The correlation between the hardness and tribological behaviour of electroplated chromium coatings sliding against ceramic and steel counterparts

Electroplated chromium (Cr) coatings with different hardness were electrodeposited on steel substrate through adjusting the concentration of rare earth in a Sargent bath (CrO3 250 g/l, H2SO4 2.5 g/l). The results show that with a Si3N4 ceramic counterpart, the wear rate of electroplated Cr coatings increases with the increase of the hardness owing to the delamination wear mechanism; while with a steel counterpart, the wear rate of electroplated Cr coatings decreases with increasing hardness thanks to the abrasion wear mechanism. The wear mechanism may be dictated by the adhesive force between the sliding pairs and the possibility of abrasive particles formation that weak adhesive force between the ceramic counterpart and electroplated Cr coatings can hardly result in the adhesion, transfer of material and formation of abrasive particles on the tribosurface of the electroplated Cr coating, and the frictional shear energy tends to transform to dislocation and deformation energy stored inside the material instead of friction heat; therefore, the delamination wear is more likely to occur on the tribosurface. Whereas, the strong adhesive force between the steel counterpart and electroplated Cr coatings will result in the adhesion, transfer of material and formation of the abrasive particles on the tribosurface, the frictional shear energy would be allowed to transform to cutting and plough energy; hence, the adhesive and abrasive wear may occur.