Description of the thesis topic

The development of new materials that enable increasing the operating temperatures of jet engines is one of the key factors contributing to the improvement of their performance (thrust-to-weight ratio) and their efficiency (reduction of pollutant emissions). When used in the manufacture of turbine disks, superalloys must meet conflicting requirements: high tensile strength at the bore of the disk, which is subject to the highest mechanical stresses, combined with good creep resistance at the rim of the disk, which is exposed to the highest temperatures. An increase in turbine operating temperatures thus affects the entire disk, necessitating the improvement of the static and creep mechanical performance of the materials used across the entire temperature gradient. For the manufacturing of turbine disks, nickel-based superalloys are essential materials due to their properties and stability at high temperatures. Notably, precipitation-hardened alloys with the γ'' phase, such as Inconel 718 (considered as the reference alloy), stand out from γ'-phase-hardened alloys, commonly used, as they offer excellent manufacturability (forgeability, rollability, repairability, weldability). However, their operating temperature limit is lower compared to γ'-phase-hardened alloys. For example, Inconel 718 exhibits excellent tensile mechanical properties up to 600-650°C, beyond which the metastable γ'' phase transforms into a stable δ phase without hardening potential. The development of new superalloys hardened by a stable γ'' phase at temperatures above 700°C represents a significant pathway for improving the efficiency and performance of future jet engines.
This thesis therefore aims to develop new nickel-based superalloys with γ'' phase precipitation hardening, offering stable properties at higher temperatures (target 800-900°C) than existing alloys. This work is based on a combination of numerical methods for the accelerated search of promising compositions and advanced characterization techniques for the analysis and optimization of microstructures. The main goal is to understand the mechanisms of γ'' phase formation in order to identify promising alloy compositions.

Work Context

The Institute Jean Lamour (IJL) is a joint research unit of CNRS and Université de Lorraine.
Focused on materials and processes science and engineering, it covers: materials, metallurgy, plasmas, surfaces, nanomaterials and electronics.
The IJL has 263 permanent staff (30 researchers, 134 teacher-researchers, 99 IT-BIATSS) and 394 non-permanent staff (182 doctoral students, 62 post-doctoral students / contractual researchers and more than 150 trainees), of 45 different nationalities.
Partnerships exist with 150 companies and our research groups collaborate with more than 30 countries throughout the world.
Its exceptional instrumental platforms are spread over 4 sites; the main one is located on Artem campus in Nancy.

The position is located in a sector under the protection of scientific and technical potential (PPST), and therefore requires, in accordance with the regulations, that your arrival is authorized by the competent authority of the MESR.

Constraints and risks

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