Copper-based Friction Materials Research Articles

Braking performance of copper-based friction materials reinforced by AlCoCrFeNi high-entropy alloy

It is essential to improve the braking performance of friction materials for the high-speed train. Copper-based friction materials reinforced with AlCoCrFeNi high-entropy alloy contents of 0-40 wt% were prepared by powder metallurgy, and the braking performance of these materials at braking speeds of 40, 80, 120 and 160 km/h was investigated. The composition of AlCoCrFeNi HEA particles changes due to the elemental diffusion and alloying between AlCoCrFeNi HEA particles and the copper matrix during sintering. With the AlCoCrFeNi content increasing, the amount of interfaces between AlCoCrFeNi particles and Cu matrix increase and the bending strength of the materials decreases, owing to the formation of oxides. The friction coefficient, braking time and absorbing power of copper-based friction materials can be significantly improved by adding AlCoCrFeNi particles. However, the improvement in their wear resistance is not significant. The spalling pits and oxides are detected on the worn surfaces. The dominant wear mechanisms of copper-based friction materials are spalling and oxidation.

Synergy between carbon fibers and copper-plated graphite on tribological performance of Cu-based composites

Various types of copper-based friction materials were prepared by blending different lubrication components in anticipation of improving the performance and reliability of high-speed train brake pads. The effects of copper-plated graphite (CG), carbon fiber (CF), MoS2 (MS), CG-CF (GF), and CG-MS (GM) on copper-based friction materials for high-speed braking were researched. The tribological properties were appraised on a pin-on-disk testing machine. The mechanical characteristics, micro morphology, element mapping, and tribo-layer were studied by the hardometer, densitometer, SEM, EDS, LSK, and XPS. GF sample has the best comprehensive performance. At 250–350 km/h, it exhibits the most consistent friction coefficient and lowest wear. Additionally, under water spray condition, the friction coefficient remains stable around 0.3 and the fluctuation range is the smallest. Through exploring the variations in element distribution, friction surface, section, and wear debris, the wear forms and mechanisms of materials were revealed. In addition, the synergistic action of copper-plated graphite and carbon fibers was elucidated.

Effect of Iron Powder Type on Friction and Wear Properties of Copper-Based Friction Powder Metallurgy Material

The sintered copper-based friction materials for high-speed train brake pads have a complex composition that should possess good physical, mechanical, and tribological properties in practical applications. For this article, four kinds of friction materials were prepared by powder metallurgy technology and the effects of iron powders on the microstructural and tribological properties of copper-based friction materials were characterized using a scanning electron microscope (SEM) and x-ray diffraction (XRD). The results showed that iron powder as an enhancing component could effectively change the friction and wear properties of the experimental materials. The copper-based friction materials containing hydroxy iron (1–5 μm) have a relatively higher coefficient of friction: The friction coefficient was significantly improved by 16.8% compared with reduced iron under a rotation speed of 4000 r/min. The friction coefficient of friction material containing water-atomized iron powder is relatively reliable with 3000–7000 r/min speed range. In a high-speed environment, the friction surface of material containing reduced iron or hydroxy iron (1–5 μm) mainly has cracks and brittle fractures, and the material containing hydroxy iron (10 μm) or water-atomized iron has an obvious layered structure and shows fatigue wear.

Influences of CrFe granularity and proportion on braking performance and dynamic response of Cu-based pads

In this study, the effects of granularity and proportion of CrFe on both braking performance and dynamic characteristics of copper-based friction materials were investigated. Braking tests and analyses of microstructure, elements, and vibration were conducted. Braking performance was evaluated using a scale pin-on-disc testing machine. Dynamic response was investigated by piezoelectric accelerometer and vibration signal analysis. Results show that the material containing 10% fine ferrochrome particles has the most stable friction coefficient and the lowest wear rate, particularly at high speeds (300–350 km/h). Moreover, by increasing the fine chromium iron content, high-frequency vibration and squeal noise are suppressed. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, and laser scanning confocal microscopy were also conducted. Vibration signals were analyzed using fast Fourier Transform. These tests reveal the mechanism of the appropriate CrFe size and content to improve the braking ability and steadiness of pads for high-speed trains. This research is anticipated to be used as a beneficial reference for the design and manufacture of high-performance and environmentally friendly brake pads.

Effect of Wet Granulation on Tribological Behaviors of Cu-Based Friction Materials.

