NEW TECHNIQUE OF MEASURING DENDRITE GROWTH VELOCITIES IN UNDERCOOLED METALLIC MELTS

A new technique is developed and described which allows the measuremen t of dendrite growth velocities in undercooled melts in an electromagn etic levitation facility. The triggering of nucleation at the bottom o f the liquid drop ( = beginning of growth at t = t ) and the end of r ecalescence ( = end of growth at t = t++ ) are detected by a capacitan ce proximity sensor and a photodiode, respectively. Dendrite growth ve locities are determined as the ratio 2R0/(t++ - t), where 2R0 denotes the vertical diameter of the drop. First results on pure Ni demonstra te the capability of the method to produce less scattered data than ot her techniques.