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The tribological performance of two polymeric friction modifiers, one based on an ester‐based compound and another based on an ethoxylated fatty ester and an organic friction modifier, oleamide, was studied at 50, 90 and 140°C using a Mini Traction Machine equipped with optical interferometry and electrical contact resistance. The ability to form surface film is found to vary among the friction modifiers and with temperature and rubbing duration. Despite a thinner film being formed, polymeric friction modifier (PFMs) exhibited lower friction and wear than oleamide at all the studied temperatures. Further, the PFMs reduced boundary friction more effectively at higher temperature. In accordance with lower boundary friction, a smoother surface topography characterized by low wear was exhibited by PFM lubricated surfaces at higher temperatures. Scanning electron microscopy‐energy dispersive x‐ray analysis and time‐of‐flight secondary ion mass spectrometry provided insights on the tribofilm formation. The improvement in the tribological performance of PFMs is attributed to temperature‐induced conformation transition of adsorbed polymer chains on the surface. The results are corroborated by data obtained from dynamic light scattering and gel permeation chromatography. [ABSTRACT FROM AUTHOR]

Purpose: The aim of this study is to experimentally analyze the friction and wear responses of different steels to different surface films generated in oil-lubricated tribological contacts. Design/methodology/approach: Tribological experiments were conducted using a 100Cr6 bearing ball sliding against a V155 carbon steel disk and 316L stainless steel disk, respectively. Lubricants with additives known to form zinc dialkyl-dithiophosphate (ZDDP) or Ca tribofilms were used. Findings: Both of the ZDDP and Ca tribofilms helped stabilize the friction coefficient of the carbon steel and stainless steel. The ZDDP tribofilm could effectively protect the carbon steel from wear, in contrast to the stainless steel, whereas the wear of both carbon steel and stainless steel could be significantly reduced by the Ca tribofilm. In the case of neither ZDDP nor Ca tribofilms formation, the 100Cr6 ball was worn by the V155 disk and generated a special surface topography. A polishing wear mechanism was proposed to explain the wear of the 100Cr6 ball. Originality/value: This study clearly shows the different friction and wear responses of steels to the different surface films and the response is dependent on the tested steel. [ABSTRACT FROM AUTHOR]

Everyday, we interact with screens, sensors, and many other devices through contact with the skin. Experimental efforts have increased our knowledge of skin tribology but are challenged by the fact that skin has a complex structure, undergoes finite deformations, has nonlinear material response, and has properties that vary with anatomical location, age, sex, and environmental conditions. Computational models are powerful tools to dissect the individual contribution of these variables to the overall frictional response. Here, we present a three-dimensional high-fidelity multilayer skin computational model including a detailed surface topography or skin microrelief. Four variables are explored: local coefficient of friction (COF), indenter size, mechanical properties of the stratum corneum, and displacement direction. The results indicate that the global COF depends nonlinearly on the local COF, implying a role for skin deformation on the friction response. The global COF is also influenced by the ratio of the indenter size to the microrelief features, with larger indenters smoothing out the role of skin topography. Changes in stiffness of the uppermost layer of skin associated with humidity have a substantial effect on both the contact area and the reaction forces, but the overall changes in the COF are small. Finally, for the microrelief tested, the response can be considered isotropic. We anticipate that this model and results will enable the design of materials and devices for a desired interaction against skin. [ABSTRACT FROM AUTHOR]

AlSi7Mg/SiCp aluminium matrix composites (AMCs) with a high ceramic content (35 vol.%) that were produced by using the field-assisted sintering technique (FAST) were subjected to tribological preconditioning and evaluated as a potential lightweight material to substitute grey cast iron brake discs. However, since an uncontrolled running-in process of the AMC surface can lead to severe wear and thus to failure of the friction system, AMC surfaces cannot be used directly after finishing and have to be preconditioned. A defined generation of a tribologically conditioned surface (tribosurface) is necessary, as was the aim in this study. To simulate tribological conditions in automotive brake systems, the prepared AMC samples were tested in a pin-on-disc configuration against conventional brake lining material under dry sliding conditions. The influence of the surface topography generated by face turning using different indexable inserts and feeds or an additional plasma electrolytic treatment was investigated at varied test pressures and sliding distances. The results showed that the coefficient of friction remained nearly constant when the set pressure was reached, whereas the initial topography of the samples studied by SEM varied substantially. A novel approach based on analysing the material ratio determined by 3D surface measurement was developed in order to obtain quantitative findings for industrial application. [ABSTRACT FROM AUTHOR]

In this study, the influence of the in-situ tribo-oxide-layer on non-lubricated tribological behaviours of LM27/SiCp composites was studied at different applied loads. For this purpose, LM27/SiCp composites were manufactured by stir casting route with reinforcement of different amounts (3–12 wt.%) and different sizes (fine: 1–20 µm and coarse: 106–125 µm) of SiCp. A comprehensive characterization of the friction and wear mechanisms ranging from mild to severe wear for oxidative and delamination at a contact pressure of 0.125–0.624 MPa was discussed. Results indicate that the friction and wear behaviour is strongly influenced by the morphology and the nature of the oxide scale on the wear track. In-situ formation of oxide layers on the contact region of the specimen supports the self-lubrication which supports better wear performance of LM27/SiCp composites. However, these study portraits that composite with 12wt. % fine size SiCp exhibits better wear performance in comparison to the other developed composites. [ABSTRACT FROM AUTHOR]

