Particle size distribution for additive manufacturing powder using stereological corrections

Additive manufacturing powders require well-defined Particle Size Distributions (PSDs) and spherical morphology for good powder flowability. To simplify characterisation processes, powders can be prepared using standard metallurgical preparation techniques, followed by optical imaging to determine the PSD of cross-sectioned particles. However, this measured PSD typically provides underestimates of the true diameters; hence, stereological corrections must be applied. Three stereological correction methods: the Scheil-Schwartz-Saltykov (SSS) method; the Goldsmith and Cruz-Orive (GCO) method and a Finite Difference Method (FDM) are assessed. Laser Size Diffraction (LSD) analysis provided the ground truth data. Particle cross-sections of 2,280 powder particles (Ti-6Al-4V) were analysed in the size range of 9–76 μm. The mean absolute errors were found to be 2.3% for the SSS method, 2.4% for the GCO method, and 1.6% for the FDM method. Hence, whilst all three methods provided an improved estimate of the PSD, FDM was determined the most effective method in this case.