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ISSN 1005-0302
CN 21-1315/TG
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      28 November 1994, Volume 10 Issue 6 Previous Issue    Next Issue
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    Articles
    Structure and Deformation of Intermetallic Beryllides
    TG.Nieh(Lawrence Livermore National Laboratory, P.O.Box 808, L-350, Livermore, CA 94551, USA )
    J. Mater. Sci. Technol., 1994, 10 (6): 391-405. 
    Abstract   HTML   PDF (4430KB)
    Intermetallic beryllides are potential light-weight, high-temperature structural materials. In this paper. the processing techniques, microstructure. deformation, and oxidation properties of intermetallic beryllides are described. In addition to nickel beryllides (NiBe). which is treated as a model system.other high beryllium-containing refractory beryllides, such as Nb2 Be17. VBe12. are also studied.The room temperature deformation and high-temperature creep properties of these beryllides are repor4ed. At room temperature. NiBe exhibits certain tensile ductility (~ 1 .3%). but all other beryllides are essentially brittle. Nonetheless, these beryllides become ductile at temperatures above approximately 1000℃. Their creep properties are presented. The creep properties are compared with those of intermetallic aluminides. Also. a comparison is made between the ductile-to-brittle transition behaviour of intermetallic beryllides and that of aluminides. Although beryllides are generally oxidation resistant at high temperatures, some beryllides, e.g., ZrBe13, suffer the pest reaction during oxidation at intermediate tem peratures. The pest mechanisms are proposed
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    Segregation Behaviour and Microstructure of Alloy 718VADER Ingot
    Yueguang YU; Jie FU and Xishan XIE(University of Science and Technology Bejing, Beijing, 100083, China)Jialong XU and Chunyong JING(Shanghai Iron and Steel Research Institute, Shanghai, 200940, China)
    J. Mater. Sci. Technol., 1994, 10 (6): 406-410. 
    Abstract   HTML   PDF (2429KB)
    The segregation behaviour and miclostructure of an alloy 718 VADER ingot in comparison with a VAR ingot were studied. The results show that one serious problem of the alloy 718 VADER ingot is dealing with radial chemistry gradients (especially macro-segregation in Nb). The main factor of Nb gradient forming is the flow of Nb rich fluid through passages among the cellular structures driven by centrifugal force from the rotating mold, Detailed structure and micro-segregation studies on ingots impress us that the VADER process does not show the advantage on the improvement of micro-segregation especially in Nb. The cellular structure produced by the VADER process is no more effective in reducjng Nb micro-segregation during homogenization treatment than the dendritic structure by the VAR process. Experimental results lead us to believe that the VADER process is unsuitable to manufacture alloy 718.
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    Corrosion Behaviour of Stainless Steel in Acidic Water-Organic Solvent Mixtures
    A .A.Khedr; I.Z.Selim; K.M.El-Sobki and O.S.Shehata(Physical Chemistry Dept., National Research Centre, Dokki, Cairo, Egypt)
    J. Mater. Sci. Technol., 1994, 10 (6): 411-417. 
    Abstract   HTML   PDF (713KB)
    Electrochemical behaviour of stainless steel type 430 in acidic solutions of methanol, ethanol and in their binary mixtures with water (from 0 to 100% alcohol) at 25℃ has been studied. using potentiostatic poIarization technique and weight loss method. It was found that the corrosion rate of the metal was affected by the physico-chemical properties of the media such as, viscosity, state of solvation, molar volume contraction, proton availability and dielectric constant, it was demonstrated from the potentiostatic study that the active passive transition strongly depended on the concentration of the acid, and on the water content of the media.
