“…Therefore, the liquid film under PEGM lubrication had a large thickness and attained elastohydrodynamic lubrication. The thick liquid film prevented the direct contact of the friction pairs, and thus, the tribochemical reaction could not be triggered, making the COF relatively high. , With the increase of the temperature, the boundary lubrication became dominant due to the decreased dynamic viscosity. Since the liquid film became thinner, the roughness asperities of the friction pair collided violently.…”