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.

Three-dimensional molecular dynamics (MD) simulation is used to study the atomic-scale indentation process of a spherical diamond tip in contact with a copper substrate. In the indentation simulations, the force-displacement curve is obtained and compared with a modified elastic solution of Hertz. The contact area under different indentation depths is also investigated. The force-displacement curve under different maximum indentation depths is obtained to investigate elastic-plastic deformation during the loading and unloading processes.

Polycrystalline diamond (PCD) bearings are designed for use in extreme environments; this includes process-fluid-lubricated applications such as those in oil and gas drilling turbines and marine hydrokinetic (MHK) energy machines. Past uses of PCD bearings in oil and gas down-hole tool applications have proven them to be robust, long lived, and rugged [1]. To be effective in MHK machines, PCD bearings must demonstrate adequate bearing efficiency and life in a submerged marine environment not nearly as severe as an oil well bore or a gas well bore. This paper discusses the advantages PCD bearings could provide when used in underwater MHK energy machines. Laboratory test results are presented that can help predict the performance of PCD in these MHK applications. Results from three types of tests are presented including tests that measure bearing capacity, those that observe and qualify hydrodynamic properties during testing, and those that evaluate diamond wear rates through a test representing the life time of a bearing in a MHK energy application. Failure tests conducted to measure bearing capacity revealed the PCD bearing could well endure conditions found in MHK machines, and coefficient of friction (COF) tests demonstrated the PCD ability to move from a boundary lubrication regime, to mixed mode lubrication, and then become hydrodynamic. The PCD wear test was designed to simulate years in the life of a tidal stream power generator, an MHK energy machine, and showed the PCD life is more than adequate for the MHK application. Bearing capacity, COF, and wear observed during laboratory testing illustrate that PCD thrust bearings can provide a robust, long lasting, and low maintenance bearing in MHK applications.

In this study, the lubricant depletion caused by laser heating was investigated for lubricant films with thicknesses greater than and less than one monolayer. The conventional lubricants Zdol2000 and Ztetrao12000 were used. It was found that the critical temperature at which lubricants start to deplete by laser heating strongly depends on the lubricant film thickness. To analyze the lubricant depletion mechanism, we carried out temperature programmed desorption (TPD) spectroscopy on the tested lubricant films. It was found that the lubricant depletion characteristics induced by laser heating could be explained using the experimental TPD spectroscopy results for the tested lubricant films. It was also found that the depletion mechanism involved the desorption or decomposition of the lubricant molecules that interacted with the diamond-like carbon thin films when the lubricant film thickness was less than one monolayer.

In this study, friction and wear tests were performed in order to investigate the effect of sliding velocity and normal load on the friction and wear characteristics of multi-layered diamond-like carbon (DLC) coating used for machine elements (automotive engine tappet, etc). Friction and wear tests against AISI 52100 bearing steel ball were performed under various sliding velocities (0.25, 0.5, 1 and 2 m/s) and normal loads (6.13, 20.7 and 49.0 N). As a result of test, kinetic friction coefficients and wear rates of multi-layered DLC coating and AISI 52100 bearing steel were obtained under each test condition. The result showed that the kinetic friction coefficients and wear rates generally decreased with the increase in sliding velocity and normal load.

Thin hard physical vapour deposited (PVD) coatings are today frequently used in order to improve the tribological performance of forming tools, cutting tools, and machine elements [1]. PVD TiN coating is widely used in high-speed steel cutting tools. Studies on the friction, wear characteristics and failure mechanisms of this coating have shown that it can reduce wear and diminish the failure of components. This coating frequently offers good corrosion protection and surface finish, high wear resistance and low coefficient of friction. On the other hand, PVD DLC (diamond-like carbon) coating provides a low friction and a high sliding wear resistance to enhance the tribological behavior and the durability of running components. DLC is becoming widely used as surface coating for machine components in lubricated systems, especially in the automotive industry. DLC coatings are nowadays frequently used in applications under high stress and/or under boundary or mixed lubrication regime and the range of use for these coatings keep growing rapidly.

In this study, nanostructured diamond (NSD) films were grown, by microwave plasma assisted chemical vapor deposition (MP-CVD) technology, on WC-Co drills for performance enhancement in dry drilling of A390 alloys. Surface cobalt was removed by a well-controlled precision etching process. H 2 /CH 4 gas mixture with a small amount of N 2 was applied to produce NSD films. Moreover, slight hone was applied to the cutting edges prior to the NSD deposition to relieve residual stresses generated by thermal mismatch in depositions. The results show feasibility of dry drilling of A390 alloys by NSD coated drills, substantially outperforming carbide drills.

