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ISSN 1005-0302
CN 21-1315/TG
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      28 May 1999, Volume 15 Issue 03 Previous Issue    Next Issue
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    Research Articles
    Surface Nanocrystallization (SNC) of Metallic Materials-Presentation of the Concept behind a New Approach
    Ke LU, Jian LU
    J. Mater. Sci. Technol., 1999, 15 (03): 193-197. 
    In this paper, a concept of surface nanocrystallization (SNC) of metallic materials is introduced. Three types of SNC processes are classified. Different SNC mechanisms and possible techniques for SNC are discussed with emphasis on mechanically induced surface self-nanocrystallization. Further development and prospects are addressed with respect to the properties and behaviors of the materials with a nanocrystalline surface. Enhancement of the behavior of the engineering materials by means of the SNC technology and its industrial application possibilities are analyzed.
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    Structure and Magnetic Properties of Nd-Fe-B/a-Fe Nanocomposite Magnets by Co, Nb, Dy Substitutions
    Jian ZHANG, Xiaokai SUN, Wei LIU, Baozhi CUI, Xinguo ZHAO, Zhidong ZHANG
    J. Mater. Sci. Technol., 1999, 15 (03): 198-202. 
    Structure and magnetic properties of the nanocomposite magnets prepared by mechanical alloying procedure with composition 55 wt pct Nd (Fe0.92B0.08)5.5+45 wt pct a-Fe, 55 wt pct Nd(Fe0.8-xCo0.12Nbx B0.08)5.5+45 wt pct a-Fe (x=0.00, 0.01, 0.03) and 55 wt pct (Nd0.9Dy0.1) (Fe0.77Co0.12Nb0.03B0.08)5.5+45 wt pct a-Fe were studied. It was found that substitution of Co for Fe could significantly improve the permanent magnetic properties of the nanocomposite magnets and typically, the maximum magnetic energy product was increased from 104.8 kJ/m3 (13.1 MGOe) to 141.6 kJ/m3 (17.7 MGOe). In contrast to the case of conventional nominally single-phase magnets, the addition of Nb results in promoting the growth of a-Fe grain and is thus unfavorable for the improvement of permanent magnetic properties of the nanocomposites. Although the addition of Dy can increase the coercivity of the magnets, the increase of magnetic anisotropy of hard phase leads to decrease of the critical grain size of soft phase. Additionally it causes the difficulty of preparing the nanocomposites because it is more difficult to control the grain size of soft phase to meet the requirement of appropriate exchange coupling between hard and soft grains.
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    Thermodynamic Calculation of the SrO-Nb2O5 System
    Ying YANG, Hao YU, Zhanpeng JIN
    J. Mater. Sci. Technol., 1999, 15 (03): 203-207. 
    The SrO-Nb2O5 quasibinary system is assessed using the Calculation of Phase Diagram (CALPHAD) technique. A set of self-consistent parameters is obtained and the calculated phase diagram is consistent with the experimental data. It is suggested that further tentative investigation is required especially in the SrO-riched region.
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    Pitting Corrosion Behaviour of Monel-400 Alloy in Chloride Solutions
    V.K.Gouda, I.Z.Selim, A.A.Khedr, A.M.Fathi
    J. Mater. Sci. Technol., 1999, 15 (03): 208-212. 
    Pitting corrosion behavior of Monel-400 alloy in 3.5 wt pct NaCl sodium chloride solution has been investigated using the cyclic potentiodynamic anodic polarization technique. The effects of chloride ion concentration, pH values and different temperatures on the pitting parameters were determined. The morphology of the pits produced after anodic polarization treatments were inspected by scanning electron microscope (SEM). The results indicated that, the increase in chloride ion concentration shifts Epit and Eprot of the alloy toward negative values and the pitting potential is much more dependent on pH value in the basic region. The breakdown of passivity with increasing temperature may be due to kinetic changes of passivating films and dissolution rate of the alloy in its passive state.
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    An Application of the Modified Shear Lag Model to Study the Influence of Thermal Residual Stresses on the Stiffness and Yield Strength of Short Fiber Reinforced Metal Matrix Composites
    Zhonghao JIANG, Jianshe LIAN, Shangli DONG, Dezhuang YANG
    J. Mater. Sci. Technol., 1999, 15 (03): 213-221. 
    The modified shear lag model proposed recently was applied to calculate thermal residual stresses and subsequent stress distributions under tensile and compressive loadings. The expressions for the elastic moduli and the yield strengths under tensile and compressive loadings were derived which take account of thermal residual stresses. The asymmetries in the elastic modulus and the yield strength were interpreted using the derived expressions and the obtained results of the stress calculations. The model predictions have exhibited good agreements with the experimental results and also with the other theoretical predictions.
