May 31, 2022
16:00
Lovain-La-Neuve
Place Sainte Barbe, auditorium BARB93
For the degree of Doctor of Engineering Sciences and Technology
High entropy alloys (HEAs) have attracted a lot of attention in recent years, with the promise of new alloy systems with outstanding (combinations of) structural (and functional) properties. However, in-depth investigations of HEAs mechanical properties in direct comparison to conventional alloys have been seldom reported. The goal of this thesis was to characterize two so-called Cantor-based HEAs, CoCrFeMnNi and CoCrNi alloys, and to compare them to reference conventional alloys in the framework of structural materials for cryogenic applications, namely stainless steels (type 304L and 316L), iron-nickel alloys (Invar and Fe9Ni), and a high Mn TWIP steel (Fe-22Mn-0.5C). 
To this end, the selected alloys were tested at room and cryogenic temperatures, and thoroughly characterized in terms of microstructure, hardening and fracture properties. The essential work of fracture (EWF) method is well suited to quantify the fracture resistance of ductile thin sheets and was extensively used in this work. One of the outcomes of the thesis is an improved EWF methodology that minimizes the required material while keeping the same statistical error on the extracted EWF value. Among the seven investigated materials, HEAs showed excellent tensile and fracture properties both at 293 K and 77 K. However, stainless steels keep exhibiting even better performances in terms of strength, ductility, and fracture toughness.
Jury members :
- Prof. Pascal Jacques (UCLouvain, Belgium), supervisor
- Prof. Thomas Pardoen (UCLouvain, Belgium), supervisor
- Prof. Sandra Soares-Frazao (UCLouvain, Belgium), chairperson
- Prof. Aude Simar (UCLouvain, Belgium)
- Prof. Stéphane Godet (ULB, Belgium)
- Dr. Jean-Denis Mithieux (Aperam, France)
- Prof. Dierk Raabe (Max-Planck Institute, Allemagne)
- Prof. Guillaume Laplanche (Ruhr-Universität Bochum, Allemagne)