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 March 2009, Volume 25 Issue 02 Previous Issue    Next Issue
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    Articles
    Non-isothermal Crystallization Kinetics of Polyamide 6/Diamine-modified MWNTs Nanocomposite
    Hong Meng,Guoxin Sui,Guangyou Xie,Rui Yang
    J. Mater. Sci. Technol., 2009, 25 (02): 145-150. 
    Abstract   HTML   PDF (836KB)

    The non-isothermal crystallization kinetics of polyamide 6/diamine-modified multi-walled carbon nanotube (PA6/D-MWNT) nanocomposite was investigated by differential scanning calorimetry (DSC). The modified Avrami equation, the Ozawa equation and the combined Avrami/Ozawa equation were employed to analyze the non-isothermal crystallization data. The crystallization activation energies were also evaluated by the Kissinger method. It was found that the combined Avrami/Ozawa equation could successfully describe the non-isothermal crystallization process. The results showed that D-MWNTs not only acted as effective hetero-geneous nucleating agents for PA6 and noticeably increased the crystallization temperature of PA6, but also influenced the mechanism of nucleation and crystal growth of PA6 and then reduced the overall crystallization rate of the neat PA6 matrix. The crystallization activation energy for the nanocomposite sample was greater than that of the neat PA6, which indicated that the addition of D-MWNTs hindered the mobility of PA6 chain segments.

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    Magnetization Reversal for Ni Nanowires Studied by Micromagnetic Simulations
    Nianmei Han,Guanghua Guo,Lamei Zhang,Guangfu Zhang,Wenbin Song
    J. Mater. Sci. Technol., 2009, 25 (02): 151-154. 
    Abstract   HTML   PDF (1036KB)

    The magnetization reversal mechanisms for Ni nanowires with different diameters were investigated by micromagnetic simulations. The results show that the reversal mechanisms are significantly dependent on the diameter of wire. For very thin wires, the reversal occurs by pseudo-coherent rotation. With increasing diameter, magnetization reversal takes place via different nucleation (the transverse domain wall and the vortex domain wall) and subsequent propagation. The reason of transition from the transverse domain wall to the vortex domain wall is given by analytical studies. With further increase of the diameter, the reversal nuclear domain wall becomes tundish-shaped form. As the diameter increases, the width of wall becomes larger.

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    Preparation of α-Fe2O3 Nanodisks by Blocking the Growth of (001) Plane
    Baoliang Lv,Yao Xu,Dong Wu,Yuhan Sun
    J. Mater. Sci. Technol., 2009, 25 (02): 155-158. 
    Abstract   HTML   PDF (1364KB)

    Based on the difference of hydroxy group configuration on different planes of α-Fe2O3 nanoparticles, using the special adsorption and coordination of phosphate on the (001) plane of α-Fe2O3 , well-crystallized and well dispersed α-Fe2O3 nanodisks with diameter of 150-200 nm and thickness of 40-80 nm were synthesized via a hydrothermal method. The magnetic properties of synthesized nanodisks were investigated. It was found that the nanodisks possessed a saturation magnetization (Ms) of 0.38 emu/g, a remanent magnetization (Mr) of 0.031 emu/g and a coercivity of 452.91 Oe at room temperature. The Mr and coercivity of synthesized α-Fe2O3  nanodisks are higher and the Ms is lower than those of other previously reported α-Fe2O3 nanostructures.

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    Epoxy Resin/Nano Ni@C Composites Exhibiting NTC Effect with Tunable Resistivity
    Bangwen Zhang,Baowei Li,Changsheng Xie
    J. Mater. Sci. Technol., 2009, 25 (02): 159-163. 
    Abstract   HTML   PDF (581KB)

    Epoxy resin/Ni@C nanoparticle composites with aligned microstructure were prepared by using a procedure of magnetic field assisted curing. The results show that the resistivity of composites exhibits negative temperature coefficient (NTC) effect above room temperature, and can be adjusted by varying the content filler and the magnitude of magnetic field applied. Hill0s quantum tunneling model was modified to understand the electrical conduction mechanism in the composites. It shows that the NTC effect ascribes to the dominant thermal activated tunneling transport of electron across adjacent nanoparticles, as well as the low thermal expansivity of epoxy resin matrix.

