The effect of powder reuse on the surface chemical composition of the Scalmalloy powder in Powder Bed Fusion - Laser Beam process

The powder quality is one of the main factors to be considered in laser powder bed fusion (PBF-LB/M) production closely connected with the performance of the final component. Only powders with spherical particles, a low percentage of satellites, a narrow particle size distribution, controlled internal defects and a strongly limited surface oxide layer are acceptable for PBF-LB/M production. Gas atomisation is the main production method that permits to achieve the restrictive standards of the PBF-LB/M powder; however, it is energy-intensive and characterised by limited productivity. These considerations justify the key role of the reuse of the unmelted metal powder in obtaining a more sustainable PBF-LB/M process. Nevertheless, the reuse of the powder leads to significant changes in the particle morphology, particle size distribution and surface chemical composition, which can compromise the bulk properties. Powder surface oxide is one of the most impactful problems for the PBF-LB/M production, and Al-based alloys are particularly prone to this phenomenon. With the aim to study the effect of the powder reuse, a surface chemical analysis on gas atomised Scalmalloy powder was performed through the X-ray photoelectron spectroscopy investigation before and after seven jobs with 32 h as overall build time. Results obtained for virgin and recycled Scalmalloy powders revealed remarkable differences in depth and composition of the surface oxide layer. The 57% increase in the oxide layer thickness and the formation of carbides during PBF-LB/M production can have harmful effects on bulk properties.