Microstructure evolution of gas-atomized Fe–6.5 wt% Si droplets

Abstract

The magnetic Fe–6.5 wt% Si powder was produced by gas atomization and its microstructure was also investigated. The secondary dendritic arm spacing (SDAS) is related to the droplet size, λ = 0.29 · D0.5, and the numerical solidification model was applied to the system, giving rise to the correlation of microstructure to the solidification process of the droplet. It is found that the solid fraction at the end of recalescence is strongly dependent on the undercooling achieved before nucleation; the chances for the smaller droplets to form the grain-refined microstructures are less than the larger ones. Furthermore, the SDAS is strongly influenced by the cooling rate of post-recalescence solidification, and the relationship can be expressed as follows, \(\lambda = 74.2 \cdot {\left({\dot T} \right)^{- 0.347}}\). Then, the growth of the SDAS is driven by the solute diffusion of the interdendritic liquids, leading to a coarsening phenomenon, shown in a cubic root law of local solidification time, \(\lambda = 10.73 \cdot {\left({{t_f}} \right)^{0.296}}\).

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ACKNOWLEDGMENT

Appreciation is expressed to Dr. W. Löser for many valuable discussions and for his constructive comments on the manuscript. The authors would like to acknowledge the financial support received from China National Natural Science Foundation (No. 51074104), China National Basic Research Development Project (973 Program: No. 2010CB630802), and Innovation and Creativity Fund of Shanghai University. Instrumental Analysis & Research Center of Shanghai University provided facility for the study of the microstructures.

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Correspondence to Changjiang Song.

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Li, K., Song, C., Zhai, Q. et al. Microstructure evolution of gas-atomized Fe–6.5 wt% Si droplets. Journal of Materials Research 29, 527–534 (2014). https://doi.org/10.1557/jmr.2014.12

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