Microstructure evolution of Cu-Pb monotectic alloys during directional solidification

Planar, cellular and dendrite morphologies were observed at different concentrations in the directional solidification of Cu-Pb monotectic alloys. In Cu-Pb hypomonotectic alloys, the directional solidification microstructure changes fi＇om columnar dendrite to the irregular rod composite structure with increasing lead content and growth rate. In Cu-Pb hypermonotectic alloys, the structure changes from the band structure and elongated droplets to irregular rod composite structure with increasing growth rate. The range of composition of forming the rod composite structure around the monotectic points increases with the increasing growth rate. The transient morphology of Cu-Pb alloys in the directional solidification was obtained. The solid/liquid interface of Cu-Pb alloys presents planar and the second liquid droplets are pushed by growing front under the high temperature gradient. With increasing growth rate or decreasing temperature gradient the planar interface becomes unstable and the cellular structures with L2 phase at the cell boundaries are developed.