Effect of zinc dialkyldithiophosphate as additive in liquid paraffin on friction and wear properties of filled polytetrafluoroethylene composites

Polytetrafluoroethylene (PTFE ) composites filled with copper and nickel participates, respectively, were prepared by means of compression molding and sintering in air. The friction and wear behaviors of the resulting filled PTFE composites sliding against SAE-52100 steel in a block-on-ring contact configuration and under the lubrication of liquid paraffin or liquid paraffin-zinc dialkyldithiophosphate (ZDDP) were investigated on an MM-200 test rig. The distributions of Zn and S on the worn steel surface sliding against PTFE or its composites were determined by means of energy dispersive X-ray analysis. It was found that the PTFE composites showed greatly decreased friction coefficients as they slid against the steel under the lubrication of liquid paraffin and liquid paraffin containing ZDDP as the additive. At the same time, liquid paraffin and liquid paraffin-ZDDP as the lubricants contributed to significantly decrease the wear scar width of the PTFE-30%Ni composite, but they had little effect on the wear scar width of the PTFE-30%Cu composite. Moreover, ZDDP as the additive was beneficial to increasing the wear-resistance of the PTFE composites but had little effect on the friction-reducing ability of the base stock. The antiwear ability of the ZDDP additive was attributed to its physico-chemical adsorption on the contact surface of the frictional pair and the formation of an adsorbed boundary-lubricating layer thereon.