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    Graphitization in CK 45 Steel
    A.R. Kiani-Rashid
    J. Mater. Sci. Technol., 2009, 25 (02): 164-168. 
    Abstract   HTML   PDF (685KB)

    The purpose of this study was to determine the influence of heat treatment cycle on graphite phase formation on CK 45 steel. The presence of well distributed graphite in the matrix is responsible for the good mechanical and thermal properties of this kind of alloy. Such properties include excellent wear resistance, higher resistance to thermal shock, and higher resistance to oxidation at high temperature. A number of specimens were made up of appropriate design to provide the experimental materials. The transformation phase to a free carbon microstructure during graphitization under different conditions was then examined for the most successful experimental steels. Austenitising temperature of 920°C and the following isothermal heat treatment of 750°C at different holding times were used. Microstructures were examined by OM (optical microscopy) and SEM (scanning electron microscopy). Furthermore, it was found that isothermal transformation at 750°C for different soaking times produced a typical microstructure. Also, the amount of graphite increased with increasing isothermal heat treatment time. Heat treatment leading to supersaturation of iron with carbon was described and some of the consequences of the supersaturation were presented. Finally, the formation of the thermodynamically stable state of the graphite taken from the supersaturated solid solution was discussed.

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    SCC of X70 and Its Deteriorated Microstructure in Simulated Acid Soil Environment
    Zhiyong Liu,Guoli Zhai,Xiaogang Li,Cuiwei Du
    J. Mater. Sci. Technol., 2009, 25 (02): 169-174. 
    Abstract   HTML   PDF (1143KB)

    In order to study the stress corrosion cracking (SCC) of X70 pipeline steel and its weld joint in acid soil environment of southeast of China, two simulating methods were used here. The one was to obtain the bad microstructures in heat a®ected zone by annealing at 1300°C for 10 min and air cooling to room temperature, the other was to get a series of simulating solutions of the acid soil environment. SCC susceptibilities of X70 pipeline steels before and after being normalized in the simulated solutions were studied by slow strain rate test (SSRT) and microstructural observation of fracture areas. Potentiodynamic polarization curves were used to study the electrochemical behaviour of different microstructures. SCC does occur to both the as-received material and normalized microstructure after heat treatment as the polarization potential decreased. Hydrogen embrittlement (HE) is indicated occurring to all tested materials at -850 mV (vs SCE) and -1200 mV(vs SCE). The SCC mechanisms are different within varying potential range. Anodic dissolution is the key cause as polarization potential higher than null current potential, and HE will play a more important role as polarization potential lower than the null current potential.

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    Behavior of AISI 316L Steel Subjected to Uniaxial State of Stress at Elevated Temperatures
    Josip Brnic,Jitai Niu,Marko Canadija,Goran Turkalj,Domagoj Lanc
    J. Mater. Sci. Technol., 2009, 25 (02): 175-180. 
    Abstract   HTML   PDF (2386KB)

    This paper presents an experimental investigation on an AISI 316L stainless steel regarding mechanical properties and short uniaxial creep tests at elevated temperatures. The short time creep tests were carried out under different but constant stresses. The obtained data of ultimate tensile strength, yield strength, creep curves and effects of elevated temperatures on mechanical properties were presented. For a selected rheological model, material parameters were obtained. As a justification, such rheological model is implemented in the finite element procedure for an uniaxially stressed specimen in selected environmental conditions.

