Diamond-like carbon (DLC) films are excellent candidates to improve tribological properties of silicon nitride (Si 3 N 4 ) ceramic elements. Particular attentions have been paid to the preparation and analysis of DLC films on rings and discs. However, few researches on fabrication of DLC films on ball surfaces were carried out, especially on ceramic ball surfaces, because it is hard to achieve uniform coatings on ball surfaces. In this paper, DLC films on ceramic ball surfaces were studied with both experiment and FEA method. DLC films were deposited on Si 3 N 4 ceramic ball and disc surfaces with plasma immersion ion implantation and deposition techniques (PIII-D). Surface topography of ceramic balls before and after coated with DLC films showed that DLC films on ceramic ball surfaces were uniform. Tribological tests under dry friction were conducted with a ceramic ball sliding against ceramic disc and, alternatively, one of the two surfaces was coated with DLC films. The tests demonstrated that DLC films on disc surfaces were worn, while ball surface films were partly flaked. 3-D FEA models of ceramic ball sliding against ceramic disc were built and the ceramic ball/disc was coated with DLC films alternatively. DLC films were supposed to be bonded with ceramic substrates. The FEA stress fields in DLC films and on film/substrate interface showed that DLC films had great effects on stress distribution due to the low frictional coefficient and material difference from substrates. The friction force caused an increment of the stress near surfaces during sliding process, and the material difference leaded to discontinuous stress distribution on film/substrate interface. The shear stress on film/substrate interface was very slightly different between DLC films coated on ceramic balls and discs. Under almost the same shear stress, the flakes and wear of DLC films were mainly determined on the adherence of DLC films to ceramic substrates.

The aim of this study is to perform detail experimental mapping of the lubricating film thickness of bovine serum (BS) within the contact between an artificial metal or ceramic femoral head and a glass disc and analyze effect of proteins on the film formation under rolling/sliding conditions. The film thickness was studied experimentally using an optical test rig as a function of time under variety of constant mean speeds. Chromatic interferograms were recorded with a high-speed digital camera and evaluated with thin film colorimetric interferometry. Under pure rolling conditions it was observed that the central film thicknesses increased with time for all measurements. When the disc was slower than head then the measured central film thicknesses achieved values only about some few nanometres, whereas when the tests were realized with faster disc then measured central film thicknesses achieved significantly higher values. Distribution of the film thickness within the contact zone is not homogeneous and two different film thickness regions can be found; thicker protein film and thinner base film that both show specific behaviour over time. This study showed that protein formation plays an important role in the lubrication processes of artificial joints of the human. Due to challenging of this study the more complex research work is carried out at the present time.

Slip and fall accidents are a major source of occupational accidents. The coefficient of friction (CoF) that is required for gait is approximately 0.2. Floor roughness has been demonstrated to affect the available CoF. Building on this knowledge, this research aims to investigate the effect of changing floor roughness on two components of friction: adhesion and hysteresis. The experiments were carried out using a custom developed pin-on-disk type tribometer. Two common types of rubber shoe material, with Shore A hardness 50 and 95, were slid over ceramic tiles that were prepared to different roughness levels. The tiles were abraded using aluminum oxide media (commonly called “sand blasting”). Three levels of roughness were achieved, measured using the average peak height (Rz) with a stylus profilometer: 16.6 μm, 24.3 μm, and 34.6 μm. The experiments were conducted at 0.01 m sec-1 at a contact pressure of 266.1 kPa under ambient conditions to specifically examine the role of adhesion and hysteresis in the absence of hydrodynamic effects. The coefficient of friction was recorded without lubricant (dry) and lubricated with: 2% detergent solution, canola oil, and SAE 75W140 gear oil. Hysteresis was measured with SAE 75W140 because the high lubricity of the gear oil minimizes adhesion. Adhesion in dry and wet conditions was measured by subtracting the hysteresis from the coefficient of friction. Hysteresis was found to increase from 0.101 to 0.358 for the hard rubber and from 0.269 to 0.611 for the soft rubber when floor roughness was increased from 16.6 μm and 34.6 μm. Higher roughness was also associated with a decrease in dry adhesion from 0.651 to 0.277 for the hard rubber and from 0.435 to 0.041 for the soft rubber. Wet adhesion decreased from 0.285 to 0.049 for soft rubber on detergent. Canola oil, for both hard and soft, and detergent combined with hard rubber did not make a significant difference in the adhesion available. Hysteresis, which is a more robust form of friction in the presence of fluids, was found to be positively correlated with floor roughness while adhesion was negatively correlated with roughness. This indicates that increased floor friction is associated with better floor slip-resistance in the presence of fluids. Abrasively blasting floor tiles to increase the roughness of the floor surface, may lead to improved boundary lubrication friction, particularly when accompanied by soft shoe materials.

