Started in 1985 Semimonthly
ISSN 1005-0302
CN 21-1315/TG
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The journal has been awarded the excellent periodical in China, and its articles are covered by SCI, EI, CA, SA, JST, RJ, CSA, MA, EMA, AIA etc., PASCAL web. ISI web of Science,SCOPUS.

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      28 May 2008, Volume 24 Issue 03 Previous Issue    Next Issue
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    Research Articles
    Formation Mechanism of Chunky Graphite and Its Preventive Measures
    Hideo Nakae, Sanghoon Jung, Ho-Chul Shin
    J. Mater. Sci. Technol., 2008, 24 (03): 289-295. 
    Abstract   HTML   PDF (9278KB)
    The formation mechanism of chunky graphite has been reviewed and studied. The study consisted of a unidirectional solidification method, a small droplet method and a furnace cooling method. Four kinds of iron samples were prepared, namely, the pure Fe-C, Fe-C-S, Fe-C-Ce and Fe-C-Si-Ce alloys, and three kinds of nickel samples, namely the Ni-C, Ni-C-S and Ni-C-Mg alloys. The results of the unidirectional solidification of the Ni-C alloys showed that spheroidal graphite is not observed in the continuous solidified region, in which only flake-like graphite is observed, while spheroidal graphite is usually observed in the quenched liquid region.The existence of spheroidal graphite in the solidified phase is recognized only in the discontinuous growth mode of the Ni-C-Mg alloy solidified at 150 mm/h. This means that the spheroidal graphite is directly crystallized from the melt and entrapped by the flake-like chunky graphite that is formed by the continuous growth mode. In the small droplet method, a small piece of the Fe-C or Fe-C-Ce sample was melted on a pure graphite plate then cooled at a different cooling rate in a He-3%H2 atmosphere. The graphite in the Fe-C-Ce alloy is usually spherical. Nevertheless, the graphite morphology of the final solidified area changed from spherical to chunky and chunky to ledeburite with an increase in the cooling rate. This means that the chunky graphite is formed in the residual liquid region by the solidification into Fe-graphite system. The sample was cooled in a furnace, and the graphite morphology changes from spherical to chunky and chunky to ledeburite with the decrease in the Si content. These phenomena can be confirmed by the cooling curves of these samples.
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    Effect of Sn on the Microstructure and Mechanical Properties of Mg-5Al-2Si Alloys
    Sangwon Lee, Bonggyu Park, Yongho Park, Ikmin Park
    J. Mater. Sci. Technol., 2008, 24 (03): 296-298. 
    Abstract   HTML   PDF (1813KB)
    The effect of Sn addition on the microstructures and mechanical properties of Mg-5Al-2Si alloys was investigated with variations of Sn contents (3 and 6 wt pct). The microstructure of the alloy was characterized by the presence of Mg2Sn particles within matrix and at grain boundaries. As the Sn contents increased, yield and ultimate tensile strength were increased at room temperatures and 150℃. Creep properties were improved with the increasing amount of Sn due to the fine precipitation of Mg2Sn phases within grain during creep.
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    Investigation on Structure and Properties of Brass Casting
    M.M.Haque, A.A.Khan
    J. Mater. Sci. Technol., 2008, 24 (03): 299-301. 
    Abstract   HTML   PDF (5589KB)
    In this work, alpha (α) brass was poured in green sand mould and metallic chill mould at about 1050℃. Sand casting method and metallic chill casting method are representing the slow and fast cooling rates of the castings, respectively. The slow cooling rate in the sand mould produces larger grains, while the metallic chill mould produces smaller grains in the castings. As the grain size decreases, the strength of the cast brass increases; micro-porosity in the casting decreases and the tendency for the casting to fracture during solidification decreases. Thus, the faster cooling rate casting offers higher strength, density and hardness compared to the slow cooling rate casting.
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    Mg Alloy Foam Fabrication via Melt Foaming Method
    Donghui YANG, Changhwan SEO, Bo-Young HUR
    J. Mater. Sci. Technol., 2008, 24 (03): 302-304. 
    Abstract   HTML   PDF (1119KB)
    For the first time AZ91 (MgAl9Zn1) and AM60 (MgAl6) Mg alloy foams with homogeneous pore structures were prepared successfully via melt foaming method using CaCO3 as blowing agent. It is revealed that the blowing gas to foam the melt is not CO2 but CO, which comes from liquid-solid reaction between Mg melt. The reaction temperature is more than 100℃ lower than CaCO3 decomposition, which makes Mg alloy melts foam into cellular structure much more easily in the temperature range from 690℃ to 750℃.