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    Tensile and Impact Properties of Shielded Metal Arc Welded AISI 409M Ferritic Stainless Steel Joints
    K. Shanmugam,A.K. Lakshminarayanan,V. Balasubramanian
    J. Mater. Sci. Technol., 2009, 25 (02): 181-186. 
    Abstract   HTML   PDF (2820KB)

    The present study is concerned with the effect of filler metals such as austenitic stainless steel, ferritic stainless steel and duplex stainless steel on tensile and impact properties of the ferritic stainless steel conforming to AISI 409M grade. Rolled plates of 4 mm thickness were used as the base material for preparing single pass butt
    welded joints. Tensile and impact properties, microhardness, microstructure and fracture surface morphology of the joints fabricated by austenitic stainless steel, ferritic stainless steel and duplex stainless steel filler metals were evaluated and the results were reported. From this investigation, it is found that the joints fabricated by
    duplex stainless steel filler metal showed higher tensile strength and hardness compared to the joints fabricated by austenitic and ferritic stainless steel filler metals. Joints fabricated by austenitic stainless steel filler metal exhibited higher ductility and impact toughness compared with the joints fabricated by ferritic stainless steel and duplex stainless steel filler metals.

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    Corrosion and Fatigue Testing of Microsized 304 Stainless Steel Beams Fabricated by Femtosecond Laser
    Qiang Zhang,Xingpeng Guo,Nengli Dai,Peixiang Lu
    J. Mater. Sci. Technol., 2009, 25 (02): 187-193. 
    Abstract   HTML   PDF (1540KB)

    The 304 stainless steel (SS) microcantilever specimens with dimensions of 30 μm×30 μm×50 μm (thickness× width×length) were fabricated by femtosecond (fs) laser. The microsized cantilevers of good quality with structure and dimensions according commendably with that of the designed cantilever were obtained. The result shows that fs laser micromachining is a promising method for directly fabricating metallic microcomponents. Corrosion and fatigue properties of microsized specimens were carried out on the microsized 304 SS cantilever beams by a newly developed fatigue testing machine. The results show that the microsized 304 SS specimens appear to have an improved resistance towards localized corrosion compared to ordinary-sized 304 SS specimens after the static corrosion testing. The testing result shows that the presence of corrosive solution reduces the fatigue lifetime of the 304 SS specimen by a factor of 10-100. The maximum bending loads measured by fatigue testing machine decrease rapidly at the terminal stage of environment assisted fatigue testing. Corrosion fracture first occurred at the range of notch with a higher tensile bending stress, and exhibited clear evidence of trans-columnar fracture detected by SEM (scanning electron microscopy).

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    Boundary Element Method (BEM) Analysis for Galvanic Corrosion of Hot Dip Galvanized Steel Immersed in Seawater
    Xiao Tang,Yuzhi Zhang,Meng Liu,Yan Li
    J. Mater. Sci. Technol., 2009, 25 (02): 194-198. 
    Abstract   HTML   PDF (1436KB)

    A numerical analysis of galvanic corrosion of hot-dip galvanized steel immersed in seawater was presented. The analysis was based on the boundary element methods (BEMs) coupled with Newton-Raphson iterative technique to treat the nonlinear boundary conditions, which were determined by the experimental polarization curves. Results showed that galvanic current density concentrates on the boundary of steel substrate and zinc coating, and the sacrificial protection of zinc coating to steel substrate results in overprotection of steel cathode. Not only oxygen reduction but also hydrogen reduction could occur as cathode reactions, which probably led up to the adsorption and absorption of hydrogen atoms. Flat galvanized steel tensile sample shows a brittle behavior similar to hydrogen embrittlement according to the SSRT (show strain rate test) in seawater.

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    Cementite Decomposition in Spherical Graphite Iron by Electropulsing
    Qingchun Li,Guowei Chang,Qijie Zhai
    J. Mater. Sci. Technol., 2009, 25 (02): 199-202. 
    Abstract   HTML   PDF (1291KB)

    The influence of electropulsing on cementite decomposition in the spherical graphite iron has been studied.  The results indicated that the cementite was decomposed in a short time by high current density electropulsing. With increasing electropulsing time, the in situ nucleation of graphite in cementite was accompanied with the quick decomposition of cementite. The dislocation accumulation adjacent to the cementite and the quick diffusion of carbon atom by electropulsing were main reasons for the quick decomposition of cementite. The in situ nucleation of graphite in the cementite resulted from the dislocation climbing crossing the cementite lamellae.

