Phase transformation and morphology of the intermetallic compounds formed at the Sn–9Zn–3.5Ag/Cu interface in aging

The morphology and phase transformation of the intermetallic compounds (IMCs) formed at the Sn–9Zn–3.5Ag/Cu interface in a solid-state reaction have been investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), electron diffraction (ED), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The monoclinic η′-Cu6Sn5 transforms to the hexagonal η-Cu6Sn5 and the orthorhombic Cu5Zn8 transforms to the body-centered cubic (bcc) γ-Cu5Zn8 as aged at 180 °C. The scallop-shaped Cu6Sn5 layer is retained after aging at 180 °C for 1000 h. In the solid-state reaction, Ag is repelled from η′-Cu6Sn5 and reacts with Sn to form Ag3Sn, and the Cu5Zn8 layer decomposes. Kirkendall voids are not observed at the Sn–9Zn–3.5Ag/Cu interface even after aging at 180 °C for 1000 h.