Reverse V-shaped wear rate vs. friction velocity curve of hard chromium coating and its inspiration for anti-wear coating design

In this research, the friction and wear behaviors of hard chromium (Cr) coating under harsh accelerated friction test conditions (unlubricated reciprocating friction with hard Al2O3 ceramic ball as counterpart) were investigated. The results show that hard Cr coating exhibits comparatively consistent tribological performance through the combination of oxidation wear, abrasive wear and plastic deformation mechanisms in general; it shows relatively low rate of wear in a wide range of friction frequency, and even at higher sliding frequencies its wear rate decreases with increasing frequency; its wear rate-friction velocity (or frequency) curve is in reverse V shape. It has been revealed that these surprising features of hard Cr coating are closely associated with its relatively high micro-hardness and compact frictional oxide thin film. This study enlightens a desirable direction for anti-wear coating design.