Effect of Growth Rates and Temperature Gradients on the Spacing and Undercooling in the Broken-Lamellar Eutectic Growth (Sn-Zn Eutectic System)

Abstract

The Sn-Zn system has a eutectic structure of a broken lamellar type. Dependence of the broken-lamellar spacing λ and the undercooling ΔT on V and G were investigated, and the relationship between them was examined. A Sn-Zn (99.99%) high-purity eutectic alloy was melted in a graphite crucible under vacuum atmosphere. This eutectic alloy was directionally solidified upward with a constant growth rate V (8.30 µm/s) and different temperature gradients G (1.86–6.52 K/mm), and also with a constant temperature gradient (6.52 K/mm) and different growth rates (8.30–165.13 µm/s) in a Bridgman-type directional solidification furnace. The lamellar spacings λ were measured from both transverse and longitudinal sections of the specimen. The λ values from the transverse section were used for calculations and comparisons with the previous works. The undercooling values ΔT were obtained using growth rate and system parameters K 1 and K 2. It was found that the values of λ decreased while V and G increased. The relationships between lamellar spacing λ and solidification parameters V and G were obtained by linear regression analysis method. The λ2 V, ΔTλ, ΔTV −5, and λ3 G values were determined using λ, ΔT, V, and G values. The experimentally obtained values for the broken-lamellar growth (Sn-Zn eutectic system) were in good agreement with the theoretical and other experimental values.