EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

The powder as raw material, either for powder bed or blown powder technologies, constitutes an important strategy in metal additive manufacturing (AM). Metal powder used for powder bed fusion AM is characterized by high surface reactivity due to the large surface area of the powder that is about 10 000 times larger than the surface if the bulk material of the same mass. This results in the powder surface chemistry, determined initially determined by powder manufacturing method and alloy composition. This initial chemical composition is, however, not stable and progressively changes with time in dependence on powder handling procedures and especially processing by metal additive manufacturing. Changes in powder surface chemistry during powder reuse and hence its processability are determined by alloy composition and AM technology in general as well as hardware design and processing conditions in particular.
Paper summarizes recent experimental observations and theoretical simulations of the changes in powder surface chemistry during the whole life-cycle of metal powder: from its manufacturing using different powder manufacturing technologies through powder handling and AM processing by variety of powder manufacturing methods. Results of the qualitative and quantitative analysis of the powder surface chemistry by surface-sensitive chemical analyses using XPS, AES, HR SEM+EDX, etc. are presented and combined with thermodynamic and kinetic simulation. Results indicate significant enrichment in the thermodynamically stable surface oxides in case of high-alloyed powders during both, Electron Beam Melting (EBM) and Laser Powder Bed Fusion (LPBF). However, powder degradation processes differ significantly in dependence on AM technology/hardware and alloy composition. Generic model of the powder degradation, depending on the alloy composition, during different AM processes, is elaborated. Effect of the reused powder on the defect formation during AM processing is discussed as well.