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John P Dear - One of the best experts on this subject based on the ideXlab platform.
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parametric optimisation and Microstructural Analysis on high power yb fibre laser welding of ti 6al 4v
Optics and Lasers in Engineering, 2016Co-Authors: L Chen, C M Davies, John P DearAbstract:Abstract In this work thin sheets of Ti–6Al–4V were full penetration welded using a 5 kW fibre laser in order to evaluate the effectiveness of high power fibre laser as a welding processing tool for welding Ti–6Al–4V with the requirements of the aircraft industry and to determine the effect of welding parameters including laser power, welding speed and beam focal position on the weld microstructure, bead profile and weld quality. It involved establishing an understanding of the influence of welding parameters on Microstructural change, welding defects, and the characteristics of heat affected zone (HAZ) and weld metal (WM) of fibre laser welded joints. The optimum range of welding parameters which produced welds without cracking and porosity were identified. The influence of the welding parameters on the weld joint heterogeneity was characterised by conducting detailed Microstructural Analysis.
L Chen - One of the best experts on this subject based on the ideXlab platform.
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parametric optimisation and Microstructural Analysis on high power yb fibre laser welding of ti 6al 4v
Optics and Lasers in Engineering, 2016Co-Authors: L Chen, C M Davies, John P DearAbstract:Abstract In this work thin sheets of Ti–6Al–4V were full penetration welded using a 5 kW fibre laser in order to evaluate the effectiveness of high power fibre laser as a welding processing tool for welding Ti–6Al–4V with the requirements of the aircraft industry and to determine the effect of welding parameters including laser power, welding speed and beam focal position on the weld microstructure, bead profile and weld quality. It involved establishing an understanding of the influence of welding parameters on Microstructural change, welding defects, and the characteristics of heat affected zone (HAZ) and weld metal (WM) of fibre laser welded joints. The optimum range of welding parameters which produced welds without cracking and porosity were identified. The influence of the welding parameters on the weld joint heterogeneity was characterised by conducting detailed Microstructural Analysis.
A. Chehaidar - One of the best experts on this subject based on the ideXlab platform.
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Microstructural Analysis of nanostructured amorphous silicon–germanium alloys: Numerical modeling
Journal of Non-crystalline Solids, 2011Co-Authors: R. Ben Brahim, A. ChehaidarAbstract:Abstract A detailed Microstructural Analysis of amorphous silicon–germanium alloys with germanium fraction ranging from 0.1 to 0.5 is performed by means of a numerical modeling technique. By substituting Ge atoms for Si atoms in nanoporous paracrystalline network of amorphous silicon, several amorphous silicon–germanium structures have been generated then relaxed. The main aim of our work is to study the effect of compositional heterogeneities on the structural properties of amorphous silicon–germanium alloys in comparison with the standard case, that of a homogeneous random distribution of the atoms. In the present work we envisage the two-phase amorphous silicon–germanium model proposed by Goerigk and Williamson to interpret their anomalous small-angle X-ray scattering measurements; it consists on a mixture of Ge-rich and Ge-poor domains at the nanoscale. The microstructure of our structural models is analyzed by examining the macroscopic mass density, the X-ray diffraction intensity, the radial distribution functions, the bond lengths and the coordination numbers within the first coordination shell of Si and Ge atoms.
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Microstructural Analysis of atomistic models of Si-rich amorphous silicon-germanium alloys
Journal of Non-crystalline Solids, 2011Co-Authors: R. Ben Brahim, A. ChehaidarAbstract:Abstract A detailed Microstructural Analysis of amorphous silicon–germanium alloys with Ge fraction ranging from 0.1 to 0.5 is performed by means of a numerical modeling technique. By substituting Ge atoms for Si atoms in the nanoporous paracrystalline network of amorphous silicon, several amorphous silicon–germanium structures have been generated. Our main aim in the present work is to study the effect of compositional heterogeneities on the structural properties of amorphous silicon–germanium alloys in comparison with the standard case, that of a homogeneous random distribution of the atoms. We have limited ourselves here to the borderline case, that of segregation of Ge atoms at the nanoscale. The microstructure of our structural models is analyzed by examining the macroscopic mass density, the intensity of X-ray diffraction, the pair distribution functions, the bond lengths and the coordination numbers within the first coordination shell of Si and Ge atoms. Our structural models account for the experimentally derived mass densities regardless of the Ge distribution pattern. They also account for the intense small-angle X-ray scattering observed for some amorphous silicon–germanium samples. The short-range compositional disorder, reflected in the bond lengths and the coordination numbers within the first coordination shell of Ge atoms, is found to be very sensitive to how these atoms are arranged in the alloys.
