Use of Bimodal Particle Size Distribution in Selective Laser Melting of 316L Stainless Steel

Abstract

Spherical powders with single-mode (D50 = 36.31 µm), and bimodal (D50,L = 36.31 µm, D50,s = 5.52 µm) particle size distribution were used in selective laser melting of 316L stainless steel in nitrogen atmosphere at volumetric energy densities ranging from 35.7–116.0 J/mm3. Bimodal particle size distribution could provide up to 2% greater tap density than single-mode powder. For low laser power (107–178 W), where relative density was <99%, bimodal feedstock resulted in higher density than single-mode feedstock. However, at higher power (>203 W), the density of bimodal-fed components decreased as the energy density increased due to vaporizing of the fine powder in bimodal distributions. Size of intergranular cell regions did not appear to vary significantly between single-mode and bimodal specimens (0.394–0.531 µm2 at 81–116 J/mm3). Despite higher packing densities in powder feedstock with bimodal particle size distribution, the results of this study suggest that differences in conduction melting and vaporization points between the two primary particle sizes would limit the maximum achievable density of additively manufactured components produced from bimodal powder size distribution.