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

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      28 September 2006, Volume 22 Issue 05 Previous Issue    Next Issue
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    Research Articles
    Electrochemical Corrosion Behavior of the DLC Coated and Uncoated NiTi Alloys
    Jiehe SUI, Wei CAI, Liancheng ZHAO
    J. Mater. Sci. Technol., 2006, 22 (05): 577-580. 
    Abstract   HTML   PDF (322KB)
    A dense and well-adhered diamond-like carbon (DLC) coating was prepared on the nickel-titanium (NiTi) alloys by plasma immersion ion implantation and deposition (PIIID). Potentiodynamic polarization tests indicated the corrosion resistance of the NiTi alloys was markedly improved by the DLC coating. The Ni ions release of the NiTi alloys was effectively blocked by the DLC coating.
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    A Comparison between TGT and Cz Grown Nd:YAG
    Benxue JIANG, Jun XU, Hongjun LI, Jingya WANG, Guangjun ZHAO
    J. Mater. Sci. Technol., 2006, 22 (05): 581-583. 
    Abstract   HTML   PDF (427KB)
    Large sized neodymium-doped Y3Al5O12 (Nd:YAG) laser crystals have been grown by temperature gradient technique (TGT) method and compared with Czochralski (Cz) method. The comparison of these two crystal growth methods has been listed. The results showed that the TGT method has many advantages over the Cz method. The concentration distribution of Nd ions in the crystals was determined and the absorption spectra of these crystals have been investigated and compared. The TGT grown highly doped Nd:YAG crystal has a larger absorption FWHM than that of Cz grown Nd:YAG crysral. Highly doped Nd:YAG (~2.8 at. pct) crystals could be obtained by TGT.
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    Influence of CaCO3 Whisker Content on Mechanical and Tribological Properties of Polyetheretherketone Composites
    Youxi LIN, Chenghui GAO, Ning LI
    J. Mater. Sci. Technol., 2006, 22 (05): 584-588. 
    Abstract   HTML   PDF (410KB)
    The mechanical and tribological properties of polyetheretherketone (PEEK) composites filled with CaCO3 whisker in various content of 0~45% (wt pct) were investigated. The composite specimens were prepared by compression molding. Tribological testing of composites in dry wear mode against carbon steel ring was carried out on a MM200 block-on-ring apparatus. Data on neat PEEK were also included for comparison. It was observed that inclusion of CaCO3 whisker affected the most mechanical properties and the friction and wear in a beneficial way. With an increase in CaCO3 whisker content, friction coefficient continuously decreased but the trends in wear performance varied. The specific wear rate showed minima as 1.28×10-6 mm3/Nm for 15% CaCO3 whisker inclusion followed by a slow increase for further CaCO3 whisker addition. In terms of friction applications, when the tribological and mechanical properties are combined, the optimal content of CaCO3 whisker in the filled PEEK should be recommended as 15% to 20%. Fairly good correlations are observed in friction coefficient vs bending modulus and wear rate vs bending strength, confirming that the bending properties prove to be the most important tribology controlling parameters in the present work.
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    Microstructure and Tribological Properties of Plasma-sprayed Nanostructured Sulfide Coating
    Yang XU, Yaohui GUAN, Zhongyu ZHENG, Xiaohui TONG
    J. Mater. Sci. Technol., 2006, 22 (05): 589-593. 
    Abstract   HTML   PDF (726KB)
    The friction and wear properties of plasma-sprayed nanostructured FeS coating were investigated on an MHK-500 friction and wear tester under both oil lubrication and dry friction condition. The microstructure, worn surface morphology and phase composition of the coating were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). It was found that the coating was mainly composed of FeS, a small quantity of Fe1-xS and oxide were also found. The coating was formed by small particles of 50~100 nm in size. The thickness of the coating is approximately 150 μm. The friction-reduction and wear-resistance properties of plasma-sprayed nanostructured FeS coating were superior to that of GCr15 steel substrate. Especially under oil lubrication condition, the friction coefficient of nanostructured FeS coating was 50% of that of GCr15 steel, the wear scar widths of the coating were also reduced to nearly 50% of that of GCr15 steel under high load. The failure of the coating was mainly attributed to plastic deformation under both oil lubrication and dry friction condition.
