Response of primary dendrite distribution to deceleration growth conditions in a Sn-Ni peritectic alloy

The primary dendrite arm spacing (PDAS) λ₁ and its distribution of primary Ni₃Sn₂ phase has been examined in directionally solidified Sn-36 at.%Ni peritectic alloys during the transient conditions attending deceleration. Dependences of λ₁ on both the deceleration rate and solidification time have been investigated through the statistical techniques including minimal spanning tree (MST) and Voronoi polygon. The existence of a range of PDAS is confirmed, and this range Δ is closely related with the deceleration rates. This range also increases with increasing solidification time at a fixed deceleration rate. Both the analyses by MST and Voronoi polygon show that the distribution of λ₁ is greatly influenced by decelerating growth condition. The range of λ₁, Δ can well reflect the history-dependent growth of primary dendrite arms. In addition, due to the solidification characteristic of Sn-Ni peritectic system, λ₁ does not response quickly to the variation in growth conditions.