Understanding the non-monotonic variation in the corrosion rate of Sn-Ni coatings with Ni addition by the analysis of texture and grain boundary constitution of the matrix phase and spatial distribution of the intermetallic phase in the coating microstructure.

Abstract

Sn-Ni coatings (0–13 wt% Ni) were electrodeposited on mild steel. The highest (Rp = 18,561.1 Ω·cm2) and the lowest (Rp = 4756.7 Ω·cm2) corrosion resistance was observed for Sn-6 wt% Ni and Sn-13 wt% Ni coating, respectively. Higher corrosion resistance of Sn-6 wt% Ni coating was due to low energy (100) surface texture, low energy CSL boundaries and formation of Ni3Sn4 phase at grain boundaries. Higher corrosion rate of Sn-13 wt% Ni coating was due to highest fraction of high energy high angle grain boundaries, higher matrix strain and higher volume fraction of cathodic Ni3Sn4 phase.