ED Sciences Physiques et de l'Ingénieur
Study of corrosion and stress-corrosion cracking mechanisms of stainless steel designed by wire arc additive manufacturing
by Herick RODRIGUES NASCIMENTO (I2M - Institut de Mécanique et d'Ingénierie de Bordeaux)
The defense will take place at 14h00 - Amphithéâtre La Rochefoucauld Liancourt (LRL) Esplanade des Arts et Métiers 33405 TALENCE ENSAM Campus de Bordeaux
in front of the jury composed of
- Olivier DEVOS - Professeur - Université de Bordeaux - Directeur de these
- Hercilio GOMES DE MELO - Professeur - Universidade de São Paulo - Rapporteur
- Sabrina MARCELIN - Ingénieure de recherche - INSA Lyon - Rapporteur
- Juan CREUS - Professeur des universités - La Rochelle Université - Examinateur
- Catherine GUERRE - Ingénieure de recherche - CEA Saclay - Examinateur
- Isabelle AUBERT - Maître de conférences - Université de Bordeaux - CoDirecteur de these
This thesis investigates the impact of mechanical-corrosion coupling on austenitic stainless steel 316L, comparing conventional manufacturing with Wire and Arc Additive Manufacturing (WAAM). Pitting corrosion mechanisms were examined on both undeformed and plastically deformed specimens. Additionally, the 316L WAAM steel underwent heat treatment to homogenize its microstructure, followed by electrochemical analysis to evaluate its corrosion sensitivity with and without plastic deformation. Due to the multi-scale microstructural heterogeneity of as-built 316L WAAM, pits predominantly form near critical inclusions and sigma-phase-rich regions, which act as preferential corrosion sites. Despite the microstructural differences between conventional and WAAM 316L, no significant variation in the passive film breakdown potential was observed. Under plastic deformation, the passive film breakdown potential in conventional 316L exhibits a non-linear variation, whereas in WAAM, it remains stable. However, a similar trend is noted in pit initiation behavior. These variations are attributed to differences in the passive film properties, as described by the PLM model. Heat treatment at 1200 °C for 2 hours homogenizes the microstructure and recrystallizes the grains but does not significantly enhance resistance to pitting corrosion. In contrast, an extended treatment at 1200 °C for 4 hours reduces the size of critical inclusions, leading to a notable improvement in corrosion resistance. When plastically deformed, 316L WAAM treated at 1200 °C for 2 hours behaves similarly to conventional 316L. Finally, the PLM model does not fully account for the variations in passive film breakdown potential, likely due to the high density of inclusions.