Melt Flow and Micro-Segregation in Unidirectional Dendritic Growth

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Effects of melt flow on dendritic interface are investigated in the unidirectional solidification. They are studied for (a) the dendritic growth in viscous-fingers in Hele-Shaw cell, experimentally, (b) predictions of tip radius of curvature and the growth rate of the primary dendrite arm, theoretically and for (c) effects of melt flow(convection) on characteristic dimensions of dendrite near the tip.Through the experimental study on the dendritic growth in viscous-fingers in Hele-Shaw cell, the governing equations for viscous-fingers and that of solidifications have shown to be in good correspondence, if one replaces the pressure in viscous-finger to the temperature in solidification in their equations. The shape of interface of viscous-finger is very similar to that of dendrite in solidifications, when a groove is attached on the plate of the Hele-shaw cell. The viscous-finger dendrite is experimentally very useful in studying the growth mechanism of secondary-arms, because their dim … More ensions are larger than that of usual metal dendrite and the pressure near the tip is easily observed.Through the theoretical study of tip radius of curvature and the growth rate of the primary dendrite arm, a new growth mechanism is proposed. It takes into account the contribution of tangential growth on the interface that is driven by the gradient of curvature of the interface. The tip radius of curvature and the growth rate of dendrite are predicted in the solidification of undercooled pure melt. The predictions agreed well with the experiments given in the solidification of succinonitrile dendrite.Through the numerical study of melt flow(convection) near the dendrite tip, it is shown that the characteristic dimensions of dendrite suffers very serious effects by the flow. IF the flow is in same direction of the growth rate of dendrite and faster than the growth rate of dendrite, then the growth rate becomes smaller and it would diminish in some extreme growth condition.The melt flow is studied and shown to contribute to the dimensions of dendrite in the solidifications, especially in the region near the tip of dendrite. This study would contribute to clarify the growth mechanism of secondary-arms. Less