Large undercooling, rapid solidification and nucleation mechanism in multi-stage atomization

The large undercooling and rapid quenching during multi-stage atomization were studied both theoretically and experimentally. Results show that these two processes are related closely to, and promoted by, each other. The extent of the undercooling of droplets is dependent on the alloy composition and powder size. Experiments on Sn-Pb alloys reveal that the extent of undercooling has a linear relationship with the logarithm of the mean powder size. Based on the present results, a mechanism of the preferred nucleation on the surface oxide is proposed, to give a quantitative interpretation of the experimental observations. (C) 2001 Published by Elsevier Science Ltd.