Université Paris 13, Sorbonne Paris Cité, Institut Galilée Laboratoire

Université Paris 13, Sorbonne Paris Cité, Institut Galilée
Laboratoire des Sciences des Procédés et des Matériaux
Soutenance de Thèse
Abdelouahab OUAREM
Comportement mécanique et évolutions microstructurales sous compression
quasi-statique et dynamique de polycristaux CFC et HC: effet de la taille des grains
Mechanical behavior and microstructural evolutions under quasi-static and
dynamic compression loading of FCC and HCP polycrystals : effect of grain size
mardi 11 septembre 2012 à 14 H
Salle de Conférence du Bât. L1
Abstract:
The present work is devoted to the analysis of the strain rate and grain size effects on the deformation mechanism
activated during plastic deformation of two polycrystalline materials: (i) zinc (Zn), a crystal with hexagonal compact
packing structure, having grain size in the micro and ultrafine grain ranges (~ 300 µm and 200 nm, respectively),
loaded under quasi-static and dynamic compression conditions, up to a strain rate of ~ 10 5 s-1 (by use of a Direct
Impact Hopkinson Pressure Bars (DIHPB); (ii) electrodeposited nickel (Ni), a face-centered cubic structure with grain
size of 5 µm deformed in compression under dynamic conditions using DIHPB. Significant differences in terms of
micro-mechanisms of deformation in the two regimes were found: (i) At lower strain rates, up to ~ 102 s-1, dislocationbased plasticity was observed in both Ni and Zn. Extensive twinning occurred only in the case of micrometer grainsized Zn, indicating a grain size dependence of twinning; (ii) In the dynamic regime (> 103 s-1) plastic deformation
induced a significant increase of the temperature within the samples. This increase of temperature was significant
enough to induce recovery and/or dynamic recrystallization. As consequence two phenomena were observed
depending on the structure under investigation: for Ni, the resulting microstructure and mechanical properties were
similar to that of the initial state, dominated by annealing twins and equiaxed and randomly oriented grains. For micrograined Zn a tremendous grain refining was found. As a consequence, twinning was inhibited. To clarify this point,
additional investigations were carried out on coarse-grained CP-Ti deformed in both quasi-static and dynamic regimes.
It was found that twinning was the main deformation mechanism. Indeed, the larger the strain rate and grains size, the
larger the twin density. On the one hand, these results clearly demonstrate the grain size effect on the occurrence of
mechanical twinning in HCP materials. On the other hand, the effect of the strain rate on twinning was found to depend
on the material under investigation. Compared to Ti, the lower homologous temperature T/T m of Zn probably plays a
key role, as it may induce dynamic recovery/recrystallization as far as the present experimental conditions are
concerned.
Composition du jury :
Prof. Kei AMEYAMA, Ritsumeikan University, Shiga, Japon, Rapporteur
Dr J. DOUIN, CEMES, Toulouse Rapporteur
Prof. A. ABDUL-LATIF, UP 8, Examinateur
Prof. Salah RAMTANI, UP 13, Examinateur
Dr, HdR, H. COUQUE, Nexter-Munitions, Bourges, Examinateur
Dr D. TINGAUD, UP 13, Examinateur
Prof. G. DIRRAS, UP 13, Directeur de Thèse