Effect of Pressure on Boundary Slip of Thin Film Lubrication Using Atomistic Simulation

Mechanical systems on all length scales may be subjected to nanoscale thin film lubrication(TFL). Molecular dynamics(MD) simulations were conducted to investigate the lubrication mechanism and boundary slip of squalane confined in nanogap at 293 K with two different film thicknesses and a wide range of pressures. The molecular distribution, density and velocity profiles of squalane were analyzed. The results show that the lubricant atoms tend to form layers parallel to the wall, but the lubricant molecules orient randomly throughout the film in the directions both parallel and perpendicular to the wall. Most squalane molecules appear twisted and folded, and extend to several atomic layers so that there are no slips between lubricant layers. The distances between the lubricant layers are irregular rather than broadening far away from the walls. The boundary slip at the interface of bcc Fe(001) and squalane only occurs at high pressure because of the strong nonbond interactions between lubricant atoms and wall atoms. The tendency of boundary slip is more obvious for films with thinner film thickness. According to the simulations, the relationship between the slip length and the pressure is given.

Effects of surface nanostructure on boundary lubrication using molecular dynamics

Molecular dynamics simulations are used to study the boundary lubrication behaviors of squalane lubricant between two iron wall structures during shearing at different pressures and temperatures.Boundary lubrication models with a smooth iron wall and a nanostructured iron wall,respectively,are constructed,and the density distribution of the lubricating film and the velocity distribution in the shearing process are analyzed.The mechanical response of the solid wall is output,and the friction coefficient is calculated.A tribological test is performed with a UMT-2 tribometer under sliding conditions to evaluate the reliability of the simulation method.The results show that the surface nanostructure has a significant effect on the film thickness and delamination of the lubricating film but little effect on the velocity distribution of the lubricating film.The nano strip groove helps to reduce the friction coefficient of the boundary lubrication system.

MECHANISM OF BOUNDARY LUBRICATION UNDER POINT CONTACT

The acid number of the mixed solution of 150SN oil and oleic acid characterizes the volume content of oleic acid in the solution, based on which the adsorptive capability of oleic acid is studied on the 45 steel balls and disks. Boundary lubrication tests are carried out on a self designed ball-on-disk machine, The base oil is pure 150SN oil, and oleic acid as additive are added into the lubricant. Disks have surface roughness values （Ra） of 0.8 μn and 0.4 μn. The electrical contact resistance method is used to determine the lubrication status. Hypothesize that the molecular film is monomolecular layer in condensed state and the opposing surfaces are completely separated by molecular film. A boundary lubrication model is established according to experimental results and hypothesizes. The experimental and calculatienal results show that the adsorption of polar molecules on steel surface is the main factor to form the boundary lubrication film. Load and sliding speed contribute little to the friction coefficient of boundary lubrication. The properties of steel surface and additive for the lubricant significantly influence on the characters of boundary lubrication. The smaller the surface roughness value is, the smaller the friction coefficient of the boundary lubrication is.

Boundary lubrication by adsorption film

A complete understanding of the mechanism of boundary lubrication is a goal that scientists have been striving to achieve over the past century.Although this complicated process has been far from fully revealed,a general picture and its influencing factors have been elucidated,not only at the macroscopic scale but also at the nanoscale,which is sufficiently clear to provide effective instructions for a lubrication design in engineering and even to efficiently control the boundary lubrication properties.Herein,we provide a review on the main advances,especially the breakthroughs in uncovering the mysterious but useful process of boundary lubrication by adsorption film.Despite the existence of an enormous amount of knowledge,albeit unsystematic,acquired in this area,in the present review,an effort was made to clarify the mainline of leading perspectives and methodologies in revealing the fundamental problems inherent to boundary lubrication.The main content of this review includes the formation of boundary film,the effects of boundary film on the adhesion and friction of rough surfaces,the behavior of adsorption film in boundary lubrication,boundary lubrication at the nanoscale,and the active control of boundary lubrication,generally sequenced based on the real history of our understanding of this process over the past century,incorporated by related modern concepts and prospects.

The Lubricating Effectiveness of S-Mo Extreme Pressure Additive and Its Anti-wear Mechanism

A kind of novel compound containing S and Mo elements was synthesized. Its chemical structure was characterized by elemental analysis, IR and 3MR. hs anti-wear property and the load-carrying capacity, as an extreme pressure （EP） additive of lubricating oil, were investigated using a four-bull tester. The experimentul results show that the additive exhibits a superior anti-wear property and a high load-carrying capacity . The presence of other additives does not interfere with the anti-wear prnperty of the extreme pressure additive. The influences of load and temperature on the propert） of the additive were examined. The possible mechanism uas investigated by means of sufface analysis of the tested steel ball specimen , using XPS. The lubricatian films formed on the rubbing surface are mainly composed of MoS2, MoO3 and MoO2.

