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Diffraction X in-situ sous sollicitation dynamique : caractérisation cristallographique des transformations polymorphiques de l’étain

Abstract : The purpose of this thesis is to collect experimental information about materials undergoing phase transitions under dynamic loading in order to improve current models and numerical simulations. More specifically, we focus on the polymorphic transformation of tin between β and γ phases. A review of the literature enabled to draw the evolution of several physical parameters, including phase transitions, under both quasi-static and dynamic loading. Significant discrepancies are observed on the pressure and temperature conditions for the β-γ transition between dynamic loading and the static phase diagram. Current measurement techniques usually implemented for this type of experiment are not sufficient to explain the origin of this phenomenon. X-ray diffraction is a complementary technique which enables to investigate the crystallographic configuration as well as the microstructure of a material. The continuous improvement of X-ray generation techniques has provided X-ray sources capable of generating intense short pulses to perform X-ray diffraction under shock loading. X-ray diffraction experiments were carried out in two facilities: CEA Gramat,using an X-Pinch generator, and the Advanced Photon Source in Chicago, using asynchrotron beam. Shocks were generated by plate impact experiments with a gas gun launcher. In both cases, a specific synchronization system was designed to probe the shocked state reached by the material under investigation. This technique was coupled with time-resolved velocity measurements to estimate the shock pressure state reached during the experiment and verify the synchronization. A specific tool was designed and developed to simulate diffraction patterns. It facilitates the experiment design and helps to better identify the crystallographic configuration behind the diffraction pattern.Shocks were performed both above the transition pressure, to identify the γ phase, and below the transition to study the evolution of the β structure. Similar results were obtained at both CEA Gramat and the Advanced Photon Source. Diffraction patterns recorded in from (100), (110), (001) and (111) single crystals above the expected phase transition showed that the diffraction pattern of the β phase was observed to disappear, but no clear evidence of the formation of the γ phase could be detected. Diffraction patterns for shocks of increasing pressure enabled to observe new phenomena concerning the (110) β phase before its disappearance. The comparison of the release diffraction patterns enlightened significant differences between high and low pressure experiments. On this new experimental basis, some hypothesis could be proposed regarding the material dynamic behavior. Finally, several prospects were identified, including new tests in the different facilities to deeper investigate this behavior and hopefully confirm the different hypotheses.
Keywords : X-Pinch Plate impact
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David Palma de Barros. Diffraction X in-situ sous sollicitation dynamique : caractérisation cristallographique des transformations polymorphiques de l’étain. Autre. ISAE-ENSMA Ecole Nationale Supérieure de Mécanique et d'Aérotechique - Poitiers, 2021. Français. ⟨NNT : 2021ESMA0015⟩. ⟨tel-03613080⟩

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