Abstract
The active modulation and control of the liquid phase separation for high-temperature metallic systems are still challenging the development of advanced immiscible alloys. Here we present an attempt to manipulate the dynamic process of liquid-liquid phase separation for ternary Fe47.5Cu47.5Sn5 alloy. It was firstly dispersed into numerous droplets with 66 ~ 810 μm diameters and then highly undercooled and rapidly solidified under the containerless microgravity condition inside drop tube. 3-D phase field simulation was performed to explore the kinetic evolution of liquid phase separation. Through regulating the combined effects of undercooling level, phase separation time and Marangoni migration, three types of separation patterns were yielded: monotectic cell, core shell and dispersive structures. The two-layer core-shell morphology proved to be the most stable separation configuration owing to its lowest chemical potential. Whereas the monotectic cell and dispersive microstructures were both thermodynamically metastable transition states because of their highly active energy. The Sn solute partition profiles of Fe-rich core and Cu-rich shell in core-shell structures varied only slightly with cooling rate.
Highlights
The objective of the present work is to realize the active modulation of liquid phase separation of ternary Fe47.5Cu47.5Sn5 alloy by containerless rapid solidification inside drop tube
The EDS analysis results demonstrate that the solutes Cu and Sn are expelled from the Fe-rich core, whereas the Fe solute is rejected from the Cu-rich shell during liquid phase separation for alloy droplets with 188~646 μ m diameters
The 3D phase field simulation discloses that the two-layer core shell structure is the most stable phase separation pattern, since it corresponds to the state with the lowest chemical potential
Summary
Both DSC thermal analysis and bulk undercooling experiments indicate that liquid Fe47.5Cu47.5Sn5 ternary alloy does not exhibit phase separation if its undercooling is smaller than 51 K. The multiple solidification characteristics of liquid ternary Fe47.5Cu47.5Sn5 alloy appear under free fall condition: monotectic cell, core shell and dispersed structure with the decrease of droplet diameter. At the largest droplet diameter of 810 μ m, primary α Fe phase grows into a monotectic cell of nubbly structure, which is surrounded by the grey (Cu) solid solution phase resulting from the first peritectic reaction, that is L + γ Fe → (Cu). Based on the experimental results, the dispersed and core-shell morphologies are the main structures of ternary Fe47.5Cu47.5Sn5 alloy Their forming probabilities at the different droplet diameters provide some important information to investigate the liquid phase separation characteristics of ternary Fe47.5Cu47.5Sn5 alloy under the free fall condition. The middle sized droplets are easy to experience macroscopic phase separation and form the core-shell structures
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