Tribological properties of composite electrochemical nickel-based coatings

Composite electrochemical coatings based on nickel with colloidal graphite and graphite bisulphate as a disperse phase are obtained. The electrodeposition of the coatings in a variable potential mode is studied. It is determined that the coefficient of sliding friction for the developed coatings decreases by a factor of two in comparison with nickel coatings without the dispersed phase. It is shown that the coefficient of friction for the coatings decreases as the thickness of the electrolytic deposit rises.     

Studies on friction and transfer layer: role of surface texture

Friction influences the nature of transfer layer formed at the interface between tool and metal during sliding. In the present investigation, experiments were conducted using “Inclined Scratch Tester” to understand the effect of surface texture of hard surfaces on coefficient of friction and transfer layer formation. EN8 steel flats were ground to attain surfaces of different textures with different roughness. Then super purity aluminium pins were scratched against the prepared steel flats. Scanning electron micrographs of the contact surfaces of pins and flats were used to reveal the morphology of transfer layer. It was observed that the coefficient of friction and the formation of transfer layer depend primarily on the texture of hard surfaces, but independent of surface roughness of hard surfaces. It was observed that on surfaces that promote plane strain conditions near the surface, the transfer of material takes place due to the plowing action of the asperities. But, on a surface that promotes plane stress conditions the transfer layer was more due to the adhesion component of friction. It was observed that the adhesion component increases for surfaces that have random texture but was constant for the other surfaces.     

Effect of surface roughness and surface texture on scuffing

This paper discusses the results of disk tests designed to examine the effect of surface roughness and surface texture on scuffing and related behavior. AISI 9310 steel disk of varying surface roughness and surface texture, along with a MIL-L-7808G lubricant, were used. It is shown that, under otherwise comparable situations, (a) an increase in the composite surface roughness increases the coefficient of friction at scuffing, decreases the scuff failure load, and decreases the critical temperature, (b) the cross-ground disks give a lower coefficient of friction at scuffing and a higher scuff failure load than the circumferentially-ground disks, but nearly the same critical temperature, and (c) an increase in the sliding velocity or sum velocity, at a constant sliding-to-sum velocity ratio, decreases the coefficient of friction at scuffing, decreases the scuff failure load, and decreases the critical temperature.The superior performance of the cross-ground disks compared with the circumferentially-ground disks is attributed to the effect of surface texture on microelastohydrodynamic action. The variations of the oil film thickness ratio at scuffing, the coefficient of friction at scuffing, and the critical temperature with respect to surface roughness, surface texture, and operating variables have been shown to correlate well with a dimensionless parameter $\text{ξ}{}_{\mathrm{?}}$.     

Surface texture of the milled surface of aluminum-ceramic composite

Journal of Mechanical Science and Technology - The work concerns the assessment of the parameters of the geometric structure of the surface of an aluminum-ceramic composite after milling in various...     

Tribological properties of nickel-based self-lubricating composite at elevated temperature and counterface material selection

Solid lubricating materials are necessary for development of new generation gas turbine engines. Nickel-based self-lubricating composites with graphite and molybdenum disulfide as lubricant were prepared by powder metallurgy (P/M) method. Their tribological properties were tested by a MG-2000 high-temperature tribometer from room temperature to 600 °C. The structure of the composite was analyzed by XRD and worn surface morphologies were observed by optical microscope. The effects of counterface materials on tribological behavior of composites were investigated. It was found that chromium sulfide and tungsten carbide were formed in the composite by adding molybdenum disulfide and graphite, which were responsible for low-friction and high wear-resistance at elevated temperatures, respectively. The average friction coefficients (0.14–0.27) and wear rates (1.0–3.5 × 10⁻⁶ mm³/(N m)) were obtained for Ni–Cr–W–Fe–C–MoS₂ composite when rubbed against silicon nitride from room temperature to 600 °C due to a synergetic lubricating action of graphite and molybdenum disulfide. The optimum combination of Ni–Cr–W–Fe–C–MoS₂/Ni–Cr–W–Al–Ti–C showed lower friction than other counter pairs. The graphite played the main role of lubrication at room temperature, while sulfides were responsible for low friction at high temperature.     

