Influence de la microstructure sur les mécanismes d'endommagement thermomécanique de revêtements à base d'acier inoxydable AISI 316L réalisés par projection dynamique par gaz froid "cold spray"

Abstract : Aluminum alloys are commonly used in the automotive industry for lightening and power gain of thermal engines. However, thermomechanical properties are not often high enough to undergo the in-service stresses while the engine is running. High performance materials are needed. A novel approach to reach these high performances is to develop specific coatings using the cold spray route. This thermal spray process is based on the plastic deformation of sprayed powders at a supersonic velocity onto a substrate resulting in so called « splats » and stick to the surface. In this thesis, thermomechanical damage of cold-sprayed 316L-matrix composite coatings are studied. Prior to the study of composites, the elaboration steps of 316L in the cold spray coatings are established. Powder and coatings are studied to determine the influence of the cold spray process. Microstructural analyse involved optical microscopy, SEM, chemical analysis EDX and image analysis. Cristallographic analyse were performed by EBSD and DRX. Interfaces between splats are specifically studies by TEM. These consist of a crucial actor in the cohesion of coatings. Then, softer powder of Cu and harder powder of Ni700 are mixed with 316L and cold sprayed to build composite coatings. Their influence on the microstructure through the creation of new interfaces is observed. Last but not least, mechanical properties of the different coatings are compared. Hardness and tensile tests are used for quasi-static loading characterization whereas impact-sliding tests are used for dynamic loading characterization. Results and the local observation of the microstructural response to these macroscopic loadings give an insight into major damage mechanisms of cold sprayed composite coatings.
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Raphaël Maestracci. Influence de la microstructure sur les mécanismes d'endommagement thermomécanique de revêtements à base d'acier inoxydable AISI 316L réalisés par projection dynamique par gaz froid "cold spray". Matériaux. PSL Research University, 2016. Français. ⟨NNT : 2016PSLEM017⟩. ⟨tel-01561419⟩

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