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    Effect of Reaction Layers on the Residual Stress of the Brazed TiC Cermets/Steel Joints
    Lixia Zhang,Jicai Feng
    J. Mater. Sci. Technol., 2009, 25 (02): 203-207. 
    Abstract   HTML   PDF (1512KB)

    For the first time, considering the effect of reaction layers, numerical simulation calculation of residual stress on brazed TiC cermets/steel joint was studied by finite element method (FEM). The calculation results show that, when the joint is brazed at 1123 K for 300 s (low brazing parameters), the maximum shear stress value occurs on (Cu, Ni) layer near TiC cermets, which is 92.16 MPa as the temperature is 300 K. When the joint is brazed at 1273 K for 900 s (high brazing parameters), the maximum shear stress value occurs on (Cu, Ni)+(Fe, Ni) layer, which is 39.18 MPa as the temperature is 300 K. The fracture sites of the joints obtained from numerical simulation calculation accord with experimental results.

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    Structure and Thermal Parameters of Ni20Pd80 Alloy
    S. Ahmad,A.B. Ziya,A. Aziz,Z.I. Zafar
    J. Mater. Sci. Technol., 2009, 25 (02): 208-210. 
    Abstract   HTML   PDF (423KB)

    The structure and thermal parameters of Ni20Pd80 alloy were studied by X-ray diffraction(XRD). The diffraction experiments performed in the temperature range of 308-1100 K revealed that the alloy formed a face centered cubic (fcc) A1-type structure. The temperature dependence of the lattice parameters was investigated by using the Bragg line displacement method showing that the lattice parameter increases with the increase of temperature. The mean linear thermal expansion (MLTE(%)), coe±cient of thermal expansion (CTE, α), the characteristic Debye temperature (θD) and mean square amplitudes of vibration were determined from XRD data. The value of Debye temperature was found to be 253 K. It was found that temperature factor was independent of the static displacements.

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    Intrinsic Strengthening of Coherent Twin Boundaries in Copper
    Yanfen Luo,Yuchen Wang,Yanbo Wang,Yuanming Wang,Manling Sui
    J. Mater. Sci. Technol., 2009, 25 (02): 211-214. 
    Abstract   HTML   PDF (1065KB)

    Molecular dynamics (MD) simulations were applied to simulate the deformation process of copper with different density of parallel coherent twin boundaries (TBs). It is shown that the strength of perfect copper crystal enhances with increasing coherent TB density. Based on the local hydrostatic pressure analysis, we found that stress concentrations are more likely to form in the interior of the crystal rather than around the TBs. Since the dislocation nucleation is suppressed in the vicinity of the coherent TBs and each TB plane hinders dislocations from propagating, the coherent TBs can be regarded as an intrinsic strengthening phase relative to perfect crystal.

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    A Comparative Study of Elastic Constants of NiTi and NiAl Alloys from First-Principle Calculations
    Jianmin Lu,Qingmiao Hu,Rui Yang
    J. Mater. Sci. Technol., 2009, 25 (02): 215-218. 
    Abstract   HTML   PDF (205KB)

    To investigate the origin of the strong dependence of martensitic transformation temperature on composition, the elastic properties of high temperature B2 phases of both NiTi and NiAl were calculated by a first-principle method, the exact-muffin orbital method within coherent potential approximation. In the composition range of 50-56 at. pct Ni of NiTi and 60-70 at. pct Ni of NiAl in which martensitic transformation occurs, non-basal-plane shear modulus c44 increases with increasing Ni content, while basal-plane shear modulus c′ decreases. In the above composition ranges however the transformation temperature of NiAl increases with increasing Ni content while that of NiTi decreases from experimental observation. The softening of c′ is experimentally observed only in NiAl, and the decrease of c′ with increasing Ni content is responsible for the increase of transformation temperature. The result of the present work demonstrates that, besides c′, c44 also influences the martensitic transformation of NiTi and plays quite important a role.

