Cellular growth during transient directional solidification of Pb-Sb alloys

Cellular spacings and solidification thermal variables were determined for three dilute Pb-Sb alloys, which were solidified under unsteady-state heat flow conditions. The experiments have been carried out by using a casting assembly, which was designed in such way that the heat was extracted only through the water-cooled system at the casting bottom, promoting vertical upward directional solidification. An experimental approach, based on thermal readings collected at six different positions from the casting surface, was used in order to quantitatively determine the solidification thermal variables: tip growth rate and cooling rate of Pb-0.3 wt%Sb, Pb-0.85 wt%Sb and Pb-1.9 wt%Sb alloys castings. After grinding, polishing and etching procedures, both longitudinal and transverse sections of the castings were characterized by a typical cellular microstructure which prevailed along the entire casting. The cell spacing variation with cooling rate and tip growth rate was characterized by −0.55 and −1.1 experimental power laws, respectively. The experimental cell spacings were compared with the theoretical predictions furnished by cellular growth models.