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CN 21-1315/TG
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      28 September 1993, Volume 9 Issue 5 Previous Issue    Next Issue
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    Twinning in Intermetallic Compounds Are Long Shear Vectors and/or Shuffles Really Necessary?
    F.M.Chu David P.Pope Dept.of Materials Science and Engineering,University of Pennsylvania,Philadelphia,PA 19104,USA
    J. Mater. Sci. Technol., 1993, 9 (5): 313-321. 
    Abstract   HTML   PDF (1130KB)
    In this paper the geometric description and general theory of mechanical twinning are reviewed, the twins in general lattices and superlattices are summarized, and the kinetic process by which mechanical twins form is revisited. A case study of mechanical twinning of HfV2+Nb, (cubic) Laves phase, is presented and the synchroshear of selected atomic layers is proposed to explain the physical process of twin formation. If the twins form in this way, then long shear vectors and / or atomicshuffles are not really necessary.
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    Some Further Considerations about the Theory of Elastic Stress Transfer from Partially Embedded Axially Loaded Fiber to Matrix
    Shaoyun FU Benlian ZHOU Chiwei LUNG International Center for Materials Physics,Institute of Metal Research,Academia Sinica,Shenyang 110015,China
    J. Mater. Sci. Technol., 1993, 9 (5): 322-326. 
    Abstract   HTML   PDF (420KB)
    In this paper the elastic stress transfer from the fiber to the matrix is analysed for fiber-reinforced composites when the fiber is loaded axially.The dependence of the elastic stress transfer on the as- pect ratio of the fiber,the volume fraction of the fiber,the fiber-to-matrix elastic modulus ratio and the Poisson's ratio of the fiber and the matrix has been shown in detail.
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    Atomistic Simulation of Interaction between Grain Boundary and Dislocations in Ni_3Al
    Dongliang LIN(T.L.Lin) Da CHEN Min LU Department of Materials Science,Shanghai Jiaotong University,Shanghai,200030,China
    J. Mater. Sci. Technol., 1993, 9 (5): 327-337. 
    Abstract   HTML   PDF (1113KB)
    The embedded atom type potentials and static relaxation method combined with a steepest decent computational technique have been used to simulate the interaction between the grain boundary (GB) and dislocations in Ni_3Al alloys.The focus has been placed on the energy feature of the interaction,the distortion of GB structural units,and the dislocation core structure near the GB.Im- plication has also been made on the results for the understanding of the mechanism responsible for B-enhanced ductility.
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    Fractal Dimensions of Hydrogen Induced Brittle Fracture of Titanium Aluminide
    Yue ZHANG Yanbin WANG Lijie QIAO Wuyang CHU Chimei HSIAO Dept.of Materials Physics,University of Science and Technology,Beijing,Beijing,100083,China
    J. Mater. Sci. Technol., 1993, 9 (5): 338-342. 
    Abstract   HTML   PDF (1128KB)
    The relationship between the stress intensity factor K_1~* required for brittle crack initiation and propa- gation and the fractal dimension D_F of the fracture surface was derived,i.e, InK_1~*=(1/2)In2γE'+(1/2)In(d_f/L_0)(1-D_F) The real surface energy can be calculated based on the measured linear relation of the InK_1~* vs D_F, The equation is not only suitable for the overload fracture but also for the delayed fracture,e.g. hydrogen induced cracking (HIC) and stress corrosion cracking (SCC).The experiment results showed that the hydrogen induced delayed cracking occurred in the Ti-24AI-11 Nb alloy during dy- namic charging,and the threshold stress intensity factor was very low,i.e..K_(IH)/K_(IC)= 0.43.The ex- perimental relationship between the stress intensity factor K_1~* and D_F was consistent with the theo- retical equation.
