Gradation of oxidational wear of metals

This paper considers mild-oxidational wear of metals by studying their behavior under friction with different loads. Low carbon, steel and copper are chosen as the model materials. We show that tribo-oxidation and the structure of surface layers of materials, both formed in the process of plastic deformation during friction, provide the boundary conditions of mild and severe wear. Oxidational wear is predominant when structural changes are minimal. As the load increases, oxidational wear is at first accompanied by metallic wear and afterwards the oxidational wear accompanies the metallic wear. The structure of the metal surface layers changes gradually during these processes, so that the strengthening of the metal is high enough to withstand friction forces. When the magnitude of frictional forces becomes higher than the maximal strength of the plastically deformed metal, the transition to severe wear occurs.The composition of different types of oxides and the fineness of wear particles varies with the friction conditions. Under light load friction conditions, fine wear particles are formed. These particles contain oxides of high oxygen content. As the friction conditions become tougher, in particular when the load increases, large-sized wear particles are formed. These particles contain oxides of a higher metal content. Phase composition and fineness of wear particles are used for gradation of mild wear.Analyses of phase composition of oxides and estimation of the fineness of wear particles are suggested as a method of wear character diagnostics. The electron diffraction method of the study of wear particles is used for this analysis in order to evaluate and choose appropriate friction and wear conditions.     

Microstructural Characterization of Wear Particles Formed During Tribological Stressing of TiC and Ti(C,N) Coatings

An attempt was undertaken to obtain a better understanding of the tribological properties of two wear-resistant coatings on tool steel by structural and microchemical analysis of wear particles using a transmission electron microscope. Coatings were deposited by physical vapor deposition and plasma-assisted chemical vapor deposition techniques and tribological properties were derived from reciprocating sliding tests of the coatings against alumina balls. Three types of wear particles were identified by electron diffraction and energy dispersive X-ray spectroscopy: nanocrystalline rutile (TiO₂), nanocrystalline graphite and microcrystalline graphite. Low coefficients of friction, of the order of 0.2, were attributed to the formation of solid lubricant films of sub-stoichiometric TiO_2-x Magnéli phases and/or graphite.     

A Model for Polymer Composite Wear Behavior Including Preferential Load Support and Surface Accumulation of Filler Particulates

A rule-of-mixtures model is developed for the time-dependent wear and friction behavior of polymer matrix materials containing particulate filler inclusions, based upon the specific wear rates of filler and matrix materials. The model accounts for the accumulation of wear-resistant filler particles within the near-surface region of the composite as sliding proceeds. Account is also made for preferential support of the normal load by filler particles at the sliding surface. Though particle/matrix interfacial shear stress and particle aspect ratio do affect initial transient behavior, wear rate, and friction are independent of preferential load support under steady-state conditions. The model indicates that steady-state composite wear rate can be most affected by the specific wear resistance of the filler particles, as well as the volume fraction filling of particles into the polymer matrix.     

WC颗粒增强镍基涂层改善制动盘组织与磨损性能

为提高汽车制动盘耐磨和高温氧化性能,延长其使用寿命,采用激光熔覆技术在中碳钢表面制备了以WC颗粒为增强相的Ni基复合涂层.借助SEM和XRD等表征手段对制动盘表面涂层进行了组织和物相分析,利用维氏硬度计测试了制动盘表面涂层截面显微硬度分布,通过摩擦磨损实验研究了制动盘表面涂层的磨损性能.研究表明,制动盘表面涂层主要由γ-（Ni,Fe）固溶体、均匀分布WC颗粒和碳化物抗磨损相组成.涂层平均显微硬度HV0.2670,显微硬度值波动较小较为平稳,证明涂层组织比较均匀.在多种强化效果共同作用下,制动盘表面涂层的磨损量与基材相比明显减小,仅为基材的20％,抗磨损性能显著提高.     

高水基液压阀陶瓷摩擦副摩擦学性能研究

为选择适合的高水基乳化液液压阀摩擦副材料,探讨ZrO2与不同结构陶瓷组成的摩擦副在高水基乳化液润滑状态下的摩擦磨损特性。采用摩擦磨损试验机,在不同载荷和滑动速度下,研究在高水基乳化液介质中4种不同陶瓷材料（ZrO2、Al2O3、Si3N4和SiC）分别与ZrO2配副的摩擦学性能,并探讨不同组合陶瓷摩擦副的磨损机制。结果表明：在高水基乳化液中,各陶瓷的摩擦因数均随着滑动速度的增大而降低,其中Al2O3陶瓷的摩擦因数最小;ZrO2、Al2O3和Si3N4陶瓷的摩擦因数受载荷的影响较小,SiC陶瓷的摩擦因数则随着载荷的增大而骤增;各陶瓷的磨损体积都随着速度和载荷的增大而增大,其中Al2O3/ZrO2陶瓷摩擦副的磨损体积最小,其磨损机制以磨粒磨损和微疲劳磨损为主。研究表明,在不同工况下,Al2O3与ZrO2陶瓷配副的摩擦因数和磨损体积均为最低值,更适合作为高水基乳化液液压阀的摩擦副材料。     

