Containerless Solidification Processing and Phase-Field Simulation for Ternary Fe-Cu-Co Peritectic Alloy Under Reduced-G
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ONE series of engineering and functional materials are peritectic system alloys and the growth mechanisms of liquid peritectic alloys play a crucial role in determining their industrial applications.[1–6] Typical peritectic solidification mechanisms are usually selected during the conventional solidification, and the solidified microstructure appears as the primary phase surrounded by the peritectic phase.[1,6] As these peritectic alloys are subjected to high undercooling processing, the familiar solidification behavior changes remarkably, and one of these other various solidification mechanisms is metastable liquid phase separation.[7–14] Most of the previous studies for metastable liquid phase separation have focused on the binary Fe-Cu,[7–9] Co-Cu,[11,12] and Cu-Cr,[13,14] peritectic alloy systems. The metastable liquid phase-separation behavior of ternary peritectic-type alloys is considerably more complex than that of binary peritectic-type alloys, and in addition, the solidification
F.P. DAI, Y.H. WU, W.L. WANG, and B. WEI are with the MOE Key Laboratory of Material Physics and Chemistry under Extraordinary Conditions, Northwestern Polytechnical University, Mail box 624, West 127, Youyi Road, Xi’an, Shaanxi 710072, P.R. China. Contact e-mail: [email protected] Manuscript submitted April 25, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS A
kinetics and microstructure characteristics are not completely understood. Therefore, systematically investigating the complex solidification mechanisms of ternary peritectic alloys, especially those that display metastable phase separation in a highly undercooled state, is of great importance. In recent years, many efforts have been made to understand the phase separation of undercooled liquid peritectic alloys by various methods, such as electromagnetic levitation,[6,15] ultrasonic levitation,[16,17] aerodynamic levitation,[18,19] drop tube,[1,6] and gas atomization.[20–22] In contrast to other methods, the drop tube not only provides a containerless environment and microgravity states, but also subdivides the alloy sample into numerous droplets by different sizes. It is desirable to study the effects of the containerless environment, microgravity and droplet size on the solidification behaviors. As the metastable liquid phase separation often occurs for binary Fe-Cu and Co-Cu peritectic-type alloys with large positive mixing enthalpy[7] and the elements of Fe and Co are soluble with each other at any proportion, a ternary Fe45Cu40Co15 peritectic-type alloy was selected as the research object in Figure 1(a). The drop tube technique was used to systematically investigate the solidification kinetics and microstructure characteristics of the Fe45Cu40Co15 peritectic alloy for gaining deeper understandings. Furthermore, the metastable phase-separation kinetics were theoretically explored using a phase-field
model. Special attention was paid to understand the selection principle of solidification behavior, the formation mechanisms of typical macrosegregation structures, and the fl
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