Par GDRi Mecano le 25 April 2020 à 17:42
Supervision: Dr. Antoine GUITTON (antoine.guitton[at]univ-lorraine.fr) Prof. Thierry GROSDIDIER
Location: LEM3, Université de Metz, France
Financial support: CNRS Grant (starting October 1th, 2020 ; 3 years duration).
Keywords : Max Phases, MXenes, hydrogen storage, Microstructural analysis, Electron microscopy.
Solid state storage of hydrogen in low pressure tanks (ground transportation purposes) can take advantage of the reversible transformation of metal into metastable metal-hydrides within an appropriate temperature range. Such storage systems using Mg hydrides is safe and lightweight but exhibit a low charge and discharge kinetic even at relatively high temperatures (>200°C). To overcome these limitations, new alloys and microstructural modifications are explored. Understanding the effects of structural defects and catalysts on the physical mechanisms involved in the hydride nucleation and growth reaction is however needed and difficult: hydrides are unstable under vacuum.
Mn+1AXn phases (n = 1 to 3, M being a transition metal, A an A-group element and X = N or C) are nanolaminated ternary compounds–synthesized by powder metallurgy from cheap and widely available elements. Because of their anisotropic layered structure, the MAX-phases can theoretically store large amounts of hydrogen in solid solution. MAX phases are also precursors for MXenes, one of the largest families of two-dimensional materials. In the form of stacks, these materials have demonstrated remarkable performance as (co-) catalysts for key fuel cell reactions and are promising for hydrogen storage.
In this thesis, we will explore the influence of microstructural defects (dislocations, grain boundaries, heterophasic interfaces) on the fundamental mechanisms of hydrogen storage in MAX phases, MXenes and their Mg-based nanocomposites. This thesis is part of a collaboration project between several laboratories – LEM3 (Metz, France), Institut Pprime (Poitiers, France), IC2MP (Poitiers, France), GPM (Rouen, France), Beijing Jiaotong University (China) and I2CNER (Japan) –
More details HERE
Par GDRi Mecano le 25 April 2020 à 17:27
Supervision: Marc Legros (marc.legros[at]cemes.fr), Julio Cesar Brandelero (Mitsubishi Electric)
Location: CEMES (Toulouse)
Financial support: CIFRE Grant (starting on October 1th, 2020 ; 3 years duration).
Keywords : Al microstructure, oxidation, grain boundaries, thermal & electrical cycling, electron &ion microscopy.
Power devices, such as MOSFETs and IGBTs, are key components of the continuous growth of power electronics applications ranging from domotics to energy conversion. Their reliability becomes critical in transportation and off-shore applications. Anticipating or even preventing their failure is a key technical issue.
In recent years, several weak spots have been identified in the structure of modern Si-based power devices, and some solutions (packaging) have already been found to increase their resistance to disruption. However, the aging of the top metal source and wire bondings, mainly made of Al or Al alloy has persisted as an intrinsic weak link, degrading the electrical performance of the device over time. This occurs through mechanisms that involve grain boundary diffusion, crack formation and surface/interface oxidation, also driven by stresses arising from thermal mismatch between the metal and the silicon. The goal of this thesis is to find methods (fresh devices processing, circuitry modification) favoring the self-healing or the non propagation of these cracks.
More details HERE
On the Mitsubishi Electric Research site
Par GDRi Mecano le 21 April 2020 à 01:58
DEFORMATION MICROMECHANISMS AND TENSILE PROPERTIES OF ADVANCED SINGLE CRYSTAL NICKEL-BASED SUPERALLOYS
Supervision: Jonathan Cormier (Pprime Institute, Poitiers), Florence Pettinari-Sturmel (CEMES-Université Paul Sabatier, Toulouse)
Financial support: MESR Grant (starting on November 1th, 2020 ; 3 years duration).
Keywords : Ni-based superalloys, Mechanical properties, Tensile tests, Deformation micro-mechanisms, Dislocations, Transmission electron microscopy.
Subject and challenge of the project: Single crystal nickel-based superalloys are widely used for aero- engines components, because of their superior high temperature mechanical resistance in order to fulfill several requirements: i) a high !' solvus temperature; ii) a high amplitude of !/!' mismatch; iii) a density as low as possible and iv) a good phase stability. A new-generation Pt-containing superalloy has been developed between ISAE-ENSMA/Institut Pprime and SAFRAN in France . This new alloy is considered as a potential alloy for future airfoils.
The aim of this study is thus to concentrate the efforts on the tensile behavior understanding. Tensile tests will be performed at a given temperature (in the range 500 °C – 800 °C) for the three SXs (CMSX-4 Plus, TMS-238 and TROPEA), which differ in chemical composition. The final goal will be to confirm the effect of the chemical composition and to understand how it influences the controlling deformation parameters.
The experimental approach will consist in the realization of tensile tests at ISAE-ENSMA/Institut Pprime (Poitiers) during the first year. A complete analysis of the microstructure and the deformation micromechanisms will be carried out at CEMES using Transmission Electron Microscopy (conventional TEM, in situ TEM tensile tests, TEM spectroscopies: EELS and EDX), during the next two years. The final goal is to identify and quantify the physical parameters controlling the tensile properties at temperature lower than 800 °C for different SXs.
More details here
Par GDRi Mecano le 12 April 2020 à 23:08
Missions / PhD topic
The successful candidate will join the I3EM (“In situ, Interferometry and Instrumentation for Electron Microscopy”) team at CEMES-CNRS and will study the modifications of electric and magnetic fields by light absorption in nanostructured semiconductor materials using in situ electron holography.
Supervisors: Sophie MEURET (firstname.lastname@example.org) and Christophe GATEL (email@example.com)
URL official offer : https://bit.ly/3bNIfNU
Type of Contract: PhD
Contract Period: 36 months
Expected date of employment: 1 October 2020 but flexible
Proportion of work: Full time
Remuneration: 2135€ brut/month
Desired level of education: Master
- More details here
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