Nanostructured carbon coating-orientant and its interaction with boundary lubricating layers

In previous works we have shown that to improve oil lubricity one should increase the orientability of the working surfaces of solid bodies. This can be achieved by applying special carbon orientant coatings to ensure the formation of highly oriented boundary layers whose molecules acquire some orientation under the effect of the solid-phase force field. The level of the orientation effect and coating characteristics are dependent on its synthesis parameters, which makes it possible to regulate them during coating application. It is shown that with increasing structural ordering of the boundary layers, the friction coefficient decreases, thus widening the limits of resistance to temperature. In contrast, tribological tests of traditional carbon coatings of the amorphous structure are devoid of the above-described effect. The estimate of the total activation energy of failure of the boundary layers for steel samples with a polycrystalline coating-orientant has proved this value to be much higher than for the same steel with a coating without the orientant coating properties.     

Friction and Wear Characteristics of C/Si Bi-layer Coatings Deposited on Silicon Substrate by DC Magnetron Sputtering

The tribological behavior of carbon/silicon bi-layer coatings deposited on a silicon substrate by DC magnetron sputtering was assessed and compared to that of amorphous carbon and silicon coatings. The motivation was to develop a wear resistant coating for silicon using thin layers of amorphous carbon and silicon. Wear tests were conducted by sliding a stainless steel ball against the coating specimens under applied normal loads in the range of 20?~?50?mN. Results showed that the wear rate of the bi-layer coating was strongly dependent on the ratio of thickness between the carbon and silicon layers. The wear rate of the bi-layer coating with 25?nm thick carbon and 102?nm thick silicon layers was about 48 and 20 times lower than that of the single-layer amorphous carbon and amorphous silicon coating, respectively. In addition, the steady-state friction coefficient of the bi-layer coating could be decreased to 0.09 by optimizing the thickness of the layer. Finally, a model for the wear reduction mechanism of the carbon/silicon bi-layer coating was proposed.     

In situ observation of the initial growth process of carbon nanotubes by time-resolved high resolution transmission electron microscopy

We succeeded in plan-view dynamic observation of the initial formation process of carbon nanotubes from β-SiC( 1 1 1 ) surfaces by time-resolved high resolution transmission electron microscopy. At 1360 °C, the flakes of graphite layers of a fibre orientation were formed on the SiC( 1 1 1 ) surfaces. From the graphite layers, carbon nanotubes were formed perpendicular to the ( 1 1 1 ) plane of the SiC. A scanning tunnelling microscopy observation showed that the end of carbon nanotube was closed. These results indicate that the caps of the carbon nanotubes are formed by a lift of a part of the graphene along the [ 1 1 1 ] direction of the SiC through generation of pentagons and heptagons. Two types of carbon nanotube, single-wall and double-wall, were observed in plan-view images. Different image intensity between an outer ring and an inner ring in double-wall nanotubes suggests that the inner layers of multiwall nanotubes are formed after the outer ones.     

Model of scuffing based on the vulnerability of an elastohydrodynamic oil film to chemical degradation catalyzed by the contacting surfaces

A model of scuffing is developed based on the premise that metallic surfaces can catalyze degradation of the lubricant film in situ. A failure mechanism for elastohydrodynamic films based on rapid decomposition of mineral and synthetic oils involving chemical reaction between entrapped oil and the containing surfaces is proposed. It is suggested that this destruction of the elastohydrodynamic oil film allows adhesion between nascent metal of opposing surfaces in the contact which in turn causes scuffing. Suppression of scuffing by the application of coatings that do not catalyze the oil decomposition and by the action of some lubricant additives which may block the catalytic effect of metallic surfaces is discussed. Effect of solid lubricant films and contaminant layers on scuffing is also described.     

