EFFECT OF EXTERNAL HEAT EXTRACTION ON DENDRITIC GROWTH INTO UNDERCOOLED MELTS

Solidification characteristics in most rapid solidification processes are controlled by heat extraction by the chill substrate and by melt u ndercooling, especially near the substrate. A dendrite growth model fo r this situation is derived in the present study. The model involves c ombined effects of the undercooled melt and the substrate as effective heat sinks. A dendrite is assumed to grow into an undercooled melt, w ith heat evolution at the dendrite tip occurring both into the underco oled melt and into the chill substrate through the growing solid. The significance of the proposed dendrite model and the stability of dendr ite growth under the thermal conditions considered are discussed, usin g the Fe-Cr-Ni alloy system as an example.