다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

EMS-A software package for electron diffraction analysis and HREM image simulation in materials science

Overview of constitutive laws, kinematics, homogenization and multiscale methods in crystal plasticity finite-element modeling: Theory, experiments, applications

High angle boundaries formed by grain subdivision mechanisms

A special deformation technique, equal channel angular extrusion, (ECAE) to control materials structure, texture and physico-mechanical properties is described in detail. The paper presents a continual analysis of stress, strain, shear planes, steady and localized flow, multipass processing which define microstructural effects and are critical for attained results. Links between macromechanics of simple shear and grain refinement are outlined.

Equal channel angular extrusion: from macromechanics to structure formation

Silicon bicrystals have been fabricated by sintering together single crystal {001} and {111} wafers with low angle misorientations In the range of 0.5 to 3.0 degrees. The interfaces in these bicrystals contain regular arrays of screw dislocations with observed spacings of 10 to 40 nm. The dislocations were decorated with copper which was first sputter-deposited on an external surface, then diffused into the interface by annealing the bicrystal at 400°C for 15 minutes. Analytical electron microscopy was used to characterize the spacing, orientation, and copper concentration of these dislocation arrays. The electrical properties of both decorated and undecorated bicrystals were determined using a two-probe step I-V method, and the behavior of both types of bicrystals compared.

The Structural and Electrical Characterization of Copper Decorated Boundaries in Silicon Bicrystals

Transmission electron microscopy has been used to study the atomic and dislocation structure of deformed and undeformed Σ13 {510} boundary in Si. It is shown that there are several alternative structures for this boundary, which may be separated by imperfect and partial grain boundary dislocations. It is also shown that the dissociation of crystal lattice dislocations which interact with the boundary during deformation results is far more complicated than simple geometrical models applicable in monatomic materials predicts.

Dislocation Dissociation in the Σ13 Grain Boundary in Silicon

Transmission Electron Microscope characterization of a slip propagation event in alpha brass

Silicon bicrystals containing Σ =3(60°/[111] 1,2 ) twin boundaries have been fabricated by sintering together single crystal (IMi) :vafers (which deviated from the exact (111) by upto ±4′). Transmission electron microscopic investigation revealed the boundaries to be near-twin boundaries having a superposed tilt component. The grain boundary dislocation structure of these boundaries has been studied in a transmission electron microscope (TEM) and interpreted as arising from the interaction of a large tilt component with a smaller twist component, to give the observed low energy configuration.

Structure of Perturbed Twin Boundaries in Silicon

In body centered cubic (bcc) β titanium alloys, the precipitate most commonly found in the β matrix is the hexagonal closed packed (hcp) α phase, with the two often in the Burgers orientation [1]. The anisotropy present in the α/β interfacial structure influences the morphology of the α precipitate, and structural defects, such as dislocations and ledges present in the α/β interface, may also affect precipitate-dislocation interactions, and so change the deformation mechanisms. Recently, three different fine scale alpha microstructures in a metastable beta titanium alloy, Ti-5Al-5Mo-5V-3Cr (Ti5553), have been investigated by Zheng et al, classified as refined, more-refined, and super-refined α microstructures [2-5]. The refined α microstructures (number density ≤10/mm), shown in Fig. 1, were produced by step-quenching from above the β transus to 600°C, and rapidly heating (rate ~100°C/min) the as-quenched material to 600°C [2, 3]. It is observed a) that the nucleation and growth of the α plates is extremely rapid, and b) that they align along three specific crystallographic orientations. In order to understand the mechanism of formation of the refined α microstructure in these alloys, a detailed study of the α/β interface structure in the early stages of α phase precipitation, is required.

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William A.T. Clark

Papers

The Structural and Electrical Characterization of Copper Decorated Boundaries in Silicon Bicrystals

Dislocation Dissociation in the Σ13 Grain Boundary in Silicon

Transmission Electron Microscope characterization of a slip propagation event in alpha brass

Structure of Perturbed Twin Boundaries in Silicon

Characterization of Alpha/Beta Interface Structure in a Titanium Alloy Using Aberration-Corrected Scanning Transmission Electron Microscope