TEM-EDX Observations of the Microstructure of Electrodeposited Ni-Sn Alloys

The microstructure of Ni-Sn alloys electrodeposited at 50–5000 A/m^2 from 65°C chloride solutions containing 5–40 metal% of Sn were analyzed by TEM-EDX. NiSn alloy deposition showed a characteristic behavior in that Ni and Sn were codeposited at an atomic ratio of 1:1 under a wide range of solution compositions and current densities. Ni and Sn EDX mapping images of a cross section of Ni-50 at% Sn alloy deposited at over 1000 A/m^2 showed a lamellar pattern parallel to the interface between substrate and deposit, indicating the alternate deposition of Ni-Sn alloys with different compositions. The Ni-Sn alloys were identified by EDX line analysis as Ni3Sn4 and Ni3Sn2. It was concluded that Ni-50 at%Sn alloys deposited over 1000 A/m^2 were not composed of the previously reported metastablephase NiSn single alloy, but instead consisted of both Ni3Sn4 and Ni3Sn2 alloys in a thermodynamically stable phase.