Insights into the in-situ ODS 304L stainless steel processed by laser powder bed fusion through oxygen content regulation and the effect on microstructure and mechanical properties

Laser powder bed fusion (LPBF) is a widely used and well-developed additive manufacturing approach. To meet the higher material performance requirements for the fourth-generation nuclear power reactors, LPBF processing combined with oxide dispersion strengthening (ODS) is currently of interest among new materials designs and developments by dispersing nanoscale Y2O3 particles into the feeding powders to obtain the LPBF- ODS materials. Oxygen exposure and its introduction in the solvation cell, on the other hand, are usually considered detrimental but impossible to eliminate completely during the LPBF process. The understanding of this unavoidable process, however, is still limited. Here we develop a new LPBF-ODS design approach based on in-situ oxygen content regulation during the LPBF process. The oxygen content of the environment chamber was artificially adjusted through an online monitoring system to activate the reaction between oxygen and metal elements, thus forming the dispersed oxide particles in situ. Four batches of LPBFed 304L stainless steel samples were successfully processed under different oxygen levels to investigate the reinforcing effect of in-situ chemical alloying. The results show that the dispersed oxide particles are formed through the LPBF in- situ alloying approach with an average nanoscale dimension of approximately 46 nm. The number density of oxide particles increases to 11.4 particles /μm2 with the increase in oxygen content, playing a role in refining and stabilizing the cellular structure. The in-situ alloyed ODS material exhibits enhanced yield strength (up to ∼ 675 MPa) while keeping ductility not heavily affected (elongation up to ∼ 39%), which is competitive within the range of tensile properties reported for ODS alloys prepared by mechanical alloying (MA). This study analyzes the main mechanism of yield strength enhancement through the interaction between the nano- scale oxide particles and dislocation entanglement cells, providing a new idea for the subsequent preparation of high-performance LPBF-ODS alloys.