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Role of Edge and Screw Dislocations in Deformation of Metals

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Journal of materials Science & Technology 1995年第2期11卷 133-136页

作者： Chiwei LUNG(international Centre for materials {2., Institute of Metal Research,chinese academy of sciences, shenyang, 110015, china) Inst of Metal Research Shenyang China

It was widely accepted that the screw dislocation is responsible for the strong temperature dependence of the yield stresses observed in bcc metals. In this paper, we show the role of edge dislocations in the deformation of metals and point out that in some cases, its main contribution to the plastic flow behaviour cannot be ignored.

关键词： Crystal structure

Unusual Behaviour of Dislocation Velocity Exponent in Dislocation Multiplication Model

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Journal of materials Science & Technology 1998年第3期14卷 215-218页

作者： Xaowei WANG(international Centre for materials {2., Institute of Metal Research, chinese academy of sciences,shenyang 110015, china) international Centre for materials {2. Institute of Metal Research Chinese Academy of Sciences Shenyang 110015 China

The chaotic behaviour of dislocation multiplication process was investigated. The change of Lyapunov exponent which is used to determine the stability of quasi-periodic and chaotic behavior as well as that of equilibrium points, and periodic solution was reported by using an iteration model of dislocation multiplication. An unusual behavior of Lyapunov exponent and Feigenbaum exponent which respond to the geometric convergence of orbit from bifurcation to chaos was shown by dislocation velocity exponent m and there is a distinction on the tendency of convergence for the dislocation multiplication model when it was compared with logistic map. It is reasonable for the difference to be analyzed from the materials viewpoint. (Edited author abstract) 9 Refs.

关键词： Unusual Behaviour of Dislocation Velocity Exponent in Dislocation Multiplication Model

Multirange Fractals in materials: Applications to Fracture and Mechanical Alloying under Ball Milling

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Journal of materials Science & Technology 1997年第4期13卷 255-259页

作者： Chiwei LUNG(international Centre for materials {2., Institute of Metal Research,chinese academy of sciences, shenyang 110015, china) international Centre for materials {2. Institute of Metal Research Chinese Academy of Sciences Shenyang 110015 China

A new model of multirange fractals is proposed to explain the experimental results observed on the fractal dimensions of the fractured surfaces in materials. A new explanation to the Williford's multifractal curve on the relationship of fractal dimension with fracture properties in materials has been given. It shows the importance of fractorizing out the effect of fractal structure from other physical causes and separating the appropriate range of scale from multirange fractals. Mechanical alloying process under ball milling as a non-equilibrium dynamical system has been also analyzed.

关键词： Ball Applications to Fracture and Mechanical Alloying under Ball Milling Multirange Fractals in materials

Effects of Positron Diffusion and Its Application in Composite System

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Journal of materials Science & Technology 2000年第3期16卷 311-314页

作者： Jian JIANG, Xinzhang ZHOU and ChiWei LUNG (international center for {2. physics, Institute of Metal Research, chinese academy of sciences, shenyang 110015, china) international center for {2. physics Institute of Metal Research Chinese Academy of Sciences Shenyang 110015 China

The effects of positron diffusion on the measured S parameter have been investigated by a point-source diffusion model and a δ function method. Firstly, the theoretical analyses of the effects are presented for the samples of a homogeneous semi-infinite medium and a film of definite thickness. Then the results are used to analyze the S parameters in several composite systems and interface models.

关键词： Effects of Positron Diffusion and Its Application in Composite System

Universality and Specificity of Fractal Dimension of Fractured Surfaces in materials

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Journal of materials Science & Technology 2000年第1期16卷 1-4页

作者： Chiwei LUNG and Shenggang WANG (international Centre for materials {2., Institute of Metal Research, chinese academy of sciences, shenyang 110015, china) international Centre for materials {2. Institute of Metal Research Chinese Academy of Sciences Shenyang 110015 China

After calculation on the fracture angles under various conditions of specific surface energies with different symmetry operations of rotation, the complicated behavior of dependence of fractal dimension on the structure of crystal is shown. It is found that the crack propagates along the weakest crystal plane no matter what the direction of the maximum stress is if the anisotropy is sufficiently strong; and then, the fractal dimension of the fractured surfaces might be determined by the approximate fractal structure already existed in the material. Specificity of the fractal dimension of fractured surfaces would be easy to appear in this case. Reversely, the crack propagates along the direction of the maximum stress no matter what direction of the weakest crystal plane is if the anisotropy is sufficiently weak. Universality of the fractal dimension of fractured surfaces would be possible to appear in this case. In many real materials, universality and specificity of the materials are associated. The fractal dimension measured may more or less be influenced by the structure of materials and it shows its universality through the specificity of materials.

关键词： Universality and Specificity of Fractal Dimension of Fractured Surfaces in materials

Effects of Distribution of Induced Defects on Positron Diffusion

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Journal of materials Science & Technology 2000年第1期16卷 73-75页

作者： Xinzhang ZHOU, Jian JIANG and Chiwei LUNG (international center for {2. physics, Institute of Metal Research, chinese academy of sciences, shenyang 110015, china) international center for {2. physics Institute of Metal Research Chinese Academy of Sciences Shenyang 110015 China

The effects of distribution of induced defects on the positron diffusion was studied by using the point-source diffusion model and 6 function method.

