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Dislocation Structure (dislocation + structure)
Selected AbstractsCharacterization of dislocation structures in copper single crystals using electron channelling contrast technique in SEMCRYSTAL RESEARCH AND TECHNOLOGY, Issue 3 2009Xiao-Wu Li Abstract The dislocation structures induced by low-plastic-strain-amplitude cyclic deformation of [111] multiple-slip-oriented Cu single crystals were investigated using electron channelling contrast (ECC) technique in scanning electron microscopy (SEM). At a low plastic strain amplitude ,pl of 8.8 × 10,5, the saturated dislocation structure is mainly composed of labyrinth-like vein structure (or irregular labyrinths), and the cyclic hardening behavior at such a low ,pl is interpreted as being the result of dislocation multiplication by a Frank-Read mechanism. As ,pl increases to 4.0 × 10,4, the unsaturated dislocation structure exhibits two kinds of distinctive configurations, i.e., dislocation walls and misoriented cells. Interestingly, these misoriented dislocation cells are strictly aligned along the primary slip plane (111), constituting a unique persistent slip band (PSB) structure. Here, these cells are thus called PSB cells. In addition, there is a locally distinctive region comprising some cells having a recrystallization-like feature in the whole structure of PSB cells. The formation of the structure of PSB cells is discussed. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Warm Laser Shock Peening Driven Nanostructures and Their Effects on Fatigue Performance in Aluminum Alloy 6160,ADVANCED ENGINEERING MATERIALS, Issue 4 2010Chang Ye Warm laser shock peening is an innovative manufacturing process that integrates laser shock peening and dynamic aging to improve materials' fatigue performance. Compared to traditional laser shock peening (LSP), warm laser shock peening (WLSP) , i.e., LSP at elevated temperatures , provides better performance in many aspects. WLSP can induce nanoscale precipitation and high density dislocation arrangement, resulting in higher surface strength and lower surface roughness than LSP, which are both beneficial for fatigue life improvement. Due to pinning of the dislocation structure by nanoscale precipitates , so-called dislocation pinning effects , the relaxation of residual stress and surfaces dislocation arrangement is significantly reduced. In this study, AA6061 alloy is used to evaluate the WLSP process. It is found that the fatigue life improvements after WLSP are not only caused by large compressive residual stress and high density dislocations but also by the higher stability of the residual stresses and surface strength during cyclic loading. [source] X-ray diffractometry and topography of lattice plane curvature in thermally deformed Si waferJOURNAL OF SYNCHROTRON RADIATION, Issue 1 2008J. M. Yi The correlation between the microscopic lattice plane curvature and the dislocation structure in thermal warpage of 200,mm-diameter Czochralski Si (001) wafers has been investigated using high-resolution X-ray diffractometry and topography. It is found that the (004) lattice plane curvature is locally confined between two neighboring slip bands, with the rotation axis parallel to the slip bands. High-resolution topography reveals that the curvature resulted from a fragmented dislocation structure. The local confinement is attributed to the multiplication of the dislocations that are generated between the two slip bands. [source] Synthesis of Conducting Polymer Spiral Nanostructures Using a Surfactant Crystallite TemplateMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 11 2009Yong Wang Abstract The present work describes, for the first time, the synthesis of spiral nanostructures of conducting polymers by chemical oxidant polymerization using a hydrated surfactant (sodium dodecyl sulfonate (SDSn)) crystallite template. A spiral dislocation structure on the surface of a hydrated SDSn crystallite has been observed and is responsible for the growth of the spiral nanoarchitecture of conducting polymers (polypyrrole, polyaniline). Ammonium peroxydisulfate (APS) has a strong tendency to induce the formation of a spiral dislocation structure of hydrated SDSn crystallites. The mechanism of adsorption of pyrrole or aniline oligomers on the steps of dislocation is proposed for the growth of conducting polymer spirals. [source] Prediction of intragranular strains in metallic polycrystals with a two-level homogenisation approach: Influence of dislocation microstructure on the mechanical behaviourPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2006D. Gloaguen Abstract A two-level homogenisation approach is applied to the micro-mechanical modelling of the elasto-plasticity of polycrystalline materials during various strain-path changes. The model is tested by simulating the development of intragranular strains during different complex loads. Mechanical tests measurements are used as a reference in order to validate the model. The anisotropy of plastic deformation in relation to the evolution of the dislocation structure is analysed. The results demonstrate the relevance of this approach for FCC polycrystals. