This dissertation addresses two critical issues in the deformation of nc metals and alloys: (1) A stress-induced genuine grain growth after the plastic deformation rather than just a change of the grain shape; (2) A systematically quantitative study of micrsostructural evolution during the plastic deformation. These two critical issues point to the deformation of nc materials with the average-grain sizes within the range of 10 to 50 nm, which is the most interesting and controversial region in the current time. The current study provides a systematic and detailed microstructural evolution for this region, which is definitely beneficial for the investigation of the deformation mechanism in this region, especially for the simulation. The main experimental and data-analysis methods employed in this research are synchrotron high-energy X-ray diffraction, X-ray line profile analysis, and texture analysis. The combination of these methods is beneficial to the accurate microstructural interpretation of the bulk materials.

The present PhD project was carried out as part of an EPSRC Leadership Fellowship for the study of irradiation damage in zirconium alloys. The National Nuclear Laboratory (NNL) directly supported the project in terms of additional funding and insightful discussions regarding irradiation damage in zirconium alloys. The research carried out within the project aims to gain a better understanding of both a- and c-loops, formed during irradiation damage in zirconium alloys. A range of techniques have been utilised to assess the morphology and density of the dislocation loops after proton-irradiations. These techniques include transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS) and line profile analysis (LPA) using synchrotron X-ray diffraction (SXRD) profiles and analysing the data utilizing the extended convolutional multiple whole profile (CMWP) analysis software. The effect of experimental conditions on dislocation loop formation and stability of a-loops during post-irradiation annealing have also been investigated. Proton-irradiations were carried out on the commercial alloys Zircaloy-2, Optimized ZIRLOTM and also on binary Zr-0.1Fe and Zr-0.6Fe alloys. A mechanism has been proposed as to the effect of Fe redistribution on dislocation loop formation. By comparing proton-irradiated Zr-0.1Fe and Zircaloy-2 alloys it was possible to investigate the effect of increased amount of Fe redistribution, which occurs from secondary phase particle (SSP) dissolution, on the microstructural features that develop during irradiation. Zircaloy-2 has a higher density of SPPs and these are more homogenously distributed throughout the matrix in comparison to the Zr3Fe SPPs found in the Zr-0.1Fe alloy. It was found that Fe redistribution facilitates the formation of Fe-rich nano-precipitation. Bright-field STEM imaging has been used to image a- and c-loops and it was found that Zircaloy-2 had a lower dislocation line density compared to Zr-0.1Fe for both types of loops at similar damage levels. Therefore it has been proposed that Fe redistributed from SPPs precipitates in the matrix and the subsequent irradiation-induced precipitates act as annihilation sites for point defects; therefore preventing the formation of new dislocation loops and the growth of existing loops. In order to assess the effect of proton-irradiation temperature on a-loops, Zircaloy-2 and Optimized ZIRLOTM were proton irradiated to 2.3 dpa at 280°C, 350°C and 450°C. It was found that the a-loop density dropped in both alloys as irradiation temperature was increased and the a-loop diameter decreased. The changes in the density and size were more dramatic in Zircaloy-2 and this was explained by the presence of fine irradiation induced clustering of Nb seen in Optimized ZIRLOTM. These trends were calculated from both STEM imaging and CMWP, highlighting the suitability of using CMWP to investigate irradiation-induced dislocations. Finally the stability of the a-loops in proton-irradiated Zr-Fe binary alloys were investigated using novel in-situ SXRD and TEM annealing experiments. From CMWP analysis of the profiles generated during the in-situ annealing of a Zr-0.6Fe 3 dpa sample it was shown that the majority of the annealing takes place between 300°C-400°C. This was highlighted by a period of no change in the dislocation density up to 300°C, after which the density drops dramatically. In-situ annealing of a 1.5 dpa Zr-0.1Fe sample in the TEM allowed for the observation of a-loop gliding along prismatic planes enabling the annealing process taking place between 280°C-450°C, i.e. a similar temperature range at which SXRD analysis indicates the greatest level of annealing.