Purpose: During the production of cardboard food cans, the packaging bottom and the cylindrical wall are joined in the seaming process. In order to achieve a high-quality, crack-free surface of the cardboard seam, low friction between the seaming chuck and the cardboard must be ensured. The goal of this study was to minimise the friction between the seaming chuck and the cardboard can surface. Design/methodology/approach: Tribological properties of the seaming chuck were optimised by adjusting its material properties, surface topography and surface energy followed by measurements of the resulting friction response in sliding contact with a representative paper sample. Findings: A strong correlation between the surface free energies of the tribological samples and their measured coefficients of friction was observed, indicating that in tribological tests, adhesion was the dominating friction mechanism. Furthermore, the fact that the smoother samples yielded higher friction values than the rougher ones is most likely also correlated with the higher adhesion of the smoother samples originating from their larger contact area. Research limitations/implications: The existing results indicate that for tribological optimisation of paper and cardboard contacts primarily the adhesive friction component should be considered – by either reducing the surface free energy of the counter-body or optimising its surface topography. Practical implications: By applying the selected solution concept, a friction reduction of more than 50% as compared to the benchmark was achieved. Originality/value: The present study provides a guideline for tribological optimisation of paper and cardboard contacts. Peer review: The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-02-2020-0064/ [ABSTRACT FROM AUTHOR]

Purpose: Additive manufacturing (AM) is a promising alternative to the conventional production methods (i.e., machining), providing the developers with great geometrical and topological freedom during the design and immediate prototyping customizability. However, frictional characteristics of the AM surfaces are yet to be fully explored, making the control and manufacturing of precise assembly manufactured mechanisms (i.e., robots) challenging. The purpose of this paper is to understand the tribological behavior of fused deposition modeling (FDM) manufactured surfaces and test the accuracy of existing mathematical models such as Amontons–Coulomb, Tabor–Bowden, and variations of Hertz Contact model against empirical data. Design/methodology/approach: Conventional frictional models Amontons–Coulomb and Tabor–Bowden are developed for the parabolic surface topography of FDM surfaces using variations of Hertz contact models. Experiments are implemented to measure the friction between two flat FDM surfaces at different speeds, normal forces, and surface configuration, including the relative direction of printing stripes and sliding direction and the surface area. The global maximum measured force is considered as static friction, and the average of the local maxima during the stick-slip phase is assumed as kinematic friction. Spectral analysis has been used to inspect the relationship between the chaos of vertical wobbling versus sliding speed. Findings: It is observed that the friction between the two FDM planes is linearly proportional to the normal force. However, in contrast to the viscous frictional model (i.e., Stribeck), the friction reduces asymptotically at higher speeds, which can be attributed to the transition from harmonic to normal chaotic vibrations. The phase shift is investigated through spectral analysis; dominant frequencies are presented at different pulling speeds, normal forces, and surface areas. It is hypothesized that higher speeds lead to smaller dwell-time, reducing creep and adhesive friction consequently. Furthermore, no monotonic relationship between surface area and friction force is observed. Research limitations/implications: Due to the high number of experimental parameters, the research is implemented for a limited range of surface areas, which should be expanded in future research. Furthermore, the pulling position of the jaws is different from the sliding distance of the surfaces due to the compliance involved in the contact and the pulling cable. This issue could be alleviated using a non-contact position measurement method such as LASER or image processing. Another major issue of the experiments is the planar orientation of the pulling object with respect to the sliding direction and occasional swinging in the tangential plane. Practical implications: Given the results of this study, one can predict the frictional behavior of FDM manufactured surfaces at different normal forces, sliding speeds, and surface configurations. This will help to have better predictive and model-based control algorithms for fully AM manufactured mechanisms and optimization of the assembly manufactured systems. By adjusting the clearances and printing direction, one can reduce or moderate the frictional forces to minimize stick-slip or optimize energy efficiency in FDM manufactured joints. Knowing the harmonic to chaotic phase shift at higher sliding speeds, one can apply certain speed control algorithms to sustain optimal mechanical performance. Originality/value: In this study, theoretical tribological models are developed for the specific topography of the FDM manufactured surfaces. Experiments have been implemented for an extensive range of boundary conditions, including normal force, sliding speed, and contact configuration. Frictional behavior between flat square FDM surfaces is studied and measured using a Zwick tensile machine. Spectral analysis, auto-correlation, and other methods have been developed to study the oscillations during the stick-slip phase, finding local maxima (kinematic friction) and dominant periodicity of the friction force versus sliding distance. Precise static and kinematic frictional coefficients are provided for different contact configurations and sliding directions. [ABSTRACT FROM AUTHOR]