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Peculiarities of dislocation photoluminescence in germanium with quasi-equilibrium dislocation structurePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2007S. Shevchenko Abstract The dislocation photoluminescence (DPL) at 4.2 K was studied in germanium (Ge) single crystals of n- and p-type with quasi-equilibrium structure of 60° dislocations. The DPL spectra for different samples were decomposed on Gaussian lines (Gm -lines) over the range 0.47-0.58 eV characterized by practically the same peak energies Em and the widths under 15 meV. The G-lines with Em , 0.55 eV were ascribed to the radiation of regular segments of 60° dislocations with different stacking fault (SF) widths , between 30 and 90° partials. An increase of the dislocations density up to ND , 107 cm,2 was found to result in a considerable growth of the intensity of the G-lines with Em <0.513 eV. The factors, which promote the appearance of different , values for quasi-equilibrium 60° dislocation structure, are discussed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Characterization of dislocation structures in copper single crystals using electron channelling contrast technique in SEMCRYSTAL RESEARCH AND TECHNOLOGY, Issue 3 2009Xiao-Wu Li Abstract The dislocation structures induced by low-plastic-strain-amplitude cyclic deformation of [111] multiple-slip-oriented Cu single crystals were investigated using electron channelling contrast (ECC) technique in scanning electron microscopy (SEM). At a low plastic strain amplitude ,pl of 8.8 × 10,5, the saturated dislocation structure is mainly composed of labyrinth-like vein structure (or irregular labyrinths), and the cyclic hardening behavior at such a low ,pl is interpreted as being the result of dislocation multiplication by a Frank-Read mechanism. As ,pl increases to 4.0 × 10,4, the unsaturated dislocation structure exhibits two kinds of distinctive configurations, i.e., dislocation walls and misoriented cells. Interestingly, these misoriented dislocation cells are strictly aligned along the primary slip plane (111), constituting a unique persistent slip band (PSB) structure. Here, these cells are thus called PSB cells. In addition, there is a locally distinctive region comprising some cells having a recrystallization-like feature in the whole structure of PSB cells. The formation of the structure of PSB cells is discussed. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A Polycrystalline Approach to the Cyclic Behaviour of f.c.c. Alloys , Intra-Granular HeterogeneityADVANCED ENGINEERING MATERIALS, Issue 9 2009Xavier Feaugas For several decades, the plastic deformation mechanisms of f.c.c. metals under cyclic loading have received considerable attention. The extensive work on this subject has gradually lead to the identification of the physical processes to be included in a formal scheme of fatigue behavior. Accordingly, we propose a review of the physical mechanisms of plastic deformation in f.c.c. metals and alloys to define the state-of-the-art and motivate future studies. The aim is to demonstrate the importance of a good knowledge of the heterogeneous nature of deformation at the intra-granular scale in defining a physical model of cyclic behavior. A large characterization of the different stages associated with the evolution of heterogeneous dislocation structures during tensile and cyclic loadings is given for an austenitic stainless steel AISI 316L. A unified view of these various structures is proposed in the form of a modified Pedersen's map [,max,=,f(,pcum), where ,max is the maximum plastic strain and ,pcum the cumulative plastic strain] in the case of tensile loading and different kinds of cyclic loading: uni-axial and multi-axial tests under stress or strain amplitude control. The specificities of each domain defined in the map are discussed in terms of long-range internal stresses in order to formalize, in a simple composite scheme, the intra-granular stress,strain field. The importance of taking into account this scheme and the nature of the different dislocations populations in a polycrystalline model is illustrated. [source] Modeling and simulation of induced anisotropy and directional hardening effects due to an evolving microstructure in metalsPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2005J. Wang The purpose of the current work is the formulation, numerical implementation and application of a material model for anisotropic hardening in metals taking the interplay between the the direction of inelastic deformation, the orientation of dislocation structures, and the current deformation/loading direction into account. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||