Shape characterisation for mounted additive manufacturing powders

Particle morphology plays a role in the flowability of powders used in additive manufacturing processes. Hence, shape properties of feedstock must be routinely assessed and controlled. There are various particle shape analysis methods, but it is necessary to develop an easily accessible methodology for additive manufacturing users, particularly for small and medium-sized enterprises. The work presented here utilises standard metallurgical laboratory equipment and automated image analysis algorithms to analyse particle shape measurements from digital 2D images of cross-sectioned powders mounted in polymer. Particle circularity, convexity, and solidity measures are determined from the 2D images. There are stereological errors introduced when a three-dimensional particle is sectioned onto a two-dimensional plane for observation. The effectiveness of the 2D approach is evaluated by comparing results to benchmark 3D powder data. The proposed method is applied to three unprocessed Ti-6Al-4 V powders produced via gas atomisation, plasma atomisation, and ultrasonic processing. Benchmark comparisons with commercial 3D analysis revealed errors under 7.4 % for circularity, 2.2 % for convexity, and 3.9 % for solidity. The gas-atomised powder consistently showed the lowest mean shape descriptor values (circularity = 0.867, convexity = 0.970, solidity = 0.949), indicating higher levels of irregularity and agglomeration, while the ultrasonically processed powder showed the highest mean shape descriptor values (circularity = 0.947, convexity = 0.986, solidity = 0.978) indicating superior particle circularity in the 2D analysis. The results show the extent of the applicability of the 2D approach for cursory and comparative analysis of powders and their morphology.