Ceramic rolling element bearings have promising applications in extreme operating conditions such as high speed, high temperature, and heavy load. In this study, a hybrid silicon nitride ceramic ball bearing lubricated with high temperature grease is presented. The structure and parameters of the bearing are specially designed to satisfy the requirement of grease lubrication, high temperature and high speed conditions. A test rig was developed for the experiments of ceramic bearing performance. The experimental results show that grease lubricated ceramic bearings with fine design have excellent high speed and high temperature performance. By analyzing the operation performance and failure bearing inspection, the failure modes of grease lubricated ceramic bearings is analyzed. Thermal instability caused by the grease insufficient supply is the main factor of failure.

Some thin films were prepared as solid lubricants on the surfaces of silicon nitride ceramic disk and ball. DLC film about 500–800 nm thickness was deposited on the ceramic surfaces using ion implantation and deposition technology. The surface roundness measure results, as well as 80 to 90 nm, showed that DLC film was shaped uniformly on the ceramic ball surfaces. The ball-on-disk tests showed DLC coating on silicon nitride surfaces could lead the friction coefficient to about 0.1 and endure about 7h at 1.5GPa and 30 mm/s. Ball milling technology was employed to prepare MoS2 film on the ceramic ball surfaces. The film thickness and tribological test results showed that the thin MoS2 film on the ball surfaces, which hardly changed the surface roughness, also improved their wear behaviors.

Natural refrigerants have gained significant interest due to environmental reasons. Among different natural refrigerants such as water, air, and ammonia, Carbon dioxide (CO 2 ) is the main candidate to replace commonly used hydrofluorocarbon (HFC) refrigerants in air-conditioning compressors due to its environmental benefits. One of the main advantages of implementing CO 2 , from an environmental point of view, lies in its relative low global warming potential (GWP) which is three orders of magnitude lower than commonly used HFC refrigerants. Coupled with the new refrigerants is also the need to use some form of protective coatings on the tribopairs. In this study unlubricated (presence of CO 2 refrigerant only) experiments were performed to evaluate the tribological performance of three different polymeric-based coatings deposited on Durabar G1 gray cast iron disks. Specifically, Fluorolon 325, Impreglon 1704 PEEK, and PEEK/Ceramic/ PTFE blends were tested against 52100 hardened steel pins. Results showed lower friction coefficient and wear in the Fluorolon 325 case compared to the Impreglon 1704 PEEK and PEEK/Ceramic/PTFE coatings. These results are comparable with earlier studies using PTFE-based coatings [1].

A stochastic analysis was derived for the lapping process of magnetic recording heads. Numerical results of the final surface roughness, material removal rate, and wear coefficient are presented in terms of material properties, applied pressure, topographies of original ceramic surface and lapping plate surface, kinematics, diamond particles density and sizes of lapping plate. The estimated final roughness is in good agreement with experimental results.

