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Brake pads play a vital role in controlling the operation of high-speed trains with over 300 km/h. Currently the copper-based composites produced by powder metallurgy techniques have been proved as one of the ideal materials. However，the braking performance is strongly influenced by the chemical composition, production, microstructure as well as the working conditions. The intrinsic mechanism of the thermal fade and wear loss under thermal and mechanical coupled influence has not yet been fully revealed. As of late, machine learning algorithms have attracted widespread attention and extraordinary results has been accomplished in materials science and engineering. In this study the algorithms for predicting the braking performance of copper-based brake pads are developed. A new PM copper-based alloy, was designed via the models of the coefficient of friction (COF) and wear loss. The braking test results of this alloy show that the average COF was 0.37 at stable stage I and thermal recession decrease only 0.012 at stage II when under 350 km/h/0.48 MPa continuous braking for 10 times. And the total wear loss is only 1.30 g when under braking from 200 km/h to 350 km/h with pressure from 0.31 MPa to 0.48 MPa. Compared with the commercial brake pads, our designed alloy exhibits excellent braking performance with COF for thermal fade reduced to 21% and the total wear loss reduced to 20%.

• High-performance copper-based brake pads that meet the service requirement with the speed range of 50–380 km/h were prepared. • The deteriorated tribological and noise performance induced by the increased content of flake graphite was revealed. • The deterioration mechanisms related to the flake graphite were eludicated. Enhancing the lubricity of copper-based brake pads has been viewed as a crucial strategy to boost braking performance. Flake graphite and the oxide film are two substances that are widely concerned with providing lubrication at the friction interface. However, the results from full-scale dynamometer in this work indicate that the increased content of flake graphite with stronger lubrication and iron particles that accelerate the generation of oxide film lead to a deterioration in tribological and noise performance. This is manifested by high sensitivity to clamping force, significant fading behavior, increased sound pressure level and high-frequency noise. The evidence from the worn surface suggests that flake graphite is susceptible to peeling off from the friction surface, thereby amplifying the instability of the friction surface. The unstable existence of both flake graphite and oxide film during emergency braking actually diminishes the lubrication of the friction interface, likely resulting in the degraded braking performance. The indication suggests that the development of high-performance copper-based brake pads should aim to achieve a harmonization of diverse properties, rather than emphasizing only specific aspects. [ABSTRACT FROM AUTHOR]

Copper-based brake pads have played a pivotal role in the braking systems of commercial high-speed trains travelling at speeds ranging from 200 to 350 km/h. In this study, the braking performance and friction and wear mechanism of copper-based brake pads at 400 km/h were further evaluated using a full-scale dynamometer. The results show that under repeated emergency braking conditions at 400 km/h, the mean friction coefficient can be maintained at about 0.3 and remains stable within six braking cycles. Subsequently, a fade phenomenon in the mean friction coefficient emerges accompanied by a significant increase in braking distance, while the mean wear loss is relatively high throughout the entire testing process. Microstructural characteristics of the friction film and matrix indicate that strong oxidation plays an important role in the failure process of the brake pads. The friction film primarily composed of oxides exhibits numerous defects, which are susceptible to peeling off during braking, thereby compromising wear resistance. Additionally, as the braking cycles accumulate, oxidation gradually invades and weakens the matrix, leading to violent migration of the copper-rich friction film across the friction interfaces and resulting in the deterioration of friction performance. This work provides valuable insights into the failure behavior of copper-based brake pads at higher braking speeds and can provide potential direction for further improving their performance. • The failure mechanism under repeated emergency braking at 400 km/h were revealed. • The evolution of wear mechanism with the increased braking cycles were elucidated. • The failure mechanism related to oxidation was proposed. [ABSTRACT FROM AUTHOR]

High-performance copper-based brake pads were prepared by the traditional powder metallurgy method, and the commercial copper-based brake pads were used as a comparison. The braking performance under the different braking speeds was studied on MM-1000Ⅱ friction and wear tester, and the surface morphology of the brake pads and the brake discs were analyzed. The results show that, with the increase of the braking speed, the friction coefficient of the self-made brake pads first decreases and then increases, while the friction coefficient of the commercial brake pads remains unchanged after decreasing. The reduction of friction coefficient is related to the formation of friction film. With the further increase of the braking speed, the rupture of the friction film results in the increase of the friction coefficient, while the softening of copper makes the friction coefficient decrease. The change of friction coefficient is subject to the combined action of the friction film and the copper softening. In the speed range of 180~350 km/h, the self-made copper-based brake pads have the higher friction coefficient and wear resistance than the commercial ones, and show the higher friction coefficient fluctuation in the process of the continuous emergency braking.

