Wear behaviour of hydrogenated DLC in a pin-on-disc model test under lubrication with different diesel fuel types

The wear behaviour of hydrogenated diamond like-carbon (DLC) coating in DLC/steel tribological contact in a pin-on-disc model test under lubrication with two diesel fuels is presented in this work. The first diesel fuel was standard EN590 that contained ester-based antiwear additives. In contrast to EN590, the second diesel fuel, called GDK650, did not contain antiwear additives. It was experimentally observed that the antiwear additives are detrimental to the DLC. The effects of load, speed and temperature on the DLC and steel counterbody wear were investigated. Steel counterbody wear volume was found to be not affected by pressure, temperature, speed and lubricant, whereas the DLC-coating revealed correlation between the parameters and wear rate. Regarding the results of the tribological tests under both diesel lubrications, new mathematical wear laws were developed.     

Tribological behavior of PEEK-based materials under mixed and boundary lubrication conditions

In modern industries, more and more mechanical components are exposed to mixed and even boundary lubrication conditions, inducing fast wear and even scuffing of the motion systems. In order to enhance the lifetime and reliability of the motion systems, replacing metal–metal friction pairs by metal–polymer ones can be one of the most effective approaches. The present work focuses on tribological behavior of pure polyetheretherketone (PEEK) and a formulated PEEK composite lubricated with diesel and engine oil. It was demonstrated that in mixed and boundary lubrication regimes the structure of PEEK materials affect significantly the tribological performance. Formation of a tribofilm on the surface of metallic counterbody plays an important role on the tribological behavior of the PEEK-based materials.     

Acoustic spectrometry as used for the evaluation of tribological systems

A study is presented of tribological metal-polymer systems. Parameter analysis by acoustic emission resulting from external friction was used. The experimental results obtained for metal-polymer friction pairs are dependent on various factors including load, velocity of relative travel, microgeometry of the contacting surfaces, physicomechanical properties of the materials and testing period. The rates of acoustic emission, the total acoustic emission and the magnitude of the frequency emission spectrum were used as informative characteristics concerning friction and wear kinetics. A number of general relations were determined for friction pairs, reflecting the influence of these factors on the acoustic activity of a rubbing contact. A relation was discovered between the mode of wear for polymers and the acoustic emission parameters. An assumption was made concerning the correlation between polymer mass loss by wear and the energy of acoustic emission as based on the model under consideration for failure of a simple contact spot.     

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.     

Influence of counterbody material on wear of ta-C coatings under fretting conditions at elevated temperatures

The high temperature tribological performance of tetrahedral amorphous carbon coatings has been analyzed at elevated temperatures up to 250 °C in air against three different counterbody materials—steel 100Cr6, α-alumina and silicon nitride. The results show that the counterbody material influences the friction and wear behavior and therefore coating life time strongly. This effect is well known for these coatings at room temperature under dry environmental conditions, equivalent to conditions above 100 °C when water molecules desorb from the surface. However, the sharp difference in tribological performance between silicon nitride on the one hand and alumina and steel on the other hand cannot be understood in this context. Analyzing the friction behavior during the running-in phase, it is evident that only alumina and steel form a stable interface with constant low friction and relatively low wear rates. Silicon nitride forms an unstable interface with fluctuating COF and relatively high wear rates due to its own inherent tendency to tribo-oxidation.     

Tribological Properties of Nanodiamond-Epoxy Composites

Owing to its superior mechanical properties, nanodiamond (ND) holds great potential to improve tribological characteristics of composites. In this study, we report on the wear and dry friction of epoxy-ND composites prepared from as-received and aminated ND across the length scale range from macro to nano. Comparison of macroscale, microscale, and nanoscale frictional behavior shows that ND is highly effective in improving the wear resistance and friction coefficients of polymer matrices across the different length scales. Although with both types of ND wear resistance and friction coefficients of epoxy-ND composites were significantly improved, aminated ND outperformed as-received ND, which we account to the formation of a strong interface between aminated ND and the epoxy matrix. This study also shows that agglomerates within epoxy-ND composites containing 25?vol.% ND were able to wear an alumina counterbody, indicating very high hardness and Young??s modulus of these agglomerates, that can eventually replace micron sized diamonds currently used in industrial abrasive applications.     

Tribochemical processes in epoxyorganic textolite–steel friction pair

The role of a phenol formaldehyde oligomer additive to the epoxy binder in friction of organic textolite is studied. It is shown that, in the course of friction, the polymer surface becomes enriched in the tribochemically stable phenolic component, while new C=O and O–C–O bonds appear that result from the oxidation of the aliphatic epoxy groups of macromolecules. During friction, the aliphatic component of the polymer specimen is predominantly involved in reactions with the counterbody; this selective wear makes the outer surface of the polymer specimen less hydrophilic. Comparative tribological and thermofrictional tests have shown that, unlike the phenol structure, the use of an epoxy-phenolic structure in the materials reinforced by polyoxadiazole fabrics is more efficient at low temperatures, while phenol formaldehyde binder exhibits better stability at high temperatures.     