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    Element Analysis of Ceramic Coatings under Spherical Indentation with Metallic Interlayer: Part II Ring Crack
    Minh-Quy LE, Seock-Sam KIM
    J. Mater. Sci. Technol., 2006, 22 (05): 594-598. 
    Abstract   HTML   PDF (2390KB)
    Spherical indentation of ceramic coatings with metallic interlayer was performed by means of axisymmetric finite element analysis (FEA). Two typical ceramic coatings with relatively high and low elastic modulus deposited on aluminum alloy and carbon steel were considered. The fracture mechanics of the ceramic coatings mechanisms due to occurrence of surface ring cracks extending traverse the coating thickness under spherical indentation are investigated within the framework of linear fracture mechanics. The J-integral associated to such cracks was computed. The evolution of J-integral vs the crack length and the indentation depth was studied. The effects of the interlayer, the coating and the substrate on the J-integral evolution were discussed. The results show that a suitable metallic interlayer can improve the fracture resistance of the coating systems under the same indentation conditions through reducing the J-integral.
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    Simulations of the Dependence of Gas Physical Parameters on Deposition Variables during HFCVD Diamond Films
    Aiying WANG, Kwangryeol Lee, Chao SUN, Lishi WEN
    J. Mater. Sci. Technol., 2006, 22 (05): 599-604. 
    Abstract   HTML   PDF (1019KB)
    During the growth of the hot filament chemical vapor deposition (HFCVD) diamond films, numerical simulations in a 2-D mathematical model were employed to investigate the influence of various deposition parameters on the gas physical parameters, including the temperature, velocity and volume density of gas. It was found that, even in the case of optimized deposition parameters, the space distributions of gas parameters were heterogeneous due primarily to the thermal blockage come from the hot filaments and cryogenic pump effect arisen from the cold reactor wall. The distribution of volume density agreed well with the thermal round-flow phenomenon, one of the key obstacles to obtaining high growth rate in HFCVD process. In virtue of isothermal boundary with high temperature or adiabatic boundary condition of reactor wall, however, the thermal round-flow was profoundly reduced and as a consequence, the uniformity of gas physical parameters was considerably improved, as identified by the experimental films growth.
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    Microstructure and Mechanical Properties of Nano-crystalline Al-8 wt pct Ni Alloy
    M.Abou Zied
    J. Mater. Sci. Technol., 2006, 22 (05): 605-610. 
    Abstract   HTML   PDF (465KB)
    Microstructure and mechanical properties of ball-milled Al-8 wt pct Ni ribbon have been investigated by X-ray diffraction (XRD) and continuous Vickers hardness test, respectively. The results indicate that, the main phases of this alloy are α-Al and orthorhombic-Al3Ni. The lattice parameter of α-Al increases with increasing milling time. From the elastic constant of Al, the average contrast factors of the (111), (200), (220), (311) and (222) Bragg0s reflections for pure edge and pure screw dislocations in fcc crystals with a/2<110>{111} slip system were calculated. The average grain size and dislocation parameters as a function of milling time have been investigated using the modified Williamson-Hall plot and the Warren-Averbach equation, respectively. An attempt has been made to correlate the micro-hardness of milled ribbon with their grain size through the Hall-Patch relationship: HV0:01 = 742.45 < D >-1/2 +401.55 (kg/mm2).
