石墨烯/MoS2复合涂层多环境下的摩擦学性能

以MoS2作为润滑剂,以石墨烯(GE)作为润滑添加剂,采用喷涂法在GCr15钢样片表面制备不同含量的GE/MoS2复合涂层。利用HSR-2M型高速往复式摩擦磨损试验机测试涂层在干摩擦及海水环境中的摩擦磨损性能,并分析了磨痕形貌及磨损机制。结果表明:添加适量石墨烯可明显改善MoS2涂层的摩擦磨损性能,且海水环境中涂层的摩擦因数、磨损率均低于干摩擦;在干摩擦和海水环境下,随着石墨烯含量的增加,GE/MoS2复合涂层的摩擦因数和磨损量均呈现先下降后上升的趋势,当石墨烯质量分数为0.8%时,摩擦磨损性能最优。干摩擦下MoS2涂层的磨损机制为疲劳磨损、黏着磨损和磨粒磨损,GE/MoS2复合涂层主要为磨粒磨损;而在海水环境下几种涂层均仅出现磨粒磨损。     

不同介质下CrN_X薄膜的摩擦学特性研究

采用电弧离子镀技术在45#钢衬底表面沉积了CrNX薄膜.用显微硬度计测试了薄膜的硬度,用X射线衍射仪分析了薄膜的相结构,用球-盘式摩擦磨损试验机评价了在不同介质条件下(干摩擦、水润滑、油润滑)CrNX薄膜的摩擦学性能,用表面轮廓仪测试了磨痕处的磨痕轮廓,用扫描电镜(SEM)观察了薄膜磨痕形貌.结果表明,相对于干摩擦,水润滑和油润滑条件下,CrNX薄膜的摩擦因数和磨痕深度都有明显降低的趋势.干摩擦条件下薄膜主要表现为磨粒磨损;水润滑条件下,主要表现为腐蚀磨损;油润滑条件下由于油膜在两摩擦表面的吸附,薄膜几乎无磨损.     

射频磁控溅射法制备二硫化钼薄膜

用射频磁控溅射法在GCr15钢表面制得了MoS2薄膜。通过扫描电镜、摩擦磨损以及划痕试验仪研究了工艺参数对薄膜形貌和性能的影响。结果表明:采用射频溅射法,在功率200W、工作气压3Pa、时间2h条件下制备的MoS2薄膜性能最佳;沉积过程中沉积原子从衬底表面获得足够的扩散能量时薄膜按层状模式生长,扩散能量不足时薄膜按层岛复合模式生长;MoS2薄膜摩擦因数低,具有优良的摩擦学特性。     

溅射沉积MoS_2/Sb_2O_3复合润滑膜的摩擦磨损过程与失效分析

采用UMT-2型球-盘摩擦磨损试验机研究溅射沉积MoS2/Sb2O3复合固体润滑膜的滑动摩擦磨损寿命,采用显微镜分析球-盘摩擦副在不同磨损阶段的磨损形貌与磨损状况,并对磨痕位置S、Mo元素进行XPS分析。结果表明:在摩擦磨损寿命试验过程中,摩擦副的接触方式最开始的点接触逐步过渡到面接触;MoS2固体润滑膜对滑动摩擦副的延寿作用是基底材料表面的有效厚度润滑膜及MoS2对摩擦偶件(钢球)的转移;机械磨损的剪切剥离效应是润滑失效的主要原因,MoS2的氧化在一定程度上加剧了润滑失效的进程。     

碳离子注入对硅片微动磨损性能的影响

对单晶硅片〈111〉进行了注入剂量为2×10~(16) ions·cm~(-2)、注入能量分别为60 keV和80 keV的碳离子注入,采用X射线衍射仪研究了碳离子注入前后硅片晶体结构的变化,采用UMT-2型微动摩擦试验机进行了微动摩擦磨损试验,采用超高精度三维形貌仪测量了硅片的磨痕深度,采用S-3000N型扫描电子显微镜分析了硅片的磨损形貌及磨损机理。结果表明:碳离子注入改变了硅片的晶体结构,使晶体无序化;硅片的摩擦因数和磨痕深度均随着载荷、微动振幅的增加而增大;碳离子注入后硅片的减摩效果和抗磨性能得到明显改善,当载荷达到一定值后,随着时间的延长,碳离子注入层逐渐被磨破,摩擦因数迅速增大;注入能量为60 keV硅片的减摩抗磨性能较好;碳离子注入前后硅片的磨痕均呈椭圆形,注入后磨痕面积小且表面损伤程度较轻,磨损机制以磨粒磨损为主。     

