Started in 1985 Semimonthly
ISSN 1005-0302
CN 21-1315/TG
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      28 September 2000, Volume 16 Issue 05 Previous Issue    Next Issue
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    Research Articles
    Trend and development of semi-solid metal processing
    Xianfeng PAN, Haifeng ZHANG, Aimin WANG, Bingzhe DING, Keqiang QIU, Zhuangqi HU
    J. Mater. Sci. Technol., 2000, 16 (05): 453-460. 
    Abstract   HTML   PDF (1810KB)

    This paper reviewed the trend and development of semi-solid metal technique. The processes and mechanisms for producing slurry of SSM and its industrial applications have been summarized and discussed. Discussions on the basic rheological theory are presented for more applications. Further consideration of the development and application of SSM technique is also proposed.

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    Temperature fluctuation synthesis/simultaneous densification and microstructure control of titanium silicon carbide (Ti3SiC2) ceramics
    Zhimei SUN, Yanchun ZHOU
    J. Mater. Sci. Technol., 2000, 16 (05): 461-465. 
    Abstract   HTML   PDF (1392KB)
    A novel temperature fluctuation synthesis/simultaneous densification process was developed for the preparation of Ti3SiC2 bulk ceramics. In this process, Si is used as an in-situ liquid forming phase and it is favorable for both the solid-liquid synthesis and the densification of Ti3SiC2 ceramics. The present work demonstrated that the temperature fluctuation synthesis/simultaneous densification process is one of the most effective and simple methods for the preparation of Ti3SiC2 bulk materials providing relatively low synthesis temperature, short reaction time, and simultaneous synthesis and densification. This work also showed the capability to control the microstructure, e.g., the preferred orientation, of the bulk Ti3SiC2 materials simply by applying the hot pressing pressure at different stages of the temperature fluctuation process. And textured Ti3SiC2 bulk materials with {002} faces of laminated Ti3SiC2 grains normal to the hot pressing axis were prepared.
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    Synthesis of SiC/Al co-continuous composite by spontaneous melt infiltration
    Guangwei HAN, Di FENG
    J. Mater. Sci. Technol., 2000, 16 (05): 466-470. 
    Abstract   HTML   PDF (1318KB)
    Investigation has been made on the process of synthesizing SiC/Al co-continuous composite by spontaneous melt infiltration. It is found that nitrogen atmosphere is an indispensable factor for spontaneous infiltration of melt Al into SiC preform with continuous porosity. The critical temperature for spontaneous infiltration occurrence can be lowered and spontaneous infiltration rate increased by doping a small amount of Mg into the Al alloy. Adding fine SiO2 powders into the ceramic preform can play the similar role as Mg-doping by increasing wetting through the chemical reaction of 3SiO(2)+4Al=2Al(2)O(3)+3Si at the infiltration front. Infiltration rate can also be increased by Si-doping to lower the viscosity of the molten Al alloy. In addition, sufficient Si content in the molten Al is also indispensable to avoid the formation of Al4C in the synthesized composite.
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    Tensile elastic modulus, strength and fracture of delta-Al2O3f/Al alloy composites
    GuoZheng KANG, Qing GAO, Jixi ZHANG
    J. Mater. Sci. Technol., 2000, 16 (05): 475-480. 
    Abstract   HTML   PDF (1761KB)
    Based on the experimental and theoretical analysis, the tensile elastic modulus, strength and fracture characteristics of squeeze casting delta-Al2O3/Al alloy composites were studied. The fracture characteristics of composites were observed by SEM. The elastic modulus was predicted by the finite element method based on the energy equivalence principle, and the strength was predicted by the statistical integration average method using the maximum energy criterion of composite strength. In the prediction, the distribution density functions of the fiber's orientation and length were considered. These functions were gained by experimental measurement. It is shown that the predicted results are in agreement with the experimental values well and the microstructure feature of composites controls the fracture characteristics.
