Tribological performance of B4C modified C/C-SiC brake materials under dry air and wet conditions

In this work, boron carbide (B₄C) was selected as additive to improve the tribological performance of C/C-SiC brake materials. It contained four phases (C, B₄C, Si and SiC) in B₄C modified C/C-SiC (C/C-B₄C-SiC) brake materials. Its wear rates were much less than that of C/C-SiC, especially at high braking speeds. The introduction of B₄C particles could reduce the braking temperature. During the braking process, B₄C in the material can be oxidized to B₂O₃. The flow of B₂O₃ could cover the interface of carbon fiber and PyC to prevent them from oxidation and thereby reduce the oxidative wear of the brake materials. Under wet conditions, the braking property of C/C-B₄C-SiC brake materials did not degrade, whereas the braking process was found to be stable.     

混杂纤维含量对树脂基摩擦材料摩擦磨损性能的影响

为了研究多种只由非金属混合组成的增强纤维对树脂基摩擦材料摩擦磨损性能的影响,以腰果壳油改性酚醛树脂（CNSL）为基体,按不同比例加入玻璃纤维、碳纤维和芳纶浆粕纤维,采用热压烧结技术制备摩擦材料。利用与高速钢配副的环块摩擦磨损试验机研究摩擦材料在不同制动工况下的摩擦磨损性能,并利用扫描电子显微镜分析了材料的磨损形貌。结果表明,玻璃纤维、碳纤维、芳纶浆粕纤维的体积比分别为4 %、10 %、3 %所组成的摩擦材料（P3）的硬度比其体积比分别是7 %、4 %、6 %的摩擦材料（P1）和其体积比分别是1 %、7 %、9 %的摩擦材料（P2）的硬度大;在不同的制动条件下,样品P1的摩擦因数最大,P3次之,P2最小,样品P3和P2的相对磨损率相似且比较稳定,约为样品P1的1~1/5,样品P3表现出最佳的摩擦学性能;摩擦材料和对偶材料的磨损形式主要为磨粒磨损。     

Microstructures and tribological behaviors of Cf/C-SiC composites tailored by Cu and Fe-Si matrices

Ternary Cu-Fe-Si alloy were applied to modify tribological behavior of carbon fiber/carbon-silicon carbide (C_f/C-SiC) composites by reactive melt infiltration. Microstructures, physical properties and tribological properties on a full-scale train brake test rig of the modified composites were studied. Results indicate that both Cu and Fe-Si alloy as matrices lead to significantly enhanced thermal conductivity and compressive strength for C_f/C-SiC composites. Moreover, the average friction coefficient of the modified composites is between 0.25 and 0.55, which is higher than that of copper metal matrix composites. In addition, the average volume wear rate of the modified composites is only 0.168 cm³/MJ. The C_f/C-SiC composites modified by Cu and Fe-Si alloy with improved physical properties and tribological properties meet the technical requirement and show high application potential in express train brake systems.     

Simultaneous enhancement of friction and wear resistance for high-speed braking system with Cr3C2-NiCr-coated brake disk

The current steel brake disk and Cu-based powder metallurgy brake pad used in high-speed trains suffer fading coefficient of friction (COF) and excessive wear, resulting in a shorten lifetime and numerous exhausted brake disks. High-velocity oxygen fuel (HVOF) spray-prepared coatings have proven their ability to improve COF and decrease wear rate. In this article, Cr₃C₂-NiCr coating was sprayed on a steel brake disk, and a series of emergency braking tests under dry and wet conditions were performed on a subscale brake dynamometer, to comprehensively evaluate the braking performance of coated brake disk. The results showed that the coated brake disk exhibits a higher COF at 380 km/h, which effectively inhibits the COF fade compared to the steel brake disk case. The coated brake system also achieves a lower wear rate of the brake pad at 380 km/h, showing the desired high COF and low wear rate properties of the braking system. Additionally, the coated brake disk maintained surface integrity even after severe braking tests, highlighting its potential in the braking system. Based on the characterizations of wear debris and brake pads, a harder and thinner oxide friction film plays a crucial role in achieving the excellent braking performance in coated brake disk cases.     

