【作者】 冯雪君；

【导师】 杨志伊；

【作者基本信息】 中国矿业大学 ， 机械设计与理论， 2009， 博士

【摘要】 润滑油性能取决于润滑油中添加剂的含量及性能,性能优良的添加剂能够大大提高润滑油的极压、耐磨性能。纳米润滑油添加剂和磁流体润滑是近年来国内外研究热点。国内外研究表明,多种类型的纳米粒子添加到润滑油中可以大大改善润滑油性能,达到抗磨减磨的目的。磁流体润滑与常规润滑相比较,在外加磁场作用下,能准确地充满润滑表面,实现连续润滑。但是,很多国内外关于纳米添加剂和磁流体润滑的研究往往侧重于某一方面,缺乏系统性。本文中制备的纳米MnZnFe₂O₄为磁性颗粒,平均粒径为5.2nm。纳米MnZnFe₂O₄磁性颗粒既可以无外加磁场下,作为普通纳米润滑油添加剂直接加入到润滑油中,也可以在外加磁场下实现磁流体润滑。本文是从影响润滑和摩擦的几个重要因素来综合讨论纳米添加剂、磁场对于润滑油润滑与摩擦性能的改变,从而探讨其作用机理:1)黏度特性。无论在流体动压润滑、弹流润滑、薄膜润滑以及边界润滑中,润滑油的黏度都会影响油膜的形成、油膜的厚度、油膜的形态以及油膜的承载能力。2)成膜能力。若润滑油具有高的成膜能力,就能使润滑油在摩擦过程中能够快速形成稳定的、高强度的、厚的油膜,隔开摩擦界面,从而改善润滑油的极压、耐磨性能,达到抗磨减磨的目的。3)承载能力。承载能力是润滑油膜强度大小的标志。4)摩擦学特性。摩擦系数、磨斑直径、摩擦温升是润滑性能的综合表现。研究表明,添加纳米磁性颗粒润滑油,无外加磁场下:①质量分数小于5%时,黏度降低;质量分数小于50%时,黏度增加缓慢;质量分数大于50%时,黏度大幅增加。②质量分数小于5%时,黏度降低,但润滑油油膜强度大幅提高,较基础油承载能力增加2倍以上。③相同工作条件下,较基础油油膜中心厚度增加,特别是形成薄膜润滑的转化膜厚增加3倍。④高载和启动阶段,较基础油摩擦系数降低,磨斑直径减小。外加磁场下,添加纳米磁性颗粒润滑油较基础油:黏度、承载能力进一步提高,而同等条件下的摩擦系数、磨斑直径进一步减小。因此,笔者提出:无外加磁场作用下,若磁性颗粒之间的间距减小到一定值,磁性颗粒之间、磁性颗粒与金属表面之间也会形成较弱的磁力矩,使得部分相邻磁性颗粒形成动态聚集,部分磁性颗粒吸附于金属表面,有助于快速形成强度高且厚的物理吸附膜。而外加磁场可以进一步提高润滑油黏度,增大摩擦副表面吸附势能,还可能使得磁性颗粒之间形成较短的、不稳定的颗粒链,有助于快速形成强度更高、更厚的物理吸附膜。试验证明外加磁场可以进一步提高添加纳米磁性颗粒润滑油的摩擦学性能,并快速形成高强度的物理吸附膜,改善高载和启动阶段的润滑性能。在试验及理论分析的基础上,本文建立了无外加磁场下和外加磁场下,含纳米磁性颗粒润滑油薄膜润滑物理模型,为研究添加纳米磁性颗粒润滑油润滑机理提供了理论基础。更多还原

【Abstract】 Performance of lubricant oil depends on additive contents and its properties. High performance additives can largely improve the load-carrying and antiwear capacity of lubricant oil. Nanoparticles as lubricant additives and magnetic fluid lubrication are research hotspots at home and abroad. Researches show that lubricant performance can be largely improved with different types of nanoparticles. Magnetic fluid lubrication can brim lubricant surfaces and realize continuous lubrication. However, studies on the nano additives and magnetic fluid lubrication tend to focus on one aspect, are not systematic.MnZnFe₂O₄ magnetic nanoparticles with a mean particle size of 5.2nm can be prepared. MnZnFe₂O₄ magnetic nanoparticles can be directly added into lubricant oil and also be used as magnetic additives under external magnetic field.This article had a comprehensive discussion on the effect of nano-additives, magnetic field on the lubrication and friction properties from some important impact factors and studied lubricant mechanism:1) Viscosity . In terms of hydrodynamic lubrication, elastohydrodynamic lubrication, thin film lubrication and boundary lubrication, the lubricant viscosity will affect the film formation, film thickness, film morphology, as well as the load-carrying capability.2) The film-forming ability. With a high film-forming ability, lubricant oil can quickly form a stable, high strength, thick film which separate friction interface in the friction process,and get better anti-wear ,friction-reducing capability.3) Load carrying capability. Load-carrying capacity indicates lubricant film strength.4) Tribological properties. Friction coefficient, wear scar diameter, oil temperature assess the comprehensive lubricant performance .The results showed that: For the lubricant oil with magnetic nanoparticals as additive, under no magnetic field,①When mass fraction was less than 5.00%, the viscosity was reduced; when the mass fraction was less than 50%, more than 5.00%, the viscosity increases slowly; when the mass fraction was greater than 50%, the viscosity increased significantly.②when the mass fraction was less than 5%, viscosity decreases, while oil film strength increased greatly and load-carrying capability increased to 2 times that of the base oil.③In the same working conditions, film center thickness increased, especially critical film thickness of the thin film lubrication increased to 3 times that of the base oil.④Compared with the base oil, friction coefficient and wear scar diameter decreased at high-load and start-up phase. Under external magnetic field, lubricant oil with magnetic nanoparticals as additive exhibited a better performance than base oil: viscosity, load-carrying capacity further increased, while the friction coefficient, the wear scar diameter further decreased in the same conditions.Therefore, it was pointed out: When distance is smaller to some value, weak magnetic-moment will be formed among magnetic particles, magnetic particles and the metal surface. It makes part of the adjacent magnetic particles form a dynamic aggregation, some magnetic particles be adsorbed on the metal surface, which contribute to form a high strength and thick physical adsorbed film.The external magnetic field can further enhance the viscosity and the surface adsorption potential of the friction pair. It can also help to form shorter, unstable particle chains among the magnetic nanoparticles. So a higher strength, thicker adsorbed film is formed rapidly. Experiment showed that magnetic field can further improve tribological properties of lubricating oil with magnetical nanoparticles as additive, and help to form a high-intensity physical adsorbed film quickly, improve the lubrication performance in high-load and start-up state.Based on the test and theoretical analysis, physical models of thin film lubrication which contained magnetic nanoparticles under no external magnetic field and external magnetic field was established. It provides a theoretical basis to study the lubricant mechanism of lubricant oil with magnetic nanoparticles as Additive.更多还原