Macrosegregation driven by movement of minor phase in (Al0.345Bi0.655)90Sn10 immiscible alloy

Abstract

Formation of macrosegregation structure in (Al 0.345 Bi 0.655 ) 90 Sn 10 (mass percent, the same below) immiscible alloy was investigated by spraying its melt into silicone oil. Two kinds of typical macrosegregation structures were obtained in the dispersed alloy spheres: core/ shell structure and crescent structure. Based on the estimated temperature field inside the alloy spheres, the velocities of thermal Marangoni, solutal Marangoni, and Stokes motions of the Bi-rich minor droplets were calculated. Analysis shows that surface segregation, Soret effect, thermal Marangoni motion, solutal Marangoni motion, and Stokes motion play a key role in the formation of Al/Bi-Sn core/shell structure. If the liquid alloy spheres solidify on the condition that the radius of the Bi-rich minor droplets is smaller than a critical value, it will form Al/Bi-Sn core/ shell structure, while the crescent structure will be formed when the liquid alloy spheres frozen on the condition that the radius of the Bi-rich minor droplets exceeds the critical value.

Metastable monotectic phase separation in Co–Cu alloys

“…In our experiment, the higher melting point phase (here the Corich phase) has the higher surface tension which in turn drives inward migration. This is in line with the observation that in Co-Cu alloys, surface segregation arises due to the phase with the lower surface tension completely wetting the higher energy phase and adhering to the surface of the parent droplet in order to minimise its Gibbs energy [37,38].…”

“…The strong interplay of interfacial energy with temperature and/or composition gradients in immiscible alloys leads to Marangoni convection which, in the microgravity environment, has been used to explain the formation mechanism of core-shell structures [1,4,[6][7][8][9][10][11][12][13]. In such an environment, for instance during free fall, a temperature gradient between the surface and centre of the falling droplet may be developed.…”