纳米陶瓷添加剂在润滑油中的摩擦学性能研究

采用摩擦磨损试验机考察了纳米陶瓷添加剂的抗磨和极压性能,利用扫描式电子显微镜观察磨损表面的形貌,对它的摩擦学性能进行了研究.结果表明:当润滑油中含有少量纳米陶瓷粒子时,就能大幅度提高润滑油的抗磨和极压性能,其最佳含量为3%,与ZDDP进行对比的试验显示,在低负荷长时间磨擦性能方面ZDDP远不如纳米陶瓷添加剂,含有纳米陶瓷添加剂的润滑油在低负荷长时间摩擦过程中,主要发生的是疲劳磨损和擦伤.     

电镀废液回收纳米铜粉作为润滑添加剂的摩擦学性能研究

以化学还原法从电镀铜废液中回收的纳米铜粉为固体润滑油添加剂,在四球式摩擦磨损试验机上研究纳米铜粉的加入量对润滑油摩擦学性能的影响。采用SEM、EDAX等分析磨斑表面,初步探讨纳米铜粉抗磨减摩机制。结果表明:纳米铜粉的添加显著提高基础油的抗磨减摩性能,当纳米铜粉加入量为0.3%(质量分数)时,其摩擦因数和磨斑直径分别比基础油减小33.4%和19%。含纳米铜粉润滑油在高载荷下具有更好的抗磨减摩性能。纳米铜粉在摩擦过程中抗磨减摩机制主要为填充作用和沉积自修复膜作用机制。     

矿物质润滑油添加剂对钢/铝锡合金摩擦副摩擦学性能的影响

利用销盘式磨损试验机研究了一种矿物质润滑油添加剂对钢/铝锡合金摩擦副摩擦学性能的影响,并考察了这种添加剂对实际工况下铝锡合金轴瓦的作用效果。采用AFM、SEM/EDS等仪器对摩擦副表面进行了分析。结果表明,矿物质添加剂在低载荷比高载荷条件下的减摩抗磨效果明显;试验时间越长,添加剂的作用越充分,圆盘表面的Al-Sn共晶体的分布越分散,减摩效果越明显;添加剂降低了摩擦表面的粗糙度,显著地提高了摩擦副的减摩抗磨性能,延长了使用寿命;添加剂作用后的摩擦表面发现了少量的Fe元素,并发现个别添加剂粒子和磨损粒子在铝锡合金表面的镶嵌和沉积,添加剂提高了其承载能力。     

超细蛇纹石粉体改善润滑油摩擦磨损性能的研究

采用行星式高能球磨机制得平均粒径为0.22μm的超细蛇纹石粉,在四球摩擦磨损试验机上研究了超细蛇纹石粉加入量及载荷对润滑油减摩抗磨性能的影响。结果表明,添加超细蛇纹石粉对提高润滑油的减摩抗磨性能有显著的作用,超细蛇纹石粉含量为0.3%时,其摩擦因数减小26.2%,磨斑直径降低19.8%;超细蛇纹石粉润滑油在高载荷下具有很好的减摩性能。钢球表面磨斑能谱分析表明,磨斑表面有超细蛇纹石粉修复镀层产生。     

纳米Sn粒子的制备及其作润滑油添加剂的摩擦学性能研究

用化学还原法制备了表面经油酸修饰的纳米Sn粒子,并在透射电镜(TEM)下观测到所制备的纳米Sn粒子呈球形、平均粒径为20 nm。在MSR-10D四球摩擦磨损试验机上考察了纳米Sn粒子作为CF-4 15W/40润滑油添加剂的摩擦学性能,并在扫描电子显微镜(SEM)和能谱分析仪(EDS)上对钢球磨斑表面进行了形貌观测和表层成分分析。试验结果表明,纳米Sn粒子作为润滑油添加剂具有一定的减摩性能和较好的抗磨性能,当所添加的体积分数仅为0.1%时,添加纳米Sn粒子润滑油的摩擦力比基础油降低了16.64%,其磨斑直径比基础油减小了38.4%。分析认为,纳米Sn粒子通过隔离摩擦表面而改善了润滑油的减摩抗磨性能。     