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    Hot Deformation Behavior of 2124 Al Alloy
    S.Ramanathan, R.Karthikeyan, V.Deepak Kumar, G.Ganesan
    J. Mater. Sci. Technol., 2006, 22 (05): 611-615. 
    Abstract   HTML   PDF (807KB)
    The mechanical behavior of 2124 Al alloy produced by powder metallurgy was investigated with compression test at different temperatures and strain rates. The tests were performed in the temperature range of 300℃~500℃ and at strain rates from 0.001 s-1 to 1.0 s-1. The compression flow curves exhibited an initial sharp increase with strain, followed by monotonous hardening. The maximum stress decreased with decreasing strain rate and increasing temperature. The hot deformation characteristics of the material were studied using processing maps. The domain of safety and unsafe regime were identified and validated through microstructural examination.
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    Microstructural Evolution of Ti-5.6Al-4.8Sn-2Zr-1Mo-0.35Si-0.7Nd Titanium Alloy with Carbon Additions
    Shangzhou ZHANG, Yuan GAO, Ziquan LIU, Yuyin LIU, Rui YANG
    J. Mater. Sci. Technol., 2006, 22 (05): 616-620. 
    Abstract   HTML   PDF (1529KB)
    The effect of carbon addition on microstructural evolution was studied in a near-α titanium alloy (Ti-5.6Al-4.8Sn-2Zr-1Mo-0.35Si-0.7Nd). It was found that flake and ribbon titanium carbides with a NaCl crystal structure formed in the as-cast alloys with carbon additions of over 0.17 wt pct. Flake carbide particles are the product of eutectic transformation and precipitate from the high-temperature β phase. The ribbon carbide particles are primary phases formed prior to the nucleation of any metallic phases. The as-cast alloys with carbide precipitation after heat-treatment at βt-30℃ followed by water quenching showed the spheroidization of α lamellae and partial dissolution of carbide particles. After annealing at βt+15℃, carbide particles are mostly distributed at the grain boundary and spheroidized through mixed grain boundary plus bulk diffusions.
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    Formation of AlN from Secondary Al Resources
    M.Bahgat, M.Radwan, F.E.Farghaly
    J. Mater. Sci. Technol., 2006, 22 (05): 621-624. 
    Abstract   HTML   PDF (1176KB)
    Synthesis of AlN by NH4Cl-assisted direct nitridation of secondary Al resources was studied. Aluminum alloy scrap contained Mg and Zn element was used. Milled Al scrap (-1 mm) was mixed with NH4Cl and heated at 1000℃ for 1 h in presence of 1 L/min N2 flow gas. The nitrided product was evaluated by X-ray diffraction semi-quantitative analysis and scanning electron microscopy (SEM). Aluminium nitride of 90.5% concentration was obtained with a hexagonal crystalline form. AlN is mostly formed in nano-whisker morphology (50~150 nm) which is homogenously distributed.
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    Mechanical and Transformation Behaviors of a C-Mn-Si-Al-Cr TRIP Steel under Stress
    Xiaodong WANG, Baoxu HUANG, Yonghua RONG, Li WANG
    J. Mater. Sci. Technol., 2006, 22 (05): 625-628. 
    Abstract   HTML   PDF (565KB)
    Transformation induced plasticity (TRIP) steels combine high strength and excellent ductility, making them suited for application in crash-relevant parts in the automotive industry. However, the high Si contents in the conventional TRIP steel will generate surface defects on the hot rolled strip, which is difficult to process in continuous galvanizing lines. In order to solve the above problem the TRIP steel with the addition of Al replacing majority of Si was designed. In the present paper, the volume fraction of various phases in a C-Mn-Si-Al-Cr TRIP steel was determined by metallographic examination and X-ray diffraction analysis, and the multi-phase microstructures were characterized using an atomic force microscope based on their height difference. Tensile tests were performed at different temperatures ranging from -40℃ to 90℃. The results show that transition temperature MSσ in the present TRIP steel cannot be determined due to its lower volume fraction of retained austenite, different from the conventional TRIP steel. While the yield stress and tensile strength at different temperatures are higher than those of the conventional TRIP steel, which is attributed to the addition of Cr. In order to evaluate the effect of martensitic transformation on the total elongation, the sample without retained austenite obtained by quenching in liquid nitrogen was carried out under tensile test. The results indicate that the elongation of the original sample containing 9% retained austenite is about 20% higher than that of the sample quenched in liquid nitrogen, which demonstrates that the retained austenite plays an important role in improving the elongation of the TRIP steel.
