Thesis proposal (M/F) - Study of the mechanical resistance to impacts and optimization of coatings subjected to severe tribological conditions

Job Description

Thesis Subject

Context, issues, and objectives

Studies conducted under severe friction conditions for SAFRAN Aircraft Engines (SAE)—characterized by high sliding speeds and normal pressures combined with quasi-instantaneous loading—representative of those encountered in the blade root/rotor connection of a turbojet engine [1], [2], have led to surface deterioration. This deterioration depends on several physical and mechanical properties (oxidation, adhesive and abrasive wear, etc.) and has revealed the appearance of localized cracks.
Within the framework of the Multi Arc Oxidation (MAO) project, undertaken in collaboration with SAE and the IRT M2P [3], [4], these cracks preferentially propagate at the coating/substrate interface in the case of bulk titanium alloy (Ti6Al4V) materials coated with protective deposits (MAO). This phenomenon compromises the effectiveness of the surface property improvement process for this specific application.
The challenge of this thesis is to develop discriminating tests to effectively guide the selection of coatings. These tests, simple and cost-effective, will be carried out upstream of friction tests to select the most promising coatings before undertaking more specific, expensive, and complex tribological tests that reproduce real contact conditions. The adopted approach will focus on a methodology highlighting the dialogue between experimentation and modeling, coupling experimental phases and modeling of the observed phenomena.
Initially, various coatings will be subjected to a simple, reproducible, and low-cost experimental testing protocol to evaluate their mechanical performance before engaging in more complex and representative tribological tests. Coatings will be assessed using impact tests performed with an instrumented ballistic bench. A steel or tungsten projectile will be launched at controlled velocity onto temperature-regulated specimens. This experimental setup will allow the characterization of different damage mechanisms (plastic deformation, cracking, coating/substrate decohesion, or densification) depending on the applied energy level. Repeated impacts, either localized in the same area or distributed in a grid, will also be studied to explore potential mechanical fatigue phenomena. The relevance and reliability of this experimental device have already been validated through several research collaborations conducted between 2023 and 2025 with Safran Tech, Safran Aircraft Engines, and Safran Ceramics. It will be complemented by Acoustic Emission (AE) analysis, a non-destructive testing technique involving the measurement and interpretation of the acoustic signature of damage mechanisms [5]. The data collected during impact tests will be used in parallel to develop a dynamic damage modeling approach for coatings, based on a micro-macro methodology [6], which will interact with the experimental protocol to establish energetic criteria for the activation of damage mechanisms.
The synergy between experimental and theoretical results from the coating damage characterization phase will lead to the establishment of selection criteria before implementing friction campaigns. Samples exhibiting different types and degrees of damage, as well as intact ones, will be selected for tribological tests. These tests will be conducted under dry friction using a ball-on-flat tribometer (RTEC500). They will determine the friction coefficient, wear rates, and dominant wear mechanisms. The integration of a debris analyzer on the tribometer will also provide the ability to monitor, in real time, the evolution of contact forces and the production of wear particles (third body).
During the RTEC500 tribometer tests, the experimental data collected will be dedicated to the development of a semi-analytical model of the dry friction process under the tribological conditions of the study. This will provide a deeper understanding and better control of the thermomechanical phenomena involved in these specific tribological interactions. Indeed, the confinement of the contact during a test makes it difficult, if not impossible, to access the evolution of damage mechanisms. Therefore, the sole availability of post-mortem ex-situ analysis justifies the design of tools to aid in understanding the wear resistance of the tested coating. For this purpose, the theoretical approach can rely on the experience acquired by the LEM3 (Thermomechanics of Rapid Contact - TRC) team in terms of semi-analytical modeling of dry friction.
The team is developing a thermomechanical model [6-7] whose coupling of mechanical and thermal problems will allow, based on the morphology at the microscopic scale and the 3D geometry of the contact, the thermophysical properties of the materials involved, and the friction conditions (speed, normal force, and hybrid surface geometry) during tribological tests, the determination of mechanical responses (local shear stress and contact pressure) and thermal responses (local temperatures and heat flux distribution generated by friction energy dissipation. Although this approach has so far only been applied to high-speed friction cases, it can be adapted to the low sliding speeds imposed on the RTEC tribometer, provided that appropriate accommodations and supplements are made. For this, an accurate representation of the ball/structured surface contact area during friction tests will be necessary. The geometric characterization of the contact will be carried out using an estimation based on Hertzian contact theory in elasticity and/or existing models of elastoplastic behavior in abrasion and indentation (ploughing) [8-9]. Furthermore, the modeling will need to account for adhesive wear of the contact through the implementation of an energetic formulation [10] in its algorithm. The various constitutive modules of the friction model (mechanical, thermal, coupling and wear energetics) will be optimized by repeatedly adjusting the theoretical results to those of the tribological tests throughout the coating tribological characterization process. In addition, the modeling of the ball-on-flat contact will be conducted using two complementary approaches: two-body friction (ejection of debris) and three-body friction (recirculation of debris in the interface) [11-12]. Both behaviors have already been observed and highlighted in Pavlik's thesis [13]. Once again, the Experimentation-Model dialogue will consist of comparing real and theoretical wear profiles and validating the developed model
References :
[1] Chassaing G., Pougis A, Philippon S, Lipinski P, Meriaux J, Faure L. : Initiation of adhesive wear during frictional interaction at very high velocity for a Ti6Al4V tribopair. Proc 13th World Conf. Titan, pp. 5–7, (2016)
[2] Chassaing G, Faure L, Philippon S, Coulibaly M, Tidu A, Chevrier P, et al. : Adhesive wear of a Ti6Al4V tribopair for a fast friction contact, Wear, vol. 320, pp. 25–33, (2014)
[3] Marquer M., Philippon S, Faure L., Chassaing G., Tardelli J., Demmou K. : Influence of two APS coatings on the high-speed tribological behavior of a contact between titanium alloys. Tribology International, 136 :13-22, 2019
[4] Bahr H-A, Fischer G, Weiss H-J. : Thermal-shock crack patterns explained by single and multiple crack propagation. J Mater Sci, vol. 21, pp. 2716–20, (1986)
[5] Thomas Le Gall. Simulation de l'émission acoustique : Aide à l'identification de la signature acoustique des mécanismes d'endommagement. Matériaux. Thése. Université de Lyon, 2016. Français.
[6] Atiezo M. K., Chen W., Dascalu C.: Loading rate effects on dynamic failure of quasi-brittle solids: Simulations with a two-scale damage model. Theoretical and Applied Fracture Mechanics, vol. 100, pp. 269-280, 2019.
[7] Coulibaly M., Chassaing G., Philippon S.: Thermomechanical coupling of rough contact asperities sliding at very high velocity. Tribology International, Vol. 77, pp. 86-96, 2014.
[8] Coulibaly M., Chassaing G. : Thermomechanical modelling of dry friction at high velocity applied to a Ti6Al4V- Ti6Al4V tribopair. Tribology International, Vol. 119, pp. 795-808, 2018.
[9] Mishra T., de Rooij M., Shisode M., Hazrati J., Schipper D. J.: Analytical, numerical and experimental studies on ploughing behavior in soft metallic coatings. Wear, Vol. 448-449, 2020.
[10] Bousselham A.: Caractérisation mécanique de matériaux hétérogènes par indentation instrumentée : dialogue modèle/expérience. Thèse de l'Université de Lille, soutenue le 8 décembre 2021.
[11] Fouvry S., Liskiewicz T., Kapsa P., Hannel S., Sauger E.: An Energy Description of Wear Mechanisms and Its Applications to Oscillating Sliding Contacts. Wear, 255(1–6), pp. 287–298, 2003.
[12] Godet M.: Third-bodies in tribology. Wear, 136(1), pp. 29–45, 1990.
[13] Descartes S., Desrayaud C., Niccolini E., Berthier Y.: Presence and role of the third body in a wheel–rail contact. Wear, 258(7–8), pp. 1081–1090, 2005.
[14] Pavlik A., Marcos G., Coulibaly M., Vincent J., Czerwiec T., Philippon S.: Improving the surface durability of patterned AISI 316LM steels by nitriding treatment for dry friction sliding. Tribology International Vol : 146 : 2020

