Effects of Gas Atomization Reaction Synthesis Powder Size on ODS Steel Consolidated via Laser Powder Bed Fusion

Oxide dispersion strengthened metals are desired for structural applications at elevated temperatures. ODS ferritic steels are particularly valued in the nuclear industry for their high resistance to radiation damage and creep resistance at elevated temperatures. While the introduction of nano-scale oxides improves performance, it does create issues for manufacturability. Structural materials can be desired in complex geometries, and welding pieces of ODS steel to make these shapes can influence the population of oxides at the joints, potentially weakening the material. Another downside to traditional processing routes is the tedious mechanical alloying of oxides with steel powder, which is a potential source for impurity contamination. Gas atomization reaction synthesis was used to produce steel powder necessary for ODS steel production, bypassing the mechanical alloying step while also introducing the pre-alloy to oxygen during solidification. Consolidation of powder through the additive manufacturing technique laser powder bed fusion is considered in order to be able to produce complex near-net shaped parts without the need to weld consolidated parts together. Powder was sieved into two separate size batches for printing in order to understand how powder size can influence the microstructure and performance of printed ODS steel. Powder of varying sizes were characterized via TEM to understand how microstructure changes with size. Printed samples where characterized via TEM to understand the phases present after printing, and to measure the nanoscale oxide size distribution and density. Optical microscopy, SEM, and hardness testing was done on consolidated samples to understand microstructure, porosity, and mechanical performance.