Effect of current density,MoS 2 content and bath agitation on tribological properties of electrodeposited nanostructured Ni-MoS 2 composite coatings

Nanostructured nickel coatings with molybdenum disulphide particles were electrodeposited to form composite coatings. Three different current densities, i.e. 3, 5 and 7 A/dm² were investigated initially. The best results were obtained with 5 A/dm² for codeposition of nanostructured Ni-MoS₂ composite coatings. With the addition of 1–4 g/L molybdenum disulphide to the bath, the weight percentages of MoS₂ particles in the coatings were 23–38%. This increase of MoS₂ content was accompanied with decrease in friction coefficient of the coatings from 0.35 to 0.08. Wear resistance of the coatings was increased with increasing MoS₂ content and the weight loss was decreased from 1.4 to 0.7 mg. Hardness was decreased from 585 to 400 VHN with increasing the MoS₂ content. By increasing bath agitation speed up to 150 rpm, more MoS₂ particles were embedded in the matrix and the coatings showed better wear resistance. However, increase of agitation speed from 150 to 200 rpm caused a decrease of MoS₂ particles in the nickel matrix due to the turbulent motion of particles in the bath. Overall, it was shown that the lubricating effect of MoS₂ in the coating was more influential than the nanocrystallinity of the nickel matrix in improving tribological properties of these composite coatings.