关键词： Effects of Distribution of Induced Defects on Positron Diffusion

Energy Spectrum of YAG:Cr3+ and Thermal Shifts of Its R Lines

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Communications in Theoretical physics 2005年第7期44卷 165-170页

作者： MA Dong--Ping CHEN Ju--Rong Department of Applied physics, Sichuan University, Chengdu 610065, china {2. Centre for materials physics, the chinese academy of sciences, shenyang 110015, china Department of Applied physics Sichuan University Chengdu 610065 China international Centre for materials {2. the Chinese Academy of Sciences Shenyang 110015 China

Traditional ligand-field theory has to be improved bv taking into account both "pure electronic" contributionand electron-phonon interaction one （including lattice-vitbrational relaxation energv）. By means of improved ligand-fieldtheory, R1, R2. R3′, R2., and R1′ lines, U band, ground-state zero-field-splitting （GSZFS） and ground-state g factors aswell as thermal shifts of R1line and R2.ine of YAG:Cr3+have been calculated. The results are in very good agreementwith the experimental data. In contrast with ruby, the octahedron of ligand oxygen ions surrounding the central Cr3+ion in YAG:Cr3+is compressed along the [111] direction. Thus, for YAG:Cr3+and ruby, the splitting of t2. 4A2.or t2. 2.)has opposite order, and the trigonal-field parameters of the two crystals have opposite signs. In thermal shifts of R1andR2.ines of YAG:Cr3+, the tetnperature-dependent contributions due to EPI are dominant.

关键词： improved ligand-field theory electron-phonon interaction Stokes shift energy spectrum thermal shift g factor

Properties of nonadiabatic quantum fluctuations of the strongly coupled electron-phonon systems

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Science china(physics,Mechanics & Astronomy) 2008年第3期51卷 258-268页

作者： PANG XiaoFeng Institute of Life Science and Technology,University of Electronic Science and Technology of china,Chengdu 610054,china {2. Centre for materials physics,chinese academy of sciences,shenyang 110015,china Institute of Life Science and Technology University of Electronic Science and Technology of China Chengdu China international Centre for materials {2. Chinese Academy of Sciences Shenyang China

A new variational-ansatz of states of electrons and phonons was proposed on the basis of the Holstein model in strongly coupled electron-phonon systems for studying the influence of nonadiabatic phonon fluctuation,arising from the motion and density fluctuation of electrons,on the properties of ground state,uncertainty relation,stability of polarons,charge density wave (CDW) and phonon staggered ordering. The new ansatz represents the correlation among the displacement and squeezing states of phonons and polaron’s state of electrons as well as the squeezing-antisqueezing effect. The correlation and squeezing-antisqueezing ef-fect result in the decrease of ground state energy,enhancement of stability of the systems,increase of binding energy of the polarons,weakening of the growing speed of polaron narrowing of the electron band,increase of the charge density wave order and suppression of the increased tendency of anomalous quantum fluctuation of the phonons in such a case,when compared with the uncorrelated case in the systems. The results obtained show that the ground state determined by the new state ansatz is most stable,thus the new ansatz describing the properties of the coupled electron phonon systems is very relevant and available,especially in strongly coupled and largely squeezed cases.

关键词： squeezing-antisqueezing effect state-ansatz polaron coupled electron-phonon systems quantum fluctuation

Positron Lifetime Study of the Single-Phase B2.Ni_(100-x)Al_x and Ni_(50-x)Co_xAl_(50) Intermetallics

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Journal of materials Science & Technology 2000年第4期16卷 379-382页

作者： Rongshi CHEN, Jianting GUO and Wenlong ZHOU (Department of Superalloys, Institute of Metal Research, chinese academy of sciences, shenyang 110015,{2.) Liangyue XIONG (international center for materials physics, and Liaoning Key Laboratory for materials Department of Superalloys Institute of Metal Research Chinese Academy of Sciences Shenyang 110015 China Liaoning Key Laboratory for materials and Hydrogen Institute of Metal Research Chinese Academy of Sciences Shenyang 110015 China

In order to understand the point defect structure in NiAl Intermetallic compound, the positron lifetime in binary Ni_(100-x)Al_x (53≥x≥45) and ternary B2.Ni_(50-x)Co_xAl_(50) (x=0, 5, 10, 15) intermetallic compounds as a function of composition were measured. It is shown that the positron lifetime spectra of these compounds can be consistently expressed by single-component lifetimes. The positron lifetime value in ternary Ni_(50-x)Co_xAl_(50) alloy is independent of Co content and equal to that detected in both stoichiometric and Al-rich NiAl. From an analysis of the present results, it is suggested that the constant lifetime ofт≈180 ps should be ascribed to saturation trapping and annihilation of positron exclusively at Ni vacancy, no evidence for the presence of Al vacancy is available.

关键词： x)Co_xAl Intermetallics x)Al_x and Ni