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    Characterization of Tensile Strain Hardening Behaviors for 32Mn-7Cr-1Mo-0.3N Cryogenic Austenitic Steel
    Liang QIU, Ruidong FU, Cunyu WANG, Yangzeng ZHENG
    J. Mater. Sci. Technol., 2006, 22 (05): 629-633. 
    Abstract   HTML   PDF (999KB)
    The strain hardening behaviors of 32Mn-7Cr-1Mo-0.3N austenitic steel were characterized by a simple and effective method. The results show that Hollomon relationship is not applicable during total uniform deformation stage. The flow equation was proposed, lnσ=aexp(lnε=b)+c. The variation rates of strain hardening exponents with true strain at 77 K are obviously higher than that at other temperatures and the value of d2σ/dε2 becomes positive during high strain stage. The characters of this variation are principal reasons for increasing elongation at 77 K. The forming of mechanical twin as well as ε-martensite leads to a high elongation at 77 K.
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    Transformation, Deformation and Microstructure Characteristics of Ru50Ta50 High Temperature Shape Memory Alloy
    Zhirong HE, Fang WANG, Jing'en ZHOU
    J. Mater. Sci. Technol., 2006, 22 (05): 634-638. 
    Abstract   HTML   PDF (936KB)
    The basic martensitic transformation (MT) properties of Ru50Ta50 alloy, i.e. MT temperature (MTT), temperature hysteresis (ΔT), and MT heat (ΔH) were investigated in this paper. The effects of heat treatment and thermal cycling on MT behavior of Ru50Ta50 alloy, the deformation and microstructure characteristics of Ru50Ta50 alloy were also studied for its engineering application as high temperature actuator/sensor materials by means of differential scanning calorimetry, X-ray diffraction, transmission electron microscope, optical microscope, and hardness test. The results showed that a two-stage reversible MT takes place in Ru50Ta50 alloy. The two-stage MT starting temperatures (MS1 , MS2 ) and the temperature hysteresis (ΔT1, ΔT2) are 1047, 784 and 11, 14℃, respectively. No significant effect of aging treatment and thermal cycling on MTT and ΔT of Ru50Ta50 alloy were observed, but ΔH decreases slowly with increasing thermal cycles. The hardness and brittleness of Ru50Ta50 alloy are high. The deformation mode of RuTa alloys is twinning.
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    Approximate Design of Alloy Composition of Cathode Target
    Jun ZHANG, Yu ZHANG, Li LI, Guoqiang LIN, Chuang DONG
    J. Mater. Sci. Technol., 2006, 22 (05): 639-642. 
    Abstract   HTML   PDF (217KB)
    An empirical formula for composition demixing analysis in cathodic arc ion plating using alloy target is established based on the concepts of average charged state and relative demixing parameter. The level of composition demixing effect is presented by demixing degree of one element. For binary constituent alloy target, the composition change trend in coating is discussed and the limit of demixing degree for each element is determined. The content of one element with higher average charged state gets larger in coating than in alloy target, at meantime, the content of one element with lower average charged state gets less. For each one of the two constituents, the less the atom percent in alloy target, the larger the difference of its contents between the coating and the target. For triple constituent alloy target, the content change of one element with moderate average charged state is discussed in detail. Its content in coating getting larger or less is determined by the combination result of the contents of the other two elements in alloy target. For a given content of the element with moderate average charged state in triple alloy target, the content deviation level of that element from coating to alloy target will be not larger than that using binary alloy target containing only that element and one of the two others. According to the wanted coating composition, the composition design of alloy target is easily deduced from the formula.
