Effect of recycling on internal and external defects of Ti-6Al-4V powder particles for electron beam melting process

Electron Beam Melting is an additive manufacturing process that allows the creation of high-resolution parts with complex shapes, starting from a powder feedstock and using an electron beam as the energy input. Due to the high costs of the powder, the excess one must be reused otherwise a high percentage of unused powder would be lost after the printing process. The virgin and reused powders may have not the same characteristics, and therefore the printed parts may not have the same final quality which is detrimental to mechanical performances. However, this topic still needs research, as the influence of recycling on powder characteristics is not fully understood. In this study, the internal defects, and their distribution in virgin and recycled Ti-6Al-4V powders particles, are investigated by means of an optical microscope. For the analysis of the surface morphology and the external characteristics, it was used the Scanning Electron Microscope (SEM). At the end, a commercial software ImageJ was used in order to provide some quantitative results on the internal porosity percentage. The results demonstrate the dependence on the powder atomization process, which is primarily responsible for the micro-porosities, due to the trapped gas in virgin powders, and the rough surface morphology, including the presence of various satellites. As the number of reuses increases, the quantity of satellites decreases, probably due to the partial melting on the surface, which consequently returns in rougher surfaces of the recycled powder particles. In addition, most of the internal porosities disappeared making the cross-sectional faces of the particles near fully dense.