Your Work Environment

Candidate profile

The candidate must hold a university degree (engineering and/or master's) enabling them to enroll in a doctoral program. They should have knowledge of material mechanics, associated characterization methods, and experimental techniques. The multidisciplinary nature of the project as a whole (design of impact tests, mechanics, materials and coatings, modeling) will require strong theoretical knowledge in the relevant fields, a degree of autonomy, the ability to synthesize information, and a sense of coordination and planning. A keen interest in experimentation and a team spirit that allows you to integrate into the research team and interact easily with different people are additional assets for successfully completing this thesis.



Good oral and written communication skills in English are essential. Knowledge of French may be an advantage.

Host team and partners

The thesis will be carried out at LEM3 - Laboratory for the Study of Microstructures and Materials Mechanics in Metz and is part of its development and research projects. LEM3 is a joint research unit (UMR) affiliated with the University of Lorraine, the CNRS, and Arts et Métiers. Its activities are organized into three scientific departments:
Department 1 MMSV - Mechanics of Materials, Structures and Living Organisms;
Department 2 IMPACT - Microstructure Engineering, Processes, Anisotropy, Behavior;
Department 3 TPRIOM - Thermomechanics of Processes and Tool-Material Interactions.
The doctoral student will be part of the “Thermomechanics of Rapid Contact - TRC” research area in Department 3 (T-PRIOM).

Doctoral school
As a doctoral student in France, you will be enrolled at the University of Lorraine and will be part of the C2MP doctoral school (Chemistry, Mechanics, Materials, Physics). You will have the opportunity to benefit from a wide range of training courses during your doctoral studies.

Application
Applications must be sent to supervisors by email before Monday, April 30, 2026. The email must include a resume, copies of master's/engineering transcripts (except for the final semester, which is still being validated at the time of application), and a cover letter related to the position.

Compensation and benefits

Compensation

2300 € gross monthly

Annual leave and RTT

44 jours

Remote Working practice and compensation

Pratique et indemnisation du TT

Transport

Prise en charge à 75% du coût et forfait mobilité durable jusqu’à 300€

About the offer

About the CNRS

The CNRS is a major player in fundamental research on a global scale. The CNRS is the only French organization active in all scientific fields. Its unique position as a multi-specialist allows it to bring together different disciplines to address the most important challenges of the contemporary world, in connection with the actors of change.

CNRS

The research professions