Reduced wear and friction enabled by graphene layers on sliding steel surfaces in dry nitrogen

We report on the friction and wear behavior of graphene-lubricated 440C steel test pairs in dry nitrogen under different loads. Tribological test results have revealed that a few-layer graphene is able to drastically reduce the wear and the coefficient of friction (COF) of 440C steel during the initial sliding regime and under low load conditions. Specifically, the COF has been reduced from ≈1 for bare steel to 0.15 for steel covered by a low concentration of graphene flakes. Such low COFs have persisted for thousands of sliding passes, even though the graphene layers formed on sliding surfaces have not been continuous or continuously replenished; they were made of a few sheets of graphene. The wear rates of the steel test pairs have been also reduced (by as much as two orders of magnitude), again despite the very sporadic and thin nature of the graphene layers. A possible explanation for the low friction and wear reduction is that graphene as a two-dimensional material shears easily at the sliding contact interface and, hence, provides low friction.