Process parameter analysis of inertia friction welding nickel-based superalloy

A two-dimensional axisymmetric model for the inertia friction welding (IFW) of a nickel-based superalloy was developed. The influences from the axial pressure, initial rotational speed, and moment of inertia of the flywheel on the interface temperature and axial shortening were systemically examined. The analysis shows that the mechanical energy mainly depends on the initial rotational speed, and a relatively high axial pressure will increase conversion efficiency from mechanical energy to effective welding heat. The axial shortening is found to be approximately proportional to the square of initial rotational speed while logarithmical to the axial pressure. Based on this work, the weldability criteria for IFW nickel-based superalloy was established. Additionally, the approach for welding parameter optimization was performed considering the evolution of temperature profiles from various parameters. The results show that the axial pressure has a more obvious effect on the width of high-temperature zone than the rotational speed during the quick shortening stage.     

Ceramic-ceramic composite materials with improved friction and wear properties

Dry friction and wear tests were performed with self-mated couples of SiC containing 50% TiC, Si₃N₄---BN, SiC---TiB₂ and Si₃N₄ with 32% TiN at room temperature and 400°C or 800°C.Under room temperature conditions, the friction coefficient of the couple SiC---TiC/SiC---TiC is only half of that of the couple SiC/SiC and the wear is one order of magnitude smaller. At 400°C, it exceeds the friction coefficient of SiC/SiC except at the highest sliding velocity of 3 m s⁻¹. At lower sliding velocities the wear coefficient of SiC---TiC/SiC---TiC is lower than that of SiC/SiC.The couple Si₃N₄---TiN/Si₃N₄---TiN exhibits high friction coefficients under all test conditions. At room temperature the wear volume of the self-mated couples of Si₃N₄ and Si₃N₄---TiN after a sliding distance of 1000 m is similar, but Si₃N₄---TiN shows a running-in behaviour. At 800°C the wear coefficient of Si₃N₄---TiN/Si₃N₄---TiN is approximately two orders of magnitude smaller than that of Si₃N₄/Si₃N₄, and equal to those at room temperature. At 22°C the addition of BN reduces the friction of Si₃N₄. The wear coefficient is independent of sliding velocity and the self-mated couples showing running-in. Friction and wear increase with increasing temperature. The wear coefficient of SiC---TiB₂ above 0.5 m s⁻¹ at 400°C is advantageously near 10⁻⁶ mm³ (Nm)⁻¹. With the other test conditions the wear behaviour is similar to SSiC.     

Effect of testing conditions on friction and wear of a polyetheretherketone-based composite

Friction and wear characteristics of a type of polyetheretherketone (PEEK)- based composite were evaluated under two different loading pressures and sliding speeds (P = 1.0 MPa, V = 1.0 m/s and P=2.0 Mpa, V=3.3 m/s). The material was in contact with steel surfaces of two different roughnesses (Ra=0.15 μm and Ra=0.33 μm). Interface temperature, coefficient offriction, depth wear rate, and specific wear rate of the polymer composite changed considerably with the PV value and the counterface roughness. The interface temperature increased with increasing PV value, whereas the friction coefficient decreased. The depth wear rate at the higher PV value was much higher than that at lower PV. In addition, the rougher counterface resulted in a higher friction coefficient, depth wear rate, and specific wear rate, when the PV value was fixed. The effect of counterface roughness on the specific wear rate at the higher PV value was smaller than that at the lower PV. Further variations in friction and wear with testing conditions are discussed along with the corresponding microscopic observations of the worn polymer surfaces and the polymer transferred counterfaces.     

