Abstract
The growth velocity during solidification of an undercooled melt of a Co-Cu al- loy processed by electromagnetic levitation was measured using a high speed video camera. Applying a model of local non-equilibrium solidification, theoretical predictions of den- drite growth velocity and dendritic growth radii are compared with high-accuracy mea- surements of the growth kinetics. As the undercooling ΔT reaches a critical value consistent with the dendrite growth velocity being equal to the atomic diffusion speed VD in bulk liquid, ΔT = ΔT(VD), the velocity-undercooling relationship exhibits a break-point. A dis- tinct change in the dendritic growth mechanism exists with the onset of complete solute trapping and chemically partitionless solidification of the core of the main stems of the den- drites occurs. A complete transition to the thermally controlled growth of dendrites occurs at ΔT = ΔT(VD) that leads to essential changes in the microstructure of dendritic patterns The phenomenon of dendritic fragmentation in Co-Cu melts, solidifying at Δ T< ΔT(VD), is discussed.
Published Version
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