PhD opportunities

Development of a continuous weaveable oxide ceramic fiber: Relationship between Process - Microstructure - Thermo-mechanical properties

Thesis proposal

Area of expertiseMaterials science and engineering
Doctoral SchoolISMME - Systems Engineering, Materials, Mechanics, Energy
SupervisorMme Marie-Hélčne BERGER
Co-supervisorM. Sebastien JOANNES
Research unitCentre of materials
Contacthttps://www.mat.minesparis.psl.eu/formation/doctorat/propositions-de-sujets-de-these/
Starting dateOctober 1st 2022
KeywordsAlumina precursor , phase transformations , sintering , microstructure , - defects - brittle fracture , plasticity - scale transition
AbstractWeavable oxide ceramic fibers form the architecture of many ceramic matrix composites (CMC) used in industrial structural parts under extreme environments. In land or aeronautical turbines, for example, these low-density refractory materials are damage-tolerant and make it possible to significantly increase the operating temperatures of turbines, their efficiency and reduce the emission of polluting gases. The development of these CMCs is based on the availability of continuous fibers, about 10µ in diameter. These fibers are manufactured by roving several hundred fibers, via the spinning of an organometallic precursor and its calcination, thus involving an assembly of complex technological bricks, covering a wide range of processes and scientific skills, from organic chemistry to the sintering of fine-grained ceramics, via techniques specific to the textile industry. The whole is therefore based on a strongly multi-scale approach, which will be found in the characterization methods and their interpretation. This link between process, microstructure, and thermomechanical properties from the fiber to the roving will be at the heart of the proposed doctoral work for the development of an alpha alumina fiber with submicron grains up to the industrial scale.

Context and challenges:
Currently, no continuous, weavable oxide fiber is produced and marketed in Europe. The DITF (Deutsche Institute für Textil & Faserforschung) has published very promising results on a pre-pilot scale. In order to address high-growth, high-value-added markets, and in line with its environmental commitments, Saint-Gobain has established a collaboration with the DITF for the development and manufacture of these continuous oxide ceramic fibers. The Materials Center of Mines Paris has 40 years of experience in the microstructural and mechanical characterization of these very specific objects. This tripartite partnership aims to develop on a continuous pilot an alumina fiber with mechanical properties similar to those of non-European manufacturers.

Scientific objectives:
To achieve the thermomechanical properties required for these fibers, it is essential to be able to master, through strict control of the polymer and the process, the development of microstructures during ceramization and sintering. In particular, the role of intergranular chemistry and impurities will have to be related to the kinetics of phase transformation and grain growth as a function of process parameters (temperature and atmosphere). The origin of extrinsic defects will be investigated in relation to the statistical distribution of stresses at breakage of unit fibers. The modeling of the mechanical behavior of the strand will be deduced. Finally, the mechanical behavior in tension and creep up to 1000C will be established and the occurrence of plasticity will be related to the local mechanisms of grain sliding/rotation.

Methodology:
Mechanical tests (tensile creep) on single fibers and on strands from 25°C to 1000°C.
Scanning electron microscopy
Transmission electron microscopy
X-ray diffraction in temperature
Multiscale modeling of mechanical behavior
ProfileTypical profile for a thesis at MINES ParisTech: Engineer and / or Master of Science - Good level of general and scientific culture. Good level of knowledge of French (B2 level in french is required) and English. (B2 level in english is required) Good analytical, synthesis, innovation and communication skills. Qualities of adaptability and creativity. Teaching skills. Motivation for research activity. Coherent professional project.

Applicants should supply the following :
• a detailed resume
• a copy of the identity card or passport
• a covering letter explaining the applicant’s motivation for the position
• detailed exam results
• two references : the name and contact details of at least two people who could be contacted
• to provide an appreciation of the candidate
• Your notes of M1, M2
• level of English equivalent TOEIC
to be sent to recrutement_these@mat.mines-paristech.fr
FundingConvention CIFRE