To further aid understanding, the morphology and elemental distributions of the AISI 52100 counterface ball from FGO-CMMC (0.25CD) sliding were investigated by SEM and EDX (Figure ). The SEM image of the counterface shows that the contact area has suffered minimal damage, as the topography and roughness have not increased significantly (c.f. counterfaces from GO-CMMC (0.25CD) and Cu ref(0.25CD) , sliding; Figure ). Raman analysis of the contact area shows no evidence of typical graphitic bands at 1360 and 1680 cm -1 , indicating no graphene-based transfer films are formed. Moreover, EDX maps of C, Cu and F confirm that the counterface contains minimal copper and carbon on the surface, but its surface is fluorine-rich. The formation of the fluorinated steel surface is consistent with a tribochemical reaction between FGO and steel under a sliding load.