Measurement and Prediction of Layered Solidification Patterns Formed on Impact Surface of Molten Metal Drops

The spreading and solidification of molten metal drops are essential physical processes that determine the mechanical properties of the products obtained with additive manufacturing, such as metal 3D printing and sintering. To obtain higher mechanical strength for the products, one needs to prevent the molten metal solid interface from forming gas pores and layers. We experimentally investigated the formation mechanism of layered solidification patterns by directly observing the impact dynamics with the molten tin drops on a sapphire substrate under reduced pressures of argon gas environment. We also quantitatively evaluate the relevant lengths of the air and the solidified layers using a laser microscope. As a result, we revealed that ambient pressure hardly affected the air layer depth, which was instead determined by heat conduction. We also found that the width of the solidified layer correlated to the rim diameter increasing monotonically as the drop spreads.