Residual oxygen content and powder recycling: Effects on surface roughness and porosity of additively manufactured Ti-6Al-4V

The PBF-LB/M (laser-based powder bed fusion of metals) process is associated with high as-built surface roughness and surface texturing caused by a variety of process inherent effects. It is well known that surface roughness is influenced by the applied processing parameters and correlates with porosity. In terms of reactive materials like Ti-6Al-4V, also the powder recycling grade and especially the residual oxygen content within the processing atmosphere play important roles regarding process stability, reproducibility and part properties. Therefore, this study investigated the influence of the residual oxygen content on porosity and surface roughness for virgin as well as recycled powder by employing DoE techniques. Within the examined range, unlike for the roughness, no significant influence of residual oxygen content and powder constitution on porosity could be detected. It could be shown that the reproducibility of relative density mainly depends on the processing parameter combination. Furthermore, powder recycling led to higher top and side surface roughness and a dependence of surface texture on processing parameters could be demonstrated.