Secondary and tertiary dendrite arm spacing relationships in directionally solidified Al-Si alloys

Secondary, λ2, and tertiary, λ3, dendrite arm spacings have been measured from Al-Si alloys which were directionally solidified as functions of growth velocity,V, temperature gradient,G, and composition,Co. Both λ2 and λ3 decreased as the imposed growth velocity and silicon concentrations were increased, and for each function a systematic variance in the rate was seen. Complications with measuring secondary arm spacings are shown and it was found that the tertiary arm data agree much better with coarsening theory, the implication being that λ3, when measurable, is a more representative and reliable measure of the solidification history than λ2.