Creep behavior of Sn–Bi solder alloys at elevated temperatures studied by nanoindentation

Abstract

The creep mechanisms of eutectic Sn–Bi alloy were evaluated with indentation constant strain rate (CSR) method at elevated temperatures. The activation energy (Q) and creep stress exponent (n) of eutectic Sn–Bi alloy and other alloy compositions were measured in the temperature range from 25 to 100 °C. Prior to this, the indentation CSR testing protocol for evaluation of Q and n was validated through evaluating the pure Sn (grain size >100 µm) at various temperatures. The creep mechanism of large grain-sized Sn was found to be dislocation climb controlled by core diffusion in bulk. Dislocation climb though core diffusion and power-law breakdown were suggested to be the deformation mechanism for pure Bi and Sn–3%Bi alloy, respectively. For the two-phased eutectic Sn–Bi alloy, the creep mechanism was found to be strain rate and temperature dependent. Individual constituent phases were found to take turns to dominate the creep rate at different strain rates.