Nonequilibrium kinetics of phase transitions in the boundary friction mode

A nonequilibrium evolution thermodynamic model is presented, which describes the processes developing in the boundary friction mode. The excessive volume parameter is introduced to describe the lubricant state; it has a minimum value in the case of the solid-like structure of the lubricant and increases during melting. The source of entropy growth which results from the external energy inleak during the deformation of the lubricant owing to the shear of the rubbing surfaces, is taken into account. It is shown that the stick-slip mode of motion occurs within wide ranges of the parameters; this is caused by periodic phase transitions of the first-order between the structural states of the lubricant. The effect of the shear velocity, load, and temperature on the pattern of stick-slip friction is studied.