Microstructural properties and peritectic reactions in a binary Co–Sn alloy by means of scanning electron microscopy and atom probe tomography

Recent studies of lithium-ion batteries suggest that the use of binary CoSn alloys as anodes should provide an improvement over currently used anode materials. However, the implementation of CoSn alloys is challenging due to uncertainties regarding the phase transformations within this system. In order to understand these, we evaluate the compositions of different intermetallic compounds produced via the peritectic reactions, nucleate and grow within the microstructure of binary Sn − 25 at.% Co by employing atom probe tomography (APT). The stoichiometric $\mathrm{C}\mathrm{o}\mathrm{S}\mathrm{n}$ phase, which is produced upon the cooling of the melt, is not only found as part of the peritectic solidification sequence but also as clusters within the pure Sn phase. The ${\mathrm{C}\mathrm{o}\mathrm{S}\mathrm{n}}_2$ phase was found as a nano sized layer and is attributed to the peritectic reaction between the $\mathrm{C}\mathrm{o}\mathrm{S}\mathrm{n}$ phase and the pure Sn phase. The production of the ${\mathrm{C}\mathrm{o}\mathrm{S}\mathrm{n}}_3$ compound was enhanced by the phase transformation of the ${\mathrm{C}\mathrm{o}\mathrm{S}\mathrm{n}}_2$ phase. Furthermore, ${\mathrm{C}\mathrm{o}\mathrm{S}\mathrm{n}}_3$ clusters had formed in the pure Sn phase. A limited solubility within the pure Sn phase was also determined to be (0.6 ± 0.1) at.% Co.