Tribological tests are adopted to estimate the kinetic friction coefficient (COF) of the material of interest according to the American Society for Testing and Materials (ASTM) standard. Typically, for the measurement process, several replicas, as well as a postprocessing data treatment, are necessary to take into account the observed casual variability of the measurand. This article describes a statistical approach aiming to highlight the running-in phase and the most significant time intervals during the steady-state for each test replica. A two-steps procedure based on the adoption of the bootstrap method allows the automatic detection of the running-in time interval and the outlier filtering of the steady-state. Experimental activity has been carried out by performing multiple tests through the ball-on-flat tribometer in order to verify the improvement allowed by the authors’ proposal about the dry friction COF measurement in terms of both accuracy and repeatability. [ABSTRACT FROM AUTHOR]

Abstract Cutting fluid in machining process brings negative impacts on environment and operator health. Excessive cutting fluid is required and consumed in machining difficult-to-machine materials with high-pressure coolant supplies (HPCS). Dry cutting as clean manufacturing technology can eliminate the cutting fluid hazards. This work investigated the tool usage assessment, machining process variables, and surface topography under dry and HPCS conditions employing uncoated WC/6%Co fine tools. The Product Sustainability Index (PSI) approach was applied to establish the sustainability assessment involving machining process and surface quality. Tool life of dry cutting (v = 75 m/min, f = 0.1 mm/rev) achieved 75.8% of corresponding HPCS. Normal wear stage proportion in dry cutting was relatively larger. Higher cutting parameters exacerbated tool wear rate resulting in rapid edge damage, especially in dry cutting. The cutting forces, friction coefficient and specific cutting energy were associated with Ti-6Al-4V softened and specific tribological behaviors accompanied with different cutting parameters. The decisive factor of Sa depended on feed rates. Feed marks in dry cutting were eliminated due to heat softening and lateral pressure, resulting in Sa decreasing. The noticeable difference existed in Sdr for dry cutting while HPCS had a slight fluctuation for the whole cutting parameters. Under dry cutting (v = 75 m/min, f = 0.1 mm/rev), the highest sustainability index was obtained 70.0. The results indicated that dry cutting provided environmental friendliness, cleaner productions and helped to enhance sustainability. Graphical abstract Image 104 Highlights • Cooling methods with dry v. s. HPCS in turning Ti-6Al-4V were investigated. • Tool usage, process variables, and 3D surface topography were analyzed. • Product Sustainability Index (PSI) approach was applied to establish the sustainability assessment. • Under dry cutting (v = 75 m/min, f = 0.1 mm/rev), the highest PSI was 70.0. [ABSTRACT FROM AUTHOR]

An experimental study on the tribology behavior and mechanism of NBR-Steel pair has been carried out. Abrasive paper was used to polish the NBR surface. The influences of surface topography on the friction coefficient were investigated based on the block-on-ring tribometer. Results show that polishing with abrasive paper is an effective method to reduce the friction coefficient of NBR on steel. Superlubricity was also found in the test. A new method to explain the superlubricity based on the contact angle and surface molecular structure was put forward in this work. Abrasive paper polishing changes the surface asperities, so affects the contact angle, so as to influence the boundary limiting shearing strength, and then causes the superlubricity. During the friction process the microstructure obviously changed, along with mechanical breaking of the molecular chain. [ABSTRACT FROM AUTHOR]

The work aims to study tribology performance of dialkyl dithiocarbamic borate ester. A new extreme pressure and anti-wear additive of dialkyl dithiocarbamic borate ester(CNSB) was synthesized. When dialkyl dithiocarbamic borate ester was added to the base oil in proper proportions, the result was lubricating oil. Tribology performance of various lubricating oil was investigated by using a four-ball tester. Surface topography of wear scar was observed through scanning electron microscopy. By observing wear scar diameter, friction coefficient, maximum nonseizure load and surface topography of wear scar, the tribology performance and friction mechanism was investigated. With the increase of quality fraction of additive CNSB, friction coefficient, wear scar diameter and friction coefficient decreased rapidly, but the maximum nonseizure load increased significantly. The wear scar diameter of oil samples with 1.5% addition amount of CNSB decreased by 28.95%. The friction coefficient of oil samples with 2.0% addition amount of CNSB decreased by 34.48%. The maximum nonseizure load of oil samples with 2.0% addition amount of CNSB increased by 539 N. In the course of friction, the synthetic CNSB was decomposed. The appeared active S elements and a small number of N and B elements formed lubrication protective film, resulting in lower friction coefficient and good wear resistance. [ABSTRACT FROM AUTHOR]

Despite environmental concerns, the automotive, aerospace and other manufacturing industries still extensively use hard-chrome coatings. This is mainly due to the coatings' ability to combine unmatched aesthetics with high hardness, excellent wear resistance, low friction and good corrosion protection in aggressive environments. However, the performance of hard-chrome coatings is dependent on the micro cracks developed during the deposition process. These cracks alter the surface topography, which has a major influence on the tribological performance of the contact, especially under mixed lubricated conditions. The aim of this study was to investigate the effect of a coating's crack density and a post-polishing process on the friction and wear performance of hard-chrome coatings. Three different crack densities combined with a post-polishing process were tested using the ball-on-disc configuration in a poly-alpha-olefin oil (PAO) lubricated point contact. The results clearly show that for hard-chrome coatings and random, non-uniform crack-type textures the size and density of the crack pattern determine the friction and wear performance of the contact. For the investigated contact conditions the best performance, i.e., low friction, fast running-in and minimum wear, was obtained when combining medium-density cracks of ∼3% and the post-polishing. [ABSTRACT FROM AUTHOR]

