Localized Particle Segregation Induced by Leidenfrost Droplet Motion across Superheated Powder Bed.

The mechanical properties of metallic parts additively manufactured through powder bed techniques are highly dependent on the particle size distribution of the powder bed. The ability to locally modify the particle size distribution in the powder bed would enable novel heterogeneous metallic parts with site-specific properties to be fabricated. To date, there is no simple method to achieve this localized segregation. Here, we show how Leidenfrost droplets traveling at a constant speed can be employed to locally segregate particles within the powder bed. Powder particles are fluidized, landing along the slope of the traveling droplet's path. As the particles tumble down the slopes, large particles are sieved out, leading to their preferential deposition in the wake of the droplet path. Our results show that the amount, as well as the proportion, of large particles deposited increases with a thicker powder bed layer and a slower droplet velocity. This is due to the increased availability and participation rate of large particles. Large particle deposition pattern changes with these parameter variations. Increasing the proportion of large particles in the powder bed from 33.3 to 50.0 wt % confirmed these trends. Changing the Leidenfrost droplet fluid from water to ethanol led to a lower fluidization velocity, which also encouraged further deposition and segregation of large particles, particularly at low powder bed thicknesses. With these sophisticated outcomes, the Leidenfrost droplet system is shown to be a promising localized particle segregation technique.