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

Abstract

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 (k 2 ) of the primary Ni 3 Sn 2 phase and the specific surface area (S V ) of dendrites. It was shown that peritectic reaction could retard the increase of k 2 and decrease of S V 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.

Detachment of secondary dendrite arm in a directionally solidified Sn-Ni peritectic alloy under deceleration growth condition

“…2 correspond to primary Ni 3 Sn 2 phase, peritectic Ni 3 Sn 4 phase and the eutectic. What is distinct from our previous researches with constant growth velocity2829 is that, obvious detachment of secondary dendrite arms from primary dendrite arms can be observed. Figure 3 shows a typical detachment process of secondary dendrite arms during solidification.…”

“…Further observation shows that this detachment is inclined to occur at the thinner secondary dendrite arms which are more likely to dissolve during the detachment process28. Both the TGZM and Gibbs-Thomson effects are involved during solidification of this Sn-Ni peritectic alloy29.…”

“…1b. This furnace is consisting of a resistance furnace, a water cooled liquid metal bath filled with a liquid Ga-In-Sn alloy, and an adiabatic zone which is located between the heater and the cooler, as previously described2829. The microstructures of directionally solidified Sn-36at.%Ni peritectic alloy at different deceleration rates (−2.22 × 10 −10  ~ −16 × 10 −10 m/s 2 ) are presented in Fig.…”

“…To better understand this detachment process during peritectic solidification, the present paper aims to characterize the detachment of secondary dendrite arm in response to the deceleration growth condition in directionally solidified Sn-36at.%Ni peritectic alloy. Although it has been confirmed that the coarsening process could be more accurately described through S V 28293031, the detachment can not be directly observed from specific surface area S V . Thus both secondary dendrite arm spacing λ 2 and S V will be used to describe the detachment during coarsening process in the present work.…”

“…Dendrite morphology has been frequently encountered in many peritectic alloys with industrial applications, such as Ti-Al23, Fe-Ni24, Pb-Bi25, Nd-Fe-B26 and Al-Ni27 et al Previous works have demonstrated the obvious retard/acceleration of dendrite coarsening by peritectic reaction28/temperature gradient zone melting (TGZM) effect2729. However, the detachment of secondary dendrite arm which is closely related to the coarsening process has never been analyzed in a peritectic system.…”