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Microstructural Analysis of nanoporous paracrystalline atomistic models of amorphous silicon
Journal of Non-crystalline Solids, 2007Co-Authors: A. Chehaidar, T. ChermitiAbstract:A detailed Microstructural Analysis of amorphous silicon is performed via numerical modeling technique. Nanoporous paracrystalline models have been proposed. Intermixed nanocrystallites and nanovoids of various sizes and concentrations have been introduced into a continuous random network that was generated with a vacancy model. Using the conjugate gradient method, the structures have been relaxed by minimizing their total strain energy described by the anharmonic Keating model. The obtained nanoporous structures are energetically competitive with the voidless paracrystalline networks. Nanoporous models with large voids are energetically more favorable than those with small voids. The nanoporous paracrystalline model is less dense than the crystalline phase, contrary to the paracrystalline model. This density decreases with increasing the void size for a fixed void volume fraction. Nanoporous paracrystalline structures reproduce the experimental structure factor better than the paracrystalline network. They account for, in particular, the intense small-angle scattering observed for some a-Si samples. The paracrystallites form amorphous zones but with local and topological ordering neatly better than the surrounding matrix. Such structural heterogeneity gives so a satisfactory explanation of the nanoscale fluctuation electron microscopy data reported recently by Treacy and Gibson.
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Microstructural Analysis of paracrystalline atomistic models of amorphous silicon
Journal of Non-crystalline Solids, 2006Co-Authors: A. Chehaidar, H. KhelifiAbstract:A detailed Microstructural Analysis of amorphous silicon is performed by means of a numerical modeling technique. Paracrystalline models of amorphous silicon, first proposed by Treacy, Gibson and Keblinski, have been generated. Nanocrystallites of various sizes and concentrations have been introduced into a continuous random network that was generated with a vacancy model. Using the conjugate gradient method, the structures have been relaxed by minimizing their total strain energy described by the anharmonic Keating model. The computed pair correlation functions of these structural models bring to the fore a unique behavior of the paracrystalline networks in the context of diffraction experiments; they appear amorphous as the continuous random network model. The paracrystalline model remains denser than the crystalline phase, contrary to experimental observations. However, the former is found to be less homogenous than the CRN model, thus giving a satisfactory explanation of the nanoscale fluctuation electron microscopy data reported recently by Treacy and coworkers.
A Caballero - One of the best experts on this subject based on the ideXlab platform.
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xrd Microstructural Analysis of mullites obtained from kaolinite alumina mixtures
Journal of The European Ceramic Society, 2000Co-Authors: M A Sainz, F J Serrano, J M Amigo, J Bastida, A CaballeroAbstract:Abstract A Microstructural study of mullite obtained by the reaction sintering of kaolinite–α–alumina mixtures in the range 1150–1700°C has been performed by using X-ray line profile analyses together with scanning and transmission electron microscopy equipped with microAnalysis by energy dispersion (SEM-EDS, TEM-AEM). Two kinds of morphology corresponding to primary (elongated grains) and secondary (equiaxed grains) mullite have been observed. A bimodal crystallite size distribution has been detected through XRD Microstructural Analysis from 1300°C. The results obtained by this method are compared with SEM/TEM data.
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XRD Microstructural Analysis of mullites obtained from kaolinite–alumina mixtures
Journal of The European Ceramic Society, 2000Co-Authors: M A Sainz, F J Serrano, J M Amigo, J Bastida, A CaballeroAbstract:Abstract A Microstructural study of mullite obtained by the reaction sintering of kaolinite–α–alumina mixtures in the range 1150–1700°C has been performed by using X-ray line profile analyses together with scanning and transmission electron microscopy equipped with microAnalysis by energy dispersion (SEM-EDS, TEM-AEM). Two kinds of morphology corresponding to primary (elongated grains) and secondary (equiaxed grains) mullite have been observed. A bimodal crystallite size distribution has been detected through XRD Microstructural Analysis from 1300°C. The results obtained by this method are compared with SEM/TEM data.
C M Davies - One of the best experts on this subject based on the ideXlab platform.
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parametric optimisation and Microstructural Analysis on high power yb fibre laser welding of ti 6al 4v
Optics and Lasers in Engineering, 2016Co-Authors: L Chen, C M Davies, John P DearAbstract:Abstract In this work thin sheets of Ti–6Al–4V were full penetration welded using a 5 kW fibre laser in order to evaluate the effectiveness of high power fibre laser as a welding processing tool for welding Ti–6Al–4V with the requirements of the aircraft industry and to determine the effect of welding parameters including laser power, welding speed and beam focal position on the weld microstructure, bead profile and weld quality. It involved establishing an understanding of the influence of welding parameters on Microstructural change, welding defects, and the characteristics of heat affected zone (HAZ) and weld metal (WM) of fibre laser welded joints. The optimum range of welding parameters which produced welds without cracking and porosity were identified. The influence of the welding parameters on the weld joint heterogeneity was characterised by conducting detailed Microstructural Analysis.