DENDRITIC GROWTH IN UNDERCOOLED METALS.

The experimental measurement of the rate of motion of the thermal front generated in an undercooled melt by the release of the latent heat of fusion in nickel, nickel-copper and nickel-silver alloys are presented. These observations were recorded using a high speed motion picture technique to record the growth of the first solid from the melt. The resultant growth velocities as determined by the thermal front motion are summarized for nickel, nickelcopper and nickel-silver alloys. In addition to the growth velocities, the final macrostructure is evaluated with respect to crystallographic orientation and correspondence of dendrite growth direction to growth velocity maxima. The variation in final macrostructure and microstructure in the absence and presence of a grain boundary migration inhibiter are considered. Similar growth studies in the low melting point metal, gallium, are reviewed. The high speed photographic technique applied to the measurement of the solid-liquid interface motion in the undercooled gallium permits dendrite growth velocities to be measured. The initial dendrite directions and relation to the final solidified gallium ingot are considered. In this lower melting point metal the initial solid dendrites formed can be seen in the high speed photographs taken during recalescence as well as in the completely solidified ingot. Author