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.

Nanocrystalline diamond (NCD) offers great potential for many micro-mechanical systems, particularly where low fiction, thermal mismatch and mechanical integrity are of great importance. The reduction of grain size in NCD films to a few nanometers is, however, accompanied by a significant change in morphological, chemical, mechanical and wear properties. The evaluation of these properties is therefore necessary before designing NCD-coated micro-mechanical components for which reliability, wear and long lifetime are critical issues.

Experimental evaluation of hardness, adhesion and Young’s modulus has been performed on polyimide polymeric coatings used in LCD displays and on composite polymer-based materials used in automobiles and aircraft. A novel Universal Nano+Micro Tester UNMT-1 with a nano-analyzer module NA-2 has been utilized. It measures scratch-hardness of coatings and thin films, utilizing the same nano-tip for both scratching and nano-imaging under the constant load. It measures scratch-adhesion with the same diamond tip for both scratching and nano-imaging under the continuously-increasing load. It evaluates homogeneity of films and composite materials by simultaneous Young’s modulus and topography nano-mapping, with a diamond nano-tip in a tapping mode, while frequency and phase of its vibrations are analyzed. The Young’s modulus maps allowed us to evaluate the distribution of SiO/Si02 particles embedded in araldite, with varying SiO/Si02 concentration. While the topography images could not distinguish between the particles and polymeric matrix, the nano-mechanical maps revealed the effects of particle concentration and agglomeration on the local modulus of the material and the relationship between the SiO/Si02 uniformity and uniformity in modulus. The nano-scratches of 60-nm polyimide coatings at progressively increasing and constant loads generated adhesion and scratch-hardness data, respectively. Within the applied loads of 20 to 100 μN, we observed and determined both the critical load, at which the coating was delaminated from the glass substrate, and a corresponding lateral delamination force. The mutually complimentary nano-images and force graphs coincided nicely.

Recent improvements in growth methodologies have decreased the grain sizes and thicknesses of polycrystalline diamond films to the nanometer range, while also increasing the film uniformity and growth rate and preserving the outstanding mechanical properties of diamond. This is rendering such films more technologically and commercially viable. Ultrananocrystalline diamond (UNCD) are the thinnest (<200 nm) and smoothest (Rq < 10 nm) diamond films available.[1] These films demonstrated self-mated friction coefficients as low as near frictionless carbon (μ < 0.007) in environments with sufficient humidity, and the corresponding wear rates could not be measured using scanning white-light interferometry. However, their response to environmental conditions (e.g. relative humidity, ambient species, velocity, and temperature) had not been systematically explored in the past. This study focused on identifying conditions that contribute to favorable tribological performance. We find low friction performance at humidity levels below 1.5% in both nitrogen and argon environments.

Wear at the nanoscale is a key limitation of conventional silicon and silicon nitride atomic force microscope (AFM) probe tips. Tip degradation and contamination induced by tip-sample interactions can result in decreased resolution and uncertainty in AFM measurements. Prediction and control of the wear behavior is challenging since there is no rigorous theory for the wear of a <100 nm asperity. However, ultrananocrystalline diamond (UNCD) and diamond-like carbon (DLC) are potentially ideal materials for AFM probe applications because of their high stiffness and hardness, low surface roughness, low macroscale friction coefficient and wear, and chemical inertness. The nanoscale adhesion and wear behavior of UNCD, DLC, silicon, and silicon nitride AFM probes have been characterized through systematic AFM wear tests and characterization of the corresponding nanoscale modification of the tips through transmission electron microscopy (TEM) imaging, AFM-based adhesion measurements, and AFM-based blind reconstruction of the tip shape. Our results demonstrate that significant reductions in the nanoscale wear can be achieved through the use of these carbon-based materials. We will discuss how the nanoscale wear behavior of the tips can be linked to their intrinsic materials properties through consideration of the mechanics and physics of nanoscale contacts.

The incorporation of silver into the diamond-like carbon (DLC) coatings has shown excellent potential in various applications; therefore the surface and tribological properties of silver-containing DLC thin films deserve to be investigated. In this study we have deposited silver-containing hydrogenated and hydrogen-free DLC coatings by plasma immersion ion implantation and deposition (PIII-D) methods. Atomic force microscopy (AFM) and nano-scratch tests were used to study the surface and tribological properties. The silver incorporation had only slight effects on hydrogenated DLC coatings. However, the incorporation of silver has significant effect on hydrogen-free DLC of smoothing the surface and increasing the surface energy. Those effects have been illustrated and explained in the context of experimental results.