It is virtually impossible to follow through changes in surface topography and analyse wear mechanisms of the friction components of a hip joint prosthesis under in vivo conditions. Only under laboratory conditions can analysis of operation process of friction pairs be undertaken. Research on wear mechanisms and formation of surface topography at the subsequent stages of operation process (during in vitro testing) analyzed in this work is a new approach to the current problem concerning investigation and analysis of the lifespan of an artificial hip joint. The paper presents issues of artificial hip joint wear mechanisms and methods for studying changes in the surface topography of a ball-and-socket friction pair at the subsequent stages of tribological research. The subjects of research were co-acting components of an artificial hip joint: a metallic ball and a polymeric socket. Tribological tests were performed with a hip joint simulator replicating the physiological movements and working conditions of the natural hip joint. After each stage of tribological tests, the surface texture of friction pair components was measured using a white light interference microscopy. In addition, the surface topography was examined before and after the operation process, using a coordinate measuring machine as well as an optical microscope. Based on the results, changes in surface topography (its functional properties) occurring at the subsequent stages of tribological tests were assessed. The wear mechanisms of the interacting components, i.e. abrasion, fatigue and adhesion, were identified. [ABSTRACT FROM AUTHOR]

This paper aims at an improved understanding of the influence of different cooling and lubrication conditions on the tribological behavior at extremely high contact pressures. A novel tribometer was used to investigate the tribological behavior of the material pairing AISI 4140 Q + T and WC-Co carbides, which is common in cutting processes. Regarding the cooling and lubrication conditions, dry condition, liquid nitrogen (LN 2), carbon dioxide snow (CO 2), and two different types of sub-zero metalworking fluids (sub-zero MWF) were investigated. The tribological behavior is analyzed on the basis of the thermo-mechanical load in the tribological contact, the coefficient of friction, and the surface topography of the friction partners. Furthermore, the influence of the hydrodynamic lubrication gap height, resulting from different types of sub-zero metalworking fluids, on the lubricating effect is investigated. The analysis shows that the use of cryogenic media resulted in a substantial reduction of the thermal load. However, the coefficients of friction as well as the topography of the friction partners indicate that a lubricating effect can only be achieved up to a contact pressure of roughly 2100 MPa. In contrast, both types of sub-zero MWFs led to a high lubricating effect even at contact pressures of up to 3600 MPa. By using both types of sub-zero MWFs at a supply temperature of -30 °C a high cooling effect was also achieved. A higher hydrodynamic lubrication gap height can be beneficial for the lubricating effect depending on the type of sub-zero MWF. In this context, however, further friction-reducing effects such as adsorption films need to be considered. [Display omitted] • Novel tribometer is presented and integrated in a turning machine. • Transfer of the contact conditions during chip formation to tribological tests. • Investigation of several contact conditions as well as cooling and lubricating conditions that occur in cutting processes. • Analysis based on hydrodynamic lubrication theory in the context of cutting processes. • Identified ranges of contact pressures for which different cooling lubrication strategies lead to advantageous results. [ABSTRACT FROM AUTHOR]

Wear tests were conducted using a ball-on-disc tester. In the experiment, a 42CrMo4 steel disc with a hardness of 40HRC was placed in contact with a 100Cr6 steel ball with a diameter of 6.35 mm. The hardness of the ball was set to 62HRC. Disc samples were prepared to obtain surfaces in range to the Sq parameter but of less than 0.5 μm. Dry tests were carried out. During the tests, the friction force was monitored as a function of time. Disc and ball wear was measured after the tests using a white light interferometer Talysurf CCI Lite. To decrease variations in the experimental results, during the tests, wear debris was continuously removed from the disc surfaces. It was found that the initial surface topography has a significant influence on friction and wear levels under dry sliding conditions. It was also identified the correlation between several surface topography parameters and friction and wear. [ABSTRACT FROM AUTHOR]

The good physical and chemical properties of CFRPEEK make it advantageous as a friction pair for water hydraulic components. This paper investigated the effects of surface topography and wettability on the tribological properties of CFRPEEK and 316 L under water lubrication, with emphasis on four topographies of hemispherical pit, conical pit, ellipsoidal pit and wedge-shaped pit. From the experimental results, the ellipsoidal pit CFRPEEK samples exhibited the best tribological properties and better wettability. An interesting phenomenon was found that when the contact angle of the CFRPEEK sample is small, the friction coefficient and the wear scar depth are also small. In conclusion, taking the ellipsoidal pit as the surface topography of the CFRPEEK sample is conducive to improving its wettability, and promote the formation of stable water film, thereby improving its performance, reducing wear and increasing its service life. [ABSTRACT FROM AUTHOR]

Al-2.26% Mg alloy reinforced with Al 3 Zr particles was synthesised by Direct Melt Reaction in situ technique. Wear rate, wear rate/vol% Al 3 Zr (normalised with respect to amount of Al 3 Zr), normalised wear, and wear coefficient have been evaluated. At different combinations of normal load and sliding velocity two modes of wear i.e. mild/oxidative and severe/oxidative-metallic modes are observed. With increase in the amount of high hardness Al 3 Zr particles, composites can be used even at higher load and sliding velocity while still being in mild wear regime. Coefficient of friction (COF) has fluctuating tendency with sliding distance. COF shows a decreasing trend with load, whereas, with sliding velocity and composition trend is reversed. Low wear and high COF indicates its suitability in brake materials. [ABSTRACT FROM AUTHOR]

