Started in 1985 Semimonthly
ISSN 1005-0302
CN 21-1315/TG
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      28 September 1995, Volume 11 Issue 5 Previous Issue    Next Issue
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    Progress in Numerical Simulation of Solidification Process of Shaped Casting
    Baicheng LIU; Houfa SHEN and Wenzhen LI(Department of Mechanical Engineering, Tsinghua University, Beijing, 100084, China)(To whom correspondence should be addressed)
    J. Mater. Sci. Technol., 1995, 11 (5): 313-322. 
    Abstract   HTML   PDF (4220KB)
    Solidification simulation of manufacturing shaped casting which plays an important role in asSuring the soundness and quality of castings, in minimizing the trial production time and in reducing the manufacturing cost becomes one of the hottest topics of the new research frontiers of foundry technology at home and abroad. Practical three dimensional computer numerical simulation system for temperature distribution during solidification as well as shrinkage cavity and porosity prediction has already been put into application all over the world. Further fundamental researche5 on fluid flow, thermal stress and micro-modeling as well as practical approaches of numerical simulation of solidification process of shaped castings for routine analysis of foundry industry are still underway.
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    Effect of Accelerated Ageing on the Dielectric Behaviour of Some Varnish Dry Films
    S.A.El-Henawii(Faculty of Science, Helwan University, Cairo, Egypt)
    J. Mater. Sci. Technol., 1995, 11 (5): 323-328. 
    Abstract   HTML   PDF (489KB)
    The variation of the dielectric constant e' and the dielectric loss e" of polyesteramide, alkyd polyesteramide and alkyd varnish dry films were measured within the frequency range from 105 to 107 Hz and the temperature range from 20 to 50℃. The varnish films were subjected to accelerated ageing by heating at 110℃ for diferent durations. The efect of the accelerated ageing on e' and e" were measured. The activation energy and the entropy change of dielectric relaxation for the dry films before and after ageing were also calculated. All the results obtained were recorded and discussed in correlation with the molecular structure of the investigated varnishes.
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    Spray Atomized and Codeposited Al-Li Based Metal-matrix Composites Processing and Properties
    E. Raskin; S. Nayim;M.Polak and J.Baram(Materials Engineering Dept., Ben-Gurion University of the Negev, Beer-Sheva, Israel )A.N.Sembira(Nuclear Research Center, Negev, Beer-Sheva, Israel)(To whom correspondence should be addressed)
    J. Mater. Sci. Technol., 1995, 11 (5): 329-339. 
    Abstract   HTML   PDF (4461KB)
    In spray atomization and codeposition, a molten stream of metal is disintegrated into a fine dispersion of droplets by high velocity gas jets. The resulting semi-solidified droplets are directed towards a substrate where they impact and collect as rapidly solidified splats. Relatively high rates of solidification are achieved as a result of the thinness of the splats and the rapid heat extraction during flight and upon impacting with the substrate. The processing method uses codeposition of the metallic semi-solidified droplets (metallic matrix) with the injected reinforcement ceramic particles. In the present paper, the microstructures, mechanical properties, interfacial properties, thermal stability and aging behaviour of spray atomized and codeposited Al-Li-X MMC's (injected X=SiC, Al2O3) are reported and correlated to the processing conditions.
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    A Fractal Study on Brittle-Ductile Transition for Ti-24Al-11Nb Alloy
    Guoliang CHEN;Yandong WANG;Yuanding HUANG;Zuqing SUNand Wangyue YANG(State Key Lab. for Adv. Met, Mater., University of Science and Technology Beijing, Beijing, Beijing, 100083, China)(To whom correspondence should be addressed)
