材料期刊网

Structures and Properties of LiF Cluster-assembled Nanofilms

Guanghou WANG(National Lab. of Solid State Microstructures , Nanjing University , Nanjing 210093 , China)Fengqi LIU(Center for Advanced Studies in Science and Technology of Microstructures , Nanjing 210093 , China)

材料科学技术（英文）

We have studied structures and properties of nanostructured films prepared with nanometersized lithium fluoride(LiF) clusters by inert gas condensation method, and then characterized by transmission electron microscope, Fourier transform infrared spectra and Raman scattering spectra, etc. Following important results are obtained: Multi-order-like Raman scatterings from LiF clusters are obtained, including the fine structure of the spectra. The observed Raman peaks are discussed in terms of surface optical modes, Lo. To, LA modes and their combination form.As the cluster size decreases, the phonons are confined in nanoscale so that the q vector selection rule is relaxed or even totally free of q conservation, and prohibition at the first- and third-order scatterings in the bulk LiF crystal is relaxed. The sudece modes appear and play an important role in Raman scattering processes. The infrared absorption spectra are obtained with different deposition conditions. When the clusters are in the medium size range from ～7 to 15 nm, most infrared absorption peaks are second-order feature, and no single surface mode emerges. For the smaller clusters, molecular-like vibration is observed whereas the broad band of long wavelength transverse-optical modes appear from 580 to 400 nm-1 for the clusters larger than 19 nm

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Laboratory of Solid State Microstructures(LSSMS)

材料科学技术（英文）

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SUPERPLASTICITY AND SOLID STATE BONDING OF TITANIUM ALLOYS

R. Ya. Lutfullin , O.A. Kaibyshev , R.V. Safiullin , O.R. Valiakhmetov and M.H. Mukhametrahimov Institute for Metals Superplasticity Problems , Russian Academy of Sciences , Ufa 450001 , Russia

金属学报(英文版)

Experimental results related to solid state weldability of superplastic titanium alloys are presented. A correlation between superplastic flow and enhanced solid state weldability was established. It has been experimentally shown that a drop in the lower superplastic flow temperature with decreasing mean grain size provides an opportunity to decrease the temperature at whicmethods for titanium alloys.

关键词: superplasticity , null , null

Solid state reaction of Mg with Ni under high pressure

High Pressure Research

Solid state reaction of Mg with Ni was processed under static high pressure and nanocrystalline Mg2Ni was obtained. An unknown phase was also formed at lower temperature. The relation between the mean grain size of Mg2Ni and the synthetizing pressure is given, and its mechanism is discussed.

关键词: solid state reaction;high pressure;nanocrystalline;Mg2Ni;mean grain;size;unknown phase;ab(2)-type intermetallic compounds;crystal-structure

Lattice instability in the solid-state amorphization of Fe(Al) solid solutions by mechanical alloying

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

Solid-state and liquid-state interfacial reactions between Sn-based solders and single crystal Ag substrate

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

CLAS+FROST: new generation of photoproduction experiments at Jefferson Lab.

中国物理C

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SOLID-STATE AMORPHIZATION REACTION IN POLYCRYSTALLINE NI AND AMORPHOUS SI MULTILAYER

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

SOLID-STATE DISPLACEMENT REACTION OF FE AND CUO INDUCED BY MECHANICAL ALLOYING

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

THE APPARENT VISCOSITY OF SEMI-SOLID AZ91D ALLOY AT STEADY STATE

Z.S. Zhen , W.M. Mao , 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 , null , null , null , null