The Arts et Métiers campus Arts et Métiers is pleased to invite you to the thesis defense of Lisa Germain, doctoral student at the MSMP laboratory, on December 13, 2022.
Title: Stress-diffusion coupling. From interstitial problems to gas nitriding of steels
Summary of work:
For many years, understanding the coupling between a mechanical stress field (applied or residual) and a chemical field in a material diffusion process has been a major area of study. Long-range interstitial diffusion, in the case of gas nitriding for example, causes high stress gradients associated with phase transformations (short-range diffusion). Diffusion-precipitation phenomena are well known and simulated in the laboratory. However, stress-diffusion coupling remains a significant problem. Two phenomena relating to long-distance diffusion have been highlighted: the effect of homogeneous stress (Fickian term) and the stress gradient (Nernstian term). In addition, mechanical pretreatment is frequently coupled with thermochemical treatment, which leads to phenomena that are rarely decoupled from incompatible plastic deformations and residual stresses. Numerical approaches limited to long-range diffusion and experimental approaches were then carried out to address these issues. Stress-diffusion coupling was simulated numerically (1D and 2D) and applied to a binary system (Fe-N) using the thermodynamics of irreversible processes. The effects of a homogeneous stress and a stress gradient were highlighted by numerical simulations. The results revealed that the Fickian coupling factor must be approximately 10 times lower than the diffusion coefficient. D to have a significant impact on kinetics. In order to compare these theoretical results with reality, nitriding experiments were carried out on 33CrMoV12-9 steel.
Keywords: Diffusion; stress-diffusion coupling; gas nitriding; residual stress; plastic deformation; elastic deformation
Jury:
- Benoît PANICAUD, LASMIS, UTT: rapporteur
- Julien TEIXEIRA, IJL, University of Lorraine: rapporteur
- Luc PICHON, Institut P’, University of Poitiers: examiner
- Laurent BARRALLIER, MSMP, Arts et Métiers examiner
- Sébastien JÉGOU, MSMP, Arts et Métiers examiner
Practical information:
Location: Arts et Métiers Campus Arts et Métiers (room H015)
Time: 9:30 a.m.
The defense can also be followed via videoconference using a Teams link.
