【作者】 江华；

【导师】 侯献军；

【作者基本信息】 武汉理工大学 ， 车辆工程， 2024， 博士

【摘要】 机械零部件运动副之间的摩擦磨损会使润滑剂长时间处于高温重载的混合润滑状态下。传统的润滑剂由于较差的理化性能,在界面接触点由摩擦产生的瞬时高温会使边界润滑膜剥脱,从而导致润滑不良/失效,较难满足现代摩擦润滑工艺的发展需求。为其能在更宽泛的温度和载荷范围内高效润滑,本文以复合Mo S₂/h-BN纳米微粒作为两种不同黏度基础油（聚α烯烃PAO6和5W-40）的润滑添加剂,深入研究纳米润滑油（Nanolubricants,NL）的理化特性及其摩擦学行为,揭示复合纳米颗粒强化传热及高效润滑机制,研究成果将为高性能复合纳米润滑添加剂在机械零部件中的应用提供潜在学术和工程价值。主要研究内容如下:（1）针对纳米颗粒分散在基础油中容易造成团聚等分散不良问题,提出一种具备良好分散稳定性的复合配方纳米润滑油设计及制备方法。采用机械球磨法辅助液相共混法合成经过控形改性的复合Mo S₂/h-BN纳米微粒,并结合两步法制备复合纳米润滑油。综合考察纳米颗粒浓度、超声时间、表面修饰剂浓度及种类、纳米颗粒形貌等制备因素对油溶性纳米润滑油分散稳定性的影响规律。对比单一和复合纳米颗粒在基础油中的分散行为,并评估复合纳米颗粒在不同黏度基础油中的分散性能。结果表明,与单一纳米润滑油相比,由于复合纳米颗粒间的强协同作用导致静电斥力的增加及空间位阻的形成,其分散稳定性能得到更显著的改善,为后续理化性能和摩擦学行为研究提供了良好的保障。（2）针对传统润滑油较快的氧化速率及较低的导热系数等理化性能问题,深入研究复合配方纳米材料及制备因素对各类润滑油流变特性、润湿性能、热稳定性及其传热行为等热物理化学特性的影响规律。利用动力黏度测试方法研究复合纳米颗粒浓度、剪切速率和温度对基础润滑油动力黏度的影响规律。结果发现,纳米润滑油动力黏度随着纳米颗粒浓度有所提升但随温度呈指数下降,基础油和纳米润滑油在不同条件下均出现剪切变稀现象,属于非牛顿流体范畴。利用接触角测量仪对纳米润滑油在钢界面的润湿性能进行了综合评估,实验表明复合纳米颗粒的相互作用降低了固液界面的接触角,使得基础流体的吸附和润湿性能得到显著改善。利用热重分析仪测试纳米润滑油的热重（Thermogravimetric Analysis,TGA）和导数热重（Derivative Thermogravimetry,DTG）曲线对其高温稳定性进行表征,结果发现复合纳米润滑油在高温下的起始温度和燃尽温度均滞后于基础油,表现出优异的抗高温氧化性能。使用瞬态热线法对纳米润滑油的导热系数进行测量,实验得到最优浓度下复合纳米润滑油的导热系数比PAO6和5W-40基础油分别提高约15.8%和15.9%。（3）针对热传导实验不足以从原子层面揭示纳米润滑油传热机制问题,建立一种基于固液耦合的高精度复合纳米润滑系统分子动力学（Molecular dynamics,MD）传热模型。应用平衡分子动力学模拟策略对复合Mo S₂/h-BN纳米颗粒在基础油中的热传输行为进行系统的研究,以探索复合纳米颗粒浓度、协同作用及温度等理化因素对纳米润滑油导热性能的影响。通过径向分布函数（Radial distribution function,RDF）、均方根位移（Mean square displacement,MSD）、系统能量和分子动力学原子轨迹图协同分析复合纳米材料对基础油分子的致密程度和强化传热过程的影响规律,及研究复合纳米润滑油中液固分子的微运动、微结构及液固分子间的相互作用对纳米润滑油热传输行为的变化规律,从微观尺度上揭示复合纳米润滑油热传输行为机制。模拟结果发现,随着纳米颗粒浓度和温度的增加,纳米微粒的相互吸引变得更加显著,增强了界面效应,从而使得导热系数得到明显改善。研究结果将为探寻润滑过程中固液两相流强化传热行为与边界润滑膜的演变规律提供重要参考价值。（4）针对传统润滑油易发生高温氧化从而导致润滑不良问题,全面研究不同基础油基复合纳米润滑油的摩擦学性能并揭示在边界润滑状态下的减摩抗磨机理。利用四球摩擦磨损试验台架评估纳米颗粒浓度、载荷和表面修饰对于摩擦系数（Coefficient of friction,COF）和磨斑直径（Wear scar diameter,WSD）的影响规律,使用场发射扫描电子显微镜（Field emission scanning electron microscope,FE-SEM）、能谱仪（Energy dispersive spectrometer,EDS）、Mapping元素分析、Raman光谱及X射线光电子能谱（X-ray Photoelectron Spectroscopy,XPS）分析磨损界面微观形貌、织构及其潜在的化学反应。由于复合纳米颗粒的特殊空间层状结构,在润滑过程中出现层间滑移和剪切滑移,使得运动副接触界面产生具有高法向承载能力和低切向阻力的界面层,促进润滑保护膜的形成,进一步避免或延迟摩擦界面之间的直接接触。结果表明,相对于基础油PAO6和5W-40,经过0.2 wt%的复合纳米润滑油润滑的COF和WSD分别降低约37.0%、26.9%和42.3%、26.2%。更多还原

【Abstract】 The friction and wear between the moving pairs of mechanical components leads the lubricant to be in a high-temperature and heavy-load mixed lubrication state for a long time.Traditional lubricants have poor physical and chemical properties,and the instantaneous high temperature generated by friction at the interface contact point can cause the boundary lubrication film to peel off,resulting in poor lubrication/failure,and making it difficult to meet the development needs of modern friction lubrication processes.In order to be continuously and effectively lubricated by lubricants in a wider temperature and load range,this research intends to use hybrid Mo S₂/h-BN Nanoparticles as additives for two different viscosity base oils（polyαolefin 6 and 5W-40）.In-depth research on the physical and chemical properties and tribological behavior of composite nanolubricants were conducted to reveal the enhanced heat transfer and efficient lubrication