Formation mechanism of banded structure during directional solidification of Sn-Cd peritectic alloy under convection condition

摘要

Directional solidification experiments of Sn-0.75 wt%Cd and Sn-1.6 wt%Cd peritectic alloys have been conducted under convection condition to investigate the formation mechanism of banded structure. Many types of banded structure were obtained, which cannot be interpreted by the Karma's model. The reason for this conflict is that there are many banded structure formation mechanisms such as abundant nucleation, regrowth, fast radial cellular growth and radial competitive growth under convection condition, but the Karma's model only considers the abundant nucleation and ignores other mechanisms. The analyses showed that these formation mechanisms changed along with an increase in alloy composition. Based on these analyses, a simple modified banding window, which considered these different formation mechanisms, has been presented. Compared with the banding window defined by the Karma's model, this modified banding window contained it and could predict different banded structure formations under convection condition appropriately.