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    High Temperature Mechanical Properties of Ni-Al-Cr Based Alloys for Advanced Die-Materials Applications
    W.Y.Kim, H.S.Kim, T.Y.Ra, H.J.Bang, Y.G.Yoo, I.D.Yeo
    J. Mater. Sci. Technol., 2008, 24 (03): 305-308. 
    Abstract   HTML   PDF (1880KB)
    In this study, we report on advanced Ni3Al based high temperature structural alloys with Zr and B addition in order to apply in the fields of die-casting and high temperature press forming as die materials. Microstructures and mechanical properties of Ni3Al based intermetallic alloys produced by vacuum arc melting were investigated in terms of phase analysis by using a scanning electron microscope (SEM) equipped with an X-ray energy dispersive spectrometer (EDS), an X-ray diffractometer (XRD) and tensile test. The duplex microstructural feature consisting of γ′ matrix phase and small intermetallic dispersoids was observed to be distributed over the whole microstructure. The ultimate tensile strength of the present alloy was superior to commercial iron-based and Ni-based die-materials especially in the high temperature region.
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    Effects of Mo and Zr on Microstructure, Mechanical Properties and Wear Resistance of Fe-Al Based Alloys
    I.D.Yeo, T.Y.Ra, H.S.Kim, H.J.Bang, Y.G.Yoo, W.Y.Kim
    J. Mater. Sci. Technol., 2008, 24 (03): 309-312. 
    Abstract   HTML   PDF (1882KB)
    In this work the microstructure, mechanical properties and wear resistance of Fe-Al based alloys with various alloying elements were studied. The microstructures were examined by optical and scanning electron microscopy (SEM) equipped with an energy dispersive X-ray spectroscope (EDS). Two types of alloys were prepared by vacuum arc melting. One is Fe-28Al based alloys (D03 structured) with and without alloying elements such as Mo and Zr. The other one is Fe-35Al based alloys (B2 structured) produced with the same manner. For both types of alloys, Mo addition had found to exhibit an equiaxed microstructure, while dendritic structure was observed to show the effect of Zr addition. These microstructural features were more evinced with increasing content of alloying element. Concerning the mechanical properties and wear resistance, Fe-35Al based alloys were superior to Fe-28Al based alloys over the whole temperature range investigated.
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    Effect of Si Content on Mechanical Properties of a Mo and V Free Low Alloy Cast Steel for Automobile Cold Pressing Die
    B.H.Kim, J.S.Shin, S.M.Lee, B.M.Moon, H.D.Kim, S.Y.Ju, O.Y.Choi
    J. Mater. Sci. Technol., 2008, 24 (03): 313-316. 
    Abstract   HTML   PDF (374KB)
    The effects of Si content on combinations of important properties such as hardness, hardenability, and weldability in addition to strength increment were systematically investigated to develop a Mo and V free low alloy cast steel for automobile cold pressing die insert. For the evaluation of the applicability as the die insert, the mechanical properties were measured after spheroidization annealing (SA), quenching and tempering (Q/T), and flame hardening (FH) treatments, respectively. The developed 0.8%–1.6%Si containing Mo and V free alloy cast steels showed excellent matrix strengthening effect, hardenability, and weldability, fulfilling the industrial criterion of the mechanical properties for the die insert.
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    Microstructure and Peritectic Reaction within As-solidified Mg–Zn–Y Alloy
    Diqing WAN, Gencang YANG
    J. Mater. Sci. Technol., 2008, 24 (03): 317-320. 
    Abstract   HTML   PDF (0KB)
    An investigation on the microstructure and peritectic reaction involving icosahedra phase (I-phase) and crystalline phase (W-phase) within Mg–Zn–Y alloy during conventional solidification technology and rapid quenching was carried out. The solidification process of the peritectic reaction is discussed in details. It is shown that there is no obvious crystallographic relationship between the W-phase and I-phase during the solidification of Mg–Zn–Y alloy.
