Dependency of eutectic spacings and microhardness on the temperature gradient for directionally solidified Sn-Ag-Cu lead-free solder

Sn-3.5 wt.%Ag-0.9 wt.%Cu alloy was directionally solidified upward at a constant growth rate (V = 7.20 μm s−1) with different temperature gradients (G = 2.48-6.34 K mm−1) by using a Bridgman type directional solidification furnace. The eutectic microstructures of directionally solidified Sn-3.5 wt.%Ag-0.9 wt.%Cu alloy were observed to be plate and rod structures from quenched samples. The values of eutectic spacings (λ) and microhardness (HV) were measured from both transverse and longitudinal sections of the samples. The dependence of eutectic spacings (λ) and microhardness (HV) on the temperature gradient (G) were determined by using linear regression analysis. According to these results, it has been found that, the value of λ decreases with the increasing the value of G and whereas, the value of HV increases for a constant growth rate. The results obtained in the present work were also compared with the previous similar experimental results obtained for binary and ternary alloys.