Started in 1985 Semimonthly
ISSN 1005-0302
CN 21-1315/TG
Impact factor:6.155

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 November 2005, Volume 21 Issue 06 Previous Issue    Next Issue
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    Research Articles
    New Technique of Casting-rolling Strips for Semi-solid Magnesium Alloys
    Shuisheng XIE, Maopeng GENG, Xinmin ZHOU, Ying ZHANG, Songyang ZHANG, Yanchun WANG, Guojie HUANG
    J. Mater. Sci. Technol., 2005, 21 (06): 785-787. 
    Abstract   HTML   PDF (1235KB)
    The conjugation of semi-solid process technique and casting-rolling technique applied to produce the magnesium strips was studied. The semi-solid slurry has been prepared continuously by the mechanical method and its temperature was controlled strictly at the same time. AZ91D and AZ31 casting magnesium alloys were applied to the experiment. The casting-rolling strips with non-dendritic structure were obtained and its main mechanical property is better. The process ability of the casting-rolling strips was studied. It is significative to link the semi-solid process techniques and casting-rolling techniques, through which we can get high quality magnesium alloy strips with non-dendritic structure and improve the overall properties of the products.
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    Fabrication of Porous Bulk Metallic Glass
    Keqiang QIU, Yinglei REN
    J. Mater. Sci. Technol., 2005, 21 (06): 788-790. 
    Abstract   HTML   PDF (258KB)
    An open-cell porous bulk metallic glass (BMG) with a diameter of at least 6 mm was fabricated by using an U-turn quartz tube and infiltration casting around soluble NaCl placeholders. The pore formation and glassy structure were examined by optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results show that the pores or cells are connected to each other and the specimen is composed of a mostly glassy phase. This paper provides a suitable method for fabrication of porous BMG and BMG with larger size in diameter.
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    Effect of Cooling History on Yield Ratio of Fine-grain Ferrite/Pearlite Steel
    Fuxian ZHU, Xin LI, Yanchun LIU, Xianghua LIU, Guangfu SHE, Zhongping ZHANG
    J. Mater. Sci. Technol., 2005, 21 (06): 791-794. 
    Abstract   HTML   PDF (707KB)
    Effect of different cooling history on yield ratio of HP295 steel for welded gas cylinder was studied and the result implied that both fine microstructure and good mechanical properties can be attained by using two-stage cooling and controlling the coiling temperature. The yield ratio of HP295 steel sheet was reduced to less than 0.8 by two-stage cooling process. The pass percent of yield ratio was enhanced from less than 90% to 100%. The mechanical properties satisfied the criteria of GB6653-1994.
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    Numerical Modeling of Growth Kinetics of Pro-eutectoid Ferrite Transformed from Austenite in Fe-C-∑X Alloys
    Zhenyu LIU, Guodong WANG, Toshio Narita
    J. Mater. Sci. Technol., 2005, 21 (06): 795-798. 
    Abstract   HTML   PDF (575KB)
    In the present paper, a numerical modeling was developed to simulate the growth kinetics of ferrite transformed from austenite in Fe-C-∑X (X denotes substitution elements, such as Mn, Ni, Cr etc.) steels by solving the diffusion equation using finite difference method (FDM). Coupled with the kinetic modeling, thermodynamic calculations were carried out to determine the γ/α phase equilibrium conditions using a para-equilibrium (PE) model. The dissipation of free energy for γ→α phase transformation due to the so-called solute drag effect (SDE) was taken into account in the thermodynamic modeling. With this modeling, simulations on the growth kinetics of ferrite in the steels containing austenite-stabilizing and ferrite-stabilizing elements (such as Ni, Mn and Si, Cr, respectively) were performed, which indicates that it deviates from the parabolic growth rate law after the initial stage of transformation. The results were compared with the experimental values given by Bradley and Aaronson, showing that this model has a reasonably good accuracy to predict the growth kinetics of ferrite.
