Hydrogen addition and surface modifications for enhanced corrosion of TWIP steels for bioresorbable stent applications by Sarah REUTER

Pour l’obtention du grade de Docteur en sciences de l’ingénieur et technologie

Fe-based alloys are of increasing interest for the use as bioresorbable materials. Their mechanical properties are adequate for the use as stents but they present too slow degradation rates. Alloying with Mn allows to achieve excellent work-hardening, further increasing the mechanical properties, and renders the Fe alloy more susceptible to corrosion. Nevertheless, high amounts of insoluble hydroxides are formed during Fe-Mn corrosion, which increase the local pH, favouring the deposition of salts coming from the blood environment. Altogether, these layers hinder the oxygen diffusion from the electrolyte towards the metal surface, decreasing the corrosion rate with time.

The present thesis aims at increasing the corrosion susceptibility of Fe-Mn-C Twinning Induced Plasticity (TWIP) steels in Simulated Body Fluid (SBF). Local acidification can lead to an enhanced dissolution of the corrosion layers, achieving increased corrosion rates. A novel way to acidify the local environment is explored in the present work: the release of hydrogen previously charged within the steel. It is found that H charging achieves only slight increase in corrosion susceptibility due to the low hydrogen presence not allowing to completely counter the complex interactions with the electrolyte. Its influence on the corrosion properties is compared to PLA-coating and Cu-coating on TWIP steel. Both techniques have proven to effectively increase the corrosion properties of Fe-based alloys. The influence of hydrogen on the corrosion kinetics is similar to PLA-coating but smaller than Cu-coating. Cu-coated and H-charged samples present similar corrosion products morphologies, whereas the PLA-coated samples present higher iron hydroxides presence, leading to heavy red/orange corrosion products.

Jury members :

• Prof. Pascal Jacques (UCLouvain), supervisor
• Prof. Laurent Delannay (UCLouvain), chairperson
• Dr. Quentin Van Overmeerre (UCLouvain), secretary
• Prof. Dominique Lison (UCLouvain)
• Prof. Xavier Feaugas (Université de La Rochelle, France)
• Dr. Xavier Vanden Eynde (CRM Group, Belgium)
• Dr. Dimitri Mercier (Chimie Paris Tech, France)

Pay attention :

The public defense of Sarah Reuter scheduled for Wednesday 29 September at 4:30 p.m will take place in the form of a video conference Teams