ED Sciences Chimiques
Data-driven development of high entropy superalloys
by Wei-Chih LIN (ICMCB - Institut de Chimie de la Matière Condensée de Bordeaux)
The defense will take place at 14h00 - 401 DELTA building, 101, Section 2, Kuang-Fu Road, Hsinchu 300044, Taiwan R.O.C.
in front of the jury composed of
- Stéphane GORSSE - Professeur associé - Université de Bordeaux - Directeur de these
- An-Chou YEH - Professeur - National Tsing Hua University - CoDirecteur de these
- Hideyuki MURAKAMI - Professeur - National Institute for Materials Science - Rapporteur
- Yu-Chieh LO - Professeur associé - National Yang Ming Chiao Tung University - Examinateur
- Anna FRACZKIEWICZ - Directrice de recherche - MINES Saint-Etienne - Rapporteur
- Wen-Jay LEE - Docteur - National Center for High-Performance Computing - Examinateur
This study has implemented an active learning process aimed at identifying Refractory High Entropy Alloys (RHEAs) with enhanced oxidation resistance. The performance of the 11 active learning alloys surpassed that of random alloys prior to active learning. Moreover, throughout the active learning process, there was a consistent decrease in specific mass gain across all iterations. By combining Senkov's criteria with the results obtained from active learning, alloys such as AlCrMoTa, CrMoTaTi, AlCrMoTaTi, and Al0.5CrMoNbTaTi were identified as promising candidates. Notably, Al0.5CrMoNbTaTi demonstrated superior high-temperature mechanical properties, highlighting its potential for advanced applications. This study introduces a novel methodology that effectively balances oxidation resistance and high-temperature mechanical performance in RHEAs. The multi-objective optimization model proved its capability to design alloys under varying constraints, while the further refined PBR-oxidation model delivered enhanced predictive accuracy for oxidation behavior in experimental series compared to the original model. By integrating active learning techniques with well-established criteria, these approaches provide a robust framework for the systematic design and optimization of RHEAs. This paves the way for the development of materials with exceptional performance in demanding high-temperature environments.
ED Sciences Physiques et de l'Ingénieur
Optical generation of localized polar elastic structures in chiral liquid crystals
by Nicolas BRUNI (Laboratoire Ondes et Matière d'Aquitaine)
The defense will take place at 14h00 - Amphithéâtre 3 351 cours de la Libération Bâtiment A9 33400 TALENCE
in front of the jury composed of
- Etienne BRASSELET - Directeur de recherche - Université de Bordeaux, CNRS - Directeur de these
- Gonzague AGEZ - Maître de conférences - Université de Toulouse - Rapporteur
- Jean-François HENNINOT - Professeur des universités - Université d'Artois - Rapporteur
- Bruno ZAPPONE - First Researcher - Università della Calabria - Examinateur
- Claire MEYER - Maîtresse de conférences - Université de Picardie Jules Verne - Examinateur
- Laurent DUPONT - Professeur - IMT Atlantique - Examinateur
Frustrated cholesteric liquid crystal films are systems that can host a wide range of localized elastic structures whose topological properties are non-trivial. Since their first experimental observation more than 50 years ago, these structures have aroused interest both fundamentally as model systems allowing the study of 3D topological structures in condensed matter physics, and in applied physics, thanks to the possibility of producing reconfigurable optics. In this experimental thesis work, we study using a laser beam the controlled generation of localized structures whose supramolecular 3D structure is polar. After introducing the context of this work in the first chapter, we demonstrate in the second chapter that the polarization state of the writing laser beam allows full control over the polarity of the written structure, whose « up/down » state depends upon the « up/down » spin state of the incident photons in the case of a circularly polarized laser beam. The demonstration is then extended to the case of elliptically polarized beams. A mechanism is proposed, supported by numerical simulations, in order to explain the morphogenesis of the written structures. This sheds light on the respective roles of light and matter chirality, and highlights the importance of non-adiabatic propagation of light without neglecting the transfer of spin angular momentum of light inside the liquid crystal medium. Our results also reveal the role of laser-induced heating in the early stages of the writing process. In the third chapter, we propose an experimental variant in which the effects of laser-induced heating are suppressed. We show that the directional writing of polar structures is preserved but with the added bonus of readressability of the structures. Moreover, we directly evidence experimentally the role of spin angular momentum deposition of light in matter. In the fourth chapter, we propose an experimental approach that allows us to neglect the effects of optical reorientation in order to keep only those of laser-induced heating. By taking optical control of the resulting temperature gradients, we once again demonstrate the possibility of writing supramolecular polar structures on demand. All above experiments call for the development of a bijective approach to the topological encoding of matter by light, exploiting its polarization and spatial degrees of freedom as well as the optical topological textures that result from their coupling.