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

Peng Peng,Jiangong Li,Xinzhong Li,Yanqing Su,Jingjie Guo,Hengzhi Fu

doi:10.1038/srep27682

Peng Peng, Jiangong Li + Show 4 more

Open Access

https://doi.org/10.1038/srep27682

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Abstract

In order to better understand the detachment mechanism of secondary dendrite arm during peritectic solidification, the detachment of secondary dendrite arm from the primary dendrite arms in directionally solidified Sn-36at.%Ni peritectic alloys is investigated at different deceleration rates. Extensive detachment of secondary dendrite arms from primary stem is observed below peritectic reaction temperature TP. And an analytical model is established to characterize the detachment process in terms of the secondary dendrite arm spacing λ2, the root radius of detached arms and the specific surface area (SV) of dendrites. It is found that the detachment mechanism is caused by not only curvature difference between the tips and roots of secondary branches, but also that between the thicker secondary branches and the thinner ones. Besides, this detachment process is significantly accelerated by the temperature gradient zone melting (TGZM) effect during peritectic solidification. It is demonstrated that the reaction constant (f) which is used to characterize the kinetics of peritectic reaction is crucial for the determination of the detachment process. The value of f not only changes with growth rate but also with solidification time at a given deceleration rate. In conclusion, these findings help the better understanding of the detachment mechanism.

Highlights

One of the most visually prominent features of dendritic structures is the secondary side branch
Nor does attention has been paid to research on the detachment of secondary dendrite arm through alternately changing growth rate in peritectic systems. 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
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 described[28,29]

Summary

Introduction

One of the most visually prominent features of dendritic structures is the secondary side branch. In addition to the coarsening process, the detachment of secondary arms and higher order dendrite arms might occur within the developing dendritic mushy zone[7] if dendritic structures were held long enough either isothermally or during solidification. The evidence of detachment was found by side-branch remelting[19] during in situ study on detachment using transparent organic systems, which enabled the role of solute trapping and local solute/solvent diffusion in the neck regions associated with side-arm attachment[20] to be clarified Given these considerations, detachment of secondary dendrite arms obviously occurs as a natural part of dendrite ripening processes[18]. It is of great significance to describe the detachment of secondary dendrite arms during the solidification process with stepwise decrease of growth velocity

Results

Discussion

Conclusion