    J. Mater. Sci. Technol., 1995, 11 (5): 340-344. 
    Abstract   HTML   PDF (3038KB)
    The mechanical behaviours of Ti-24Al-11Nb alloy in the brittle-ductile transition (BOT) have been investigated by using three-point bending tests. The temperature dependence of the fractal dimensions and fractal characterization of fracture surfaces are presented. The probable mechanism controlling BDT of intermetallic alloys are proposed according to fractal geometry.Additionally. it is found that there is a positive relationship between the fractal dimension and fracture toughness in BDT for Ti-24Al-11Nb alloy
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    Sintering Caβ″/β/α-Al_2O_3 High Temperature Oxygen Sensor
    Yanruo HONG;Liansheng LI and Fengge ZHANG(National Laboratory on Solid Electrolytes and Metallurgical Measurements, University of Science and Technology Beijing, Beijing, 100083, China)(To whom correspondence should be addressed)
    J. Mater. Sci. Technol., 1995, 11 (5): 345-348. 
    Abstract   HTML   PDF (256KB)
    An extended-life and ultra-low oxygen sensor has been fabricated by using polycrystalline Caβ″/β/α-Al2O3 as a solid electrolyte. Five reference electrodes CaO+O2, Caβ″/β/α-Al2O3 (powder)+O2,Cr+Cr2O3, Nb+NbO and Mo+MoO2 were tested in order to select a better reference electrode for this sensor. The limit of determining oxygen activity and the extended-life of the sensor were also tested in this study.
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    Fluence Dependence of Mean Sputter Depth for Bombarded Pt-Cu and ~(10)B-~(11)B Binary Materials
    Liping ZHENG(Shanghai Institute of Nuclear Research, Chinese Academy of Sciences, Shanghai 201800, China)(To whom correspondence should be addressed)Risheng LI(Laboratory of Atomic Imaging of Solids, Institute of Metal Research,Chinese Academy of Sciences
    J. Mater. Sci. Technol., 1995, 11 (5): 349-352. 
    Abstract   HTML   PDF (356KB)
    The mean sputter depth depends on the surface composition gradient during ion implantation.For the high fluence ion implantation into a Pt-Cu alloy, the surface composition gradient of Cu is so large that the difference in mean sputter depth between Pt and Cu, is significant. However, for the high fluence ion implantation into 10B-11B isotope mixture, the surface composition gradient of 10B is so small that the difference in mean sputter depth between 10B and 11B is insignificant.
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    Study of Carbon-poor Regions of Austenite during Bainitic Incubation Period by SAM
    Xiaolei WU;Husheng JIA;Xiyan ZHANG and Mokuang KANG(Dept. of Materials Science & Engineering, Northwestern Polytechnical University, Xi'an, 710072, China)(To whom correspondence should be addressed)
    J. Mater. Sci. Technol., 1995, 11 (5): 353-357. 
    Abstract   HTML   PDF (457KB)
    The variation of carbon composition in undercooled austenite during bainitic incubation period has been investigated in 40CrMnSiMoVA by scanning auger microprobe (SAM). The results show that the outstanding diffusion and redistribution of carbon occur in isothermally reacted specimens. This leads to the formation of carbon-poor regions (CPR) near austenite grain boundaries and in austenite grains. The carbon content in CPR exceeds the equilibrium carbon composition of ferrite. Furthermore, it is indicated that the existence of CPR is thermodynamically possible.
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    Effects of Hydrogen on Behaviour of Low Cycle Fatigue of 2.25Cr-1Mo Steel
    Guangwei HAN and Di FENG (Central Iron & Steel Research Institute, Beijing, 100081, China)(To whom correspondence should be addressed)Yujiu SONG(Dept. of Mater. Sci. & Eng., Xi'an Jiaotong University, Xi'an 710049, China)
    J. Mater. Sci. Technol., 1995, 11 (5): 358-362. 
    Abstract   HTML   PDF (2284KB)
    The effects of hydrogen atoms on behaviour of low cycle fatigue of 2.25Cr-1Mo steel have been investigated in present work. The results indicate that the cyclic softening rate and low cycle fatigue life are respectively increased and reduced remarkably by hydrogen atoms. In addition, hydrogen atoms make the original stress amplitude of low cycle fatigue increase, which is because of the drag effect of hydrogen atoms on the moving dislocations. Analyses using electron microscopy show that hydrogen atoms accelerate crack initiation of low cycle fatigue from inclusion and transfer the source of low cycle fatigue crack from the surface of specimen to the inclusion, which results in the marked decrease of low cycle fatigue life. The increase of cyclic softening rate for hydrogen charged specimen is due to hydrogen atoms accelerating the initiating and growing of microvoids from the secondary phase particles in the steel. The reducing of the drag effect of hydrogen atoms on moving dislocations is also helpful to the increase of the cyclic softening rate.
