Frictional performance and near-surface evolution of nanocrystalline Ni-Fe as governed by contact stress and sliding velocity

► Nanocrystalline Ni-Fe can exhibit high or low friction coefficient (0.2 or 0.8) depending on normal force and sliding velocity. ► The low friction coefficient is associated with the formation of an ultra-nanocrystalline surface tribolayer. ► The high friction coeffiecient is associated with the cyclic delamination and reformation of the ultra-nanocrystalline tribolayer. ► These two regimes of behavior can be rationalized on the basis of stress fields determined by finite element analysis of sliding contact.