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

Nickel-tungsten (Ni-W) alloy coatings (similar to 2, 4, 7, 10, and 13 wt% tungsten) were electrodeposited over mild steel. Corrosion rate (i(corr) value) decreased for the initial addition of tungsten (similar to 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 i(corr) 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 Sigma 3 CSLs, absence of twist grain boundaries (special boundaries), and high fraction Sigma 9 CSLs (which possess high grain boundary energy than Sigma 3 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 Sigma 3 CSLs, and uniform strain distribution.

Automated summary

The corrosion rate of nickel-tungsten alloy coatings is significantly affected by the tungsten content. Coatings with 7wt% tungsten exhibit lower corrosion rates due to a lower proportion of high-angle grain boundaries and uniform strain distribution, while coatings with 13wt% tungsten have higher corrosion rates attributed to a higher proportion of high-angle grain boundaries and small-sized grains.