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    Computer Simulation of the Structure and Properties of Nanocrystals
    Da CHEN(Dept. of Materials Science, Shanghai Jiao Tong University, Shanghai, 200030, China)
    J. Mater. Sci. Technol., 1994, 10 (6): 418-424. 
    Abstract   HTML   PDF (832KB)
    This paper provides a computer modeling method for the study of nanocrystals. Structural features,such as the boundary component proportion, the reduced density proportion, the excess lattice parameter, and the radial distribution function, have been atomistically simulated. The energy and elastic properties also have been investigated. Simulation results indicate that the structure of grain boundaries in nanocrystals is different from those of the amorphous and the gas, or rather, it is a special structure with some degree of short-range order. Moreover, the structure of crystallites is not entirely the same as that in the perfect crystal lattice. The present simulation method may become one of the foundations of the theoretical study of nanocrystals.
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    Acid-base and Electron Donor Properties of Pr_6O_(11)and Its Mixtures with Alumina
    S.Sugunan; G.D.Rani and P.A. Unnikrishnan(Dept. of Applied Chemistry, Cochin University of Science and Technology, Kochi, India)
    J. Mater. Sci. Technol., 1994, 10 (6): 425-429. 
    Abstract   HTML   PDF (476KB)
    The electron donor properties of Pr6O11 activated at 300, 500 and 800℃ are reported from the studies on adsorption of electron acceptors of various electron affinity (7, 7, 8, 8-tetracyanoquinodimethane , 2. 3. 5. 6-tetrachloro-1, 4-benzoquin one, p-dinitrobenzene, and m-dinitrobenzcne) in three solvents (acetonitrile, 1,4-dioxan and ethyl acetate). The extent of electron transfer during adsorption is understood from magnetic measurements and ESR spectral data. The corresponding data on mixed oxides of Pr and Al are reported for various compositions. The acid / base properties of these oxides are determined using a set of Hammett indicators.
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    Structure and Magnetic Properties of Fe_(76.5)Si_(13.5)B_9Cu_1 Alloy with Nanoscale Grain Size
    Fei ZHOU; Kaiyuan HE; Lizhi CHENG and Zuhan LAI(Dept. of Materials Science and Engineering, Northeastern University, Shenyang, 110006, China)( Dept. of Phys., Northeastern University)
    J. Mater. Sci. Technol., 1994, 10 (6): 430-434. 
    Abstract   HTML   PDF (533KB)
    The structure and magnetic properties of Fe76.5Si13.5B9Cu1 alloys with a nanocrystalline (NC) bcc Fe(Si) phase trom about 23 to 46 nm in diameter, which were first formed into amorphous ribbons and then annealed at various temperatures between 703 and 773 K, have been investigated. At annealing temperatures from 703 to 748 K, the single NC bcc(Si) phase is obtained in the crystallized alloys. The grain size and the Si-content in the NC bcc Fe(Si) phase for the alloys annealed at different temperatures are presented. The soft magnetic properties and the saturation magnetostriction for the alloys with the NC bcc Fe(Si) phase are also measured. The results show that, the saturation magnetizotion and the permeability are improved for the alloys with only the NC bcc Fe(Si) phase and become better with decreasing of the NC bcc phase size, and the saturation magnetostriction declines for the alloys with increasing Si-content in the NC bcc Fe(Si) phase.
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    Deformation and Dislocation Structure in L1_2 Titanium Trialuminide Alloys
    Gengxiang HU; Shipu CHEN; Xiaohua WU; Yonghua RONG and Xiaofu CHEN(Dept. of Materials Science, Shanghai Jiao Tong University, Shanghai, 200030, China)
    J. Mater. Sci. Technol., 1994, 10 (6): 435-440. 
    Abstract   HTML   PDF (2842KB)
    The deformation behaviour and the nature of dislocations of the Al3Ti-base L12 alloya modified with Fe and Mn etc, were investigated. The results show that the deformation and fracture character istics are closely related to the alloy compositions. The effect of hot-working process on the room tem perature ductility is remarkable, not only resulting in an appreciable improvement of compressive properties but also showing a 0.28% plastic strain in tensile test. The SISF dissociation of a < 110>dislocations on {111} planes was found at room temperature. The determined dissociation scheme is consistent with the mechanical behaviour of these alloys in the lower temperature region.
