Atomic-level study of AuSn-Au5Sn eutectic interfaces

Au-20Sn solder is obtained through severe plastic deformation and subsequent spheroidization of Au-20Sn eutectic alloys, which are composed of alternating intermetallic compounds delta-AuSn and xi & PRIME;-Au5Sn. Understanding AuSn-Au5Sn eutectic interfaces is essential for processing the Au-20Sn solder. Here, we studied the delta-AuSn/xi & PRIME;-Au5Sn eutectic interfaces at different deformation sates by electron backscattered diffraction analysis, high resolution transmission electron microscope, and first-principles density-function theory (DFT) calculations. We observed three orientation relationships and corresponding interfaces. One is thermally preferred during casting, and the other two are formed during the hot rolling process. Crystallographic analysis and DFT calculations suggest that the dominant orientation relationship is attributed to the small lattice mismatch and the low interface formation energy. These results provide insights for understanding the interface effect on microstructure evolution of ingot Au-20Sn alloys during severe plastic deformation.