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MMMB Research Seminar
November 9, 2018 @ 11:30 am - 12:30 pm
New stainless steel technologies with high mechanical performance and corrosion resistance
Prof. Caroline Richard, University of Tours, France
In the aeronautics industry, stainless steels are used on structural parts such as landing gears for example or other structural parts. These stainless steels used are usually precipitation hardened steels or bearing steels or conventional steels to which coating or surface treatment must be provided. However, these steel families are either not hard enough or corrode or crack due to corrosion -fatigue, or the coatings used do not respect environmental constraints. A real technological breakthrough is therefore required, and new grades must be developed. The study was focused on the analysis of the tribological, corrosion and tribocorrosion behaviour of new martensitic stainless steels and their degradation mechanisms for different aeronautical applications, e.g. actuators. For this, electrochemical, tribo-electrochemical and ex-situ surface analysis techniques were used. Wear damage was found to be critically affected by the hardness of the material and its hardening during sliding. Martensitic stainless steels showed higher scratch wear resistance but higher wear material loss when compared to the austenitic stainless steel (as reference). Corrosion resistance of martensitic stainless steels is driven by their passivity, whose kinetics can be described through a high field conduction model. Passive dissolution rate depends on the surface chemistry of the material, thus decreasing with the Cr content in the passive film. Degradation mechanisms involved in tribocorrosion of martensitic stainless steels included plastic deformation, shakedown and low-cycle fatigue. The consequences of those involved mechanisms depended on the prevailing electrochemical conditions.
ABOUT THE SPEAKER:
Caroline Richard is a senior professor at the University Of Tours, France, since 2010. After a qualification in solid-state chemistry and metallurgy at Paris-Sud University and a pHD in materials science and engineering at the University of Technology of Compiegne (UTC), she was an Assistant Professor at Roberval Laboratory FRE CNRS-UTC 2012 from 1993 to 2010, involved in durability of surfaces of materials (tribology, lubrication and corrosion, surface treatments, bio materials). She was a project leader in the frame of several industrial contracts with national and international companies (Arcelor Mittal group, Saint-Gobain group, Thyssen-Krupp Sofedit, Airbus, Technip (Total group), Safran Group, Vallourec -Manessmann, etc.) in the field of materials working industries with the development of tribometers at high temperature for simulation of hot rolling process or for other hot manufacturing processes. Since 2016, her current laboratory is GREMAN UMR CNRS 7347, involved in materials for energy, microelectronic packaging (brazing process, SLID process, lead-free solders, new sintered metallic solders, and piezoelectric ceramic) and also materials for health (functionalized bio materials for bone tissue engineering, surface treatments for titanium alloys).