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ISSN 1005-0302
CN 21-1315/TG
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Current Issue
 28 May 2005, Volume 21 Issue 03 Previous Issue    Next Issue
Research Articles
 Select TMR at 4.2 K for Amorphous Magnetic-Tunnel-Junctions with Co60Fe20B20 as Free and Pinned Layers Feifei LI, Xiufeng HAN, Lixian JIANG, Jing ZHAO, Lei WANG, Rehana Sharif J. Mater. Sci. Technol., 2005, 21 (03): 289-291.  Abstract   HTML   PDF (405KB) Single barrier magnetic-tunnel-junctions (MTJs) with the layer structure of Ta(5)/Cu(30)/Ta(5)/Ni79Fe21(5)/Ir22Mn78(12)/Co60Fe20B20(4)/Al(0.8)-oxide/Co60Fe20B20(4)/Cu(30)/Ta(5) [thickness unit: nm] using the amorphous Co60Fe20B20 alloy as free and pinned layers were micro-fabricated. The experimental investigations showed that the tunnel magnetoresistance (TMR) ratio and the resistance decrease with increasing dc bias voltage from 0 to 500~mV or with increasing temperature from 4.2 K to RT. A high TMR ratio of 86.2% at 4.2 K, which corresponds to the high spin polarization of Co60Fe20B20 55%, was observed in the MTJs after annealing at 270℃ for 1 h. High TMR ratio of 53.1%, low junction resistance-area product RS of 3.56 kΩμm2, small coercivity Hc of ≤4 Oe, and relatively large bias-voltage-at-half-maximum TMR with the value V1/2 of greater than 570 mV at RT have been achieved in such Co-Fe-B MTJs.
 Select Nickel Oxide/Carbon Nanotubes Nanocomposite for Electrochemical Capacitance Kui LIANG, Kayhyeok AN, Younghee LEE J. Mater. Sci. Technol., 2005, 21 (03): 292-296.  Abstract   HTML   PDF (437KB) A nanocomposite of nickel oxide/carbon nanotubes was prepared through a simple chemical precipitation followed by thermal annealing. The electrochemical capacitance of this electrode material was studied. When the mass fraction of CNTs (carbon nanotubes) in NiO/CNT composites increases, the electrical resistivity of nanocomposites decreases and becomes similar to that of pure CNTs when it reaches 30%. The specific surface area of composites increases with increasing CNT mass fraction and the specific capacitance reaches 160 F/g under 10 mA/g discharge current density at CNT mass fraction of 10%.
 Select Synthesis and Characterization of Nanocapsules of a-Fe(NiCoAl) Solid-solution Dianyu GENG, J.C.Kim, C.J.Choi, Chonglin CHEN, Xinguo ZHAO, Zhidong ZHANG J. Mater. Sci. Technol., 2005, 21 (03): 297-300.  Abstract   HTML   PDF (384KB) α-Fe(NiCoAl) solid-solution nanocapsules were prepared with pure powders of Fe, Ni, Co and Al by the plasma arc-discharging using a copper crucible. The shapes of the nanocapsules are in polyhedrons with the core/shell structure. The body centered cubic (BCC) phase is formed in the core. The size of the nanocapsules is in the range of 10~120 nm and the thickness of the shell is 4~11 nm. Saturation magnetization Js=150 Am2/kg and coercivity iHC=24.3 kA/m are achieved for the nanocapsules.