Tribological behavior of blends of incompatible super high-molecular weight polyethylene and polymethyl methacrylate synthesized in supercritical carbon dioxide

Monolithic specimens of the polymer-polymer blends of super high-molecular weight polyethylene and polymethyl methacrylate are synthesized by the polymerization of methyl methacrylate on powdered super high-molecular weight polyethylene in air and supercritical CO₂. These systems are the blends of two linear polymers. The study of the tribological behavior of the composites at various sliding velocities has shown that the specimens synthesized in supercritical CO₂ are advantageous in the friction coefficient and frictional temperature. The poorer tribological behavior of the composite produced in air is caused by the tribochemical processes resulting in counterbody wear.     

电流对铬青铜/紫铜摩擦学特性的影响

采用自制的销盘摩擦磨损试验机,在载流条件下对铬青铜QCr0.5/T2铜的摩擦学特性进行了研究,结果表明电流对摩擦因数和磨损率具有显著影响,电流越大,磨损率越高,摩擦副磨损越严重,摩擦因数越大。载流条件下,摩擦表面发生电点蚀,并出现局部熔化和雨滴状金属颗粒。     

Role of contact frequency on the wear rate of steel in discontinuous sliding contact conditions

This work presents a novel approach of sliding ball-on-disk wear tests where the disc material is investigated. Each part of the wear track on the disc is in discontinuous contact with the counterbody. The contact frequency at each part of the wear track on the disc with the counterbody is defined by the rotation frequency of the disc. The sliding speed is however a function of both the rotation frequency and wear track diameter. In this work, the effect of the contact frequency on friction and wear was investigated on carbon steel in discontinuous sliding contact with corundum balls. Various sliding speeds were used while maintaining the contact frequency at a fixed value, and various contact frequencies were applied at constant sliding speeds.The wear rate of the disk material is shown to depend not only on the usual wear test parameters, namely sliding speed and contact load, but also on contact frequency. Moreover, contact frequency is shown to be a key factor determining the wear mode even at constant sliding speed and load. At contact frequencies above 9 Hz, the dominant wear mechanism is oxidational wear, while at frequencies below 4 Hz the dominant wear mechanism is adhesive wear. This transition from adhesive to oxidational wear takes place together with a change in the type of debris generated and in the value of the coefficient of friction.The validity of the Garcia-Ramil-Celis model proposed earlier for discontinous sliding contact conditions, is demonstrated for the case of carbon steel disks sliding against a chemically inert counterbody.     

Correlation Between Tribological Parameters and Wear Mechanisms of Homogeneous and Heterogeneous Material

This study intended to investigate the effect of tribological parameters on wear mechanisms and friction coefficient for homogeneous and heterogeneous materials. Particularly, effects of particle geometry and normal load on the tribological behaviour of an aluminium alloy and nodular cast iron have been developed. These materials are used in two industrial applications. The first one is used to transport granular material. It has been shown that damage of used truck’s buckets is produced. However, the nodular cast iron is used in automobile industry thanks to its lower density, good wear resistance and its low friction coefficient. A scratch test was used and the wear mechanisms were observed for different attack angles. The normal load was also varied and correlation between wear mechanisms, tribological parameters and friction coefficient was highlighted.     

Tribological behavior and topography of friction surfaces of diamond-like coatings in contact with steel,silicon nitride,and quartz glass

The paper presents the study results of the tribological behavior and surface topography formed at friction of diamond-like coatings against indenters made of silicon nitride, quartz glass, and steel. It is shown that the tribological behavior depends on the nature and hardness of the counterbody material whose wear causes changes in the surface topography of the diamond-like coating at the nanometer level. At friction of the diamond-like coating against the silicon nitride indenter surface asperities are deformed plastically and the deformation rate is governed by the coating structure.     

基于能量耗损的摩擦学系统状态识别方法研究

通过对摩擦学系统的能量流监测,结合状态识别方法的分析,提出了基于磨损与振动能量损耗监测方法,建立了能量损耗的机械设备状态监测框架模型。分析指出,磨损与振动都是能量耗损行为,且二者的相关性采用齿轮疲劳试验证实。研究表明,基于齿轮磨损的光谱分析的元素相对质量分数的累积相对标度和振动信号时域的均方根值的累积相对标度具有很好的相关性,这表明齿轮磨损和振动具有很好的相关性,因此摩擦学系统的状态识别与故障诊断采用能量损耗监测的方法是可行的。     

Friction and wear of powder coatings of epoxy composites with alumosilicate nanoparticles

The paper studies the effect of alumosilicate nanofillers of tubular and lamellar shape on the friction and wear of epoxy composites. It is shown that the influence of concentration and shape of the fillers on the tribological behavior of the composites is due to variations in their viscoelastic properties and shielding of the contact area of the matrix material with the metallic counterbody by the filler particles. The data evidence that at equal concentrations of alumosilicate fillers in the epoxy matrix, the best tribological characteristics are provided in the case of tubular-shaped particles.     