Because of the excellent thermal conduction, corrosion resistance, and tribological properties, copper-based friction materials (CBFMs) were widely used in airplanes, high-speed trains, and wind power generation. With operating speed continuously increasing, CBFMs are suffering more complicated and extreme working conditions, which would cause abnormal abrasion. This paper presents an experiment to investigate how the tribological behaviors of CBFMs are regulated by granulation technology. Samples were prepared by the method of granulation and cool-pressed sinter. The tribological properties of specimens with different granule sizes were studied. The results showed that granulation could improve the tribological properties of CBFMs. The friction coefficient (COF) increased first and then decreased with increasing granule size. Specimen fabricated with 5-8 mm granules obtained the lowest COF, which was reduced by 22.49% than that made of powders. Moreover, the wear rate decreased first and then increased as granule size increased. The wear rate of samples prepared by granules 3-5 mm was lower than that of all of the other samples. This is because the structured samples prepared by wet granulation can promote the formation of secondary plateaus, which are beneficial for enhancing tribological properties. This makes granulation a promising method for enhancing the tribological performances of CBFMs.

Effect of iron addition on the structure and properties of copper-based friction powder material used under friction conditions with lubrication

Machines and mechanisms contain units responsible for their movement and stopping, and such units use friction materials. These units include oil-cooled brakes, hydromechanical transmissions, and clutches. They use mainly copper-based friction materials providing the high coefficient of friction and wear resistance. These materials feature by effective heat dissipation since a large amount of heat is released in these areas for a short period of time. The paper presents the results of studies into the effect of iron addition into a frictional powder material based on BrO6 and BrO12 bronze on its structure, mechanical and tribotechnical properties. It was shown that the introduction of iron contributes to an increase in the coefficient of friction from 0.034 to 0.055 for the BrO6-based friction material and from 0.042 to 0.073 for the BrO12-based friction material. It was determined that the ultimate compression strength of the BrO12-based friction material is 340 MPa without iron addition, 310 MPa at 10 vol.% of iron, and 180 MPa at 50 vol.% of iron. This is due to the fact that the iron content of more than 30 vol.% results in the change of the frame structure of the material to the matrix one having a sintering temperature higher than the temperature used in the paper for friction material sintering. It was found that for the BrO6-based friction material there are both rounded and elongated inclusions in the copper phase up to 2.5 μm in size with the iron content of 30–50 %. In the BrO12-based material there are more iron inclusions in the copper phase and their size are much larger, the length of inclusions reaches 20 μm, and the iron content in them is 49–73 %.

Effect of Silicon Carbide Nanoparticles on the Friction-Wear Properties of Copper-Based Friction Discs.

To study the influence of nano-additives on the friction-wear characteristics of friction materials, the nano-sized silicon carbide particles which have excellent chemical and physical properties are considered to add in composite to form the modified friction material. The influence of the silicon carbide nanoparticles (SCN) on the friction-wear characteristics of copper-based friction materials (CBFM) is investigated via the SAE#2 (made in Hangzhou, China) clutch bench test with the applied pressure, rotating speed, and automatic transmission fluid (ATF) temperature taken into account. Moreover, the variations of friction torque and temperature are considered to evaluate the friction performance, and the variable coefficient is employed to describe the friction stability. The wear characteristics of friction materials are investigated by the disc changes in thickness and micro-morphology. The results show that the CBFM with SCN can provide a higher friction torque, which increased by 30% to 50% compared with CBFM. The variable coefficient of CBFM with SCN changes from 674 to 52 with the rotating speed raised from 600 rpm to 3000 rpm, which shows that the friction stability is relatively worse. Furthermore, the micromorphology shows that the CBFM with SCN has lower porosity and surface roughness, which increases the microscopic contact area and the coefficient of friction (COF). Simultaneously, the reduction in porosity also leads to a decrease in the cooling quality, bringing about a rapid temperature rise. Thus, the wear amount of CBFM with SCN increases significantly, especially for the friction disc in the axial middle position.

Влияние добавки порошка биоуглерода, полученного из скорлупы кедрового ореха, на триботехнические свойства фрикционного материала на основе меди, работающего в условиях граничного трения

Влияние добавки порошка биоуглерода, полученного из скорлупы кедрового ореха, на триботехнические свойства фрикционного материала на основе меди, работающего в условиях граничного трения

Friction materials inspired by characteristics of bio-based silica and its hardening process

Designing and developing composites with excellent mechanical, friction, and durability properties at low cost has long been highly desirable for the applications of friction materials. Herein, we employed a cost-effective method to obtain bio-based silica (RHC-SiO2) from gasified rice husk carbon (RHC). Subsequently, inspired by the characteristics of RHC-SiO2 and its hardening process, we report a simple and efficient so-called “hybrid pressing and sintering molding” method for manufacturing copper-based friction materials (CFMs). The CFM-R4 (CFM with 4% RHC-SiO2) possesses a unique combination of high hardness (55.50 H V), low density (0.62 g/cm3), low wear rate (0.081%), suitable friction coefficient (0.26), and good durability. Based on the cost-effective method, the increased and decreased stages of RHC-SiO2 yield were determined mainly by reaction rate and compatibility, respectively. Compared with CFM-0 (CFM without SiO2), the CFM with RHC-SiO2 possesses better mechanical and friction properties. In view of high-performance and eco-friendly, such CFM with RHC-SiO2 would hold a promising application in friction fields such as transmission, differential, and synchronizer.

