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This paper aims to study the friction layer and tribological property of polyimide (PI)–matrix composites under different friction speeds.

Friction tests were conducted under friction speeds ranging from 20-120 km/h and pressure of 0.57 MPa by a pin-on-disk tribometer.

The results indicate that the friction coefficient decreases with the increasing of the friction speed. Under different friction speeds, the structure of the friction layer and debris are different, which affects the actual tribological performance of the composites. At low friction speed, the morphology of the friction layer is mainly particulate. The higher level of clenching action between the friction pair leads to a high friction coefficient, and the morphology of the particles in the particulate zone and the wear debris are mostly equiaxial particles. At high friction speed, the morphology of the friction layer is mainly a compact zone. The reduction of the surface roughness leads to a low friction coefficient. The debris collected on the counter surface at high friction speeds are mostly big sheets, and the morphology of the particles in the particulate zone is mostly rod-like. Controlling the conditions of the disk and the pin can reveal the influence of friction speed on the friction layer. The wear mechanisms at different friction speeds are also discussed.

By controlling the conditions of the disk and the pin to reveal the influence of friction speed on the friction layer, and the evolutions of the friction layer, wear debris were carefully inspected with the aim of demonstrating the relationship between friction speed and wear mechanism of PI–matrix composites.

This paper aims to study the micro-structure evolution of friction layers to optimize the friction and wear behaviors of TiAl-based material. It further enlarges the scope of using TiAl alloys and increase in the service life of TiAl alloy-made mechanical components, especially under some extreme conditions.

To study the structure evolution of friction layers, the HT-1000 tribometer is used to study the friction and wear properties of as-prepared samples. With the assistance of field emission scanning electron microscopy and an electron probe micro-analyzer, the stratified structures in cross-sections and a surface morphology of the wear scars are well characterized. A ST400 surface profiler helps in better understanding of the three-dimensional texture profiles of wear scars. X-ray diffractometer (XRD) is also used to analyze phases in the as-prepared samples.

An analysis method on the micro-structure evolution can provide better views to understand the influence of friction layers on the tribological behavior, at different wear stages. It finds that the micro-structure evolution of friction layers has an immediate effect on the friction coefficients and wear rates of TiAl-based material. It also proves to be a useful tool for evaluating the behaviors in friction and wear of TiAl-based material.

The findings of this paper provide better assistance to explore the effect of friction layers on the friction and wear behaviors of TiAl-based materials. The results help in deep understanding of the micro-structure evolution of friction layers. It also increases the service life of TiAl-based mechanical components.

Using typical structure of asphalt pavement in Harbin area of China, and the formula of generalized friction coefficient between base and surface layers of asphalt pavement in cold area is established.

Through structural characteristics analysis of asphalt pavement in cold area, the generalized formula of friction coefficient between base and surface layers of asphalt pavement in cold area is derived. The formula can quickly calculate the friction coefficient between layers of asphalt pavement.

Based on quantitative analysis to the contacting state between layers of asphalt pavement in cold area, the relationships between generalized friction coefficient and resilient modulus of asphalt mixtures, temperature shrinkage coefficient and temperature have been established.

The findings can enrich the description methods about the contacting state between layers of asphalt pavement, and have a certain theoretical and practical value. Through the application of the formula of generalized friction coefficient between layers, it can provide a technical basis for the asphalt pavement design, construction and maintenance in cold area.

The purpose of this paper is to reveal the mechanism of graphene low-temperature friction and provide a theoretical basis for the application of graphene.

A probe etching model of graphene on the copper substrate was established to obtain the friction pattern of graphene with different layers in the temperature interval from 100 to 300 K. The friction mechanism was also explained from a microscopic perspective based on thermal lubrication theory. Low-temperature friction experiments of graphene were carried out by atomic force microscopy to further verify the graphene low-temperature friction law.

Graphene nanofriction experiments were conducted at 230–300 K. Based on this, more detailed simulation studies were performed. It is found that the combined effect of thermolubricity and thermal fluctuations affects the variation of friction. For monolayer graphene, thermolubricity is the main influence, and friction decreases with increasing temperature. For multilayer graphene, thermal fluctuations gradually become the main influencing factor as the temperature rises, and the overall friction becomes larger with increasing temperature.

Graphene with excellent mechanical properties provides a new way to reduce the frictional wear of metallic materials in low-temperature environments. The friction laws and mechanisms of graphene in low-temperature environments are of great significance for the expansion of graphene application environments.

Serpentine is usually added into the lubricant oil to form a self-repairing protective layer on worn ferrous surface. But few works have paid close attention to the preparation of composites with the addition of serpentine. In this work, serpentine reinforced Al matrix composites were successfully prepared to be industrial lubrication components. And its fabricating parameters, compressive strength and tribological properties were analyzed.

An MM-W1 three-pin-on-disk apparatus was used to investigate the tribological properties. The worn surface, microstructure and cross-sectional morphologies were characterized by scanning electron microscopy equipped with energy dispersive spectroscopy. The compression test was carried out on a universal testing machine. An X-ray diffractometer was used to investigate the phase constitutions. The decomposition temperature of serpentine powders was investigated by a thermal analyzer, which allows simultaneous differential scanning calorimetry and thermogravimetry. With the help of finite element method model, a diagrammatic model of the self-repairing surface layer was developed to analyze the anti-friction mechanism.