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    Thermodynamics of Bainitic Formation in Carbon-depleted Region in Fe-C Alloys
    Xiaolei WU; Xiangkang MENG; Xiyan ZHANG; Yanqing YANG and Mokuang KANG(Dept. of Materials Science and Technology, 401, Northwestern Polytech. University, Xi'an, 710072, China)
    J. Mater. Sci. Technol., 1994, 10 (6): 441-444. 
    Abstract   HTML   PDF (382KB)
    Thermodynamic analysis for the formation of bainitic ferrite in carbon -depleted region has been conducted. The results show that the driving force of bainitic formation increases with depleting of carbon in parent austenite and with decreasing the transformation temperature. The critical driving force (absolute value) at the Bs temperature is 600-1 200 J / mol, which increases as the mean carbon content of Fe-C alloys increases. The freshly-formed bainitic ferrite has partial supersaturation of carbon, which increases smoothly with decreasing the transformation temperature Therefore, the displacive formation of bainitic ferrite in carbon-depleted region is thermodynamically feasible in the whole temperature range of bainitic reaction.
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    Influence of Ageing Heat Treatment on the High Cycle Fatigue of an 8090 Al-Li Alloy
    Suhua AI; Zhongguang WANG; Yun ZHANG and Zhuangqi HU(State Key Laboratory for Fatigue and Fracture of Materials, Institute of Metal Research,Chinese Academy of Sciences, Shenyang 110015, China)
    J. Mater. Sci. Technol., 1994, 10 (6): 445-450. 
    Abstract   HTML   PDF (2424KB)
    Fatigue lives for the smooth and notched specimens of 8090 Al-Li alloy jn the different ageing conditions have been studied. For the smooth samples of 8090 alloy the artificial ageing results in an increase in fatigue life in comparison with natural ageing. On the contrary, the notched specimens of 8090 alloy in the naturally aged condition show higher fatigue life than in the peak-aged. The exposure to either the peak-aged or naturally aged leads to superior fatigue properties of Al-Li alloy to the traditional high strength aluminum alloys of 7075 and 2024, especially in the latter aged condition. In all ageing conditions, i,e. naturally, under-, peak- and over-aged, the peak-aged 8090 alloy displays the highest fatigue life and the over-aged material has a minimum value at the same stress amplitude. The difference in fatigue life is mainly attributable to the size and distribution of strengthening precipitates as well as the wide of precipitate free zones (PFZ's) along grain boundaries.
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    Investigation on the Initial Stage of Film Growth in Situ
    Zhenzhong QI; Guopin DU; Hanqi KE and Weiguo YAO(Institute of Solid State Physics, Chinese Academy of Sciences, Hefei, 230031, China)
    J. Mater. Sci. Technol., 1994, 10 (6): 451-454. 
    Abstract   HTML   PDF (433KB)
    The initial stage of Ag film growth on Cu(100). Ta(100) and Ta(110) single crystals as well as YBaCuO on Si single crystal covered by Pd was investigated in situ by means of LAS 600 surface analysis system with a sputtering source in sample preparation chamber. The results show that the initial state for Ag / Cu(100) film growth is typical S-K model, for Ag / Ta(100) and Ag / Ta(110)they have the same S-K characteristics, but due to the different surface energies of two crystalline planes. there is some difference for Ag / Ta (100) and Ag / Ta(110). YBCO sputterjng process is rather complex and Cu is the first element appearing in the film.
