Indentation size effect and micromechanics characterization of intermetallic compounds in the Au-Sn system

The indentation size effect and the micromechanics characterization of intermetallic compounds in the Au-Sn system have been investigated by nanoindentation, using continuous multi-cycle loading mode and load-control mode, respectively. An analytic model based on the enlarged plastic zone and the maximum allowable density of geometrically necessary dislocation was established to describe the relationship between the indentation hardness and depth. Our new model gives better predictions of the indentation hardness of Au5Sn, AuSn and AuSn2 for small indentation depths compared to the Nix-Gao model. Pop-in events in the load-displacement curves corresponding to the peaks in the normalized velocity-load curves represent the elastic-plastic or harden-yield transition during indentation. A viscoplastic creep equation was employed to evaluate the creep behavior of the Au-Sn intermetallics. The stress exponents (n) can be well defined into two stress regimes: the high stress regime (HSR) and the low stress regime (LSR). In the HSR, dislocation motion is the dominant creep mechanism with n>5, while in the LSR, grain boundary sliding dominates the creep of Au5Sn and AuSn2 with n≈2, and dislocation viscous glide dominates the creep of AuSn and AuSn4 with n around 3.