一种水基钻井液超支化高分子润滑添加剂

传统润滑处理剂设计主要基于油脂的液体润滑理论,忽略了钻井液固相在钻具与井壁极压受限空间内的边界承载和润滑作用。为此,根据Stribeck曲线分析了符合钻进过程的边界润滑行为,并结合人体工学润滑理论,提出了超支化高分子井壁润滑模型及构效关系,采用发散法合成了以乙二胺为内核的超支化高分子聚(丙烯酸甲酯—乙二胺,PMA-EDA),表征了合成产物结构,进行了超支化高分子PMA-EDA与膨润土粒子的成膜检测,并以PMA-EDA为润滑添加剂构建了水基钻井液体系,评价了该体系的应用性能。研究结果表明:(1)目标合成产物PMA-EDA具有超支化构型,其热解温度达到225℃;(2)超支化高分子PMA-EDA可以通过多点吸附,改善与膨润土片层的桥接方式,促进生成具有一定强度的致密、韧性边界润滑膜;(3)对于构建水基钻井液体系,润滑添加剂浓度为4%,可以满足钻井液强润滑性以及热稳定性要求。结论认为,高润滑性能水基钻井液显示出了区别于传统水基钻井液的降摩减磨优越性,其性能评价也进一步证实了超支化分子强化边界润滑成膜模型理论的科学性和实用性。

变黏度液体静压轴承的温升特性研究

采用广泛使用的有限元法难以探究温升的影响对液体静压轴承动态特性的影响,为此,提出了一种基于有限差分法的变黏度液体静压轴承动态润滑仿真算法,对变黏度液体静压轴承的温升特性进行了研究。首先,改进了油腔的热力学边界条件,以拓宽其适用范围,使其适用于油腔尺寸较大的液体静压轴承;然后,基于有限差分法处理了Reynolds方程、流量连续方程、能量方程以及黏温方程,从而建立了基于MATLAB的液体静压轴承变黏度热流动态润滑模型;最后,采用仿真计算的方法,分析了偏心率ε为0.1~0.4、主轴转速n为3000 r/min~10000 r/min(线速度为14.1 m/s~47.1 m/s)时,油膜压力与温升的变化机理。研究结果表明:当主轴转速从3000 r/min增大到10000 r/min时,转速的增大会使得液体静压轴承的承载力因动压效应的增大而增大,但其油膜的平均压力却因温度的升高、油膜黏度的降低而下降了约24%;主轴偏心率的增大会导致油膜温度聚集,而主轴转速的增大则导致油膜温升增大,故当偏心率ε=0.4而转速n=10000 r/min时,油膜的温升较大,且热量发生聚集,其最高温升可达39.5℃;主轴转速越高,液体静压轴承内热油携带对温升的影响越显著。该研究结论可以为温升影响下高速液体静压轴承的轴心轨迹与动态特性的研究提供理论基础。

含氮杂环衍生物的制备及其性能评价

为了减缓页岩气井钻采过程中金属设备出现的腐蚀与磨损问题,以苯并三氮唑、甲醛、苯乙酮、氯乙酸钠为原料制备出一种具有缓蚀性能、润滑性能的含氮杂环衍生物ZP来延长钻井金属设备的使用寿命。采用失重法、电化学法分析含氮杂环衍生物ZP在腐蚀介质中的缓蚀行为,采用极压润滑仪、四球摩擦磨损试验机测试其在盐水钻井液中的润滑效果,通过分子动力学模拟法研究含氮杂环衍生物ZP对N80钢表面的吸附性能。实验表明:含氮杂环衍生物ZP在盐水钻井液以及盐水溶液中均表现出优异的缓蚀性能,使N80钢的腐蚀速率远小于0.0760 mm/a,其缓蚀效率高于70.00%,且属于以抑制阴极过程为主的混合控制型缓蚀剂。含氮杂环衍生物ZP分子可自发吸附在铁晶胞表面,挤走表面H2O分子,形成一层致密的油膜,起到润滑作用,使盐水钻井液的润滑系数低于0.100,且与盐水钻井液具有良好的配伍性能。

Comparative study on boundary lubrication of Ti_(3)C_(2)T_(x) MXene and graphene oxide in water

The emerging use of two-dimensional(2D)nanomaterials as boundary lubricants in water offers numerous benefits over oil-based lubricants;whereas the friction reduction varies significantly with nanomaterial type,size,loading,morphology,etc.Graphene oxide(GO)and Ti_(3)C_(2)T_(x)MXene,a relatively new 2D material,are investigated as boundary lubricants in water in this study.The contact pair mainly includes Si3N4 balls and Si wafer.The results found(1)monodispersed GO offers better lubricity than monodispersed MXene under identical concentration and testing conditions;and(2)the mixed dispersion of GO and MXene(0.1 mg/ml:0.1 mg/ml)produced the lowest friction coefficient of~0.021,a value 4×and 10×lower than that produced by comparable mono-dispersions of GO or MXene,respectively.Wear track analysis,focused ion beam microscopy,in-situ contact observation,and atomic force microscopy(AFM)characterization suggest(1)GO nanoflakes have higher adhesion than MXene and are more easily adsorbed on the tribopairs’surfaces,and(2)GO/MXene tribofilm has a layered nanostructure constituting GO,MXene,amorphous carbon,and TiO_(2).We further hypothesized that the high lubricity of GO/MXene results from the synergy of GO’s high adhesiveness,MXene’s load support ability,and the low shear strength of both constituents.The present study highlights the key role of tribofilm stability in water-based boundary lubrication using state-of-the-art 2D nanomaterials.