Copper-based sintered friction materials are most suitable for heavy-duty off-road vehicles, trains, aircraft, and military applications. This present study aims to investigate the tribological performance, dominating wear mechanism of an existing copper-tin sintered friction material that is being used in armoured fighting vehicle. The brake pad was tested as per IS 2742 using the chase test machine. Especially fade cycle was carried out till 441℃ to analyze the frictional response of the material. Physical, mechanical, and tribological properties were evaluated as per industrial standards. Morphological analysis was carried out using field emission scanning electron microscopy, and wear debris analysis was carried out using scanning electron microscopy–energy dispersive X-ray analysis and X-ray diffraction analysis. The dominating wear mechanisms were found to be delamination and abrasive wear. The investigated results showed a less wear rate of 0.05 cm3/MJ. However, results seem to be better for high-energy applications by exhibiting excellent mechanical properties. [ABSTRACT FROM AUTHOR]

The braking performance of copper-based brake pads containing Cu-coated SiO2 and uncoated SiO2 was tested on a reduced-scale dynamometer. Results showed that both the stability of the friction coefficient and the wear resistance are improved and the fade phenomenon of the friction coefficient is effectively alleviated during continuous emergency braking (350 km/h, 0.48 MPa) by introducing Cu-coated SiO2 into the copper-based brake pad. The better braking performance is closely related to the improved interfacial bonding and the firm pinning of SiO2 particles on the friction surface. The copper coating on SiO2 reduces the spalling of SiO2 particles from the copper matrix during the braking process. Therefore, for the sample containing Cu-coated SiO2, the SiO2 particles pinned on the friction surface act as trapping sites for wear debris, promoting the formation of secondary plateaus. As a result, the existence of stable primary and secondary plateaus in the braking process promotes the stability of the friction coefficient. [ABSTRACT FROM AUTHOR]

Understanding the wear behavior of Cu-based brake pads, which are used in high-speed railway trains and aircraft, is essential for improving their design and safety. Therefore, the wear mechanism of these pads has been studied extensively. However, most studies have focused on the changes in their composition and not the effects of their manufacturing conditions. In this study, we fabricated commercial Cu-based brake pads containing Fe, graphite, Al2O3, and SiO2 using spark plasma sintering under different conditions. The microstructures and mechanical properties of the pads were investigated. The pads were tribo-evaluated using the ball-on-disc test under various load conditions. Their worn surfaces were analyzed using X-ray diffraction analysis, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and confocal microscopy in order to elucidate their wear mechanism. In addition, the dynamometer test was performed to confirm whether their wear behavior would be similar under actual conditions. Finally, a comparative analysis was performed using the ball-on-disc test. The results indicated that the brake pads with the same composition but fabricated under different sintering conditions exhibited different wear characteristics. We believe that this research is of great significance for understanding the wear mechanism of Cu-based brake pads and improving their design and hence their performance.

Al 2 O 3 fiber was introduced into copper-based brake pads in order to improve the braking performance under high speed and heavy load. Two fabricated samples containing Al 2 O 3 fiber and no fiber additive were tested on a reduced-scale dynamometer using a special designed braking testing procedure. The results indicated Al 2 O 3 fiber additive mainly contributes to promote the increase of friction coefficient at relative low braking speeds and pressures and helps to stabilize the friction coefficient at high braking speed and heavy load. The addition of Al 2 O 3 fiber can also greatly reduce the wear loss of brake pads. Moreover, the sample with Al 2 O 3 fiber exhibits the lower maximum temperature during braking. Further, the relationship between braking properties and tribo-film is clearly revealed. • The high-performance copper-based brake pad containing Al 2 O 3 fiber was fabricated. • The effect of Al 2 O 3 fiber on the variation of braking performance and tribo-film caused was revealed. • The main factors and mechanisms influencing the characteristic of tribo-film were elucidated. [ABSTRACT FROM AUTHOR]

Understanding the wear behavior of Cu-based brake pads, which are used in high-speed railway trains and aircraft, is essential for improving their design and safety. Therefore, the wear mechanism of these pads has been studied extensively. However, most studies have focused on the changes in their composition and not the effects of their manufacturing conditions. In this study, we fabricated commercial Cu-based brake pads containing Fe, graphite, Al2O3, and SiO2 using spark plasma sintering under different conditions. The microstructures and mechanical properties of the pads were investigated. The pads were tribo-evaluated using the ball-on-disc test under various load conditions. Their worn surfaces were analyzed using X-ray diffraction analysis, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and confocal microscopy in order to elucidate their wear mechanism. In addition, the dynamometer test was performed to confirm whether their wear behavior would be similar under actual conditions. Finally, a comparative analysis was performed using the ball-on-disc test. The results indicated that the brake pads with the same composition but fabricated under different sintering conditions exhibited different wear characteristics. We believe that this research is of great significance for understanding the wear mechanism of Cu-based brake pads and improving their design and hence their performance. [ABSTRACT FROM AUTHOR]

The braking performance of copper-based brake pads containing different carbon fiber (CF) content was evaluated on a reduced scale dynamometer. The results show that the introduction of CF has a pronounced impact on the microhardness and plastic deformation resistance of the tribo-film. Compared with graphite, nano CFs has higher specific surface energy and is easy to react with iron to form cementite. On the one hand, the cementite containing iron particles in the sub-friction surface has high strength, which plays a strong supporting role on the friction surface; on the other hand, the cementite participating in the formation of the tribo-film also strengthens the tribo-film and reduces the oxidation degree of iron. All of those contribute to the formation of tribo-film with high plastic deformation resistance, which imparts the low transfer rate of tribo-film in the process of high-energy braking, so as to stabilize the friction coefficient and reduce the wear loss. In the range of 0–1.2 wt% CF, the 0.4 wt% CF can make the copper-based brake pad exhibit the best wear resistance and the most stable friction coefficient (0.357–0.372) during continuous high-speed emergency braking. • 0.4 wt% carbon fiber is the optimum content for copper-based brake pad to exhibit the best braking performance. • Appropriate carbon fiber content can promote the formation of high-strength matrix and tribo-film. • High-strength friction surface is the guarantee of stable friction coefficient. [ABSTRACT FROM AUTHOR]