The running-in of amorphous hydrocarbon tribocoatings

Amorphous hydrocarbon (a-C: H) films have enormous potential as low friction, wear resistant coatings. Here. we present a plasma assisted chemical vapour deposition process for a-C: H that exhibits growth rates of 100 nm min(-1) and higher. The tribological performance of the resulting a C : H films has been studied experimentally by reciprocating sliding of all a-C: H-coated Si3N4 ball oil all a-C: H-coated 100Cr6 steel substrate and by subsequent micro Raman spectroscopy of the wear track. Running-in of the coatings is observed and characterised by it rapid decrease ill the friction coefficient accompained by a significant increase ill sp(2) hybridisation ill the wear track. Ill order to gain a deeper understanding of the underlying running-in mechanisms the sliding of two a-C: H films under a load of 5 GPa has been studied by classical molecular dynamics employing a range-corrected Brenner bond-order potential. The simulations reproduce the experimental trends and explain the running-in by a combination of smoothing and chemical passivation of both tribosurfaces. Consequently, both mechanisms should be controlled in order to produce tribological coatings for applications with optimum energy-efficiency.