Additive manufacturing of in-situ particle reinforced ODS/NDS alloys utilizing the process atmosphere

Oxide and nitride dispersion strengthened steels (ODS/NDS) show great potential for applications in the energy and aerospace sector. Manufacturing of these alloys is challenging as a homogeneous particle distribution in the materials is required which is typically only achieved by Powder Metallurgy routes or Additive Manufacturing (AM). Various strategies including powder decoration and powder blending are used in AM to process ODS alloys. Utilization of the process atmosphere in AM processes (PBF-LB, DED-LB) has recently received attention to process in-situ ODS alloys. In our work, we study the ability to use reactive process atmospheres (e.g. CO2, N2) to process in-situ ODS and NDS alloys with tunable properties. The particle properties (e.g. size and distribution) are affected by the thermal field during processing, which is controlled by manufacturing parameters. For this purpose, Fe-Ti alloy specimens are processed by PBF-LB/M and DED-LB/M under Ar, CO2 and N2 atmosphere. The extent of the material-gas interaction is determined by the composition of alloy and atmosphere as well as the manufacturing parameters. Increasing melt pool surface temperatures and melt pool lifetimes enhances the interaction with the process gas and increases the gas uptake from the atmosphere. In-situ oxygen-, nitrogen- and carbon-rich particles are formed in the melt pool affecting microstructure and improving strength by particle reinforcement and grain refinement. Particle size and distribution are correlated to the melt pool lifetime and cooling rates. The composition of the in-situ formed nanoparticles changes with Ti, O, C, N concentrations in the melt pool.