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    Graphite Nucleation in Cast Iron Melts Based on Solidification Experiments and Microstructure Simulation
    Andreia Sommerfeld, Bernd Bö, ttger, Babette Tonn
    J. Mater. Sci. Technol., 2008, 24 (03): 321-324. 
    Abstract   HTML   PDF (1831KB)
    Microstructure strongly influences the mechanical properties of cast iron. By inoculating the melt with proper inoculants, foreign substrates are brought into the melt and eventually the graphite can crystallize on them. The elements and substrates that really play a role for nucleation are yet unknown. Until now there is very little knowledge about the fundamentals of nucleation, such as composition and morphology of nuclei[1,2]. In this work we utilized EN-GJL-200 as a base material and examined several produced specimens. The specimens were cast with and without inoculants and quenched at different solidification states. Specimens were also examined with a high and low oxygen concentration, but the results showed that different oxygen contents have no influence on the nucleation in cast iron melts. Our research was focused on the microscopic examination and phase-field simulations. For studying the samples we applied different analytical methods, where SEM-EDS, -WDS were proved to be most effective. The simulations were conducted by using the software MICRESS®[3], which is based on a multiphase-field model and has been coupled directly to the TCFE3 thermodynamic database from TCAB. On the basis of the experimental investigations a nucleation mechanism is proposed, which claims MnS precipitates as the preferred site for graphite nucleation. This theory is supported by the results of the phase-field simulations.
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    Relationship between Primary Crystal Temperature and Carbon Equivalent in Cast Iron
    T.Kanno, I.Kang, T.Kikuchi, K.Hayashi, Y.Maruyama
    J. Mater. Sci. Technol., 2008, 24 (03): 325-326. 
    Abstract   HTML   PDF (515KB)
    CE (=%C+(1/3)×(%Si)) does not suit experiment results in many cases. In this work, the effect of alloy elements on primary crystal temperature was measured and the relationship between primary crystal temperature (Tc) and carbon equivalent (CEL) was investigated. The results show that Tc (Celsius degree) =1650-110×(%C)-25×(%Si)+3×(%Mn)-35× (%P)-71×(%S)-2×(%Ni)-7×(%Cr); CEL=%C +0.23×(%Si)-0.03× (%Mn)+0.32×(%P)+0.64×(%S) +0.02×(%Ni)+0.06×(%Cr). That is, in hypo eutectic composition, carbon equivalent should be calculated with CEL=%C+ 0.23×(%Si), not with CE=%C+(1/3) ×(%Si).
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    High Temperature Corrosion of Fe-C-S Cast Irons in Oxidizing and Sulfidizing Atmospheres
    Thuan-Dinh NGUYEN, Dong-Bok LEE
    J. Mater. Sci. Technol., 2008, 24 (03): 327-329. 
    Abstract   HTML   PDF (3422KB)
    The corrosion behavior of spheroidal graphite and flake graphite cast irons was studied in oxidizing and sulfidizing atmospheres between 600 and 800℃ for 50 h. The corrosion rate in the sulfidizing atmosphere was faster than that in air above 700℃, due to the formation of the Fe0.975S sulfide. The corrosion rate of the spheroidal graphite cast iron was similar to that of the flake graphite cast iron.
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    Effects of Heat Treatment on Hardness and Dry Wear Properties of a Semi-Solid Processed Fe-27 wt pct Cr-2.9 wt pct C Cast Iron
    A.Wiengmoon, T.Chairuangsri, N.Chomsang, N.Poolthong, J.T.H.Pearce
    J. Mater. Sci. Technol., 2008, 24 (03): 330-334. 
    Abstract   HTML   PDF (5050KB)
    Effects of heat treatments on hardness and dry wear properties of a semi-solid processed Fe-26.96 wt pct Cr-2.91 wt pct C cast iron were studied. Heat treatments included tempering at 500℃, destabilisation at 1075℃ and destabilisation at 1075℃ plus tempering at 500℃, all followed by air cooling. Electron microscopy revealed that, in the as-cast condition, the primary proeutectic austenite was round in shape while the eutectic M7C3 carbide was found as radiating clusters mixed with directional clusters. Tempering did not change the microstructure significantly when observed by scanning or transmission electron microscopy. Destabilisation followed by air cooling led to a precipitation of secondary M23C6 carbide and a transformation of the primary austenite to martensite. Precipitation behaviour is comparable to that observed in the conventionally cast iron. Tempering after destabilisation resulted in a higher amount of secondary carbide precipitation within the tempered martensite in the eutectic structure. Vickers macrohardness and microhardness in the proeutectic zones were measured. Dry wear properties were tested by using a pin-on-disc method. The maximum hardness and the lowest dry wear rate were obtained from the destabilisation-plus-tempering heat treatment due to the precipitation of secondary carbides within the martensite matrix and a possible reduction in the retained austenite.
