Effect of magnetic field on periodic structure formation in Pb-Bi and Sn-Cd peritectic alloys

Unidirectional solidification of Pb-33 at%Bi and Sn-1.0 at%Cd alloys was performed under magnetic fields up to 8 MA/m (10 T). The rejection of the lighter Bi at the solidifying front strongly initiates the convection in the Pb-Bi alloy, while the rejection of the heavier Cd stabilizes the diffusion layer in the Sn-Cd alloy. For the Pb-33 at%Bi alloy, a periodic structure was observed at growth rates of 0.42 and 0.56 mu m/s under any magnetic fields up to 8 MA/m. The imposition of the magnetic field clearly increased length of the periodic structure formation. On the other hand, no significant effect of the magnetic fields on the banded structure was observed for the Sn-1.0 at%Cd alloy. The experimental results were consistently explained by the proposed model that considered instability of the side-by-side growth. The periodic structure originated in the peritectic systems itself and the unsteady flow in melt may act as a trigger. The periodic structure observed in peritectic systems can be generalized as the dissipative structure.