The surface layer of friction plastics

The tribological problems of plastics used for friction brakes with particular emphasis on the design problems of materials with optimal characteristics for the working conditions of shoe brakes for underground railways were investigated. The phenomena associated with the friction and wear of these materials were identified by examining the surface layers of samples using the following techniques: optical and scanning electron microscopy, X-ray microanalysis and thermogravimetric analysis at temperatures up to 1270 K. A model of the structure of the surface layer of friction materials was developed. It consists of five layers which differ in composition, structure and properties. This model is important in the development of new friction materials with specified tribological characteristics.     

Ultralow-friction and wear properties of IF-WS<Subscript>2</Subscript> under boundary lubrication

Tested in boundary lubrication, inorganic fullerene-like WS₂ nanoparticles used as additives in oil present interesting friction reducing and anti-wear properties. A dispersion with only 1 wt% of particles leads, from a contact pressure of 0.83 GPa, to a drastic decrease of the friction coefficient below 0.04 and to very low wear. High resolution transmission electron microscopy (HRTEM), Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), Raman Spectroscopy and video imaging were used to explain the lubrication mechanisms. A structural modification of fullerene-like nanoparticles into sheets during the friction test was evidenced to be the main effect at the origin of these properties.*To whom correspondence should be addressed. E-mail: lucile.joly-pottuz@ec-lyon.fr     

Impact wear resistance of WC/Hadfield steel composite and its interfacial characteristics

A composite coating of WC/Hadfield steel was fabricated through centrifugal casting process to improve the impact wear resistance of Hadfield steel under the conditions of low or medium impact energy. The interfacial structure between WC ceramic particle and the steel matrix was analyzed with scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). The impact wear tests at different impact energy were carried out on a MLD-10 type impact wear rig to investigate the wear-resistant properties of three kinds of composites with different WC particle sizes. For comparison, the wear tests of Hadfield steel were also carried out under the same conditions. The results show that WC particles are partially dissolved in the steel during centrifugal casting. The elements W, C and Fe in steel react to form new carbides such as Fe₃W₃C or M₂₃C₆, which precipitate around former WC particles forming fine particles during subsequent solidification. So the interface between WC particles and Hadfield steel matrix is a strong metallurgical bonding. The composite reinforced with smaller WC particles has better impact wear resistance than that of Hadfield steel regardless of impact energy level. Whereas, the composite reinforced with larger WC particles has better impact wear resistance property than that of Hadfield steel when the impact energy is small but an opposite result is gained when the impact energy is higher. So, it is very essential to choose suitable size of WC particles as reinforcement in Hadfield steel to make the composite material more durable in the service conditions.     

水凝胶/热塑性聚氨酯复合材料在水润滑条件下的摩擦学性能

为提高水润滑轴承的承载能力，利用水凝胶在水润滑条件下的水合作用来改善热塑性聚氨酯（TPU）轴承材料的摩擦学性能。利用聚乙烯醇、海藻酸钠、壳聚糖等材料制备水凝胶颗粒，并通过熔融共混法制备水凝胶/TPU复合材料；在0.3和0.5 MPa的载荷下测试复合材料的摩擦磨损性能，利用激光干涉表面轮廓仪和扫描电子显微镜观察其磨损表面形貌，分析其磨损机制。结果表明：水凝胶微粒可以通过水合润滑改善摩擦副的润滑条件，从而降低摩擦因数和磨损量，提高复合材料的摩擦性能；水凝胶质量分数4%时复合材料具有最佳的摩擦磨损性能，其在0.3和0.5 MPa工况下相对于TPU试样的平均摩擦因数减少率分别为52.31%和43.94%。研究结果为开发高性能水润滑轴承材料提供了一种方法。     

基于制动器摩擦副销-盘试验的第三体摩擦磨损特性研究

风电制动器因其制动工况多变,摩擦副表面的第三体成分复杂且大小各异,在第三体影响下摩擦副的摩擦磨损特性仍有待研究。以服役期内风电制动器摩擦副为研究对象,对附着在风电制动器摩擦副表面的第三体成分及尺度进行检测。检测结果表明,风电制动器摩擦副表面第三体的主要成分为铁铜磨屑及沙石颗粒,且其尺度均在百微米级。利用销-盘摩擦磨损试验机研究具有上述成分及尺度第三体对摩擦副摩擦磨损特性的影响。试验结果表明：摩擦初期第三体在摩擦副间产生滚动起减摩作用,摩擦因数大幅减小;随着磨损程度的加剧,摩擦因数大幅上升,摩擦副提前进入剧烈磨损阶段;铁颗粒会加剧摩擦副磨损缩短其使用寿命,沙颗粒会导致制动过程摩擦力矩大幅波动,铜颗粒会导致制动力的不足。     