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    Comparative Study of Bond Orientational Order and Pair Analysis in Describing Local Symmetry in Liquid Metals
    Kuiying CHEN; Hongbo LIU and Zhuangqi HU(State Key Lab. of RSA, Institute of Metal Research, Chinese Academy of Sciences, Shenyang, 110015, China)(To whom correspondence should be addressed)
    J. Mater. Sci. Technol., 1995, 11 (5): 363-368. 
    Abstract   HTML   PDF (594KB)
    The similarity and difference between the bond orientational order and pair analysis methods have been first identified with the help of molecular dynamics simulation and the steepest descent minimization of potentials techniques. The binary liquid K-Rb alloys are chosen as an example.Results show that the bond orientational order parameters may be a relevant direct measurement on the perfection of an icosahedron. The PA formula (1551 bonded pairs) is, however, responsible for the total number of various icosahedra. In addition, it is found that pair analysis approach is more sensible to local structure than that for bond orientational order.
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    Electronic Structure Effect on Model Cluster for L1_2 Structure of Al_3Ti Intermetallic Compound with an Addition of Alloying Elements Fe, Ni and Cu
    Senying LIU; Rongze HU; Dongliang ZHAO and Chongyu WANG(Central Iron and Steel Research Institute, Beijing, 100081, China)(To whom correspondence should be addressed)Ping LUO(National Research Cent or Certified Materials, Beijing, 100013, China)Zhongjie P
    J. Mater. Sci. Technol., 1995, 11 (5): 369-372. 
    Abstract   HTML   PDF (328KB)
    By use of self-consistent field Xα scattered-wave (SCF-Xα-SW) method, the electronic structure was calculated for four models of Ti4Al14X (X=Al, Fe, Ni and Cu) clusters. The Ti4Al14X cluster was developed based on L12 Al3Ti-base intermetallic compound. The results are presented using the density of states (DOS) and one-electron properties, such as relative binding tendency between the atom and the model cluster, and hybrid bonding tendency between the alloying element and the host atoms. By comparing the four models of Ti4Al14X cluster, the effect of the Fe, Ni or Cu atom on the physical properties of Al3Ti-based L12 intermetallic compounds is analyzed. The results indicate that the addition of the Fe, Ni or Cu atom intensifies the relative binding tendency between Ti atom and Ti4Al14X cluster. It was found that the Fermi level (EF) lies in a maximum in the DOS for Ti4Al14Al cluster; on the contrary, the EF comes near a minimum tn the DOS for Ti4Al14X (X=Fe, Ni and Cu) cluster. Thus the L12 crystal structure for binary Al3Ti alloy is unstable, and the addition of the Fe, Ni or Cu atom to Al3Ti is benefical to stabilize L12 crystal structure. The calculation also shows that the Fe, Ni or Cu atom strengthens the hybrid bonding tendency between the central atom and the host atoms for Ti4Al14X cluster and thereby may lead to the constriction of the lattice of Al3Ti-base intermetallic compounds.