摩擦磨损试验磨痕检测新方法的研究

介绍了一种基于图像处理技术的摩擦磨损试验磨痕测量新方法,即磨损量的数字图像测量法.该方法与传统的磨损量测量方法(如:称重法、测量直径法、表面形貌法、光干涉法等)相比较,能在一定程度上实现磨痕的在机检测和磨损量的快速计算,从而达到磨痕测量手段的非接触、快速及自动化.     

Mo/MoS2-Pb-PbS复合薄膜的真空摩擦学行为研究

多组元复合是提高润滑薄膜苛刻工况下服役性能的有效方法。采用“射频磁控溅射+低温离子渗硫”复合工艺,在9Cr18轴承钢表面制备了Mo/MoS2-Pb-PbS复合固体润滑薄膜;利用自主研制的MSTS-1型多功能真空摩擦磨损试验机研究了8×10-5 Pa真空条件下法向载荷和滑动速率对Mo/MoS2-Pb-PbS复合薄膜摩擦学性能的影响。结果表明,在所设定的5种滑动速率下,Mo/MoS2-Pb-PbS薄膜的摩擦因数随滑动速率的增大而缓慢减小,磨损率经一定周次的跑合后逐渐趋于稳定;在不同的法向载荷下,随着载荷的增大,薄膜的摩擦因数呈近似抛物线增大,变化范围在0.03～0.24之间;薄膜表面的磨痕宽度同样随着载荷的增大而增大。     

碳黑对MoS2纳米润滑油的摩擦磨损性能影响

以PAO6润滑油为基础油,MoS2为纳米添加剂,制备质量分数为0.02％的纳米润滑油.通过自主研制的缸套-活塞环摩擦实验台,对添加不同浓度碳黑颗粒的MoS2纳米添纳米润滑油的摩擦学性能进行研究;通过电子扫描显微镜(SEM)对缸套表面磨痕进行观察.结果表明,低浓度的碳黑(0.01wt％和0.1wt％)可以进一步改善纳米润滑油的摩擦系数(降低7.7％和1.5％);任何浓度的碳黑都会导致纳米润滑油的抗磨性能恶化,甚至比未添加任何纳米颗粒的基础油的磨损量高约5～7倍;缸套的磨痕分析表明,碳黑通过破坏MoS2纳米润滑油在摩擦副表面形成抗磨损膜的稳定性,加剧零件磨损.     

在往复滑动条件下摩擦噪声发生时磨痕形貌的观察

为了进一步认识在有摩擦噪声期间磨痕形貌与噪声之间的关系，采用两种常用的铁路车辆制动闸瓦材料进行摩擦噪声试验。试验中测取了不同循环次数时摩擦振动三维加速度、噪声声压等动态信号，并提取了相应的磨痕形貌。通过对磨痕形貌的激光共焦扫描显微镜(OLS)、SEM及光学显微镜观察，研究了噪声出现区域的形貌变化。研究结果显示磨痕上有摩擦噪声区域的形貌与无摩擦噪声区域的形貌有一定差别。     

