Structural morphologies of Cu-Sn-Bi immiscible alloys with varied compositions

The macroscopic morphology of Cu-Sn-Bi immiscible alloys with compositions varying from hypomonotectic, monotectic to hypermonotectic alloys was experimentally investigated by conventional casting method. It is shown that the hypomonotectic and monotectic alloys present a core-shell morphology composed of Bi-rich core and CuSn-rich shell. In contrast, the hypermonotectic alloys, as the fraction of Bi increased, transform from a triple-layer morphology, a core-shell morphology with CuSn-rich core and Bi-rich shell, to a uniform morphology with fine CuSn-rich phase dispersing in Bi-rich matrix. Besides, the effect of velocity of solidification front on formation of core-shell morphology for the critical composition in hypermonotectic alloys was studied by casting molten alloy into molds with different radii. The relation between the volume fraction of two immiscible liquid phases and morphology was clarified for hypermonotectic alloys. The solidification paths of alloys under all compositions were discussed. (C) 2012 Elsevier B.V. All rights reserved.