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    Further Investigation on the Correlation between Ionization Potential and Superconductivity of Oxides
    Wei CHEM and Ruzhang MA(Dept. of Materials Physics, University of Science and Technology Bejing, Bejing, 100083, China)
    J. Mater. Sci. Technol., 1994, 10 (6): 455-458. 
    Abstract   HTML   PDF (342KB)
    The relations of oxygen content, critical temperature TC and mean ionization potential < U0> of superconducting oxides are reported. We found that in oxides oxygen is the major element which governs their < U0> te values and thus oxygen content plays an jmportant role in their superconducting properties. As for Y(123)- and T1-systems oxygenation may improve their TC values, but for Biand Hg-systems oxygenation process is not so important. In Y(123), as the oxygen content increase results in the increase of TC upon < U0>to, while the substitution of Ba2+ by Sr2+ causes the decrease of TC upon < U0 >. These results may provide some clues about the superconductivity of oxides and support further that < Uo > is really a good criterion for oxide superconductivity. Two kinds of possible superconducting oxides are predicted in this paper according to the mean ionization potential criterion.
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    Influence of Rare-Earth Elements on Electrical Properties of Pd
    Fei WEN; Yuantao NING; Huaizhi ZHAO and Deguo DENG(Kunming Institute of Precious Metals, Kunming, 650221, China)
    J. Mater. Sci. Technol., 1994, 10 (6): 459-462. 
    Abstract   HTML   PDF (425KB)
    The influence of RE (RE = La, Ce. Pr. Nd, Sm, Eu, Gd. Tb. Dy, Er, Yb) additives with dilute concentrations on the electrical properties of Pd has been studied. All RE elements increase the specific resistivity (ρ) and decrease the resistance temperature coefficient (α) of Pd. and (ρ.α) Pd-RE ls equal to (ρ· α)Pd.The RE elements before Gd reduce the thermo-emf of Pd on Cu. other heavy RE enhance the thermo-emf.The experimental data of normalized Pd-0.1 at.-%RE alloys indicate that the effect of light RE additives on the specific resistivity of Pd is larger than that of heavy RE and Ce. Eu and Yb show anomalous strong effect. The valence and atomic size are main factors influencing the electrical properties.
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    Ceramics Surface Modification by Excimer Laser Metal Coating
    Weidou ZHU and Haicheng GU(Dept. of Materials Science and Engineering, Xi'an Jiaotong University, Xi'an, 710049, China)
    J. Mater. Sci. Technol., 1994, 10 (6): 463-465. 
    Abstract   HTML   PDF (1226KB)
    Thin metallic layers (~ 2 μm) of Ni were deposited on polycrystalline Al2O3. ZrO2 and (Ce-TZP)+Al2O3 ceramic substrates. and further irradiated with pulsed excimer (Xeno chloride) laser pulses. The laser energy density was varied from 0.21 to 0.81 J / cm2 to optimize bending strength. For ZrO2 ceramic, it was found that the strength increases from 530 to 753 MPa at 0.51 J / cm2 irradiation. For Al2O3 and (Ce-TZP)+ Al2O3 the fracture strength also increases in varying degree. The causes of strength increment were discussed.
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    Wettability of Ni-base Reactive Brazing Alloys on Alumina
    Chuangeng WAN(Welding Division, Dept. of Materials Engineering, Jilin University of Technology, Changchun, 130025, China)Polyvios Kritsalis and Nicolas Eustathopoulos(Lab. de Thermodynamique et Physico-Chimie Metallurgiques, ENSEEG, Institut National Pol
    J. Mater. Sci. Technol., 1994, 10 (6): 466-468. 
    Abstract   HTML   PDF (1108KB)
    The influences of the additions of Ti or / and Si on the wettability of Ni-base alloys on alumina were investigated with the sessile drop method. The interfacial chemical reaction products were analyzed by scanning etectron rnicroscope and microprobe. Their effects on the wettability and the affecting factors for them to be produced were discussed. A new Ni-base braze alloy (NiFeCr10Si15Ti) was designed for brazing alumina with the superior qualities such as low contact angle (less than 25 degrees), high work temperature (near 1073 K) and good resistance to oxidations, etc.
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ISSN: 1005-0302
CN: 21-1315/TG
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