 Select Investigation on a Non-cyanide Plating Process of Ni-P Coating on Magnesium Alloy AZ91D Bonian HU, Gang YU, Jueling CHEN, Ying LI, Liyuan YE J. Mater. Sci. Technol., 2005, 21 (03): 301-306.  Abstract   HTML   PDF (316KB) In this research we presented a non-cyanide plating process of Ni-P alloy coating on Mg alloy AZ91D. By applying a new process flow of electroless nickel plating in which zinc coating is used as transition of Ni-P coating on Mg alloy AZ91D, the process of copper transition coating plated in the cyanides bath can be replaced. A new bath composed of NiSO4 was established by orthogonal test. The results show that zinc transition coating can increase the adhesion and protect the Mg alloy substrate from the bath corrosion. The optimal plating bath composition is NiSO4•6H2O 20 g/L, NaH2PO2•H2O 20 g/L and C6H8O7•H2O 2.5 g/L, and optimal bath acidity and optimal plating temperature are pH 4.0 and 95℃, respectively. The present process flow is composed of ultrasonic cleaning→alkaline cleaning→acid pickling→activation→double immersing zinc→electroplating zinc→electroless nickel plating→passivation treatment. The present non-cyanide process of electroless nickel plating is harmless to our surroundings and Ni-P coating on Mg alloy AZ91D produced by present process possesses good adhesion and corrosion resistance.
 Select X-ray and Magnetoresistance Measurements of Electrodeposited Cu-Co Granular Films Suwei YAO, Haixia WU, Weiguo ZHANG, Hongzhi WANG J. Mater. Sci. Technol., 2005, 21 (03): 307-310.  Abstract   HTML   PDF (434KB) Granular CoxCu1-x alloy films were prepared by electrodeposition at room temperature directly onto semiconducting Si substrate. X-ray diffraction (XRD) revealed that the as-deposited films formed single phase metastable fcc alloy structure. The fcc lattice parameter α was found to decrease linearly with increasing Co concentration x in the studied range. The giant magnetoresistance (GMR) of the films was improved after annealing. Pure Co fcc diffraction peaks were observed in the diffractogram of the annealed sample, indicating phase separation occurred upon annealing. The optimal annealing temperature was 450℃. The maximum of magnetoresistance (MR) ratio 8.21% was obtained for the Co20Cu80 thin film after annealing at 450℃ for 1 h. The saturation field decreased upon annealing in the MR curves of Co20Cu81 film.
 Select In Situ Scanning-Tunneling-Microscope Observation on Dissolution of a Cu-20Zr Film Haibo LU, Guoze MENG, Ying LI, Fuhui WANG J. Mater. Sci. Technol., 2005, 21 (03): 311-314.  Abstract   HTML   PDF (775KB) A nanocrystalline coating of Cu-20Zr (in wt~pct) was obtained on glass by magnetron sputtering. The corrosion behavior of the Cu-20Zr film in 0.001 mol/L HCl solution was investigated using potentiodynamic polarization and in situ electrochemical scanning-tunneling-microscopy (ECSTM). Results demonstrated that the film exhibits active behavior. Microscopic pitting corrosion and tunneling are caused by localized electrodissolution of Zr atoms and the diffusion of Cu atoms at surface defects.
 Select Influences of Sputtering Angles and Annealing Temperatures on the Magnetic and Magnetostrictive Performances of TbFe Films Hongchuan JIANG, Wanli ZHANG, Wenxu ZHANG, Shiqing YANG, Huaiwu ZHANG J. Mater. Sci. Technol., 2005, 21 (03): 315-318.  Abstract   HTML   PDF (659KB) To increase the low-field magnetostriction of TbFe films, the influences of sputtering angles and annealing temperatures on its magnetic and magnetostrictive performances were systematically investigated. With the change in sputtering angles from 90℃ to 15℃, the in-plane magnetization of TbFe films, at 1600 kA• m-1 external field, is strongly increased. An enhancement in the in-plane magnetostrictive coefficient of the films at 40 kA•m-1 is also observed. A detection of magnetic domains by MFM (magnetic force microscopy) indicates that the easy magnetization direction shifts gradually from perpendicular to parallel to the film plane with decreasing sputtering angles. Annealing can enhance the magnetization and magnetostriction of the TbFe films. However, at too high annealing temperature, both the magnetization and magnetostriction of the TbFe films were suppressed to some extent.