Tribotechnical Properties of a Copper-Based Powder Friction Material with the Addition of Iron-Chromium Alloy Powder

The results of studying the effect of the additive powder of the iron-chromium alloy PH-30 on the tribological properties of a composite friction material based on copper operating in the conditions of boundary friction are presented. It is shown that the introduction of 10 to 40 vol % PH-30 powder helps to increase the coefficient of friction from 0.042 to 0.075. It is found that at 10 vol % PH-30 the material’s wear is minimal and is 4 μm/km, while at 40 vol %, catastrophic wear is observed, exceeding 20 μm/km. The limit value of the material’s wear of 9 μm/km is noted with the powder content of PH-30 of less than 28 vol %. The increase in the tribotechnical properties of copper-based friction material with the addition of PH-30 powder is explained by the action of not only the PH-30 powder itself but also Fe4Cu3, FeSn intermetallide, and solid ceramic particles of chromium carbide Cr23C6 formed on the surface after sintering.

Effect of Oil Groove Depth on Friction Performance of Copper based Friction Materials with Different Graphite Content

Copper-based friction materials with different oil groove depth and graphite content were prepared by powder metallurgy process. The effect of oil groove depth on the friction performance of copper based friction materials with different graphite content at different linear velocities was studied. The results show that the dynamic friction coefficient of material decreases with the increase of oil groove depth at low linear velocity of 16.5m/s, and increases with the increase of oil groove depth when linear velocity is ≥ 20m / s. With the increase of oil groove depth and graphite content, the heat resistance of the friction material increases and the wear rate decreases.

The synergistic effect of carbon materials on properties of copper-based friction materials

PurposeThis study aims to investigate the effect of combined use of granular graphite and petroleum coke on the properties of copper-based friction materials and the friction and wear mechanisms.Design/methodology/approachCopper-based friction materials with different proportions of petroleum coke and granular graphite were prepared by using powder metallurgy. The friction surfaces were analyzed.FindingsChanging the ratio of petroleum coke/granular graphite affects the formation of oxides and sulfides on the surface of the materials. Increasing the petroleum coke promotes the production of metal sulfide and sulfate in the friction materials and reduces coefficient of friction (COF) and wear. Increasing petroleum coke also increases the amount of carbonic oxide (CO) released during the braking process and promotes the reduction process of iron oxide on the friction surface.Originality/valueThe synergistic effect of carbon materials on copper-based friction materials was studied in terms of the tribological chemical reaction. This research provides useful information for the selection of carbon materials in friction materials.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-02-2020-0075/

Wear Mechanism of Copper-based Powder Metallurgical Friction Materials with Different Graphite Content

Copper-based friction materials with different graphite contents were prepared by powder metallurgy process. The influence of graphite content on the surface hardness of friction materials was studied by Bush hardness tester. By means of scanning electron microscope (SEM) and energy dispersive spectrometer (EDS), the wear morphology and composition of friction materials were studied, and the wear mechanism was analyzed. The results show that the graphite content has little effect on the surface hardness of friction materials, and the surface hardness mainly depends on the copper matrix and its alloy elements. The main wear mechanism of copper based friction materials is plough type abrasive wear. Graphite has good lubricity and can reduce the wear.

Influence of Carbon-Containing Additives in the Composition of Copper-Based Friction Material on Boundary Friction in Mineral and Synthetic Oils

This study provides the results of analyzing the influence of carbon-containing powder additives in the form of powders of fine GK-1 pencil graphite, GE-1 coarse graphite, and foundry coke fractions smaller than 63 and 100–200 μm on the setting and transfer of materials using mineral and synthetic oils. It is established that foundry coke powder allows for improving the resistance of material during seizure. Thus, an increase in the seizure load from 1.4 to 1.7 MPa for mineral oil and from 1.0 to 1.4 MPa for synthetic oil is registered at a sliding speed of 2 m/s. The use of finely dispersed pencil graphite as part of the friction material during friction in synthetic oil increases the speed during seizure; thus, an increase in speed up to 4 m/s is registered at a load of 1 MPa, while an increase in speed for pure 12% bronze is not higher than 2 m/s.

