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MSR : Development of experimental tools and methods for quantitative analysis.

Recrystallization at 1000°C in-situ of an austenitic steel sample
Recrystallization at 1000°C "in-situ" of an austenitic steel sample preformed at high temperature and observed through sequential EBSD cartographies.
• With the help of the MEA group, a heating stage for in-situ thermal treatments in a scanning electron microscope has been developed, built and refined. This setup is unique, to our knoweledge, not only for its performance at high temperatures (1200°C), but also for its very fast heating and cooling rates (on the order of 100°C.s-1). It allows one given zone of a sample submitted to subsequent thermal treatments to be sequentially followed [e.g. Bozzolo et al., Mat. Charact. 70 (2012) p28].


 Map of local disorientations measured by EBSD
Map of local disorientations measured by EBSD on a partially recrystallized tantalum sample. Left: raw image. Right: filtered image.
• The determination of dislocation densities and stored energies is a key aspect in studying recrystallization. We have developped a procedure for treating EBSD maps, based on the Kamaya method, that allows for significant reduction of noise in the evaluation of geometrically necessary dislocations using intragranular orientation gradients [Moussa et al., Ultramicroscopy 179 (2017) p63]. Moreover, a 4 year project ECOS-South France – Argentina in collaboration with Pr. Javier Signorelli (CONICET Rosario), whose goal is precisely the development of these kinds of tools, began on January 1st 2017.


 Superposition of phase and orientation mappings
Superposition of phase and orientation mappings obtained through the i-Chord technique on AD730. Of remark is the resolution of the submicronic secondary precipitates.
• γ-γ' nickel base superalloys present a problem concerning the discrimination of γ and γ' phases using EBSD techniques due to their crystallographic similarity. We have surmounted this difficulty for primary γ' precipitates using a coupled EBSD/EDS acquisition technique without increasing the time it takes to capture an image [Charpagne et al., J. of Microscopy 263 (2016) p106]. We have also evaluated the performances of another orientation mapping method based on ion-matter interactions (iCHORD) regarding the γ/γ' discrimination problem with the collaboration of Cryril Langlois from the INSA of Lyon and OrsayPhysics. The neighboring illustration shows, that using this method, secondary precipitates of submicronic size can be resolute.
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