LIU Junming LIU Zhiguo WU Zhuangchun Nanjing University
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China LIU Junming
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lecturer
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National Laboratory of Solid State Microstructuros
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Nanjing University
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Nanjing 210008
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China
金属学报(英文版)
The profile features of the solidifying interface of the irregular Al-Si eutectic during directional solidification are studied by numerically solving a nonlinear coupling equation of directional solidification of this eutectic.The critical splitting point of the solidifying interface coincides with the maximum value of its position and corresponds to the marginal stability point.Argument is presented that the interlamellar spacing for local regular structure selects the critical splitting state of the α(Al)-liquid interface as its operating point,and the oper- ating point of the average interflake spacing for the irregular structure is the critical splitting state of the β(Si)-liquid interface.The scaling laws derived,which have the more general forms than the classic Jackson-Hunt scaling,gained support from the experimental results.
关键词:
irregular Al-Si eutectic
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null
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Physical Review B
Metastable Fe100-xAlx alloys have been formed by ball milling of elemental Fe and Al powders: supersaturated body-centered-cubic solid solutions for x less than or equal to 70, and an amorphous phase for x > 70. Quantitative x-ray-diffraction measurements show that the total root-mean-square displacement (rms) and the static rms in the Fe100-xAlx solid solutions increase significantly with increasing Al content, The total rms at the instability point, however, reaches only 6.8% of the nearest-neighbor distance and is far below the critical value predicted by the Lindemann melting criterion, suggesting that the Lindemann melting criterion is not applicable for the solid-state amorphization. Instead. the Debye temperature of the supersaturated Fe100-xAlx alloys was observed to drop by similar to 22% at the point of amorphization, implying a corresponding softening in the average shear modulus of similar to 40%, which agrees with the microhardness measurements. These results strongly support the empirical elastic instability criterion For the solid-state amorphization process.
关键词:
to-glass transition;crystal;transformation
Journal of Alloys and Compounds
Growth kinetics and interfacial morphologies of the intermetallic compounds (IMCs) between single crystal Ag and Sn-4Ag, Sn-3Cu and Sn-37Pb solders were investigated by solid-state aging at 160 degrees C and liquid-state aging at 260 degrees C. Isothermal equation of chemical reaction and phase diagrams were used to explain the effects of Ag, Cu and Pb on the growth kinetics of IMCs under solid-state and liquid-state aging conditions. The diffusion coefficients for the three solder joints of Sn-4Ag/Ag, Sn-3Cu/Ag and Sn-37Pb/Ag were calculated after solid-state and liquid-state aging. It is found that Pb can effectively retard the growth of IMCs during liquid-state aging but has little influence on the growth rate of IMCs during the solid-state aging. Some local small cracks were frequently observed in the Cu(6)Sn(5) particles near interfaces of the Sn-3Cu/Ag solder joints after solid-state aging for several days. However, there were no such local small cracks when solders or interfaces did not contain the Cu(6)Sn(5) particles after the same aging time. (C) 2008 Elsevier B.V. All rights reserved.
关键词:
Ag single crystal substrate;Lead-free solder;Intermetallic compounds;(IMCs);Growth kinetics;Local cracks;lead-free solders;electroless ni(p) metallization;intermetallic;compound;cu-sn;joints;ni;bi;nanoindentation;microstructure;wt.percent
Journal of Applied Physics
Interdiffusion-induced solid-state amorphization reaction (SSAR) in polycrystalline Ni/amorphous Si multilayers has been studied using an in situ x-ray diffraction technique together with transmission electron microscope observations, The amorphization reaction was found to occur both on the Ni/Si interfaces in terms of a planar-layer growth model and along the grain boundaries in the Ni sublayers. Thermodynamic and kinetic interpretations for the SSAR at grain boundaries are presented and an amorphous growth model is also suggested for elucidating the SSAR in polycrystalline Ni/amorphous Si multilayers.
关键词:
x-ray-diffraction;thin-films;silicon
Materials Science and Engineering a-Structural Materials Properties Microstructure and Processing
We report on studies of solid state redox reactions induced by mechanical alloying (MA). The displacement reaction in the Fe-CuO system during MA may be completed by two steps: a rapid self-sustaining combustion reaction process, followed by a gradual reaction process. High densities of point and lattice defects, as well as a fine dispersion of reactants, are introduced in the powder mixture during MA. In addition, the displacement reaction in the Fe-CuO system produces a large negative heat. This combination of factors makes the redox reaction occur in the reaction regions, accompanied by self-heating. The self-heating may raise the temperature up to ignition temperature for a combustion reaction; this ignition temperature is greatly decreased by ball-milling. Combustion then takes place. The displacement reaction may be carried out rapidly during combustion. Complete reduction of copper oxides, including the intermediate oxidation state phase, Cu2O, appearing immediately after combustion, is observed after prolonged milling, during which the reduction is gradual; a similar self-sustaining reaction mechanism works in local reaction regions.
关键词:
amorphous-alloys;powders
Z.S. Zhen
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W.M. Mao
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S.J. Yan
金属学报(英文版)
The Rheological behavior of semi-solid AZ91D at steady state is studied using a Couettetype viscometer in the present paper. The results show that the apparent viscosity ofsemi-solid AZ91D at the steady state increases with the solid fraction increasing, andgoes up sharply when the solid fraction reaches a certain value, which is called criticalfraction. In addition, the apparent viscosity of semi-solid AZ91D at the steady statetakes on a distinct downtrend with the shearing rate increasing, which indicates astrong shear thinning property. In addition, the critical solid fraction becomes higherunder larger shearing rate, owing to the more globular shape of the solid particles.Based on the present experiment results, an empirical equation is built as that, relatingthe steady state apparent viscosity of semi-solid AZ91D with the solid fraction fs andshearing rate γ at the same time: ηapp=10. 74exp(6.95fs)γ-0.86.
关键词:
Rheological behavior
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null
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null
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null
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Yinxiao DU
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Ming LEI
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Hui YANG
材料科学技术（英文）
By a facile and efficient solid-state reaction route using an organic reagent cyanamide (CN2H2) as a precursor with another one being metal oxides, we successfully synthesized seven technologically important metal nitrides including cubic VN, CrN, NbN, hexagonal GaN, AlN, BN, and WN at moderate temperatures. The experimental results show that cyanamide (CN2H2) is a powerfully reducing and nitridizing reagent and the metal oxides are completely converted into the corresponding nitride nanoparticles at lower temperatures than that reported in the conventional methods. It is found that CN2H2 can exhibit some interesting condensation processes, and the final products, highly active carbon nitride species, play a crucial role in the reducing and nitridizing processes.
关键词:
Nitride
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null
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null
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