[Thesis defense] Inès ADDI ‘Temperature-dependent plasticity of hexagonal materials: in situ analyses and scale-transition models’

The thesis defense will also be available by videoconference on Zoom: https://univ-nantes-fr.zoom.us/j/89950141026

Composition of the jury:

Reviewers:

• Mr Stéphane ALLAIN, Professor, Université de Lorraine
• Ms Delphine RETRAINT, Professor, Université de Technologie de Troyes

Examiners:

• Mr Damien FAURIE, Professor, Université Sorbonne Paris Nord
• Ms Nathalie GEY, CNRS Research Scientist
• Mr Jean-Charles STINVILLE, Associate Professor, University of Illinois Urbana-Champaign

Thesis supervisor:

• Mr David GLOAGUEN, Professor, GeM, Nantes Université

Co-supervisors:

• Mr Pierre-Antoine DUBOS, Associate Professor (HDR), GeM, Nantes Université
• Mr Baptiste GIRAULT, Associate Professor (HDR), GeM, Nantes Université

Abstract:

Hexagonal close-packed materials such as titanium (Ti) and cobalt (Co) exhibit thermal, elastic and plastic anisotropy. Their deformation results from the activation of, and competition between, several mechanisms, in particular crystallographic slip and mechanical twinning, together with an allotropic transformation between the hexagonal and cubic phases in the case of Co. How these properties and deformation mechanisms evolve with temperature, however, remains poorly documented, although it directly governs the thermomechanical behaviour of these materials. This thesis therefore aims to characterise the temperature dependence of the thermoelastic properties and of the plastic deformation mechanisms of polycrystalline Ti and Co. An experimental methodology based on in situ thermomechanical tests was developed, combining electron backscatter diffraction (EBSD), to follow microstructural changes during deformation, and X-ray diffraction (XRD), to determine strains at the scale of the diffracting volumes. The XRD measurements were coupled with self-consistent micromechanical models in order to relate the responses observed at the grain scale to those of the polycrystal. This work provides new data on the thermoelastic properties and critical resolved shear stresses of Ti and Co at high temperature, and highlights the influence of texture, temperature and phase fractions on the activation of deformation mechanisms. Coupling in situ characterisation with multiscale modelling thus contributes to a more complete description of the thermomechanical behaviour of hexagonal materials.

Seminar room 17.200 – Building 17 – IUT de Saint-Nazaire