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    Preparation and characterization of BAS reinforced with SiC platelets
    Jiancun RAO, Jiancheng GU, Yu ZHOU, Feng YE, Tingquan LEI
    J. Mater. Sci. Technol., 2000, 16 (05): 481-485. 
    Abstract   HTML   PDF (1586KB)
    BAS glass-ceramic powders were prepared by sol-gel processing. SiC platelets reinforced BAS glass-ceramic matrix composites with high density and uniform microstructure could be made using hot-pressing method. The related processing parameters were studied in this work, including effects of additional seed on transformation from H to M of barium aluminosilicate. DTA method was used to determine exact time to press mixture powders during hot-pressing for the purpose of effective densification. Microstructure and mechanical properties of the composites were investigated by mean of SEM, XRD and TEM techniques as well as three points bending test and single edge notched beam measurement. The results showed that the flexural strength and fracture toughness value of the BAS glass-ceramic matrix composites could be effectively improved by the addition of the SiC platelets. But the relative densities of composites were slightly decreased. The main toughening mechanism is crack deflection, platelets' pull-out and bridging. The increased value of flexural strength is contributed to the load transition effect from matrix to SiC platelets.
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    Quasi-carbon fibers and the composites
    Lulu SONG, Weihong ZHONG, Zuoguang ZHANG, Zhijie SUN
    J. Mater. Sci. Technol., 2000, 16 (05): 486-490. 
    Abstract   HTML   PDF (1250KB)
    The aim of this report is to study the properties of quasi-carbon fibers (QCF) prepared from the PAN fiber precursor by pyrolysis at a temperature between 400 degrees C and 1200 degrees C. The resistivity of QCF with different heat-treated temperature (HTT) was investigated by a Hall-35 testing system, and the flexural properties of the result composites (QCFC) are also discussed. In addition, the scanning electronic microscope (SEM) was utilized to observe the surface morphology of QCF and the fracture section of QCFC obtained from flexural testing.
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    Investigation of transformation for ultrahigh strength steel Aermet 100
    Liuding WANG, Lin LIU, Chengxi AO, Xiaojun LIU, Changle CHEN, Mokuang KANG
    J. Mater. Sci. Technol., 2000, 16 (05): 491-494. 
    Abstract   HTML   PDF (925KB)
    The heat-stagnation curves of two quenched and cryogenically treated ultrahigh strength AF1410 and Aermet 100 steels during heating and cooling in furnace have been measured. The results showed that the curve displayed an abnormal terrace in the course of heating, and within the temperature range corresponding to the terrace, the formation and growth of both cementite Fe3C and secondary hardening phase M2C in the steel make the carbon content in matrix obviously vary. It is in the region of terrace that the optimum combination of tensile strength and fracture toughness is obtained because of secondary hardening. Based on the measured heat-stagnation curve, several transformation points have been determined and the correctness was also verified by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Furthermore, the influence of heating rate and tempering temperature on the crystal structure and stability of austenite has been studied.
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    Electronic structures and alloying behaviors of ferrite phases in high Co-Ni secondary hardened martensitic steels
    Guoying ZHANG, Meiguang ZENG, Guili LIU
    J. Mater. Sci. Technol., 2000, 16 (05): 495-498. 
    Abstract   HTML   PDF (798KB)
    The electronic structure of ferrite (tempered martensite phase) in high Co-Ni secondary hardened martensitic steel has been investigated. The local density of states (LDOS) of alloying elements in the steel displays the relationship between solid solubility and the shape of the LDOS. The bond order integral (BOI) between atoms in the steel shows that the directional bonding of the p orbital of Si or C leads to the brittleness of the steel. At last, Sigma BOI between atoms demonstrate that C, Co, Mn, Cr, Mo, Si strengthen the alloyed steel through solid-solution effects.