几种微粒经纳米化后的润滑性变化

将微米级石墨、铜Cu、铝Al、锡Sn加于000#脂中进行超细纳米化加工制成纳米润滑脂。用四球机分别考察了制备的纳米润滑脂和其它微米级固体润滑剂(PTFE、MoS2、SiO2)以及含常用化学反应型抗磨极压剂(MoDTC、ZDTP和硫化异丁烯)的脂的摩擦性能。结果表明,经纳米化后Cu、Al、Sn和石墨的减摩效果和抗磨性比含微米级的相应脂都有了很大提高。承载能力试验表明只有纳米Sn承载能力比研磨前明显提高,因此纳米Sn显现最好综合摩擦特性,其减摩性、抗磨性、承载能力稍逊于化学反应型MoDTC。电镜TEM分析表明,含微粒润滑剂的摩擦特性同粒子材料的硬度、熔点有关,其中Sn较软,熔点低(232℃),延展性好,所以润滑性最好。Auger能谱分析表明,纳米粒子的润滑作用是由于它们在摩擦面上形成了物理沉积层。     

环保型纳米润滑材料的研究

从环保角度,选择了两种纳米材料作为润滑油抗磨、极压添加剂。介绍了纳米材料的制备,根据亲水亲油平衡值(HLB)选择了合适的表面活性剂,并将其加入到含有单种或两种复合纳米粒子的润滑油中进行表面改性,采用四球摩擦磨损试验机测定含纳米粒子的润滑油的摩擦学性能。结果表明:含纳米粒子的润滑油具有良好的抗磨减摩性能,且含复合纳米粒子的润滑材料的抗磨减摩性能比单种纳米粒子的润滑材料的抗磨减摩性能好。这里还探讨了纳米润滑材料的抗磨减摩机理。     

纳米陶瓷润滑油添加剂润滑机制研究

研究了纳米陶瓷润滑油添加剂的润滑机制.采用四球试验机考察了纳米陶瓷润滑油的抗磨性能和极压性能,利用NT场致发射扫描式电子显微镜、高分辨率扫描电子显微镜、X射线光电子能谱仪,观察了磨损表面的纳米粒子形貌,分析了磨损表面的形貌及表面元素成分.结果表明,纳米陶瓷润滑油润滑时,摩擦表面的磨斑很光滑,磨斑表面有Si3N4存在;纳米陶瓷添加剂具有很好的抗磨和极压性能;纳米陶瓷粒子具有"滚珠效应".     

油酸修饰纳米铜粉的摩擦学性能研究

采用了液相还原修饰法,在溶液中直接合成了油酸表面修饰的纳米Cu微粒。在四球摩擦擦损试验机上考察了其作为润滑油添加剂在45#变压器油中的摩擦学性能。结果表明:制备的纳米Cu微粒粒径在20~50 nm之间,且分布均匀;较低载荷下,纳米Cu微粒对油品的润滑性能没有影响,当载荷达到600 N以上时,其抗磨减摩性能有显著的提高。XPS分析表明,较高载荷下的摩擦表面形成了单质铜和油酸的沉积膜,正是这层沉积膜的作用使得纳米Cu微粒具有优异的抗磨减摩性能。     

纳米级金属粉对润滑油摩擦磨损性能的影响

在ＭＨＫ－５００型环块摩擦磨损试验机上,研究了纳米级金属粉加入到矿物油中的润滑性能,结果表明, 加有纳米级金属粉的润滑油表现出优良的抗磨性能,三乙醇胺与铜粉复配具有复合效应。     