切削余量对多层复合轴承摩擦磨损性能的影响

主要研究了切削余量对涡旋式压缩机动静盘专用聚四氟乙烯多层复合轴承的微观结构与摩擦学性能的影响。研究结果表明,随着切削余量的增大,裸露的铜含量增多,润滑剂组份降低;随着切削余量的增大,PTFE多层复合材料的摩擦系数表现出逐渐增大的趋势,而磨损率呈现先降低后增大的趋势,并且当切削余量为0.05mm时,复合轴承具有最佳的耐磨性;为有效地提高轴承的装配间隙,防止轴承高速运动产生较大的振动,应将轴承内表面车削0.05mm后装配应用。     

Physical nature and properties of dynamic surface layers in friction

Simulations of the dynamic processes in micro contacts with the Method of Movable Cellular Automata (MCA) show that their common feature is formation of a boundary layer where intensive plastic deformation and mixing processes occur. The boundary layer is well localized and does not spread to deeper layers. We call this layer a ‘quasi-fluid layer’. The thickness of the boundary layer is roughly proportional to the viscosity of solid. This parameter thus should play an important role in determining the wear rate of materials in friction.To better understand the physical nature of the dynamic surface layers, we consider a simplified model of a solid consisting of many thin sheets, interacting with each other according to a ‘friction law’ of Coulomb type. A quasi-fluid layer is always developing if the ‘friction law’ does allow a bi-stability in some range of stresses with one static and one dynamic state at the same stress.The existence of the boundary layer motivates us to change the existing approach to calculating wear in frictional contacts. The wear should be understood not as ‘fracture’ but as ‘mass transport out of friction zone’. The process of stochastic transport of wear particles in the closed friction zone is at the same time the main mechanism of development of surface topography.A very important fact is that the conditions for appearance of a quasi-fluid layer depend on the minimal size of structural elements of the medium, which means that this effect cannot be principally described in the frame of a continuum model.     

Increasing nanohardness and reducing friction of nitride steel by laser surface texturing

Laser surface texturing is often employed to improve tribological performances of mating surfaces. The principal aim of the present work is to study local modifications induced by laser beam during the texturing process (microdimpling), on the mechanical properties of a 30NiCrMo12 nitride steel.A brief tribological characterization was initially made in order to verify the improvement of tribological behaviour ensured by microdimpling. Friction measurements were carried out in lubricated flat-on-flat and round-on-flat configurations.A sub-surface characterization was performed by focused ion beam cross-section and imaging. Modified material layers were discovered in correspondence of laser-affected zones around dimples, where grain dimensions were observed to be reduced. To quantify this phenomenon, a new theoretical energetic model was developed.Hardness measurements were performed by atomic force microscope nanoindentation. This approach allowed to observe an hardening effect moving from bulk material to dimple edges. Therefore, the theoretical model was integrated with the Hall-Petch's law in order to quantify the observed hardening behaviour.     

Effects of laser surface texturing on friction behavior of silicon nitride under lubrication with water

Water lubrication is one of the candidates of the tribo-system with low negative environmental impact. It is well known that some kinds of ceramics show excellent tribological properties under lubrication with water. The characteristic improvement was attempted by giving texturing to Si₃N₄ so that the water lubrication might spread as a representative of the ecotribology system. The surface laser texturing showed the friction reducing effect under the sliding condition of the low bearing characteristic number. The mechanism of the triblogical property improvement by the laser surface texturing was discussed based on the experiment results and the surface analytical results.     

Studies on friction and wear properties of surface produced by ultrasonic vibration-assisted milling

The grinding of elliptical gears on a computer numerical control (CNC) gear grinder with conical wheel is studied according to the mesh theory of elliptical gears. Two machining methods form the machine structure and movement, namely a mobile grinding wheel type and a fixed grinding wheel type. Mathematical models of the movement relation for the elliptical gear grinding process are built up. Since the teeth of the elliptical gears are different from each other, their generating length is also different. Based on the analysis of generating and indexing movement, a universal generating length formula of each tooth is proposed. Basic machining parameters of each tooth, for these two types of machines, are computed using a practical example. The dynamic simulation of generating track is given. The research results show that the grinding of elliptical gears with a CNC conical wheel gear grinder is feasible.     

