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Strengthening mechanisms associated to anisotropic precipitates in an Al-Li-Cu alloy of third generation

Abstract : The age-hardening AA2198 alloy is mainly used in aeronautic applications. The anisotropic T1 - Al2LiCu phase gives the main contribution to strengthening in this system. The main objective of this study is to understand the strengthening mechanisms in terms of interactions between the dislocations and the T1 plate-like precipitates. The first step consists in the development of a characterization procedure adapted to the T1 phase (characterization of the diameter, thickness and volume fraction of the T1 plates). The thermo-mechanical treatment is adapted in order to vary the T1 parameters independently and the yield strength evolution is systematically measured and that permits the investigation of the relationship between the T1 microstructure and the yield strength variations. The experimental data base that is generated allows testing and improving the existing yield strength models. An energetic approach of the shearing mechanisms is used to model precisely the yield strength evolution for a high number of microstructures. The decrease in yield strength after the peak is solely explained by invoking the shearing mechanism. The investigation of the plasticity phenomenon associated to the T1 phase, with the study of the shear bands and of the work hardening behavior, is the last step of this work. A shearing-to-by-passing transition is found to occur for long-over ageing times.
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Thomas Dorin. Strengthening mechanisms associated to anisotropic precipitates in an Al-Li-Cu alloy of third generation. Materials. Université de Grenoble, 2013. English. ⟨NNT : 2013GRENI031⟩. ⟨tel-01200540⟩

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