中国有色金属学报(英文版)
Transactions of Nonferrous Metals Society of China
| Vol. 27 No. 7 July 2017 |
（1. School of Materials Science and Engineering, Southwest Jiaotong University, Chengdu 610031, China;
2. Foundation Institute of Materials Science, Bremen University, Bremen 28359, Germany;
3. National Engineering and Technology Research Center for Nonferrous Metal Matrix Composites, General Research Institute for Nonferrous Metals, Beijing 100088, China）
Abstract:Different sized single droplets of Cu-6%Sn alloy were prepared by drop on demand (DOD) technique. The secondary dendrite arm spacing was measured and correlated with the droplet cooling rate by a semi-empirical formula. The microstructure of droplets was observed by optical microscopy (OM) and electro backscatter diffraction (EBSD). The dendrite feature of single droplets depends on solidification rate, cooling medium and flight distance. When droplets collide with each other at temperatures between solidus and liquidus, the dendrites and grains are refined obviously possibly because the collision enhances the heat transfer. The cooling rate of colliding droplets is estimated to be more than 4×104 K/s based on a Newton’s cooling model. The dendrites grow along the colliding direction because of the temperature gradient induced by the internal flow inside the droplets.
Key words: impinging droplet; secondary dendrite arm spacing; cooling rate; heat transfer; drop on demand
