Tribological behavior of carbon fiber reinforced ZrB2 based ultra high temperature ceramics

The tribological behavior of ultra-high temperature ceramic matrix composites (UHTCMCs) was investigated to understand these materials in friction applications. Samples consisting of pitch-based randomly orientated chopped carbon fiber (CF) reinforced ZrB₂-10 vol% SiC were prepared (ZS). The tribological behavior was tested on a self-designed dynamometer, coupling the UHTCMC pads with either carbon fiber reinforced carbon−silicon carbide (C/C-SiC) or steel disks, with two applied contact pressures (1 and 3 MPa) and the surface microstructures were analyzed to unravel the wear mechanisms. Even at high mechanical stresses, tests against the C/C-SiC disk showed stable braking performance and wear. The abraded material from a steel disk formed a stable friction film by fusing together harder pad particles with abraded steel, which reduced wear and stabilized the braking performance. The high values of coefficient of friction obtained (0.5–0.7), their stability during the braking and the acceptable wear rate make these materials appealing for automotive brake applications.     

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.     

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.     

Microstructure of friction surface developed on carbon fibre reinforced carbon–silicon carbide (Cf/C–SiC)

We have used TEM to study the microstructure of friction surface of carbon fibre/carbon–silicon carbide composites brake discs after multi braking stop by using organic pads. A friction surface layer was developed consistently on the top of Si regions of the composites, but inconsistently on that of SiC and C. Inside the layer, amorphous silicon/silicon oxides appeared extensively with various non-metallic and metallic crystallites dispersed inside with sizes ranging from a few nanometers to several microns. A coherent interface between the friction layer and the composite surface was established under the braking conditions, whilst its sustainability varied notably in SiC and C regions. Microcracking near the friction surface appeared in SiC and C_f/C regions largely due to the extensive ductile deformation of SiC and weak interfaces between C and C_f. Material joining mechanisms were discussed to enlighten the friction transfer layer development on the surface of the composite discs.     

Braking Behavior of C/SiC Composites Prepared by Chemical Vapor Infiltration

Carbon fiber-reinforced silicon carbide matrix composites have the potential to overcome the shortcoming of the currently used carbon/carbon friction materials in aircraft brakes. In this article, the carbon/silicon carbide (C/SiC) composites were prepared by chemical vapor infiltration method, and the brake disks with different densities and component content were finally obtained. The friction coefficient and friction stability can be significantly improved by increasing both material density and carbon content. When the density of C/SiC composite is 2.3 g/cm³, the coefficient of friction measured is 0.23, the coefficient of friction stability remains about 0.43, the liner wear rate is less than 9.3 μm/cycle, and the weight wear rate is less than 9.1 μm/cycle. The rapid increase of friction coefficient approaching the end of braking is mainly related to the increasing of surface temperature in a short time and the enhanced adhesion and abrasion of contact conjunctions and asperities. The C/SiC composites exhibited a good stability of braking against fading versus the braking number and surface temperature. The surfaces of C/SiC brake disks were covered with wear debris including the fragment of carbon fibers after the braking tests. The wear on the surfaces is significantly determined by cyclic mechanical and thermal stresses, which result in the micro-cracks in the SiC matrix, the thin flakes of the surface materials as well as the grooves.     

不同种类酚醛树脂黏结剂对摩擦材料性能的影响

分别以未改性通用酚醛树脂、特殊改性刹车片专用酚醛树脂、腰果壳油改性酚醛树脂、丁腈橡胶改性酚醛树脂为黏结剂,玄武岩纤维、钢纤维为增强纤维制备四种酚醛树脂基摩擦材料.对试样进行物理性能、机械性能和摩擦磨损性能测试.结果 表明,四种摩擦材料的密度相差不大,未改性通用酚醛树脂基摩擦材料的硬度符合刹车片使用要求,腰果壳油改性酚醛...     