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    Fabrication of Near Net Shape Metallic Foam via Plaster Mould
    Young-Hwan Song, Hwan-Goo Seon, Soo-Han Parka, Min-Jae Jeong, Bo-Young Hur
    J. Mater. Sci. Technol., 2008, 24 (03): 335-339. 
    Abstract   HTML   PDF (1245KB)
    Fabrication characteristics are unstable in direct foaming method. Therefore, most of near net-shape metallic foams are produced, and investigated by powder metallurgy. Direct foaming method, however, has many benefits (i:e. reduce the unit cost of goods and fabrication process etc.) to fabrication of metallic foams. In this article, the fabrication characteristic of near net-shape metallic foams by direct foaming method was evaluated. Al and Plaster was used for base material and mould material respectively. Ca and TiH2 were added to molten Al as thickening and blowing agent for stable condition of bubbles. Thickening time was about 10 min with a stirring speed of 600 r/min. Foaming time was 30-120 s for evaluation of the optimum foaming condition. Amount of agent was selected by pre-experimental data. Porosity of near net-shape goods was measured by Archimedes method. On the other hand, it seems that increasing poring time and thickening agent make the poor porosity
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    Dendrite Spacing Selection during Directional Solidification of Pivalic Acid-Ethanol System
    Myung-Jin Suk, Young-Min Park, Youn-Che Kim
    J. Mater. Sci. Technol., 2008, 24 (03): 340-342. 
    Abstract   HTML   PDF (603KB)
    Unidirectional solidification of pivalic acid (PVA)-ethanol (Eth) mixture was performed to examine whether an allowable range of primary dendrite spacing definitely exists at a given growth velocity and how the range is history-dependent. PVA-0.59 wt pct Eth was unidirectionally solidified in the range of growth velocity 0.5–64 μm/s at the temperature gradient of 2.3 K/mm. Sequential change in growth velocity was imposed to determine the upper and lower limits for the allowable range of stable spacing. An allowable range of the steady state primary spacing was observed at a given growth velocity, and the extent of the range seems to be dependent on the degree to which step-increase or step-decrease in growth velocity is accomplished. As the degree of sequential change in growth velocity increases, the history-dependence of the selection for the primary dendrite spacing tends to disappear.
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    Effect of Ni Contents on the Microstructure and Mechanical Properties of Martensitic Stainless Steel Guide Roll by Centrifugal Casting
    Vill, o Thursdiyanto, Eun-Jae Bae, Eung-Ryul Baek
    J. Mater. Sci. Technol., 2008, 24 (03): 343-346. 
    Abstract   HTML   PDF (3470KB)
    A novel process based on centrifugal casting was developed to produce martensitic stainless steel for guideroll materials. Centrifugal casting provides a lower production cost and less of the thermal cracking defects which normally occur in the overlaid welding process. In this study, the effects of Ni on the microstructure and mechanical properties of martensitic stainless steel were investigated. The results show that the addition of Ni resulted in a decrease in the volume fraction of delta ferrite and an increase in the volume fraction of the retained austenite, respectively. Moreover, a tensile strength of 1600 MPa with an elongation of 4% were obtained after tempering at 500℃ for 2 h. These values were higher than those obtained by using the conventional overlaid process.
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    Temperature and Thermal Stress Distribution for Metal Mold in Squeeze Casting Process
    K.H.Chang, G.C.Jang, C.H.Lee, S.H.Lee
    J. Mater. Sci. Technol., 2008, 24 (03): 347-350. 
    Abstract   HTML   PDF (3603KB)
    In the squeeze casting process, loaded high pressure (over approximately 100 MPa) and high temperature influence the thermo-mechanical behavior and performance of the used metal mold. Therefore, to safely maintain the metal molds, the thermo-mechanical characteristics (temperature and thermal stress) of metal mold in the squeeze casting must be investigated. In this paper, temperature and thermal stress distribution of steel mold in squeeze casting process were investigated by using a three-dimensional non-steady heat conduction analysis and a three-dimensional thermal elastic-plastic analysis considering temperature-dependent thermophysical and mechanical properties of the steel mold.
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    Application of Integrated Database to the Casting Design
    In-Sung Cho, Seung-Mok Yoo, Chae-Ho Lim, Jeong-Kil Choi
    J. Mater. Sci. Technol., 2008, 24 (03): 351-355. 
    Abstract   HTML   PDF (4206KB)
    Construction of integrated database including casting shapes with their casting design, technical knowledge, and thermophysical properties of the casting alloys were introduced in the present study. Recognition technique for casting design by industrial computer tomography was used for the construction of shape database. Technical knowledge of the casting processes such as ferrous and non-ferrous alloys and their manufacturing process of the castings were accumulated and the search engine for the knowledge was developed. Database of thermophysical properties of the casting alloys were obtained via the experimental study, and the properties were used for the in-house computer simulation of casting process. The databases were linked with intelligent casting expert system developed in center for e-design, KITECH. It is expected that the databases can help non casting experts to devise the casting and its process. Various examples of the application by using the databases were shown in the present study.
