A simple technique for the measurement of dendritic growth rates in undercooled metallic melts and its application to Ni and Ti

The technique is based on the detection of the recalescence at two opposite points on the surface of a levitated melt by means of photo-diodes. Nucleation is externally triggered within the field of view of one detector, so that the dendritic growth rate is given by dividing the specimen diameter by the delay time between the two diode signals. In pure element melts the undercooling can be determined directly from the photo-diode signals, providing a high time resolution for the temperature measurement. The technique was first tested on Ni melts, since comparable results are available from the literature. Dendritic growth rates were then measured in undercooled Ti melts. The results are discussed in the light of dendritic growth theories.