Role of IMCs in the Spreading-Retracement Process of Sn Droplets Impacting Cu and Stainless Steel Substrates

Rapid printing of three-dimensional (3D) structures can be achieved using 3D printing technology based on homogeneous metal microdrop jetting. This process has several advantages over powder 3D printing technologies as it includes a wide range of jetting materials and unconstrained free forming and does not require expensive specialized equipment. In this study, the dynamic wetting behavior of Sn droplets impacting on copper and stainless steel surfaces was investigated using a combination of experiments and simulations. The coupled level-set volume-of-fluid method was used to establish a numerical model of molten metal droplets impinging on high-temperature substrates and to explore the role of intermetallic compounds (IMCs) in the spreading-retracement process. The results showed that the dynamic wetting processes of Sn droplets on Cu and stainless steel surfaces were significantly different from each other, primarily because of the difference in their intrinsic contact angles and the generation of IMCs in the Sn/Cu system. Moreover, the IMCs had little effect on the droplet spreading process, but had an inhibitory effect on the retracement phenomenon, and the degree of this effect gradually increased as the retracement process continued.