mechanism of hybrid nanoparticles.The research results will provide potential academic and engineering value for the application of hybrid nanolubrication additives with high performance in mechanical parts.The main contents and conclusions are as follows:（1）Aiming at the issue that nanoparticles dispersed in base oil can easily cause agglomeration and other bad dispersion problems,a design and preparation method of a hybrid formula nanolubricant with good dispersion stability is proposed.Shape-controlled and modified hybrid Mo S₂/h-BN nanoparticles were synthesized using mechanical ball milling together with liquid phase blending methods,and hybrid nanolubricating oil was prepared by combining the two-step method.Comprehensive investigation of the influence of preparation factors such as nanoparticle concentration,ultrasound time,surface modifier concentration and type,and nanoparticle morphology on the dispersion stability of oil-soluble nanolubricants was conducted.A comparison of dispersive behavior of mono nanoparticles and hybrid nanoparticles in base oils,and an evaluation of the dispersion properties of hybrid nanoparticles in base oils of different viscosities were also performed.The results show that compared with mono NL,due to the strong synergistic effect between hybrid nanoparticles leading to the increase of electrostatic repulsion and the formation of steric hindrance,the dispersion stability of hybrid NL is further improved,which provides suitable guarantee for subsequent research on physicochemical properties and tribological behavior.（2）In view of the physicochemical properties of traditional lubricating oils such as quicker oxidation rate and lower thermal conductivity,the influence of hybrid formulation nanomaterials and preparation factors on the rheological properties,wetting properties,thermal stability and heat transfer behavior of various lubricants were deeply studied.The dynamic viscosity testing method was used to study the influence of hybrid nanoparticle concentration,shear rates and temperatures on the dynamic viscosity of base oil.The results show that the dynamic viscosity of NL increases with the concentration of nanoparticles but decreases exponentially with temperature.Both base oil and NL exhibit shear thinning phenomenon under different conditions,belonging to non-Newtonian fluids.A contact angle measuring instrument was used to comprehensively evaluate the wetting properties of nanofluids onto the steel interface,which showed that the interaction of hybrid nanoparticles reduced the contact angle at the solid-liquid interface,significantly improving the adsorption and wetting properties of the basic fluid.A thermogravimetric analyzer to test the Thermogravimetric Analysis（TGA）and Derivative Thermogravimetry（DTG）curves of NL was used to characterize its high-temperature stability.It was found that the starting temperature and burnout temperature of the hybrid NL at high temperatures lagged behind that of the base oil,showing excellent resistance to high-temperature oxidation.The thermal conductivity of the nanofluid was measured using the transient hot-wire method.The experiment results showed that the thermal conductivity of the hybrid NL at the optimal concentration was approximately 15.8%and 15.9%higher than that of the PAO6 and 5W-40 base oils respectively.