Synthèse de stratégies de fabrication pour la maîtrise de la microstructure des pièces produites par dépôt de matière sous énergie concentrée

Metal additive manufacturing is a process that builds objects layer by layer, producing the material simultaneously with the object. A major industrial challenge is to achieve optimal material properties based on mechanical stresses. However, the mechanical properties depend on the microstructure.In the literature, various levers have been identified to modify the microstructure in additive manufacturing. However, some of these are difficult to implement for a given machine-material pair, require adding extra equipment, or lengthen the manufacturing time.Modulating the energy input through laser power and scanning speed parameters remains practical, although these parameters directly influence the bead geometry.This thesis aims to develop manufacturing strategies that enable the simultaneous production of the desired geometry and microstructure, the latter potentially varying within a single part, for directed energy deposition (DED) processes.The experimental studies conducted in this work for the IN718 material examine two main levers for microstructure control: active cooling during manufacturing and variation of the scanning speed. Active cooling significantly influences the microstructure in laser-powder processes, while its effect is negligible in laser-wire processes. The impact of scanning speed variations on the microstructure and geometry of the parts is also evaluated.Based on these results, a trajectory generation method is developed, ensuring geometric integrity while achieving the desired microstructural variations. The obtained trajectory can be executed with or without tilting the nozzle relative to the part.The developed algorithm is finally applied to a simplified case of a single-bead wall, demonstrating its effectiveness in producing parts with a microstructure gradient. The combination of scanning speeds and variable active cooling proves particularly effective, resulting in significant microstructural variations from one end of the part to the other.