Enhancing AW/EP property of lubricant oil by adding nano Al/Sn particles

This paper presents results of experiments to enhance antiwear/extreme pressure (AW/EP) properties of a lubricant oil by adding metal nano particles. In this experiment, Al, Sn and Al + Sn nano-particles were selected as trial additives. The AW and EP properties were evaluated on Four-Ball test machine, while the feature and composition of the wear scar surface were investigated by scan electron microscope (SEM) and energy dispersion spectrum (EDS). The test results show that the AW and EP performance can be improved within a wide load range by adding Al + Sn nanoparticles. Analysis of the enhancement mechanism has also been conducted in this experiment and presented in this paper. It is found that nano-Sn particles can be deposited on the friction surface when the pressure was moderate and act as AW additive. It is also found that the nano-Al particles can be deposited under the condition of high load pressure and act as EP additive. Thus, the AW and EP properties of tested lubricant oil have been improved at the same time due to adding both Al and Sn.     

An ESCA study of the effectiveness of antiwear and extreme‐pressure additives based on substituted phosphorodithioate derivatives,and a comparison with ZDDP

Ashless substituted dithiophosphoric acid derivatives (ADPs) are a new generation of multifunctional additives with promising antiwear (AW) and extreme‐pressure (EP) characteristics. Three such additives synthesised in the authors' laboratory have been evaluated for their AW and EP properties by standard four‐ball friction and wear tests. The friction‐reducing properties of these additives were compared with those of a commercial zinc dialkyldithiophosphate (ZDDP). It was found that the phosphorodithioate compounds studied here possessed excellent AW/EP properties. Their AW characteristics were found to be comparable to those of ZDDP at low loads. However, at higher loads they show inferior AW characteristics in comparison to ZDDP. Nevertheless, ADP derived from cashew nut shell oil had a higher load‐carrying capacity than ZDDP. The mechanism of the AW and EP behaviour exhibited by the different additives was investigated using X‐ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and scanning electron microscopy (SEM) of the worn surfaces formed during friction. XPS and AES analyses of the worn surfaces reveal that the tribochemical film formed on the ADP‐tested surfaces consisted mainly of metal phosphates and only a small amount of metal sulphides, even though the ADPs contained twice the number of sulphur atoms than phosphorus atoms. The ZDDP‐tested surface showed a mixture of metal sulphides and metal phosphates. Alkylamino substitution appeared to have no significant effect on the AW/EP properties of the additive. XPS and AES analyses also revealed that the tribochemical film formed on an ADP‐tested surface was thicker than that present on the ZDDP‐tested surface at low loads, whereas at higher loads the reverse was true. The higher weld load obtained for the blend containing cashew nut shell oil‐derived ADP is attributed to the thicker adsorbed reaction film formed on the surface due to the long alkyl groups present in the original additive structure. Short‐chain alkyl groups, however, form only a thin adsorbed layer, which may get rubbed off during the friction at high load. The low sulphide formation on ADP‐tested surfaces was attributed to the absence of any metal atom in the additive, which would help in the formation of metal sulphides during tribofragmentation and further tribochemical reactions.     

Tribological behavior of vegetable oil-based lubricants with nanoparticles of oxides in boundary lubrication conditions

This work studied the development of vegetable based lubricants and the addition of oxides nanoparticles (ZnO and CuO) as additive for extreme pressure (EP), exploring the EP and oil base influence in tribological behavior. The results showed that with the addition of nanoparticles to conventional lubricant, the tribological properties can be significantly improved. A smoother and more compact tribofilm has formed on the worn surface, which is responsible for the further reduced friction and wear. Also, lubricants developed from modified vegetable oil can replace mineral oil, improving the tribological and environmental characteristics. However, the addition of nanoparticles in vegetable base lubricants is not beneficial to wear reduction.     