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    Bond Strength of the Sn-Ti-Ⅹ Ternary Active Solders on Sialon Ceramic
    Aiping XIAN Zhongyao SI Institute of Metal Research,Academia Sinica,Shenyang,110015,China
    J. Mater. Sci. Technol., 1993, 9 (5): 343-349. 
    Abstract   HTML   PDF (2700KB)
    The bond strength of the Sn based ternary active solders,Sn-5Ti with various contents of Ag,Cu,In, Ni or AI on sialon ceramic was investigated by the ceramic/ceramic joint joining.The bond strength of Sn-STi (about 80 MPa) may increase to 90-100 MPa by small addition of Ag or Cu (about 5-10%).A little Ni (about 1-3%) in the solder is slightly beneficial,but too more Ni (more than 5%) is harmful.Small addition of In is trivial,but too more In is detrimental.On the other hand,small addi- tion of AI in the active solder decreases greatly the bond strength of the solder,therefore it is very harmful.In discussion,three suggestions for selection of the third element to increase the bond strength of the soft solders on ceramic,i.e.with a high surface energy,benefiting to wetting on ce- ramic and strengthening the soft solder itself,have been made.
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    Structure of Plasma-sprayed ZrO_2/(Ni/AI)Interface
    Zhengyi LIU Hancun CHEN Yuzhi CHUANG (Y.C.Chuang) South China University of Technology,Guangzhou,510641,China
    J. Mater. Sci. Technol., 1993, 9 (5): 350-354. 
    Abstract   HTML   PDF (1566KB)
    The structures of plasma-sprayed ZrO_2/(Ni/AI) interface before and after hot isostatic pressing (HIP) treatment were studied by TEM,ED and X-ray diffraction analysis.Plasma-sprayed ZrO_2/(Ni/AI) interfacial region is of definite thickness and consists of multi-phase structures. Amorphous ZrO_2 sublayer,amorphous plus microcrystalline ZrO_2 sublayer and NiO were found in the interface.NiO phase formed by the reaction between ceramic coating and metallic substrate in local regions.However.the thickness and amount of NiO trended to increase and the distribution of NiO particles trended continuously when the coating was subjected to HIP treatment.HIP treatment can accelerate the diffusion of atoms in the interfacial region.
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    Atomistic Simulation of Phase Transformation and Fracture in Ordered Intermetallics
    P.C.Clapp C.S.Becquart D.Kim Y.Shao J.A.Rifkin Center for Materials Simulation,Institute of Materials Science,University of Connecticut,Storrs,CT 06269-3136,USA
    J. Mater. Sci. Technol., 1993, 9 (5): 355-359. 
    Abstract   HTML   PDF (660KB)
    A review of computer simulations carried out at our Center for Materials Simulation applied to stud- ying the different atomistic processes of fracture and displacive (martensitic) transformations is pres- ented.Since these processes can happen extremely rapidly and involve only a small number of atoms initially,they are ideally suited for molecular dynamics type simulations which can currently only span times of the order of one nanosecond and involve at most a million atoms.A method is also presented for simulating much larger samples for much longer times through the use of the Monte-Carlo technique combined with a Ginzburg-Landau free energy functional,where the rele- vant material parameters are determined from molecular dynamics runs on the same alloy system.A summary of studies on fracture simulations in the ordered intermetallics NiAI and RuAl is given,as well as a discussion of the observation and analysis of the heterogeneous nucleation of the martensitic transformation in NiAI which shows localized soft mode phenomena.It is concluded that computer simulations,whether of the atomistic molecular dynamics type or of the larger scale Monte-Carlo variety,are rapidly becoming of greater and greater use in understanding the properties of solids under a wide rancle of temperature and stress conditions.
