Tribological performance of an organic friction modifier (glycerol monooleate – GMO), an anti-wear additive (zinc dialkyldithiophosphate – ZDDP) and its combination was studied using a ball-on-disc tribometer equipped with optical interferometry at 90 °C and 140 °C. Higher temperatures were needed for the formation of additive layers and chemically reactive anti-wear protective layers. Comparison of Stribeck curves obtained after different rubbing durations showed that GMO reduced friction at low speed sliding-rolling contact. Despite notable decrease in the base oil viscosity with increase in temperature — in turn, increasing the severity of asperity contact — GMO exhibited enhanced frictional performance. The presence of ZDDP alone in the formulation led to significant increase in friction at both low and high temperatures, with the thickness of tribofilm unaffected after prolonged rubbing. The addition of friction modifier to ZDDP-based formulation reduced the friction in the boundary lubrication regime where longer rubbing aided in effective friction reduction at higher temperature. For the binary additive system, the friction coefficient was found to lie between the values corresponding to the single additives. The observed tribological response is attributed to preferential adsorption of the friction modifier over ZDDP and/or ZDDP decomposition products. This notion was corroborated by the results obtained from static and dynamic time-of-flight secondary ion mass spectrometry (ToF-SIMS) and energy-dispersive X-ray spectroscopy (EDX) analysis of the disc surface post tribological measurement. The concentration gradient of different chemical species detected in the tribofilm correlated with the frictional performance of the additives. Analysis of surface roughness and wear scar width showed an improvement in wear performance at higher temperature suggesting the friction modifier and anti-wear additive adsorbed on the surface providing a mechanical barrier. A synergistic effect on the wear performance was observed for GMO + ZDDP-based formulations, which resulted in a smaller wear scar compared to the individual additives.

在90°C和140°C下使用配备光学干涉仪的圆盘摩擦计，研究了有机摩擦改进剂（单油酸甘油酯-GMO），抗磨添加剂（二烷基二硫代磷酸锌-ZDDP）及其组合的摩擦学性能。 。形成添加剂层和化学反应性抗磨保护层需要更高的温度。比较不同摩擦时间后获得的Stribeck曲线，结果表明GMO降低了低速滑动接触时的摩擦。尽管基础油粘度随温度的升高而显着降低，进而增加了粗糙接触的严重程度，但GMO的摩擦性能却得到了提高。配方中仅ZDDP的存在会导致低温和高温下的摩擦力显着增加，长时间摩擦后，摩擦膜的厚度不受影响。在基于ZDDP的配方中添加摩擦改进剂可减少边界润滑状态下的摩擦，在这种情况下，较长时间的摩擦有助于在高温下有效降低摩擦。对于二元添加剂体系，发现摩擦系数介于对应于单一添加剂的值之间。观察到的摩擦学响应归因于摩擦改性剂比ZDDP和/或ZDDP分解产物优先吸附。静态和动态飞行时间二次离子质谱（ToF-SIMS）和摩擦测量后的磁盘表面能量色散X射线光谱（EDX）分析获得的结果证实了这一观点。在摩擦膜中检测到的不同化学物质的浓度梯度与添加剂的摩擦性能相关。表面粗糙度和磨损痕迹宽度的分析表明，高温下的磨损性能有所改善，表明摩擦改性剂和抗磨添加剂吸附在表面上提供了机械屏障。对于基于GMO + ZDDP的配方，观察到了对磨损性能的协同作用，与单独的添加剂相比，磨损痕迹更小。