Application and conceptual explanation of an energy-based approach for the modelling and prediction of sliding wear

Establishing an accurate predictive model for wear will result in major improvements in the efficiency, lifetime, cost and performance of many engineering systems. The authors have previously proposed a practical energy-based model to describe the tribological damage using energy dissipation. In this work, the capacity of this method to simplify the complex wear phenomenon was determined, and the applicability of this method to forecast the wear behaviour of materials was investigated. The wear results for a W–Cu electrical contact composite were utilised to determine the practical value of the model. Numerical integration of friction force–distance diagrams was used to evaluate the energy dissipation. Linear and non-linear least squares methods were applied to find the optimal curve fitting. It is shown that this model can be applied in two general forms: (1) a graphical method and (2) an explicit formulation. Both of these forms are shown to be capable of providing the necessary information, based on a limited number of initial tests, to predict unknown wear data (volume loss, lifetime, energy) without the need for morphological observations.     

The structure and tribological behavior of nanocomposite carbide coating on steel 45

It is shown that fullerene black interacts with the steel 45 surface and forms a nanocomposite coating including orthorhombic iron carbide Fe₃C with crystallites sized 100–150 nm and dispersed spots of fullerene black with particles sized 40–50 nm. Tribotests show the coefficient of friction of the composite coating to be three-four times lower and the wear resistance about two times higher than these parameters for original annealed steel 45. It is proved that in friction, frictional transfer occurs of hard high-disperse wear products of the coating carbide base and fullerene black to the counterbody, which encourages the decrease in the friction of the pair with one of its elements coated with Fe₃C-fullerene black. The causes of the improved tribological behavior of the carbide coating are discussed.     

Friction and wear of polyamide-6 powder coatings gradient-filled by metal nanofilms

The tribological properties of PA-6 and PA-6-based coatings with surface layers gradient-filled with tin, lead, and bismuth nanofilms in a concentration of up to 1.2 wt % are compared. It has been found that differences in the tribological behavior of the composites are due to the adhesion of the filler metals to the counterbody material. It has been shown that the hardness of the friction surface of the composites depends on the susceptibility of the filler metals to strain hardening and explains differences in the values of their wear.     

Analysis of Sliding Wear Characteristics of BFS Filled Composites Using an Experimental Design Approach Integrated with ANN

Short fiber-reinforced polymer composites are used in numerous tribological applications. In the present work, an attempt was made to improve the wear resistance of short glass fiber (SGF)-reinforced epoxy composites by incorporation of microsized blast furnace slag (BFS) particles. The effect of various operational variables and material parameters on the sliding wear behavior of these composites was studied systematically. The design of experiments approach using Taguchi's orthogonal arrays was used. This systematic experimentation led to identification of significant variables that predominantly influence the wear rate. The Taguchi approach enabled us to determine optimal parameter settings that led to minimization of the wear rate. The morphology of worn surfaces was then examined by scanning electron microscopy and possible wear mechanisms are discussed. Further, in this article, the potential of using artificial neural networks (ANNs) for the prediction of sliding wear properties of polymer composites is explored using an experimental data set generated from a series of pin-on-disc sliding wear tests on epoxy matrix composites. The ANN prediction profiles for the characteristic tribological properties exhibited very good agreement with the measured results, demonstrating that a well-trained network was created. The simulated results explaining the effect of significant process variables on the wear rate indicated that the trained neural network possessed enough generalization capability to predict wear rate from any input data that are different from the original training data set.     

Tribological behaviour and wear mechanism of MoS2–Cr coatings sliding against various counterbody

MoS₂–Cr coatings with different Cr contents have been deposited on high speed steel substrates by closed field unbalanced magnetron (CFUBM) sputtering. The tribological properties of the coatings have been tested against different counterbodies under dry conditions using an oscillating friction and wear tester. The coating microstructures, mechanical properties and wear resistance vary according to the Cr metal-content. MoS₂ tribological properties are improved with a Cr metal dopant in the MoS₂ matrix. The optimum Cr content varies with different counterbodies. Showing especially good tribological properties were MoS₂–Cr8% coating sliding against either AISI 1045 steel or AA 6061 aluminum alloy, and MoS₂–Cr5% coating sliding against bronze. Enhanced tribological behavior included low wear depth on coating, low wear width on counterbody, low friction coefficients and long durability.     

Investigation of the structure,composition, and properties of the carboplasic contact surface in tribotests

The processes evolving on carboplastic surfaces during contact interaction with a steel counterbody are discussed. The structure, composition, and tribological properties of the film of secondary structures appearing during friction are investigated. The dependences of the friction coefficient and wear on pressure and sliding velocity are established. The results of comparative tests allow us to identify FUT B83 as the carboplastic with the lowest friction coefficient and UGET as the carboplastic with the greatest wear resistance.