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    Microstructure and Wear Resistance of Ductile Cast Iron Laser Clad with Ni-Ti-Co-C
    Jingfei LUAN, Ji, ong HU, Zhenfeng ZHOU, Hongying WANG
    J. Mater. Sci. Technol., 1999, 15 (03): 222-224. 
    Using electrode as laser cladding materials, the microstructure and wear resistance of laser-clad layer of ductile cast iron was studied. The laser-clad layer can be subdivided into the melted zone where existed large amounts of austenite, graphite nodules and some carbide, and the solid state transformation zone which included martensite and austenite below the melted zone. The Ti combined with C to form TiC, increasing the wear resistance. The Co significantly increased the wear resistance compared with Ti.
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    Microstructure of Al-Si Alloys Rapidly Solidified from the Different Temperature Melts
    Manchang GUI, Jun JIA, Guangsheng SONG, Qingchun LI
    J. Mater. Sci. Technol., 1999, 15 (03): 225-228. 
    Hypo- and hyper-eutectic Al-Si alloys were rapidly solidified from the low or high temperature melt using water quenching and melt-spinning technique. The differences in microstructure of rapid solidification alloys were studied by scanning and transmission electron microscopy, and X-ray diffraction methods. The primary silicon in the Al-22(wt pct)Si alloy quenched in room temperature water from high temperature melt was smaller than that quenched from low temperature melt. Compared with the ribbons spun from low temperature melt, the ribbons spun from high temperature melt had finer Al-rich and Si-rich phase particles in either Al-7(wt pct)Si or Al-18(wt pct)Si alloy. The mechanism was explained by the nature of the liquid structure.
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    Densification of the Tungsten Heavy Alloys at 1473 K and Fabrication of W-Mo System FGM with Density Gradient
    Huaping XIONG, Lianmeng ZHANG, Junguo LI, Runzhang YUAN
    J. Mater. Sci. Technol., 1999, 15 (03): 229-232. 
    The tungsten heavy alloys with Ni-Al and Fe-Al additives were sintered by hot-press method at 1473 K for 1 h. It was found that the relative density of the W-Fe alloy could be increased evidently by addition of Al. However, the relative density of W-Ni-Al alloy with low content of Al was conversely decreased considerably compared with that of W-Ni alloy. The causes have been studied. The sintering experiments of Mo alloy and W-Mo alloys with 3 wt pct Fe-1.5 wt pct Al additives were also carried out under the same sintering condition of low temperature. Finally, W-Mo system FGM with density gradient was successfully fabricated. Its density changed gradually from 17.0´103 kg/m3 to 9.5´103 kg/m3 within the middle 1.1 mm thickness range.
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    Microstructure and Wear Resistance of In situ TiCp Composite Coating by Laser Cladding
    Xiaolei WU, Guangnan CHEN
    J. Mater. Sci. Technol., 1999, 15 (03): 233-238. 
    A new in situ method was realized by one step laser cladding to produce Ni-base alloy composite coating reinforced by in situ reacted and gradiently distributed TiCp particles. The submicron TiCp particles were formed and uniformly distributed because of the in situ reaction and trapping effect under the rapid solidification condition. And, TiCp particles were of gradient distribution on a macro scale and their volume fraction increased from 1.86% at the layer/substrate interface to a maximum 38.4% at the surface of the layer. Furthermore, the in situ generated TiCp/g-Ni interfaces were free from deleterious surface reactions. Additionally, the clad coating also revealed a high microhardness of gradient variation with the layer depth and the superior abrasive wear resistance.
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    Establishment of the Constitutive Relationship for MP159 Alloy
    Shiqiang LU, Baozhong SHANG, Zijian LUO, Fangchang ZENG
    J. Mater. Sci. Technol., 1999, 15 (03): 239-244. 
    The constitutive relationship for MP159 alloy, a kind of high strength cobalt-base superalloy, was studied based on the experimental results of compression tests carried out in the THERMECMASTER--Z hot work simulating test machine. The constitutive relationship model using Zener-Hollomon parameter as primary variable is proposed, and the constitutive equation for MP159 alloy is firstly formulized. This equation well represents the relationship of flow stress with thermomechanical parameters, i.e. strain, strain rate and temperature, in a large deformation (a true strain of 1.10) and a wide range of deformation temperatures and strain rates. It can be used for the finite element simulation of plastic forming process and the dissipative structure theory and dynamic material modeling.
