Tribological and thermal characteristics of reduced phosphorus plain ZDDP oil in the presence of PTFE/FeF3/TiF3 under optimized extreme loading condition and a break in period using two different rotational speeds

Abstract

There is a recent concern about the effects of P-containing anti-wear additives in regard to emissions reduction in automobiles and trucks. Research described here is aimed at providing good friction and wear performance while reducing suspected catalyst poisoning effects from compounds like zinc dialkyl dithiophosphate (ZDDP). The effects of adding submicron particles of titanium fluoride or iron fluoride along with polytetrafluoroethylene to ZDDP were investigated with bearing steel using a sliding ball-on-ring apparatus that operates under boundary lubrication. An optimized load of 336 N (2.6 GPa Hertzian contact pressure) and 60 μl of oil quantity were used to run several tests using 0.05 P% plain ZDDP with and without additives (1% catalysts and 2% PTFE) under two different speeds (3.14 m/s for the first 943 m (5000 revolutions) then 2.2 m/s until failure or 18,856 m (100,000 revolutions) whichever comes first) and steady state speed of 2.2 m/s. Special attention was paid to the effects of running-in and temperature. Therefore, a break in period of 3 min was chosen when the tribotest temperature reached 100 °C. Results showed that 0.8% FeF3+0.2% TiF3 and 2% PTFE additives when combined with 0.05 P% (phosphorus) ZDDP plain oil performed better than that when ZDDP is used alone. Thermally treated surfaces showed better coating and support our findings. A good transfer layer under extreme pressure was responsible for improving the antiwear resistance of additives and for lowering the wear volume and wear debris as it is evident by SEM and TEM images.