Comparative study on the tribological properties of the polyimide composites reinforced with different fibers

In this study, friction and wear of polyimides reinforced by carbon, glass, aramid, and nano‐alumina fibers were studied and comparatively evaluated against Si₃N₄ on a ball‐on‐disk test rig under dry rotating and reciprocating sliding, and coefficient of friction and wear rate were considered as responses. The worn surfaces of the composites were examined by scanning electron microscopy to reveal wear mechanisms of the materials' damage. Wear mechanisms are found to be dependent on the test conditions and mechanical properties of the composites itself. It was proven that different reinforcements had different effects on the friction and wear behavior of the polyimide composites to a great extent. The testing condition also had an important role on the tribological properties of the same materials. The best performance was shown by glass fiber‐reinforced polyimide composites owing to their excellent strength and hardness which can share the applied load on the sliding surface. POLYM. COMPOS., 37:2541–2548, 2016. © 2015 Society of Plastics Engineers     

Tough and wear-resistant carbon fiber reinforced TiC-based composite prepared by alloyed melt infiltration at low temperatures

To improve the toughness and friction properties of carbon fiber reinforced ceramic matrix composite, a Cu alloy modified carbon fiber reinforced TiC based ceramic matrix composite was designed and prepared by TiCu alloy melt infiltration at low temperatures up to 1100 °C. The as-produced composite was mainly composed of carbon, TiC, Ti₃Cu₄, TiCu₄ and Cu phases. Due to the ductile Cu alloy introduced into the matrix, the composite showed good mechanical performance especially the fracture toughness. The flexural strength reached about 248.36 MPa while the fracture toughness was up to 15.78 MPa·m^1/2. The high toughness of the composite was mainly attributed to the fiber bridging, fiber pull-out, interface debonding, crack propagation and deflection. The tribological performance of the as-produced composite was measured using SiC and 440C stainless steel balls as counterparts, respectively. The as-prepared composite exhibited good wear resistance and the wear mechanism was discussed based on the microstructural observations.     

Tribological behavior of three‐dimensional braided carbon fiber reinforced polyetheretherketone composites

Three‐dimensional (3D) braided carbon fiber reinforced polyetheretherketone (denoted as CF_3D/PEEK) composites with various fiber volume fractions were prepared via hybrid woven plus vacuum heat‐pressing technology and their tribological behaviors against steel counterpart with different normal loads at dry sliding were investigated. Contrast tribological tests with different lubricants (deionized water and sea water) and counterparts made from different materials (epoxy resin, PEEK) were also conducted. The results showed that the incorporation of 3D braided carbon fiber can greatly improve the tribological properties of PEEK over a certain range of carbon fiber volume fraction (V_f) and an optimum fiber loading of ∼54% exists. The friction coefficient of the CF_3D/PEEK composites decreased from 0.195 to 0.173, while the specific wear rate increased from 1.48 × 10⁻⁷ to 1.78 × 10⁻⁷ mm³ Nm⁻¹ with the normal load increasing from 50 to 150 N. Abrasive mechanism was dominated when the composites sliding with GCr15 steel counterpart under dry and aqueous lubrication conditions. Deionized water and sea water lubricants both significantly reduced the wear of the CF_3D/PEEK composites. When sliding with neat PEEK counterpart, the CF_3D/PEEK composites possess lower friction coefficient than those against epoxy resin and GCr15 steel counterparts. In general, CF_3D/PEEK composites possess excellent tribological properties and comprehensive mechanical performance, which makes it become a potential candidate for special heat‐resisting tribological components. POLYM. COMPOS., 36:2174–2183, 2015. © 2014 Society of Plastics Engineers     

Anisotropic tribological behavior of LSI based 2.5D needle-punched carbon fiber reinforced Cf/C–SiC composites

C_f/C–SiC composites were fabricated via liquid silicon infiltration with 2.5D needle-punched carbon fiber reinforced C_f/C composites. The effect of surface topography and carbon content of the C_f/C–SiC composites on the tribological properties was researched by the ball-on-disk reciprocating tribometer. The results indicate that different fiber layers and cross-section of the composites have various surface topography and show significant differences in the friction and wear properties. By the wear morphology and model analyses, the reason for the tribological anisotropy of the composites is that the distribution of carbon and SiC phases in the composites are inhomogeneous caused by the difference of the carbon fiber orientation and the relative content in each layer. Moreover, the wear rate of the short-cut fiber web layer was the lowest and there is an obvious linear decrease in coefficient of friction with increase of carbon content. The present work explains why the tribological properties of the composites are inconsistent and provides a way to adjust the friction properties of composite materials by optimizing the friction surface.     