烷基硫代磷酸稀土盐的制备及摩擦学特性研究

以异丙醇或异辛醇、五硫化二磷、稀土氯化物为原料 ,合成了四种油溶性二烷基二硫代磷酸稀土盐 .以红外光谱和化学分析确定了所合成稀土盐的结构和化学组成 .在四球实验机上研究了几种稀土盐抗磨添加剂在不同加入量的情况下的最大无卡咬负荷及在不同负荷下抗磨损能力 ,并与二烷基二硫代磷酸锌的性能进行了比较 .结果表明 :本研究制备的油溶性二异丙基二硫代磷酸镧LaDDP - 3、二异丙基二硫代磷酸钕Nd DDP - 3和二异辛基二硫代磷酸镧LaDDP - 8、二异辛基二硫代磷酸钕NdDDP - 8具有比二烷基二硫代磷酸锌(ZnDDP)好的抗磨性能和减摩性能 .EDXA分析表明在实验条件下 ,稀土元素摩擦扩渗进入了材料的表面 。

点接触边界润滑吸附膜计算模型

根据2个假设提出1种边界润滑的计算模型,通过吸附热理论对公式进行修正,利用自行设计的球-盘摩擦磨损试验装置,在汉硬脂酸的石油醚溶液中进行试验,所用45#钢盘的表面粗糙度分别为0.2μm和0.4μm,对理论计算数据和实验数据进行对比,并分析温度和速度等参数对摩擦系数的影响.结果表明,计算结果和实验数据的变化趋势吻合,摩擦系数随着温度增加而增大,随速度增加略有减小.

硫、磷系添加剂在菜子油中的响应性

以菜子油为基础油,在四球摩擦磨损实验机上分别考察了硫系添加剂T321与T307以及磷系添加剂P120对菜子油的耐磨性和极压性能的影响·结果表明,在菜子油中分别加入T321、P120和T307能够降低磨损、提高润滑油膜的承载能力和极压载荷·对钢球表面的能谱分析结果表明,在摩擦磨损过程中,含上述添加剂的菜子油在摩擦过程中发生了摩擦化学变化,生成了由菜子油三甘油酯和添加剂化学产物组成的边界润滑膜,从而改善抗磨性能并提高承载能力·

球盘机构中边界吸附膜形成的研究

研究了润滑剂在45#碳素结构钢和聚四氟乙烯(PTFE)2种不同固体表面的润湿性能;在球-盘摩擦机构中,分别使用45#碳素结构钢和PTFE作为摩擦副进行试验,研究了4种不同类型系统中润滑和吸附特性。结果表明,2种润湿性能好的材料接触时,边界润滑性能最佳,而润湿性较好的球和润湿性较差的盘接触的润滑性能最差,盘的润湿性能对润滑系统更为重要,在一定范围内提高速度和载荷,可以提高润湿性较差材料的边界润滑性能。

分子动力学模拟剪切速度对纳米间隙中角鲨烷界面滑移的影响

采用聚合物一致性力场(PCFF),分别在7种剪切速度V和3种油膜厚度h下对纳米间隙中润滑剂角鲨烷进行分子动力学模拟,分析固液界面的密度、分子和流速的分布,探究纳米薄膜润滑的润滑机理和剪切速度对界面滑移的影响。结果表明,纳米间隙中润滑剂存在分层现象,各层间距相近,并非越远离固体壁面层间距越大,层间距约为角鲨烷分子单个C C键距离的3~4倍;随着油膜厚度的减小,纳米间隙中润滑剂层状分布越明显,固化层密度越大;当油膜厚度为3.44 nm时,固液界面滑移现象明显,滑移长度b值随着V先增大后减小,当V为22.8 m·s^(-1)时,b达到最大值4.35 nm;根据模拟和计算结果,给出滑移长度与剪切速度的关系公式。

固体粒子分散体系润滑剂对接触疲劳前期影响的研究

针对固体粒子分散体系润滑剂的粒子大小的不同，提出了赫兹压力下降与油膜高粘吸附两种物理模型，并分析了两种单分散介质的润滑剂对接触疲劳前期（即裂纹萌生之前）的影响结果，还解释了疲劳试验结果的某些现象．

四种合成油微动磨损性能比较研究

本文对GCr15钢/45#钢摩擦副在聚醚、合成酯、聚α-烯烃和硅油润滑下的切向微动磨损性能进行了实验研究.结果表明:在微动滑移区,与干摩擦相比,不同合成油润滑下的摩擦系数和磨损降低幅度不同.极性聚醚和合成酯形成的边界吸附膜使微动的摩擦系数比聚α-烯烃和硅油低;硅油表面张力小且黏压系数最低,形成的油膜最薄且更易在摩擦表面微裂纹中渗透,导致较大的稳态摩擦系数和磨损;聚α-烯烃润滑下微动初期形成的白层有助于降低磨损.