Tribological Behavior of Nickel-Doped Diamond-Like Carbon Thin Films Prepared on Silicon Substrates via Magnetron Sputtering Deposition

In this study, nickel-doped diamond-like carbon (Ni-DLC) thin films were deposited on silicon (Si) substrates using a magnetron cosputtering system by varying DC power density applied to a Ni target at a fixed DC power density applied to a carbon (C) target. Their tribological properties were systematically investigated using a ball-on-disc microtribometer. The tribological results showed that increasing the DC power density applied to the Ni target more than 0.49 W/cm² significantly increased the friction and wear of the Ni-DLC films due to the degraded sp³-bonded cross-linking structures of the films. However, the much lower friction and wear of the Ni-DLC-coated Si samples than those of the uncoated Si sample implied that the Ni-DLC films could effectively prevent their Si substrates from wear. It could be concluded that the Ni-DLC films could be used as high wear-resistant coatings for micromold applications because their tribological properties were significantly influenced by the DC power density applied to the Ni target.     

Friction coefficient and wear rate of sputter-deposited thin films and plasma-sprayed thick coatings at high temperatures in room air

Silver, calcium fluoride (CaF_x with x = 1.85) and chromium-carbon (Cr₃C₂) thin films were deposited onto various tribological test specimens by sputtering. The friction properties of sputter-deposited Ag and CaF_x single layers as well as Ag/CaF_x multilayer films were determined by ball-on-disk tribological tests conducted in room air under various experimental conditions. The tribological properties (friction coefficient and wear rate) of sputter-deposited CaF_x films were also determined at 500°C by pin-on-disk tribological tests performed with pin specimens made of cobalt-based alloy (alacrite). Chromium-carbon films sputter-deposited onto alacrite disk and counterfaces were found to be of interest for reducing the formation of alacrite wear debris in the wear tracks; thus reduced friction coefficient and wear rate values were obtained. The friction behavior of sputter-deposited CaF_x/Cr₃C₂ thin bilayer structures and plasma-sprayed (PS) chromium carbide/Ag/BaF₂-CaF₂ eutectic composite coatings (PS-212 type coatings) was investigated by plane-on-plane tribological tests conducted in room air at 500°C and 700°C. The friction performance of solid lubricant thin bilayer films was compared with that of thick PS-212 type coatings similar to coatings developed by NASA.     

Steam and Water Lubrication of Quasicrystalline Films

The present work reports on the comparison of tribological properties between quasicrystalline and approximant films under steam and water lubrication. These films have nearly the same stoichiometry, which allows evaluation of the quasicrystalline structure as compared with the crystalline structure of the approximant. The goal of this study is to determine the effects crystal structure has on tribological properties and to study the general tribological behavior of quasicrystals in a steam and water environment. AlCuFe quasicrystals coatings were deposited by unbalanced magnetron sputtering. The test films were 10 m thick deposited on a 1inch diameter Al₂O₃ disk and a 1/4inch diameter Al₂O₃ ball. Data were collected under water and steam lubricated conditions. Friction coefficients and wear rates of quasicrystals and approximants were nearly indistinguishable. During water lubrication, quasicrystals act similar to ceramics where surface smoothing and hydrodynamic lift control the friction and wear properties. With steam-lubricated conditions, the friction and wear process is controlled by brittle fracture and third body abrasion. Generally, less than 5% difference in the friction and wear properties were observed between the icosahedral quasicrystal phase and the approximant phase.     