Tribological behavior of short‐fiber‐reinforced polyimide composites under dry‐sliding and water‐lubricated conditions

Polyimide composites reinforced with short‐cut fibers such as carbon, glass, and quartz fibers were fabricated by the polymerization of monomer reactants process. The mechanical properties of the composites with different fiber contents were evaluated. The friction and wear properties of the polyimide and its composites were investigated under dry‐sliding and water‐lubricated conditions. The results indicated that the short‐carbon‐fiber‐reinforced polyimide composites had better tensile and flexural strengths and improved tribological properties in comparison with glass‐fiber‐ and quartz‐fiber‐reinforced polyimide composites. The incorporation of short carbon fibers into the polyimide contributed to decreases in the friction coefficient and wear rate under both dry and water‐lubricated conditions and especially under water lubrication because of the boundary lubrication effect of water. The polyimide and its composites were characterized by plastic deformation, microcracking, and spalling under both dry and water‐lubricated conditions, which were significantly abated under the water‐lubricated condition. The glass and quartz fibers were easily abraded and broken; the broken fibers transferred to the mating metal surface and increased the surface roughness of mating stainless steel, which led to the wear rate increasing for the glass‐fiber‐ and quartz‐fiber‐reinforced polyimide composites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Tribological behavior and applications of carbon fiber reinforced ceramic composites as high-performance frictional materials

Due to the favorable tribological, mechanical, chemical, and thermal properties, carbon fiber reinforced ceramic composites, especially carbon fiber reinforced carbon and silicon carbide dual matrix composites (C/C–SiC), has been considered as high-performance frictional materials. In this paper, current applications and recent progress on tribological behavior of C/C–SiC composites are reviewed. The factors affecting the friction and wear properties, including the content of silicon carbide and carbon matrix, carbon fiber preform architecture, as well as the matrix modification by alloy additives and C/C–SiC composites under various test conditions are reviewed. Furthermore, based on the current status of researches, prospect of several technically available solutions for low-cost manufacturing C/C–SiC composites is also proposed.     

Effect of Braking Speed on Friction and Wear Behaviors of C/C-SiC Composites

Carbon fiber-reinforced silicon carbide matrix composites (C/C-SiC) have received considerable attentions because of their superior friction and wear behaviors. In this paper, C/C-SiC composites were fabricated by the reaction melt infiltration method, and the braking performance, the microstructure of friction surface, and wear debris at different braking speeds were also investigated. The mean coefficient of friction increases to the maximum value of 0.52 at 10 m/s and then declines afterwards with an increase in the braking speed. The higher coefficient of friction at low braking speed indicates the excellent braking performance of the C/C-SiC composites for low braking energy. Excellent wear resistance is demonstrated by the low wear rate of the C/C-SiC composites in comparison with C/C composites.     

Investigation of the influence of CuO filler and carbon fiber on wear and transfer film of nylon composites

Nylon 1010 composite specimens were prepared with CuO filler and short carbon fiber (CF) as the reinforcement. Friction and wear behavior of composite materials was investigated in a ring‐block wear tester. The results show that carbon fiber was more effective in reducing friction and wear of nylon than CuO filler. Nylon composite with 20% CF and 10% CuO content filler had the lowest wear rate that could not be obtained with any proportion of the fiber or the filler alone. It was found that the transfer film on the counterpart of 20% CF–10% CuO–nylon was thin, continuous, and uniform. These differences in tribological performance have been studied according to the synergism between the carbon fiber and CuO filler. The tribochemical studies by X‐ray photoelectron spectroscopy (XPS) revealed that pure Cu, Cu₂O, and Cu(OH)₂ were produced due to the decomposition of CuO during sliding. Carbon fiber promoted the process of tribochemical reactions of CuO, which generated more pure Cu particle and then self‐lubricating transfer film including pure Cu was formed on the steel counterpart.© 2003 Wiley Periodicals,Inc.J Appl Polym Sci 91: 2397–2401, 2004     