Friction Reduction in Elastohydrodynamic Contacts by Thin-Layer Thermal Insulation

Reducing friction is of utmost importance to improve efficiency and lifetime of many products used in our daily lives. Thin hard coatings like diamond-like carbon (DLC) have been shown to reduce friction in full-film-lubricated contacts. In this work, it is shown that contrarily to common belief, the friction reduction stems mainly from a thermal phenomenon and not only a chemical/surface interaction one. It is shown that a few micrometer-thin DLC coating can significantly influence the thermal behavior in a lubricated mechanical system. The presented simulations, validated by experiments, show that applying a thin DLC coating to metal surfaces creates an insulating effect that due to the increased liquid lubricant film temperature at the center of the contact, locally reduces lubricant viscosity and thus friction. The results of the investigation show that the addition of thin insulating layers could lead to substantial performance increases in many applications. On a component level, the contact friction coefficient in some common machine components like gears, rolling element bearings, and cam followers can potentially be reduced by more than 40 %. This will most likely open up the way to new families of coatings with a focus on thermal properties that may be both cheaper and more suitable in certain applications than DLC coatings.     

The Effect of Phosphazene additives to passivate and stabilize lubricants at the head/disk interface

There have been a number of applications for lubricant additives in the disk drive media area, the first of which was for pseudo-contact recording with inductive heads (tri-pad sliders) in an effort to stabilize the head/disk interface and minimize lube decomposition under hot/wet conditions. A number of additives have been tried which include antioxidants as well as Lewis bases, the latter in an effort to passivate the catalytic activity of the Lewis Acid sites on the slider which results in the decomposition of the perfluoropolyether (PFPE) lubricants such as Z-Dol, AM and Z-Tetraol. In addition to this passivation action of the phosphazene toward catalytic decomposition of the lubricant, it has recently been reported that the use of X-1P (a cyclic phosphazene) also enhances reflow of the lube, increasing the durability of the head disk interface. In this regard there are still a number of unanswered questions that pertain to the mechanism of the interaction of the X-1P with the lubricant and/or carbon to cause this increase in mobility of the lubricant resulting in the enhanced durability.There are numerous technical issues associated with the use of the various additives with the main one being compatibility between the additive and the PFPEs as well as the carbon surfaces on which they are coated. These issues include bonding, phase separation of the components, and the transfer mechanism for the additive to the slider where the passivation is required.In this paper, we will look at the interaction of the X-1P with the carbon overcoat on the media in an effort to try to better understand the mechanism of such an interaction and its effect on the mobility of the lubricant as well as the amount of bonded lube on the disks.     

铜型添加剂摩擦修复作用的可行性研究

通过实验室实验和实际应用试验考察了铜型添加剂的摩擦修复作用,结果表明：铜型添加剂在摩擦条件下可在表面生成单质铜,随着负荷和温度升高,铜微粒、铁的磨损微粒、铜铁合金相互熔合扩散共晶焊接在摩擦面上形成修复膜。对梯级负荷１６００Ｎ时修复膜的厚度进行了估算,并建立了修复膜的作用模型。     

Effect of vacuum annealing on tribological behavior of nanosized diamond-like carbon coatings produced by pulse vacuum-arc method

Results of tribotests of nanosized carbon coatings formed on silicon surfaces by the pulse vacuum-arc method at various orientations of substrates with regard to a carbon plasma flow are presented; the tribotests were carried out for as-deposited coatings and coatings annealed in vacuum at 600 and 800°C. It has been shown that, among as-deposited coatings, the carbon coating deposited on a substrate perpendicular to the axis of the plasma flow has the highest wear resistance. An increase in the wear resistance of diamond-like carbon coatings after annealing at 600°C has been found.     

Hard carbon coatings and boundary lubrication of steel parts

It is shown that the composition and structure of diamond-like carbon coatings deposited on friction surfaces of steel parts of lubricated friction units have a substantial effect on the degree of the orientation of molecules of a lubricant in a boundary film and, therefore, on the antifriction behavior of the lubricant under boundary lubrication conditions. We present the results of research carried out in recent years at the Department of Friction, Wear, and Lubrication of the Blagonravov Institute of Machine Science of the Russian Academy of Sciences in collaboration with the Chemical Faculty of the Lomonosov Moscow State University and the 25th State Research Institute of the Ministry of Defense of the Russian Federation in order to enhance the lubricity of oils, as well as to simplify and cheapen their compositions, which is of great importance from the viewpoint of ecology.     

