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L'équipe "Physique, Mécanique et Plasticité" (Département SI2M) de l'Institut Jean Lamour accueille Antoine Guitton (Paul Scherrer Institut – Neutrons and X-rays for Mechanics of Materials – Villigen-PSI, Switzerland) pour un séminaire intitulé :
"Deformation mechanisms of MAX phases & Effect of strain path changes on metal plasticity"
Date et lieu :
Vendredi 27 mars 2015 à 8h15
Institut Jean Lamour
Site de Saurupt, Nancy
Salle de réunion (2eme étage)
Deformation mechanisms of MAX phases:
It is commonly believed that plastic deformation mechanisms of MAX phases consist in basal dislocation glide, thus forming pile-ups and walls. The latter can form local disorientation areas, known as kink bands. Nevertheless, the elementary mechanisms and the exact role of microstructural defects are not fully understood yet. Here we present a multi-scale experimental study of deformation mechanisms of the Ti2AlN MAX phase. At the macroscopic scale, two kinds of experiments were performed. In-situ compression tests at room temperature coupled with neutron diffraction brought new insight into the deformation behavior of the different grain families in the polycrystalline Ti2AlN. Compression tests from the room temperature to 900 °C under confining pressure were also performed. At the mesoscopic scale, deformed surface microstructures were observed by SEM and AFM. These observations associated with nanoindentation tests showed that grain shape and orientation relative to the stress direction control formation of intra- and inter- granular strains and plasticity localization. Finally, at the microscopic scale, a detailed dislocation study of samples deformed under confining pressure revealed the presence of dislocation configurations never observed before in MAX phases, such as dislocation reactions, dislocation dipoles and out-of-basal plane dislocations. In the light of these new results, mechanical properties of MAX phases are discussed.
Effect of strain path changes on metal plasticity:
Most of the knowledge on mechanical behavior has been derived from conventional uniaxial tests. However industrial production of metallic components consists in many strain path changes, which modify drastically their mechanical response. In this framework, in-situ testing can give valuable insights on deformation mechanisms which could appear or could be modified during strain path changes. With the on-going miniaturization of engineering components there is an increasing need for novel deformation devices that can handle samples below the micrometer scale.
While in-situ miniaturized uniaxial deformation set-ups are nowadays relatively common, miniaturized multi-axial deformation devices are less frequent yet. For instance there exist only few biaxial tensile set-ups combined either with a SEM observations (Tasan et al. Exp. Mech, 2012) or coupled with x-ray reflection diffraction (Geandier et al., Rev. Sc. Inst., 2010). But none combines nanometer scale deformation with in-situ microscopy observations or with transmission x-ray diffraction on small bulk materials.
In this framework, we have developed a miniaturized biaxial tensile machine working either in synchrotron (for transmission or reflection x-ray diffraction) or in SEM environments for in-situ measurements of bulk metallic sheets. Technological challenges such as sample shape optimization, sample machining and machine design will be presented.