Effect of growth rates and temperature gradients on the lamellar spacing and the undercooling in the directionally solidified Pb–Cd eutectic alloy

Lead–cadmium of high (99.99%) purity eutectic alloy was melted in a graphite crucible under vacuum atmosphere. These regular eutectic alloys were directionally solidified upward with a constant growth rate of 8.3 μm/s, and different temperature gradients G (∼1.6–6.4 K/mm range), and also with a constant temperature gradient (∼6.4 K/mm) and different growth rates V (8.3–165.5 μm/s range) in the Bridgman-type directional solidification furnace. The lamellar spacings λ were measured from both transverse section and longitudinal section of the specimen. The variations of λ with respect to G and V were determined by using linear regression analysis. The dependence of λ on ΔTe (the extremum undercooling) was also analysed. The variation of ΔTe with V at constant G and with G at constant V were investigated. According to these results, it has been found that λ decreases with the increasing values of G and V. Also ΔTe increases with increasing V for a constant G and with the increasing G for a given V, respectively. The results obtained in this work have been compared with the Jackson–Hunt eutectic theory and the previous experimental results.