Wear and Friction Characteristics of Magnetorheological Fluid under Magnetic Field Activation

In this article, wear and friction characteristics of a magnetorheological (MR) fluid were studied under different magnetic fields. Using a pin-on-disc tribometer, the wear loss and friction coefficient were obtained with and without a magnetic field. The friction and wear of three typical materials under magnetic field were investigated at various normal loads and rotating speeds. After the wear tests, the worn surfaces of specimens were observed using a scanning electron microscope (SEM) in order to investigate the wear mechanisms, and the contacting surfaces were analyzed by energy-dispersive X-ray spectroscopy (EDS) to investigate the variation of elemental composition on the worn surface. Test results showed that the MR fluid exhibits better tribological characteristics under a magnetic field compared to the case without a magnetic field. The general morphology of the MR particles and wear debris was observed to assist with the analysis of friction and wear. The SEM micrographs and EDS spectra of the worn surfaces showed that the predominant wear mechanism in the case of the steel and brass specimens was abrasive wear by asperities and MR particles on the worn surfaces, whereas a mixed wear mechanism that included adhesive wear and abrasive wear was observed in the case of the aluminum specimen.     

Sliding Wear Behavior of HVOF-sprayed Cr3C2–NiCr/CeO2 Composite Coatings at Elevated Temperature up to 800 °C

Four types of Cr₃C₂–NiCr coatings containing different fractions of CeO₂ additive were deposited using high velocity oxy-fuel spraying. Hardness tester, X-ray diffractometer, contact surface profiler, and scanning electron microscope equipped with energy dispersive spectrometer were employed to characterize the microhardness, phase composition, surface roughness, and microstructure of as-sprayed coatings. At the same time, the friction and wear behavior of the as-sprayed coatings sliding against Si₃N₄ ball at room temperature and elevated temperature of 400 or 800 °C under unlubricated condition was evaluated using an oscillating friction and wear tester. The worn surfaces of the composite coatings and Si₃N₄ counterpart balls were analyzed by means of scanning electron microscopy, X-ray diffraction, and three dimensional non-contact surface profiler. The friction and wear mechanisms of the coatings with and without CeO₂ additive were comparatively discussed. Results show that the composite coatings doped with CeO₂ had better wear-resistance than that without CeO₂, and the coating containing 4 wt% CeO₂ showed the best wear-resistant property. The improved wear-resistant properties of the composite coatings doped with CeO₂ were attributed to the refined microstructure and improved mechanical properties induced by CeO₂.     

重型汽车中桥减速器润滑油中磨损颗粒分析

重型汽车中桥减速器在工作过程中其摩擦副接触表面因相对运动而产生的磨损颗粒进入润滑油中,导致润滑油性能下降;磨损颗粒随润滑油进入摩擦副接触表面,摩擦副磨损加剧。根据重型汽车的运行特点,每隔一定里程数对减速器润滑油进行取样,综合分析在用润滑油中磨损颗粒物的大小、形貌及成分。结果表明：减速器在用润滑油中磨损颗粒主要成分是铁屑和铜屑,磨损颗粒主要来自于球面垫片（铜）及其配副的摩擦以及齿轮副间的摩擦。具体分析磨损颗粒产生过程及形成机制,为重型汽车中桥减速器中运动摩擦副的设计及制造提供理论依据。     

Orientation Effects in Filled Plastics Bearing Materials

The development of antifriction materials based on lamellar solid lubricants dispersed as fillers in thermoplastic compounds is briefly reviewed. Experimental evidence is offered to account for the wide variations in friction and wear properties reported, in terms of flow orientation and cross-flow migration of the filler particles. These findings confirm the importance of finish machining operations on the rubbing surfaces. Preliminary evidence is also offered for the disruption of particle orientation by polymer crystallization processes where the particles are small. Experimental methods used are: image analyzing microscopy, X-ray diffraction, and a specially developed friction testing machine for molded plastics samples.     

Tribological Enhancement of Aluminum by Porous Anodic Films Containing Solid Lubricants of MoS2 Precursors©

Porous anodic films containing molybdenum disulfide precursors were developed for self-lubricating purposes on aluminum by an initial anodizing and a subsequent re-anodizing process. The self-lubricating films were then examined with respect to the morphology, microstructure, and composition of the anodic film material and the lubricant, using X-ray diffraction, electron microscopy, energy dispersive X-ray analysis and X-ray photo-electron spectroscopy. The dry sliding wear of aluminum supporting such self-lubricating films was significantly reduced, as a result of greatly reduced coefficients of friction. The enhanced lubricity, due to the MoS₂ precursors contained within the porous anodic film, leads to wear mode changes from severe abrasive and adhesive wear for uncoated aluminum, to a mild film fatigue wear, for aluminum supporting the self-lubricating anodic films. The wear mechanism change is suggested by the wear and friction curves, as well as confirmed by wear track morphology.     

