Tribological Properties of Polymer Friction Improvers Combined with MoDTC/ZDDP at Different Temperatures

Abstract

To expand the applications of polymer friction modifiers in low viscosity oils suitable for hybrid power systems, the tribological properties of five kinds of oil samples at different temperatures were studied, which were compounded with polymer friction modifiers Perfad XG 2500, molybdenum dialkyl dithiocarbamate (MoDTC), zinc dialkyl dithiophosphate (ZDDP). When Perfad XG 2500 is used alone, it forms a brush-like surface film at low temperatures, which can provide lower initial friction. With the rise in temperature, its antifriction effect decreases significantly, which is related to the desorption behavior of physical film. When Perfad XG 2500 is combined with MoDTC, it has the best synergistic antifriction effect, and the average friction coefficient is reduced by a maximum of 20.83% (90 °C). Its friction coefficients decrease significantly with the increase in temperature due to the dissociation process of MoDTC catalyzed by high temperature. However, there are many furrows on the worn surfaces, and the sharp features of the profiles are obvious. When Perfad XG 2500 is combined with ZDDP, it has the best synergistic anti-wear effect, and the total wear depth is reduced by 49.6%. Its worn surface is smooth and defect-free, with minimal residual strain. The friction coefficients are hardly affected by temperature, and the average friction coefficient is reduced by a maximum of 14.4% (30 °C). When Perfad XG 2500, MoDTC and ZDDP are used together, the average friction coefficient is reduced by up to 15.2% (30 °C). Its friction coefficient increases slightly with the rise in temperature. The reason for its moderate tribological performance may be related to the superficial competition of various additives.