 Select Superelasticity of NiTi Shape Memory Alloy Thin Films Zhenyu YUAN, Dong XU, Zhican YE, Bingchu CAI J. Mater. Sci. Technol., 2005, 21 (03): 319-323.  Abstract   HTML   PDF (358KB) The superelastic properties of NiTi thin films prepared with sputtering were studied. To characterize their superelasticity, tensile and bulging and indentation tests were performed. The measured mechanisms using these three methods were compared, and the factors that influence superelasticity were described.
 Select Corrosion Penetration and Crystal Structure of AA5022 in HCl Solution and Rare Earth Elements A.A.El-Meligi, S.H.Sanad, A.A.Ismail, A.M.Baraka J. Mater. Sci. Technol., 2005, 21 (03): 324-330.  Abstract   HTML   PDF (530KB) Al-alloy (AA5022) corrosion penetration (CP) and crystal structure were investigated after running static immersion corrosion tests in 1 mol/L HCl solution and different concentrations of rare earth elements (La3+), (Ce3+) and their combination, at different temperatures. X-ray diffraction (XRD) was used to examine the surface structure before and after immersion, and secondary electron detector (SED) was operated to study surface morphology. In 1 mol/L HCl solution the corrosion penetration increased with increasing temperature and immersion time. The increase of La3+ concentrations up to 1000×10-6 g/L led to the decrease in the corrosion penetration, and the decrease in Ce3+ concentrations up to 50×10-6 g/L decreases the corrosion penetration of the alloy. Mix3 (combination of La3+ and Ce3+) dramatically reduced the corrosion penetration. This suggests that a synergistic effect exists between La3+ and Ce3+. The reaction kinetics both in absence and presence of La3+ and Ce3+ and their combination would follow a parabolic rate law. The XRD patterns revealed that the intensities of certain hkl phases are affected. The crystalline structure has not been deformed either before or after testing and there are no additional peaks except that of the as-received alloy. In the case of accelerating CP, the surface morphology shows that the roughness and voids of surface are increased.
 Select Microstructure, Textures and Deformation Behaviors of Fine-grained Magnesium Alloy AZ31 Ping YANG, Zude ZHAO, Xueping REN, Shaodong HUANG J. Mater. Sci. Technol., 2005, 21 (03): 331-337.  Abstract   HTML   PDF (1044KB) Channel die compression and initial textures are used to activate different deformation mechanisms in a fine-grained magnesium alloy AZ31. The $\sigma$-$\varepsilon$ curves, microstructures and, particularly, textures are analyzed to reveal different deformation mechanisms and to compare with those of coarse grained samples. Dominant double-prismatic slip, {101ˉ2} twinning and basal slip are detected in three types of samples, respectively, which is similar to those of coarse grained samples. The detrimental effect of shear band formation or {101ˉ1} twinning is limited in fine grained microstructure. In addition to the higher flow stress at low temperature an early decrease in flow stress at higher temperature is also found in fine-grained samples in comparison with their coarse-grained counterparts. This softening is ascribed to the early dynamic recrystallization or grain boundary glide.
 Select Irregular-Mode Cracking in Fe-3 wt pct Si Alloy Yu Qiao J. Mater. Sci. Technol., 2005, 21 (03): 338-342.  Abstract   HTML   PDF (472KB) Due to the non-uniform nature of crack advance, when a cleavage front encounters a high-angle grain boundary, instead of simultaneous break-through along the whole boundary, the front transmission mode can be irregular, which results in a higher fracture resistance and a tortuous percolation behavior. In this paper, this phenomenon is studied quantitatively through the analysis on the work of separation and the change in strain energy for an Fe-3 wt pct Si alloy. The influences of the crystallographic misorientations, the break-through mode, the cleavage front profile, and the grain boundary properties are discussed in detail.