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    Influence of Processing Parameters on the Mechanical Properties of a Plasma Radical Nitrided SCM440 Steel
    Seok-Hwan Ahn, Insup Lee
    J. Mater. Sci. Technol., 2008, 24 (03): 356-358. 
    Abstract   HTML   PDF (683KB)
    Plasma radical nitriding was performed to harden the surface of SCM440 steel for 1-10 h at temperature range of 450-550℃. This process involved the use of NH3 gas instead of N2 gas employed for the well-established plasma nitriding method. No compound layer was formed during this process except the experiment carried out at 500℃ for 10 h. The main phase produced in the diffusion zone was identified to be γ′-Fe4(N, C). A diffusion depth increased with increasing treatment temperature and time (up to about 250 μm). The surface hardness of radical nitrided layer was about two times higher than that of the untreated surface. The tensile test was carried out to estimate the mechanical properties of surface-hardened SCM440 steel prepared at various plasma radical nitriding treatment time and temperature. The influence of radical nitriding treatment on the tensile strength of the specimen was found to be insignificant. The highest value of the ultimate tensile strength was obtained in the experiment carried out at 500℃ for 1 h. However, the elongation was greatly affected by the radical nitriding processing parameters. The maximum value of elongation, which is equal to about 18.1%, was also obtained under the condition of 500℃ for 1 h.
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    Virtual Mold Technique in Thermal Stress Analysis during Casting Process
    Si-Young Kwak, Jae-Wook Baek, Jeong-Ho Nam, Jeong-Kil Choi
    J. Mater. Sci. Technol., 2008, 24 (03): 359-363. 
    Abstract   HTML   PDF (3622KB)
    It is important to analyse the casting product and the mold at the same time considering thermal contraction of the casting and thermal expansion of the mold. The analysis considering contact of the casting and the mold induces the precise prediction of stress distribution and the defect such as hot tearing. But it is difficult to generate FEM mesh for the interface of the casting and the mold. Moreover the mesh for the mold domain spends lots of computational time and memory for the analysis due to a number of meshes. Consequently we proposed the virtual mold technique which only uses mesh of the casting part for thermal stress analysis in casting process. The spring bar element in virtual mold technique is used to consider the contact of the casting and the mold. In general, a volume of the mold is much bigger than that of casting part, so the proposed technique decreases the number of mesh and saves the computational memory and time greatly. In this study, the proposed technique was verified by the comparison with the traditional contact technique on a specimen. And the proposed technique gave satisfactory results.
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    Numerical Simulation of Stress and Deformation for a Duplex Stainless Steel Impeller during Casting and Heat Treatment Processes
    Lugui CHEN, Yong LING, Xiuhong KANG, Lijun XIA, Dianzhong LI
    J. Mater. Sci. Technol., 2008, 24 (03): 364-368. 
    Abstract   HTML   PDF (1189KB)
    A large-scale, thin wall duplex stainless steel impeller with complex geometry was deformed severely and unpredictably during casting and heat treatment processes resulted in dimensional failure for the final part. In this paper, the distortion of the impeller during casting and heat treatment was calculated. A commercial software, Experto-ViewCast, was used to simulate the transient heat transfer, solidification and mechanical behaviors during the casting and the heat treatment process. The coupled set of governing differential equations for mass, energy and mechanical balance were solved by finite control volume and finite element method. A thermoelastic-visco-plastic rheological model was used to compute the constrained shrinkage of the casting. At each time increment, a coupling of the heat transfer and mechanics was performed. Comparison of the experimental measurements with the model predictions showed good agreement. From the calculated displacements of key points of the blade, the proper inverse displacements were determined to provide an optimum casting pattern and to achieve a uniform and reasonable machining allowance for both faces of the blade.
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    Experimental Study and Numerical Simulation of Directionally Solidified Turbine Blade Casting
    Jing YU, Qingyan XU, Baicheng LIU, Jiarong LI, Hailong YUAN, Haipeng JIN
    J. Mater. Sci. Technol., 2008, 24 (03): 369-373. 
    Abstract   HTML   PDF (3579KB)
    The directional solidification process of turbine blade sample castings was investigated in the work. Variable withdrawal rates were used in one withdrawal process and compared with the other using uniform rate. A mathematical model for heat radiation transfer and microstructure simulation of directional solidification process was developed based on CA-FD method. The temperature distribution and microstructure were simulated and compared with the experimental results. The stray grains were predicted and compared with the experimental results. The uneven temperature distribution of platform was the main reason of the formation of stray grains.