In about a decade, since interest about boundary lubrication properties of diamond-like carbon (DLC) coatings exists, mainly chemical aspects of the DLC lubrication were investigated, i.e. focusing on interactions between various additives and coatings, while physical aspects of coating-oil interactions were not discussed in a greater extent. To elucidate some of these effects, we have analyzed the friction behaviour of DLC coatings and steel under different boundary lubrication conditions by using polyalphaolefin (PAO) base oils having different viscosity grades. Based on this, we have identified several tribo-physical effects in these contacts and for the purposes of this paper we briefly discuss the physical adsorption between the oils and the DLC surfaces, clearly indicating existence of rather strong physically adsorbed layers, which were able to resist high shear stresses under severe boundary lubrication.

Silicon wafers were exposed to an oblique Ar + ion beam to create arrays of surface ripples. Atomic force microscope (AFM) imaging revealed that the rippled (textured) surfaces exhibited highly anisotropic morphologies. Nanoscale friction experiments performed with different diamond tips illustrated a dependence of the coefficient of friction on tip radius, normal load, and sliding direction. Changes in the coefficient of friction are interpreted in terms of the applied normal load and varying contributions of the adhesion friction mechanism.

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 research project investigated the wheel wear and tribological characteristics in wet, dry and minimum quantity lubrication (MQL) grinding of cast iron. Water-based Al 2 O 3 and diamond nanofluids were applied in MQL grinding process and the results were compared with those of pure water. During the MQL grinding using nanofluids, a dense and hard slurry layer was formed on the wheel surface and could benefit the grinding performance. Experimental results showed that G-ratio, volume of wear of the grinding wheel vs. the volume of material removed, could be improved with high concentration nanofluids. Nanofluids showed the benefits to reduce grinding forces, improve surface roughness, and avoid workpiece burning. Compared to dry grinding, MQL grinding could significantly reduce the grinding temperature.

In conventional liquid lubrication it is assumed that surfaces are fully wetted and no slip occurs between the fluid and the solid boundary. Under the “no slip” condition the maximum shear gradient occurs at the fluid-surface interface. When one or both surfaces are non-wetted by the fluid, boundary slip can occur due to weak bonding between the fluid and the solid surface, which reduces shear stresses in the fluid adjacent to the non-wetted surface. A thrust bearing tribometer was used to compare the performance of “no slip” hydrodynamic thrust bearings with bearings surfaces that were made to slip at the interface between the surface and fluid. Hydrophobic surfaces on both runner and bearing were achieved with the deposition of hydrogenated diamond like carbon (H-DLC) films, produced by plasma-enhanced CVD on titanium alloy surfaces. Hydrophilic surfaces were created through the surface modification of DLC. A mixtures of water and glycerol was used as the lubricant. The tests were conducted using different constant bearing gaps. The normal load and the torque or traction force between the rotating runner and hydrodynamic thrust bearing were measured with load cells. The experimental results confirmed that load support is still possible when surfaces are partially-wetted or non-wetted.

Diamond Like Carbon (DLC) coatings are becoming very popular for automotive tribo-components as they can offer excellent tribological properties resulting in improved fuel economy and reducing dependence on harmful components of existing additives. The tribochemical interactions of low hydrogen containing DLC coating with lubricants, basically customised for ferrous materials, are yet to be well understood. In this work, an experimental study has been performed to understand the synergistic and antagonistic effects of low friction and antiwear additives on a 15 at. % hydrogen containing DLC coating. Surface sensitive analytical techniques, such as atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) were used to perform physical and chemical characterization of the tribofilms.

The friction properties of a range of boundary lubricating additives in DLC-DLC sliding-rolling, lubricated contact have been investigated. Two types of DLC have been studied, one hydrogenated diamond-like and the other a non-hydrogenated graphitic type. The graphitic-type DLC coating gave initially very low boundary friction with additive-free base oil but after a few minutes of rubbing in thin film conditions this rose to the higher value produced immediately by the diamond-like DLC. With the graphitic-type DLC, ZDDP formed a thin patchy film while MoDTC produced a marked reduction of friction. Lateral force microscopy showed that the latter resulted from the formation of low friction material on the asperity peaks. Some organic friction modifiers preserved the low friction of g-DLC during prolonged rubbing. MoDTC and ZDDP were also effective in reducing friction on diamond-like DLC.