Phase-field modeling of wetting and balling dynamics in powder bed fusion process

Abstract

In a powder bed fusion additive manufacturing process, the balling effect has a significant impact on the surface quality of the printing parts. Surface wetting helps the bonding between powder and substrate and the inter-particle fusion, whereas the balling effect forms large spheroidal beads around the laser beam and causes voids, discontinuities, and poor surface roughness during the printing process. To better understand the transient dynamics, a theoretical model with a simplified 2D configuration is developed to investigate the underlying fluid flow and heat transfer, phase transition, and interfacial instability along with the laser heating. We demonstrate that the degree of wetting and fast solidification counter-balance the balling effect, and the Rayleigh–Plateau flow instability plays an important role for cases with relatively low substrate wettability and high scanning rate.

Contact-Free Support Structures for the Direct Metal Laser Melting Process

“…Moreover, other precautions such as a contour laser scan following the core (hatch/inskin) laser scan provide a smoother surface by re-melting the rougher pre-solidified surface during the core laser scan [ 25 , 26 , 27 ]. During PBF, the surface roughness is determined by the predominance of different mechanisms such as stair stepping [ 28 ], balling effect [ 29 ], powder sticking [ 27 ], etc. at different build orientations.…”

Dendritic Morphology and Growth Inhibition of Ice Crystals in Sucrose Solutions

“…Because of the heat, solute, and ice crystallization involved in the freezing process, dynamic analysis at the crystal level is fairly complicated. In this study, we investigate the growth inhibition and dendritic formation of a continuous ice microstructure due to the sucrose effect using the phase-field method coupled with Flory–Huggins solution theory, , which has advantages in describing the phase transition dynamics without knowing and tracking the phase boundary in priori . − The phase-field method has been applied in a variety of process simulations involving different materials such as recent works in additive manufacturing, − welding, and desalination processes. In particular, the solutal effect on the growth of dendritic patterns in binary metal alloys has been studied extensively. − The Wheeler–Boettinger–McFadden (WBM) model ,, and Kim–Kim–Suzuki (KKS) model considered two concentration fields, and the diffuse interface was treated as a mixture of solid and liquid.…”

Phase transition engineering for effective defect passivation to achieve highly efficient and stable perovskite solar cells

“…This phenomenon is observed when the molten part forms a liquid bridge between the powder, which can be widely observed in various solid powders or nanoparticles. 63–65 After 15 s, a larger coalescence of DOFo and movement of DOFo from the perovskite surface to GBs was observed than at 10 s. This indicates that all DOFo was sufficiently liquefied with fluidity in ∼15 s, and spontaneous passivation occurred due to strong electrostatic interaction with the grain boundaries where several ionic defects exist. 66–68 Finally, after an annealing time of 30 s, most DOFo forms a large crystal and is located in the GBs.…”