Effect of nitrogen atmosphere on the printability, microstructure, precipitation, and mechanical properties of laser powder bed fused Fe-xCr alloys

The role of the nitrogen atmosphere on the microstructure and tensile properties of laser powder bed fused (PBF-LB/M) Fe-xCr (x=0, 5, 10, 15, 24wt.%, mixed using elemental Fe and pre-alloyed Fe-46 wt.% Cr powders) binary alloys was investigated and compared with those fabricated under an inert (argon) atmosphere. Microstructural characterization reveals the variations of grain morphology with the chemical composition and the distinct effects of nitrogen on grain refinement and texture. Additionally, PBF-LB/M performed under the nitrogen atmosphere leads to the formation of Cr and Fe nitrides in the alloy. Significant enhancements in strength were observed in Fe, Fe-5Cr, and Fe-10Cr fabricated under nitrogen atmosphere due possibly to the solid solution and precipitation strengthening caused by dissolved nitrogen and the nitrides, respectively. However, the Fe-15Cr and Fe-24Cr alloys processed under the nitrogen atmosphere are brittle and crack upon PBF-LB/M due to the residual stresses. The findings in this work enrich the understanding of the effects of fabrication atmospheres in additive manufacturing, insights of which can be extended to diverse categories of alloys.