Thèse Corrosion Sous Contrainte des Vitroceramiques Regions de Vitesses Elevees de Propagation de Fissure H/F - Doctorat.Gouv.Fr

Établissement : Université Paris-Saclay GS Physique
École doctorale : Physique en Ile de France
Laboratoire de recherche : CEA/SPEC - Service de Physique de l'Etat Condensé
Direction de la thèse : Cindy ROUNTREE ORCID 0000000343497064
Début de la thèse : 2026-10-01
Date limite de candidature : 2026-08-31T23:59:59

L'objectif de cette thèse est d'établir le lien entre la (nano/micro)-structure et la CSC des vitrocéramiques dans les régions II et III. Pour cela, deux compositions de vitrocéramiques sont considérées à différents taux de cristallisation : une à base de disilicate de lithium, largement utilisée en médecine dentaire, et une autre à base d'aluminosilicate de zinc à fort intérêt pour les applications optiques. Ces deux compositions génèrent la formation de cristaux de type, taille et forme qui leur sont propres. D'une part, la structure des vitrocéramiques sera analysée à différentes échelles caractéristiques (celles des cristaux, du verre résiduel et de la vitrocéramique elle-même) en utilisant des techniques complémentaires : RMN, DRX, MEB et microscopie à champ proche (AFM). D'autre part, des expériences de PDM seront menées pour obtenir les courbes de CSC dans les régions II et III. Il s'agira finalement de caractériser post-mortem les surfaces de rupture par AFM, et d'analyser la statistique des rugosités à l'aide de certains outils de la physique non-linéaire pour en extraire les longueurs caractéristiques pertinentes. C'est la mise en regard de l'ensemble de ces données acquises qui permettra d'atteindre une vision holistique du problème.

Material failure is a concern for scientists and engineers worldwide and all material types. This includes glass-ceramic, which are used in optical thermometry applications, kitchen utensils, dental materials, etc. In glass-ceramics, crystals are intentionally formed in a glassy matrix; this allows for glass-ceramics can take advantage of the benefits of both components: glasses and ceramics. Nevertheless, glass-ceramics, like oxide glasses, have a significate drawback: they are brittle. Oxide glasses are well known to undergo dynamic fracture (crack propagation velocity of ~km/s, as in the case of a glass crashing to the floor and shattering); yet, glasses are also sensitive to another fracture mode less noticeable, where crack fronts grow sub-critically (as in the case of a slow crack in a windshield due to an impact). It is called the stress corrosion cracking (SCC). These cracks grow because the crack front interacts with the environment (in particular relative humidity and temperature), and the crack front velocity (v) depends on the local stress felt by a crack tip, coined the stress intensity factor (K\_I) (Figure 1) [1]. However, the stress corrosion behavior in glass-ceramics is significantly understudied in literature and remains poorly understood. Recently, studies have been initiated to characterize region I in glass-ceramics (v < 10^(-6) m/s) with conventional imaging methods. Between Region I and catastrophic failure, there are two Regions II and III (10^(-6) 'm/s'v10^3 'm/s' ), which are difficult to probe using the current method due to spatial-temporal experimental constraints, yet their characterization is imperative for bridging the gap between the environmental limit (K\_e) and catastrophic failure.

The thesis goal is to investigate the link between (nano/micro-) structures and the SCC behaviour in glass-ceramic (GC) at relatively high crack propagation velocities (Region II and III). To do so, two types of glass-ceramic will be studied at different crystal volume fraction: Lithium disilicate, a reference GC widely used in dental application, and a more complex gahnite-based GC attractive for optical applications. Both GC have their own specific crystal type, size and shape. On one hand, the GC structure will be examined at different scales characteristic of the residual glass, the crystals and the GC itself using complementary and advanced technics such as NMR, XRD, SEM and by near field microscopy (AFM). On the other hand, PDM measurements will be performed to obtain the SCC curve in region II and III. The fracture surface will also be characterized by AFM and the roughness statistics will be analyzed by different statistical tools (stochastic modelling, fractal analysis) to extract characteristic lengths. All acquired data will be combined to reach a holistic viewpoint.

This is why a new experimental tool (coined the potential drop method, PDM) will be used. PDM consists in deposing parallel conductive strips at the surface of a sample using lithography techniques in a cleanroom. Subsequently, the crack front location in time is tracked via an oscilloscope, as the crack front servers the parallel conductive strips. Our team has already implemented this method on large PMMA samples [2] and are in the process of extending it to oxide glasses.

Étudiant(e) issu(e) d'une formation en sciences des matériaux, chimie ou physique, mécanique des matériaux et/ou de la science des surfaces. La curiosité, la motivation pour réaliser un travail expérimental et la capacité à travailler à la fois en équipe et en autonomie sont des compétences recherchées. Une expérience en laboratoire de chimie et/ou salle blanche est un plus.