Effects of process atmosphere on additively manufactured FeCrAl oxide dispersion strengthened steel: Printability, microstructure and tensile properties

In this study, the effects of using a reactive process atmosphere (premixed Ar–O₂ mixture and N₂) on additively manufactured FeCrAl oxide dispersion strengthened (ODS) steel are evaluated by investigating the oxygen/nitrogen content of the as-built material, geometric characteristics and stability of the molten pool, microstructural feature, second phase formation and tensile properties. It was found that the use of reactive process gas within the building chamber allowed for in-situ alloying in the molten pool. With increasing oxygen content in the building chamber, more oxygen was dissolved by the molten pool allowing for more oxide formation. However, oxide agglomeration and coarsening were also seen to occur. When printing under the N₂ process atmosphere, the nitrogen content in the as-built material increased, and the oxide agglomeration and coarsening were alleviated. A smaller depth-to-width ratio of the molten pool and a more uniform low-angle grain boundaries (LAGBs) distribution in the as-built material were realized when printing under Ar-1% O₂ or N₂ process atmosphere. Nitrogen, as low-cost gas, can be considered to replace traditional Ar as shielding gas for improved mechanical properties of as-built parts.