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    Texture Evolution in Heavily Cold-Rolled FeCo-2V Alloy during Annealing
    Jiangning Deng,Yanling Yang,Yandong Wang,Jingeng CHEN,Rulin Peng
    J. Mater. Sci. Technol., 2009, 25 (02): 219-224. 
    Abstract   HTML   PDF (1840KB)

    The recrystallization texture evolution in heavily cold-rolled (93%) FeCo-2V alloy with annealing temperature and time was investigated by X-ray diffraction and electron backscatter diffraction. It was found that the orientation density of α-fiber texture component fluctuates with increasing annealing temperature and time. The transmission electron microscopy images show that abundant precipitates appear inside the recrystallized grains and around the grain boundaries. The amount and size of  the precipitates also vary with annealing temperature and time. The enhancement of the α-fiber coincides well with the increase of number density of fine precipitates, indicating that the fine precipitates facilitate the development of α-fiber. The annealing texture evolution observed in the FeCo alloy could be attributed to the facilitating e®ect of the precipitates on the development of α-fiber and the ordering process.

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    Influence of Al Content on the Atmospheric Corrosion Behaviour of Magnesium-Aluminum Alloys
    Ruiling Jia,Chuanwei Yan,Fuhui Wang
    J. Mater. Sci. Technol., 2009, 25 (02): 225-229. 
    Abstract   HTML   PDF (1514KB)

    The influence of Al content on the Mg-Al alloys corrosion performance during sodium chloride induced atmospheric corrosion has been studied. It was found that the corrosion rate of three Mg-Al alloys was accelerated with increasing Al content. The poor corrosion resistance was attributed to the galvanic coupling between the α  phase and eutectic phase or ® phase and the formation of porous corrosion products.

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    Aging Strengthening in Rapidly Solidified Cu-Cr-Sn- Zn Alloy
    Juanhua Su,Fengzhang Ren,Baohong Tian,Pin Liu,Qiming Dong
    J. Mater. Sci. Technol., 2009, 25 (02): 230-232. 
    Abstract   HTML   PDF (326KB)

    It is known that the strength of alloys can be successfully improved by rapid solidification. The paper presents a process where Cu-Cr-Sn-Zn lead frame alloy is produced by rapid solidification and aging. The microcrystalline structure of rapidly solidified Cu-Cr-Sn-Zn alloy is smaller grain structure examined by optical metallography. The effects of aging processes on the microstructure and properties of the lead frame alloy were investigated. Aged at 500°C for 15 min the fine coherent precipitates Cr distribute in Cu matrix observed by transmission electron microscopy and the properties of hardness and electrical conductivity properties can reach 178HV and 61%IACS, respectively.

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    La-doped Copper Nitride Films Prepared by Reactive Magnetron Sputtering
    Xing0ao Li,Jianping Yang,Anyou Zuo,Zuobin Yuan,Zuli Liu,Kailun Yao
    J. Mater. Sci. Technol., 2009, 25 (02): 233-236. 
    Abstract   HTML   PDF (564KB)

    Copper nitride film (Cu3N) and La-doped copper nitride films (LaxCu3N) were prepared on glass substrates by reactive magnetron sputtering of a pure Cu and a pure La targets under N2 atmosphere. The results show that La-free film was composed of Cu3N crystallites with anti-ReO3 structure with (111) texture. The formation of the LaxCu3N films is affected strongly by La, and the peak intensity of the preferred crystalline [111]-orientation decreases with increasing the concentration of La. High concentration of La may prevent the formation of the Cu3N from crystallization. Compared with the Cu3N films, the resistivity of the LaxCu3N films have been decreased.