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    Effects of Chloride Ion on the Texture of Copper and Cu-ZrB2 Coatings Electrodeposited from Copper Nitrate Solution in Different Plating Modes
    Dongming GUO, Min ZHANG, Zhuji JIN, Renke KANG
    J. Mater. Sci. Technol., 2006, 22 (05): 643-646. 
    Abstract   HTML   PDF (444KB)
    For the first time, the texture of copper and Cu-ZrB2 coatings produced from copper nitrate solution was studied. Chloride ion shows different effects on the deposit texture under direct current (DC) and pulse current (PC) conditions. Copper deposits are strongly <220> textured in DC plating with and without chloride ion. While in PC condition, the predominant texture shifts from <220> to <200> as the chloride ion concentration exceeds 20 mg/l. The addition of ZrB2 particles enhances the cathodic polarization of copper deposition, which improves the growth of (111) plane. However, this improvement can be eliminated by further addition of chloride ion.
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    Fatigue Damage Accumulation of Steel/rubber Composite
    Zhenhui TIAN, Huifeng TAN, Xingwen DU
    J. Mater. Sci. Technol., 2006, 22 (05): 647-650. 
    Abstract   HTML   PDF (522KB)
    The fatigue damage accumulation of [±20℃] laminated steel cord reinforced rubber composite under T-T loading was studied. Results indicate that the increase in the cyclic maximum strain exhibits three-stage tendency in the process of fatigue. The macroscopic fatigue damage initiates from the ends of steel cords in the form of cylindrical crack. Damage propagates along with the increase in crack numbers, the cord/matrix interface debonding and the growth of interply cracks. By using the dynamic creep as parameter, a linear fatigue damage accumulation model was established. This model can be used under dual loading conditions to estimate the residual fatigue life of the specimen.
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    Comparison between Double Crystals X-ray Diffraction and Micro-Raman Measurement on Composition Determination of High Ge Content Si1-xGex Layer Epitaxied on Si Substrate
    Lei ZHAO, Yuhua ZUO, Buwen CHENG, Jinzhong YU, Qiming WANG
    J. Mater. Sci. Technol., 2006, 22 (05): 651-654. 
    Abstract   HTML   PDF (496KB)
    It is important to acquire the composition of Si1-xGex layer, especially that with high Ge content, epitaxied on Si substrate. Two nondestructive examination methods, double crystals X-ray diffraction (DCXRD) and micro-Raman measurement, were introduced comparatively to determine x value in Si1-xGex layer, which show that while the two methods are consistent with each other when x is low, the results obtained from double crystals X-ray diffraction are not credible due to the large strain relaxation occurring in Si1-xGex layers when Ge content is higher than about 20%. Micro-Raman measurement is more appropriate for determining high Ge content than DCXRD.
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    TEM specimen preparation for Al-based amorphous alloys
    Hongwang YANG, Xinchun CHANG, Wanliang HOU, Jianqiang WANG
    J. Mater. Sci. Technol., 2006, 22 (05): 655-658. 
    Abstract   HTML   PDF (403KB)
    Transmission electron microscopy (TEM) is usually used to identify the amorphicity. However, some artifacts may be introduced due to improper TEM foil preparation. In this paper, three Al-rich metallic glasses with and without a glass transition were selected for characterizing the effect of the electropolishing condition on the as-quenched structure during TEM specimen preparation. It is shown that the occurrence of the modulated bright-dark structure under TEM observation is closely sensitive to the electropolishing condition, which suggests us being careful about the possible artifacts induced by specimen preparation when examining amorphous alloys under TEM.