耐热性汽车制动材料的研究

围绕耐热性汽车制动材料的研制，用索氏抽提法测定了双酚Ａ型苯并恶嗪中间体在路易斯酸和六次甲基四胺作用下树脂的固化程度，同时利用ＩＲ、ＤＴＡ、ＴＧＡ等测试方法研究了固化物的结构和热稳定性。制备了以该树脂为基体的制动材料，测定了制动材料的热膨胀性及摩擦磨损性能，结果表明，开环聚合酚醛树脂具有良好的热稳定性，其制动材料高温摩擦系数稳定，热恢复性良好，热膨胀小。     

改性酚醛树脂摩擦材料研究进展

介绍了用于汽车制动片摩擦材料的常用改性酚醛树脂及其发展,根据国外摩擦材料研究的专利和信息,指出了摩擦材料的研究重点。     

Microstructure and tribological properties of PIP-SiC modified C/C–SiC brake materials

A combination method of precursor infiltration and pyrolysis (PIP), chemical vapor infiltration (CVI) and liquid silicon infiltration (LSI) was proposed to prepare PIP-SiC modified C/C–SiC brake materials. The SiC ceramic matrix pyrolyzed by polymethysilane (PMS) homogeneously dispersed in the fiber bundles region, which improved the plough resistance of local C/C region and the wear resistance of C/C–SiC brake materials. When the braking speed rises to 28 m/s, the fluctuation range of friction coefficient was limited to 0.026. The linear wear rate of the as-prepared composites was could be ~50% less than that of C/C–SiC, when the braking speed was above 15 m/s (for instance, the wear rate of 1.02 μm/(side·cycle) at 28 m/s less than 2.02 μm/(side·cycle) of traditional C/C– SiC). The fading ratio D of CoF under wet conditions was ~11%. The results showed that introducing PIP-SiC could stabilize the braking process and effectively prolong the service life of C/C–SiC brake materials.     

Oxidation behaviour of C/C–SiC brake discs tested on full-scale bench rig

C/C–SiC composites are considered to be strong candidates for the new generation of high-speed train brake discs. To achieve a better application, it is necessary to improve understanding of the oxidation behaviour of C/C–SiC brake discs after a full-scale bench test rig. In this study, full-scale braking bench tests for C/C–SiC self-mated brake pairs were conducted under a braking speed of 350–420 km/h and a braking pressure of 17–28 kN. Moreover, the oxidation behaviour and mechanisms of the C/C–SiC brake discs during the practical braking process were investigated. The results indicate that the oxidation behaviour is highly dependent on the friction surface region of the C/C–SiC brake disc owing to the distribution of microcracks, the formation of friction films, the difference in temperature, and the contact content with O₂. Specifically, the oxidation depths of the friction layer on the inner circumferential surface, middle friction surface, and outer circumferential surface were 278.3, 252.1, and 359.9 μm, respectively. Furthermore, the oxidation reaction preferentially occurs in the active area of the C fibre and pyrolytic carbon (PyC) during the braking process.     

汽车传动和制动系统的陶瓷摩擦材料探秘

在汽车的制动系统中,制动摩擦片是最关键的安全零件,所有制动效果的好坏都是制动摩擦片起决定性作用,所以说,好的制动摩擦片是人和汽车的保护神。针对研制开发新型摩擦材料已成为相关行业的当务之急,论述了汽车陶瓷制动摩擦片材料引领时尚潮流,分析了陶瓷制动摩擦片的性能优势,介绍了摩擦材料的技术要求及陶瓷制动摩擦片的关键技术,提出了我国陶瓷制动片产品走向国际中高端市场。     

Thermal analysis of bulk carbon-carbon composite and friction products derived from it during simulated aircraft braking

Friction layer and friction debris samples obtained from commercially available carbon-carbon composite brake material (3D, C/C PAN CVI) by sub-scale dynamometer testing at 50% relative humidity and 100% normal aircraft landing energy have been characterized by multiple thermo-analytical techniques to investigate adsorption/desorption phenomena of physically bonded moisture and formation and decomposition of oxygen-containing structures. Thermogravimetric Analysis/Fourier Transform Infrared Spectroscopy, Temperature Programmed Reduction and Pyrolysis-Gas Chromatography-Mass Spectrometry experiments with friction layer and friction debris were accompanied with release of H₂O, CO₂ and CO on heating. These products are not observed when comparable analyses with the bulk brake material were performed. These data reflect significant oxidation of the original brake material and indicate that gaseous products (carbon oxides, H₂O) are released from the modified brake material during heating to temperatures approximating those experienced during typical aircraft braking.     

