In the absence of a nickel-top layer (i.e. in the ML (Cu) case), the oxides generated on the surface of the tribofilm remain on the sliding track, leading to high concentrations of lessductile copper(I) oxide-impregnated surfaces. This results in the accelerated degradation of the GnP tribofilm, which, as a consequence of higher friction, promotes fatigue wear of the counterface ball and eventual mechanical failure of the coating as a whole.