Travail de fin d'études et stage[BR]- [BR]-

Abstract

This study investigates the design and initial assessment of corrosion-resistant High Entropy Alloys (HEAs) processed by Laser Powder Bed Fusion (LPBF) using mixtures of commercially available metallic powders. Candidate compositions were first screened through CALculation of PHAse Diagrams (CALPHAD) based on thermodynamic calculations using Thermo-Calc and thermodynamic prediction tools such as Valence electron concentration (VEC), atomic size mismatch, or configurational mixing entropy. These candidate compositions were then tested using Differential Thermal Analysis (DTA) to predict equilibrium phases, to identify solidification events, and to evaluate microstructural trends as a function of composition. DTA-based microstructural characterization highlighted a progressive increase in phase complexity with aluminum additions, guiding the selection of two compositions, one Al-free and another with low aluminum content, for LPBF printing. Single track experiments were used to establish a viable processing window, followed by fabrication of cubic samples produced under a range of laser power from 100 to 200W, and a scan speed ranging from 200 to 1,000mm/s. Part quality was quantified using helium pycnometry and 3D optical profilometry, while Optical Microscopy (OM), Scanning Electron Microscopy (SEM), Electron BackScatter Diffraction (EBSD), and Energy-Dispersive X-ray spectroscopy (EDX) were carried out to analyze phase constitution, grain morphology, porosity, cracking, and chemical heterogeneities. The results demonstrate that densification and porosity are strongly dependent on processing parameters, whereas surface quality is additionally influenced by spatter and shielding gas flow-related depositions. Regardless of composition and parameter set, intergranular hot cracking was systematically observed, and oxide inclusions were detected at both micro- and nano-scale. Non-metallic inclusions were predominantly aluminum oxides in Al-containing samples, and silicon oxides in Al-free samples, in both cases the inclusions often exhibited chemically stratified interfacial layers. Overall, aluminum addition improved bulk quality within the tested process window but did not suppress cracking, emphasizing the need for composition specific LPBF optimization and improved control of powder chemistry and oxidation during processing.