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    Study of Solidification Shrinkage of Ductile Iron in Dry Sand Molds
    Jiarong LI, Baicheng LIU
    J. Mater. Sci. Technol., 1999, 15 (03): 245-250. 
    The effects of metallurgical and processing parameters on the formation of solidification shrinkage in ductile iron have been studied, considering the parameters of carbon equivalent, inoculation, casting modulus and pouring temperature within specific ranges of these variables. Based on the orthogonal experiments, the metallurgical and processing parameters of the minimum casting shrinkage and the maximum casting shrinkage were obtained, and the effects of metallurgical and processing parameters on the formation of shrinkage cavities and porosities in ductile iron castings were discussed. A regression equation relating these variables to the formation of shrinkage was derived based upon the orthogonal experiments conducted.
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    Rheological Behaviors of Polymer Melts and Concentrated Solutions
    Mingshi SONG, Wen ZHOU, Guixian HU, Lijiang HU
    J. Mater. Sci. Technol., 1999, 15 (03): 251-262. 
    The memory function and elastic modulus were introduced into the O-W-F type of constitutive equations with the Cauchy-Green and Finger tensors for simple fluid, and then the concrete constitutive equation and material function for polymeric suspensions in the different flow fields were formulated: 1) Viscosity and first normal-stress difference coefficient in the shear flow field; 2) Tensile viscosity at the uni-axial elongation flow field; and 3) Dynamic viscosity and modulus in the dynamic field. Then the dependence of the material function on the deformation rate and weight fraction of fillers was discussed, and the shear flow curves with four characteristic regions ( I-low shear rate plateau region, II-apparent yielding region, III-intermediate rate plateau region, and IV-shear thinning region.) were explained theoretically. Finally, it was verified by a number of experimental values for the rheological suspensions and the viscoelastic and mechanical behaviors can be predicted by the molecular theory of non-linear viscoelasticity for polymeric suspensions.
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    Synthesis and Characterization of Some Transition Metal Chelates of 5-(1-Hydroxy-6-Naphthylazo-3-Sodium Sulphonate) Thiobarbituric (L1) and Barbituric (L2) Acids
    Nabil S. Youssef, K.H.Hegab
    J. Mater. Sci. Technol., 1999, 15 (03): 263-266. 
    Some transition metal chelates of two ligands L1 and L2 were prepared and characterized by elemental analysis. The IR and 1H NMR spectra of several chelates of two ligands L1 and L2 showed the involvement of the azo group in chelation with the transition metal ions, in most of the studied chelates, and that the two ligands L1 and L2 showed the involvement of the azo group in chelation with the transition metal ions, in most of the studied chelates, and that the two ligands L1 and L2 were coordinated either in the enol or the keto form. IR spetra also showed that Fe(III)-, Ni(II)-, Mn(II)-, VO(II)-L1 and Cu(II)-L2 chelates behaved in a bidentate manner, in contrast with the two (1:1) M:L cobalt chelates with the two ligands are tridentate. TG analysis indicated the presence of three to twelve water molecules of hydration eliminated on heating up to 150°C and one or two coordinated water molecules removed at 150-180°C. The octahedral structure is proposed for all the chelates, except Cu(II)-L2 and Ni(II)-L1 chelates which have square planar geometry, based on their electronic spectra.
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    Numerical Simulation of Thermal Stress of Shaped Casting Based on Rheological Model
    Jinwu KANG, Baicheng LIU, Shoumei XIONG
    J. Mater. Sci. Technol., 1999, 15 (03): 267-270. 
    In order to study the thermal stresses at the mushy zone, a three dimensional rheological model [H]-[H|N]-[N|S] including elastic, visco-elastic and visco-plastic elements was established, its algorithm and codes for finite element method were also developed. A FDM/FEM integrated analysis system of thermal stresses was built based on the integration of this procedure with thermal analysis by finite difference method. A steel sample casting with a hot spot was simulated in order to validate this system, and the calculated and experimental results were in good agreement.