Investigation on the Fabrication and Properties of the Cu Base Friction Composites

Cu-based friction materials were prepared by powder metallurgy technology. The effect of Fe content on friction and wear properties of Cu-based friction materials has been investigated. The results indicate that Fe content has great effects on the wear ability of Cu-based friction materials. Fe works as frictional component in copper-based friction materials, influening the mechanical and frictional property of materials. With increasing Fe content, the hardness and friction coefficient of Cu-based friction materials stability increase, the wear rate of the friction materials decreases. When Fe content is 6%, the materials posses stably high friction factors, as well as good wear ability.

Influence of Copper Frictional Material Composition on Structure and Tribotechnical Properties

Abstract—The article describes the effect of tin and graphite content in the composition of a copper-based friction material (FM) on the structure, tribological properties, and formation of the contact surface. It is shown that an increase in tin from 6 to 12 wt % leads to an increase in the friction coefficient and a decrease in the running-in time for wear resistance. When the tin content in the friction material is 6 wt %, during friction, plastic flow of the contact surface material occurs with the formation of a “third” layer. The type and content of graphite also significantly affect the tribotechnical properties of the FM: an increase in graphite content of more than 20 vol % increases the friction coefficient; when GK-1 pencil grade graphite is used, the friction coefficient increases to a lesser extent than for GE-1 elemental grade graphite, and the wear resistance increases by 2.5–3.0 times.

Comparison of the Friction and Wear Characteristics between Copper and Paper Based Friction Materials.

Copper-based friction material (CFM) and paper-based friction material (PFM) are the two most commonly used clutch friction materials. The friction and wear characteristics of these two kinds of friction materials under dry conditions were investigated by the pin-on-disc test over a broad range of applied loads, rotating speeds and ambient temperatures. Before experiments, the running-in test was conducted to stabilize the coefficient of friction (COF) and wear amount of the test samples. After experiments, the metallographic micrographs of the tested samples were presented to investigate the wear mechanisms. Experimental results showed that both the COF and wear depth of the CFM are much greater than these of PFM. The COF of CFM decreases with the increase of applied load, and changes slightly with the variation of rotating speed, whereas it increases first and then decreases with the increase of ambient temperature. However, the COF of PFM decreases dramatically with the increase of the rotating speed and ambient temperature, while it remains stable at first and then decreases slowly as the applied load increases. Additionally, under such three working conditions, the wear depth of CFM changes linearly, while the wear depth of PFM varies greatly. This study can be used as a guide for selecting friction materials for clutches with different applications.

Effect of ferroboron particle size on the tribological properties of copper-based powder metallurgy brake materials

Copper-based friction materials are prepared by powder metallurgy process. The effect of different sizes of ferroboron powder on the properties of materials has been studied. The results show that the variation of ferroboron size has no significant effect on the density and porosity of samples. The hardness decreases more obviously with ferroboron size decreasing. At the initial braking speed of 100 km h−1, the friction coefficient and wear rate increase with ferroboron size reducing, and the wear of the material is mainly abrasive wear. At a large initial braking speed (≥150 km h−1), with the decrease of the ferroboron size, the friction coefficient decreases and the wear rate increases, and the wear is mainly the mixture of oxidation wear and adhesive wear.

Effect of graphite type on the contact plateaus and friction properties of copper-based friction material for high-speed railway train

Copper-based friction materials containing the same graphite concentrations but varied proportion of granular graphite to flake graphite were prepared by powder metallurgy for high-speed railway trains. The friction coefficient and specific wear rate were tested on pin on disc machine. The results showed that the addition of appropriate granular graphite can improve the magnitude and stability of friction coefficient and help to form the secondary plateaus on friction surface. However, excessive addition of granular graphite led to a significant decrease in friction coefficient. The flake graphite had better lubricity but promoted the occurrence of delamination due to its weak strength. Statistical analysis revealed that the specific wear rate was negatively linear correlated with the graphite coverage area on the friction surface. In addition, there was a critical plateau coverage on friction surface, above which the specific wear rate can be effectively reduced. Comprehensive evaluation of the magnitude and stability of the friction coefficient as well as wear rate, the ratio of 5 wt% granular graphite to 5 wt% flake graphite is the most suitable for high performance copper-based friction material.

Sintered Copper-Based Powder Friction Material Filled with Fullerene-Like Glass Carbon

Existing compositions of sintered copper-based powder friction materials have been analyzed. It has been indicated that these materials, which operate under lubricating conditions, usually contain fine pencil-type or coarse casting graphite as an antiseize additive. As a friction additive, oxide and carbide powders and other high-melting materials are used. In this work, the results of investigations of tribotechnical properties of the sintered powder friction material based on copper filled with glass carbon are given. It is shown that its use provides an increase in the friction coefficient of the material with a decrease in wear over the period of its operation.