Development of C/C–SiC Brake Pads for High-Performance Elevators

Novel C/C–SiC materials have been developed for their use as brake pads for high-speed elevators. Under dynamic and stationary conditions, these materials exhibit high thermal shock resistance, high coefficients of friction, and extremely low wear rates. In addition, it has been found that the SiC content of the C/C–SiC materials on the friction surface heavily influences the frictional behavior. Low-cost materials based on short fiber reinforcement and on drastically reduced process times showed their high potential for the manufacture of cost-efficient brake pads.     

摩擦材料用改性酚醛树脂的研究进展

综述了摩擦材料用改性酚醛树脂(PF)的研究进展,其中分别对钼、硼无机物改性PF和聚酰胺、腰果壳油、桐油、亚麻油、橡胶等有机物改性PF进行了讨论,并对纳米PF树脂和复合改性PF进行了介绍。改性PF的性能得到了显著改善,用其作基体制备的摩擦材料具有摩擦系数稳定、磨损率低等优点。     

混杂纤维增强酚醛闸片在提速列车上的应用研究

采用混杂纤维作增强材料并以改性酚醛树脂为基体制成提速列车用的制动闸片。在1∶1列车动力试验台上对闸片的应用特性进行了测试。试验结果表明，研制的制动闸片在紧急制动、常规制动、洒水制动、坡道调速制动和静摩擦情况下的摩擦性能均十分理想，而且摩擦系数的离散性很小。实验发现，摩擦工作面的成膜控制是解决制动闸片的速度敏感性和温度敏感性问题的关键。     

Tribological behavior and wear mechanism of C/C–SiC brake discs based on third-body layer

C/C–SiC composites are promising candidates for heavy-duty tracked vehicle brake discs. A third-body layer (TBL) can be formed on the surface of C/C–SiC self-mated brake discs, which has an important impact on tribological behavior and wear mechanism of brake discs. Herein, the formation conditions and evolution process of TBL and its effect on friction and wear properties were investigated. An appropriate braking pressure and speed (P and V) are beneficial to the cutting of asperities and refinement of wear debris on the contact surface, which are preconditions for the formation of original TBL. The original TBL can be formed under the P·V of 12, 15, and 16, which effectively improve braking stability and reduce the wear rate. During the continuous braking process, the original TBL undergoes growth, stabilization, destruction, and regeneration. Under the frictional heat and compressive stress, wear debris gradually evolves into a uniform and dense TBL. The average coefficient of friction and wear rate reach to the lowest value of .446 and 38.5 × 10⁻³ cm³/MJ, respectively. A continuous high temperature in the later stages of braking leads to severe oxidative wear. The newly formed TBL covers the original surface to form a multilayered structure, indicating the TBL undergoes destruction and regeneration.     

Preparation and Dynamometer Tests of 3D Needle‐Punched C/C‐SiC Composites for High‐Speed and Heavy‐Duty Brake Systems

Three‐dimensional (3D) needle‐punched C/C‐SiC brake composites were fabricated by chemical vapor infiltration combined with liquid silicon infiltration. The microstructures, properties, and dynamometer tests for different high‐speed and heavy‐duty brake systems had been investigated. The results indicated that the value of flexural strength and compressive strength can reach 182 Mpa and 234 MPa, respectively. Their thermal conductivity remained between 15–21 W/m/K between room temperature and 1100°C. The dynamometer test of 3D needle‐punched C/C‐SiC brake disk and pads for high‐speed trains, according to the procedure of International Union of Railways, showed that the coefficient of friction (μ) was about 0.32 and not sensitive to the brake speeds. After four times of emergency stops, the linear wear rate of the C/C‐SiC pads was 0.481 cm³/MJ. The C/C‐SiC brake pairs of vehicle were tested with inertia dynamometer according to SAE's J2522 testing procedure, and the characteristic values of the C/C‐SiC brakes indicated that the hot fade was almost 0. The C/C‐SiC pads were matched with C45 steel disk and tested for engineering machineries brake system, and the wear rate of C/C‐SiC pads was 4.2 μm/cycle and less than one‐sixth of that of the traditional powder metallurgy brake pad. The 3D needle‐punched C/C‐SiC brake composites have been demonstrated to be the top choice for advanced friction materials of high‐speed and heavy‐duty brake systems.     

