The effect of Cu grain size on transition from EHL to BL regime (Stribeck curve)

Recently friction and wear of copper (Cu) samples (the average grain size, d = 30 μm) rubbed against a hardened steel in steady friction were studied. The effects of load and sliding velocity were interpreted by the Stribeck curve and the transitions from elasto-hydrodynamic lubrication (EHL) to boundary lubrication (BL) region were analyzed. It was shown that the wear rate is proportional to a load both in the EHL and in the BL regions. The hardness of thin surface layers saturates during repeating sliding of Cu that is close to the hardness of nanocrystalline Cu produced by different severe plastic deformation (SPD) processes.