Extraordinary Solidification Mechanism of Liquid Alloys Under Acoustic Levitation State

• Published in: Advanced materials (Weinheim) 2023-12, Vol.35 (50), p.e2206464-n/a
• Main Authors: Geng, Delu, Yan, Na, Xie, Wenjun, Lü, Yongjun, Wei, Bingbo
• Format: Article
• Language: English
• Subjects: Acoustic levitation; Acoustic streaming; Acoustics; Cavitation; Copper; Copper base alloys; Crystal growth; dendritic and eutectic growth; drop dynamics; Droplets; Eutectic alloys; Fluid dynamics; Free surfaces; Germanium; Globules; Liquid alloys; Liquid flow; liquid undercooling; Materials processing; microgravity state; Nickel; Nucleation; Phase separation; Physical properties; Potential flow; Radiation pressure; Solidification; Sound waves; space simulation; Supercooling; Surface waves; Ultrasonic imaging
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.202206464

The acoustic levitation of various materials can be realized by highly intensive ultrasound, which provides a free surface and containerless state for materials processing under space simulation conditions. The nonlinear effects such as acoustic radiation pressure, acoustic streaming, and ultrasonic cavitation open up special access to modulate the fluid dynamics and solidification mechanisms of liquid materials. Here, the physical characteristics of liquid flow, undercooling capability, phase separation, and crystal nucleation and growth within acoustically levitated droplets are explored comprehensively to reveal the extraordinary solidification kinetics of liquid alloys. The sectorial shape oscillations of the 2nd to 10th order modes accompanying internal potential flow are observed for water droplets with modulated ultrasound amplitudes, while the enhanced ultrasound intensity promotes ice nucleation and thus reduces water undercooling. The migration of Sn‐rich globules during phase separation of immiscible Al–Cu–Sn alloy is dominated by the droplet deformation and rotation related to acoustic levitation. The high undercooling states of liquid Ag–Cu–Ge and Ni–Sn alloys during acoustic levitation result in the refinement of (Ag) dendrites and the formation of anomalous (Ni+Ni3Sn) eutectics. The ultrasound–liquid interaction also induces surface waves during the containerless solidification of Ag–Cu and Ni–Sn eutectic alloys. Acoustic levitation is an advanced containerless processing technique for simulating a space environment, and provides an effective approach to modulate the fluid dynamics and solidification mechanisms of liquid materials. The physical characteristics of liquid flow, undercooling capability, phase separation, crystal nucleation, and dendritic and eutectic growth within acoustically levitated droplets are demonstrated comprehensively to reveal the extraordinary solidification kinetics of liquid alloys.