 Select Saturation Dislocation Microstructures of Double-slip-oriented Copper Single Crystal during the Corrosion Fatigue in a 0.5 mol/L NaCl Aqueous Solution Jihong YANG, Xinping ZHANG, Yiuwing MAI, Weiping JIA, Shouxin LI, Wei KE J. Mater. Sci. Technol., 2005, 21 (03): 343-346.  Abstract   HTML   PDF (475KB) Copper single crystal specimens with the longitudinal axis parallel to the [013] double-slip-orientation were grown through Bridgman technique. The fatigue tests were performed using a symmetric tension-compression load mode at room temperature in an open-air and a 0.5 mol/L NaCl solution, respectively. The dislocation microstructures were observed with scanning electron microscopy (SEM) by the electron channeling contrast (ECC) and transmission electron microscopy (TEM). The results show that the saturation dislocation microstructures during the corrosion fatigue in the aqueous solution of 0.5~mol/L NaCl, mainly consisted of labyrinth, wall and vein dislocation structures, which differs from the dislocation structures of the walls and veins in an open-air environment.
 Select Development of a Nickel-base Cast Superalloy with High Strength and Superior Creep Properties Jieshan HOU, Jianting GUO, Lanzhang ZHOU, Zhijun LI J. Mater. Sci. Technol., 2005, 21 (03): 347-352.  Abstract   HTML   PDF (869KB) Derived from Russian alloy CHS88U, six experimental Ni-base alloys named as A to F in the Ni-Cr-Co-W-Ti-Al-Hf system are designed, evaluated and processed. One of these alloys, F, shows excellent high temperature tensile strength and ductility with superior creep rupture properties. As predicted by using modeling tools such as PHACOM and NEW PHACOMP, there is hardly the tendency for formation of topologically close-packed phase (TCP) phase in alloy F. Furthermore, through microstructural observation, it is also found that no TCP phase is formed in alloy F after long-time exposure at high temperature. So alloy F has well balance of phase stability and mechanical properties in view of application for gas turbines. It is proved that d-electron approach can be applied for design and development of nickel-base superalloys for gas turbine application.
 Select Research on Ultrafine Tungsten Carbide-Cobalt (WC-Co) Cemented Carbide Rods of Miniature Drills for Highly Integrated Printed Circuit Board (PCB) Xiaoliang SHI, Gangqin SHAO, Xinglong DUAN, Runzhang YUAN J. Mater. Sci. Technol., 2005, 21 (03): 353-356.  Abstract   HTML   PDF (473KB) Nanocrystalline tungsten carbide-cobalt (WC-Co) composite powders produced through spray thermal decomposition-continuous reduction and carburization technology were used to prepare Φ3.25 mm×38 mm ultrafine tungsten carbide-cobalt (WC-Co) cemented carbide rods through vacuum sintering plus sinterhip technology. The microstructure, Vickers hardness, density and Rockwell A hardness (HRA), transverse rupture strength (TRS), saturated magnetization and coercivity force were tested. The results show that the average grain size of the sintering body prepared through vacuum sintering plus sinterhip technology was 430~nm; transverse rupture strength (TRS) was 3850 MPa; Vickers hardness was 1890 and Rockwell A hardness of sintering body was 93. High strength and high hardness ultrafine WC-Co cemented carbide rods used to manufacture printed circuit board (PCB) drills were obtained.
 Select Influence of Microstructures and Textures on the Torsional Behavior of Pearlitic Wires Y, ong LIU, Qiwu JIANG, Gang WANG, Y, ong WANG, A.Tidu, Liang ZUO J. Mater. Sci. Technol., 2005, 21 (03): 357-360.  Abstract   HTML   PDF (360KB) The microstructure, texture characteristics and torsion ability of two kinds of steel wires were investigated. The eutectoid steel wires were produced by hot and cold drawing with severe deformation. The torsinability of steel wires was measured under two cases, i.e. there exists either fiber texture or circular texture. The results showed that the torsional behavior of the steel wires was affected by their textures and microstructures. The {110}<110> circular texture weakened the torsion ability of the wires. The torsion fracture behavior of {110}<110> texture wires is related to the fact that only two slip systems were activated under simple shear strain deformation.
