On the nanoscale oxide dispersion via in-situ atmospheric oxidation during laser powder bed fusion

Abstract

In-situ oxidation during laser additive manufacturing (AM) is considered a more economical approach to producing AM oxide dispersion-strengthened (ODS) alloys. However, there is very few success in making AM ODS alloys with oxide density comparable to commercial ODS alloys made by conventional means. To explore the key mechanisms that prevent the high-density dispersion of nanoscale oxides during in-situ reactive AM, we investigated oxide dispersion by in-situ gas-phase reaction during laser powder bed fusion (LPBF) with respect to oxygen gettering elements with different oxygen affinity, getter concentration, atmospheric oxygen level, and laser parameters. Our results show that in-situ oxidation in a high-oxygen printing atmosphere during LPBF AM cannot effectively produce good-quality ODS steels, even when the amount of oxygen pick-up from the atmosphere into the melt pool is comparable to the oxygen level in commercial ODS alloys. We found that surface oxidation and oxide agglomeration in the melt pool prevent the high-density dispersion of nanoscale oxides. In addition, oxide agglomeration also contributes to a higher amount of manufacturing defects. Powder spattering plays a secondary impact on oxygen loss.