Effect of the type and concentration of lubricating additives on the antiwear and extreme pressure properties and rolling fatigue life of a four‐ball tribosystem

Tests were performed on two different four‐ball testers. The first was used to determine antiwear (AW) and extreme pressure (EP) properties at sliding friction. The second was used to assess the surface fatigue (pitting) life at rolling movement. Lubricating oils of various chemical compositions were tested. A base mineral oil was blended with two different commercial packages of lubricating additives of AW and EP types. The AW additives contained ZDDP and were blended with the base oil at 0.2 and 3wt %. The EP additives were organic compounds of sulphur and phosphorus, blended with the base oil at 1 and 10wt %. It is shown that AW additives not only improve AW and EP properties but also — at 0.2% — are beneficial for the fatigue life. An increase in the concentration of AW additives leads to an improvement of AW and EP properties but — for one of the packages — reduces the fatigue life. EP additives — at 1% concentration — significantly improve EP properties, and to a lesser extent AW properties. Such a concentration of EP additives has no influence on the fatigue life. An increase in the concentration of EP additives leads to a further improvement of EP and AW properties. However, this is accompanied by a considerable decrease in the fatigue life. By using a scanning electron microscope and energy dispersive spectrometer for analysis of the worn surface, mechanisms of action of various lubricating additives under different friction conditions were identified. Copyright © 2006 John Wiley & Sons, Ltd.     

Tribological evaluation of coconut oil as an environment-friendly lubricant

Increased concerns about environmental damage caused by mineral oil based lubricants, has created a growing worldwide trend of promoting vegetable oil as base oil for automobile lubricants. Coconut oil, which is abundantly available in southern states of India, is reportedly being widely used as two-stroke engine lubricant (2T oil) by autorikshaw¹ drivers. A survey among the users of coconut oil as 2T oil brought forth complaints of increased engine wear. This paper presents tribological properties of coconut oil evaluated using a four-ball tester and a test rig to test the wear on two stroke engines. The influence of an antiwear/extreme pressure (AW/EP) additive on the tribological performance of coconut oil was also evaluated experimentally. The addition of the AW/EP additive has brought about considerable reduction in wear with coconut oil as 2T oil.     

A method for testing lubricants under conditions of scuffing. Part II. The anti-seizure action of lubricating oils

This paper describes an investigation of lubricating oils under extreme-pressure (EP) conditions in a specially modified four-ball tester. A new test method developed at the Tribology Department of ITeE described in Part I of this paper was used. In this, during a test run, the applied load is increased continuously and the friction torque is measured. A sudden increase in the friction torque indicates the collapse of the lubricating film — where scuffing is initiated. The load at this moment is called the scuffing load. If the load is increased further, it is possible to observe scuffing propagation until seizure occurs, i.e., a defined, maximum friction torque is reached. Thus, scuffing is considered as a process leading to seizure. Using the method, tribological experiments were performed employing various lubricating oils consisting of viscosity-index improvers and antiwear (AW) and extreme-pressure (EP) additives added to a base oil. Mineral and synthetic base oils of different kinematic viscosities were used. The aim was to investigate the influence of such lubricants on scuffing initiation and propagation with the present methodology. In Part I it was shown that scuffing initiation depends strongly on the kinematic viscosity of the lubricant; the higher the viscosity, the greater the scuffing load. The presence of AW and EP additives in the lubricant increases the scuffing load significantly. It was also shown that the kinematic viscosity of the lubricant oils has no effect on scuffing propagation. However, scuffing propagation is significantly mitigated by AW and, to a greater extent, by EP additives. The results of surface analyses show the decisive nature of the chemical reactions of AW and EP additives with the steel ball surface under scuffing conditions, as well as the possible diffusion of sulphur and phosphorus. Chemical reactions and diffusion lead to the creation of an inorganic surface layer (probably iron sulphide), the good anti-seizure properties of which limit scuffing propagation.     

Tribological behaviour of antiwear additives used in hydraulic applications: Synergistic or antagonistic with other surface-active additives?

