Texture and grain boundary engineering in nickel coating with tungsten addition and its effect on the coating corrosion behavior

Abstract Nickel‑tungsten (Ni W) alloy coatings (~2, 4, 7, 10, and 13 wt% tungsten) were electrodeposited over mild steel. Corrosion rate (icorr value) decreased for the initial addition of tungsten (~2, 4, and 7 wt%) to reach a minimum of 7 wt% tungsten. For higher tungsten additions (10 and 13 wt%), the corrosion rate again increased to values that were 88% higher than the pristine Ni coating. Between pristine Ni and Ni-7 wt% W, a 51% decrease in the icorr value was measured. Between Ni-7 wt% W and Ni-13 wt% W, a 72% increase in the icorr value was noticed. The highest corrosion rate for Ni-13 wt% W was attributed to small-sized grains and a high fraction of high-angle grain boundaries (HAGBs). The high corrosion rate in pristine Ni coating was attributed to high coating strain and non-uniform strain distribution, a low fraction of Ʃ3 CSLs, absence of twist grain boundaries (special boundaries), and high fraction Ʃ9 CSLs (which possess high grain boundary energy than Ʃ3 CSLs). The lowest corrosion rate in Ni-7 wt% W coating was attributed to lower HAGB fraction than the Ni-13 wt% W coatings, a relatively higher fraction of Ʃ3 CSLs, and uniform strain distribution.