Comparative assessment of gas and water atomized powders for additive manufacturing of 316 L stainless steel: Microstructure, mechanical properties, and corrosion resistance

In this study, the microstructure, and mechanical properties of 316 L stainless steel (SS316L) produced by laser powder bed fusion (LPBF) using water-atomized (WA) and gas-atomized (GA) powders were compared. The results showed that the use of WA powder, with a finer average particle size and better spreadability, led to significantly higher values of tensile strength (UTS), yield strength (YS), elongation (El%), and toughness in the WA samples (728 MPa, 580 MPa, 31.8%, and 215 J/m3, respectively) compared to the GA sample (602 MPa, 503 MPa, 25.2%, 145 J/m3, respectively). The WA samples also exhibited a non-uniform hardness distribution and superior work-hardening rate due to the presence of multiple inclusions that tightly bound to the matrix and created stress fields, increasing the required energy for dislocation motion. The higher solidification rate of melt pools in the WA sample left more intensive residual stress with distorted grains, exhibiting a higher grain orientation spread (GOS). Additionally, a multitude of geometrically necessary dislocations (GNDs) formed around the boundaries of elongated grains with tilted boundaries to maintain lattice continuity, resulting in a higher kernel average misorientation (KAM) and congestion of low-angle grain boundaries (LAGBs), particularly in the WA sample. XRD patterns confirmed the higher lattice distortion in the WA sample, and the smaller cellular structures observed in SEM images were consistent with the higher dislocation density observed in the WA specimens. Finally, the WA sample exhibited lower surface roughness and rather higher resistance to corrosive media containing chlorides.