目的 结合基础摩擦学实验和分子动力学模拟,从原子层面动态掲示片层MoS2和球形TiO2纳米粒子间的协同润滑机制。方法 用物理分散法制备出质量分数为0.2% MoS2纳米流体、0.2% TiO2纳米流体、0.1% MoS2+0.1% TiO2的纳米复合流体。通过分散性实验、四球摩擦磨损实验和非平衡分子动力学模拟,从宏观到微观尺度研究纳米流体的分散稳定性、运动模式、抗磨减摩行为和与温度的关联性,并通过FIB-TEM对摩擦界面形成原位摩擦膜的结构和成分进行分析。结果 复合纳米流体的极压性能显著增强,最大无卡咬负荷值达922 N,较单一MoS2和TiO2分别提升23.6%和14.7%。其平均摩擦系数（0.068）亦低于单一组分。磨斑形貌分析显示,复合体系表面划痕浅且均匀,磨斑直径（0.705 mm）最小,抗磨损性能最优。分子动力学模拟进一步动态呈现出复合体系中MoS2的层间滑移与TiO2的滚动运动,导致该体系拥有最低的平均摩擦力（0.003 nN）和法向应力（0.697 GPa）,同时改善高温下的摩擦学性能。结论 MoS2的层间滑移与TiO2的滚动机制（物理协同）,显著降低界面剪切阻力与应力集中。摩擦界面生成了厚度约20 nm的原位摩擦膜,主要成分为摩擦化学产物FeO、MoO3和Fe2O3（化学协同）,有效隔离金属直接接触。MoS2/TiO2纳米复合流体通过“物理滑移/滚动+化学反应膜”的双重协同机制,实现了优异的抗磨减摩性能。
Abstract
This study presented a comprehensive investigation into the synergistic enhancement of tribological performance through the combination of MoS2 and TiO2 nanoparticles (NPs) in a water based nanofluid. An integrated methodology combining fundamental tribological experiments with atomic-scale molecular dynamics (MD) simulations was employed to dynamically reveal the underlying cooperative lubrication mechanisms. The experimental phase involved the preparation of three distinct nanofluids using a physical dispersion method: a 0.2wt.% MoS2 nanofluid, a 0.2wt.% TiO2 nanofluid, and a composite nanofluid containing 0.1wt.% MoS2+0.1wt.% TiO2. The base fluid was formulated with organic molybdenum, glycerol, triethanolamine, sodium hexametaphosphate and sodium dodecyl benzene sulfonate. The dispersion stability of these nanofluids was rigorously evaluated through sedimentation tests and Zeta potential measurements. Tribological performance was assessed with a four-ball friction and wear tester. Key parameters including the maximum nonseizure load, average friction coefficient, and wear scar diameter were measured under controlled conditions. Wear scar morphology was analyzed by laser confocal microscopy, while the structure and composition of the in-situ formed tribofilm were characterized via focused ion beam transmission electron microscopy (FIB-TEM) and X-ray photoelectron spectroscopy (XPS). Complementing the experiments, non-equilibrium MD simulations were performed to gain atomistic insights into the dynamic shear behavior at the friction interface. These simulations tracked parameters such as friction force, normal stress, and temperature distribution over time.
The results demonstrated a clear synergistic effect in the MoS2/TiO2 composite nanofluid. Dispersion stability tests showed that MoS2/TiO2 nanofluid exhibited the highest Zeta potential absolute value (41.5 mV), indicating excellent colloidal stability, attributed to the intercalation of spherical TiO2 by layered MoS2, which acted as a physical barrier against agglomeration. Tribological tests revealed that MoS2/TiO2 nanofluid significantly outperformed its single-component counterparts. It achieved a maximum nonseizure load of 922 N, representing improvements of 23.6% and 14.7% over pure MoS2 (746 N) and TiO2 (804 N) nanofluids, respectively. The average friction coefficient of MoS2/TiO2 nanofluid was 0.068, lower than that of MoS2 (0.075) and TiO2 (0.079) nanofluids. Furthermore, it produced the smallest wear scar diameter (0.705 mm) and the most uniform, shallow surface scratches, confirming its superior wear resistance. MD simulations provided a dynamic, atomic-scale visualization of the synergistic mechanism. In the composite system, the MoS2 nanosheets facilitated interlayer sliding, effectively reducing shear resistance. Concurrently, the TiO2 NPs primarily exhibited a rolling motion, which was maintained and protected from embedding into the iron surface by the shielding effect of the MoS2 layers. This cooperation resulted in the lowest average simulated friction force (0.003 nN) and normal stress (0.697 GPa), compared with the single-component systems. The temperature distribution along the contact region was also more uniform in the hybrid system, indicating better management of frictional heat due to the combined load-bearing and stress-dispersing actions of both NPs. Post-test analysis of the wear scar using FIB-TEM confirmed the formation of a dense, uniform, and adherent tribofilm approximately 20 nm thick on the steel ball surface under MoS2/TiO2 nanofluid lubrication. EDS mapping confirmed the diffusion of Mo, S, and O elements into the near-surface region. XPS analysis identified the tribofilm's chemical composition, revealing the presence of FeO, MoO3, and Fe2O3. These oxides were products of tribochemical reactions induced by the high pressure and temperature at the contact interface. They formed a protective layer that prevented direct metal-to-metal contact. Meanwhile, the fragmented NPs (MoS2 and TiO2) adsorbed onto this reacted layer, contributing through mechanisms such as interlayer shear (MoS2), rolling and polishing (TiO2), and filling, creating a multi-functional, synergistic lubrication system.
关键词
润滑 /
表面 /
纳米粒子 /
摩擦学行为 /
协同作用
Key words
lubrication /
surface /
nanoparticles /
tribological behavior /
synergistic effect
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基金
河南省青年科学基金项目（262300421918）
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