In-Situ Characterization of Pore Formation Dynamics in Pulsed Wave Laser Powder Bed Fusion

• Published in: Materials Vol. 14; no. 11; p. 2936
• Main Authors: Hojjatzadeh, S. Mohammad H., Guo, Qilin, Parab, Niranjan D., Qu, Minglei, Escano, Luis I., Fezzaa, Kamel, Everhart, Wes, Sun, Tao, Chen, Lianyi
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 29-05-2021; MDPI
• Subjects: additive manufacturing; Continuous radiation; Coordination compounds; Emissions control; Experiments; Imaging techniques; Laser beam melting; laser powder bed fusion; Lasers; Mechanical properties; pore; Pore formation; Powder beds; Printing; pulsed emission; Solidification; Synchrotron radiation; Synchrotrons; X ray imagery; X-ray imaging
• ISSN: 1996-1944; 1996-1944
• DOI: 10.3390/ma14112936

Laser powder bed fusion (LPBF) is an additive manufacturing technology with the capability of printing complex metal parts directly from digital models. Between two available emission modes employed in LPBF printing systems, pulsed wave (PW) emission provides more control over the heat input compared to continuous wave (CW) emission, which is highly beneficial for printing parts with intricate features. However, parts printed with pulsed wave LPBF (PW-LPBF) commonly contain pores, which degrade their mechanical properties. In this study, we reveal pore formation mechanisms during PW-LPBF in real time by using an in-situ high-speed synchrotron x-ray imaging technique. We found that vapor depression collapse proceeds when the laser irradiation stops within one pulse, resulting in occasional pore formation during PW-LPBF. We also revealed that the melt ejection and rapid melt pool solidification during pulsed-wave laser melting resulted in cavity formation and subsequent formation of a pore pattern in the melted track. The pore formation dynamics revealed here may provide guidance on developing pore elimination approaches.