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    Synthesis and Properties of Magnetic Nanoparticles
    Sixin LI, Jiancheng ZHANG, Yue SHEN, Bo NI, Jingang ZHANG
    J. Mater. Sci. Technol., 2006, 22 (05): 659-663. 
    Abstract   HTML   PDF (1208KB)
    The uniform mesoporous SBA-15 consisting of SiO2 with long-range channels offers an excellent host material to synthesize or assemble the magnetic nanocomposites, such as Fe, Ni. In this paper, highly dispersed and uniform iron nanoparticles were incorporated into the pore channels of SBA-15 through a newly developed strategy in which some kinds of coupling agents were used to entrap the nanoparticles into the silica framework. The X-ray diffraction (XRD), fourier transmission infrared spectroscopy (FTIR), high-resolution transmission electronic microscopy (HRTEM) and energy dispersive X-ray spectroscopy (EDX) were performed to further identify the successful incorporation and grafting of iron. Compared with other ordinary non-assembled magnetic nanoparticles, the assembled Fe nanoparticles with the diameter even in the size range of 5~6 nm still have better magnetic properties.
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    Dynamics of Polymeric Fluids: Part II The Molecular Theory of Die Swell: Correlation of Ultimate Die Swelling Effect to the Molecular Parameters and the Operational Variables
    Mingshi SONG, Qiang XU, Guixian HU, Sizhu WU
    J. Mater. Sci. Technol., 2006, 22 (05): 664-676. 
    Abstract   HTML   PDF (881KB)
    A general expression for the correlation of the simple shear (tan ) to the molecular parameters and the shear rate ( ) was deduced. It shows that the simple shear (tan ) may be resolved into free recoil (recoverable strain) and viscous heating (unrecoverable strain). The magnitudes of the simple shears for recoil (tan E) and (tan V) for viscous heating not only depended on the molecular parameters and the operational variables, but also on the exponential fractions of the recoverable (1- ) and unrecoverable ( ) conformations for recoil and viscous heating. Therefore the magnitudes of the simple shears (tan E) for recoil and (tan V) for viscous heating are, respectively, expressed as the partition function to the (1- )th power and the partition function to the ( )th power. Thus correlations of the total recoil and the ultimately recoverable strains to the molecular parameters [ , a, η0, GN0 and (1- )] and the operational variables ( ), (L=D) and tr) were deduced respectively, which show that at very different shear rates ( ) the polymeric liquids may exhibit a very different viscoelastic behaviors. After introducing the uniform two-dimensional extension, the definition of swelling ratio and the ratio of L to D [De=(L/D)], two expressions for the ultimate die swelling effect and the ultimate extrudate swelling ratio BEVT5 to the molecular parameters [ , a, η0, GN0 and (1- )] and the operational variables ( , (L/D) and tr) were obtained. The two correlation expressions were verified by the experimental data of high-density polyethylene (HDPE) which shows that the two correlation expressions can be used to predict the correlations of the ultimate extrudate swelling behaviors of polymeric liquids to the molecular parameters and the operational variables.
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    Field Emission Characteristics of Conducting Polymer Films Conditioned by Electric Discharge
    Guohong LAI, Zhenglin LI, Lan CHENG, Junbiao PENG
    J. Mater. Sci. Technol., 2006, 22 (05): 677-680. 
    Abstract   HTML   PDF (1024KB)
    A pure conducting polymer (PANI-CSA) film conditioned by an electric discharge was tentatively utilized as an cathode for emitting electrons under electric fields. The emission of electrons was observed using a phosphor (ZnO:Zn) screen excited by electrons from the conditioned film. The film morphology was investigated using a scanning electron microscope and it was found that undulate whisker-like sites formed on the surface. The emission was presumably due to the undulate whisker-like sites. The field enhancement factor was estimated to be as high as 1150. The electron emitting process of the PANI-CSA film conditioned by electric discharge was also discussed.
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    Fine machining of large-diameter 6H-SiC wafers
    Xiufang CHEN, Juan LI, Deying MA, Xiaobo HU, Xiangang XU, Minhua JIANG
    J. Mater. Sci. Technol., 2006, 22 (05): 681-684. 
    Abstract   HTML   PDF (457KB)
    Three main machining processes of large-diameter 6H-SiC wafers were introduced in this paper. These processes include cutting, lapping and polishing. Lapping causes great residual stresses and deep damage layer which can be reduced gradually with subsequent polishing processes. Surfaces prepared by mechanical polishing (MP) appeared a large number of scratches with depth of 5~8 nm. These scratches can be effectively removed by chemo-mechanical polishing (CMP). After CMP, extremely smooth and low damage layer surface with roughness Ra=0.3 nm was obtained. Atomic force microscopy (AFM) and optical microscopy were used to observe the surface morphology of samples and a high resolution X-ray diffractometer (HRXRD) was used for the crystal lattice perfection of the subsurface region. Changes of surface residual stresses during machining processes were investigated by HRXRD.
