PhD Thesis in materials chemistry "Development of barrier coatings against carbon diffusion during SPS process" (M/W).

16 Jan 2024
Job Information

Organisation/Company

CNRS

Department

Laboratoire Interdisciplinaire Carnot de Bourgogne

Research Field

Chemistry
Physics
Technology

Researcher Profile

First Stage Researcher (R1)

Country

France

Application Deadline

5 Feb 2024 - 23:59 (UTC)

Type of Contract

Temporary

Job Status

Full-time

Hours Per Week

35

Offer Starting Date

1 Aug 2024

Is the job funded through the EU Research Framework Programme?

Not funded by an EU programme

Is the Job related to staff position within a Research Infrastructure?

No

Offer Description

The doctoral work will be carried out within the ICB laboratory (Dijon) (http://icb.u-bourgogne.fr ). The ICB laboratory is a joint research unit (UMR 6303) between CNRS (the French National Centre for Scientific Research) and the University of Burgundy, formed by 300 physicists, chemists, engineers, and technicians located in the Bourgogne-Franche-Comté region, with sites in Dijon, Le Creusot, Chalon-sur-Saône, and Belfort (Sévenans). The thesis research will take place within the Metallurgical Processes, Durability, and Materials Department (PMDM), where experimental expertise is complemented by predictive thermodynamic simulation (phases formed and diffusion calculations). Sintering tests will be conducted in Dijon, in the framework of the CALHIPSO/EQUIPEX+ platform (ANR-21-ESRE-0039). The ICB laboratory also hosts a platform (ARCEN-CARNOT) dedicated to the physicochemical and microstructural characterization of powders and sintered materials: SEM-EDX, XRD, SIMS, and more. PVD coatings will be developed at LaBoMaP (http://labomap.ensam.eu ). Further in-depth characterizations (TEM-EDX) will be carried out at CEMES in Toulouse (https://www.cemes.fr ) to complement the understanding of diffusion mechanisms at the graphite/powder sinter interface.

The improvement of the durability properties of metal parts is a major issue for many industrial sectors, such as aeronautics, aerospace, military, etc. The choice of the manufacturing process directly influences the microstructure and, therefore, the properties of the metallic alloys. A fine and homogeneous microstructure, ensuring better use properties, is usually sought. In this context, the elaboration of metallic parts by powder metallurgy techniques, typically pressure-assisted sintering processes such as spark plasma sintering (SPS), represents a relevant way to explore, as an alternative to conventional manufacturing processes (casting, forging, or machining). During SPS, the powder inserted in a mold is densified by the simultaneous application of heating (via a pulsed direct current) and pressure (via a uniaxial charge). This fast sintering limits grain growth. SPS makes possible, in a single stage, the elaboration of high-performance materials and structural elements, with improved mechanical properties, even if in the case of parts having large sizes and/or complex shapes.
SPS main advantages are:
- the elaboration of fine, homogeneous, and original microstructures, leading to improved mechanical properties in service conditions;
- the process flexibility, allowing the elaboration of materials with new and controlled chemical compositions;
- the possibility to produce near net shape or net shape parts, even in the case of complex shapes, allowing to reduce, or even eliminate, subsequent machining costs
However, one of the major issues of the SPS process, which requires the use of graphite tooling (punches and die), is the carbon contamination of the metallic powder. In addition, graphite foils are inserted between the powder and the surfaces in contact with the tooling to ensure good electric, physical, and thermal contact of the tooling-powder assembly, but also to facilitate the sample demolding and to preserve the tooling that one wishes to reuse. In the case of metal powders, carbon diffusion from graphite foils leads to the formation of secondary and usually undesirable phases (generally carbides) at the surface of the sintered sample and to carbon diffusion towards the bulk. In the case of easy machinable materials, surface carbides can be removed by machining; however, the major problem is that carbon diffusion at grain boundaries and in the bulk is an irreversible phenomenon, responsible for the degradation of the use properties of the sintered materials. Moreover, in the case of low-carbon precipitation hardening maraging steels, hardly machinable, the carbon contamination of the powder during sintering enhances carbides precipitation (typically molybdenum carbides). This phenomenon reduces the amount of available alloying elements in the metallic matrix to form the intermetallic compounds responsible for the material strengthening. Whatever the used grade and the intended application, carbon contamination of the metallic powder during SPS must be considered and given special attention.
The objective of the thesis will be to study the diffusion phenomena occurring during the SPS process at the interface between graphite tooling parts and metallic powder and to develop solutions to limit/avoid carbon diffusion using physical vapor deposition (PVD) technology. One of the advantages of the PVD technique is to ensure perfect control of the thickness of the film deposited on any type of substrate, while allowing uniform coverage of the surfaces, even in the case of complex shapes and large dimensions. Thus, this technology allows also to envisage the deposition of a protective coating directly on the graphite die and punches.
Within the framework of the thesis, a PVD coating of a carbide-forming element (of the order of a few micrometers) will be applied, in a first time, on the graphite foils before SPS. The study will begin with the sintering of pure iron powder, before moving to a maraging steel grade. Initially, the reactive system will be investigated without any protection against carbon diffusion, i.e. with uncoated graphite. Then, the same SPS experiments will be carried out using PVD-coated graphite foils. The choice of the element (or the combination of elements) to be deposited by PVD will be guided by a thermodynamic modeling step. After SPS, the interface between the sintered powder and the graphite foil (coated and uncoated) will be carefully characterized at different scales and using several techniques: SEM-EDX, EBSD, DRX and µ-DRX, TEM-EDX. Carbon diffusion will be followed by SIMS and EPMA profiles. The most promising coating solutions developed and retained in the case of the graphite foils can then be transposed to an industrial scale, through the use of PVD-coated dies and punches (simple shapes).
This thesis is part of the ANR project OEDIPUS (DévelOppemEnt De matérIaux métalliques Performants par coUplage SPS-PVD - Developement of improved metallic materials by coupling SPS and PVD techniques) coordinated by the University of Burgundy (ICB laboratory, Dijon) and whose partners are ENSAM (LaBoMaP, Cluny), CEMES (Toulouse) and the start-up SINTERMAT (Venarey-les- Laumes).

Requirements

Research Field

Chemistry

Education Level

Master Degree or equivalent

Research Field

Physics

Education Level

Master Degree or equivalent

Research Field

Technology

Education Level

Master Degree or equivalent

Languages

FRENCH

Level

Basic

Research Field

Chemistry

Years of Research Experience

None

Research Field

Physics

Years of Research Experience

None

Research Field

Technology

Years of Research Experience

None

Additional Information

Website for additional job details

https://emploi.cnrs.fr/Offres/Doctorant/UMR6303-MARARD-001/Default.aspx

Work Location(s)

Number of offers available

1

Company/Institute

Laboratoire Interdisciplinaire Carnot de Bourgogne

Country

France

City

DIJON

Geofield

Where to apply

Website

https://emploi.cnrs.fr/Candidat/Offre/UMR6303-MARARD-001/Candidater.aspx

Contact

City

DIJON

Website

http://icb.u-bourgogne.fr/

STATUS: EXPIRED