Pore Formation and Polymer Thermal Debinding during Vapor-Induced Phase Separation-Enabled Metal Printing

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Metal additive manufacturing has been of great interest for the fabrication of complex metallic components ranging from automobile parts to jet engines to medical implants. Despite its advantages over conventional metal fabrication methods, current metal additive manufacturing technologies are subject to challenges including handling metal powders, which can be explosive, and fabricating parts with heterogeneous materials to enhance part properties. This project aims to explore a room-temperature polymer binder-assisted metal printing technology, which uses suspension inks made of metallic powders and dissolved polymer. The new process has two advantages: (1) using metal-polymer suspension inks reduces the hazards of handling and inhaling metallic powders for machine operators; and (2) heterogeneous materials can be deposited by adjusting the metal composition of suspension inks. Simultaneously this project will stimulate science-based manufacturing education to broaden the participation of underrepresented and minority students in STEM and prepare a manufacturing workforce for the fast-evolving manufacturing industry.Of various metal printing technologies, powder bed fusion (PBF) and directed energy deposition (DED) are the most common modalities. PBF and DED are energy-driven high-temperature printing processes and require handling metal powders before and after printing. Advances in bound powder extrusion allow the use of metal powders pre-bound in the form of a filament, which, however, limits the choices of materials. The vapor-induced phase separation-enabled three-dimensional printing technology (VIPS-3DP) utilizes metal-polymer suspensions as build materials and VIPS as the solidification mechanism. The resultant metal-polymer green parts are further processed for polymer thermal debinding and sintering to get final metallic parts. The objective of this research is to study the effect of the VIPS-induced solidification of polymer binder on the formation of an interconnected pore space in metal-polymer green parts during printing and the effect of the resulting interconnected pores on the crack occurrence during polymer thermal debinding. The research will be implemented via two tasks: (1) theoretical modeling of the porous microstructure evolution and thermal debinding processes, and (2) experimental characterization of printed green, brown, and final parts in terms of their microstructure and mechanical properties. The resulting knowledge of the VIPS-induced porous microstructure and its effect on thermal debinding may lead to new sustainable metal additive manufacturing technologies.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.