Thermal,hydrolytic, anticorrosive,and tribological properties of alkyd‐silicone hyperbranched resins with high solid content

Novel alkyd hyperbranched resins (AHBRs) modified with a Z‐6018 silicone (a polysiloxane intermediate) and with high solid content were synthesized by etherification reaction using an acid catalyst. Different molar ratios of AHBR to silicone were used. Structural, thermal, hydrolytic, anticorrosive, and tribological properties were studied using infrared (IR) analysis, nuclear magnetic resonance (NMR), vapor pressure osmometry (VPO), thermogravimetric analysis (TGA), acid value, electrochemical impedance spectroscopy (EIS), and pin‐on‐disk friction. IR and NMR provide evidence of grafting of the silicone on AHBR; the efficiency of grafting was quantified by TGA. Thermal stability was studied also by acid value analysis. Grafting increases the number average molecular mass, enhances thermal stability, and improves significantly hydrolytic stability. Corrosion resistance on steel is improved by two orders of magnitude, hence our modified materials can be used as highly effective anticorrosion coatings. Grafting lowers dynamic friction dramatically, more so at higher concentrations of silicone. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

A new strategy for high-value reutilization of recycled carbon fiber: Preparation and friction performance of recycled carbon fiber felt-based C/C-SiC brake pads

To achieve the high-value reutilization of recycled carbon fiber (rCF), a new strategy of preparing rCF-based C/C-SiC brake pads is proposed in this work. The results show that the rCF possesses crystal structure and tensile strength comparable with those of virgin CF (vCF) exception of pyrolytic char adhering to the surface of rCF after pyrolysis. The rCF was converted into C/C composites through impregnation-pyrolysis. Pyrolytic char was found to have no evident negative effect on the densification rates of the rCF C/C composites. By reactive melt infiltration, the rCF C/C-SiC composites were fabricated based upon the rCF C/C composites. The achieved rCF C/C-SiC composites do not differ markedly from the vCF group control in terms of microstructure and bending strength. Furthermore, the thermal diffusion coefficients of the rCF C/C-SiC composites are very close to those of vCF C/C-SiC composites in the temperature range 25°C-300 °C. The coefficient of friction values of the rCF C/C-SiC composites are as stable as those of vCF control group, both being maintained at approximately 0.4 during friction test, whether at 25 °C or 300 °C. The wear rate of the rCF C/C-SiC composites is 3.8 μm·min⁻¹, nearly indistinguishable from that of the vCF C/C-SiC composites, i.e., 4.5 μm·min⁻¹, further suggesting that the two materials resemble each other closely. The rCF C/C-SiC composites exhibit great potential for use as alternative brake pads to serve auto braking systems. This work opens up a new path for high-value reuse of rCF.     

低碳、节能为车用陶瓷材料带来无限商机

作为机动设备和车辆零部件,刹车制动部件是机动设备与车辆最主要的安全部件之一。提高安全性能、减少环境污染和噪音污染、延长使用寿命应该是摩擦材料发展的大趋势。在很多车用制动摩擦材料中,陶瓷刹车片凸显优势,它是摩擦材料中的一个有潜力的新品种,具有明显的性能优势而极具市场前景。针对车用陶瓷材料的市场商机,介绍了汽车制动器摩擦材料的发展变迁,阐述了车用陶瓷及刹车材料的产品结构及应用范围,研究了陶瓷刹车片使用中的性能特征;同时指出了车用陶瓷及刹车材料的研发和未来前景。