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 v=A·ΔTα, where ΔT is the undercooling, A is a pre-exponential factor which was found to be 1.146×10−4 m s−1 K−α and α=2.48. The recalescence rate, Ṫ, is generally given by Ṫ=B·ΔTβ. The result obtained for cobalt is B=2.79×102 K1−β s−1 and β=1.066.