This study is aimed at investigating the influence of counter surfaces׳ topography on tribological behavior of several carbon-filled polyphenylene sulfide (PPS) composites in water lubricated contacts. The results of this study showed significant increase in wear rate of pure, graphite and/or multi-walled carbon nanotubes filled PPS composites with increase in mean slope of profile along the sliding direction (Δ α y ). This is while SCF filled PPS composites exhibited 1–3 orders of magnitude lower wear rate with little dependence on counter surface roughness characteristics. Among the roughness parameters studied, R pk and lay orientation played a more significant role in friction, and R pk and Δ α y were found to correlate best with the wear rate of the composites not containing SCF in their matrices. [ABSTRACT FROM AUTHOR]

Tribological properties of acid and alkali solutions on glass surface were studied in aqueous environment using a ball-on-disc reciprocating configuration. Interactions between lubricants and sliding surfaces produce different surface topographies. The lubricating ability of each kind of surface topography was evaluated using the same base oil. Wear tracks which were smooth or with grooves on the surfaces had high coefficient of friction in reciprocating sliding tests. However, surfaces with pits exhibited much lower friction than that the others. Low friction coefficients could be achieved after the running-in process with acidic solutions, accompanied by the formation of a pitted topography on the wear tracks. Especially, the friction coefficient was found to be below 0.01 during the steady sliding period, except at the reversal positions. Such good lubricity could be attributed to the micro-sized pits. [ABSTRACT FROM AUTHOR]

MoS 2 and WS 2 nano-objects have been studied in tribological applications and increasingly in other applications where nano-objects come into sliding contact with each other. Fundamental friction studies on a single nano-object are of interest. In this research atomic force/friction force microscopy (AFM/FFM) studies have been conducted on MoS 2 and WS 2 nanotubes to study scale effects and analyze the contributions of surface topography and orientation effects on friction. Variations in friction force due to topography were determined to be as a result of the ratchet mechanism and “collision” effect. There were no orientation effects on coefficient of friction on either of the nanotubes. [ABSTRACT FROM AUTHOR]

The aim of the present work was to investigate the influence of humidity and corrosion in a high-salinity environment on the friction and wear behaviour of three brake disc materials. Experiments were conducted using a commercially built disc-on-pin machine (SRV4, Optimal Instruments, Germany). Three different disc brake materials were used: cast iron (type FG25), chromium bearing steel (type 100Cr6) and an aluminium-based composite Al MMC (type A359/SiC p ). The pin in all tests was a commercial automotive brake pad material. The results showed that the friction coefficients and the wear rate for all tested materials were sensitive to increasing normal load and the sliding speed. At increased humidity level, a water film formed and behaved as a lubricant. The corrosion due to salt spray had a larger influence on the tribological behaviour of the cast iron and the chromium steel than it did on the Al MMC. The Al MMC A359/SiC p exhibited a better tribological behaviour than the other brake disc materials used in this investigation under the given test conditions. [ABSTRACT FROM AUTHOR]

In any attempt to theoretically calculate the real contact area for 3D engineering surfaces, a criterion is needed to identify the relevant asperity-peaks that carry the load in tribological contacts. In our recent work, we investigated how different, available 2D criteria affect the properties of the theoretically determined asperity-peaks in 2D surfaces. In this work, however, we focused on a 3D surface characterisation. The effect of different asperity-peak identification criteria on the properties of the asperity-peaks (numbers, radii and heights) is studied in the 3D domain. Several different criteria that take into account the number of neighbouring points, the distances between them (lateral resolution) and their heights were evaluated for real measured surfaces with five different surface roughnesses in the broad engineering range of arithmetic surface roughness from S a =0.005µm to S a =0.529µm. From the results it follows that all three chosen asperity-peak identification criteria (5PP-3D, 9PP-3D and 9PP-R-3D) result in reliable asperity-peak properties, and none of them can be favoured based on a theoretical evaluation only. There are, however, important differences between them. The data resolution in the x and y directions has a very important influence on the numbers, radii and heights of the asperity-peaks, and the results suggest that the data's lateral resolution, below 1µm, should be used for the relevant asperity-peak identification. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents an investigation on the correlation between surface topography and its mechanical properties measured by a novel multi-function tribological probe microscope (TPM) at the micro/nanometre level. Four surface functions of topography, friction, nano-hardness and Young's modulus are measured over a range of materials, on a point-by-point basis using the TPM. The capability of multi-function mapping of the TPM allows the cross correlation to be carried out, in order to investigate the influence of one function on another, especially the surface topography's effect on its mechanical properties. A general negative correlation between surface topography and hardness/Young's modulus has been found for most homogeneous surfaces, which indicates a modulation effect of surface geometrical features on its mechanical properties. [Copyright &y& Elsevier]