多元CrMoSiCN系列薄膜结构及摩擦学特性研究进展

从三元含Mo的Cr-Mo-N、Mo-Si-N、Mo-C-N薄膜到四元Cr-Mo-Si-N、Mo-Si-C-N薄膜,综述多元系列薄膜的结构、力学及摩擦学性能的研究进展;分析在不同气体压力、制备方法与参数、不同元素含量下薄膜结构的变化,阐述薄膜结构与其力学性能和摩擦学特性的关联。指出:多元Cr-Mo-Si-C-N系列薄膜结构、硬度、摩擦因数强烈受到薄膜中Mo、Si、C、N元素含量的影响,其中力学特性还与薄膜微结构紧密相关;薄膜的摩擦学特性与晶粒生长细化和作为润滑剂的无定形基质有关;在摩擦过程中发生的摩擦化学反应也有效地提高了薄膜的耐磨性。对于四元Cr-Mo-C-N和多元Cr-Mo-Si-C-N薄膜,建议进一步研究在水润滑与非润滑的不同条件下,例如在海水或者空气干摩擦环境下,是否由于薄膜结构组分的不同而有效地形成含Mo的氧化物的自润滑膜,以提高薄膜在更多场合下的适应性和减摩性。     

不同碳原子数及羟基数醇中Ti3SiC2/Si3N4摩擦副的摩擦学性能

Ti_3SiC_2和Si_3N_4等陶瓷材料是一种潜在的生物燃料发动机及功能性运动部件材料,为研究其在醇类生物燃料及润滑剂中的摩擦学性能,利用往复式摩擦试验机研究Ti_3SiC_2/Si_3N_4摩擦副在不同碳原子数直链醇(乙醇、丁醇、辛醇和十二醇)和不同羟基数醇(乙二醇和丙三醇)液体介质中的摩擦学性能。结果表明:Ti_3SiC_2/Si_3N_4在醇介质中的摩擦因数随碳原子数和羟基数的增加而减小,总体平均摩擦因数在0.06～0.11范围内变化,但丁醇中摩擦因数最高,为0.25;Ti_3SiC_2/Si_3N_4配副的磨损率均随碳原子数和羟基数的增加而减小,Ti_3SiC_2的磨损率在4.48×10~(-7)～9.33×10~(-9) mm~3/(N·m)范围内变化,Si_3N_4的磨损率在4.05×10~(-6)～2.91×10~(-7)mm~3/(N·m)之间变化,其中在辛醇和十二醇中几乎没有磨损。研究表明:在醇介质中Ti_3SiC_2/Si_3N_4摩擦副的摩擦状态属于边界润滑状态,摩擦界面微凸体和磨屑的犁沟效应是造成高摩擦的主要原因;摩擦化学反应是Ti_3SiC_2/Si_3N_4在醇介质中的摩擦行为的一个特点,摩擦化学磨损和磨粒磨损是材料磨损的主要机制;链长越长、羟基越多,醇的黏度越大,承载能力越强,犁沟效应和磨粒磨损降低,摩擦因数和磨损率也降低。     

Tribological Properties of Langmuir–Blodgett Films on Silicon Surface in Microscale Sliding Contact

Microtribological properties of Langmuir–Blodgett (LB) films transferred from behenic acid (BehA), 2,4-heneicosanedione (HD) and its copper complex ((HD)₂Cu) onto silicon surface were examined. To better understand the wear resistance performance of these LB monolayers, a comparison was made with a chemically grafted octadecyltrichlorosilane (OTS) monolayer. Auger electron spectroscopy (AES) was used for identification of the chemical composition of the monolayers, worn areas and counterpart surfaces. We observed that the studied LB films in microscale sliding contact exhibited stable friction properties comparable to OTS, and better wear performance than OTS at high contact pressure. The tribological properties of these LB monolayers were explained in terms of molecular packing density and molecular transfer to the counterpart surface. The relationship between the wear resistance of the studied LB films and the degree of molecular packing of the surfactants indicated that the wear properties of the LB films are strongly associated with the degree of molecular packing. We suggest that the steady low friction and high wear resistance of the BehA monolayer may partly be attributed to the transfer of the amphiphilic molecules to the counterpart surface in the contact region.     