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    Migration of Oxides in a Composite Coating and Its Effect on Inhibiting Coating Degradation
    Xinqing MA Tiefan LI Institute of Corrosion and Protection of Metals,Academia Sinica,Shenyang,110015,China
    J. Mater. Sci. Technol., 1993, 9 (5): 360-364. 
    Abstract   HTML   PDF (1892KB)
    Based on the fact that the dispersed rare earth oxide particles in an electrolytic co-deposited Ni-R_2O_3 layer migrated and accumulated at the substrate/coating interface immediately after aluminizing,the mechanism of migration of the oxides and its effect on the behaviour of degradation of the coatings oxidized at 1100℃ were studied in this paper.The Ni-R_2O_3 layers were treated in vacuum at 900℃ and aluminized at 1100℃ separately.The results indicated that the migration and accumulation of R_2O_3 particles were favorable to the gathering of R_2O_3 at higher temperatures,and the small size oxides were easier to migrate and gather.The drawing effect of grain boundary was used to explain this behaviour.The microstructures of the coatings oxidized at 1100℃ were ob- served.It was found that the coating degradations were related to the amount and distribution of the accumulated R_2O_3 at the alloy/coating interface.Three typical kinds of the accumulated layers were identified.The continuous oxide layers acted as diffusion barrier which could inhibit the coat- ing degradation effectively.
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    Relationship between Magnetomechanical Damping Capacity and Vibration Modes
    Junsheng LU Baorong WU Dept.of Alloy Steel,Central Iron and Steel Research Institute Beijing,100081,ChinaG.J.Wang Dept.of Materials Science and Engineering,University of Pennsylvania,Philadelphia,PA 19104,USA
    J. Mater. Sci. Technol., 1993, 9 (5): 365-368. 
    Abstract   HTML   PDF (325KB)
    The mathematical expressions for magnetomechanical damping capacity are presented by applying Smith-Birchak's model in torsion pendulum and cantilever beam.The peak value ψ_p is found to be related to physical parameters and material constants in the form Kλ_s=αψ_pε_p.which can be used to estimate the magnetostrictive constant λ_s from the damping capacity-strain amplitude curve.A good agreement of experimental data and theoretical prediction was observed in HIDAMETS Cr15A13NiCu.
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    Formation of PFZ and Its Effect in a RSP AI-Li Alloy
    Liang ZHEN Yuexian CUI Dezhuang YANG Department of Materials Science,Harbin Institute of Technology,Harbin,150006,ChinaShenglong DAI Guifu YU Beijing Institute of Aeronautical Materials,Beijing 100095,China
    J. Mater. Sci. Technol., 1993, 9 (5): 369-372. 
    Abstract   HTML   PDF (1202KB)
    The formation of precipitation free zone (PFZ) and its effect in a RSP AI-Li alloy has been studied. The results show that PFZ is easy to form when aged at 190℃,but there is no equilibrium phase on grain boundaries.The growth of PFZ in the alloy is different from that in conventional AI-Li alloys, The effect of PFZ is of great importance because of its large volume fraction in the alloy.It offsets the beneficial effect of RSP,and is thought to be an important factor that leads to the poor toughness and low ductility of RSP AI-Li alloy sheet.
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    Fractal Aggregation of Nonequilibrium Iodine
    Jizhong ZHANG Xiaojun YANG Hengde LI Dept.of Materials Science and Engineering,Tsinghua University,Beijing,100084,China
    J. Mater. Sci. Technol., 1993, 9 (5): 373-375. 
    Abstract   HTML   PDF (726KB)
    A large number of particles evaporated from liquid iodine deposited on the wall of a glass container. The deposits demonstrate three structural shapes:globule chain,network formation,and dendrite. The globule chain displays clearly self-similar feature,and can be characterized by fractal geometry. The fractal dimension of the globule chain patterns ranges from D=1.50 to 1.75.The in situ sublimat- ing process of an iodine fractal aggregate was observed.It revealed reversal of the random growth process under nonequilibrium condition.The analytical results show that the nucleation-aggregation (NA) model can explain the growth process of iodine fractal aggregate.