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    Role of disclinations and nanocrystalline state in the formation of quasicrystalline phases on mechanical alloying of Cu-Fe powders
    R.Subramanian, S.S.Raznakrishnan, P.Shankar
    J. Mater. Sci. Technol., 2000, 16 (05): 499-503. 
    Abstract   HTML   PDF (1097KB)
    Elemental powders of Cu and Fe were ball milled for various time durations up to 100 h. The various stages of forced alloying by ball milling, leading to instability of elemental crystalline phases and formation of quasicrystalline phases were monitored using X-ray diffraction. Diffusion of Fe into the Cu matrix is proposed as the cause which triggers the instability of crystalline phases and leads to the formation of quasicrystalline phases after 10 h of milling. Milling for 100 h resulted in two different quasicrystalline phases with different lattice constants. Role of the nanocrystalline microstructure as an important criterion for the destabilisation of crystalline phases is explained. It is suggested that the formation of nanocrystalline microstructure and their subsequent transformation into quasicrystalline phases may be associated with a continuous increase in the disclination content of the system, which had formed as a result of continued milling and mechanical deformation.
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    Relationship among parameters evaluating stress corrosion cracking
    Wuyang CHU, Lijie QIAO, Yanbin WANG
    J. Mater. Sci. Technol., 2000, 16 (05): 504-508. 
    Abstract   HTML   PDF (1014KB)
    The threshold stress, sigma(c), for sulfide stress corrosion cracking (SCC) of seven pipeline steels and five other steels, the critical stress, Sc, for seven pipeline steels and two drill rod steels with various strengths and the susceptibility to SCC, I-RA or sigma(f)(SCC)/sigma(f), for four pipeline steels, two drill rod steels and five other steels were measured. The results showed that there are no definite relationships among sigma(c), S-C and I-RA or sigma(f)(SCC)/sigma(f).
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    Oxidation behavior of Fe-Ni-Co based superalloys and influence of yttrium addition
    Jiansheng WU, Laming ZHANG, Junbiao ZHOU, Yin XU, Shaowei ZHANG
    J. Mater. Sci. Technol., 2000, 16 (05): 509-513. 
    Abstract   HTML   PDF (2163KB)
    The oxidation behavior of three Fe-Co-Ni based superalloys with different yttrium additions were investigated at 650 degrees C in air. The oxidation kinetics of the three alloys follows parabolic law initially, then follows linear law. The oxide scale formed on all three alloys consists mainly of Co dissolved Fe3O4 and partly of FeO and Fe2O3 in which Fe3O4 acts as a protective layer. An yttrium addition into the Fe-Co-Ni based superalloys improves their oxidation resistance by reducing the micro-defects in the scales. Thus, the weight gains of the alloys during the oxidation are reduced, and the transition of parabolic law to linear law is postponed. Pegging was observed on the cross section of alloy with 0.08 wt pet yttrium addition after the oxidation.
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    Solute redistribution in directional melting process
    Wanqi JIE, Xiping GUO
    J. Mater. Sci. Technol., 2000, 16 (05): 514-516. 
    Abstract   HTML   PDF (430KB)
    The solute redistribution in directional melting process is theoretically studied. Based on quantitative evaluations, uniform solute distribution in liquid and a quasi-steady solute distribution in solid are supposed. The discussion on the solute balance comes to a simple model for the solute redistribution in directional melting process. As an example, the variation of liquid composition during melting process of carbon steel is quantitatively evaluated using the model. Results show that the melting of an alloy starts at solidus temperature, but approaches the liquidus temperature after a very short transient process.
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    Refining effect of boron on hypoeutectic Al-Si alloys
    Li WANG, xiufang BIAN
    J. Mater. Sci. Technol., 2000, 16 (05): 517-520. 
    Abstract   HTML   PDF (1352KB)
    Several concepts of the grain refinement mechanism of B on hypoeutectic Al-Si alloys have been adopted: the refining effect of B on the alpha-Al and eutectic Si with the different additions of Al-B master alloys made at 850 degrees C was investigated, and the Al-B master alloys formed under different temperature conditions have been studied to explore the morphologies of AlB2 particles, slowly cooled sample with addition of Al-B was made to explore the refinement mechanism. Al-B master alloy can refine not only alpha-Al, but eutectic Si. Theoretical analysis indicates that, although AlB2 does not take part directly in the nucleation process in pure Al in the presence of Si, it provides a substrate for precipitation of a small content of Si from which alpha-Al will grow without any undercooling. When the temperature decreases to eutectic line, AlB2 subsequently nucleates eutectic Si, AlB2 particles appear in two different morphologies, namely, hexagonal platelet and tetradehedron morphology which depend on the processing temperature conditions.