Nickel-titanium (Ni-Ti) alloys are normally associated with applications that exploit their shape memory characteristics. When properly formulated and processed, however, Ni-Ti is dimensionally stable and offers a unique blend of attributes suitable for tribological applications. This paper demonstrates that Ni-Ti alloys are promising candidate structural materials for oil-lubricated rolling and sliding contact applications such as bearings and gears. Ni-Ti alloys offer a broad combination of physical properties that make it unique among bearing materials. Ni-Ti alloys are hard, electrically conductive, highly corrosion resistant, readily machined prior to final heat treatment, non-galling and non-magnetic. No other bearing alloy, metallic or ceramic encompasses all of these attributes. Spiral orbit tribometer (SOT) tests were conducted using 60NiTi balls loaded between rotating 440C disks, lubricated with synthetic oil and tested in a vacuum. Excellent tribological performance (life and friction) was observed and lubricant degradation normally associated with titanium alloys was absent. It is anticipated that the Ni-Ti family of alloys may form the basis of an entirely new class of bearing and component materials.

More than ever, the development process in the field of automotive engineering requires shorter development cycles for a higher range of vehicles. In order to meet the ambitious goals of the automotive industry regarding CO 2 reduction and at the same time increasing the vehicle requirements in view of comfort and dynamics, it is necessary to decrease the drivetrain weight. Parallel, research and development in the field of automotive engineering is e.g. characterized by power upgraded combustion engines and by higher transmission ratios in the drive train. As a result, the rising of the weight specific power should not involve a reduction of the drivetrain reliability and the related increase of the failure probability. These demands lead to the conclusion that lightweight and robust designs have to be applied for all drivetrain components. All these factors affect the dimensioning of today’s clutch systems and step up the demands for future clutch systems. Thus, organic friction facings are getting closer to their limits due to temperature resistance. Within the frame work of the Centre of Excellence in Research CER 483 “High performance sliding and friction systems based on advanced ceramics” one approach is to apply advanced ceramics as friction material for e.g. a dry running motor vehicle clutch using the ceramic specific benefits as wear and temperature resistance combined with lightweight design to fulfill today’s demands.

In the field of mechanical engineering there is a constant demand of shorter development cycles combined with increasing requirements concerning product quality and costs. To meet these demands, which can be seen as a main success factor of industrial enterprises, suitable development processes are needed. The main goal of the IPEK is to provide tools, methods and processes to support the development of complex technical systems. Representative for high loaded frictional systems with low pressure and high sliding speed, a lubricated multi-disc clutch is used as a demonstrating system. With this demonstrating system the functionality of the developed methods is validated. For this reason a prototype of a lubricated multi-disc clutch system with ceramic friction materials has been developed and built up. Experimental investigations confirmed the potential concerning power density resulting from the use of ceramic friction materials in combination with a ceramic suitable systems design.

This paper reviews the application to tribology research of the techniques of high-vacuum surface science, in particular their integration into high-vacuum tribometers. The state of the art, the varied research interests, and the rationale for requiring such research instruments are discussed. The authors have developed a new type of high-vacuum tribometer that is aimed to the detection and characterization of charged-particle triboemission. This tribometer has been successfully used to count triboemitted charges as channel-electron-multiplier pulses and their energy distribution from different material pairs (i.e., ceramics and semiconductors when scratched by a diamond pin, and ceramics-on-same-ceramics). Instrument enhancement is ongoing to include simultaneous under-vacuum photon counting and surface work-function measurement by Kelvin-probe. The enhanced facility will enable one-of-a-kind experiments by characterizations and correlations of electron and photon emission, and of surface property evolution dynamics during sliding contact.

This paper was investigated the thermo-mechanical wear mechanisms of ceramic materials under lubricated sliding condition based on the fracture mechanics. Thermo-mechanical wear model for ceramic materials was proposed, and non-dimensional parameter T for evaluation of ceramic materials was also proposed. Non-dimensional parameter T is consist of thermal load ( Th ) and Peclet number ( Pe ).

The paper presents a numerical analysis of the rolling contact between an elastic ellipsoid and an elastic-plastic flat. Numerical simulations have been performed with the help of a contact solver called Plast-Kid®, with an algorithm based on an integral formulation or semi-analytical method. The effects of the ellipticity ratio k — ranging from 1 to 16 — and of the normal load — from 4.2 to 8 GPa — are investigated. The reference simulation corresponds to the rolling of a ceramic ball on a steel plate made of AISI 52100 bearing steel under a load of 5.7 GPa . The results which are presented are first the permanent deformation of the surface, and second the contact pressure distribution, the Von Mises stress field, the hydrostatic pressure and the equivalent plastic strain state within the elastic-plastic body. A comparison with an experimental surface deformation profile is also given to validate the theoretical background and the numerical procedure.

