Measurements of dendritic growth and recalescence rates in undercooled melts of cobalt

Electromagnetic levitated liquid cobalt was undercooled with the purpose to trigger solidification at desired temperatures. Triggering was performed at the underside of the sample. The solidification velocity was determined by detecting the trigger signal and the temperature rise at the top of the sample by a pyrometer. Measurements were carried out up to 102 K below the melting point. The values of the dendritic growth rate can be well described by the theory of Lipton, Kurz and Trivedi (LKT theory) and follow upsilon = A.Delta T-alpha, where Delta T is the undercooling, A is a pre-exponential factor which was found to be 1.146 x 10(-4)ms(-1) K-alpha and alpha = 2.48. The recalescence rate, (T) over dot is generally given by (T) over dot = B.Delta T-beta. The result obtained for cobalt is B = 2.79 x 10(2) K1-beta s(-1) and beta = 1.066. (C) 1998 Elsevier Science S.A.