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    Ti/Al2O3 Functionally Gradient Material Prepared by the Explosive Compaction/SHS Process
    Yimin LI, Ziqiao ZHENG
    J. Mater. Sci. Technol., 1999, 15 (03): 271-275. 
    Ti/Al2O3 Functionally Gradient Material (FGM) was prepared by an explosive compaction/SHS process. Ten sheets of the compounding powder were laminated and pressed to get a green body of FGM. It was then compacted explosively. By burying the explosive compaction body into a stoichiometric Al/TiO2 mixture and igniting the combustion of the stoichiometric Al/TiO2 mixture, the SHS reaction of the explosive compaction body was initiated by the heat released from the combustion of the stoichiometric Al/TiO2 mixture. In this way, Ti/Al2O3 FGM was synthesized. The adiabatic temperatures of each gradient layer were calculated when the preheating temperatures were 298 K and 1173 K, respectively. The microstructure, composition and properties of Ti/Al2O3 FGM and the reaction mechanism of each gradient layer were studied. It was found that Ti/Al2O3 FGM prepared by the explosive compaction/SHS process had a high density and a high microhardness. Its structure, composition and properties showed apparent gradient distribution. The structure of the standard stoichiometric ratio gradient layer of FGM was a network structure. Its reaction mode could be described as follows: Al powder melted first, then the molten Al penetrated into the TiO2 zone and reacted with TiO2, and big pores were left in the original positions of Al powder. The reaction of gradient layers with the addition of Al2O3 as diluents was similar to that of the standard stoichiometric ratio gradient layer, so were their structure and composition. However, the reaction of gradient layers with the addition of Ti as diluents was more complex and the composition deviated slightly from the designed one.
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    Solid State Reaction Yielding a Mineral Utilizing Silica Obtained from an Agricultural Waste
    M.S.Nizami, M.K.Farooq, K.Hussain, M.Z.Iqbal
    J. Mater. Sci. Technol., 1999, 15 (03): 276-280. 
    Wollastonite, a mineral of wide industrial applications was synthesised from rice husk ash silica and limestone. A number of raw batches consisting of these starting materials, in 1:1 molar ratio, were heat treated to produce it through solid state reaction from 900℃ to 1300℃. The conducted reaction was monitored by XRD step by step. Amount of Wollastonite formed at every temperature was also studied to some extent. Analyses of the obtained data indicated that the target mineral formation was quite effective and almost proportional to a rise in temperature up to 1200℃. The results from both, XRD and chemical analysis were found in fair agreement with one another.
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    Luminescence of Unusual Bismuth in Barium Borates (BaB8O13:Bi)
    Qinghua ZENG, Tianzhi ZHANG, Zhiwu PEI, Qiang SU
    J. Mater. Sci. Technol., 1999, 15 (03): 281-282. 
    The luminescence of unusual divalent bismuth (Bi2+) in BaB8O13 is reported. The emission band with maximum peak at 592 nm corresponds to the 2P3/2®2P1/2 transition of Bi2+ in the matrix and the excitation spectrum with two bands peaked at 470 and 580 nm respectively corresponds to two split crystal-field levels of 2P3/2 state. The small Stokes shift (-350 cm-1) reflects the rigid structure of the host for the Bi2+ ions.
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    Microstructure and Properties of WC-Co/NiCrBSi Brazing Coating
    Shanping LU, Yi GUO, Liangshan CHEN
    J. Mater. Sci. Technol., 1999, 15 (03): 283-285. 
    Through rolling technology, a flexible metal cloth consisting of metal powder (NiCrBSi powder or WC-Co powder) and organism in a certain ratio were made, which could be used as brazing coating raw materials. WC-Co/NiCrBSi wear coating was fabricated through high temperature vacuum brazing after the flexible metal clothes were assembled on 42CrMo steel surface. The tensile strengths of coating self and coating/matrix approached to 100-140 MPa and 300-360 MPa, respectively, at different brazing parameters. Effect of Co on the wear property of the coating was analyzed. The abrasive wear property of WC-Co/NiCrBSi brazing coating is better than WC-17Co/NiCrBSi flame overlaying and CoCrW overlaying.
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    Effect of Boron on Carbide Morphology of High Cr Ledeburite Steel
    Shuqi WANG, Qichuan JIANG, Xianghong CUI, Zhenming HE
    J. Mater. Sci. Technol., 1999, 15 (03): 286-288. 
    The effect of boron on carbide morphology of high Cr ledeburite steel has been studied. The results showed that B had obvious influence on eutectic carbide morphology in solidification structure and carbide granulation at high temperature. The addition of 0.02-0.05 wt pct B changed carbide morphology in solidification structure from strip eutectic and rosette eutectic into divorced eutectic. B accelerated carbide granulation through increasing unstability and lattice distortion of carbide and element diffusion. Granular carbide could be achieved when heated at 1150°C for 1.5 h.
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ISSN: 1005-0302
CN: 21-1315/TG
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