MoS2-Zr复合薄膜的结构及摩擦特性研究

采用中频磁控溅射技术及多弧离子镀相结合的复合镀膜工艺,在硬质合金YT14基体上制备了MoS2-Zr复合薄膜.观察了MoS2-Zr复合薄膜表面及截面形貌,测试薄膜的厚度、结合力和显微硬度,进行摩擦磨损试验,并分析薄膜的摩擦磨损机理.结果表明,制备的MoS2-Zr复合薄膜结构致密,性能明显优于MoS2薄膜;厚度由2.0μm提高到2.5μm,结合力由28N提高到60N,显微硬度由280HV提高到900HV.MoS2-Zr复合薄膜的摩擦特性明显优于MoS2薄膜.MoS2薄膜磨损初始阶段摩擦因数只有0.06,在磨程15m后摩擦因数升到0.4.而MoS2-Zr复合薄膜的摩擦因数磨损初始阶段可达0.08,直到磨程60m摩擦因数达到0.4.薄膜的摩擦磨损过程主要是薄膜的剥落和转移的过程,复合薄膜由于结合力和硬度的提高,能够延缓薄膜的剥落及转移,提高薄膜的摩擦特性,延长薄膜的减摩润滑时间.     

Friction and wear of fullerene-like WS<Subscript>2</Subscript> under severe contact conditions: friction of ceramic materials

Recently, the behavior of inorganic fullerene-like (IF) WS₂ nanoparticles in the interface of steel-on-steel pair has been analyzed. It was shown that originally when the gap between the contact surfaces is smaller than the size of the IF nanoparticles, there is no effect of the nanoparticles on the friction force. During the test stiff IF nanoparticles can plough the surface of hard steel samples and penetrate into the interface under friction. Molecular sheets of WS₂ from the delaminated IF nanoparticles, which reside in the valleys of the rough surfaces cover the contact spots and thus decrease the number of adhered spots at the transition to seizure. The goal of the present work was to study the behavior of IF nanoparticles in the interface of ceramic surfaces. The friction tests were performed using a ball-on-flat device. A silicon nitride ball was slid against an alumina flat with maximum contact pressure close to 2 GPa. SEM, TEM and AFM techniques have been used in order to assess the behavior of IF nanoparticles in the interface. The behavior of IF nanoparticles in the much harder ceramic interfaces was found to be appreciably different from the steel pair. The pristine IF nanoparticles are damaged in the inlet of the contact during the first few cycles and thin shells of broken nanoparticles gradually cover the middle range of the contact surface. Different modes of deformation and destruction of the IF nanoparticles are exhibited when going from the middle to edge area of the contact. While aggregates of the pristine nanoparticles are formed at the edge of the contact, thin shells of broken IF nanoparticles are observed in the middle area where contact pressure is maximum. Mechanical stability and damage of IF nanoparticles in the ceramic interface are discussed.     

An Investigation on the Reduced Ability of IF-MoS2 Nanoparticles to Reduce Friction and Wear in the Presence of Dispersants

Inorganic fullerene-like molybdenum disulfide (IF-MoS₂) nanoparticles are known to exhibit great friction and wear-reducing abilities in severe boundary lubrication regimes, when added to a base oil alone. Their use in fully formulated lubricants was investigated in this study, and the tribological benefits attributed to the IF-MoS₂ nanoparticles were found to be lost in the presence of dispersants. Various experimental techniques were used on three reference oils (base oil containing only IF-MoS_2, only dispersants and both IF-MoS₂ and dispersants) in order to understand the effect of succinimide-based dispersants on the three phases needed for effective nanoparticle-based lubrication, namely (1) the passing of the nanoparticles through the contact (2) the exfoliation of the IF-MoS₂ inside the contact and (3) the adhesion of the released MoS₂ platelets on the friction surfaces. The dispersants were shown to improve the dispersion of the nanoparticles in the oil by reducing their agglomeration, but prevented the adhesion of a low-friction MoS₂ tribofilm on the steel surfaces. In-situ contact visualization revealed that the well-dispersed nanoparticles passed through the contact and exfoliated nanoparticles were observed after tribological testing. These results imply that nanoparticle dispersion itself does not seem to be an issue concerning nanoparticle effectiveness, even though the reduced agglomerate size and inertia may have affected nanoparticle flow near the contact, as well as entrapment and exfoliation conditions inside the contact. The use of succinimide-based dispersants may, however, have affected the tribochemistry of the contact, by an excessive adsorption on the steel surfaces and/or by encapsulating the released MoS₂ platelets, preventing tribofilm adhesion. A balance was finally found between nanoparticle dispersion and friction reduction, but for very low dispersant concentrations and after a running-in period. The role of succinimide-based dispersants and their effect on nanoparticle lubrication were discussed in the light of these results.     