 Select Application of Electron Energy Loss Spectroscopy and Energy Filtering Transmission Electron Microscopy for Microchemical Studies in 2.25Cr-1Mo Steel P.Parameswaran, Ilse Papst, F.Hofer, W.Grogger, V.S.Raghunathan J. Mater. Sci. Technol., 2005, 21 (03): 361-366.  Abstract   HTML   PDF (897KB) Electron enregy loss spectroscopy (EELS) and energy filtering transmission electron microscopy (EFTEM) investigation on 2.25Cr-1Mo steel was carried out to understand the nature of evolution of secondary carbides. The filtered images obtained from two different ageing treatments indicate that the steel evolves to a more stable carbide namely M23C6 in comparison to M2C. Microchemical information was generated from EELS spectra. Suitable choice for estimating the microchemical state was discussed. To evaluate the behaviour of ageing an elemental ratio of Fe to Cr is employed.
 Select Dynamic Viscoelasticity of Polyester/Rubber Composites under Cyclic Loading Yuyan LIU, Zhenhui TIAN, Zhimin XIE, Xingwen DU J. Mater. Sci. Technol., 2005, 21 (03): 367-370.  Abstract   HTML   PDF (402KB) This paper focuses on the influence of dynamic viscoelasticity and surface temperature on the fatigue mechanism and fatigue lifetime of polyester/rubber composites. Rubber composites show significant viscoelasticity during fatigue process. The variations of dynamic elastic modulus, mechanical loss angle, loss energy per cycle exhibit different trend in fatigue initial stage and final stage. Due to high viscoelasticity high heat generation occurs under cyclic loading, which leads to a high surface temperature. It is found that the variation of specimen surface temperature depends strongly on cycling frequency and stress amplitude. SEM (scanning electron microscopy) observation and static residual stiffness studies reveal that the surface temperature affects fracture morphology and fatigue lifetime of rubber composites strongly because of heat aging.
 Select Surface State of Carbon Fibers Modified by Electrochemical Oxidation Yunxia GUO, Jie LIU, Jieying LIANG J. Mater. Sci. Technol., 2005, 21 (03): 371-375.  Abstract   HTML   PDF (238KB) Surface of polyacrylonitrile (PAN)-based carbon fibers was modified by electrochemical oxidation. The modification effect on carbon fibers surface was explored using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Results showed that on the modified surface of carbon fibers, the carbon contents decreased by 9.7% and the oxygen and nitrogen contents increased by 53.8% and 7.5 times, respectively. The surface roughness and the hydroxyl and carbonyl contents also increased. The surface orientation index was reduced by 1.5% which decreased tensile strength of carbon fibers by 8.1%, and the microcrystalline dimension also decreased which increased the active sites of carbon fiber surface by 78%. The physical and chemical properties of carbon fibers surface were modified through the electrochemical oxidative method, which improved the cohesiveness between the fibers and resin matrix and increased the interlaminar shear strength (ILSS) of carbon fibers reinforced epoxy composite (CFRP) over 20%.
 Select Comparison of Structure and Properties among Various PAN Fibers for Carbon Fibers Dongxin HE, Chengguo WANG, Yujun BAI , Bo ZHU J. Mater. Sci. Technol., 2005, 21 (03): 376-380.  Abstract   HTML   PDF (388KB) To find out the high-quality polyacrylonitrile (PAN) fibers, some differences are sought by comparing domestic PAN fibers with the foreign ones. X-ray diffractometer (XRD), transmission electron microscope (TEM), Fourier transform infrared (FT-IR) spectrometer, elemental analyzer, tensile-testing machine and high-temperature differential scanning calorimeter (DSC) are used to characterize the individual microstructure, chemical structure, elemental content, mechanical properties and thermal properties. It is found that high-quality PAN fibers have high density, lower titre, higher or adequate tensile strength, and they also have better conglomeration structure, smaller crystal dimension with dispersive distribution, less microvoids and flaws.