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    Microstructure Features with Ultrafined and Purified Grains for Si-Mn Hot-rolling TRIP Steel
    Yu CHEN, Guoyi TANG, Feipeng LI, Yu ZHANG, Xiao CHEN, Pinghe LI, Wei LIU, Qing LIU
    J. Mater. Sci. Technol., 2005, 21 (06): 799-802. 
    Abstract   HTML   PDF (431KB)
    strength of 775 MPa, high elongation of 29% and low ductile-brittle transmission temperature less than -80℃ has been developed in laboratory based on the common silicon and manganese chemical composition. The experimental results showed that the microstructures were featured with ultra fine grain size less than 5 μm, appropriate retained austenite volume fraction around 11.8% and purified ferrite grain, which may result in well balanced mechanical properties for the steel.
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    Mathematical Model for Tempering Time Effect on Quenched Steel Based on Hollomon Parameter
    Nong WAN, Weihao XIONG, Jinping SUO
    J. Mater. Sci. Technol., 2005, 21 (06): 803-806. 
    Abstract   HTML   PDF (861KB)
    Through the differentiating and integrating process, a mathematical model for tempering time effect on quenched steel was derived based on the attribute of state function and the general equation of Hollomon parameter, which correlates the tempering hardness with the tempering time at different tempering temperature. Using the established model, the linear relationship between the tempering hardness and the tempering time in logarithm was proved theoretically, and the tempering hardness for various tempering time was reduced to the measurement and calculation of a hardness experiment tempered for 1~h at different tempering temperatures. Moreover, the hardness of steel 42CrMo and T8Mn tempered for various times at 200~600℃ was calculated using this method. The predicted results are in good agreement with those of the available experiments.
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    Research on the Characteristics of Hot Deformation in BT20 Titanium alloy and Its Optimum Spinning Temperature Range
    Wenchen XU, Debin SHAN, Yan LU, Chunfeng LI
    J. Mater. Sci. Technol., 2005, 21 (06): 807-812. 
    Abstract   HTML   PDF (999KB)
    Hot compression tests were conducted on a Gleeble-1500 simulator to investigate the hot deformation behavior of BT20 Ti alloy (Ti-6Al-2Zr-1Mo-1V) in the temperature range from 550 to 1000℃ at constant strain rate in the range of 0.01~1 s-1, and then the optimum spinning temperature range was determined. Moreover, tube spinning experiments were executed to verify the reasonability of the optimum temperature range. The results show that the flow stress declines gradually with increasing deformation temperature and decreasing strain rate. In α+β phase region the dynamic recrystallization is the main softening mechanism and in β phase region the hot deformation softening is controlled by dynamic recovery. In α+β phase region with reducing strain rate dynamic recrystallization is fully developed. The optimum temperature of hot spinning is 850~900℃ and that of warm spinning is 600~650℃. Meanwhile, at the temperature above 600℃ tubular workpieces of BT20 Ti alloy have been spun without surface cracks and microstructure inhomogeneity, which proves that the optimum spinning temperature range obtained through hot compression experiments is reasonable.
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    Research on Retained Austenite for Advanced Aluminum-containing Hot-rolled TRIP Steel
    Yu CHEN, Guoyi TANG, Fangyu CHEN, Pinghe LI, Sunbing ZHOU
    J. Mater. Sci. Technol., 2005, 21 (06): 813-816. 
    Abstract   HTML   PDF (366KB)
    A new type of hot-rolled transformation induced plasticity (TRIP) steel with 2.3%Al was developed to replace conventional Si-bearing TRIP steel to improve surface quality of the steel sheet. The relationship between retained austenite volume fraction and hot-rolling processing was researched by Gleeble-2000 thermo-dynamic test for the Al-bearing steel. The experimental result showed that aluminum played an important role on retaining austenite and the volume fraction increased from 4.4% to 7.5% as coiling temperature increased from 350℃ to 450℃, while coiling temperature had a stronger effect on retaining austenite than finishing rolling temperature.
