Abstract
Porosity continues to be a concern for the performance of additively manufactured parts. One source of porosity is powder-borne porosity—porosity that is contained in the powder itself. To create a fully dense part, these powder-borne pores need to be released from the melt pool. This study utilizes an in-situ x-ray imaging technique to elucidate the underlying physical phenomena driving the capture or escape of powder-borne pores in directed energy deposition (DED). In total, 80 instances of powder-borne porosity that were captured in the melt pool were identified and tracked. Ultimately, six mechanisms of pore capture and escape were identified. Pore escape was seen to occur via particle melting, pore buoyancy, Marangoni flow, and fluctuation of the liquid-vapor interface, while pore capture was seen to occur via entrainment through particle impact, Marangoni flow, and pore pinning by adjacent particles. Understanding these mechanisms and phenomena is a critical step in enabling the optimization and control of the DED process.© 2022 Society of Manufacturing Engineers (SME). Published by Elsevier Ltd. All rights reserved.This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).Peer-review under responsibility of the Scientific Committee of the NAMRI/SME.
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