Research on lamellar structure and microhardness in directionally solidified ternary Sn-40.5Pb-2.6Sb eutectic alloy

Sn-40.5 wt%Pb-2.6 wt%Sb ternary alloy was directionally solidified with a constant temperature gradient (G = 18 K/mm) and growth rates ranging from 1 μm/s to 30 μm/s. Experimental results indicated that the lamellar structure consisted of Pb-rich and Sn-rich phases. The lamellar spacings (λ) and microhardness (H_V) were measured and the H_V increased with increasing growth rate (V) or decreased with increasing lamellar spacing. The dependences of λ and H_V on V were determined by using a linear regression analysis. The relationships between the λ, V and H_V were given as: λ = 3.39 V^{- 0.51}, H_V = 12.65 V^0.11 and H_V = 16.42 λ^{- 0.2}, respectively. The fitted exponent values were in accordance with the previous experimental results obtained from Sn-Pb alloys and In-Bi-Sn ternary alloys.