Current density effect on current-carrying friction of amorphous carbon film

We report the current density effect in controlling current-carrying friction of amorphous carbon (a-C) film sliding against steel ball. The current density at the sliding interface was set to a constant value or cyclic variation value by adjusting the current intensity and the contact area for exploring the current-carrying friction behavior. The results showed that when the current density enhanced from 0 to 0.196 mA/μm2, the friction coefficient decreased from 0.20 to 0.03 and the run-in cycle shortened from about 100 to few cycles. When the current density cyclically varied during the sliding, the friction coefficient had a very fast response and followed to the corresponding value which can be adjusted by the current density. Raman spectrum analysis and TEM observation confirmed that graphene nanosheets were formed at the sliding interface and the size of graphene nanosheets depended on the current density. The mechanism of current-carrying friction behavior of a-C film sliding against steel ball was the interactions of graphene to graphene and a-C to a-C at the contact area, which was controlled by the current density. This finding shed light on the great role of the current density in current-carrying friction of a-C film.