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The flowability of metal powders is critical to many additive manufacturing (AM) processes, particularly for laser or electron-beam powder bed fusion. Many poewder features may simultaneously influence its powder flow behavior, yet how particle size distribution (PSD) individually affects its flowability has not been comprehensively evaluated. The plasma atomization technique allows the production of high-quality spherical metal powders with various PSDs. The recent development of powder characterization techniques offers an opportunity to accurately measure a variety of powder flow properties, including Hausner ratio, Hall flow rate, rheology properties. In this study, we measured the flow properties for six Ti-6Al-4V powders with distinct PSDs. Our results show that the PSD plays a significant role in powder flowability: (1) Either a larger mean particle size or a narrower PSD enhances the powder flowability; The multimodal distribution of PSD is beneficial for the powder bulk flow properties. (2) Either a larger particle mean size or a narrower PSD enhances the powder rheology. (3) Powder dynamic flowing behavior is only influenced by the powder mean size, but not affected by PSD. Powder dynamic flowability improves with increasing particle size. Furthermore, we propose a general formula that can be used to qualitatively estimate the average score of the flowability for metal powders based on the three types of indicators. This study could provide a general guide to predict metal powder flowability based on PSD. |
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