Complex phase separation of ternary Co-Cu-Pb alloy under containerless processing condition

The macrosegregation and solidification processes of ternary Co ₄₃Cu₄₀Pb₁₇ alloy have been investigated under the containerless processing condition in drop tube. The addition of Pb element is found to be quite effective to promote the phase separation of Co-Cu alloy, resulting in a macroscopic segregation pattern in ternary Co₄₃Cu ₄₀Pb₁₇ alloy. The rapidly solidified alloy droplets are characterized by core-shell structures due to the combined effects of reduced gravity and containerless state during free fall. When the droplet diameter is smaller than 450 μm, a kind of three-layer core/shell structure is formed, which consists of a Co-rich core, a Cu-rich intermediate layer and a Pb-rich surface shell. EDS analyses show that the Pb solute has a stronger affinity with Cu-rich liquid and a repulsive interaction with Co-rich liquid. The solidification process of Co₄₃Cu₄₀Pb₁₇ ternary alloy involves two successive phase separation events, a subsequent peritectic transformation and a final monotectic transformation.