Properties of Coatings Based on Carbon and Nitrogen-Doped Carbon Obtained Using a Pulsed Vacuum Arc Method

Diamond-like carbon coatings on hard-alloy substrates, including coatings doped with nitrogen about 1.0 μm thick have been obtained using a pulse vacuum-arc method. Three types of coatings have been investigated: a carbon diamond-like coating (C), a carbon coating doped with nitrogen (C: N), and a composite coating based on (C: N + C) layers. The coatings have been annealed in atmospheric air at a temperature of 400°C. The tribological characteristics (wear resistance and friction coefficient change dynamics), the adhesion strength, and the microhardness of coatings in the initial state and after annealing have been studied. The composite coating consisting of C: N + C layers surpasses the constituent coatings in properties, both in the initial state and after annealing at a temperature of 400°C.     

RP part surface quality versus build orientation: when the layers are getting thinner

Surface quality is a very important factor to be considered in determining part build orientation in rapid prototyping (RP) processes. Previous research has shown that parts built with inclined planes or curved surfaces along the build orientation have large staircase effect, thus have higher surface roughness compared to parts built with only vertical surfaces. However, as layers are getting thinner in rapid prototyping processes, the opposite might be true. In this study, a number of experiments and measurements are conducted first. In a single machine setup, two cylinders are built, one along axial direction and the other along transverse direction using an Objet® machine. Measurements have shown that surface roughness of RP parts built along the transverse direction is better than those from the axial direction. Through analysis and observation, the authors can conclude that when layers are small enough, surface curvature or slope along the build orientation may no longer be a major concern for RP part surface quality. Instead, the authors have observed that on-the-layer contour layout may cause even more serious surface quality problem. In other words, surface quality is not only dependent on build orientation, but more on scanning orientation on layers.     

Mechanisms of structural thermal adaptability of silicate coatings

The present work describes the results of experimental research of surface layers of fine silicate coatings appearing due to the minerals, such as lubricating coatings as fillers. It is shown that the structure of protective films degrades primarily due to accumulation of impurities in the boundary layer and at the inter-phase boundary with the metallic substrate, particularly carbon promoting the formation of a larger amount of crystalline structure defects. The effect of sliding velocity on the wear resistance of the silicate coating is weighed. The compatibility of friction materials and minerals is advised in order to achieve the maximum efficiency of protective coatings.     

Über einige eigenschaften von aluminium-diffusionsschichten der ferritischen art

In the past few years research has been mainly directed towards the technology of application of Al coatings. Little attention has been paid to the properties of Al coatings and to methods of controlling these properties. The diffused aluminium coating consists of several layers. The number, thickness and structure of these layers may be varied by the choice of parameters of the treatment or by different heat treatments after aluminizing.Some mechanical properties of the diffused “ferritic” Al layers formed on carbon and alloy steels by annealing have been examined. Annealing of Al coatings changes the structure of the surface layer. Instead of layers of aluminium and intermetallic compounds, a single layer of a solid solution of Al in Fe having a characteristic structure similar to pure ferrite was formed. Microanalysis has confirmed that a diffusion process leads to the formation and growth of the “ferritic” type layer.Comparative studies of the wear resistance of carbon and alloy steels without Al coatings, with diffused coatings and with an annealed Al coating of the “ferritic” type have been carried out; aluminizing and annealing increased the resistance to wear of carbon and alloy steels. The most favourable performance was observed with low-carbon mild steels. Metallographie and hardness studies have shown that structural changes of diffused Al coatings occur at high temperature.     

Effect of polydispersed structured carbon particles with plasmochemically modified surfaces on adhesive strength of tribological polyamide coatings

Samples of structured carbon particles have been obtained with a high concentration of functional oxygen-containing groups on their surfaces. The introduction of an SCP with plasmochemically modified surfaces raises adhesive strength of polyamide-6 based coatings used for tribological purposes. The mechanism of interactions between the modified surface of the carbon filler and the polyamide matrix is proposed.     

Simultaneous observation of acoustic resonance phenomena at both surfaces of a plate coated with thin layers

Acoustic resonance phenomena at the front and back surfaces of a plate coated with thin layers were successfully observed in the amplitude spectrum of the back surface echo. The amplitude ratio of spectra with and without layers takes its maximum and minimum values at the resonant frequencies of the front and back coatings and both frequencies can clearly be distinguished from each other. As an application, the thicknesses of the front and back coatings on a steel plate were measured simultaneously using their resonant frequencies, thus verifying the validity of the principle.     

