Homogeneous nucleation and anomalous dendrite growth in undercooled melts

Crystal nucleation in undercooled melts of pure Zr was studied by application of electriomagnetic and electrostatic levitation. Large undercoolings were achieved owing to containerless processing of te liquid sample. In case of eectrostatic levitation, the large undercoolings indicate the onset of homogeneous nucleation. \nDendrite growth velocities were measured on elctromagnetically levitated Al-Ni samples as a function of undercooling. In case of Al-rich Al-Ni alloys an anomalous dendritic solidification dynamics was observed such that the growth velocity is decreasing with increasing undercooling. Comparative experiments during TEXUS 44 EML3 mission may suggst that the anomalous growth kinetics is caused by gravity related phenomena.