 Select A Novel Method for Preparation of TaC Coating on C/C Composite Material Hanwei HE, Kechao ZHOU, Xiang XIONG J. Mater. Sci. Technol., 2005, 21 (03): 381-385.  Abstract   HTML   PDF (518KB) A new method for preparation of TaC coating on C/C composite material is reported. The amorphous ethylate tantalum jellied as the precursor is prepared and spread densely on the surface of the C/C composite material so as to form a multilayer film. In a graphitization furnace the multilayer film is transformed into TaC coating at various temperatures. Ethylate tantalum film is characterized by FT-IR (Fourier transform infrared) spectra, XRD (X-ray diffraction) and SEM (scanning electron microscopy) and TaC coating is characterized by XRD and SEM. At 1200℃ the coating contained TaC and Ta¬2O5, and at above 1400℃ only TaC is formed. The coating formed at 1600℃ is a continuous stratum structure, and that formed at 1600℃ is a porous net structure. Analysis on thermodynamics and formation mechanism of TaC indicates that, after ethylate tantalum is decomposed, Ta2O¬5 is first produced and then transformed into Ta2C, and newly formed Ta2C is transformed into TaC by the sufficient C at last.
 Select Microstructure and Electromechanical Properties in PMnN-PZT Ceramics Sintered at Different Temperatures Baoshan LI, Zhigang ZHU, Guorong LI, Aili DING J. Mater. Sci. Technol., 2005, 21 (03): 386-390.  Abstract   HTML   PDF (570KB) The microstructure and piezoelectric properties of Pb[(Zr0.52Ti0.48)0.95(Mn1/3Nb2/3)0.05]O3 (PMnN-PZT) ceramics have been investigated at different sintering temperatures from 1070℃ to 1280℃. The experimental results suggest that grain sizes and electromechanical properties of the ceramics show strong sintering temperature dependences. Double polarization to electric field (P-E) loops of the PMnN-PZT ceramics are assumed to be the result of the pinning effect of the defect dipoles. The results obtained through X-ray photoelectron spectrum suggest that sintering temperature affects valence of the Mn ion and quantity of oxygen vacancies. Hence, a proper explanation is proposed to illustrate the fluctuation of mechanical quality factor (Qm) due to the sintering temperature.
 Select Physical and Thermal Properties of P2O5-Al2O3-BaO-La2O3 Glasses Yang LI, Jianhu YANG, Shiqing XU, Guonian WANG, Lili HU J. Mater. Sci. Technol., 2005, 21 (03): 391-394.  Abstract   HTML   PDF (334KB) The physical and thermal properties of P2O5-Al2O3-BaO-La2O3 glasses were investigated. The effects of glass compositions on the transition temperature, thermal expansion coefficient, density, hardness and refractive index of glasses were studied. The highest hardness of the glasses is 4143.891 MPa and the lowest thermal expansion coefficient of the glasses is 71.770×10-7/℃. A phosphate glass with high mechanical strength and good thermal characteristic is obtained.
 Select Computer Simulation of the Interphase Boundary Evolution in Ni75AlxV25-x Alloy Yongsheng LI, Zheng CHEN, Yanli LU, Yongxin WANG J. Mater. Sci. Technol., 2005, 21 (03): 395-398.  Abstract   HTML   PDF (416KB) The interphase boundary evolution of ordered phase in Ni75AlxV25-x alloy during precipitation was simulated on atomic-scale based on the microscopic phase-field dynamic model. The results show that the second phase precipitated from the interphase boundary formed by the first phase and the disordered matrix at high temperature, and from the interphase boundaries of the first phase at low temperature. L12 phase had obvious selective orientation when precipitated from the interphase boundaries of D022. L12 phase nucleated easily at the interphase boundaries formed by [10] and [01] directions of D022 projection along [001] direction, and grew easily at [10] direction. There was no the selective orientation when L12 phase precipitated from the interphase boundary formed by D022 and the disordered matrix. D022 phase had the selective orientation when precipitated from the interphase boundaries of L12, and grew along the [10] direction.
