Comparative tribological study of hard and crack-free electrodeposited chromium coatings

In this study the tribological properties of single hard, single crack-free and duplex (i.e. a hard layer on top of a crack-free sub-layer) chromium coatings electrodeposited on a forged steel substrate have been investigated, using a reciprocating pin-on-plate wear testing machine. The results show that for a fixed thickness, the single hard chromium coating has the best wear resistance and the lowest coefficient of friction, while the single crack-free coating has the worst wear resistance and the highest coefficient of friction. The wear mechanism of the crack-free coating seems to be mainly adhesive, while the wear mechanism in the hard coating appears to be mainly abrasive. The wear in the duplex coating occurs by a combination of sub-layer deformation and crack formation in the surface region.