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    Pyrite Films Grown by Sulfurizing Precursive Iron of Different Crystallizing Status
    Liuyi Huang,Yanhui Liu,Liang Meng
    J. Mater. Sci. Technol., 2009, 25 (02): 237-241. 
    Abstract   HTML   PDF (1150KB)

    Precursive iron films with different grain sizes were prepared by magnetron sputtering on substrates heated at different temperatures. The iron films were sulfurized at 673 K for 20 h to form pyrite films. The structural and electrical characters were determined. High substrate temperatures produce large crystallites in the precursive iron films. The pyrite films are composed of a surface layer with coarse columnar grains and a bottom layer with fine equiaxed grains. With the increase of iron grain scale, the carrier concentration decreases and the carrier mobility increases. The electrical resistivity of the pyrite films increases to a maximum in the precursive iron films with increasing the grain size to about 39 nm. Sufficient formation and growth of iron grains result in improved crystallinity and high continuity of the pyrite films. The crystal defect density, transformation stress level and atom diffusion behavior are responsible for the characteristics of the electrical properties dependent on the crystallinity and continuity of the pyrite films or the crystallizing status of the precursive iron films.

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    Composition and Morphology of Electrodeposited CuInSe2 Precursor Films
    Fangyang Liu,Zhian Zhang,Yanqing Lai,Jie Li,Yexiang Liu
    J. Mater. Sci. Technol., 2009, 25 (02): 242-246. 
    Abstract   HTML   PDF (1072KB)

    CuInSe2 (CIS) precursor films have been prepared by electrodeposition in aqueous solution. The electrodeposited films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) for structural, morphological and componential properties. The influence of deposition potential and Na-citrate concentration on composition and morphology of electrodeposited films was studied in detail. It is found that the film morphology is strongly influenced by deposition potential and Na-citrate concentration. Films with large and homogenous grain size and ratio of Cu/In approaching 1 were obtained at deposition potentials of -0.7 and -0.75 V vs the saturated calomel electrode (SCE) and Na-citrate concentration of 500 mmol/L. Chalcopyrite phase CuInSe2 is contained in precursor films that have poor crystallinity.

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    Electrical and Mechanical Properties of PMMA/nano-ATO Composites
    Wei Pan,Huiqin Zhang,Yan Chen
    J. Mater. Sci. Technol., 2009, 25 (02): 247-250. 
    Abstract   HTML   PDF (991KB)

    Conducting nanocomposites of poly (methyl methacrylate) (PMMA) and antimony doped tin oxide (ATO) were prepared by solution blending. The influences of ATO content on the electrical conductivity, thermal stability, and mechanical properties of the nanocomposites were investigated. A homogeneous dispersion of silane coupling agent modified ATO was achieved in PMMA matrix as evidenced by scanning electron microscopy. The resultant PMMA/silane-ATO nanocomposites were electrically conductive with significant conductivity enhancement at 4 wt pct. It was found that the composition at 4 wt pct ATO gave the higher tensile strength. Furthermore, it gave the largest elongation at break value among all the compositions. Thermal stability of the nanocomposites was remarkably enhanced by the incorporation of silane-ATO.

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    Influence of Thermal Shock on the Mechanical Behavior of Si-SiC Coated Carbon/Carbon Composites
    Qiangang Fu,Hejun Li,Yongjie Wang,Kezhi Li,Lu Wei
    J. Mater. Sci. Technol., 2009, 25 (02): 251-253. 
    Abstract   HTML   PDF (1011KB)

    Si-SiC coating was prepared on the surface of carbon/carbon (C/C) composites by a two-step technique of pack cementation, and the influences of thermal shock between 1773 K and room temperature in air on the mechanical property and fracture behavior of the coated C/C were studied. The results show that, after thermal shock between 1773 K and room temperature for 5, 10 and 15 times, the flexural strength of coated composites increases by 4.29%, 15.00% and 24.20%, respectively. The toughness of the coated C/C enhances gradually during the thermal shock test. The improvement of the mechanical property after the thermal shock test is primarily caused by the weakening of the fiber-matrix interface and the reduction of residual thermal stresses by thermal shock.

