Pore elimination mechanisms during 3D printing of metals

Abstract

Laser powder bed fusion (LPBF) is a 3D printing technology that can print metal parts with complex geometries without the design constraints of traditional manufacturing routes. However, the parts printed by LPBF normally contain many more pores than those made by conventional methods, which severely deteriorates their properties. Here, by combining in-situ high-speed high-resolution synchrotron x-ray imaging experiments and multi-physics modeling, we unveil the dynamics and mechanisms of pore motion and elimination in the LPBF process. We find that the high thermocapillary force, induced by the high temperature gradient in the laser interaction region, can rapidly eliminate pores from the melt pool during the LPBF process. The thermocapillary force driven pore elimination mechanism revealed here may guide the development of 3D printing approaches to achieve pore-free 3D printing of metals.

Universal scaling laws of keyhole stability and porosity in 3D printing of metals

“…Another longstanding issue in metal 3D printing and welding is the generation of excessive porosity. Much effort has been directed at determining the physics underlying this phenomenon, as well as finding ways to eliminate or ameliorate it 20 . Several mechanisms that lead to porosity formation have been identified, such as lack of fusion 21 , instability of the depression zone 6 , vaporization of volatile elements 22 , and hydrogen precipitation 23 .…”

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

“…High-speed high-resolution X-ray imaging (at the beamline 32-ID-B of the Advanced Photon Source, Argonne National Laboratory, Lemont, IL, USA) was utilized to probe pore formation dynamics during PW-LPBF in real time [ 22 ]. The schematic of the X-ray imaging system is displayed in Figure 1 .…”

Progress on In Situ and Operando X-ray Imaging of Solidification Processes

“…Notably, their reported average melt flow velocity of the entire melt pool was 1.1 ± 0.5 m s −1 and very similar to prior work [ 58 , 161 , 163 ]. The aforementioned studies showed that most flow patterns followed a centrifugal Marangoni convection owing to the negative temperature dependant coefficient of surface tension in metallic systems [ 58 , 162 , 163 , 164 , 165 ]; however, the Marangoni convection can be reversed when there is an increase in oxygen content within the molten pool, i.e., centripetal Marangoni convection [ 152 ], resulting in a deeper molten pool, larger pore size distribution, and more frequent spatter ejection. These new insights provided detailed information regarding the influence of powder chemistry on the melt flow and defect dynamics under a wide range of processing regimes which can be used for developing a reliable high-fidelity simulation model to predict the formation of undesirable features during LAM.…”