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    Methodology of Single Crystal Growth and Microstructure Analysis of CoTi(Zr) Intermetallic Compounds
    Lijuan ZHANG, Mike L.JENKINS, Glyn TAYLO
    J. Mater. Sci. Technol., 2005, 21 (06): 817-821. 
    Abstract   HTML   PDF (762KB)
    The effects of preparation and crystal growth methods on the microstructure, composition, and oxidation of CoTi(Zr) intermetallics were dealt with . A group of methods has been used to produce CoTi and CoTi(Zr) crystals to prevent the formation of titanium oxide particles during melting and crystal growth. The results show that more oxides formed when using powdered starting materials even though the metals handled were and melted under an inert gas atmosphere; using bulk starting materials produced alloys showed less oxidation than powders, but adding a small amount of Al to getter the oxygen was not sufficient to prevent TiO2 formation. However, using a slightly reducing atmosphere during initial melting was highly effective in reducing the formation of oxide. Crystal growth carried out in Ar did not reduce the amount of oxide but only redistributed the particles. TiO2 particles were found only in the grain boundaries after crystal growing, where they obstructed grain growth. Crystal growth in a vacuum was found to be essential in producing oxide free crystals. A seed selection technique was developed and used in growing CoTi single crystals. The microstructures of the samples were determined using optical microscopy, scanning electron microscopy and transmission electron microscopy, including the morphologies, grain sizes, oxide distributions and crystal structure confirmation.
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    Role of C and Fe in Grain Refinement of an AZ63B Magnesium Alloy by Al-C Master Alloy
    Yichuan PAN, Xiangfa LIU, Hua YANG
    J. Mater. Sci. Technol., 2005, 21 (06): 822-826. 
    Abstract   HTML   PDF (1914KB)
    In this study, grain refining effect of Al-1.5C master alloy was examined on an AZ63B magnesium alloy, and the refining mechanism was studied through investigating the role of C and Fe in this process. The results show that addition of Al-1.5C master alloy leads to significant decrease of the mean grain size from about 270 μm to 50 μm at the center of the AZ63 alloy ingot. Grain refinement by carbon addition is mainly due to the heterogeneity nucleation on the Al-, C-, O-, Fe- and Mn-rich particles, but not constitutional undercooling caused by the carbon solute element. Fe plays an important role in the formation of the nucleating particles, but not acts as an inhibiting element.
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    Formation of Bulk Intermetallic Compound Ag3Sn in Slowly-Cooled Lead-Free Sn-4.0 wt pct Ag Solders
    Jun SHEN, Yongchang LIU, Yajing HAN, Peizhen ZHANG, Houxiu GAO
    J. Mater. Sci. Technol., 2005, 21 (06): 827-830. 
    Abstract   HTML   PDF (2770KB)
    Sn-Ag alloy system has been regarded as one of the most promising lead-free solder to substitute conventional Sn-Pb eutectic solder. But the formation of bulk Ag3Sn intermetallic compounds (IMCs) during reflow and post heat treatment significantly influences the performance of the solder joints. With an effort to clarify its microstructural evolution as a function of slow cooling rates, the fraction of bulk IMCs within the slowly solidified Sn-4.0 wt pct Ag solder was investigated by standard metallographic and compared with that detected by thermal analysis. It was found that the bulk IMCs fraction determined by thermal analysis corresponds quite well with the microstructure observation results. In accordance with the conventional solidification theory, the lower the applied cooling rate, the fewer the amount of bulk Ag3Sn IMCs formed in Sn-4.0 wt pct Ag alloy. In addition, Vickers hardness measurement results indicated that the relative coarse eutectic Ag3Sn IMCs distributing in the lamellar eutectic structure favored the improvement of the mechanical performance.
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    AB5-type Hydrogen Storage Alloy Modified with Ti/Zr Used as Anodic Materials in Borohydride Fuel Cell
    Lianbang WANG, Chunan MA, Xinbiao MAO, Yuanming SUN, Seijiro SUDA
    J. Mater. Sci. Technol., 2005, 21 (06): 831-835. 
    Abstract   HTML   PDF (1342KB)
    Fuel cell using borohydride as the fuel has received much attention. AB5-type hydrogen storage alloy used as the anodic material instead of noble metals has been investigated. In order to restrain the generation of hydrogen and enhance the utilization of borohydride, Ti/Zr metal powders has been added into the parent LmNi4.78Mn0.22 (where Lm is La-richened mischmetal) alloy (LNM) by ball milling and heat treatment methods. It is found that the addition of Ti/Zr metal powders lowers the electrochemical catalytic activity of the electrodes, at the same time, restrains the generation of hydrogen and enhances the utilization of the fuel. All the results show that the hydrogen generation rate or the utilization of the fuel is directly relative to the electrochemical catalytic activity or the discharge capability of the electrodes. The utilization of the fuel increases with discharge current density. It is very important to find a balance between the discharge capability and the utilization of the fuel.
