Effects of Friction Modifiers on Wear Mechanism of Some Steels Under Boundary Lubrication Conditions

The effects of some commercial friction modifiers on antiwear performance of some steels were assessed experimentally under high contact pressures. The main compounds of the friction modifiers were, respectively, calcium carboxylate compound, organic molybdenum compound, phosphorous/sulfur (P/S) chemistry and polytetrafluoroethylene (PTFE). A ball-on-disk configuration was employed in the wear tests. The sliding speed of the disk on the stationary ball ranged from 0.785 m/s to 1.885 m/s and the applied load ranged from 39.2 N to 78.5 N. Bearing steel, high-carbon steel and medium-carbon steel were used to make the members of sliding pairs. The results show that only the additives that can produce chemical films on rubbing surfaces can reduce friction more effectively. Except PTFE, the other three additives have such an effect, but not as significant as claimed. Among these, P/S chemistry is the best, but this additive can cause excessive wear on rubbing surfaces in long-time use. Mo compound can provide a significant effect of antiwear on all three types of steel subjected to high contact pressures, while Ca compound has an antiwear effect only at comparably low pressures. Both Ca and Mo compounds cause wear on rubbing surfaces in a form of parallel deep grooves. PTFE neither improves antiwear performance, nor reduces friction on the rubbing surfaces of steel.