 Select Three Dimensional Numerical Simulation for the Driving Force of Weld Solidification Cracking Zhibo DONG, Yanhong WEI, Renpei LIU, Zujue DONG J. Mater. Sci. Technol., 2005, 21 (03): 399-402.  Abstract   HTML   PDF (561KB) The double ellipsoidal model of heat source is used to analyze the thermal distributions with a three dimensional finite element method (FEM). In the mechanical model, solidification effects are treated by a dynamic element rebirth scheme. The driving force is obtained in the cracking susceptible temperature range. Moreover, this paper presents the effect of solidification shrinkage, external restraint, weld start locations and material properties on the driving force. The comparison between the simulated driving force and the experimental measurements of the material resistance predicts the susceptibility of weld metal solidification cracking.
 Select Mechanical Property Prediction of Commercially Pure Titanium Welds with Artificial Neural Network Yanhong WEI, H.K.D.H.Bhadeshia, T.Sourmail J. Mater. Sci. Technol., 2005, 21 (03): 403-407.  Abstract   HTML   PDF (1067KB) Factors that affect weld mechanical properties of commercially pure titanium have been investigated using artificial neural networks. Input data were obtained from mechanical testing of single-pass, autogenous welds, and neural network models were used to predict the ultimate tensile strength, yield strength, elongation, reduction of area, Vickers hardness and Rockwell B hardness. The results show that both oxygen and nitrogen have the most significant effects on the strength while hydrogen has the least effect over the range investigated. Predictions of the mechanical properties are shown and agree well with those obtained using the 'oxygen equivalent' (OE) equations.
 Select Effects of Surface-Active Elements Sulfur on Flow Patterns of Welding Pool Yuzhen ZHAO, Yongping LEI, Yaowu SHI J. Mater. Sci. Technol., 2005, 21 (03): 408-414.  Abstract   HTML   PDF (501KB) A 3D mathematical model is developed to calculate the temperature and velocity distributions in a moving gas tungsten arc (GTA) welding pool with different sulfur concentrations. It has been shown that, the weld penetration increases sharply with increasing sulfur content. When sulfur content increases beyond 80×10-6, the increase in sulfur content does not have an appreciable difference on the welding pool size and shape, and the depth/width remains constant. Sulfur changes the temperature dependence of surface tension coefficient from a negative value to a positive value and causes significant changes on flow patterns. The increase in soluble sulfur content and the decrease at free surface temperature can extend the region of positive surface tension coefficient. As sulfur content exceeds 125×10-6, the sign of surface tension coefficient is positive. Depending upon the sulfur concentrations, three, one or two vortexes that have different positions, strength and directions may be found in the welding pool. The contrary vortexes can efficiently transfer the thermal energy from the arc, creating a deep welding pool. An optimum range of sulfur content is 20~150×10-6.
 Select Friction Stir Weldabilities of AA1050-H24 and AA6061-T6 Aluminum Alloys Huijie LIU, Hidetoshi FUJII, Masakatsu MAEDA, Kiyoshi NOGI J. Mater. Sci. Technol., 2005, 21 (03): 415-418.  Abstract   HTML   PDF (434KB) The friction stir weldabilities of the strain-hardened AA1050-H24 and precipitate-hardened AA6061-T6 aluminum alloys were examined to reveal the effects of material properties on the friction stir welding behavior. The experimental results are obtlained. (1) For AA1050-H24, the weld can possess smoother surface ripples; there is no elliptical weld nugget in the weld; there is no discernible interface between the stir zone and the thermomechanically affected zone; and the internal defect of the weld looks like a long crack and is located in the lower part of the weld. (2) For AA6061-T6, the weld usually possesses slightly rougher surface ripples; an elliptical weld nugget clearly exists in the weld; there are discernible interfaces among the weld nugget, thermomechanically affected zone and heat affected zone; and the internal defect of the weld is similar to that of the AA1050-H24 weld. (3) The effective range of welding parameters for AA1050-H24 is narrow, while the one for AA6061-T6 is very wide. (4) The maximum tensile strength efficiency of the AA1050-H24 joints is similar to that of the AA6061-T6 joints, i.e. 79% and 77%, respectively.
