Offre de thèse - GPM/SIMAP
A first glance at the structural dependent cooperativity and the equilibrated glass reorganization in metallic glasses
Metallic glasses, that can be formed thanks to high cooling rates from the melt, typically in the order of 105 K/s, have attracted high interest from the scientific community as they find applications in many domains, such as biomedical, electrocatalysis, supercapacitor, and even space telescope. Their structural characterization, needed for property design, is challenging since they do not exhibit long-range order. As any amorphous material, it is still possible however to investigate their relaxation dynamics 1.
In metallic glasses, the viscous slowing down characterizing the transition from liquid to glass occurs similarly than it does in polymers, with a crossover mechanism precluding the segmental relaxation. Some novelties have however been recently reported that are generally not observed during polymer glass transition, such as the clear decoupling between the vitrification and the -relaxation, suggesting that the glass transition is governed by more than only one kind of motion dynamics. The metallic glasses studies have also contributed to a better understanding of the structural relaxation kinetics. They were notably used for proving the existence of multiple decays during the mechanism of disordered glass equilibration.
We propose therein to investigate two main aspects of the glass physics that have not yet been investigated for metallic glasses: the structural dependence of the cooperativity during the relaxation and the reorganization of the equilibrated glass. Regarding the cooperativity, it is largely assumed that the underlying mechanisms in organic compounds involve van der Waals carbonyl interactions, pi-stacking, electro-attractor dipoles to cite only a few. This raises a question regarding the mechanisms behind metallic glass relaxation. Regarding the equilibrated glass, it is currently proposed for polymers that it could undergo another enthalpy decay leading to crystallization during the physical ageing process, sometimes under unexpected microstructures as the process occurs in a poorly investigated temperature range. The study of metallic glasses, presenting a simpler structure and a higher purity degree than polymeric glasses, will be good candidates to better understand these phenomena, and thus predict the glass structure after the physical ageing in given conditions (time, temperature).
This thesis will be co-directed by Dr. Nicolas Delpouve and Pr. Allisson Saiter-Fourcin from the Disordered Systems and Polymers department of GPM. Considering the high cooling rates needed for the formation of the metallic glass, a large attention will be dedicated to ultrafast scanning calorimetry investigations 2. The samples will be provided by Dr. Yannick Champion (SIMAP, Grenoble).
 Champion, Y., Thurieau, N. “The sample size efect in metallic glass deformation”, Sci Rep 10, 10801 (2020).
 Jürgen E.K. Schawe, Jörg F. Löffler “Kinetics of structure formation in the vicinity of the glass transition”, Acta Materialia 226, 117630, 2022. https://doi.org/10.1016/j.actamat.2022.117630
Contact: Dr Nicolas Delpouve