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    Effect of Cu on the Spinodal Decomposition of AlZn Alloy with Symmetrical Composition
    Shiming HAO, Yuping REN, Hongxiao LI, Dapeng WANG, Gang ZHAO
    J. Mater. Sci. Technol., 2005, 21 (06): 836-840. 
    Abstract   HTML   PDF (687KB)
    The effect of Cu addition on the spinodal decomposition of the Al-Zn alloy with symmetrical compositions has been investigated by X-ray diffraction analysis. It is found that the single fcc phase can be obtained in the AlZn alloy with the addition of 2 at. pct Cu after solution treatment at 400℃ and water quenching to room temperature. The modulation structure occurs in two types of alloys aged at room temperature for 30 min. The spinodal process remarkably slows down above or at the three phase equilibrium temperature, particularly at room temperature due to the addition of 2 at. pct Cu. The spinodal time increases by 20 times when aging at 300℃ and by more than 30 times when aging at room temperature.
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    Fabrication of Titanium Diboride-Cu Composite by Self-High Temperature Synthesis plus Quick Press
    Jinyong ZHANG, Zhengyi FU, Weimin WANG
    J. Mater. Sci. Technol., 2005, 21 (06): 841-844. 
    Abstract   HTML   PDF (995KB)
    Titanium diboride based composites, good candidates for contact materials, have high hardness, Young's modulus, high temperature stability, and excellent electrical, thermal conductivity. However a good interface of TiB2/Cu is very difficult to achieve for oxidation of TiB2. To avoid this oxidation behavior, the in situ combusting synthesis technology, SHS, was used to prepare TiB2/Cu composite. The characters of Ti-B-xCu SHS were studied in detail, such as combustion temperature, products phases and grain size. Based on the experimental results a proper technology way of self-high temperature synthesis plus quick press (SHS/QP) was determined and compact TiB2/Cu composites with relative density over than 97 pct of the theoretical were fabricated by this method. The properties and microstructures of these TiB2 based composites were also investigated.
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    Wear Studies on Metal Matrix Composites: a Taguchi Approach
    S.Basavarajappa, G.Ch, ramohan
    J. Mater. Sci. Technol., 2005, 21 (06): 845-850. 
    Abstract   HTML   PDF (224KB)
    An attempt has been made to study the influence of wear parameters like applied load, sliding speed, sliding distance and percentage of reinforcement on the dry sliding wear of the metal matrix composites. A plan of experiments, based on techniques of Taguchi, was performed to acquire data in controlled way. An orthogonal array and the analysis of variance were employed to investigate the influence of process parameters on the wear of composites. The objective is to establish a correlation between dry sliding wear of composites and wear parameters. These correlations were obtained by multiple regressions. Finally, confirmation tests were conducted to verify the experimental results foreseen from the mentioned correlations.
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    Effect of Strain Rate on the Ferrite Grain Refinement in a Low Carbon Nb-Ti Microalloyed Steel during Low Temperature Deformation
    B.Eghbali, A.Abdollah-zadeh
    J. Mater. Sci. Technol., 2005, 21 (06): 851-855. 
    Abstract   HTML   PDF (532KB)
    Grain refinement is one of the effective methods to develop new generation low carbon microalloyed steels possessing excellent combination of mechanical properties. The microstructural evolution and ferrite grain refinement at the deformation temperature of 865℃, above Ar3, with different strain rates were investigated using single pass isothermal hot compression experiments for a low carbon Nb-Ti microalloyed steel. The physical processes that occurred during deformation were discussed by observing the optical microstructure and analyzing the true stress-true strain responses. At strain rates of 0.001 and 0.01 s-1, there is no evidence of work hardening behavior during hot deformation and strain-induced transformation (SIT) leads to dynamic flow softening in flow curves. Optical microscopy observation shows that ultrafine and equiaxed ferrite with grain sizes of 2μm can be obtained by applying deformation with strain rate of 0.1 s-1 due to SIT just after deformation. Furthermore, increasing the strain rate from 0.001 to 0.1 s-1 reduces both the grain size of the equiaxed ferrite and the amount of deformed ferrite.