Ceramic particles, such as SiC and Al 2 O 3 , have been used to reinforce Al alloys to improve their strength and wear-resistance. However, previous studies mainly dealt with either relatively large hard particles (from tens to hundreds of micrometers in diameter) or nanometer-sized particles with low volume fractions (a few percent). In this study, near-fully-dense (97–99%) Al 2 O 3 -Al nanocomposites with higher particle concentrations (5–15 vol%) were processed using mechanical alloying and hot isostatic pressing. Transmission electron microscopy revealed very high dislocation density in aluminum matrix for these Al 2 O 3 -Al nanocomposites. High strength (σ 0.2% : ∼500 MPa) and encouraging tribological properties have been observed. The Al 2 O 3 (15 vol%)-Al nanocomposites performed unexpectedly well when sliding against 52100 bearing steel. The friction coefficient of the nanocomposite was 55%, 37%, and 55% lower and the wear-resistance was 1500X, 30X, and 120X higher than those of pure Al, cast Al 319 alloy, and conventional Al 2 O 3 -Al composites, respectively. Wear scar examination showed severe adhesive wear on the conventional Al alloy and micro-composite surfaces; however, only mild abrasive wear was observed on the nanocomposite surfaces. It was observed that the particle concentration had to exceed a critical level (10–15 vol%) to exhibit superior wear-resistance, even though a lower level (e.g. 5 vol%) resulted in a significantly improved tensile strength.

The authors have carried out extensive measurements of electron triboemission from the scratching of ceramics and semiconductors that are briefly summarized in this paper. Analysis of the frequency-domain distribution of typical triboemission count-pulse outputs suggested that their occurrence is not Poisson’s (e.g., it is not random). This paper presents a study on the hypothesis of deterministic-chaos origin for triboemission data. Electron triboemission outputs from the ceramics alumina, sapphire, silicon nitride and the semiconductors Si and Ge are analyzed by means of extracting deterministic-chaos metrics. The results suggest that the low-level electron-emission components may be described by multiplicative processes of random initiation, while the superimposed large burst-type components may be of deterministic origin.

In an engine, the valvetrain contributes about 6–10 % of the total frictional loss depending on architecture. The cam and the tappet contact in a direct acting mechanical bucket type valvetrain offers opportunities for friction reduction. Work has been done in the past to reduce frictional loss at the cam and tappet contact through use of lightweight materials to reduce reciprocating mass, improved surface finish, and low friction thin film coatings. This investigation explored the potential for additional friction reduction through the use of novel surface textures on tappet shims. Surface textures were produced on tappet shims using two techniques: (a) regular patterns like parallel line V-grooves, and square grooves, circular V-grooves and spiral V-grooves using a diamond tool, and (b) random irregular dimples using either ceramic peening or steel shot peening. The friction performance of these shims was compared with standard production shims and isotropic finish on production shims. Friction was measured using a motored valvetrain rig using a 3.0L cylinder head. The friction response was different on each type of groove and dependent on speed and oil temperature. The shims with parallel line V-grooves showed the highest friction reduction (up to 35%) compared to production shims. There appears to be no significant difference in wear pattern on cam lobes tested against production shims and shims with parallel line V-grooves. Also, the wear rate of a shim with parallel line V-grooves was lower than the production shims. The random dimples created by peening did not offer any friction reduction, probably due to increased surface roughness.

