Response of primary dendrite distribution to deceleration growth conditions in a SnNi 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 SnNi peritectic system, λ1 does not response quickly to the variation in growth conditions.