Primary dendrite growth of Ni ₃Sn intermetallic compound during rapid solidification of undercooled Ni-Sn-Ge alloy

Liquid Ni-31.7%Sn-2.5%Ge alloy was highly undercooled by up to 238 K (0.17T _L) with glass fluxing and drop tube techniques. The dendritic growth velocity of primary Ni ₃Sn compound shows a power-law relation to undercooling and achieves a maximum velocity of 380 mm/s. The addition of Ge reduces its growth velocity as compared with the binary Ni ₇₅Sn ₂₅ alloy. A structural transition from coarse dendrites into equiaxed grains occurs once undercooling exceeds a critical value of about 125 K, which is accompanied by both grain refinement and solute trapping. The Ni ₃Sn intermetallic compound behaves like a normal solid solution phase showing nonfaceted growth during rapid solidification.