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    Preparation of Gd2O2S:Pr Scintillation Ceramics by Pressureless Reaction Sintering Method
    Jingbao Lian,Xudong Sun,Tie Gao,Qiang Li,Xiaodong Li,Zhigang LIU
    J. Mater. Sci. Technol., 2009, 25 (02): 254-258. 
    Abstract   HTML   PDF (961KB)

    Fabrication of Gd2O2S:Pr scintillation ceramics by pressureless reaction sintering was investigated. The 2Gd2O (Gd,Pr)2(SO 4)mH2O precursor was made by hydrothermal reaction using commercially available Gd2O3, Pr6O11 and H2SO4 as the starting materials. Then single phase Gd2O2SO4:Pr powder was obtained by calcining the precursor at 750°C for 2 h. The Gd2O2SO4:Pr powder compacts can be sintered to single phase Gd2O2S:Pr ceramics with a relative density of 99% and mean grain size of 30 μm at 1750°C for 2 h in flowing hydrogen atmosphere. Densification and microstructural development of the Gd2O2S:Pr ceramics were examined. Luminescence spectra of the Gd2O2S:Pr ceramic under 309 nm UV excitation and X-ray excitation show a green emission at 511 nm as the most prominent peak, which corresponds to the 3P0-3H4 transition of Pr3+ ions.

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    Synthesis and Growth Mechanism of Carbon Filaments by Chemical Vapor Deposition without Catalyst
    Shuhe Liu,Feng Li,Shuo Bai
    J. Mater. Sci. Technol., 2009, 25 (02): 259-263. 
    Abstract   HTML   PDF (2593KB)

    Carbon filaments with diameter from several to hundreds micrometers were synthesized by chemical vapor deposition of methane without catalyst. The morphology, microstructure and mechanical properties of the carbon filament were investigated by scanning electronic microscopy, optical microscopy, X-ray diffraction and mechanical testing. The results show that the carbon filament is inverted cone shape and grows up along the gas flow direction. The stem of it is formed of annular carbon layers  arranged in a tree ring structure while the head is made up of concentrical layers. The tensile strength of the carbon filament is increased after graphitization for the restructuring and growing large of graphene. The growth mechanism of carbon filament was proposed according to the results of two series of experiments with different deposition time and intermittent deposition cycles.

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    Influence of the Compacts Homogeneity on the Incidence of Cracks during Thermal Debinding in Ceramic Injection Molding
    Xianfeng Yang,Zhipeng Xie,Yong Huang
    J. Mater. Sci. Technol., 2009, 25 (02): 264-268. 
    Abstract   HTML   PDF (1016KB)

    During thermal debinding in ceramic injection molding, the inhomogeneity of green body is a key origin of cracks. In this study, the impact of low molecular weight binders on the homogeneity of the green body was investigated. Incidence of cracks during thermal debinding indicated that the volume ratio of wax to stearic acid should be out of high viscosity and incompletely wetting region. In these two formulation regions, typical inhomogeneous microstructures were observed. By mercury intrusion method, it was shown that pore size distribution of the debinded compacts was determined by thermal degradation of low molecular weight binders. A particle-rich region model was established to predict the nucleation of cracks caused by solid loading fluctuation. The criterion of cracks nucleation was that local capillary force from solid loading fluctuation was larger than the suction force from the surroundings.

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    Co-firing of LNT/Ag Multilayer Sheets Prepared by Aqueous Tape Casting
    Shaochun Li,Qilong Zhang,Hui Yang
    J. Mater. Sci. Technol., 2009, 25 (02): 269-272. 
    Abstract   HTML   PDF (780KB)

    Multilayer ceramic sheets composed of Li1.075Nb0.625Ti0.45O3 (LNT) layers and silver metal layers were fabricated by aqueous tape-casting method. LNT green tape was prepared using PVA (polyvinyl alcohol) as binder and ethylene glycol as plasticizer. The influence of the slurry composition on the rheological properties of the slurries and the properties of the resultant green tapes were studied. The slurry exhibited a typical shear thinning behavior. The increase in the PVA content increased the tensile strength of the tapes. The slip compositions with 5 wt pct PVA produced green tapes with satisfactory tensile strength. Ethylene glycol additions enhanced the flexibility of the green tapes but also produced a decrease in the tensile strength. Sliver inner-electrode was pasted on LNT green tapes and the sheets were stacked, pressed and sintered at 900°C for 2 h. SEM (scanning electron microscopy) micrographs showed that the multilayer sheets were fully dense with fairly uniform microstructure and no reaction was observed between LNT and sliver layers.