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    Negative temperature coefficient of resistivity in bulk nanostructured Ag
    Yushuang LIU, Chimei MO, Weili CAI
    J. Mater. Sci. Technol., 2000, 16 (05): 521-524. 
    Abstract   HTML   PDF (799KB)
    The change of the temperature coefficient of resistivity (cr) with the particle size, d(p), and the grain size, d(c), in the nanostructured Ag bulk samples was investigated. d(p) and d(c) were controlled by heating the nano-Ag powders over the temperature range from 393 to 453 K. The electrical resistance measurements of the nanostructured Ag bulk samples obtained by compacting the Ag powders after heat treatments showed a change in the sign of alpha with d(p) and d(c). When d(p) and d(c) are smaller or equal to 18 and 11 nm below room temperature or 20 and 12 nm above room temperature, respectively, the sign of the temperature coefficient of resistivity changes from positive to negative. The negative alpha arises mainly from the high resistivity induced by the particle interfaces with very lowly ordered or even disordered structure, a large volume fraction of interfaces and impurities existing in the interfaces, and the quantum size effect appearing in the nano-Ag grains.
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    Research on resonance mechanism of arc-ultrasonic
    Chunlei ZHANG, Minsheng WU, Honpei HAO, Z, ong HAN
    J. Mater. Sci. Technol., 2000, 16 (05): 525-528. 
    Abstract   HTML   PDF (1009KB)
    As a transmission medium, welding are can be modulated to emit ultrasonic energy by exerting high-frequency electric current. The frequency of exciting electric current has notable influence on the signals recorded by the sensors and the metallographic structures of the welds. The resonance phenomenon of are-ultrasonic has been found in the experiment. Both the resonance mechanism and the distribution of resonance frequency are discussed by the built vibration equation.
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    New dispersed phase of electrorheological fluids: TiO2 coating graphite particles
    Sujuan XU, Biao WANG, Shouqiang MEN, Kunquan LU
    J. Mater. Sci. Technol., 2000, 16 (05): 529-530. 
    Abstract   HTML   PDF (379KB)
    We have prepared novel coated particles, with a conductor graphite core and a dielectric TiO2 coating, as the dispersed phase of electrorheological fluids. One order of magnitude enhancement in the shear stress is obtained by using such composite particles, when it is compared with that of TiO2 particles. The experimental results show a way to get excellent ER system.
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    Annealing effect on mechanical properties of Ti51Ni13Pd36 high temperature memory alloy
    Huibin XU, Shuqiang HU, Chengbao JIANG, Shengkai GONG
    J. Mater. Sci. Technol., 2000, 16 (05): 531-533. 
    Abstract   HTML   PDF (730KB)
    The high temperature shape memory alloy Ti51Ni13Pd36 was subjected to a cold working and annealing treatment to improve its mechanical properties and the shape memory effect. It was found that recovery of the cold worked alloys started at near 673 K and the recrystallization temperature was at about 748 K. The grain size decreased with the increase of annealing temperature below 923 K and then increased when above 923 K. The smallest average grain size of about 3.5 mu m, which is approximately 10 times smaller than the hot rolled one, permitted the best combination of the mechanical properties in the alloy annealed at 923 K for 1 h. The cold rolling raised the peak temperature of reverse transformation. This temperature dropped very sharply when the specimen was annealed at temperatures higher than 673 K.