 Select Experimental and Finite Element Method Studies of J-Lead Solder Joint Reliability Hongtao CHEN, Chunqing WANG, Mingyu LI, Yanhong TIAN J. Mater. Sci. Technol., 2005, 21 (03): 419-422.  Abstract   HTML   PDF (873KB) A comprehensive experimental and numerical study of solder joints for plastic leaded chip carrier (PLCC) 84-Pin, 1.27 mm pitch was carried out. The reliability of solder joints was assessed through accelerated thermal cycling at the temperature range of -55℃～125℃. The samples were taken out to observe the evolution in microstructure, such as grain coarsening, initiation and propagation of cracks. It was found that the Pb-rich phases segregated gradually and formed a continuous layer adjacent to the intermetallic compound (IMC) layer with increasing the number of thermal cycles, resulting in cracks near the solder/lead interface. The response of stress and strain was studied using nonlinear finite element method (FEM), and the results agreed well with the experimental data.
 Select Experimental Verification of the Physical Model for Droplet-Particles Cleaning in Pulsed Bias Arc Ion Plating Yanhui ZHAO, Guoqiang LIN, Chuang DONG, Lishi WEN J. Mater. Sci. Technol., 2005, 21 (03): 423-426.  Abstract   HTML   PDF (326KB) It has been reported that application of pulsed biases in arc ion plating could effectively eliminate droplet particles. The present paper aims at experimental verification of a physical model proposed previously by us which is based on particle charging and repulsion in the pulsed plasma sheath. An orthogonal experiment was designed for this purpose, using the electrical parameters of the pulsed bias for the deposition of TiN films on stainless steel substrates. The effect of these parameters on the amount and the size distribution of the particles were analyzed, and the results provided sufficient evidence for the physical model.
 Select Electron-beam Treatment of Tungsten-free TiC/NiCr Cermet I: Influence of Subsurface Layer Microstructure on Resistance to Wear during Cutting of Metals V.E.Ovcharenko, Baohai YU, S.G.Psakhie J. Mater. Sci. Technol., 2005, 21 (03): 427-429.  Abstract   HTML   PDF (265KB) An experimental investigation were performed on the effect of the impulse electron-beam irradiation upon microstructure of the surface layer and on wear resistance of a cutting tool for sintered TiC/NiCr cermet. The results showed that the surface electron-beam treatment of the TiC/NiCr cermet is an efficient method for investigating the microstructure and phase composition in the surface layer of the powder composite and there are optimal regimes of electron-beam treatment, which ensure a substantial increase in the resistance of the cermet to wear during cutting of metals.
 Select Phase Separation and Theta-compositions of PPES/NMP/non-solvent Systems Yi SU, Xigao JIAN J. Mater. Sci. Technol., 2005, 21 (03): 430-432.  Abstract   HTML   PDF (194KB) Poly (phthalazinone ether sulfone) (PPES) with 1:1 and 1:3 ratios of bisphenol A (BPA) unit to phthalazinone unit were selected as samples. Polymer precipitation curves for the ternary systems PPES (1:1)/NMP/ non-solvent and PPES (1:3)/NMP/non-solvent were determined by a titration method. Comparison between two sets of data is made. Non-solvents used were H2O, ethyl ether (EE), diethylene glycol (DEGC), ethyleneglycol methylether (EGME) and butanone (BO). NMP/non-solvent theta-compositions for PPES (1:1) and PPES (1:3) were also estimated. It was found that the volume ratio of non-solvent to NMP at the property mutation or worsening of PPES membrane is close to the theta-composition.
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