This paper examines the friction and antiwear (AW) properties using SRV (Schwing–Reib–Verschleiss) tribometer and film-forming properties using atomic force microscope (AFM) of one simple model formulation containing solely AW additive and seven oils containing mixture of additives including three zinc-based packages (ZP), ZP with additional AW additives, ZP with extreme pressure (EP) additives, ZP with viscosity index improvers (VII) and one zinc-free ashless package in steel/steel contacts. VII-containing oil show lower boundary and mixed friction coefficients than the other oils. Although all AW additive-containing oils formed tribofilms, AW properties of ZPs appear to be affected antagonistically by EP additives while synergistically by VII. Zn-free additives investigated in this study show higher wear than ZPs.     

EP/AW performance evaluation of some zinc alkyl/dialkyl/alkylaryl‐dithiocarbamates in four‐ball tests

Tribochemistry, the chemistry of interacting surfaces under the influence of a lubricant, helps in the appropriate selection of suitable lubricant additives for specific uses. Modern lubricants are usually formulated from a range of petroleum base oils or synthetic fluids incorporating a variety of chemical additives for performance enhancement. Extreme‐pressure (EP) and anti‐wear (AW) additives are used extensively in lubricants for hypoid gears and metal cutting and forming operations to reduce wear, modify friction, and prevent scuffing of moving metallic parts. The present paper includes the synthesis and the evaluation of the tribological properties of 0.5% (w/v) solutions of some zinc bis‐(alkyl/dialkyl/alkylaryldithiocarbamates) in paraffin oil using 12.7 mm diameter steel bearing ball specimens in four‐ball tests. All the synthesised zinc dithiocarbamate additives in general, and zinc bis‐(morpholinodithio‐carbamate) (A₄) in particular, exhibited good AW, EP, and friction‐reducing properties. Additive A₄ especially gave low values of wear‐scar diameter and coefficient of friction at higher loads and higher values of load wear index and flash temperature parameter during EP tests (ASTM D 2783) and afforded lower values of wear‐scar diameter in a one‐hour wear test (ASTM D 2266–67). The surface topography of the wear‐scar matrix of the used ball specimens was investigated by scanning electron microscopy.     

Effects of extreme pressure and anti-wear additives on surface topography and tool wear during MQCL turning of AISI 1045 steel

The paper presents an original study of the influence of extreme pressure and anti-wear (EP/AW) additives on the surface topography of double-phase steel during turning with different cooling media and variable flow rates. The obtained surface topographies were compared using frequency and fractal analyses for dry, minimum quantity cooling lubrication (MQCL), and MQCL + EP/AW methods. Results showed that the addition of phosphate ester-based additives to an active medium caused the formation of tribofilm on the tool-chip interface and thus a change in the lubricating properties by reducing friction. The tool wear and the formation of the thin-layered tribofilm were also incorporated. The application of the MQCL method with the EP/AW additives led to a decrease in particular surface topography parameters from 8 % to 38 % in comparison with the effects of dry cutting and from 6 % to 35 % in comparison with the effects of machining under MQCL conditions. An exception was the result obtained for the surface roughness height parameter Sp, which was higher than that obtained after the MQCL + EP/AW process for the lowest investigated feed per revolution f = 0.1 mm/rev. This observation was correlated with the uneven formation of the tribofilm on the machined surface. The phosphate ester-based additive used in the MQCL + EP/AW method contributed to achieving tool wear that was less than that obtained by the processes conducted under dry and MQCL conditions.     

复合纳米润滑油添加剂的制备及其摩擦学性能

采用超声机械法制备了经过化学修饰的纳米Al2O3、SiO2、MgO复合粉体,使其稳定地分散在基础油中,考察了油的摩擦学性能,用扫描电镜(SEM)、X射线能量色谱仪(EDS)分析了摩擦副表面的形貌和组成,同时初步分析了添加剂的润滑机理.结果表明:所制备的复合纳米粉体为平均粒径58 nm的球形微粒,在润滑油中具有较好的抗磨减摩能力,表现出良好的自修复效果.