Effect of peritectic reaction on dendrite coarsening in directionally solidified Sn-36 at.%Ni alloy

摘要

Effect of peritectic reaction on dendrite coarsening was investigated in directionally solidified Sn- 36 at.%Ni peritectic alloys at different growth rates (2*200 lm/s) under constant temperature gradient. A coarsening model was used to characterize the coarsening process in terms of both the secondary dendrite arm spacing (k2) of the primary Ni3Sn2 phase and the specific surface area (SV) of dendrites. It was shown that peritectic reaction could retard the increase of k2 and decrease of SV during coarsening, which resulted from decelerating solute transport rate between adjacent dendrite arms caused by the peritectic phase enclosing the primary phase. The kinetics of the peritectic reaction that was found to be crucial to determine the coarsening process was characterized by the reaction constant (f) which not only changed with growth rates but also with solidification time in the real solidification process at a given growth rate.