Characterization of microstructural length scales in directionally solidified Sn-36%Ni peritectic alloy

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.