Growth and mechanical properties of intermetallic compound between solid cobalt and molten tin

Abstract

Transient liquid phase (TLP) bonding has gained attention due to the advantage of producing bond that has a higher melting point than the bonding temperature. Cobalt (Co) is a potential candidate for base metal in TLP bond. This work studied the interfacial reaction in binary cobalt–tin (Co–Sn) system, growth kinetics and mechanical properties of Co–Sn intermetallic compound (IMC) for transient liquid phase (TLP) joints. Dipping method was employed for the investigation of Co–Sn IMC growth. Solid Co was immersed into molten Sn statically at varying temperatures (250–300 °C) and durations (15–60 min). The IMC formed was characterized by field emission scanning electron microscope (FESEM) coupled with energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) tests and nanoindentation. The results showed the formation of a CoSn3 layer with plate-like morphology at temperature range of 250–300 °C. The thickness of the CoSn3 layer increases with dipping temperature and duration. The growth of CoSn3 is suggested to be controlled by only diffusion reaction at 250 °C. As temperature increases to 300 °C, the growth of CoSn3 is controlled by chemical reaction. The average nanohardness and Young’s modulus of CoSn3 phase reported in this work are 4.25 ± 0.6 GPa and 98.30 ± 9.0 GPa, respectively.