Observation of interface dynamics and Cu island formation at a crystalline Si/liquid Al-alloy interface

This research was performed to quantify the atomic-level dynamic behavior and the nature of Cu segregation to a crystalline Si/liquid Al-alloy interface in a partially molten Al-Si-Cu-Mg alloy. The results show that in contrast to atomistic simulations, no characteristic fluctuations were observed at a {113} Si/liquid Al-alloy interface other than a tendency to advance/recede by one or two {113} interplanar spacings. Segregation of Cu to the interface was found to occur by the formation of nano-scale fluctuating Cu islands, which had a highly reproducible orientation relationship with the crystalline Si. The fluctuating Cu islands had an approximately Gaussian distribution of heights while the widths displayed a log-normal distribution, indicative of high interfacial mobility and coalescence among islands. The presence of Cu islands was found to suppress the dynamic motion of the {113} Si solid-liquid interface. These findings reveal new and unexpected behavior about both the dynamic behavior of, and possible segregation mechanisms to, solid-liquid interfaces.