Characterization of additive manufacturing metal powders using the FT4 powder rheometer

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Powder Bed Fusion is a Additive Manufacturing technique based on the repeated spreading and melting of thinlayers of powder. As the technology evolves from the research to production, the importance of quality controlof finished parts increases. The relationships between powder feedstock, spreading dynamics and defectformation are still not fully understood, but the current understanding is that that powder voids formed afterspreading can seed defects in the finished part. Thus, high quality powders must have properties which enablethe spreading of dense, homogenous layers, free of voids and segregation. These properties must be maintainedthroughout the powder lifetime, which can include recycling, handling and extended storage periods. Despitethe importance of powder spreadability, no universal description or standard for quantitative spreadabilityexists. Currently, AM powder is characterized by tests which capture some, but not all, of the spreading-relatedproperties, while new AM-specific standards are being proposed.This proposal concerns a joint investigation between McGill University and Advanced Powders andCoatings(AP&C) to understand the strengths and weaknesses of characterizing powder spreadability using theFreeman Technology FT4 powder rheometer. Compared to conventional, gravity-based measurements like theHall flow meter, the data generated from the FT4 should should be more representative of spreading-relatedproperties because of the ability to apply precise compressive, tensile and shear forces to the powder bulk.Whether FT4 test parameters can be matched to specific powder spreading techniques will be determined overthe course of this project. If the FT4 can accurately resolve properties related to spreading, the instrument willbe used to evaluate new powder production techniques as well as support the quality management systems ofAP&C and their customers.