Nanoindentation Study of Phases in Near-Eutectic Sn-Bi Alloy

The low melting point of Sn-Bi alloys makes them promising materials for low temperature solders (L TS). However, Sn-Bi alloys are brittle under high strain-rates, presenting a major hurdle for widespread commercialisation. To formulate solutions to this problem, it is important to understand the contribution of the individual phases in the Sn-Bi alloys to their overall mechanical properties. In this work, the hardness of each phase in a near-eutectic Sn-S7wt%Bi alloy is studied using nanoindentation. Results show that the hardness of the Sn phases in the alloy is higher than that of pure Sn due to solid solution strengthening, while the primary Sn phase is harder than the eutectic Sn phase due to precipitation hardening from Bi. In contrast, the hardness of the Bi phase in the alloy is similar to that of pure Bi, as these strengthening mechanisms are minimal due to the low solubility of Sn in Bi.