Hiring Institution
Institut National des Sciences Appliquées de Lyon (INSA-L)

PhD-Awarding Institutions
Institut National des Sciences Appliquées de Lyon (INSA-L)
Deakin University (Deakin)

Download the full Position Description

Option 1

Significance of model approximations for yield strength predictions of high entropy FCC alloys

High entropy alloys (HEAs) are an exciting relatively new concept in metallurgy: multiple chemical elements at high concentrations are mixed, leading sometimes to single phase crystalline materials. Several single-phase FCC HEAs have shown impressive yield strength, due to solute strengthening, and the vast composition range of this class of materials opens many possibilities for the design of alloys with superior mechanical properties. Since their discovery, important theories have emerged to predict the composition, strain-rate and temperature dependence of their yield strength. Key ingredients to such models are dislocation/solute interactions, dislocation properties and dislocation line tension, and can be obtained either from empirical potential calculations, ab initio calculations, or from experimental data, depending on the levels of simplifications of the theories (mean/full field approach, elastic theory approximations, sum rules, etc.).
How these approximations impact predictions remains elusive, which can be a problem for alloy design. This PhD project will aim at quantifying the consequences of model inadequacies in identifying interesting alloy compositions, and then propose new methodologies for accurate predictions of FCC HEAs yield strength.

Option 2

Atomistic comprehensive insights on the dislocation properties of refractory BCC High Entropy Alloys

Within the active field of High Entropy Alloys (HEAs), the refractory subclasses of alloys are complex substitutional solid solutions made of nearly equal proportions of up to 5-6 refractory elements and have a BCC structure. They have received considerable attention due to their potential for high temperature applications: they exhibit a very high yield strength up to elevated temperatures – thus competing/superseding Ni-based superalloys, and some of them also have a significant ductility at room temperature. However, there is a lack of fundamental knowledge of the dislocation properties in RHEAs, and as a function of alloy composition, even though such properties dictate the exact nature of the mechanisms responsible for the plasticity in these complex materials. The PhD student will develop ad hoc interatomic potentials to systematically investigate the links between composition, dislocation/solute properties, and plasticity mechanisms at the atomic scale. Once these links are established, the student will be able to identify the relevant physical assumptions to be used in the development of mesoscale models of RHEAs yield strength (currently a highly controversial topic in the literature). This will also help to provide guidance for alloy design of RHEAs.

Option 3

On the use of precipitation to strengthen High Entropy alloys

High entropy alloys are an exciting relatively new concept in alloy design. Rather than taking one element and adding small amounts of others to it, high entropy alloys comprise nearly equal parts of up to five or so elements. Interest in this field was initially focused on single phase solid solution materials. More recently, however, the use of hardening precipitation – such as the one in steels or other convention alloys – has been considered to achieve better mechanical strength, leading for example to the so-called high entropy superalloys, that involve complex ordered/disordered phases.
This PhD will explore such a strengthening route by adding some specific alloying elements in small quantities to model medium entropy alloys, and by carrying out some heat treatments to involve the precipitation. The newly formed phases will be characterized in detail and their influence on the mechanical properties will be measured. The modeling of the precipitation kinetics will also be performed by physically-based models.

SIMPLIFYING APPROACH: working on MEAs to better elucidate the role of chemistry.

Prof. Michel Perez
Damien Fabregue
Matthew Barnett
Dr. Céline Varvenne

Metallurgy, mechanics of Materials