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    Improved Fatigue and Damage Tolerant Material Design for Aerospace Industry
    Yigeng XU, Jiang CHEN, Jianmin LI, Zefei ZHU
    J. Mater. Sci. Technol., 2005, 21 (06): 856-862. 
    Abstract   HTML   PDF (2797KB)
    Various micro-mechanical and micro-structural influences on fatigue crack growth resistance of the material have been investigated over the years. It is widely recognized that resistance to fatigue crack growth can be differentiated into `intrinsic' and `extrinsic'. The separation of intrinsic and extrinsic crack growth resistance has constituted a major theme of fatigue research in the last 30 years, with the concept of crack closure or crack tip shielding being used to rationalize a wide range of micro-structural and mechanical influences on fatigue crack growth behavior. An accurately quantitative understanding of intrinsic and extrinsic effects on crack growth is essential to directed alloy design for improved fatigue resistance, and/or improved structural service life. This paper presents a compliance-based crack closure measurement method and a multi-mechanism based analytical model for the separation of intrinsic and extrinsic material fatigue resistance, with application in characterizing the fatigue performance of two high strength damage tolerant airframe Al alloys.
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    Electrochemical Fabrication and Electrocatalytic Properties of Nanostructured Mesoporous Platinum Microelectrodes
    Mengyan NIE, Joanne M.Elliott
    J. Mater. Sci. Technol., 2005, 21 (06): 863-865. 
    Abstract   HTML   PDF (339KB)
    Electrodeposition from a lyotropic liquid crystal template medium was used to produce nanostructured platinum microelectrodes with high specific surface area and high mass transport efficiency. Compared to polished and conventional platinized microelectrodes, well-ordered nanostructured platinum microelectrodes exhibited enhanced electrocatalytic properties for oxygen and ascorbic acid, whilst well-ordered nanostructured platinum microelectrodes offered improved electrocatalytic properties for oxygen reduction compared to disordered nanostructured platinum microelectrodes.
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    Morphology and Mechanical Properties of PS/Al2O3 Nanocomposites Based on Selective Laser Sintering
    Zhifeng XU, Jian ZHANG, Haizhong ZHENG, Changchun CAI, Yinhui HUANG
    J. Mater. Sci. Technol., 2005, 21 (06): 866-870. 
    Abstract   HTML   PDF (514KB)
    Selective laser sintering (SLS) is a new process to prepare the polystyrene (PS)/ Al2O3 nanocomposites. In this paper, with different laser power and other processing parameters unchanged, the morphology, density and mechanical properties of the sintered specimens were investigated. It was found that nano-sized inorganic particles are uniformly located in the PS matrix and the maximum density of the sintered specimens with pure PS powder reaches 1.07 g/cm3, higher than 1.04 g/cm3 that of the sintered specimens with mixture powder. Due to strengthening and toughness of the nano-sized Al2O3 inorganic particles, the maximum notched impact strength and tensile strength of the sintered part mixed with nano-sized inorganic particles are improved greatly from 7.5 to 12.1 kJ/m2 and from 6.5 to 31.2 MPa, respectively, under the same sintering condition.
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    Optical Properties of Nb+ Ions Implanted Sapphire before and after Annealing
    Xinlian WANG, Jiarong LEI, Dezhi WANG, Ningkang HUANG
    J. Mater. Sci. Technol., 2005, 21 (06): 871-874. 
    Abstract   HTML   PDF (318KB)
    Sapphire crystals with different orientations may cone from implantation of Nb+ ions under different conditions and succedent annealing at reducing atmosphere. Optical analysis results show that the main optical absorption bands lay in the higher energy side of the spectra in the samples. The absorption curves were evaluated by Gaussian fitting based on the F-type centers, which were confirmed by luminescence measurements. The results of Gaussian fitting show that there were F center, F+ center, F2 center, F2+ center and F2+2 center in the Nb+ ions implanted sapphire. After annealing at different temperature, all types of color centers decreased, and the higher the annealing temperature, the more the defects decreased. Sub-micrometer particles were observed by the scanning electron microscopy.