Structural Characterization of Wear Debris Produced During Friction Between Two Austenitic Stainless Steel Antagonists

Ball-on-flat friction experiments between two austenitic stainless steel antagonists in sliding contact are carried out under very low loads and in two liquid environments, namely demineralized water and methanol. The wear debris produced during long-duration tests are characterized by different techniques such as X-ray diffraction, transmission electron microscopy and Mössbauer spectroscopy. Martensite is observed as a dominant phase in the wear debris but other phases have been also identified. In the debris produced under demineralized water, there is significant contribution of a second phase, which is poorly crystallized and which was identified as the hydrous iron oxide called ferrihydrite. In the debris produced under methanol, there is a remaining amount of austenite that is not transformed into martensite, and the presence of ferrihydrite has been also detected in very small quantities. The formation of the martensitic debris which occurs from the beginning of the wear tests supports the fact that under our experimental conditions the main damaging mode is abrasive wear by hard particles.     

Synthesis,characterization and tribological properties of Cu/reduced graphene oxide composites

In this paper, nano-copper/reduced graphene oxide (Cu/rGO) composites were synthesized by the facile one step in-situ reduction method. The as-prepared Cu/rGO composites were characterized by means of transmission electron microscopy (TEM), X-ray photoelectron spectroscope (XPS), X-ray diffraction (XRD) and Raman. Mechanism of reduction and growth of Cu/rGO composites were also discussed. The friction and wear properties of oleic acid (OA) modified composites as additives in poly-alpha-olefin (PAO) were investigated using four-ball wear tester.     

Tribological behaviour of plasma nitrided Ti-5Al-2Nb-1Ta alloy against UHMWPE

A detailed study has been made on the wear behaviour of untreated and plasma nitrided Ti-5Al-2Nb-1Ta orthopaedic alloy against ultra high molecular weight polyethylene (UHMWPE) using pin on disc tribometer under lubricated conditions. The effects of nitriding temperature and nitriding time on the basis of the evolution of the wear volume loss and friction coefficient were investigated. The wear resistance of the plasma nitrided alloys increased considerably when compared to the untreated alloy. The wear debris identified using X-ray diffraction measurements indicated the formation of titanium oxide and titanium oxynitride particles. The wear rate was found to increase with increase in load and sliding velocity.     

Structure and tribological characteristics of steel under melting by plasma flow and simultaneous Mo and W alloying

New findings of studies of the structural, tribological, and physicomechanical characteristics of structural steel 40Kh treated by plasma flow under melting accompanied by either tungsten or molybdenum alloying are presented. Rutherford back-scattering of ions, scanning electron microscopy (with microanalysis), X-ray fluorescent spectral analysis, X-ray phase analysis, wear-resistance tests, measurement of the coefficient of friction, and transmitting electron microscopy with diffraction are the basic research methods. It is found experimentally that a thin layer 5 μm thick saturated with nitrogen and an alloying element (Mo or W) with regularly arranged crystallites arises on the steel 40Kh surface. The crystallites in this layer have a needle- and ribbon-shaped structure. A deeper layer located about 40 μm thick consists of micro- and nanosized grains. Friction and wear studies of the plasma-flow treated (melt) samples show the steel wear resistance to increase 2–2.5 times and the coefficient of friction to decrease from 0.4–0.5 to 0.10–0.15 compared to the untreated samples.     

基于动力学特性的挖掘机工作装置端面摩擦副间隙磨损机理研究

机械动力装备中常因为作业工况恶劣导致关节端面摩擦副间隙处磨损严重,为了探讨关节端面摩擦副间隙处作业过程中磨损变化行为及作用机理,以某型号挖掘机为例,基于动力学模拟分析两种典型工况下得到动臂关节处动态载荷数据基础上,利用有限元数值模拟技术并修正Archard磨损模型计算得出端面摩擦副间隙处磨损深度与磨损次数的关系,在端面磨损试验机上验证两种工况下关节间隙处耐磨垫片磨损变化过程,在扫描电镜下观察磨损后的表面形貌分析磨损作用机理。结果表明：两种工况下,磨损区域均为环形区域;偏载工况磨损主要与接触应力值大小和偏载角度有关,磨损过程中表面产生锥刺凹坑和交叉犁沟等,磨损机制由疲劳磨损向黏着磨损转化,同时伴随有少量的磨粒磨损;满载启动回转工况磨损主要与接触碰撞程度有关,磨损形式主要为黏着磨损与磨粒磨损。此分析方法对工程机械行业分析其它动力装备关节摩擦副和工程应用具有较好的参考价值。