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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)

材料科学技术（英文）

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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Energy Minigaps in the Quantum Well Wires with Periodical Lateral Surface Structures

Zhenyan DENG , Hong SUN , and Shiwei GU (Dept. of Applied Physics , Shanghai Jiaotong University , Shanghai , 200030 , China)(To whom correspondence should be addressed)(Present address: No .5 Dept.. Shanghai Institute of Ceramics.Chinese Academy. of Sciences.

材料科学技术（英文）

Energy minigaps caused by lateral surface structures in quasi-one-dimensional GaAs/ AlAs quantum well wires are calculated with the variational and degenerate-perturbational approaches.By a coordinate transformotion. the structured interfaces of the wires are transformed into planar ones so that the boundary conditions of the electronic wave functions can be satisfied exactly on the interfaces. The dependence of the energy minigaps on the lateral surface structures are discussed.

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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)

材料科学技术（英文）

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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Perspective in Development of Shape Memory Materials Associated with Martensitic Transformation

Zuyao XU (T. Y.Hsu) (Shanghai Jiaotong University , Shanghai , 200030 , China)

材料科学技术（英文）

By consideration of the characteristics of martensitic transformation and the derivation from the application of the group theory to martensitic transformation, it may be concluded that the shape memory effect (SME) can be attained in materials through a martensitic transformation and its reverse transformation. only when there forms single or nearly single variant of martensite, with an absence of the factors causing the generation of the resistance against SME. on this principle, various shape memory materials including nonferrous alloys. iron-based alloys and ceramics containjng zirconia are expected to be further developed. A criterion for thermoelastic martensitic transformation is presented, Factors which may act as the resistance against SME in various materials are briefly described

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Temperature Effects on the Self-trapping Energy of a Polaron in a GaAs Parabolic Quantum Dot

Kadi ZHU and Shiwei GU (Institute of Condensed Matter Physics , Shanghai Jiaotong University , Shanghai , 200030 , China)(To whom correspondence should be addressed)

材料科学技术（英文）

The temperature and the size dependences of the self-trapping energy of a polaron in a GaAs parabolic quantum dot are investigated by the second order Rayleigh-Schrodinger perturbation method using the framework of the effective mass approximation. The numerical results show that the self-trapping energies of polaron in GaAs parabolic quantum dots shrink with the enhancement of temperature and the size of the quantum dot. The results also indicate that the temperature effect becomes obvious in small quantum dots

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STUDY ON THE THREESTAGE CREEP OF THE DD3SINGLE CRYSTAL SUPERALLOY

Author X.A. Zhang1) , H.Q. Xia1) , Z.T. Wu1) , Y.F. Han1) , R. Shi2) and G.X. Hu2) \= 1) Mechanical Properties Laboratory , Beijing Institute of Aeronautical Materials , Beijing 100095 , China2) The State Education Commission Open Research Laboratory for High Temperature

金属学报(英文版)

Materials and Testing, Shanghai Jiao Tong University, Shanghai 200030, ChinaManuscript received 18 October 1998 The threestage creep behavior of DD3 single crystal superalloy had been studied. The results show that the creeprupture properties of DD3 single crystal satisfy the requirements for high performance turbine blade application. The influence of crystal orientation on the creeprupture property of DD3 single crystal was tested and discussed. An engineering criterion to evaluate the regimes of secondary and tertiary creep is proposed, and this method gives a reasonable result for practical applications. The fractography and TEM micrography of the tested specimens had been studied, and it is determined that the glidecontrolled creep is the basic creep mechanism of DD3 single crystal at intermediate temperature, but the thermally activated processes become dominant at higher temperature.

关键词: threestage creep curve , null , null , null

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