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    Susceptibility to Hot Cracking and Weldment Heat Treatment of Haynes 230 Superalloy
    C.M.Cheng, C.P.Chou, I.K.Lee, I.C.Kuo
    J. Mater. Sci. Technol., 2006, 22 (05): 685-690. 
    Abstract   HTML   PDF (2370KB)
    This study investigates the susceptibility of hot cracking and weldment heat treatment of Haynes 230 superalloy. The Varestriant test was conducted to evaluate this susceptibility. Welding was performed by gas tungsten arc welding (GTAW) and plasma arc welding (PAW) with stress relief heat treatment and solid solution heat treatment. A tensile test is then performed to measure the changes in the mechanical properties of the heat treated material. The results indicate that the number of thermal cycles does not affect the susceptibility of Haynes 230 superalloy to hot cracking. However, it does increase the strain. In weldment of heat treatment, stress relief annealing increases the yield strength and tensile strength of the welded parts. The section of the tensile specimens shows fibrous fractures on the welded parts, regardless of whether they are heat-treated.
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    Phase Transformation and Thermal Stability of Aged Ti-Ni-Hf High Temperature Shape Memory Alloys
    Xianglong MENG, Wei CAI, K.T.Lau, L.M.Zhou, Liancheng ZHAO
    J. Mater. Sci. Technol., 2006, 22 (05): 691-695. 
    Abstract   HTML   PDF (736KB)
    The use of Ni-rich TiNiHf alloys as high temperature shape memory alloys (SMAs) through aging has been presented. For Ni-rich Ti80-xNixHf20 alloys, their phase transformation temperatures are averagely increased more than 100 K by aging at 823 K for 2 h. Especially for the alloys with Ni-content of 50.4 at. pct and 50.6 at. pct, their martensitic transformation start temperatures (Ms) are more than 473 K after aging. TEM observation confirmed that some fine particles precipitate from the matrix during aging. The aged Ni-rich TiNiHf SMAs show the better thermal stability of phase transformation temperatures than the solutiontreated TiNiHf alloys. The fine particles precipitated during aging should be responsible for the increase of phase transformation temperatures and its high stability.
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    Kinetics of Silver Dissolution in Nitric Acid from Ag-Au0:04-Cu0:10 and Ag-Cu0:23 Scraps
    S.K.Sadrnezhaad, E.Ahmadi, M.Mozammel
    J. Mater. Sci. Technol., 2006, 22 (05): 696-700. 
    Abstract   HTML   PDF (3608KB)
    Kinetics of dissolution of silver present in precious metal scraps in HNO3 was studied in temperature range of 26~85℃. Dissolution rate of silver was much faster than that of copper at all temperatures. Effects of particle size, stirring speed, acid concentration and temperature on the rate of dissolving of silver were evaluated. Dissolution rate decreases with particle size and increases with temperature. Dissolving was accelerated with acid concentrations less than 10 mol/L. Concentrations greater than 10 mol/L resulted in slowing down of the dissolution rate. Shrinking core model with internal diffusion equation t/τ=1-3(1-x)2/3+2(1-x) could be used to explain the mechanism of the reaction. Silver extraction resulted in activation energies of 33.95 kJ/mol for Ag-Au0:04-Cu0:10 and 68.87 kJ/mol for Ag-Cu0:23 particles. Inter-diffusion of silver and nitrate ions through the porous region of the insoluble alloying layer was the main resistance to the dissolving process. Results were tangible for applications in recycling of the material from electronic silver-bearing scraps, dental alloys, jewelry, silverware and anodic slime precious metal recovery.