（3）Aiming at the problem that thermal conduction experiments are not enough to reveal the heat transfer mechanism of nanofluids from the atomic level,a molecular dynamics heat transfer model with high-precision of hybrid nanolubricating systems based on solid-liquid coupling role was established.The equilibrium molecular dynamics simulation strategy was used to systematically study the heat transfer behavior of hybrid Mo S₂/h-BN nanoparticles in base oil,and to explore the effects of hybrid nanoparticle concentration,temperature,and synergy on the thermal conductivity of the nanofluid system.The radial distribution function（RDF）,Mean square displacement（MSD）and molecular dynamics atomic trajectory diagram are used to collaboratively analyze the density degree of the base oil molecules and the strengthened heat transfer of the hybrid nanomaterial.The influence of the micro-motion,microstructure and interaction between liquid-solid molecules in the hybrid NL on the thermal transmission behavior of the nanofluid was also investigated,revealing the thermal transmission behavior mechanism of the hybrid NL from the micro scale.The simulation results show that as the concentration of nanoparticles increases,the mutual attraction within the nanoparticles and the interface effect of the nanosystem become more significant,and the thermal conductivity was increased remarkably.The research results will provide important reference value for exploring the enhanced heat transfer behavior of solid-liquid two-phase flow and the evolution law of boundary lubrication film during the lubrication process.（4）In view of the issue of unfavorable lubrication caused by high-temperature oxidation of traditional lubricants,the tribological properties of different base oil-based hybrid NL was comprehensively studied and the friction reduction and anti-wear mechanisms under boundary lubrication conditions was revealed.A four-ball friction and wear test bench was used to evaluate the influence of nanoparticle concentration,load and surface modification on coefficient of friction（COF）and wear scar diameter（WSD）.Field emission scanning electron microscope（FE-SEM）,Energy dispersive spectrometer（EDS）,Mapping element analysis,Raman spectrum and X-ray Photoelectron Spectroscopy（XPS）were used to explore the micromorphology,texture and potential chemical reactions of the wear interface.Due to the special spatial layered structure of the hybrid nanoparticles,interlayer slip and shear slip occur during the lubrication process,causing the contact interface of the moving pair to produce an interface layer with high normal load-bearing capacity and low tangential resistance,promoting lubrication protection,and further avoiding or delaying direct contact between friction interfaces.The results show that the COF and WSD lubricated by 0.2wt%hybrid NL are reduced by 37.0%,26.9%,42.3%,and 26.2%,respectively,compared to the base oils PAO6 and 5W-40.更多还原