Influence of roughness parameters and surface texture on friction during sliding of pure lead over 080 M40 steel

In the present investigation, tests were conducted on a tribological couple made of cylindrical lead pin with spherical tip against 080 M40 steel plates of different textures with varying roughness under both dry and lubricated conditions using an inclined pin-on-plate sliding tester. Surface roughness parameters of the steel plates were measured using optical profilometer. The morphologies of the worn surfaces of the pins and the formation of transfer layer on the counter surfaces were observed using a scanning electron microscope. It was observed that the coefficient of friction and the formation of transfer layer depend primarily on the surface texture of hard surfaces. A newly formulated non-dimensional hybrid roughness parameter called ‘ξ’ (a product of number of peaks and maximum profile peak height) of the tool surface plays an important role in determining the frictional behaviour of the surfaces studied. The effect of surfaces texture on coefficient of friction was attributed to the variation of plowing component of friction, which in turn depends on the roughness parameter ‘ξ’.     

润滑接触摩擦力的往复式实验研究

在往复式试验机上研究实际加工表面球-盘式接触混合润滑摩擦特性,比较采用不同黏度润滑油光滑接触摩擦力的大小。针对表面粗糙度幅值和纹理对摩擦行为的影响进行研究,结果表明,混合润滑时较高黏度润滑油的摩擦力较小;表面粗糙度幅值在混合润滑时对摩擦力影响较大,且随速度增加而增强,边界润滑时影响很小。与纵向纹理相比,横向纹理表面的摩擦力较小且稳定,低速时这种差别更加明显。     

Effect of surface texture,moisture and wear on handling of rugby balls

Good grip of a rugby ball is essential in rugby union. New balls now have “pimples” on their surface to improve handling, but the exact effect of these has not been quantified.In this work friction tests were run on a range of pimple patterns. New and worn surfaces were used in dry, wet and muddy conditions. Finger pad and palm contacts were used. Effects of wearing different types of rugby mitt were also investigated.Balls with dense pimple pattern gave greater friction in dry conditions. Less dense pimple patterns performed better in the wet and muddy conditions.Synthetic leather mitts gave the best performance because the imposed texture was able to interlock more with the pimples on the balls.     

The effect of mechanical and chemical surface properties on the friction of magnetic tapes

Friction measurements were performed on specially prepared CrO₂ tapes sliding over a smooth glass cylinder. The effects of calendering and coating composition were investigated. Surface profiles were measured using a stylus method. The deformation properties of the surface layer were determined using dynamic indentation measurements. The chemical nature of the surface was studied by means of static secondary ion mass spectrometry. The results were interpreted on the basis of a simple friction model involving all dissipative mechanisms. Interfacial shearing and surface layer deformation induced by shearing were found to be the most important processes.     

Influence of surface texture and roughness parameters on friction and transfer layer formation during sliding of aluminium pin on steel plate

Surface texture of harder mating surfaces plays an important role during sliding against softer materials and hence the importance of characterizing the surfaces in terms of roughness parameters. In the present investigation, basic studies were conducted using inclined pin-on-plate sliding tester to understand the surface texture effect of hard surfaces on coefficient of friction and transfer layer formation. A tribological couple made of a super purity aluminium pin against steel plate was used in the tests. Two surface parameters of steel plates, namely roughness and texture, were varied in the tests. It was observed that the transfer layer formation and the coefficient of friction along with its two components, namely, the adhesion and plowing, are controlled by the surface texture and are independent of surface roughness (R_a). Among the various surface roughness parameters, the average or the mean slope of the profile was found to explain the variations best. Under lubricated conditions, stick–slip phenomena was observed, the amplitude of which depends on the plowing component of friction. The presence of stick–slip motion under lubricated conditions could be attributed to the molecular deformation of the lubricant component confined between asperities.     

Role of surface texture of harder surface on subsurface deformation

Plastic deformation and damage accumulation below the contact surfaces play an important role in sliding wear of ductile materials. In this study, metallographic techniques have been used to determine the extent of plastic deformation and strain localization events that occur at various depths beneath the worn surface in the subsurface zones of the ductile pins slid against harder plate with various surface textures. Results showed that the magnitude of plastic strain gradient and the depth of highly deformed zone correlate with coefficient of friction, which in turn depends on the surface texture of harder counterface, under both dry and lubricated conditions. It was also observed that the gradient of equivalent strain, as it approaches the worn surface, was higher under dry conditions when compared to that under lubricated conditions.