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    Dielectric Behaviour of Mixtures of Polyethylene Glycol with Propionaldehyde and Benzaldehyde
    I.M.El-Anwar and I.Z.Selim(Physical Chemistry Dept., National Research Center, Dokki, Cairo, Egypt)( To whom correspondence should be addressed)(To whom correspondence should be addressed)A.A.Foad(Faculty of Science, Helwan University, Helwan, Cairo, Egyp
    J. Mater. Sci. Technol., 1995, 11 (5): 373-379. 
    Abstract   HTML   PDF (569KB)
    The dielectric constant e' and dielectric loss e" of several mixtures of propionaldehyde-polyethylene glycol (system 1) and benzaldehyde-polyethylene glycol (system II) have been measured within the frequency band 105-107 Hz and the temperature range 20-50℃. The dielectric behaviour is discussed. on the other hand, the dielectric relaxation time T. activation energy △He, and entorpy change △Se for the dielectric relaxation as well as activation energy of viscous flow △Hv are calculated for the same temperature range. It is suggested that the observed increase in T values with glycol content is due to an increase in the hydrogen bonding in the aggregates or clusters which would be formed between the carbonyl group of the aldehyde and the hydrogen atoms from the glycot molecules. In addition, the higher values of T, △He, and △Se in case of system (II) than that in case of system (I) may be due to the greater volume of the aggregates and the stronger dipole-dipole forces in system (II) compared with those in system (I).
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    Wear Characteristics of Zirconia Toughened Ceramic Drawing Dies
    Zhigang CHEN (Ceramic Research Lab., Jiangsu University of Science and Technology, 212013, Zhenjiang, China)
    J. Mater. Sci. Technol., 1995, 11 (5): 380-384. 
    Abstract   HTML   PDF (1311KB)
    Wear resistance of several zirconia toughened ceramics in comparison with a metal-ceramic CoWC has been studied in drawing wire field test. Result indicates that the harder the ceramic die, the longer the service life. Excellent wear resistance of ceramic die is obtained with a very high hardness (19 GPa). The service life is nearly three times that of Co-WC die. SEM observation on wear surfaces showed that material removal is mainly caused by plastic flow and ploughing process. But when the ceramic is composed of zirconia, alumina and some titanium carbide, micro-chipping and tribochemical reaction take place, and wear rate increases. Wear and friction induced martensite was detected by XRD. The T-M (tetragonal to monoclinic) phase transformation has a contribution to inhibiting microfracture.
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    Effect of Heat Treatment on the Corrosion Characteristics of Al-Li Alloys
    K.H. W.Seah(Dept. of Mechanical Engineering, National University of Singapore, 10 Kent Ridge Crescent, Singapore 0511)(To whom correspondence should be addlessed)S. C. Sharma(Dept. of Mechanical Engineering, R.V.College of Engineering, Bangalore -560-059,
    J. Mater. Sci. Technol., 1995, 11 (5): 385-387. 
    Abstract   HTML   PDF (254KB)
    Experiments were conducted to study the general room temperature corrosion characteristics of heat-treated and non-heat-treated Al-Li alloys with different Li compositions. Corrosion rate was measured using both the polarisation method and the weight-loss method. It was observed that the samples with higher Li content had lower corrosion resistance than those with lower Li content. Moreover, for all the specimens tested, it was fOund that heat treatment at 180℃ for 2 h (for the purpose of precipitation hardening) severely reduced the corrosion resistance,whereas heat treatment at 180℃ for 6 h significantly increased the corrosion resistance.
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    Process of Photoluminescence and Photostimulated Luminescence in BaFBr:Eu Phosphors
    Wei CHEN (Lab. of Semiconductor Mater. Sci., Institute of Semiconductor, Chinese Academy of Sciences, Beijing, 100083, China)(To whom correspondence should be addressed)Mianzeng SU(Dept. of Chemistry, Peking University, Beijing, 100871, China)
    J. Mater. Sci. Technol., 1995, 11 (5): 388-390. 
    Abstract   HTML   PDF (324KB)
    The photoluminescence (PL) and photostimulated luminescence (PSL) of BaFBr:Eu phosphors are reported. In the photoluminescence of BaFBr:Eu, the emission of Eu2+ , e-h recombination and Eu3+ have been observed, while in the photostimulated luminescence only the emission of Eu2+ was observed. This phenomenon may be explained well by the suggestion of a two-band model for the host emission in which the host emission energy may transfer to Eu2+. The difference of excitation in those two processes results in different transfer rates which makes the PL and PSL emission different.
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ISSN: 1005-0302
CN: 21-1315/TG
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