Abstract: In this study, we investigate the running-in behavior of brass (i.e. 95% Copper and 5% Zinc) sliding against 100Cr6 under lubricated conditions. Prior to the tribological tests, the materials are characterized using microindention, nanoindentation, Focused Ion Beam analysis (FIB), X-Ray Photoelectron Spectroscopy (XPS), and White Light Interferometry (WLI) in order to quantify the mechanical properties, grain sizes, chemistry, and topography. The sliding experiments are performed using “real time” tribometry with a pin on plate tribometer with varying contact pressures (1–4MPa) and sliding velocities (10–20mm/s). We found that a significant reduction in friction during running-in occurs only at a small range of pressure (2.4–2.9MPa). We suggest that two main mechanisms are favorable for running-in. The first mechanism is the presence of ZnO in the near-surface region of the wear track, which acts as lubrication and reduces the friction. The second mechanism is the presence of C/CH X within the first 200nm of the pin which acts as a passivation layer and thus keeps the transfer film thin and stable. [Copyright &y& Elsevier]

Abstract: An experimental study of the friction-induced noise generated by the disc brake system of a passenger car is presented. In particular, the brake noise usually referred to as wire brush or roughness noise is studied. This is, in terms of frequency spectral content a broadband phenomenon, resulting from the interaction of multiple asperities in the tribological contact. A new experimental method for measurements of disc brake roughness noise is proposed, and is used in a lab environment where the vehicle speed and the brake pressure are accurately controlled. The aim is to study the influence of vehicle speed and brake pressure on the roughness noise inside the vehicle. It is shown for the specific test case that the transmission from the source to the interior is a vibro-acoustic structure-borne phenomenon. Measurements show that there is a, as expected, strong correlation between increased interior noise and both increased vehicle speed and brake pressure. [Copyright &y& Elsevier]

Abstract: The tribological mechanisms behind the initiation of material transfer and build-up of transfer layers in aluminium forming have been studied in situ in the SEM where a tip of aluminium is put into contact with a tool steel surface under controlled sliding contact conditions. By combining in situ observations with post-test high resolution FEG-SEM studies of the contacting surfaces we have shown that aluminium is immediately transferred onto the fine polished tool steel. It was also confirmed that the initial transfer occurs on a very fine scale and is localised to the surface irregularities presented by the slightly protruding carbonitrides. In contrast, the less protruding M6C carbides, as well as the martensitic steel matrix exhibit very little initial transfer. Intentionally made scratches (roughly 5μm wide and 2μm deep) across the tool surface immediately result in larger scale transfer, which grows upon further passages of work material causing a high coefficient of friction. The study illuminates the extreme value of combining the in situ technique with high-resolution scanning electron microscopy using low acceleration voltage as a mean to detect the very thin initial transfer layers. With the higher acceleration voltages normally used, the transferred aluminium becomes transparent and can hardly be detected. [Copyright &y& Elsevier]

Abstract: The dry rolling/sliding wear behaviour of Si alloyed carbide free bainitic steel austempered at different temperatures and sliding distances has been evaluated. 60SiCr7 spring steel samples were austempered in a salt bath maintained at 250, 300 and 350°C respectively for 1h. Rolling with 5% sliding wear tests were performed using self mated discs for three different test cycles, namely 6000, 18,000 and 30,000 cycles. The aim was to study the wear performance of the 60SiCr7 steel with a carbide-free microstructure containing different amounts of retained austenite. An in-depth microstructural characterization has been carried out before and after the wear tests in order to link the wear behaviour to the microstructure of each sample. The wear resistance has been expressed by means of the specific wear calculated from the mass loss after the tests. The worn surfaces were analysed by scanning electron microscopy and X-ray diffraction. Microhardness profiles were also obtained in order to analyse strain-hardening effects beneath the contact surfaces. The results indicate that the material with highest hardness—the one austempered at 250°C—exhibited the lowest wear rate in every case. It was also observed that the hardness increment and thickness of the hardened layer increases with increasing the austempering temperature and number of test cycles. Finally, the results appear to indicate that the initial roughness of the samples has no major effect in the wear rate of the samples above 2500 cycles. The higher wear performance of the sample austempered at 250°C has been attributed to its superior mechanical properties provided by its finer microstructure. It has been evidenced that all samples undergo the TRIP phenomenon since, after wear; no retained austenite could be detected by XRD. [Copyright &y& Elsevier]

Abstract: The tribological behavior of PMMA-grafted-MWCNT nanocomposite coatings that were prepared by applying the direct casting method to aluminum surfaces was investigated. Amino-functionalized MWCNTs were first covalently functionalized with PMMA to introduce the interaction force. The PMMA-g-MWCNT exhibited a higher dispersive capacity in the 6FDA-based polyimide matrix than pure MWCNT composite due to strong interfacial interactions in the nanocomposite. The maximum possible amount of PMMA-g-MWCNT was 5wt.% because excessive MWCNT in the nanocomposites makes them fragile and brittle. Sliding tests were performed in ball-on-disk configurations under dry conditions. The normal contact force was 9.7N against a 12.7-mm-diameter steel ball resulting in a Hertzian circular contact stress of 0.65GPa. The sliding speed was 0.02m/s and sliding tests were continued until the coefficient of friction stabilized. The nanocomposite coating reinforced with 3wt.% MWCNT was the most stable and had the lowest coefficient of friction in this study. This was due to the formation of a thin, uniform friction film on the wear track during sliding, and we concluded that the friction film plays an important role in facilitating the stable frictional behavior of the nanocomposite coatings. [Copyright &y& Elsevier]