Sulfate based coatings for use as high temperature lubricants

Films of CaSO₄, BaSO₄, and SrSO₄ were grown with the pulsed laser deposition technique. The high temperature lubricious properties of these films were evaluated and it was found that all three sulfates exhibited a low coefficient of friction (μ ≈ 0.15) at 600°C. X-ray diffraction studies showed the presence of carbonate crystal structures along with the sulfate crystal structures after testing. The carbonate crystal structure is composed of alternating planes of alkali earth atoms and carbonate ions. The layered structure of the carbonates may be important to the lubricating mechanism as the layered structure of the dichalcogenides contributes to their tribological properties. Various observations of the wear region suggest that the starting surface finish of the metal coupon plays a significant role in the tribological mechanism of these materials. Additional composite films containing CaSO₄ were grown with the plasma spray technique. The high temperature friction properties of these films were measured and compared to those of similar films containing CaF₂/BaF₂. Although both types of films exhibited low coefficients of friction at 600°C, analysis of the wear regions did not show the presence of CaSO₄ and CaF₂/BaF₂, respectively. Ca and/or Ba were present, though, suggesting that a new compound is formed in the wear track and that the sulfate and fluoride phases may not be providing the low friction in these composites. This revised version was published online in July 2006 with corrections to the Cover Date.     

Tribological properties of ultra-thin ionic liquid films on single-crystal silicon wafers with functionalized surfaces

Two kinds of room temperature ionic liquid (RTIL) films carrying vinyl and hydroxyl functional groups were prepared on single-crystal Si wafers by spin coating. The tribological properties of the RTIL films sliding against AISI-52100 steel ball and Si₃N₄ ball in a ball-on-plate configuration were investigated on a dynamic–static friction coefficient measurement apparatus, using perfluoropolyether (PFPE) film as a comparison. The tribological behaviors of the ionic liquid films sliding against the same counterparts at extended test durations were also evaluated using a universal UMT-2MT test rig. The morphologies of the wear tracks of the RTIL films and the counterparts were examined using a scanning electron microscope equipped with an energy-dispersive X-ray analyzer attachment. It was found that the tribological performances of the ionic liquid films were closely related to the chemical structures of the RTILs and the chemical characteristics of the substrate surfaces. The films of vinyl group functionalized ionic liquids on hydroxylated substrate and vinyl group modified substrate exhibited very good friction-reduction and wear-resistant properties. It was assumed that there were enough strong forces between the films and substrate in these cases, and the ionic liquid molecules maintained good flexibility simultaneously. The films on hydrogen-terminated and methyl-terminated substrate showed poor tribological performance, which could be related to the relatively weak forces between the films and substrates. Moreover, the films on hydroxylated substrate showed lower friction at higher sliding velocities, which was assumed to be governed by the more rapid adsorption of the ionic liquid molecules on the steel ball at a higher sliding velocity. In addition, the ionic liquid films also had excellent tribological properties as they slid against silicon nitride ball. Therefore, it was supposed that the ionic liquid films could be used as a kind of universal lubricant for various combinations of the frictional pair.     

Ag掺杂对TiO2纳米薄膜结构及摩擦学性能的影响

采用溶胶凝胶法在普通载玻片上制备了TiO2和Ag/TiO2纳米结构薄膜,利用X射线衍射仪(XRD)、X光电子能谱(XPS)、原子力显微镜(AFM)及UMT-2摩擦试验机,考察了Ag掺杂量对薄膜组成结构、表面形貌及摩擦学性能的影响。实验结果表明,Ag掺杂量对TiO2薄膜表面形貌和减摩抗磨性能产生重要影响,低掺杂时Ag自润滑性能对薄膜摩擦性能的增强作用占主导,而高掺杂时其对薄膜的影响主要表现为恶化表面,从而导致摩擦性能下降。本研究测试条件下,掺杂量为5.0%(摩尔分数)时具有最佳的耐磨寿命和最低的摩擦因数。     