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    Effects of Ta addition on NiTi shape memory alloys
    Jianlu MA, Jiangnan LIU, Zhengpin WANG, Fei XUE, Kuang-Hsi WU, Zhongjie PU
    J. Mater. Sci. Technol., 2000, 16 (05): 534-536. 
    Abstract   HTML   PDF (748KB)
    The effect of Ta addition on the martensitic transformation characteristics and the X-ray visibility on NiTi shape memory alloy have been studied in (Ni51Ti49)(1-x)Ta-x system. It was found that the transformation temperatures of the Ni51Ti49 binary alloy increased drastically by an addition of 0 similar to 4 at. pet Ta, but only slightly when the concentration exceeded 4 at. pet, the addition of Ta greatly decreases the sensitivity of the martensitic transformations to the variation in the Ni-Ti ratio. The addition of Ta to the NiTi binary alloy can improve its X-ray visibility.
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    Factors affecting transformation temperatures in Fe-Mn-Si-Cr-Ni shape memory alloy
    Yuhua WEN, Ning LI, Mingjing TU
    J. Mater. Sci. Technol., 2000, 16 (05): 537-539. 
    Abstract   HTML   PDF (681KB)
    The effects of prestrain and annealing temperature on phase transformation temperatures in Fel4Mn5Si8Cr4Ni shape memory alloy have been studied. The results showed that when the annealing temperature was 673 K, both the A(f) and the M-s temperatures increased appreciably as the prestrain increased, the A, temperature increased slightly with increasing prestrain, the resistivity difference at 303 K between the heating and cooling curve also increased with increasing prestrain, which agreed with the recovery strain. The shape memory effect in Fe-Mn-Si-Cr-Ni shape memory alloy is caused by the stress-induced gamma --> epsilon martensite transformation and its reverse transformation. When the prestrain was 10%, the M-s temperature decreased remarkably as the annealing temperature increased.
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    Size effect of electromagnetic constitutive characteristics of ultrathin Al films
    Xuedong BAI, Meng CHEN, Lishi WEN, R.F.Huang
    J. Mater. Sci. Technol., 2000, 16 (05): 540-542. 
    Abstract   HTML   PDF (485KB)
    The ultrathin aluminum films with thickness in the range of 2 similar to 60 nm have been deposited by de magnetron sputtering apparatus. Reflectance and transmittance of the obtained samples were measured with a WFZ-900-D4 UV/VIS spectrophotometer. The optical constant (n, k) and permittivity (epsilon', epsilon ") were determined by applying Newton-Simpson recurrent substitution method. The results indicate that the electromagnetic constitutive characteristic of ultrathin aluminum films is a function of thickness and has obvious size effect.
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    Nucleation of cold rolled FeCo alloy during annealing and its influence on the formation of recrystallization texture
    Guohui ZHU, Weimin MAO, Yongning YU
    J. Mater. Sci. Technol., 2000, 16 (05): 543-545. 
    Abstract   HTML   PDF (809KB)
    The orientation distribution of recrystallization grains formed during annealing, as well as their misorientation relationship to the deformation matrix in cold rolled FeCo alloy have been investigated. It was found that most of the recrystallization nuclei were located near the boundary area with rather random orientations, and their misorientation angles to the deformation matrix were generally very high. However a few nuclei were also observed inside the deformation grains, to which they had very similar orientations. Therefore the misorientation angles between the nuclei and the deformation matrix were generally very low. The orientation and the misorientation distributions of the nuclei have very strong influence on the recrystallization process which could result in a very weak recrystallization texture. The corresponding mechanism is discussed.
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    Microstructure changes during cavitation erosion for a steel with metastable austenite
    Wantang FU
    J. Mater. Sci. Technol., 2000, 16 (05): 546-548. 
    Abstract   HTML   PDF (788KB)
    The characteristics of microstructure changes during cavitation erosion (CE) were investigated by the use of XRD and TEM analyses for steel (ZG0Cr13Mn8N) with metastable austenite. The results show that the microstructure of the surface layer of the specimens consists of alpha'-martensite, metastable austenite and a few g-martensite before CE. CE obviously increases dislocation density and straight or planar dislocations on the surface, and induces gamma --> epsilon, epsilon --> alpha' and gamma --> alpha'-martensitic transformation.
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ISSN: 1005-0302
CN: 21-1315/TG
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