Dendritic solidification and fragmentation in undercooled Ni–Zr alloys

Kinetics of dendritic solidification and fragmentation of dendritic crystals in undercooled Ni–Zr samples are studied. Using the capacitance proximity sensor technique and a high-speed-camera system, the dendrite growth velocity has been measured as a function of initial undercooling in solidifying droplets processed by the electromagnetic levitation technique. Analyses of solidified droplets give evidence to a transition from coarse grained dendrites to grain refined dendrites (CG-GR) at small undercooling, a transition from grain refined dendrites to coarse grained dendrites (GR-CG) at moderate undercooling, and to a second transition from coarse grained dendrites to grain refined dendrites (CG-GR) at a higher undercooling. Predictions of a sharp-interface model are compared with the results of experiments on Ni–Zr samples.