Macro- and nanotribological properties of organosilane monolayers prepared by a chemical vapor adsorption method on silicon substrates

Organosilane monolayers are novel ultrathin films used to control the physicochemical properties, such as friction and wear, of solid surfaces. In this study, the authors prepared alkylsilane and fluoroalkylsilane monolayers with a series of chain lengths by a chemical vapor adsorption method. The monolayers tribological properties were investigated by lateral force microscope (LFM) and friction tester. LFM nanoscale measurements of tribological properties showed that alkylsilane monolayer gave lower lateral force than the Si substrate surface. The lateral force decreased as the length of the alkyl chain increased. On the macroscale, friction test revealed that the organosilane monolayers gave lower dynamic friction coefficients than the Si substrate surface in air at room temperature. The longer the alkyl chain, the greater the wear resistance of the organosilane monolayers. Friction experiments using tetradecane as a lubricant showed better tribological properties than were obtained in air. Furthermore, microscopically line-patterned two-component organosilane monolayers were prepared and their macroscopic friction behavior was investigated. Even though the height difference between the two-components was less than 1 nm, friction force anisotropy between the parallel and perpendicular directions against the line pattern was observed.     

Effect of Water Swelling on the Tribological Properties of PMMA Spin-Cast Film and Brush in Aqueous Environment

Due to their light weight, low corrosion and good tribological properties, polymer films have been widely studied in dry condition as well as recently in aqueous environment. Though the presence of water can further reduce the friction, it promotes the wear rate of the polymer films. As a remedy to decrease the wear rate of polymer films under aqueous condition, in this study, we used PMMA brush which is chemically anchored to a substrate and compared its friction and wear properties with those of conventional PMMA spin-cast film. Ellipsometry, contact angle measurements and atomic force microscopy are used to study the surface properties, e.g., wear mechanisms and wear depths of PMMA films. Under different sliding speeds and applied loads, PMMA brush showed lower friction than PMMA spin-cast film in aqueous. Moreover, it was shown that the swelling of water molecules is a dominant factor in determining the wear durability of PMMA films in which PMMA brush showed better wear performance than PMMA spin-cast film.     

Friction and Thermal Effects of Engineering Plastics Sliding Against Steel and DLN-Coated Counterfaces

Polymers are increasingly used in tribological applications, because of their self-lubricating ability, corrosion resistance and chemical compatibility. However, their performance depends strongly on the parameters of the total tribological system. Not only polymer characteristics, but also counterface properties become important because of their influence on friction and wear, on surface energy and on the thermal conductivity of the total system. Applying a Diamond-Like Nanocomposite (DLN) coating on a steel counterface can improve the tribological behaviour of the sliding couple under certain conditions. In the case of metal sliding against DLN, the high hardness and the wear resistance of the coating is advantageous for better tribological properties. However, for polymers sliding against DLN, the lower thermal conductivity of the DLN coating compared with a steel mating surface dominates friction and wear. In case of polyamides this results in worse tribological performance in contact with the DLN coating, because of polymer melting. In the case of more rigid polymers, such as, e.g., POM-H and PETP, lower coefficients of friction lead to lower frictional heat generation. In these cases, the thermal characteristics of the counterface are less important and the lower surface energy of the DLN coating is favourable for decreased adhesion between the polymer and the coating and consequently better tribological properties.     

