Wetting of microcrystalline and nanocrystalline Ni substrates by molten Sn–3.5Ag–0.7Cu alloy

Wetting behavior of molten Sn–3.5Ag–0.7Cu drops on Ni substrates with micrometer and nanometer grains was investigated using a modified sessile drop method. The wettability was poorer while the interfacial reactivity and atomic diffusivity were stronger for the nanocrystalline substrates compared with those for the microcrystalline substrates. The enhanced diffusion of the Ni atoms from the nanocrystallites greatly promoted the nucleation of the intermetallic compounds (IMCs), leading to a much thicker reaction layer and a more distinct regional distribution of the IMCs. On the other hand, the immediately roughened interface greatly decelerated the spreading of the triple line.