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    Electrical Relaxation in Mixed Alkali Bi2O3-K2O-Li2O-Fe2O3 Glasses
    E.E.Shaisha, Sh.F.El-Desouki, I.Shaltout, A.A.Bahgat
    J. Mater. Sci. Technol., 2006, 22 (05): 701-707. 
    Abstract   HTML   PDF (1039KB)
    A new glass system (Bi2O3)50(Fe2O3)10(Li2O)x(K2O)40-x, where x changes in steps of 5 mole fraction between 0 and 40, was selected to study the electrical relaxation and the mixed alkali effect (MAE) phenomena. Measurements of ac conductivity σac, dielectric permittivity ε' and loss factor tan± in the frequency range of 0.12~102 kHz and in the temperature range of 300~650 K were carried out. The temperature dependence of the ac conductivity shows a slow increasing rate at low temperature and high frequency and a rapid increase at high temperature and low frequency. At constant temperature, the ac conductivity is found to be proportional to ωs, where s is the frequency exponent, which is less than 1. Analysis of the conductivity data and the frequency exponent shows that the overlapping large polaron tunnelling (OLPT) model of ions is the most favorable mechanism for the ac conduction in the present glass system. The ac response, the dc conductivity and dielectric relaxation have the same activation energy and they originate from the same basic transport mechanism. The results of the dielectric permittivity show no maximum peak in the temperature and frequency range studied. This absence of maximum peak is an indication of non-ferroelectric behavior of all the studied samples. The MAE has been detected in the ac conductivity, which is the same as the classical MAE in the dc conductivity. The electrical parameters such as dielectric permittivity ε' and real dielectric modulus M' show a typical minimum deviation from linearity by about two orders of magnitude. The loss factor tanδ and the imaginary dielectric modulus M" are insignificantly dependent on composition even at the same transition temperature Tg.
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    External Pressure Forming and Buckling Analysis of Tubular Parts with Ribs
    Gang LIU, Xuelian YIN, Shijian YUAN
    J. Mater. Sci. Technol., 2006, 22 (05): 708-712. 
    Abstract   HTML   PDF (1125KB)
    Buckling and forming processes of tubes with varying slenderness ratio (ratio of length to diameter) under external hydraulic pressure were analyzed with three-dimensional finite element method (FEM) for studying tube external pressure forming (EPF). Buckling pressures for different tube blanks without mandrel were predicted, and an EPF of a carbon steel tube onto a mandrel with six ribs was simulated. Both thickness distribution and buckling pressure from the simulations were found to be in agreement with those from experiments. Buckling pressures are shown to be a function of the slenderness ratio. The tubular part with six ribs produced by EPF has a uniform thickness distribution, whose maximum thinning rate is only 5.9%.
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    A Numerical-analytic Method for Quickly Predicting Springback of Numerical Control Bending of Thin-walled Tube
    Mei ZHAN, He YANG, Liang HUANG
    J. Mater. Sci. Technol., 2006, 22 (05): 713-720. 
    Abstract   HTML   PDF (1820KB)
    Springback is one of important factors influencing the forming quality of numerical control (NC) bending of thin-walled tube. In this paper, a numerical-analytic method for springback angle prediction of the process was put forward. The method is based on springback angle model derived using analytic method and simulation results from three-dimensional (3D) rigid-plastic finite element method (FEM). The method is validated through comparison with experimental results. The features of the method are as follows: (1) The method is high in efficiency because it combines advantages of rigid-plastic FEM and analytic method. (2) The method is satisfactory in accuracy, since the field variables used in the model is resulting from 3D rigid-plastic FEM solution, and the effects both of axial force and strain neutral axis shift have been included. (3) Research on multi-factor effects can be carried out using the method due to its advantage inheriting from rigid-plastic FEM. The method described here is also of general significance to other bending processes.
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CN: 21-1315/TG
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