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    Preparation and Arc Breakdown Behavior of Nanocrystalline W-Cu Electrical Contact Materials
    Wenge CHEN, Zhanying KANG, Bingjun DING
    J. Mater. Sci. Technol., 2005, 21 (06): 875-878. 
    Abstract   HTML   PDF (605KB)
    Nanostructured (NS) W-Cu composite powder was prepared by mechanical alloying (MA), and nanostructured bulk of W-Cu contact material was fabricated by hot pressed sintering in an electrical vacuum furnace. The microstructure, electric conductivity, hardness, breakdown voltage and arcing time of NS W-Cu alloys were measured and compared to conventional W-Cu alloys prepared by powder metallurgy. The results show that microstructural refinement and uniformity can improve the breakdown behavior, the electric arc stability and the arc extinction ability of nanostructured W-Cu contacts materials. Also, the nanostructured W-Cu contact material shows the characteristic of spreading electric arcs, which is of benefit to electric arc erosion.
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    AC Impedance Behaviour of Black Diamond Films
    Haitao YE, Olivier GAUDIN, Richard B.JACKMAN
    J. Mater. Sci. Technol., 2005, 21 (06): 879-882. 
    Abstract   HTML   PDF (2578KB)
    The first measurement of impedance on free-standing diamond films from 0.1 Hz to 10 MHz up to 300℃ were reported. A wide range of chemical vapour deposition (CVD) materials were investigated, but here we concentrate on `black' diamond grown by microwave plasma enhanced CVD (MWPECVD). The Cole-Cole (Z' via Z'') plots are well fitted to a RC parallel circuit model and the equivalent resistance and capacitance for the diamond films have been estimated using the Zview curve fitting. The results show only one single semicircle response at each temperature measured. It was found that the resistance decreases from 62 MΩ at room temperature to 4 kΩ at 300℃, with an activation energy around 0.51 eV. The equivalent capacitance is maintained at the level of 100 pF up to 300℃ suggesting that the diamond grain boundaries are dominating the conduction. At 400℃, the impedance at low frequencies shows a linear tail, which can be explained that the AC polarization of diamond/Au interface occurs.
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    Rain Erosion Behavior of Silicon Dioxide Films Prepared on Sapphire
    Liping FENG, Zhengtang LIU, Wenting LIU
    J. Mater. Sci. Technol., 2005, 21 (06): 883-886. 
    Abstract   HTML   PDF (403KB)
    Silicon dioxide (SiO2) films were prepared on sapphire (α-Al2O3) by radio frequency magnetron reactive sputtering in order to increase both transmission and rain erosion resistant performance of infrared domes of sapphire. Composition and structure of SiO2 films were analyzed by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), respectively. The transmittance of uncoated and coated sapphire was measured using a Fourier transform infrared (FTIR) spectrometer. Rain erosion tests of the uncoated and coated sapphire were performed at 211 m/s impact velocity with an exposure time ranging from 1 to 8 min on a whirling arm rig. Results show that the deposited films can greatly increase the transmission of sapphire in mid-wave IR. After rain erosion test, decreases in normalized transmission were less than 1% for designed SiO2 films and the SiO2 coating was strongly bonded to the sapphire substrate. In addition, sapphires coated with SiO2 films had a higher transmittance than uncoated ones after rain erosion.
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    Effect of Seed Layer on the Orientation of Zinc Oxide Film on Silicon Substrate
    Mi XIAO, Makoto KUWABARA
    J. Mater. Sci. Technol., 2005, 21 (06): 887-890. 
    Abstract   HTML   PDF (1419KB)
    The effect of seed layer on the orientation of ZnO film was investigated. Before the preparation of ZnO film using sol-gel method, seed layer of ZnO was prepared in a similar way using the precursor at a rather low concentration. Experiments show that the existence of seed layer can improve the orientation of the finally prepared ZnO film, while baking temperature, baking time and precursor concentration all have effects on the final results.
