Identifications of Nanomechanical Properties of Cu-Sn Crystalline Phases

In this paper we report Young´s moduli and hardness of Cu₆Sn₅ and Cu₃Sn intermetallic compounds (IMCs) measured by nanoindentation. The samples were prepared by annealing Sn-Cu diffusion couples. Indentations performed along the directions lateral and perpendicular to the IMC layers show statistically indistinguishable Young´s moduli and hardness for each of the two IMCs, implying that these polycrystalline IMC aggregates are rather isotropic. Nanomechanical responses of the IMCs were shown to depend greatly on the strain rate during loading while independent of the strain rate during unloading. Multiple pop-in events were observed for Cu₆Sn₅ during loading at a strain rate lower than about 0.1 s^-1 to 0.5 s^-1. Topographies of the residual impressions were quantitatively measured and the pile-up features were apparent for the two IMCs.