PBF-LB/M process under a silane-doped argon atmosphere: Preliminary studies and development of an innovative machine concept

In laser-based powder bed fusion of metals (PBF-LB/M) the presence of oxygen is known to encourage embrittlement and impair the wetting properties of the substrate and solidified material. Conventionally, inert gases like argon are used to reduce the residual oxygen content within the processing atmosphere. However, especially in terms of reactive materials like titanium the remaining oxygen still causes critical oxidations. In this publication, a new approach for obtaining an oxygen-free processing atmosphere is presented. Thereby the argon shielding gas is doped with reactive monosilane to reduce the residual oxygen content to a range comparable to XHV (Extreme High Vacuum, thermodynamic oxygen activity <10−15). The handling of this new silane-containing atmosphere requires the development of a special manufacturing system. Therefore, this work elucidates the development of an innovative machine system in accordance with the VDI (German Association of Engineers) Guideline 2221. For determination and specification of the underlying requirements, the interaction of the gas mixture with various construction materials and Ti–6Al–4V powder material was investigated in a test chamber. It could be shown that metallic materials and smooth surfaces are favorable for the design while polymers are likely to degrade in silane-containing atmosphere. Further, the design of the gas flow in the build chamber was optimized using flow simulation. In order to avoid the deposition of reaction products in the process zone, a laminar flow should be established, which can be achieved by baffles and honeycomb structures.