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    Lattice Effect on the Transport Properties in Double Doped La2/3(Ca1-xSrx)1/3MnO3 Films
    Kexin JIN, Changle CHEN, Shenggui ZHAO, Yongcang WANG, Zhoumo SONG, Xiao YUAN
    J. Mater. Sci. Technol., 2005, 21 (06): 891-893. 
    Abstract   HTML   PDF (397KB)
    The transport properties in the La2/3(Ca1-xSrx)1/3MnO3 (x=0, 1/3, 2/3) films prepared using the RF magnetron sputtering method were investigated. The effect of the Ca, Sr double-doping at the $A$ position in the La2/3(Ca1-xSrx)1/3MnO3 on the structure of the targets and transport of the films has been studied. With the increase of x, the structures of the targets transform from the rhombohedral phase to the cubic phase; the metal-insulator phase transition temperature (Tp) of the films increases; and the corresponding peak resistivity decreases. All the phenomena can be qualitatively explained by the lattice effect.
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    Preparation and Properties of Macroporous Silicon Nitride Ceramics by Gelcasting and Carbonthermal Reaction
    Wen ZHANG, Hongjie WANG, Zhihao JIN
    J. Mater. Sci. Technol., 2005, 21 (06): 894-898. 
    Abstract   HTML   PDF (660KB)
    Macroporous silicon nitride (Si3N4) ceramics with high strength, uniform structure and relatively high porosity were obtained by gelcasting and carbonthermal reaction in a two-step sintering technique. Microstructure and composition were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD). Open porosity, pore size distribution and basic mechanical performance were measured by Archimedes method, mercury intrusion porosimetry and three-point bending methods, respectively. SEM and TEM results revealed that pores were formed by elongated β-Si3N4. SADP measurement proved the formation of SiC particles. The SiC granules were beneficial for the formation of high ratio elongatedβ-Si3N4, and at proper amount, they also acted as reinforcement phase. Thermodynamic analysis indicated that the mechanisms of the reactions were mainly associated with liquid-solid reaction and gas-liquid reaction.
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    Mechanical Properties and Microstructure of Si3N4-TiC Nanocomposites
    Zhijie Lü, Xing AI, Jun ZHAO
    J. Mater. Sci. Technol., 2005, 21 (06): 899-902. 
    Abstract   HTML   PDF (428KB)
    Si3N4/TiC nanocomposite ceramics have been fabricated by hot pressing technique with Al2O3 and Y2O3 as additives. The results showed that well dispersed composite powder was carried out by adding dispersant and adjusting pH values of suspensions. Remarkable increase in flexural strength at room temperatures was obtained by adding nanoparticles in Si3N4 matrix with 10% (wt pct) of nano- Si3N4 and 15% of nano-TiC. The flexural strength, fracture toughness and hardness were 1025 MPa, 7.5 MPa•m1/2 and 15.6 GPa, respectively. The microstructures of materials were analyzed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), which indicated that TiC nanoparticles distribute in the matrix and at the grain boundaries. According to the fracture form, low contents of nano particles could refine matrix grains and lead to the crack deflection as well as crack pinning. The multiplex microstructure was formed by mixing nano- Si3N4 particles. The crack trajectories exhibited crack deflection, rod-like grain bridging and pull-out.
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    Preparation and Interfacial Stability of SiCf/Ti-6Al-4V Composites Fabricated Using Powder Coated Fiber Method
    Yanhua LI, Dezhi ZHANG, Nanlin SHI, Rui YANG
    J. Mater. Sci. Technol., 2005, 21 (06): 903-908. 
    Abstract   HTML   PDF (560KB)
    SiCf/Ti-6Al-4V composites were fabricated by the powder-coated fiber method. The precursor fiber was prepared under the optimized parameter, and the composites were made using the vacuum hot pressure method. The influence of heat exposure time on products of the interfacial reaction was investigated using scanning electron microscope (SEM) and analytical transmission electron microscope (TEM) with energy dispersive spectrometer (EDS). The main products are TiC and Ti5Si3 after vacuum exposing the samples at 700℃ for 50 h. The growth dynamics of interfacial reaction products was analyzed quantitatively, which fitted the parabola rule. The activity energy of the reaction was 252 kJ•mol-1.
