Numerical simulation of Sn grain growth in composite solder joint using a modified cellular automaton model

• 3D dendritic Sn grain growth was modeled during the solidification of solder alloys. • A modified decentred cellular automaton technique with cuboctahedral envelopes was used. • The model describes the Sn grain refinement effect of the cooling rate and the nanoparticles in composite solder joints. • The model analyses the ratio of the pinning and nucleation effects in the Sn grain refinement. The quality and reliability of the solder joints, like mechanical, thermal, and electrical properties, are determined by their microstructure. In this work, a 3D numerical model was developed to investigate the dendritic Sn grain growth during the solidification by modified decentred cellular automaton technique, expanding the view on composite joints. The Sn dendritic network was covered by a cuboctahedral envelope according to the preferred growth directions. The aim was to compare the grain growth in pure and composite solder joints, which contain reinforcement nanoparticles. The results showed that the model could reproduce the experimental results and provide insight into how nanoparticles can alter grain growth behaviour. The dynamics of grain growth were considerably increased (40-60 % by pinning and nucleation effects and more than 100 % in combined) by the reinforcement nanoparticles. Furthermore, it was found that the cooling rate highly affected the grain refinement by elevating the nucleation rate. The main driving forces of the grain refinement were the decreased growth rate and additional nucleation sites.