Ultra-high molecular weight polyethylene (UHMWPE) is a popular choice for the liner material of the acetabular cup and forms one of the articulating surfaces in total joint replacements (TJRs). Evaluating the tribological characteristics of UHMWPE on immediate contact with the physiological fluid is essential to understand pathways and mechanisms of eventual failure. In this study, the friction response and interfacial shear strength of a UHMWPE-ceramic interface was quantified using atomic force microscopy (AFM) before and after exposure to bovine serum albumin (BSA) solution. A 10% protein solution concentration was used to closely mimic protein levels in human physiological fluid. Medical grade UHMWPE samples with two different surface finishing treatments, milling and melting/reforming were used in the experiments. Friction response as a function of normal load was monitored on a particular area on each sample. Fluorescence microscopy was used to assess the protein adsorption on the test area. The interfacial shear strength of the interface was calculated from the friction data using contact mechanics. Contact angle measurements were also performed on the surfaces to evaluate the surface energies before and after protein adsorption. Correlations between the friction behavior and surface energy of the surfaces are discussed.

Membrane microfiltration is a promising technology that has been shown to extend metalworking fluid (MWF) life by eliminating contaminants while allowing the fluid to stay in use. However, the efficacy of this technology is compromised by the clogging of the filter pores in a process known as membrane fouling. In this paper the fouling issue is addressed by the development of a semi-synthetic MWF specifically designed to reduce fouling of microfiltration membranes. The composition of the designed MWF is discussed and compared with a commercial MWF. Cross-flow microfiltration fouling tests were carried out in low pressure, high velocity conditions on ceramic α-alumina membranes. Several common MWF components are shown not to be factors of membrane fouling on these membranes. The flux of the designed fluid was found to reach an immediate steady-state at about twice the value of the steady-state flux of the tested commercial fluid. SEM imaging was used to further evaluate membrane fouling by each fluid. The machining capabilities of the designed fluid were examined in terms of cutting forces and machining temperature.

Polymers for tribological applications in machines offer the advantages of simple designs, reduced manufacturing complexity and lower maintenance costs. However, polymers are far more sensitive to friction-generated temperature than are metals or ceramics. Some typical tribological polymers are being evaluated in dry sliding by a thermo tribometer that uses a thrust washer configuration [1,2]. The polymer is pressed against and slides on a ring-shaped, thermocouple-instrumented metal anvil mounted on a torque cell thus providing for simultaneous measurement of friction and temperature. Previously reported finite element estimates of temperature distribution in the polymer-metal couple have been used to guide the design of and testing with the thermo tribometer [3]. Reported here are experimental results of friction and temperature rise for three polymers (acetal, nylon 6/6, UHMWPE) sliding against metal anvils (stainless steel, aluminum) with different thermal diffusivities. Results were obtained with normal pressures of 93–465kPa and sliding speeds of 0.81–4.06 m/s during the first 300 seconds of sliding.

This paper addresses the tribological challenges in the machining of compacted graphite iron (CGI) through an investigation of the effects of tool material, local tool-surface topography and Minimal Quantity Lubrication (MQL) on machining performance. CGI is a material that is being considered as an alternative to aluminum and gray cast iron (CI) for diesel engine applications — a market with large potential. Solutions for continuous cutting operations like turning and boring of CGI are constantly being sought. Prior limited work has attributed the tool wear problems encountered during CGI machining to the absence of a lubricating layer of manganese sulphide (MnS) on the cutting tool during continuous cutting at high speeds. With the aim of understanding the tribology of the tool-chip interface, experiments were undertaken using four different tool-inserts (flat-coated carbide, grooved-coated carbide, grooved-coated cermet and chamfered ceramic tool inserts) under dry and minimal quantity lubrication (MQL) conditions. Two cutting speeds (250 m/min. and 400 m/min.) with constant feed and depth of cut were tested. Post-machining analysis was conducted to determine the chip flow angle and the resultant force in each case. Results show that at low speed, the cermet tool produces a significant reduction in cutting forces in comparison to coated carbide. At high speed, cermet shows a minor increase in forces. MQL causes a decrease in forces only at low speed in all tools except the flat-coated carbide, in which case it shows a minor increase. Resultant forces show an increase with MQL usage at the high speed, suggesting a negative influence on the CGI machining performance. The work reveals that there are several complex effects observed due to the interaction between tool coating, tool topography, and lubricant action.