Synthesis, mechanical properties and biodegradability of thin films metallic glasses
The study of amorphous metal films (thin film metallic glasses, TFMGs) is receiving more and more attention due to the excellent mechanical properties: a tensile strength close to theoretical limit, high hardness and elastic deformation. Their disordered atomic structure is the source of unique physical properties that are different from their crystalline counterparts. However, studies on the synthesis and characterization of TFMGs are relatively recent, as efforts have focused on the bulk metallic glasses (BMGs). In this context, the main goal of the study is the TFMGs synthesis by magnetron sputtering on flexible polymer substrates with a structure totally or partially disordered at the nanometric scale. Structural-mechanical relationship will be identify trough the combination of x-ray diffraction, scanning electron microscope, nanoindentation, optoacoustic techniques and micro-tensile tests of films on flexible polymeric substrates. We aim to establish correlation between the elastic and plastic properties of TFMGs, and contribute to a better understanding of the microstructures and local atomic ordering influence on their mechanical properties. In addition, one application of these coatings in the biomedical field is considered, in partnership with the Laboratory for Translational Vascular Research (LVTS, INSERM U1148, Pr. F. Chaubet) who will perform specific biocompatibility tests (cells growth,…).
PhD tasks :
(i) coatings with thin films of metallic glasses on flat polymeric supports (Kapton or elastomer sheets) and curved structures of polymers obtained by 3D printing;
(ii) study of the structural and mechanical properties of hybrid materials, in particular at the polymermetal interface,
(iii) control of their degradation kinetics in simulated biological medium,
(iv) in the context of a biomedical application, the evaluation of their mechanical properties in relation to the absorption of the materials constituting the hybrid,
(v) evaluation of compatibility with human vascular cells (collaboration with the LVTS , Pr. F. Chaubet).
Further information and application:
Supervision: Prof. Philippe Djemia (LSPM, Université Sorbonne Paris Nord),
Co-supervision: Dr. Fatiha Challali, Dr. Florent Tétard
Financial support: MESR Grant (starting on September 1th 2020; 3 years duration).
Start date: September 1st 2020
More detail on the subject and information on application are available in the following document: « PhD offer-Thin film Metallic glass-LSPM-2020.pdf »
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
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
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