Influence of Storage, Processing and Reconditioning on Ti-6Al-4V ELI Powder Characteristics for Laser Powder Bed Fusion

Guarantee of consistent part quality is crucial for wide application of laser powder bed fusion (LPBF) in highly regulated industries like aerospace. Therefore, in-deep knowledge on the evolution of powder characteristics along the whole LPBF process chain and the powder re-use is essential. In this contribution, various aspects of storage and processing of Ti-6Al-4V ELI virgin and reconditioned powder, including potential sources for hydrogen, nitrogen and oxygen uptake, are discussed. The gas tightness of different commercially available 20-liter stainless steel powder tanks was evaluated. Subsequently, the more suitable gas tank was equipped with a permanent measuring system to collect temperature, oxygen, and humidity data during a typical storage interval of several months. During long-term storage oxygen content in the powder container increases steadily, but no remarkable oxygen uptake within the powder was observed. Likewise, powder handling before, during and after LPBF processing led only to a weak increase of oxygen and nitrogen content of the powder. In contrast, LPBF solid parts show increased interstitial element contents and it is concluded that the major uptake appears directly during melting under argon protective atmosphere and process associated splatter and sieve residue show remarkable enrichment in these elements. Considering the critical stages of powder aging, a representative material flows and mass balance analysis for LPBF was conducted. As an outlook, a concept for powder usage and reconditioning with virgin powder will be given. The presented results are part of the project AMTwin, which is funded by the Free State of Saxony in Germany.