Abstract: This paper describes future trends in surface metrology. Measurement techniques are briefly mentioned. A special attention was paid to tactile and optical methods. Selected problems of surface topography characterization are described. The effects of sampling and filtering on surface topography representation are analysed. Structured surfaces are becoming both technologically and economically critical. Therefore their description is a problem of a great practical importance. Multi-process textures are very important from functional point of view. Various methods of their description are compared. Surface texturing as a means for enhancing tribological properties of frictional pairs started to be extremely popular from for about last 10 years. The effects of surface texturing on improving tribological properties of sliding assemblies are analysed. The other influences of surface topography are mentioned in this paper. [Copyright &y& Elsevier]

Abstract: The tribosystem consisted of a stationary block pressed at a required load P against a ring rotating at a defined speed. Sliding was unidirectional. Block samples, made from bronze CuSn10P with 138-HB hardness, were modified using a burnishing technique to obtain surfaces with circular oil pockets. Rings were made from 42CrMo4 steel, of hardness 40 HRC, which was obtained after heat treatment. Tests were conducted at a constant speed of 0.27m/s. Before the test, an oil drop was added to lubricate sliding surfaces. A seizure resistance test was carried out at constant normal load of 2700N. Tribotests were automatically stopped when the coefficient of friction reached a limit value 0.15. Selected textured samples clearly exhibited a lifetime longer than untextured reference specimens. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports an experimental study of the effect of surface texture on cylinder liner wear. This research is important because the conjunction between piston rings and cylinder liner is one of the major sources to frictional losses in internal combustion engines. Experiments were conducted on a reciprocating tester. Specimens were cut from cylinder liners honed or plateau honed made of grey cast iron of hardness 218 HB. The honing operation was performed in order to obtain very similar values of the Sq parameter of one-process and two-process surfaces. In addition, one-process specimens characterised by different Sq parameter values were tested. Counter-specimens were made from chromium-coated steel C45. It was found that wear of two-process surfaces was lower than that of one-process surfaces characterized by the same Sq parameter. Linear wear of specimens was proportional to initial Sq parameter value. The effect of additional oil pockets created by the burnishing technique on cylinder liner wear was negligible. [ABSTRACT FROM AUTHOR]

Abstract: The use of hardened high strength steel is found in applications where high wear resistance is required. The wear properties of high strength Boron steel are well known in applications with abrasive wear from stones, ore and other hard material. A unique concept of wear protection of rails is newly presented, a wear resistant cap made of hardened high strength Boron steel. Reducing the wear of rails and wheels and controlling the frictional behavior in the wheel/rail contact are two key issues for railway owners in order to reduce the increasing costs related to higher axle loads, higher speeds, more frequent traffic, etc. Therefore, the aim of this work has been to investigate and compare the tribological properties of Boron steel and UIC 1100 rail steel in contact with Blue Light wheel steel (AAR Class C (69-JDG-8)) under dry and water lubricated conditions in a two-disc tribometer. Advanced analytical instruments including 3D optical surface profiler, micro-hardness indenter, light microscope and SEM/EDS were used to analyze the results. Results from the experiments show that the friction coefficient in tests with Boron steel is more stable both in dry and water lubricated conditions than tests including UIC 1100 rail steel used in todays application. Surface damages seen from water lubricated tests on UIC 1100 rail steel are not seen on the surface of the Boron steel discs. In all tests, the wear decreased when water was added in the contact and friction was slightly decreased. [Copyright &y& Elsevier]

Abstract: Contact between macroscopic surfaces occurs on asperities and local nano-/micro-scale asperity interactions govern macroscopic tribological behavior. Tribological phenomena like friction and wear are highly scale dependent. Friction measurement carried out in the range of micro-/milli-Newton loads are gaining prominence in the tribological research as they are bridging the gap between classical macro-scale tests and high precision nano-scale experiments. In this paper, recent advancements in micro-scale domain are discussed and compared with the existing macro- and nano-scale friction research. There exists a striking similarity between micro- and nano-scale frictional behavior of various materials and dependence of friction on capillary forces, surface topography, and phase composition of mated materials. Micro-tribological experiments not only offer precision and sensitivity of nano-scale (or LFM) measurements, but also give reliable information due to its multiple asperity contact configuration. [Copyright &y& Elsevier]

Abstract: Friction and wear are constant problems encountered in camshaft development. Among a wide amount of factors, surface topography is an important feature to improve in this complex system. Four parts of different shapes can be differentiated on an injection cam profile. Therefore the machining of such component is quite particular. Considering the complex shape of an injection cam, this paper is divided in two studies: 1. Variations of surface topography around freshly produced cams in order to emphasize the particular profile of cams which leads to a complex machining. 2. Evolution of surfaces during run-in in order to discover the effects of wear process on a group of roughness parameters. The results show a variation of density of peaks along the freshly produced cam surface and highlight also the importance of roller type on the evolution of topography. Further results show that summits of the surface are rounded off during run-in. Concerning the future, results of the study are encouraging to investigate more deeply the tribological behaviour (contact mechanic, oil film thickness) of the surfaces. [Copyright &y& Elsevier]