Friction and wear properties of polyimide matrix composites reinforced with short basalt fibers

Short basalt fiber (BF) reinforced polyimide (PI) composites were fabricated by means of compression‐molding technique. The friction and wear properties of the resulting composites sliding against GCr15 steel were investigated on a model ring‐on‐block test rig under dry sliding conditions. The morphologies of the worn surfaces and the transfer films that formed on the counterpart steel rings were analyzed by means of scanning electron microscopy. The influence of the short BF content, load, and sliding speed on the tribological behavior of the PI composites was examined. Experimental results revealed that the low incorporation of BFs could improve the tribological behavior of the PI composites remarkably. The friction coefficient and wear rate decreased with increases in the sliding speed and load, respectively. The transfer film that formed on the counterpart surface during the friction process made contributions to reducing the friction coefficient and wear rate of the BF‐reinforced PI composites. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

A focused review on the tribological behavior of C/SiC composites: Present status and future prospects

Silicon carbide-based ceramic matrix composites have received extensive attention in recent years. Many excellent reviews have reported on the tribological behavior of carbon fiber-reinforced carbon and silicon carbide dual matrix (C/C-SiC) composites. However, a systematic overview of the tribological properties of carbon fiber-reinforced silicon carbide (C/SiC) composites does not exist. This review focuses on C/SiC composites and summarizes the key factors, including internal factors (constituent content, graphitization process, material structure and fiber direction), and various test conditions (pressure and speed, dry and wet, temperature, and counterparts) that affect their tribological behavior. Their wear mechanisms under different conditions are elaborated. Finally, some potential future development directions for improving the performance of C/SiC composites are proposed to provide high-quality ceramic matrix composites for engineering applications. These directions include structural modification, matrix modification, coating technology, laser surface texturing, and material genome method.     

Effect of counterpart materials on tribological behaviors of copper impregnated carbon/carbon composite under electric current condition

Copper impregnated carbon/carbon composite (Cu-C/C composite) was fabricated for novel sliding collector material by weaving carbon fiber, heat treatment and Cu alloy impregnation. The effects of counterpart materials (Fe ball and Cu ball) on friction and wear behaviors were investigated and compared with the result of carbon contact strip used in high-speed railway. Morphology, chemical composition, phase and structure of wear surface and tribolayer were characterized to clarify tribological mechanisms. The results show that friction coefficient follows the order: Cu-C/C composite/Cu ball > carbon contact strip/Fe ball > Cu-C/C composite/Fe ball > carbon contact strip/Cu ball. The carbon crystalline of wear surface appears preferred orientation along the sliding orientation, which is benefit for boundary lubrication. When the counterpart material is Fe ball, Cu-C/C composite is superior to pure carbon strip in mechanical strength, electrical conductivity, wear resistance and friction performance.     

Microstructure and tribological properties of multilayered ZrCrW(C)N coatings fabricated by cathodic vacuum-arc deposition

In this study, a series of ZrCrW(C)N multilayer coatings with various transition layers were deposited on AISI304 stainless steel using cathodic vacuum-arc deposition in N₂–C₂H₂ gas mixture. The tribological behaviors of sliding against Al₂O₃ balls under dry friction and lubricant conditions were investigated using a reciprocating tribometer. The results demonstrated that the ZrCrW(C)N coatings comprised (Zr, Cr, W) (C, N) crystallites and an amorphous carbon phase. It possessed a nano-hardness of 35.4 GPa and an elastic modulus of 417.7 GPa. The friction coefficient of the coating was reduced by 14% compared to that of the 304 matrices, and the wear mechanism changed from adhesive wear to slight abrasive wear under the lubrication steady state. Under dry friction conditions, the ZrCrW(C)N coatings with the entire CrWN transition layer exhibited wear rates of 1.27 ± 0.04 × 10^?8 mm³ (N m)^?1, which were one order of magnitude lower than that of the 304 steel. Compared with the untreated AISI304 stainless steel, the ZrCrW(C)N coating exhibits excellent mechanical and tribological properties under lubricated and dry friction conditions, which are crucial for engineering applications.     

