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The role of alloying elements on the dissolution, passivation, & corrosion of high entropy alloys

This offer is available in the following languages:
Français - Anglais

Date Limite Candidature : vendredi 6 août 2021

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General information

Reference : UMR7197-VINVIV-001
Workplace : PARIS 05
Date of publication : Friday, July 16, 2021
Scientific Responsible name : Vincent Vivier
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 1 October 2021
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly

Description of the thesis topic

High entropy alloys (or multi-principal element alloys) represent an emerging class of materials consisting of five or more alloying elements in nearly equimolar concentrations. These alloys have demonstrated an exceptional combination of properties such as high strength and ductility, improved fatigue resistance, fracture toughness, and thermal stability and show considerable potential for use as corrosion resistant materials especially for use in extreme environments. The absence of a single primary element in the HEA, however, makes the alloy development extremely difficult. This is especially true as concerns the optimization of corrosion resistance which depends on the chemical and electrochemical interactions of the individual alloy elements.
The goal of this project is to identify the role of the individual alloy elements on the mechanisms of passive film formation and corrosion. These results should open a path towards the identification of the optimum composition / microstructure for corrosion resistance by offering a science-based guide to navigating the complex alloy compositional space.
Questions to be addressed in this PhD project include: How does the passive form on these alloys? What is the influence of halide ions on the breakdown of the passive layer? Can we study an individual event (i.e., pit) from the initiation to the repassivation steps?

Work Context

Experimental Aspects
The student will gain experience with a variety of electrochemical techniques as well as metallurgical elaboration and characterization in collaborations with our partners at ENSCP (Paris).
Electrochemistry. Conventional electrochemical methods will be used to characterize these alloys, in particular impedance spectroscopy in order to monitor operando the passive film formation/evolution as a function of time and applied potential. However, this type of research is difficult to interpret for the HEA because of the large number of elements that may contribute to the electrochemical response of the alloy. In a second step, this project will rely on a recently developed technique allowing to generate at will a single pit. It is expected to monitor the different steps of pitting corrosion from its initiation to long term propagation. In a last step, this technique will be implemented to a novel technique of element resolved electrochemistry to characterize the contribution of each individual alloying element to the dissolution and passive film formation of the alloys (available at ENSCP).
Other spectroscopic methods:
Other techniques will be used as needed including SEM analysis, various forms of surface spectroscopy such as X-ray photoelectron spectroscopy (XPS), glow discharge optical emission spectroscopy, etc.
Metallurgy: The synthesis and characterization of a high entropy alloys with variable composition and microstructure will be undertaken using specialized metallurgical processing methods. Microstructural characterization will be carried out with scanning electron microscopy, transmission electron microscopy, electron backscattered diffraction, and energy dispersive X-ray microanalysis.
Model film realization: The electrochemical characterization of oxide films with variable environment and electrochemical conditions will be investigated by preparing model oxide films on inert substrates using radio frequency sputtering under vacuum (collaboration with Brest University). In this way the contribution of the passive film to the overall dissolution / corrosion mechanism may be distinguished from that of the substrate.
Candidate Profile:
The candidate should have an Engineering and / or Master of Science degree with a good level of general and scientific culture and solid laboratory experience. Previous experience in electrochemistry would be an important asset.
The ideal candidate will be highly motivated for multidisciplined research in an important, dynamic field. The candidate should possess good analytical, synthesis, innovation and communication skills with qualities of adaptability and creativity.
Excellent English skills are necessary. Our research group functions primarily in English, all publications will be in English, and participation in international conferences will be expected.

Constraints and risks

No particular risk for this project

Additional Information

ANR project (TAPAS)

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