Primary dendrite distribution in directionally solidified Sn-36 at.% Ni peritectic alloy

The primary dendrite arm spacing and its distribution at the solid-liquid interface has been examined in directionally solidified Sn-36 at.% Ni peritectic alloys under constant temperature gradient in a range of growth rates (2-200 μm/s). Statistical analysis of the primary dendrite arm spacing on transverse sections has been carried out using the minimum spanning tree and Voronoi polygon. The frequency distribution of the number of nearest neighbors determined by the Voronoi polygon suggested that the arrangement of dendrites at the solid-liquid interface could be visualized as hexagonal tessellation. The primary dendrite arm spacing determined by the conventional area counting method and minimum spanning tree all decreased with increasing growth rate, and a range of primary dendrite spacing was present during solidification. The range first increased with increasing growth rate, but when the growth rate exceeded 20 μm/s, it turned to decrease, which can be attributed to disorder induced by growth rate and interdendritic convection.