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    Development of Ubiquitous Simulation Service Structure Based on High Performance Computing Technologies
    Sang-Hyun CHO, Jeong-Kil CHOI
    J. Mater. Sci. Technol., 2008, 24 (03): 374-378. 
    Abstract   HTML   PDF (683KB)
    The simulation field became essential in designing or developing new casting products and in improving manufacturing processes within limited time, because it can help us to simulate the nature of processing, so that developers can make ideal casting designs. To take the prior occupation at commercial simulation market, so many development groups in the world are doing their every effort. They already reported successful stories in manufacturing fields by developing and providing the high performance simulation technologies for multipurpose. But they all run at powerful desk-side computers by well-trained experts mainly, so that it is hard to diffuse the scientific designing concept to newcomers in casting field. To overcome upcoming problems in scientific casting designs, we utilized information technologies and full-matured hardware backbones to spread out the effective and scientific casting design mind, and they all were integrated into Simulation Portal on the web. It professes scientific casting design on the NET including ubiquitous access way represented by “Anyone, Anytime, Anywhere” concept for casting designs.
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    Cartesian Grid Method with Cut Cell in the Mold Filling Simulation
    Youngsim Choi, Junho Hong, Hoyoung Hwang, Jeongkil Choi
    J. Mater. Sci. Technol., 2008, 24 (03): 379-382. 
    Abstract   HTML   PDF (575KB)
    In this paper, a Cartesian grid method with cut cell has been developed to simulate mold filling of casting process. Cut cells at the cast-mold interface are generated on the Cartesian grid. With the boundary cut cells, a special treatment is necessary. That is Cartesian grid method with cut cell. A simple shape was tested and the cut cell method was compared with the traditional one on Cartesian grids. And, a developed method was applied to the real casting product simulation. Cartesian grid system causes momentum loss and unsound fluid flow patterns because of inaccurate generation of meshes. These problems have been improved by using cut cell method.
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    Die Casting Mold Design of the Thin-walled Aluminum Case by Computational Solidification Simulation
    Young-Chan Kim, Chang-Seog Kang, Jae-Ik Cho, Chang-Yeol Jeong, Se-Weon Choi, Sung-Kil Hong
    J. Mater. Sci. Technol., 2008, 24 (03): 383-388. 
    Abstract   HTML   PDF (3805KB)
    Recently, demand for the lightweight alloy in electric/electronic housings has been greatly increased. However, among the lightweight alloys, aluminum alloy thin-walled die casting is problematic because it is quite difficult to achieve sufficient fluidity and feedability to fill the thin cavity as the wall thickness becomes less than 1 mm. Therefore, in this study, thin-walled die casting of aluminum (Al-Si-Cu alloy: ALDC 12) in size of notebook computer housing and thickness of 0.8 mm was investigated by solidification simulation (MAGMA soft) and actual casting experiment (Buhler Evolution B 53D). Three different types of gating design, finger, tangential and split type with 6 vertical runners, were simulated and the results showed that sound thin-walled die casting was possible with tangential and split type gating design because those gates allowed aluminum melt to flow into the thin cavity uniformly and split type gating system was preferable gating design comparing to tangential type gating system at the point of view of soundness of casting and distortion generated after solidification. Also, the solidification simulation agreed well with the actual die-casting and the casting showed no casting defects and distortion.
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    Numerical Analysis of Secondary Cooling in Continuous Slab Casting
    Kee-Hyeon Cho, Byung-Moon Kim
    J. Mater. Sci. Technol., 2008, 24 (03): 389-390. 
    Abstract   HTML   PDF (766KB)
    In the present study, a numerical optimization program has been developed for predicting the optimal secondary cooling patterns in a continuous slab caster. Optimization strategy using Broydon-Fletcher-Goldfarb-Shanno (BFGS) method is carried out by determining the constant heat transfer coefficients in each spray zone, which could satisfy the casting conditions and metallurgical criteria specified by the engineer. From the present results, it is found that even a slight variation in the pouring temperature, allowable surface temperature, and casting speed could give rise to the changes in the cooling pattern throughout the spray zones.
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    Numerical Simulation of Microstructure and Microsegregation in Ni-Cu Alloy under Isothermal Condition
    Xiang XUE, Jinjun TANG
    J. Mater. Sci. Technol., 2008, 24 (03): 391-394. 
    Abstract   HTML   PDF (520KB)
    Phase-field method can be used to describe the complicated morphologies of dendrite growth without explicitly tracking the complex phase boundaries. The influences of initial temperature and initial concentration on dendrite growth are investigated by using the phase-field model coupling concentration field equations. The calculated results indicate that the supersaturation, which is larger in lower initial temperature and lower concentration under isothermal condition, plays a very important role in microsegregation. It is found that the larger supersaturation causes higher degree microsegregation and faster dendrite growth, and the more serious side-branchs occur. The simulated results agree well with the solidification theory.