Wear-Resistant PTFE/SiO2 Nanoparticle Composite Films

Polytetrafluoroethylene (PTFE) is a polymer that is well known for its exceptional tribological properties and, as such, it is commonly used to reduce the coefficient of friction between surfaces. In recent years it has also been established that by incorporating nanoparticle fillers in PTFE, it is possible to extend the polymer's life by reducing its wear rate. Although much study has been placed on bulk PTFE, very little study has been focused on thin films. This article demonstrates that SiO ₂ nanoparticles can be used as a filler to significantly reduce the wear of PTFE thin films while also maintaining a low coefficient of friction. The wear resistance and coefficient of friction of PTFE/SiO ₂ composite films on stainless steel substrates were tested using a linear reciprocating tribometer and compared to pure PTFE films and bare stainless steel to evaluate the benefit of incorporating the SiO ₂ filler in the film. The composite films showed a significant improvement in wear resistance when compared to pure PTFE films. The coefficient of friction for the composite film remained low and stable during a 50 g normal load friction test for a duration of approximately 300 cycles, whereas that of PTFE showed an increasing trend at onset. In addition, of 1.7 and 3.3 wt% SiO ₂ concentrations in solution, 3.3 wt% SiO ₂ showed better performance, with a much higher wear resistance than that of 1.7% SiO ₂ after being subjected to a 1,000-cycle abrasive wear test.     

Tribological properties of self-assembled monolayers on Au,SiOx and Si surfaces

Using interfacial force microscopy (IFM), the tribological properties of self-assembled monolayers (SAM) on Si surfaces produced by a new chemical strategy are investigated and compared to those of “classical” SAM systems, which include alkanethiols on Au and alkylsilanes on SiO_x. The new SAM films are prepared by depositing n-alkyl chains with OH-terminations onto Cl-terminated Si substrates. The chemical nature of the actual lubricating molecules, n-dodecyl, is kept constant in all three thin film systems for direct comparison and similarities and differences in tribological properties are observed. The adhesion strength is virtually identical for all three systems; however, frictional properties differ due to differences in film packing. Differences in the chemical bonds that attach the lubricant molecules to the substrate are also discussed as they influence variations in film wear and durability. It is demonstrated that the new SAM films are capable of controlling the friction and adhesion of Si surfaces equally well as the classical SAMs and are potentially more reproducible and more durable.     

Analysis of the tribological behaviour of polymer composite tool materials for sheet metal forming

Today's automotive industry shifts its focus on customised production, facing an increasing demand for medium and small batch production, where cost-effective manufacturability of sheet metal forming dies comes into the foreground. Filled polymers offer possibilities to fulfil such requirements in the ambit of prototype tools manufacturing or in small batch production of sheet metal components. This paper presents investigations dealing with tribological and tool design aspects of using polymeric materials for sheet metal forming purposes. Friction and wear behaviour of two polymer composites on sheet metal counterface materials have been investigated. A new testing method for wear evaluation of polymeric materials for sheet metal forming using a Strip Drawing Test facility is presented and discussed. A method to predict lifetime of polymeric stamping dies using the linear wear–distance relation W_l/s measured with the new testing method is also proposed. Significant improvements in friction and wear performance of polymer composites have been observed using sheet materials with structured surfaces. A theoretical model for abrasive friction and wear of polymer composites on sheet metal counterface material pairs has been developed, based on the results obtained by measurement of friction and wear.     

辐照对高分子材料基本性能及摩擦学特性影响的研究进展

随着空间高科技的发展,对高分子材料不断地提出更高的要求,除要求其具有良好的物理和力学性能外,还要求具有耐辐照性能。在总结了照对高分子材料基本性能及摩擦学牡性的影响的研究的同时,介绍了辐照分子材料摩磨损机理方面的初步结果。针对辐照高分子材料摩擦学研究现状,为深入研究辐照后高分子材料摩擦磨损性能变化的规律及高分子材料在辐照环境下的应用提供理论依据是很有意义的工作。     

Tribology of Unfilled and Filled Polymeric Surfaces in Refrigerant Environment for Compressor Applications

The current study examines the tribological performance of polymer/metal contacts in the presence of refrigerant versus ambient air under conditions simulating refrigeration compressors. Ten different polymers were employed as potential compressor bearing materials; four unfilled polymers and six blended polymers. All polymers were tested against cast iron samples of RMS roughness 0.3--0.5 μm and representative testing was performed against aluminum alloy disks. Experiments conducted in R-134A refrigerant exhibited slightly favorable friction and wear characteristics compared to experiments conducted in ambient air. Moreover, all blended polymers have superior tribological characteristics to unfilled polymers and metals. PEEK and polyimide in both unfilled and blended forms exhibit minimal wear and do not adversely affect the metal disks. This study also shows that although coherent, uniform films were not produced under compressor-like conditions, as evidenced by scanning electron microscopy and energy dispersive X-ray spectroscopy, the tested polymers still have favorable tribological properties and are good candidates for tribological contacts in refrigeration compressors.     

