Thermal behavior during droplet-based deposition

Abstract

When a cold metallic substrate is used, the temperature at the deposited material's surface is below the solidus temperature during the initial stages of deposition. In this case, a single droplet experiences a significant rapid quenching effect, and can attain a very high cooling rate. The temperature at the deposited material's surface constantly increases and exceeds the solidus temperature at a critical thickness. Then, the cooling rate of a droplet can be relatively large initially due to rapid quenching; however, it solidifies only partially during that time period which lasts until its temperature equals the temperature at the previously deposited material's surface. After reaching this thermal equilibrium, the droplet's cooling process is slow. When the temperature at the deposited material's surface is very close to the average initial temperature of incoming droplets, the rapid quenching effect decreases and even disappears. The cooling process of a droplet is primarily determined by heat dissipation of the local material surrounding it, and as a result, is very slow. Additionally, the deposited material can be divided into three regions with respect to its thickness; the thermal behavior of the deposited material is also related to its final thickness.