Tribochemistry of TiN films sliding against ceramic counterparts in vacuum condition and N2 atmosphere

With the rapid development of aerospace technology, the tribological performance of moving parts under extreme operating conditions has attracted a great deal of attention and interest. The application of solid lubricant coatings has become a major means of improved performance to ensure stable operation. Although molybdenum disulfide (MoS₂) and diamond-like carbon (DLC) films have excellent low coefficients of friction, they are prone to failure in vacuum because they cannot overcome the challenges of assembly in atmospheric environments. Surprisingly, unexpected results were obtained in this study using conventional nitride films. Specifically, the friction coefficient of TiN/SiC friction pair in vacuum is 0.21 and the wear rate is 8.8 × 10^?7 mm³/mN. The relatively stable friction coefficient is mainly attributed to the formation of carbonaceous lubricating layer at the interface, which is the decisive factor in reducing wear. The friction coefficient of TiN/WC friction pair under N₂ atmosphere is 0.31 and the wear rate is 4.5 × 10^?7 mm³/mN. It can be summarized as follows: first, the mechanochemical induced chemical reaction of the interface, and secondly, the thermally excited nitrogen atoms saturate the dangling bonds of the transfer film. The results further reveal the friction mechanism of TiN films with advanced ceramic materials under harsh conditions and suggest a guide for engineering applications.     

Microstructure and properties of Cu-Ti alloy infiltrated chopped Cf reinforced ceramics composites

Novel friction composites (C/C-Cu₅Si-TiC) were prepared via reactive melt infiltration (RMI) of Cu-Ti alloy into porous C/C-SiC composites. The microstructure, physical properties and tribological behaviors of the novel material were studied. Results were compared to conventional C/C-SiC composites produced by liquid silicon infiltration(LSI). The resultant composite showed the microstructure composed of Cu₅Si matrix reinforced with TiC particles and intact C/C structures. Most importantly, the composite did not present traces of free Si. As a result, the C/C-Cu₅Si-TiC composite showed higher flexural strength, impact toughness and thermal diffusivity in comparison to C/C-SiC composites. Tribological properties were measured using 30CrSiMoVA as a counterpart. In general, the C/C-Cu₅Si-TiC composites showed lower coefficient of friction(COF), but higher wear resistance and frictional stability. The improved wear resistance of the C/C-Cu₅Si-TiC composites is credited to the formation of friction films from Cu₅Si matrix. Other deformation and wear mechanisms are also described considering the microstructural observations.     

Development and tribological studies of a novel metal-ceramic hybrid brake disc

Ceramic matrix composite (CMC) friction materials show promising tribological properties. Typically, carbon ceramic brake discs consist of a C/SiC rotor which is joined to a brake disc bell. Within this work, a novel metal-ceramic hybrid brake disc, consisting of C/SiC friction segments which are mounted by screws onto an aluminum carrier body, was designed and investigated. A prototype was built which was tribologically tested with three different brake pad materials, LowMet reference, modified SF C/SiC as well as C/C. A constant starting sliding velocity of 20 m/s and braking pressures of 1, 2, and 3 MPa were investigated. To simulate emergency braking conditions 10 consecutive brake applications were carried out in close succession for each brake pad material and braking pressure. The C/C brake pad material showed the highest average coefficient of friction followed by the LowMet and C/SiC material. However, the wear rates of the C/C and LowMet material were orders of magnitude higher compared to the C/SiC material.     

Low-cost preparation and frictional behaviour of a three-dimensional needled carbon/silicon carbide composite

A low-cost carbon/silicon carbide (C/SiC) composite was manufactured by phenolic resin impregnation–pyrolysis combined with liquid silicon infiltration. The carbon fiber preform was prepared by three-dimensional needling. A carbon/carbon composite with a density of 1.22 g/cm³ after only one impregnation–pyrolysis cycle was achieved by using hot-pressing curing. The density of the final C/SiC was 2.10 g/cm³ with a porosity of 4.50% and SiC-content of 45.73%. The C/SiC composite had a high thermal conductivity of 48.72 W/(m K) perpendicular to the friction surface and demonstrated good friction and wear properties. The static and average dynamic friction coefficients were 0.68 and 0.32 (at a braking velocity of 28 m/s). The weight wear rates of the rotating disk and stationary disk were respectively 7.71 and 5.60 mg/cycle with linear wear rates, 1.67 and 1.22 μm/cycle, at a braking velocity of 28 m/s.