Abstract: Brake noise is an example of noise caused by vibrations induced by friction forces. During brake operation, the friction between the pad and the disc can induce a dynamic instability in the system. Brake squeal can occur in the frequency range between 1 and 20kHz, and more. Approaches to this problem are usually confined to the analysis of the system dynamics or to the tribological studies (analysis of the contact surfaces). In a previous dynamic analysis, the squeal events treated in this paper were identified to be dynamic instabilities of the brake system. This paper presents an experimental tribological analysis performed in parallel to the dynamic one and aimed to highlight the role of the contact problems in the squeal phenomena. The topography of the contact surface after braking phase with and without squeal is presented. The features of the third body and the surface topography were found to be completely different in the two cases. After squeal events the topography of the surface and the internal structure of the pad material close to the contact show several cracks and material exfoliations; on the contrary, after braking without squeal the contact surfaces were found to be smooth and compact. The analysis of the system vibrations during squeal and the numerical analysis of the contact stresses allow to relate these features to the fatigue excitation due to the local oscillation of the contact stresses at the contact surface at the squeal frequencies. The surface topography after squeal, by revealing several fatigue evidences, points out a further problem, i.e., the possible increasing of wear rates that are consequent to the squeal vibrations. [Copyright &y& Elsevier]

Abstract: The investigation of electrical low power switching contacts, including dry-circuit, is characterized as a highly interdisciplinary research field. The knowledge of plasma physics, the influence of kinetics on contact phenomena, material science and metallurgy, as well as thermal aspects and tribology, is demanded. The methods usually used at the Austrian Center of Competence for Tribology are e.g. defined contact make and break along two-independent axis using model switches, high-resolution measurement of displacement and electrical values, including the detection of arcs, contact force measurement in the kHz and cN range (one-axis and two-axis systems), on-line optical investigations (especially time lapse movie systems), state of the art 3D surface topography measurement of eroded contact surfaces, and (electron-) microscopical evaluation of metallographic cross sections. Some aspects of this methodology are presented in this paper. [Copyright &y& Elsevier]

The friction behaviour of gear teeth in the context of tribology can have a strong effect on housing vibration, noise and efficiency. One of the parameters that greatly influences the friction under certain running conditions is surface roughness. In this work, rough friction was studied in lubricated sliding of roller surfaces, which were manufactured to simulate the real gear surfaces. By examining 3D surface topography of two mating bodies, both surface roughness and its effect on friction behaviour can be studied. In a previous study, a rough-friction test rig has been designed, constructed and initially verified. The types of surfaces involved in this study are ground, shot-peened, phosphated and electrochemically deburred. These rollers were subjected to the same friction testing procedures. Roller surfaces were then examined, and correlation between the topography and the frictional behaviour was analysed. Friction behaviour was interpreted in terms of Stribeck curves (friction coefficient as the function of Hersey parameter (ην/p)). The results showed that electrochemically deburred and certain phosphated surfaces provide lower friction coefficient values which are competitive to fine-ground surfaces in lubricated rolling/sliding contact. [Copyright &y& Elsevier]

This research presents the analysis of metrologic and tribologic aspects of machined surfaces obtained after turning with the application of various cooling/lubricating methods. The thoroughly conducted machining tests are: dry machining, minimum quantity cooling lubrication (MQCL); minimum quantity cooling lubrication with EP/AW modifications (MQCL+EP/AW) and minimum quantity lubrication (MQL). The phosphate ester based modification in the MQCL+EP/AW method is employed in order to increase the lubricating properties of the emulsion. The surface topography, responsible for the tribological properties of mating parts, is measured. The smallest values of the surface roughness are obtained after turning under MQCL+EP/AW conditions, while the highest values of parameters responsible for oil retention in mating parts are obtained after machining with the MQL method. • Relations between machined surface integrity of AISI 1045 steel and tribology. • Occurrence of tribofilm on machined surfaces after MQCL+EP/AW and MQL. • Decreased volumetric wear on samples after MQCL+EP/AW and MQL. • Lowest friction coefficient obtained for surface after MQCL + EP/AW. [ABSTRACT FROM AUTHOR]

Abstract: (Ti,Cr)N and (Al,Cr)N thin films were prepared by nitrogen ion beam assisted deposition of Cr, Ti or Al (IBAD) atoms on a titanium, chromium or aluminium substrate. In this way, layers featuring a diverse composition were obtained. The actual profile of the implanted and deposit atoms differed from the theoretically assumed process. Some of the implanted nitrogen formed gas bubbles under the sample''s surface. The gas bubbles released the nitrogen upwards while the local temperature increased during the implantation or during a later heating process. Craters are formed from the bubbles, which were clearly visible on the AFM photographs. Annealing the modified surfaces in a vacuum always changed the surface topography of the sample. The lowest wear rate and the lowest friction coefficient were observed in the Cr–Ti–N and Cr–Al–N samples. [Copyright &y& Elsevier]