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    Effect of Variable Blank Holder Force on Rectangular Box Drawing Process of Hot-galvanized sheet Steel
    Qunqiang FU, Wei ZHU, Zhiliang ZHANG, Hongying GONG
    J. Mater. Sci. Technol., 2005, 21 (06): 909-913. 
    Abstract   HTML   PDF (1467KB)
    At first, a series of finite element method (FEM) simulation tests were used to find the critical forming conditions of hot-galvanized sheet steel during the rectangular box drawing processing when constant blank holder forces were applied. According the test results, the reasonable alteration scope of initial variable blank holder force (VBHF) was as 1.9~2.3 T. Then, based on the test productions of blank holder force, 12 typical VBHF curves were applied to perform the simulation tests by the simulation software of DYNAFORM. The simulation test results showed that VBHF had great effects on drawing formability of hot-galvanized sheet steel during the rectangular box drawing. However, the different VBHF curves were applied to control the whole drawing and it would get great different effects. At the same tine, the VBHF had great effects on the maximum thick thinning ratio, but had little effect on the maximum thick incrassation ratio. So, reasonable application of the VBHF would greatly decrease the fractures. When the VBHF profile is taken as curve L, the best effect of drawing formability could be obtained. When curve I is used, contrary effect could be gotten. The other types of curves would cause effects between above two types of VBHF curves. Finally, the actual tests were applied to check the validity of the FEM simulation tests. The results show that the FEM simulation tests are good ways for predicting and optimizing the VBHF.
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    Role of Friction in Cold Ring Rolling
    He YANG, Lianggang GUO, Mei ZHAN
    J. Mater. Sci. Technol., 2005, 21 (06): 914-920. 
    Abstract   HTML   PDF (1653KB)
    Cold ring rolling is an advanced but complex metal forming process under coupled effects with multi-factors, such as geometry sizes of rolls and ring blank, material, forming process parameters and friction, etc. Among these factors, friction between rolls and ring blank plays an important role in keeping the stable forming of cold ring rolling. An analytical method was firstly presented for proximately determining the critical friction coefficient of stable forming and then a method was proposed to determine the critical friction coefficient by combining analytical method with numerical simulation. And the influence of friction coefficient on the quality of end-plane and side spread of ring, rolling force, rolling moment and metal flow characteristic in the cold ring rolling process have been explored using the three dimensional (3D) numerical simulation based on the elastic-plastic dynamic finite element method (FEM) under the ABAQUS software environment, and the results show that increasing the friction on the contact surfaces between rolls and ring blank is useful not only for improving the stability of cold ring rolling but also for improving the geometry and dimension precision of deformed ring.
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    Numerical Simulation of Solidification Microstructure and Effects of Phase-field Parameters on Grain Growth Morphologies
    Jingfeng LIU, Ruixiang LIU, Liliang CHEN
    J. Mater. Sci. Technol., 2005, 21 (06): 921-924. 
    Abstract   HTML   PDF (1280KB)
    By a simple phase field model, a series of numerical simulations of solidification microstructure was performed to show a rich variety of dendritic patterns. At the same time, the relation between the morphology of grain growth and some parameters including the strength of anisotropy, dimensionless latent heat and the size of initial solid zone was studied. It is for the first time that patterns of grain growth were associated with the size of initial solid zone, which is an interesting issue. The possible reason for this may be that variation in the size of initial solid zone may bring about fluctuation of the interface energy, making the interface unstable.
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    Filling Rules of Bevel Gears in the Closed-die Cold Forging
    Huamin LIU, Liangju HUANG, Shenhua YANG, Shihong ZHANG
    J. Mater. Sci. Technol., 2005, 21 (06): 925-928. 
    Abstract   HTML   PDF (1056KB)
    The closed-died cold forging technology of the bevel gears used in Jada car was investigated. With the analysis of the strain field and velocity field of the plastic deformation and the endured forces of the dies, the filling rules for the metal were analyzed by the elastic-plastic finite element method (FEM). The results show that there is a great difference among closed-die cold forging, extrusion and forging, as far as the metal flowing is concerned. The outer addendum cannot be filled completely in the closed-die cold forging of the bevel gears, and the round angle will be formed. But it does not influence the application of the bevel gears. At the beginning, the rigid area is formed in the cavity of the lower die. And then it will move upwards to supply the metal for the gear filling. For the closed-die cold forging of the bevel gears, the force acting on the upper die and the lower die is significantly different.
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ISSN: 1005-0302
CN: 21-1315/TG
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