Dendritic Structure in Columnar Crystals of Binary Alloys

Abstract

A study was performed, using aluminum-rich Al-Cu and Al-Si alloys frozen unidirectionally, to make clear the effects of growth condition and solute elements on the morphology, the size of dendrite cells and the arms spacing of cellular dendrites formed in columnar crystals of binary alloys. The primary branches, which grow perpendicular to the freezing direction from the dendrite stalk, become platelike as shown previously. The dendrite cell size or dendrite width, Z, is given by the following formula:
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\ oindentwhere m is the liquidus slope, k₀ the equillibrium distribution coefficient, D the diffusion coefficient of solute in liquid phase, C₀ the solute content and V_s the cooling rate in the coexisting region of liquid and solid phases, and a₀ a constant. The dendrite arms spacing, Z_a, is proportional inversely to V_s\frac14, and independent of the solute elements.