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    Effects of Loading Paths on Hydrodynamic Deep Drawing with Independent Radial Hydraulic Pressure of Aluminum Alloy Based on Numerical Simulation
    Xiaojing LIU, Yongchao XU, Shijian YUAN
    J. Mater. Sci. Technol., 2008, 24 (03): 395-399. 
    Abstract   HTML   PDF (6613KB)
    In order to meet the forming demands for low plasticity materials and large height-diameter ratio parts, a new process of hydrodynamic deep drawing (HDD) with independent radial hydraulic pressure is proposed. To investigate the effects of loading paths on the HDD with independent radial hydraulic pressure, the forming process of 5A06 aluminum alloy cylindrical cup with a hemispherical bottom was studied by numerical simulation. By employing the dynamic explicit analytical software ETA/Dynaform based on LS-DYNA3D, the effects of loading paths on the sheet-thickness distribution and surface quality were analyzed. The corresponding relations of the radial hydraulic pressure loading paths and the part′s strain status on the FLD were also discussed. The results indicated that a sound match between liquid chamber pressure and independent radial hydraulic pressure could restrain the serious thinning at the hemisphere bottom and that through adjusting radial hydraulic pressure could reduce the radial tensile strain and change the strain paths. Therefore, the drawing limit of the aluminum cylindrical cup with a hemispherical bottom could be increased significantly.
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    Effect of Colouring Process on Pitting Susceptibility of Austenitic Stainless Steel
    S.S.Mahmoud, M.M.Ahmed
    J. Mater. Sci. Technol., 2008, 24 (03): 400-406. 
    Abstract   HTML   PDF (546KB)
    Colouring of the austenitic stainless steel alloy (20.45% Cr, 8.57% Ni) was carried out in NaNO3-KNO3 eutectic melt without and with additions of Na=O2, NaCl and their mixtures at different temperatures ranging from 400–600℃, under open-circuit and galvanostatic anodic polarization conditions. The produced colours greatly depend on the thickness of oxide films, which in turn depends on the composition of the molten bath and its temperature. The more attractive, bright, adherent and uniform coloured oxide films can be obtained at 400, 450 and 500℃ in molten nitrate bath containing NaCl and Na2O2 mixtures. The pitting corrosion susceptibility of the coloured oxide films was tested in FeCl3 and NaCl as corrosive media. The obtained results indicate that the pitting corrosion susceptibility of the coloured oxide films greatly depends on the previous operating conditions of the colouring process of the stainless steel specimens such as the composition of molten bath, temperature and technique of colouring process.
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    Ultrasonic Approach of Rayleigh Pitch-catch Contact Ultrasound Waves on CFRP Laminated Composites
    In-Young Yang, Kwang-Hee Im, Uk Heo, David K Hsu, Je-Woong Park, Hak-Joon Kim, Sung-Jin Song
    J. Mater. Sci. Technol., 2008, 24 (03): 407-409. 
    Abstract   HTML   PDF (349KB)
    CFRP (carbon fiber reinforced plastics) composite materials have wide applicability because of their inherent design flexibility and improved material properties. However, impacted composite structures have 50%–75% less strength than undamaged structures. In this work, a CFRP composite material was nondestructively characterized in order to ensure product quality and structural integrity of CFRP and one-sided pitch-catch technique was developed to measure impacted-damaged area by using an automated-data acquisition system in an immersion tank. A pitch-catch signal was found to be more sensitive than normal incidence backwall echo of longitudinal wave under defect conditions in the composite.
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    Influence of Electric Current on Kirkendall Diffusion of Zn/Cu Couples
    Yingju LI, Yuansheng YANG, Xiaohui FENG
    J. Mater. Sci. Technol., 2008, 24 (03): 410-414. 
    Abstract   HTML   PDF (811KB)
    The influence of electric current on Kirkendall diffusion in Zn/Cu couples was investigated. Under the action of different electric currents, the Zn/Cu diffusion couples were annealed at 785℃ for different holding time. The experimental results show that the displacement of the Kirkendall plane increases with increasing holding time. However, the displacement of the Kirkendall plane with electric current is larger than that without electric current. The relationship between the displacement of the Kirkendall plane and the holding time is changed under the action of electric current. The likely reason for the electric current enhancing effect is the energy transfer from electron to jumping atom, increasing the integrated diffusion coefficient, which leads to the increase in the velocity of Kirkendall plane.
