International Congress on Applications of Lasers & Electro-Optics (ICALEO)
Residual oxygen within the processing atmosphere of the laser-based powder bed fusion of metals process (PBF-LB/M) is regarded as a detrimental factor. Even with residual oxygen levels of several ppm depending on the argon purity level used, critical oxidation of reactive materials can still be initiated. In addition, conventional PBF-LB/M systems typically achieve residual oxygen contents of 700 - 1300 ppm due to limited gas tightness. This work presents a new approach for achieving strongly reduced residual oxygen contents. In the first step, it consists of using a particularly gas-tight laboratory machine. In a subsequent step, the processing is carried out under a silane-doped argon atmosphere. By admixing small amounts (<100 ppm) of the highly reactive gas silane to the argon shielding gas, an atmosphere adequate to an extreme high vacuum can be achieved. Ti-6Al-4V powder was processed with varied laser power (170 – 230 W) on an industrial machine (1000 ppm) as well as on the specialized laboratory machine under argon (200 ppm) and silane-doped argon atmosphere (<10-16 ppm). It is shown that fully dense specimens can be obtained in all investigated atmospheres. The top surface roughness was not influenced by the atmosphere or the employed machine. Variations in microstructure were mainly observed between the two machines. The hardness was significantly influenced by the choice of atmosphere, since silicon and oxygen absorption during processing led to increased hardness. This study therefore emphasizes the importance of a strictly controlled atmosphere in PBF-LB/M.