A new way to feed nanoparticles to friction interfaces

Fullerene-like WS₂ (MoS₂) nanoparticles (IF) have been studied in the past. Their efficacy as additives for lubrication fluids has been demonstrated. It was shown that the IF nanoparticles are usually delaminated in the inlet of the smooth contact. Thin sheets of broken IF nanoparticles can be entrapped between the rubbed surfaces and thus favorably affect the friction and the wear. Friction pairs at real mechanical macrosystems are often subjected to friction-induced vibrations. It was shown that the mechanical excitations can improve the supplying and preservation of fluid lubricant film in the interface. It can be hypothesized that under vibrations in a definite range of frequencies and amplitudes, the probability for small IF aggregates to be entrapped into the interface is increased. The main goal of this work was to study the effect of artificial mechanical excitations on the friction and wear of contact pairs rubbed with nanoparticles. In order to avoid friction-induced excitations, a new ball-on-flat friction device was developed. The frequency and the amplitude of the ball were varied using a motion of miniature micromotor attached to the ball holder. The behavior of IF nanoparticles in friction tests with and without external mechanical excitations was compared with the tribological behavior of the contact pair lubricated with pure paraffin oil. It was found that the external mechanical excitation of the mechanical parts rubbed with nanoparticles allows a penetration of these nanoparticles into interface. This effect leads to a remarkable shortening of the run-in period and improves the tribological properties of contact pairs. From the present results it may be anticipated that the accidental friction-induced vibrations, which are determined by the stiffness and damping force of the device, lead to preferential penetration of the IF nanoparticles into the contact area, affecting thereby the tribological behavior of the interface.     

Effect of electrochemical and mechanical parameters on the lubrication behaviour of Al2O3 nanoparticles in aqueous suspensions

The effect of alumina nanoparticles suspended in an aqueous acetate buffer solution on the tribocorrosion behaviour of a 316L steel/alumina sliding contact was investigated using a reciprocating wear test rig equipped with an electrochemical cell. Through the addition of 10% volume of alumina nanoparticles to an acetate buffer solution it was possible to reduce the coefficient of friction by a factor of 2 and the stainless steel wear by a factor of 10 and this over a range of electrochemical and mechanical conditions. The presence of alumina particles caused a significant wear on the alumina counter part. The lubricating behaviour of the suspension was comparable to a commercial oil in water emulsion used for metal cutting. The lubricating effect was attributed to a third body formed by nanoparticles trapped within the contact. The agglomeration state of the alumina particles and their size were found to play a critical role.     

Real Time TEM Imaging of Compression and Shear of Single Fullerene-Like MoS2 Nanoparticle

The deformation and degradation behavior of single inorganic fullerenes nanoparticles of MoS₂ under compression and shear has been observed in real time using a high-resolution transmission electron microscope equipped with a nanoindentation holder. The MoS₂ nanoparticles were compressed using a nanoindenter and a truncated diamond tip. For the first time, real time imaging of the deformation of individual nanoparticles clearly shows first orientation changes in the particle shape during loading process followed by a large deformation and the exfoliation of the outer sheets of the fullerene nested structure. Exfoliation was observed for a contact pressure estimated at 1 GPa. Additional sliding tests performed with the nanoindenter gave evidence for a rolling process for lower contact pressures up to 100 MPa.     

