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

► The effects of grain size of Cu on friction and wear under lubricant conditions were studied. ► Preliminary severe plastic deformation improves remarkably the friction and wear properties. ► A balance between geometrical and structure parameters is preserved in steady state. ► The parameter, K, incorporated in the Sommerfeld number, allows a prediction of the Stribeck curves.