Abstract:Sn-36%Ni peritectic alloys were directionally solidified at different growth rates under a constant temperature gradient (20 K/mm), the dependences of microstructural characteristic length scales on the growth rate were investigated. Experimental results are presented, including primary and higher order dendrite arm spacings λ₁, λ₂, λ₃ and dendrite tip radius R of primary Ni₃Sn₂ phase. Comparisons between the theoretical predictions and the experimental results show that, for the primary dendrites, λ₁=335.882v^-0.21, which is in agreement with the Kurz-Fisher model; for the secondary dendrites, λ₂=44.957v^-0.277, which is consistent with the Bouchard-Kirkaldy model; for the tertiary dendrites, λ₃=40.512v^-0.274; for the dendrite tip radius, R=22.7v^-0.36. The experimental results also show that the λ₁/λ₂ changes greatly with increasing growth rate while the λ₁/λ₃ has no significant change, indicating that tertiary dendrite arms have a more similar growth characteristics to primary dendrites compared with secondary dendrites. The λ₁/R ranges from 2 to 2.3 with the increase of growth rate.

Key words: Sn-Ni alloy; directional solidification; dendrite arm spacing; dendrite tip radius