Seminar IJL Department SI2M

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Date | Time
17/09/2018 | 14 h 00 min - 16 h 00 min

IJL, Campus ARTEM, Amphi 200


Invited Speaker: Frederic Mompiou – CEMES, Toulouse

Probing deformation mechanisms using in-situ TEM

Since a long time, miniaturized mechanical tests can be achieved in a Transmission Electron Microscope (TEM). Such a technique called in-situ deformation TEM has been developed in order to identify/characterize elementary plasticity mechanisms at the mico/nano scale and capture their dynamics. This dynamical aspect of the deformation, carried by dislocation/interfaces motion, is indeed a key aspect for a better understanding of the material properties in early deformation stages. It complements traditional “frozen” post-mortem observations, and allows a better description for larger scale models. In the recent years with the problem of “size-effect” raised by small scale objects, in-situ TEM experiments has been extensively used and many experimental set-ups (nano-indentors, MEMS) have emerged. This presentation has two objectives. First it aims at presenting the technique by itself and the informations that can be learned from such experiments. Second, i would like to show how we have used in-situ TEM experiments to address few problems in the plasticity of metals and alloys.

Local Speaker: Thomas Schenk – 304 Physics, Mechanics and Plasticity

in situ real time diffraction study of plastic transients within a single crystal superalloy following stress jumps during a high temperature creep test
Trehorel, Schenk, Jacques, Ribarik, Bastie, Cormier and Dezerald.

During high temperature creep Ni-based single crystal superalloys develop a rafted microstructure with alternate semi-coherent layers of a ductile fcc γ matrix (channels) and hard γ’ phase (rafts) with a L12Ni3Al structure, perpendicular to the [001] tensile axis. Using a simple multilayer-model, stresses and strains within both phases can be calculated: provided we know the applied load, the free lattice mismatch δ(T) and the δ┴ mismatch (in the [100] and [010] directions, due to dislocations in the γ/ γ’ interface) between both phases. We will present the used X-ray diffraction technique to follow the evolution of δ┴during an in situ high temperature (950°C) creep test. A short analysis of the experimental results for one specimen will be given.