih-Yuan Chen, Hao-Long Chen, Weng-Sing Hwang
    2006 Volume 47 Issue 4 Pages 1232-1239
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    The aim of this article is to study the influence of interfacial structure development at interface on the fracture mechanism and the bond strength of cold roll bonded Al/Cu bimetal plate. The Al/Cu bimetal plates are produced by cold roll bonding and then sintered at different conditions. The bond strength of the Al/Cu bimetal plate increases generally to maximum values and then decreases to low values with increasing sintering temperature and time. Interfacial structures develop with increasing sintering temperature and time. The main interfacial layers are Al2Cu, AlCu, Al3Cu4 and Al4Cu9. The formation and thickening of those intermetallic compounds promotes cracks propagation and weakens the bond strength of the bimetal plates. The fracture mechanism transforms from ductile to brittle cleavage with the development of interfacial structures. While the bond strength of the material starts to decrease, no obvious Kirkendall effect of void formation is observed in the present study.
    Download PDF (898K)
  • Sosoon Park, Shigeo Kitsukawa, Kenji Katoh, Sigenori Yuyama, Hiroaki M ...
    2006 Volume 47 Issue 4 Pages 1240-1246
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    In Europe and USA, in-service diagnosis technique by AE method has already been used for evaluating the corrosion damage of bottom plate of oil storage tank. However, the diagnosis technique is dependent on the empirical method without physical bases such as the mechanism of AE generation due to the corrosion of bottom plates of oil storage tank. And also the relation between the corrosion rate and AE activity has not been clarified yet. This study was designed to clarify AE source and the relation between corrosion rate and AE activity during corrosion of bottom plate in oil storage tank, in particular, on the neutral sand bed. For modeling the corrosion condition which is similar to that of an in-service tank bottom on the neutral sand, the static stress of 382 MPa had been applied on the specimen plates. We investigated experimentally the relation between the corrosion rate and AE activity during the corrosion. Furthermore, the AE source and mechanism were examined based on the SEM observation of corroded surface. From these experimental results, the validity and physical basis for quantitative evaluation of corrosion rate by means of AE was presented.
    Download PDF (309K)
  • Guangzhao Bai, Wan Jiang, Lidong Chen
    2006 Volume 47 Issue 4 Pages 1247-1249
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    The thermal conductivity of molybdenum disilicide composites reinforced with 100 nm and 0.5 μm silicon carbide particles was determined as the function of volume fraction of silicon carbide. Due to interface effect, the thermal conductivity of composites with same volume fraction of silicon carbide decreased with decreasing inclusion size. It has been found that at lower inclusion content, interfacial thermal resistance dominates in determining composite thermal conductivity, while with increasing content of dispersions, percolative thermal transport paths diminishes the effect of interfacial thermal resistance.
    Download PDF (166K)
  • Young Buem Song, Kyung-Tae Park, Chun Pyo Hong
    2006 Volume 47 Issue 4 Pages 1250-1256
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    A modified strain-induced, melt-activated (SIMA) process for semi-solid processing of alloys was proposed. In order to examine the applicability and effectiveness of the modified SIMA process, the recrystallized microstructures of a high strength 7175 Al alloy prepared by the modified SIMA processes were macroscopically compared to that of conventional process. The modified SIMA process employed casting, two stage homogenization, warm multi-forging, and recrystallization and partial melting (RAP) instead of the conventional process consisted of casting, hot working, cold working and RAP. For the alloy processed by the conventional SIMA process, the recystallized grain size decreased with increasing the cold rolling reduction ratio up to 20% and then almost unchanged. RAP treatments of the 20% cold rolled alloy at above 600°C and for longer than 30 min resulted in significant grain growth. In case of the modified SIMA process, the alloy multi-forged with the accumulated strain of about 7 and RAP at 575°C for 10 min exhibited the uniform equiaxed recrystallized grain structure similar to that of the conventional SIMA process under the optimum conditions. The improved processing efficiency of the modified SIMA process over the conventional one, i.e. removal of hot working and saving of RAP time, is attributed to the enhanced recrystallization kinetics due to a high density of Mg(Zn,Al,Cu)2 precipitates which are formed by two stage homogenization, acting as the preferential recrystallization sites and due to the driving force imposed by relatively large amount of uniform deformation by multi-forging.
    Download PDF (585K)
  • Qing Chang, Chaoli Ma, Shujie Pang, Hua Men, Tao Zhang
    2006 Volume 47 Issue 4 Pages 1257-1260
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    Glass-forming ability and mechanical properties of bulk glassy (Cu0.55Zr0.40Al0.05)99RE1 (RE=Y, Pr, Tb, Dy, Ho, Er) alloys were systematically studied. It is found that the minor addition of rare earth elements greatly improves the glass-forming ability of the studied Cu-based alloys. Critical diameter for glass formation is 3 mm for Cu55Zr40Al5 alloy and increases to 4 or 5 mm with the addition of 1 at% RE. These RE doped Cu-based glassy alloys exhibit relatively wide supercooled liquid region of 50–70 K, as well as high fracture strength of about 1900–2100 MPa.
    Download PDF (125K)
  • Guobiao Lin, Jihua Huang, Huang Zhang, Xingke Zhao
    2006 Volume 47 Issue 4 Pages 1261-1263
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    Cf/SiC composite was brazed to Ti-alloy by using interlayer of Ag-Cu-Ti-C mixed powder. Microstructure and both the room temperature and 500°C shear strengths of the brazed joint were investigated. In situ synthesized TiCx (x≤1) is formed in the brazing layer of the joint by the reaction of C and Ti in the brazing layers and provides good reinforcement and alleviation of the joint thermal stress.
    Download PDF (174K)
  • Makoto Matsuura, Kazuya Konno, Mitsuhiko Yoshida, Masahiko Nishijima, ...
    2006 Volume 47 Issue 4 Pages 1264-1267
    Published: 2006
    Released: April 15, 2006
    JOURNALS FREE ACCESS
    The microstructure of a melt-quenched Mg98Cu1Y1 alloy has been studied by high-resolution transmission electron microscopy (HRTEM) and high-angle annular detector dark-field scanning transmission electron microscopy (HAADF-STEM). We have found Cu- and Y-rich precipitates, which are uniformly dispersed in Mg-matrix grains. The precipitates are aligned parallel to the c-plane of the Mg-matrix crystal, and have the peculiar morphology consisting of a disk-shaped amorphous core sandwiched between 14H-typed long period stacking order (LPSO) crystals. A relatively stable supper-cooled liquid phase in an Mg-Cu-Y alloy system, and the formation and growth of the LPSO crystals from the amorphous phase are responsible for the peculiar morphology of the precipitates.
    Download PDF (339K)
feedback
Top