Through evaluating density and Brinell hardness, sintering at 560°C for 3 h are the appropriate parameters for fabricating the composites. Compressive strength was increased by the addition of serpentine. A self-repairing surface layer was formed, reducing the friction coefficient. And a diagrammatic model of the self-repairing surface layer was developed to analyze the anti-friction mechanism.

Serpentine was added in fabricating the Al matrix composites for the first time. Sintering parameters were optimized to make better Al/Si/serpentine composites. Compressive strength was increased by the addition of serpentine. A self-repairing surface layer was formed, reducing the friction coefficient under the dry sliding condition. And a diagrammatic model of the self-repairing surface layer was developed to analyze the anti-friction mechanism. It is hoped to be helpful in further confirming the factors for the formation of the self-repairing surface layer, and in designing a new industrial anti-friction composite used for dry sliding conditions.

The purpose of this paper is to investigate use of calabrian pine (pinus brutia) cone (CPC) dust along with borax (BX) to assess the effect of friction coefficient. Despite the number of research studies completed on the mechanism of friction in automotive brake lining materials, the phenomenon is still not fully understood. Complex mechano-chemical processes occurring on the friction interface of a composite friction material make it difficult to understand the correlation between the formulation of brake lining and the frictional performance.

In this study, the use of CPC dust along with BX has been investigated for assessing the effect on friction coefficient. CPC has resin in it. BX is a boron production which is widely used in boron glass production and in ceramic industry for increasing the heat- resistant and -forming abrasion resistant. Newly formulated brake lining material with five different ingredients has been tested under Friction Assessment and Screening Test. Friction coefficient, wear rate and scanning electron microscope for friction surface were examined to assess the performance of these samples.

Analysis of the experimental results shows that the brake lining material containing CPC and BX significantly improved the stability of the friction coefficient, fade and wear resistance.

Several investigations have been conducted to use different materials in brake pads. The brake pad standards have been provided in previous studies, as well as the aims for economical and sustainable production. In the present study, production of brake pads by CPC dust and BX has been executed. Parallel results have been presented between previously reported and present study, in view of brake characteristics and wear resistance. Use of the lower cost and productive organic sources of material are the main improvement of the present study.

Dry sliding of different components over each other results in changes of interfaces. During the running‐in procedure a surface accommodation takes place. There is transfer of material from the softer to the harder component. At the surface of a composite a friction layer is formed, which has a different chemistry than the matrix. Type of friction layer and transfer layer govern the tribological performance of a dry sliding system. In order to arrive at desired frictional properties various additives are added to composites. Change of tribological performance by use of solid lubricants in dry bearings, carbon brushes and brake linings is discussed.

In a high temperature tribometer, stationary carbon has been tested against different rotating ceramics (SiC, Si₃N₄, Al₂O₃, WC‐6Ni, MgO‐ZrO₂, (Ti, Mo)(C, N)) and stainless steel (DIN 1.4876). The rotating discs were grinded, polished and/or lapped. For most material combinations, the wear morphology is known from available literature. A transfer film with a typical wear pattern was found on the rotating disc. The combination of antimony graphite EK3245 against MgO‐ZrO₂ did not form carbonaceous transfer layer. Through advanced variation of the roughness up to R_pk=0.011 μm, the wear rate has been reduced to K_v ≈ 3.5×10⁻⁸ mm³/N m at a stable coefficient of friction in a “millirange” of μ∼0.008 for a sliding distance of 20.000 m.

The purpose of this study was to investigate the use of boric acid as a friction modifier material in brake friction composites and to determine the effect of heat treatment applied during production on braking performance.

The addition of five different amounts of boric acid was balanced with cashew, which is in the friction modifier material group. The samples were produced in the following order: dry mixing, preforming and hot-pressing. The effect of the heat treatment that can be applied after the hot-pressing process on the braking performance was investigated. The tribological and physical properties of the samples were determined using tests performed according to appropriate standards. The microstructures of the friction surfaces were investigated using scanning electron microscopy.

It was observed that the tribological properties of brake friction composites containing 20% by weight of boric acid were improved. It has also been observed that the heat treatment applied after hot pressing increased the friction coefficient of the samples by 7% on average and decreased the specific wear ratio of the samples. When the surface morphologies of the samples are examined, it is seen that the friction layers of the heat-treated samples are wider, and the microvoids and cracks are reduced.

This study showed that boric acid can be used as a friction modifier in brake friction composites. It also revealed the tribological and physical contribution of the applied heat treatment to the composite. Thus, it guides brake friction composite manufacturers in the industry and researchers working in this field.

LONG before man learnt to make fire by the friction of wood, he experienced the burden of friction in dragging home his kill. Perhaps it is not too fanciful to suppose that the torn sides of his beast gave the first solid lubricant. Blood and mutton fat were seriously recommended as lubricants for church bell trunnions as recently as the 17th century. Indoed we still reckon fatty acids the best of all boundary lubricants. The range of man's activities has increased enormously in the present century, and particularly in the last few decades. Men have circled the earth in space; a space ship is on its way to examine another planet; terrestrial man is boring to the bottom of the earth's crust; others have descended to the depths of the ocean, and oven established a home on the floor of the Mediterranean, Speeds have increased by factors of thousands, temperatures range from near absolute zero to thousands of degrees; and a new environment of high‐intensity nuclear radiation has been created. Still, objects must move over and along each other in these exotic conditions; and to a large extent solid lubricants can provide the answer to the frictional problems.