Crystal nucleation in undercooled melts of PdZr2

Crystal nucleation in undercooled melts of the stoichiometric PdZr2 compound is studied by measuring the nucleation undercooling of small droplets processed by containerless electrostatic and electromagnetic levitation. Owing to the avoidance of container walls usually acting as heterogeneous nuclei, large undercoolings are achieved. The statistics of crystal nucleation is investigated by measuring the nucleation undercooling of at least 100 melting and solidification cycles for both sets of experiments. The results are analyzed within a statistical approach based on the classical nucleation theory. Out of this two important parameters can be extracted. These are the activation energy, which needs to be overcome to form critical nuclei and, the pre-factor in the nucleation rate equation, which measures the number of potential nucleation sites per unit volume. The results are discussed with respect to the different experimental conditions, short-range order in the undercooled liquid state and its impact to the glass forming ability of this alloy. (C) 2013 AIP Publishing LLC.