Accurate statistical characterization of nanomaterials is crucial for their use in emerging technologies. This work investigates how different structural characteristics of metal nanoparticles influence the line profiles of the corresponding powder diffraction pattern. The effects of crystallite size, shape, lattice dynamics, and surface strain are all systematically studied in terms of their impact on the line profiles. The studied patterns are simulated from atomistic models of nanoparticles via the Debye function. This approach allows for the existing theories of diffraction to be tested, and extended, in an effort to improve the characterization of small crystallites. It also begins to allow for the incorporation of atomistic simulations into the field of diffraction. Molecular dynamics simulations are shown to be effective in generating realistic structural models and dynamics of an atomic system, and are then used to study the observed features in the powder diffraction pattern. Furthermore, the characterization of a sample of shape controlled Pt nanoparticles is carried out through the use of a developed Debye function analysis routine in an effort to determine the predominant particle shape. The results of this modeling are shown to be in good agreement with complementary characterization methods, like transmission electron microscopy and cyclic voltammetry.

O objetivo deste trabalho foi desenvolver e implementar uma metodologia envolvendo a análise de perfis de difração de raios X (X-ray Line Profile Analysis - XLPA) para o estudo e determinação do tamanho médio de cristalitos e microdeformação em materiais. Para isto houve o desenvolvimento de um programa computacional para facilitar o tratamento dos picos presentes em um difratograma e realizar a deconvolução de perfis através do Método de Stokes para se corrigir a contribuição instrumental nos perfis de difração. Os métodos de XLPA de espaço real estudados e aplicados neste trabalho foram os métodos de Scherrer, Williamson-Hall e Single-Line (ou Linha Única) e o método de Warren-Averbach de espaço de Fourier. Além disso, utilizando-se um modelamento matemático foi possível calcular a distribuição de tamanhos de cristalitos para um caso isotrópico, onde considerou-se a distribuição log-normal e cristalitos com forma esférica. Foi possível demonstrar que a teoria proposta pode ser considerada como uma boa aproximação avaliando-se uma razão de dispersão. As metodologias descritas acima foram aplicadas em dois materiais distintos: na liga metálica Zircaloy-4 e em ZnO. / The objective of this work was to develop and implement a methodology of X-ray Line Profile Analysis (XLPA) for the study and determination of the mean crystallite sizes and microstrains in materials. A computer program was developed to speed up the treatment of diffraction peaks and perform the deconvolution utilizing the Stokes method to correct the instrumental contribution in the X-ray diffraction measurements. The XLPA methods used were the Scherrer, Williamson-Hall and Single-Line methods, which can be called real space methods, and the Fourier space method of Warren-Averbach. Furthermore, considering a mathematical modelling it was possible to calculate the crystallite size distribution, considering the log-normal distribution and spherical crystallites. It was possible to demonstrate the proposed theory can provide reliable results evaluating a dispersion parameter. The methodologies described above were applied in two distinct materials: in the alloy Zircaloy-4 and in ZnO.

O objetivo deste trabalho foi desenvolver e implementar uma metodologia envolvendo a análise de perfis de difração de raios X (X-ray Line Profile Analysis - XLPA) para o estudo e determinação do tamanho médio de cristalitos e microdeformação em materiais. Para isto houve o desenvolvimento de um programa computacional para facilitar o tratamento dos picos presentes em um difratograma e realizar a deconvolução de perfis através do Método de Stokes para se corrigir a contribuição instrumental nos perfis de difração. Os métodos de XLPA de espaço real estudados e aplicados neste trabalho foram os métodos de Scherrer, Williamson-Hall e Single-Line (ou Linha Única) e o método de Warren-Averbach de espaço de Fourier. Além disso, utilizando-se um modelamento matemático foi possível calcular a distribuição de tamanhos de cristalitos para um caso isotrópico, onde considerou-se a distribuição log-normal e cristalitos com forma esférica. Foi possível demonstrar que a teoria proposta pode ser considerada como uma boa aproximação avaliando-se uma razão de dispersão. As metodologias descritas acima foram aplicadas em dois materiais distintos: na liga metálica Zircaloy-4 e em ZnO. / The objective of this work was to develop and implement a methodology of X-ray Line Profile Analysis (XLPA) for the study and determination of the mean crystallite sizes and microstrains in materials. A computer program was developed to speed up the treatment of diffraction peaks and perform the deconvolution utilizing the Stokes method to correct the instrumental contribution in the X-ray diffraction measurements. The XLPA methods used were the Scherrer, Williamson-Hall and Single-Line methods, which can be called real space methods, and the Fourier space method of Warren-Averbach. Furthermore, considering a mathematical modelling it was possible to calculate the crystallite size distribution, considering the log-normal distribution and spherical crystallites. It was possible to demonstrate the proposed theory can provide reliable results evaluating a dispersion parameter. The methodologies described above were applied in two distinct materials: in the alloy Zircaloy-4 and in ZnO.