Cold metal fusion additive manufacturing: Effect of particle size distribution on microstructure and density of green part under spray drying coating process

Cold metal fusion (CMF) is a sinter-based metal additive manufacturing technology that uses polymer-coated metal powders. However, the influence of the original metal powder particle size distribution (PSD) on coating quality and green part characteristics remains largely unexplored. In this study, four 316L stainless steel PSDs (fine: 15-30 μm, medium: 25-45 μm, coarse: 40-60 μm, and wide-distribution: 15-55 μm) were systematically investigated under fixed spray drying and selective laser sintering conditions. A multi-criteria evaluation comprising ΔSpan, coating efficiency, Hausner ratio, angle of repose, and relative tap density identified the medium PSD as the optimal compromise. White-light profilometry showed modest variation in Sa (10.15-11.54 μm) across PSDs, but the wide-distribution powder exhibited a negative skewness (−0.46) and low kurtosis (0.43), indicating a valley-dominated surface texture with deep connected pores exceeding 400 μm. X-ray computed tomography revealed uniform powder distribution for narrow PSDs but significant segregation for the wide-distribution powder. The absolute green part density increased with particle size (maximum 3.62 ± 0.02 g/cm3 for coarse powder), whereas the relative density decreased (maximum 58.02 ± 0.19% for fine powder). This dichotomy arises from the competing effects of metal skeleton packing efficiency and binder-induced volumetric dilution, constituting a decoupled density paradigm for CMF that is fundamentally different from selective laser melting and binder jetting. These findings provide quantitative feedstock design rules for CMF and establish a transferable methodological framework to decouple powder-intrinsic effects in sinter-based additive manufacturing.