Rapid monotectic solidification during free fall in a drop tube

Droplets of Ni-31.4%Pb monotectic alloy with different sizes are rapidly solidified during free fall in a drop tube. The theoretical calculations indicate that the undercooling was achieved before solidification exponentially depends on droplet diameter. The maximum undercooling of 241 K (0.15T _m) is obtained in the experiments. With the increase of undercooling, the volume fraction of monotectic cells increases, and the L₂(Pb) grains are refined. Calculations of the nuclcation rates of L₂(Pb) and α-Ni phases indicate that L₂(Pb) phase acts as the leading nucleation phase during the monotectic transformation.