Wetting of Cu substrates with micrometer and nanometer grains by molten Sn-3.5Ag-0.7Cu alloy

摘要

Wetting behaviors and interfacial microstructures of molten Sn-3.5Ag-0.7Cu drops on micrometer- and nanometer-grained Cu substrates were studied. The wettability of the micrometer-grained Cu substrates was found to be better than that of the nanometer-grained substrates. Moreover, Kirkendall voids were observed at the interface of the nanometer-grained Cu substrates but not of the micrometer-grained substrates. It is presumed that the nanocrystalline surfaces are more prone to adsorption of impurities, thus reducing the surface free energy. On the other hand, its atomic diffusivity is greatly enhanced. As a result, the wettability deteriorates while the Kirkendall voids readily proliferate.