NEW TECHNIQUE OF MEASURING DENDRITE GROWTH VELOCITIES IN UNDERCOOLED METALLIC MELTS

A new technique is developed and described which allows the measurement of dendrite growth velocities in undercooled melts in an electromagnetic levitation facility. The triggering of nucleation at the bottom of the liquid drop ( = beginning of growth at t = t* ) and the end of recalescence ( = end of growth at t = t++ ) are detected by a capacitance proximity sensor and a photodiode, respectively. Dendrite growth velocities are determined as the ratio 2R0/(t++ - t*), where 2R0 denotes the vertical diameter of the drop. First results on pure Ni demonstrate the capability of the method to produce less scattered data than other techniques.