MELOXEL

Context. Predicting within reasonable accuracy the durability of high value metallic materials (such as stainless steels in power plants) remains a challenge to material scientists and engineers. For instance, the major obstacle to correctly predicting the corrosion resistance of metallic alloys is the lack of knowledge regarding the influence of various parameters (mainly mechanical parameters) on pit initiation and propagation. In the last decade, a significant effort has been devoted to the development of new analytical techniques to investigate the physical and chemical parameters controlling the properties of metallic surfaces at the atomic, nano- and microscale. Techniques have widely been used to map strains under loading in air at the meso- and macroscale. However, these two sets of techniques have not been combined to propose new methods of analysis and new models for the prediction of pit initiation and propagation. Objectives. The main objective of this project is to combine different techniques in mechanics, physics and electrochemistry and to develop novel methods of analysis to solve the key issues : what is the (mechanical, electrochemical and chemical) homogeneity of a metallic alloy surface at the nano- and microscale and how does this affect passivity and the pitting susceptibility of this alloy? The project will be divided into three parts that will be performed in collaboration between ICB (University of Bourgogne, Dijon), ENSMP (Ecole des Mines de Paris) and LGECO (INSA de Strasbourg). Note that the project will also set an example of collaborative activities possible within the European Union. This future action will be supported by existing collaborations between the partners and AGH University (Krakow, Poland) in the field of local electrochemistry and the chair for surface science and corrosion (University of Erlangen, Germany) for surface analysis methods. The project will be divided into three working packages: WP1: Surface chemical composition and surface nano- and micromechanical behaviour of stainless steels after ageing; WP2: Simulation of the Surface Mechanical Behaviour of Stainless Steels after Ageing; WP3: Microelectrochemical investigation after ageing and mechanical-electrochemical analysis Expected results and long time expectation. The expected results are: - to determine the local variations of the chemical composition of passive films at the nano- and microscale - to obtain constitutive laws of passive films and to measure microstrains induced by ageing and/or straining at the nano- and microscale - to develop a new numerical approach for adaptive model reduction based on parallel computations. This will be applied to calculate microstrains gradients on materials with complex microstructure and the results will be compared to experimental mappings. Diffusion-mechanics coupled finite element computations will also be carried out. - to perform electrochemical impedance and corrosion tests at the microscale to propose mechanical-electrochemical-metallurgical criteria leading to metastable and/or stable pitting. Electrochemical results will be analysed considering the results obtained both in mechanics, surface analysis and metallurgy Regarding computational aspects, a powerful numerical tool will be available to predict the local strain field of multi-phase materials. In terms of corrosion science, reliable data which could be introduced in a mechanical-electrochemical model for describing pit initiation will be obtained. Developing quantitative models to reliably predict the dynamic performance of a material's surface is an open challenge. Overcoming this challenge will lead to improved fundamental knowledge not only in the field of corrosion resistance, but also in adhesion, biocompatibility, optical properties, tribology etc. This will lead to applications which increased European competitiveness in important industrial areas, such as communication, health and food, transportation, power generation, construction and environmental management. Another long-term expectation of this project will be to develop in-situ mechanical-electrochemical microprobes to investigate microscopic aspects which remain absolutely necessary as a control of the heterogeneities and the material with functionalized surfaces. This basic research can hardly be supported by industrial partners. However, the new expertise generated by the project will enable to deliver knowledge and technology transfer into industry (by improving the microstructure of new materials and increasing the durability of existing alloys, for example).