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    Spin injection from ferromagnetic semiconductor CoZnO into ZnO
    Gang JI, Shishen YAN, Yanxue CHEN, Qiang CAO, Wei XIA, Yihua LIU, Liangmo MEI, Ze ZHANG
    J. Mater. Sci. Technol., 2008, 24 (03): 415-418. 
    Abstract   HTML   PDF (754KB)
    2×(FeNi/CoZnO)/ZnO/(CoZnO/Co) ×2 spin-injection devices were prepared by sputtering and photo-lithography. In the devices, two composite magnetic layers 2×(FeNi/CoZnO) and (CoZnO/Co) ×2 with different coercivities were used to fabricate the ZnO-based semiconductor spin valve. Since the CoZnO ferromagnetic semiconductor layers touched the ZnO space layer directly, the significant spin injection from CoZnO into ZnO was observed by measuring the magnetoresistance of the spin-injection devices. The magnetoresistance reduced linearly with increasing temperature, from 1.12% at 90 K to 0.35% at room temperature.
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    Synthesis, Characterization and Electromagnetic Studies on Nanocrystalline Nickel Zinc Ferrite by Polyacrylamide Gel
    Ruiting MA, Yi WANG, Yanwen TIAN, Chunli ZHANG, Xikun LI
    J. Mater. Sci. Technol., 2008, 24 (03): 419-422. 
    Abstract   HTML   PDF (1006KB)
    Nanocrystalline nickel zinc ferrite powders (NixZn1-xFe2O4, A for x=0, B for x=0.2, C for x=0.5, D for x=0.8 and E for x= 1) were synthesized by polyacrylamide gel method. X-ray diffraction (XRD), transmission electron microscopy (TEM) and wave-guide were used to characterize the composition. The XRD results show that the dried gel powders are amorphous, and the characteristic peaks of the spinel Ni0.5Zn0.5Fe2O4 appear after the gel is calcined at 400℃ for 1 h. When the calcining temperatures are 600 and 800℃, the average grain sizes are identified by TEM to be 10 and 30 nm, respectively. The NixZn1-xFe2O4 powders have both dielectric loss and magnetic loss in the frequency range of 8.2–11.0GHz. With the increase of Ni2+ ions content, the dielectric parameters (ε′) and permeability (u′) of the NixZn1-xFe2O4 powders decrease while the dielectric loss (ε"), magnetic loss (u") and the reflection loss increase.
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    Process Parameter Optimization of the Pulsed Current Argon Tungsten Arc Welding of Titanium Alloyin process parameter selection of pulsed current gas tungsten arc welding of titanium alloy
    M.Balasubramanian, V.Jayabalan, V.Balasubramanian
    J. Mater. Sci. Technol., 2008, 24 (03): 423-426. 
    Abstract   HTML   PDF (542KB)
    The selection of process parameters for obtaining optimal tensile properties in the pulsed current gas tungsten arc welding is presented. The tensile properties include ultimate tensile strength, yield strength and notch tensile strength. All these characteristics are considered together in the selection of process parameters by modified taguchi method to analyse the effect of each welding process parameter on tensile properties. Experimental results are furnished to illustrate the approach.
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    Inhibition Behaviour of 2-butine1, 4diol and Tartrate Salt, and Their Synergistic Effects on Corrosion of AA3003 Aluminium Alloy in 0.5% NaCl Solution
    Taghi Shahrabi, Alireza Yazdzad, Mirghasem Hosseini
    J. Mater. Sci. Technol., 2008, 24 (03): 427-432. 
    Abstract   HTML   PDF (3200KB)
    This work intends to investigate the inhibition behaviour of 2-butine 1, 4diol and potassium sodium tartrate and their synergistic effects on 3003 aluminium alloy corrosion in 0.5% NaCl solution. Experiments were carried out by electrochemical impedance spectroscopy (EIS) and Tafel polarization method in a three-electrode cell. It was concluded that the inhibition efficiencies increased with an increase in the concentrations of inhibitors. For 2-butinel, 4diol and tartrate salt, the optimum in the inhibition efficiency, at room temperature and neutral pH, was observed for concentrations close to 10¡3 mol/L and 1.5×10-3 mol/L, respectively. The electrochemical results illustrated that 2-butine1, 4diol and tartrate salt, have significant synergistic inhibition effects on corrosion of 3003 aluminium alloy in 0.5% NaCl solution. The optimum ratio of concentrations for tartrate to alcohol was 2:1.
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CN: 21-1315/TG
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