Nonequilibrium solidification of hypercooled Co-Pd melts

Co-Pd alloy melts are characterized by a low heat of fusion and, as a consequence, by a comparably small critical undercooling for the hypercooling Limit Delta T-hyp Of the order of 300 K. It is shown that containerless processing of bulk melts by electromagnetic levitation offers undercooling levels of Delta T approximate to 350 K thus exceeding the hypercooling limit considerably. Solidification of undercooled melts from the hypercooling regime leads to rapid crystallization of the entire sample under nonequilibrium conditions. The electromagnetic levitation technique in combination with time-resolved recalescence detection was used to measure the growth velocity of Co-Pd alloy melts as a function of undercooling prior to solidification. The growth velocities of undercooled metallic melts were measured in an undercooling range exceeding the hypercooling limit. The experimental results are discussed within current theory of dendritic growth. (C) 1998 American Institute of Physics.