Influence of long-time storage or recycling on element concentrations of metallic powders

Dr. Markus Jung, David Nennstiel

Selective laser melting is a promising process for the production of metallic parts with tailored geometries. However, this process is only resource-friendly, if powders are used several times. Until now, it is not fully understood, how recycling or long-time storage of metallic powders influence the properties of 3D printed metals. This work examines the change of carbon, sulfur, oxygen, nitrogen and hydrogen concentrations with long-time storage or multiple usages. Elemental analysis was applied for the determination of carbon, sulfur, oxygen, nitrogen and hydrogen concentrations in metallic powders, as this analytical method is highly accurate, fast and easy to use. Results are more precise and detection limit is lower compared to any other analytical method. However, until now it is impossible to analyze carbon, sulfur, oxygen, nitrogen and hydrogen via one single elemental analyzer. This work describes an innovative, fully automated and energy efficient solution for the determination of all five elements carbon, sulfur, oxygen, nitrogen and hydrogen via one single elemental analyzer. For the first time, this is achieved by the application of an solid-state induction furnace for both CS and ONH analysis. Extreme temperatures of around 3000 °C, which can be necessary for ONH analysis, are realized by an innovative construction design. Moreover, the new crucible geometry for combustion method results in reduced spatter and minimized dust in the system, which is discussed in terms of maintenance, lifetime and data accuracy. It was observed, that carbon concentration increases in iron-based metals with more usages and oxygen concentration is higher for longer stored powders. Similar trends are observed for titaniumand cobalt-based powders. The influence of the change in elemental concentration on properties of 3D printed parts is discussed.