| 摘要: |
| 在润滑油中添加纳米颗粒可以有效减少摩擦磨损，大多数研究只集中在纳米颗粒的性质对摩擦性能的影响，很少考虑到颗粒粒径与表面粗糙度对摩擦性能的耦合作用。采用分子动力学(MD)模拟和试验的方法研究纳米铜颗粒添加剂粒径对润滑油摩擦性能的影响。建立具有凸峰和凹槽的粗糙壁面边界润滑 MD 模型，模拟 300 MPa 下两固体壁面相对剪切速度为 5 m / s 时，5 种粒径的纳米 Cu 颗粒分别在不同粗糙度壁面下的力学性能。定量计算出摩擦表面的应力、磨损量、摩擦力、正压力和摩擦热。同时，采用微纳米划痕仪测量含纳米 Cu 颗粒润滑油的摩擦因数。结果表明，颗粒的粒径和壁面粗糙度对润滑油的摩擦性能具有耦合作用；在剪切过程中纳米颗粒会填充壁面凹坑、形成保护膜、减少摩擦磨损、提高承载能力和降低壁面摩擦热。当壁面粗糙度较小、处于边界润滑状态时，Cu 颗粒添加剂会增大体系的摩擦力；当壁面粗糙度较大、处于混合润滑状态时，Cu 颗粒添加剂会减小体系的摩擦力；当颗粒粒径与壁面凹槽深度的比值 D / h 在 1.05~1.12 范围内，即颗粒直径略大于凹槽深度时，润滑油的摩擦性能最优，摩擦力和磨损量较小、油膜承载能力最大。分子动力学模拟和试验相结合， 建立微纳观结构和宏观特性之间的联系，探究壁面粗糙度与颗粒粒径对润滑油摩擦性能的影响机理，为预测和开发高性能新型润滑剂提供理论基础。 |
| 关键词: 边界润滑 纳米颗粒 表面粗糙度 分子动力学 |
| DOI：10.11933/j.issn.1007?9289.20220615001 |
| 分类号:TH117 |
| 基金项目: |
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| Tribological Properties of Different-sized Copper Nanoparticles Employed as Lubricating Oil Additives Using MD Simulations and Experiments |
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PAN Ling1,2, GUO Jinyang1,2, LIN Guobin1,2
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1.School of Mechanical Engineering and Automation, Fuzhou University, Fuzhou 350108 , China;2.Fuzhou Friction and Lubrication Industry Technology Innovation Center, Fuzhou 350108 , China
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| Abstract: |
| An effective method of reducing friction and wear is through the addition of nanoparticles to lubricating oil. However, although many researchers have linked the tribological properties of nanoparticles to their intrinsic properties, very few have related the tribological properties to the coupling effect of the nanoparticle size and surface roughness. Thus, the effect of the particle size of Cu nanoparticle additives on its tribological properties was investigated in this study using simulations and experiments. A boundary lubrication system model with peaks and grooves was established, and molecular dynamics(MD) simulations were used to simulate the mechanical properties of five types of nanoparticles with different sizes under a stress and relative shear velocity between the two solid walls of 300 MPa and 5 m / s, respectively. The stress, wear, friction force, positive pressure, and friction heat on the friction surface was quantitatively calculated, and the friction coefficient of the lubricating oil containing the Cu nanoparticles was measured using a micro-scratch tester. The results showed that the Cu nanoparticles increased the friction coefficient when the asperity was small and during boundary lubrication, and reduced the friction coefficient when the asperity was large and during mixed lubrication. Particularly, when the ratio of the particle diameter to the groove depth D / h was in the range of 1.05-1.12, namely, when the nanoparticle diameter was slightly larger than the groove depth, the tribological performance of the lubricating oil was excellent, the friction and wear was low, and the oil film bearing capacity was optimal. The Von Mises stress nephogram of the metal revealed that when the ratio of the particle diameter to the groove depth D / h was 1.12, the maximum stress on the solid surface was 2.45×104 MPa, which appears in the direct contact area between the upper and lower contact surface, compared to the maximum stress on the solid surface of 31.2 GPa in the lubrication system without Cu nanoparticles. Additionally, the maximum stress on the solid surface was reduced by 21.40% using Cu nanoparticles, which means that the bearing capacity of the lubrication system can be improved using the Cu nanoparticles additive. A comparison of the wear quantity of different nanoparticle sizes showed that the wear of the lubrication system containing Cu nanoparticles was smaller than that of the lubrication system without Cu nanoparticles, which indicates that Cu nanoparticles can reduce the wear of the lubrication system. When the depth of the groove h was 2.14 nm, an increase in the Cu nanoparticle size caused a reduction in the wear quantity, and when the Cu nanoparticle diameter D was 2.45 nm, the wear of the lubrication system was reduced by 20.70% compared to that in the system without Cu nanoparticles. The temperature distribution of the lubrication system showed that the highest temperature appears on the Z-axis coordinate from 3.5~4.5 nm, which is where the upper and lower solid surfaces are closest; and in the lubrication system without Cu nanoparticles, the maximum temperature of the system was 336 K. Moreover, Cu nanoparticles can reduce the temperature of the contact zone, and an increase in the nanoparticle size results in a further decrease in the maximum temperature. When D / h ＞ 1, the maximum temperature of the lubrication system during the shearing process was reduced to approximately 300 K. In the micro-scratch test, the friction coefficient of the lubricating oil containing Cu nanoparticles of different sizes was smaller than that of the pure base oil. When Ra = 50 nm, the friction coefficient of lubricants with a D = 50 nm was smaller than that with a D = 100 nm, and under a D = 50 nm, the friction coefficient of lubricants with Ra = 50 nm was smaller than that with Ra = 100 nm. This indicates that the particle size D and surface roughness Ra have a coupling effect on the lubrication performance. Finally, simulations and experiments were simultaneously employed to study the effect of the size of Cu nanoparticles additive on the tribological properties. Additionally, an MD simulation was used to compensate for the deficiencies of the test, and the test was used to verify the MD simulation to a certain extent. The results of the simulations and experiments mutually confirm that the surface roughness and nanoparticle size have a coupling effect on the tribological properties of lubricating oil, which provides a theoretical basis for the application of nanoparticles additives. |
| Key words: boundary lubrication nanoparticle surface roughness molecular dynamics |
