Pitting corrosion and mechanical properties of direct current and pulsed reverse current electrodeposited nickel-tungsten coatings

The electrochemical corrosion and mechanical properties of direct current and pulsed reverse current electrodeposited nickel and nickel-tungsten were investigated by using cyclic polarization measurement and nano-indentation techniques. Direct and pulsed reverse current electrodeposited nickel-tungsten coatings revealed a significant higher resistance to pitting corrosion when compared to direct and pulsed reverse current deposited nickel. Furthermore, pulsed reverse current electrodeposited nickel-tungsten displayed the most noble corrosion potential and higher corrosion resistance compared to direct current electrodeposited nickel-tungsten. This was attributed to the more nanocrystalline structure of the pulsed-reverse current deposited coatings when compared to that of the direct current electrodeposited nickel-tungsten. The average modulus for both direct and pulsed reverse current deposited nickel-tungsten were found to be similar but the average hardness of direct current deposited nickel-tungsten was slightly higher than that of pulsed reverse current deposited nickel-tungsten. This was attributed to the higher tungsten content (35 wt.%) in the direct current deposited nickel-tungsten coating compared to that (25 wt.%) in the pulsed reverse current deposited nickel-tungsten and is supported by our energy dispersive X-ray spectroscopy results.