Grain Size Effects on Mechanical Properties of Nanocrystalline Cu₆Sn₅ Investigated Using Molecular Dynamics Simulation

Intermetallic compounds (IMCs) are inevitable byproducts during the soldering of electronics. Cu₆Sn₅ is one of the main components of IMCs, and its mechanical properties considerably influence the reliability of solder joints. In this study, the effects of grain size (8-20 nm) on the mechanical properties (Young's modulus, yield stress, ultimate tensile strength (UTS), and strain rate sensitivity) of polycrystalline Cu₆Sn₅ were investigated using molecular dynamics simulations at 300 K and at a strain rate of 0.0001-10 ps^-1. The results showed that at high strain rates, grain size only slightly influenced the mechanical properties. However, at low strain rates, Young's modulus, yield stress, and UTS all increased with increasing grain size, which is the trend of an inverse Hall-Petch curve. This is largely attributed to the sliding and rotation of grain boundaries during the nanoscale stretching process, which weakens the interaction between grains. Strain rate sensitivity increased with a decrease in grain size.