On the Efficacy of IF–WS<Subscript>2</Subscript> Nanoparticles as Solid Lubricant: The Effect of the Loading Scheme

Fullerene-like WS₂ (MoS₂) nanoparticles (IF) have been studied in the past as solid lubricants. Using the tribological ball-on-flat experiments, it was shown that the size of the aggregates and their distribution determine the penetration and entrapping of the IF nanoparticles at the interface. It is expected that the wedge clearance at the inlet of the contact, i.e., the oblique-angle entrance to the contact zone between the two mating tribological surfaces, as well as the average surface roughness, can limit the supply of the lubricant into the interface in, e.g., the block-on-ring experiment. In the present series of experiments, the Stribeck curve was designed first using a linear loading scheme and pure oil. It was concluded that a wedge clearance (oblique-angle) in the inlet of the contact zone leads to entrapment of the IF nanoparticles and their compaction, which hamper the supply of the fluid lubricant into the interface. A ball-on-flat and flat block-on-ring friction devices with wedge clearance in the inlet of the contact can distort the efficacy of IF. Procedures for improving the supply of the IF nanoparticles to the contact zone and improving thereby their efficacy are considered.     

Tribological behaviour of MoS2 and inorganic fullerene-like WS2 nanoparticles under boundary and mixed lubrication regimes

Abstract

For several years different types of nanoparticles have been considered and studied as potential friction modifying lubricant additives. Some nanoparticles can reduce the friction coefficient by 30–70%, depending on the base oil and the experimental conditions. In the present study, an experimental analysis on tribological properties of inorganic fullerene-like metal dichalcogenides was performed in comparison with MoS₂ 2H layered structures. Tribological tests were carried out on a pin on disc tribometer in ambient air. Several contact conditions are analysed in order to realise boundary and mixed lubrication regimes. The experimental study was performed on a mineral base oil, and particle concentration effects were analysed. Antifriction properties were evaluated by measuring the friction coefficient and are presented as generalised Stribeck diagrams. Inorganic fullerene-like WS₂ and MoS₂ nanoparticles present interesting friction reduction properties when tested in boundary and mixed lubrication.     

Adhesive interaction measured between AFM probe and lung epithelial type II cells

The toxicity of inhaled nanoparticles entering the body through the lung is thought to be initially defined by the electrostatic and adhesive interaction of the particles with lung's wall. Here, we investigated the first step of the interaction of nanoparticles with lung epithelial cells using atomic force microscope (AFM) as a force apparatus. Nanoparticles were modeled by the apex of the AFM tip and the forces of interaction between the tip and the cell analyzed over time. The adhesive force and work of adhesion strongly increased for the first 100s of contact and then leveled out. During this time, the tip was penetrating deeply into the cell. It first crossed a stiff region of the cell and then entered a much more compliant cell region. The work of adhesion and its progression over time were not dependent on the load with which the tip was brought into contact with the cell. We conclude that the initial thermodynamic aspects and the time course of the uptake of nanoparticles by lung epithelial cells can be studied using our experimental approach. It is discussed how the potential health threat posed by nanoparticles of different size and surface characteristics can be evaluated using the method presented.     

Tribological properties of lubricant additives of Fe,Cu and Co nanoparticles

Tribological investigations were performed on mineral oil containing Fe, Cu and Co nanoparticles and their combinations. The tribological tests showed that each set of nanoparticles significantly reduced the friction coefficient and wear (up to 1.5 times) of friction pairs. The use of Cu nanoparticles provides the most effective reduction of friction and wear in each combination of nanoparticles. Surface analysis shows that the constituent elements of nanoparticles precipitated on the contact surface during the use of the oils with nano-additives. Different structures formed on the friction surface are observed in the contact zone and over the remainder of the ball surface. The SEM micrographs and EDX chemical analysis confirm the formation of a tribo-layer composed of the elements from the nanoparticles.     

Tribological behaviour of the self-lubricating polymers against steel 45 using different velocity

Tribological investigations of polymers and polymers with additives, using the SMC-2 device, were showed in the present work. Friction coefficient and contact temperature of sliding friction couples, containing different basic materials (PA66 and POM, with two types of nanoparticles, with five different concentrations 0; 0.5; 3; 7.5 and 15% by volume) were investigated. Self-lubricating polymers and steel friction couples have been tested without any lubrication. Research has shown, that the concentration of copper and graphite nanoparticles exceeding 5% leads to coagulation part, that reduces frictional properties of the base material.