Combined effect of powder properties and process parameters on the density of 316L stainless steel obtained by laser powder bed fusion

The laser powder bed fusion (LPBF) process is capable of producing nearly dense 316L stainless steel (SS) parts with a choice of suitable process parameters. These parameters are generally selected from an empirical process mapping involving the input variables of the process (laser power, scan velocity, layer thickness …), independently of the powder characteristics. However, the powder properties (i.e., size, morphology, flowability…) affect the complex physical phenomena involved in the LPBF process. This paper investigates the combined effect of powder properties and process parameters on the LPBF parts density. Firstly, the flowability, relative density, particle size distribution, and absorptance of several powders were measured. Then, these powders were used to produce samples with different process parameters, mainly laser power, scan velocity, and layer thickness. Additionally, computed micro-tomography scanning (µCT) and microscopic analysis methods were used to determine the porosity of the as-built samples and characterize the defects' sizes, types, and locations. The powder size was found to influence the lack of fusion and keyhole boundaries in the process map and consequently affect the operating window. The standard powders with the highest relative density and good flowability were characterized by larger operating windows compared to finer and coarser counterparts. Finally, predictive models were suggested to estimate the porosity of LPBF 316L stainless steel (316L SS) parts by taking into account the powder properties.