Les modèles basés sur la mécanique des milieux continus prévoient généralement une déformation à la rupture plus élevée, ainsi qu'une durée de vie en fluage beaucoup plus longue que les valeurs observées expérimentalement. Cette thèse met en évidence deux aspects de cette problématique en analysant l’endommagement à l'aide de tomographie in situ à rayons X de synchrotron et reconstruction 3D de la structure polycristalline par polissages successifs.L’endommagement en termes de fraction surfacique des cavités a été identifié dans les couches de reconstructions tomographiques perpendiculairement à l’axe de déformation. L'évolution de la fraction surfacique des cavités a été comparée avec le modèle de prédiction de Cocks et Ashby. Ce dernier surestime la durée de vie en fluage et sous-estime l’état de l’endommagement. L'importance de l'hétérogénéité initiale de l’endommagement et l’effet de localisation de l’endommagement est également souligné. L'amplitude de la plus grande fluctuation surfacique augmente de façon parabolique en fonction de la fraction surfacique moyenne.Une méthode de sectionnement sériel améliorée basée sur la profilométrie de surface a été développée. Elle permet la mesure précise de l'épaisseur du matériau enlevée localement. Les analyses ont montré que l'emplacement des cavités par rapport aux joints de grains et l’orientation cristallographique des grains au voisinage est similaire pour les échantillons déformé par différents mécanismes de fluage. La population relative des cavités de fluage présente aux joints de grains simples est supérieure à celle présente aux joints triples. Les cavités trouvées aux joints triples, cependant, sont plus grandes. / Power law creep damage is one of the most intriguing unsolved phenomena of materials science. Models based on continuum mechanics generally predict a much higher strain to failure, as well as a much longer creep lifetime than experimentally observed values. This thesis highlights two aspects of this problematic by analyzing creep damage in copper using in situ synchrotron tomography and 3D reconstruction of the damaged polycrystal structure by serial sectioning.Damage in terms of the area fraction of voids was first identified in slices of tomographic reconstructions of creep deformed copper. The local and global evolution of cavities area fraction was checked against the Cocks and Ashby model and it was found that the model overestimates creep lifetime and underestimates damage development. The importance of the initial damage heterogeneity and the role of damage localization are also emphasized. It was found that the amplitude of the largest damage fluctuation increases parabolically as a function of cavity’s mean area fraction.An improved serial sectioning method based on surface profilometry was developed, which allows the accurate measurement of the removed local material thickness. The 3D reconstructions enabled identifying the creep voids and the grains of the polycrystal. It was shown that with the exception of the void shape, the relationship between void location at a given grain boundary and crystallographic orientation of the neighbor grains is similar in samples deformed by different creep mechanisms. The relative population of creep voids is higher at simple grain boundaries than at triple junctions. Voids found at a triple boundary, however, are larger.

<p>  </p> <p>Due to miniaturization of electronic devices new electronic packaging strategies, such as Heterogeneous Integration Packaging (HIP), are being developed. In HIP, the space in the package is strategically mapped out to maximize the placement of components including all types of materials. Thus, there is a need to develop and understand the behavior of lower-melting point metallic interconnects as they will be located next to lower melting point materials, such as polymers. </p> <p>The composition of alloying elements in Sn-rich solder plays a pivotal role in determining the microstructural properties of the solder joint. However, the complex mechanisms governing the solidification processes of Sn-In, and Sn-Bi alloys are still not fully understood. Furthermore, the experimental characterization of phase formation poses significant challenges.</p> <p>This dissertation focuses on understanding microstructural evolution in Sn-In and Sn-Bi alloys during reflow. A systematic approach to characterizing the microstructure of alloys was developed, utilizing electron microscopy, non-destructive x-ray tomography and diffraction techniques, ranging from lab-scale to synchrotron experiments. The influence of In addition on microstructure was correlated with the mechanical behavior obtained using nanoindentation. The experimental understanding was further correlated with the Density Functional Theory (DFT) calculations. To study the Sn-Bi microstructures, the effect of experimental parameters, such as the cooling rate during solidification was elucidated. A 4D study was conducted, involving the analysis of 3D microstructures along with time evolution, to gain a comprehensive understanding of the solidification dynamics using synchrotron white beam tomography. For the first time, we observed a regular pyramidal morphology of Bi forming in the solder alloy. The 4D analysis provided crucial insights into morphology formation, growth kinetics, defect formation during solidification. The crystallographic analysis unraveled unique insights into the solid-liquid interface stability for semi-metals. Furthermore, the simultaneous Energy Dispersive Diffraction (EDD) analysis yielded a deeper understanding into the phase formation and lattice strain evolution. A fundamental relationship between the diffraction intensity and phase fractions, from imaging, was obtained. The experimental methodology developed in this work has the potential to be extended to investigate a wide range of alloy solidification mechanisms, enabling a deeper understanding of these materials.</p>