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    Preparation of Semisolid A356 Alloy Feedstock Cast via a Pipe Consisting of Partial Inclined and Partial Vertical Sections
    Xiaorong Yang,Weimin Mao
    J. Mater. Sci. Technol., 2009, 25 (02): 273-276. 
    Abstract   HTML   PDF (1733KB)

    In the present work, the microstructures of A356 feedstock cast via a pipe consisting of partial inclined and partial vertical sections were investigated. The experimental results indicate that semisolid feedstock with ideal microstructures can be obtained at higher temperatures 645°C and above by the proposed process, and the solid shell inside the pipe can be avoided at the optimum pouring temperature. Thus the process is attractive for industrial applications. The slanted angle of inclined section has an influence on the optimum pouring temperature. That is, the bigger the slanted angle, the higher the optimum pouring temperature, but accordingly, the greater the possibility of solid shell occurring inside the pipe. Therefore, small slanted angle should be considered first on the premise of ensuring a certain nucleation. The formation of semisolid feedstock is owed to the coactions of wall nucleation and stirring resulting from fluid flow. The inclined section greatly affects nucleation, and the vertical section has an important effect on both nucleation and generating stirring.

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    Investigation of Micro Formability of Bulk Amorphous Alloy in the Supercooled Liquid State Based on Fluid Flow and Finite Element Analysis
    M. Cheng,S.H. Zhang
    J. Mater. Sci. Technol., 2009, 25 (02): 277-280. 
    Abstract   HTML   PDF (833KB)

    Research results on the viscous flow deformation behavior of bulk amorphous alloy in different systems are reviewed. The material exhibits an ideal Newtonian fluid at a high temperature. Analytical solution of lamellar fluid flow behavior is used to discuss the viscous flow behavior of the bulk amorphous alloy in the supercooled liquid state. A material model, which describes such deformation behavior of Mg60Cu30Y10 amorphous alloy, is introduced into the finite element method of microforming  process. Surface feature size was investigated and found not sensitive to the micro formability. Bulk amorphous alloy may possibly be applied to micro-electro-mechanical-systems (MEMS) fabrication.

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    Parametric Analysis of Tensile Properties of Bimodal Al Alloys by Finite Element Method
    W.L. Zhang,S. Li,S.R. Nutt
    J. Mater. Sci. Technol., 2009, 25 (02): 281-288. 
    Abstract   HTML   PDF (1361KB)

    An axisymmetrical unit cell model was used to represent a bimodal Al alloy that was composed of both nano-grained (NG) and coarse-grained (CG) aluminum. Effects of microstructural and materials parameters on tensile properties of bimodal Al alloy were investigated by finite element method (FEM). The parameters analyzed included aspect ratios of CG Al and the unit cell, volume fraction of CG Al (VFCG), and yield strength and strain hardening exponent of CG Al. Aspect ratios of CG Al and the unit cell have no significant influence on tensile stress-strain response of the bimodal Al alloy. This phenomenon derives from the similarity in elastic modulus and coefficient of thermal expansion between CG Al and NG Al. Conversely, tensile properties of bimodal Al alloy are extremely sensitive to VFCG, yield strength and strain hardening exponent of CG Al. Specifically, as VFCG increases, both yield strength and ultimate tensile strength (UTS) of the bimodal Al alloy decreases, while uniform strain of bimodal Al alloy increases. In addition, an increase in yield strength of CG Al results in an increase in both yield stress and UTS of bimodal Al alloy and a decrease in uniform strain of bimodal Al alloy. The lower capability in lowering the increase of stress concentration in NG Al due to a higher yield strength of CG Al causes the lower uniform strain of the bimodal Al alloy. When strain hardening exponent of CG Al increases, 0.2% yield stress, UTS, and uniform strain of the bimodal Al alloy increases. This can be attributed to the increased work-hardening ability of CG Al with a higher strain hardening exponent.

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ISSN: 1005-0302
CN: 21-1315/TG
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