Nanolayered CrAlTiN and multilayered CrAlTiN–AlTiN coatings for solid particle erosion protection

Applying hard coatings on airfoil surfaces is proven to be an effective approach to mitigating erosion damage to engine components. Nanolayered or multilayered coatings, because of their capability of tailoring hardness and toughness through modifications in the chemistry and architecture of layer constituents, have been explored as potential candidates for this specific application. In this study, nanolayered CrAlTiN (CrN/AlTiN) coatings with different modulation periods, along with multilayered CrAlTiN–AlTiN coatings having different number of layers and different thickness of individual layers, were fabricated, characterized and evaluated. All the coatings significantly outperformed the CrN baseline in erosion resistance, and their performance was strongly affected by the bilayer period of the nanolayered coatings or the layer architectural characteristics of multilayered coatings.     

The influence of surface roughness on friction and wear of machine element coatings

The use of low friction coatings like amorphous carbon or metal-doped carbon coatings on machine elements is constantly increasing. Most often, a surface treatment, e.g. grinding and polishing or honing, is required for optimal performance of the coated machine element. This can be time consuming and costly.In this study, the effect of surface roughness on friction and sliding wear of two different coatings, one tungsten containing and one chromium containing coating, were examined using a ball-on-disc test. Ball bearing steel plates were grinded to different surface roughnesses and coated with the two different coatings.The friction was found to depend on surface roughness where the rougher surfaces gave higher friction coefficients. The wear rate for the a-C:W coating was found to be independent of the roughness, whereas the roughness had a strong influence on the wear rate for the a-C:Cr coating. This could partly be explained by a difference in wear mechanism, where fatigue wear was observed for the a-C:Cr coating but not for the a-C:W coating.     

Tribological characteristics of hardened-and-tempered structural steels turned by inserts covered with multicomponent PVD coatings

The effect of coatings deposited on cutting tools using the PVD method on the tribological characteristics of the surface layer after the finish turning of 41Cr4 and 30CrMnSi steels is considered. The tribological characteristics of the turned surfaces change substantially. The best results are achieved when using the (AlTi)N coating, which ensures substantial decreases in the coefficient of friction (by 35–40%) and the temperature in the friction zone (by up to 30%). The dependences of the wear on the friction path are linear; the wear rate of the surfaces turned by the coated tools is significantly lower than that for the surfaces turned by the uncoated tools. Compared to the uncoated R25 hard alloy, the difference in the wear rates reaches 60% in favor of (AlTi)N and (TiAl)N coatings. A decrease in the thickness of the coating from 4 to 2 μm leads to a growth in the coefficient of friction and the temperature. An X-ray structural analysis of the surface layers of the turned specimens has revealed the presence of Fe-Al solid phases, which improve the wear resistance of the surface and the efficiency of coatings like (AlTi)N.     

Coatings tribology—contact mechanisms and surface design

The fundamentals of coating tribology are presented by using a generalised holistic approach to the friction and wear mechanisms of coated surfaces in dry sliding contacts. It is based on a classification of the tribological contact process into macromechanical, micromechanical, nanomechanical and tribochemical contact mechanisms, and material transfer. The important influence of thin tribo- and transfer layers formed during the sliding action is shown. Optimal surface design regarding both friction and wear can be achieved by new multi-layer techniques which can provide properties such as reduced stresses, improved adhesion to the substrate, more flexible coatings and harder and smoother surfaces. The differences between contact mechanisms in dry, water- and oil-lubricated contacts with coated surfaces is illustrated by experimental results from diamond-like coatings sliding against a steel and an alumina ball. The mechanisms of the formation of dry transfer layers, tribolayers and lubricated boundary and reaction films are discussed.     

基于混合pi-sigma神经网络的滑油污染度分析

本文采用混合pi-sigma神经网络处理数据，对某型装备的发动机滑油系统的污染情况进行分析，基于实测数据完成了神经网络的训练和效果的检验工作。