Abstract
An oscillatory microstructure has been observed during deep-cellular growth of directionally solidified Sn–36at.%Ni hyperperitectic alloy containing intermetallic compounds with narrow solubility range. This oscillatory microstructure with a dimension of tens of micrometers has been observed for the first time. The morphology of this wave-like oscillatory structure is similar to secondary dendrite arms, and can be observed only in some local positions of the sample. Through analysis such as successive sectioning of the sample, it can be concluded that this oscillatory microstructure is caused by oscillatory convection of the mushy zone during solidification. And the influence of convection on this oscillatory microstructure was characterized through comparison between experimental and calculations results on the wavelength. Besides, the change in morphology of this oscillatory microstructure has been proved to be caused by peritectic transformation during solidification. Furthermore, the melt concentration increases continuously during solidification of intermetallic compounds with narrow solubility range, which helps formation of this oscillatory microstructure.
Highlights
Phase-field modeling by Lo et al.[13]
An oscillatory microstructure has been observed for the first time during deep-cellular growth of directionally solidified Sn–36at.%Ni alloy where both the primary and peritectic phases are intermetallic compounds with narrow solubility
The initial morphology of this wave-like oscillatory structure is caused by oscillatory convection of the mushy zone during solidification
Summary
Phase-field modeling by Lo et al.[13]. For the oscillatory structure, Park and Trivedi[8,12] have shown that this treelike structure could only be observed in a tube with larger diameter, and disappeared when the diameter of the tube is 0.6 mm or less, suggesting that melt convection has obvious influence on this structure. In the previous analyses discussed above, these non-steady state structures like banded and oscillatory structures have been confirmed to be significantly influenced by either nucleation competition between α /β phases phase or thermosolutal convection in the melt. All of these structures are observed in peritectic systems where both the primary α phase and peritectic β phase are solid solution phases. In our recent experiment, an oscillatory microstructure which only exists at few positions of the sample has been observed in directionally solidified Sn–Ni hyperperitectic alloy The size of this microstructure is much smaller as compared with previous results[8,9,10,11,12,13,14,15,16]. The aim of this article is threefold: (1) to characterize this oscillatory microstructure and analyze how this microstructure is formed; (2) to analyze the influence of convection on formation of this oscillatory microstructure through analyzing the characteristic scale of this structure; (3) to discuss whether the solute redistribution of intermetallic compounds during solidification can influence the morphology of this microstructure
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