The Microstructure Parameters And Microhardness Of Controlled Directional Solidified Sn-Ag-Cu Lead-Free Solder

Sn-Ag-Cu alloy of eutectic composition (Sn-3.5wt.%Ag-0.9wt.%Cu) was controlled directional solidified upward at a constant temperature gradient (G=2.48 K/mm) in a wide range of growth rates (3.89-173.61 μm/s) by using a Bridgman type directional solidification furnace. The eutectic microstructures were observed to be plate and rod form. 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 and microhardness (HV) on the growth rate (V) were determined by using linear regression analysis. According to these results, it has been found that, the value of λ decreases with the increasing value of V and whereas, the value of microhardness increases for a constant G. The values of bulk growth (λ2V) were also determined by using the measured values of λ and V. The results obtained in present work were compared with the previous similar experimental results obtained for binary and ternary alloys.