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    Fabrication and Microstructure of BSCCO Superconductive Wires Made by LHPG Method
    Cheng ZHANG Xin WANG Ming JIANG Jianguo HUANG Yongzhong WANG Guiwen QIAO Institute of Metal Research,Academia Sinica,Shenyang,110015,China
    J. Mater. Sci. Technol., 1993, 9 (5): 376-378. 
    Abstract   HTML   PDF (715KB)
    Laser heated pedestal growth technique (LHPG) has been used to fabricate BSCCO (BiSrCaCuO) superconductive wires.The critical current density of the wires has surpassed 5000A/cm~2 (78K, OT;cross area=1.04 mm~2).The fiber rods obtained directly from LHPG method are semiconductive and after heat treatment at temperature range from 780 to 870℃,they transformed into superconductive wires.Triple junctions and sharp grain boundary exist in the sample.HREM studies showed the intergrowth of (010) and (110),the occasional missing of CaCuO_2 layer in the 2212 phase.
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    Effect of Sintering Temperature on Microwave Absorbing Behaviour of Mn-Zn Ferrite
    Yongxue GAN Pei YI Changqi CHEN (C.Q.Chen) Dept.of Mater.Sci.Eng.,Beijing University of Aeronautics and Astronautics,Beijing 100083,China
    J. Mater. Sci. Technol., 1993, 9 (5): 379-381. 
    Abstract   HTML   PDF (460KB)
    The microwave absorbing behaviour of Mn-Zn ferrite sintered at 1100,1200,1300,1400 and 1500℃ has been investigated.The phase constitution of the ferrite was analyzed by X-ray diffraction.The results show that the ferrite sintered at 1 500℃ has better microwave absorbing prop- erty than those prepared at other temperatures,due to the increase of turbulent loss generated by the formation of excessive Fe~(2+) in deoxidizing of Fe_2O_3 at high temperatures.
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    Vinylon Reinforced Aluminium Laminate
    Guoxin SUI Zhongguang ZHENG Chengti ZHOU Changxu SHI Institute of Metal Research,Academia Sinica,Shenyang,110015,ChinaBenlian ZHOU International Centre for Materials Physics,Academia Sinica,Shenyang,110015,China
    J. Mater. Sci. Technol., 1993, 9 (5): 382-384. 
    Abstract   HTML   PDF (316KB)
    A new kind of superhybrid composite material,vinylon reinforced aluminium laminate (VIRALL),has been developed by laminating the vinylon/epoxy prepreg layers and the aluminium alloy sheets alternatively.The mechanical properties of VIRALL laminate have been tested and the results are dis- cussed in terms of laws of mixtures.About a 24% increase in tensile strength and a 36%decrease in tensile modulus to that of the corresponding aluminium were found,which kept good agreement with the laws of mixtures.Compared with the corresponding aluminium,VIRALL has lighter density and lower price.VIRALL is hoped to be a partial substitute for the civil aluminium alloy in the future.
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    Hydrogen Trapping by Dislocations and Grain Boundaries in Fe-3%Si AHoy
    Yuandong DIAO Shenyang Institute of Chemical Technology,Shenyang,110021,ChinaMingzhou CAO Xiaojing WAN Institute of Metal Research,Academia Sinica,Shenyang,110015,China
    J. Mater. Sci. Technol., 1993, 9 (5): 385-387. 
    Abstract   HTML   PDF (241KB)
    In present work,Fe-3%Si alloy specimens with various degrees of cold working and various grain sizes were chosen to determine the effect of cold working and grain sizes on the hydrogen diffusivities by electrochemical permeation method and the mechanism of hydrogen trapping by dis- ocations and grain boundaries is discussed.
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    Sodium Activity in Molten Aluminum Measured with a Solid Electrolyte
    Gang XIE Shanghai Institute of Metallurgy,Academia Sinica,Shanghai,200050,ChinaShiyin SHEN Northeast University of Technology,Shenyang,110006,China
    J. Mater. Sci. Technol., 1993, 9 (5): 388-390. 
    Abstract   HTML   PDF (231KB)
    The sodium activities in aluminium in equilibrium with cryolite-alumina melt and during electrolysis were determined by EMF with Naβ-Al_2O_3 solid electrolyte.With this sodium activities,we calculate the activities of NaF and AIF_3 in the cryolite-alumina melt.The potential difference of discharge be- tween sodium ions and aluminum ions at cathode of Hall-Heroult cell was also obtained from the sodium activity in aluminum.
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