Leonardi, Alberto (2012) Molecular Dynamics and X-ray Powder Diffraction Simulations: Investigation of nano-polycrystalline microstructure at the atomic scale coupling local structure configurations and X-ray powder Diffraction techniques. PhD thesis, University of Trento.
|PDF (Alberto Leonardi's PhD thesis - ISBN 978-88-8443-455-5) - Doctoral Thesis|
Atomistic simulations based on Molecular Dynamics (MD) were used to model the lattice distortions in metallic nano-polycrystalline microstructures, with the purpose of supporting the analysis of the X-ray powder diffraction patterns with a better, atomic level understanding of the studied system. Complex microstructures were generated with a new modified Voronoi tessellation method which provides a direct relation between generation parameters and statistical properties of the resulting model. MD was used to equilibrate the system: the corresponding strain field was described both in the core and in surface regions of the different crystalline domains. New methods were developed to calculate the strain tensor at the atomic scale. Line Profile Analysis (LPA) was employed to retrieve the microstructure information (size and strain effects) from the powder diffraction patterns: a general algorithm with an atomic level resolution was developed to consider the size effects of crystalline domains of any arbitrary shape. The study provided a new point of view on the role of the grain boundary regions in nano-polycrystalline aggregates, exploring the interference effects between different domains and between grain boundary and crystalline regions. Usual concepts of solid mechanics were brought in the atomistic models to describe the strain effects on the powder diffraction pattern. To this purpose the new concept of Directional - Pair Distribution Function (D-PDF) was developed. D-PDFs calculated from equilibrated atomistic simulations provide a representation of the strain field which is directly comparable with the results of traditional LPA (e.g. Williamson-Hall plot and Warren-Averbach method). The D-PDF opens a new chapter in powder diffraction as new insights and a more sound interpretation of the results are made possible with this new approach to diffraction LPA.
|Item Type:||Doctoral Thesis (PhD)|
|Doctoral School:||Materials Science and Engineering|
|Subjects:||Area 09 - Ingegneria industriale e dell'informazione > ING-IND/22 SCIENZA E TECNOLOGIA DEI MATERIALI|
Area 02 - Scienze fisiche > FIS/03 FISICA DELLA MATERIA
|Uncontrolled Keywords:||Nano-polycrystalline microstructure, Atomistic Modelling, Construction of nano-polycrystalline cluster, Space tessellation, Grain size distribution, Voronoi Tessellation, Modified Voronoi Tessellation, Evolutional approach, Molecular Dynamics, Strain at the atomic level, Voronoi Cell Deformation, Interference effects, Line Profile Analysis, Crystallite size, Common Volume Function, Microstrain, Whole Powder Pattern Modelling, Directional - Pair Distribution Function, Waren-Averbach analysis, Distortion field in nano-polycrystalline microstructure from MD|
|Additional Information:||ISBN 978-88-8443-455-5|
|Repository Staff approval on:||06 Dec 2012 13:56|
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