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

摘要

The Sn-Zn system has a eutectic structure of a broken lamellar type. Dependence of the broken-lamellar spacing lambda and the undercooling DELTA T on V and G were investigated, and the relationship between them was examined. A Sn-Zn (99.99 percent) 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 mum/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 mum/s) in a Bridgman-type directional solidification furnace. The lamellar spacings lambda were measured from both transverse and longitudinal sections of the specimen. The lambda values from the transverse section were used for calculations and comparisons with the previous works. The undercooling values DELTA T were obtained using growth rate and system parameters K_1 and K_2. It was found that the values of lambda decreased while V and G increased. The relationships between lamellar spacing lambda and solidification parameters V and G were obtained by linear regression analysis method. The lambda~2 V, DELTA T lambda, DELTA T V~(0.5), and lambda~3 G values were determined using lambda, DELTA T, 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.