Friction and Wear Behaviors of Several Polymers Sliding Against GCr15 and 316 Steel Under the Lubrication of Sea Water

Ocean tribology, a new research field of tribology, is currently being established and developed. The tribological behaviors of polyether ether ketone (PEEK), poly(phenyl p-hydroxybenzoate) (PHBA), polyimide (PI), and perfluoroethylene propylene copolymer (FEP) sliding against GCr15 and 316 steel rings under the lubrication of sea water were studied and compared with that under the lubrication of pure water. The results show that the friction and wear behaviors of a polymer under the lubrication of aqueous medium are not only related to the properties of polymer itself, but also to the corrosive effect and lubricating effect of the medium. When a polymer slid against GCr15 steel under sea water lubrication, the friction coefficient and wear rate of polymer were much larger than that under pure water lubrication because of indirect corrosive wear. However, when sliding against corrosion-resistant 316 steel, polymers PEEK, FEP, and PI exhibited lower coefficients of friction and wear rates under sea water lubrication, this was attributed to better lubricating effect of sea water as a result of the deposition of CaCO₃ and Mg(OH)₂ on the counterface. On the contrary, the friction coefficient and wear rate of PHBA sliding against 316 steel under sea water lubrication were larger than that under pure water lubrication, which may be related to the properties of PHBA itself.     

V含量对TaVN薄膜微观结构与摩擦学性能的影响*

为探讨V元素改善TaN薄膜摩擦学性能的机制,利用磁控溅射仪在304不锈钢基体上和单晶Si片制备不同V含量的 TaVN薄膜。使用X射线衍射仪、扫描电镜、显微硬度计、表面综合性能测试仪表征和分析薄膜的结构及性能。结果表明：TaVN 薄膜为面心立方结构,不同V含量的TaVN薄膜均在（111）晶面呈现择优取向;随着V含量的增加,TaVN 薄膜（111）晶面出现向大角度偏移的现象;不同V含量的TaVN 薄膜在扫描电子显微镜下的表面光滑平整无孔隙,膜层与基体间界面清晰,截面呈明显的柱状晶结构;随着V含量的增加,TaVN 薄膜硬度先升高后降低,当TaV靶材中V原子分数为15%时,硬度最高;随着V含量的增加,摩擦因数降低,其原因是在摩擦的过程中,薄膜中的V元素氧化形成具有自润滑效果的Magnéli 相氧化物V2O5;随着V含量的增加,TaVN 薄膜磨损机制由磨粒磨损、黏着磨损和氧化磨损转变为磨粒磨损和氧化磨损。     

A comparative study on the microstructure and tribological properties of Si3N4 and TiN films produced by the IBED method

The tribological properties of Si₃N₄ and TiN thin films produced by ion beam enhanced deposition (IBED) were compared on a SRV friction and wear testing machine. The friction coefficient of all thin films shows a descending tendency with increase in load, and is lower than that of 52100 steel. All the IBED films show a much better wear resistance than 52100 steel, especially in the higher load and frequency ranges; it can reach six times that of the latter. In order to understand the reasons for their excellent properties, the microstructure, microhardness and bonding strength with the substrate were analysed by SEM, X-ray diffraction, Knoop hardness and scratching test methods separately. The results show that the TiN(1) film exhibits the best tribological properties, which are closely related with its greater hardness and bonding strength.