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.

Les modèles basĂ©s sur la mĂ©canique des milieux continus prĂ©voient gĂ©nĂ©ralement une dĂ©formation Ă  la rupture plus Ă©levĂ©e, ainsi qu’une durĂ©e de vie en fluage beaucoup plus longue que les valeurs observĂ©es expĂ©rimentalement. Cette thèse met en Ă©vidence deux aspects de cette problĂ©matique en analysant l’endommagement Ă  l’aide de tomographie in situ Ă  rayons X de synchrotron et reconstruction 3D de la structure polycristalline par polissages successifs.L’endommagement en termes de fraction surfacique des cavitĂ©s a Ă©tĂ© identifiĂ© dans les couches de reconstructions tomographiques perpendiculairement Ă  l’axe de dĂ©formation. L’Ă©volution de la fraction surfacique des cavitĂ©s a Ă©tĂ© comparĂ©e avec le modèle de prĂ©diction de Cocks et Ashby. Ce dernier surestime la durĂ©e de vie en fluage et sous-estime l’état de l’endommagement. L’importance de l’hĂ©tĂ©rogĂ©nĂ©itĂ© initiale de l’endommagement et l’effet de localisation de l’endommagement est Ă©galement soulignĂ©. L’amplitude de la plus grande fluctuation surfacique augmente de façon parabolique en fonction de la fraction surfacique moyenne.Une mĂ©thode de sectionnement sĂ©riel amĂ©liorĂ©e basĂ©e sur la profilomĂ©trie de surface a Ă©tĂ© dĂ©veloppĂ©e. Elle permet la mesure prĂ©cise de l’Ă©paisseur du matĂ©riau enlevĂ©e localement. Les analyses ont montrĂ© que l’emplacement des cavitĂ©s par rapport aux joints de grains et l’orientation cristallographique des grains au voisinage est similaire pour les Ă©chantillons dĂ©formĂ© par diffĂ©rents mĂ©canismes de fluage. La population relative des cavitĂ©s de fluage prĂ©sente aux joints de grains simples est supĂ©rieure Ă  celle prĂ©sente aux joints triples. Les cavitĂ©s trouvĂ©es aux joints triples, cependant, sont plus grandes.