Dislocation structure and hardness of surface layers under friction of copper in different lubricant conditions

Abstract

Friction and wear of copper rubbed in the presence of lubricants over a wide range of loads and sliding velocities were studied. The results of friction and wear experiments in the boundary lubrication (BL) and elastohydrodynamic lubrication (EHL) regimes are briefly considered. The structural state of subsurface layers in different lubricant regions is studied by optical, transmission and scanning microscopy analysis. Dislocation density and Burgers vector of individual dislocations in EHL and BL lubricant regimes were determined. A laminated structure with thin and elongated grains is formed in the EHL region. A range of nanocrystalline structures with grain sizes of 20–100 nm is formed in the surface layers in the BL region. Strong plastic deformation (SPD) of thin surface layers under friction is accompanied by formation of shear bands in sublayers of contact spots. Nanohardness at thin surface layers is compared for surfaces rubbed under different lubricant regimes. The hardness of thin surface layers saturates after repeated sliding of Cu and is close to the hardness of nanocrystalline Cu produced by various SPD processes.