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.     

Effects of zirconium addition on microstructure and ablation resistance of carbon fibre reinforced carbon and SiC ceramic matrix composite prepared by reactive melt infiltration

Abstract

Carbon fibre reinforced C and SiC binary ceramic matrix composites (C/C–SiC) were fabricated by a quick and low cost reactive melt infiltration (RMI) method with Si–Zr25 and Si melts. Effects of zirconium addition in infiltrated Si melt on microstructure and ablation resistance of the composite were investigated. The composite by Si–Zr25 melt infiltration was composed of SiC, ZrC, C and a little amount of ZrSi₂ without residual silicon, overcoming the problem of residual silicon in C/C–SiC composite by Si RMI. Compared with the composite by Si melt infiltration, the ablation resistance of the composite by Si–Zr25 was greatly improved by zirconium addition due to ZrO₂ and SiO₂ protecting layer formed during ablation.     

C/C多孔体对C/C-SiC复合材料微观结构和弯曲性能的影响

以4种纤维含量相同(32%,体积分数,下同),用化学气相渗透(chemical vapor infiltration,CVI)法制备了4种密度的碳纤维增强碳(carbon fiber reinforced carbon,C/C)多孔体,基体炭含量约20%～50%.利用液相渗硅法(liquid silicon infiltration,LSI)制备了C/C-SiC复合材料,研究了C/C多孔体对所制备的C/C-SiC复合材料微观结构和弯曲性能的影响.结果表明:不同密度的C/C多孔体反应渗硅后,复合材料的物相组成均为SiC,C及单质Si;随着C/C多孔体中基体炭含量的增加,C/C-SiC复合材料中SiC含量逐渐减少而热解炭含量逐渐增加.C/C-SiC复合材料弯曲强度随着材料中残留热解炭含量增加而逐渐增加,热解炭含量为约42%的C/C多孔体所制备的C/C-SiC复合材料的弯曲强度最大,达到320 MPa.     

Preparation,ablation behavior and mechanism of C/C-ZrC-SiC and C/C-SiC composites

ZrC precursor was synthesized by a solution approach using ZrOCl₂·8H₂O, acetylacetonate, glycerol and boron-modified phenolic resin. A ZrC yield of ~ 40.56 wt% was obtained at 1500 °C in the C/Zr molar ratio of 1:1. C/C-ZrC-SiC composites were fabricated by a combined processes of chemical vapor infiltration (CVI) and precursor infiltration and pyrolysis (PIP) using the synthesized ZrC precursor. For comparison, C/C-SiC composites were prepared by CVI. Thermogravimetric analysis showed that C/C-ZrC-SiC composites exhibited better oxidation resistance than C/C-SiC composites. After oxyacetylene torch ablation, the mass ablation rate of C/C-ZrC-SiC composites was 9.23% lower than that of C/C-SiC composites. The porous ZrO₂ skeleton in the ablation center was prone to be peeled off by the flame flow, resulting in the higher linear ablation rate of C/C-ZrC-SiC composites. The oxide layers of ZrO₂ and SiO₂ were formed on the transition and brim region of C/C-ZrC-SiC composites and acted as effective heat and oxygen barriers. For C/C-SiC composites, the C-SiC matrix was severely depleted in the ablation center and the formed SiO₂ layer in the brim region could protect the matrix against further ablation.     

刹车速度对C/C-SiC复合材料摩擦磨损性能的影响

对反应熔体渗透工艺制备的C/C-SiC复合材料,在MM-1000型摩擦磨损试验机上进行了模拟飞机制动刹车实验,重点研究了C/C-SiC复合材料在不同刹车速度下的摩擦磨损性能.研究表明:随着刹车速度的增加,C/C-SiC复合材料的摩擦系数先少许增加然后再减小,在10 m/s时达到最大值0.52.磨损率在低速时保持较低的数值,随着刹车速度的增加呈线性增加,但仍小于C/C复合材料的磨损率,表明C/C-SiC复合材料具有优良的耐磨损性能.当刹车速度超过20 m/s时,由于能载水平较高,摩擦表面出现犁沟现象并形成大量球状磨屑,摩擦系数急剧减小.     

先驱体浸渗裂解法制备C/C-SiC复合材料的烧蚀性能

用先驱体浸渗裂解法制备了碳纤维增强碳(carbon fiber reinforced carbon,C/C)-SiC复合材料,用H2-D2火焰法检测其烧蚀性能.结果表明:C/C-SiC复合材料的烧蚀率随复合材料中的Si含量的增加而呈下降趋势;经过5次浸渍,C/C-SiC复合材料的密度从1.46 g/cm3增加到1.75 g/cm3,Si含量从5.06%增加到13.8%,线烧蚀率和质量烧蚀率分别下降474%和34.5%.密度为1.75g/cm3的C/C-SiC复合材料,其线烧蚀率和质量烧蚀率分别为2.22 μm/s和1.289 mg/s,其线烧蚀率和质量烧蚀率分别为密度1.78 g/cm3的C/C复合材料的21.7%和78.6%.基体中SiC的引入明显提高了C/C复合材料的抗氧化烧蚀性能.     

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.     

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.     

Microstructures and properties of Si-Zr alloy based CMCs reinforced by various porous C/C performs

C/C-SiC composites were fabricated via Si-Zr reactive alloyed melt infiltration using various C/C preforms with different porosities as reinforcements. The influence of preform porosities on the microstructure, mechanical strength and ablation resistance of the as-prepared composites were investigated. The results indicated that microstructure and properties of the C/C-SiC composites seriously depended on C/C preform porosities. The composites were mainly composed of carbon, SiC and ZrSi₂ phases, while some residual silicon still existed in the composites prepared with very large porosity preforms. Flexural strength of the composites firstly increased with increasing C/C preform porosities, then reached the highest value, 307?MPa, and finally turned to decrease with the further increasing of preform porosities. Densities of the composites increased with increasing preform porosities, while open porosities were generally small below 7%. Linear ablation rates of the composites firstly sharply decreased with increasing preform porosities and then slightly decreased to reach a balance value. In a word, C/C preform porosity was of great significance for reactive melt infiltration of C/C-SiC composites. Densities, microstructure, mechanical strength and ablation resistance of the resulting composites should be comprehensively taken into consideration to choose an optimal preform porosity for fabrication of C/C-SiC composites.     

Microstructure and mechanical properties of reaction bonded B4C-SiC composites: The effect of polycarbosilane addition

Reaction bonded B₄C-SiC composites were prepared by infiltrating silicon melt into porous B₄C-SiC green preforms at 1500 °C in vacuum. The porous green preform was obtained from a mixture of polycarbosilane (PCS) and particle size graded B₄C after pre-sintering at 1600 °C. For the first time, PCS was used to adjust the phase composition and microstructure of the reaction bonded boron carbide composites. It is indicated that the addition of PCS and its content has a significant influence on the microstructure as well as the mechanical properties of the subsequent reaction bonded B₄C-SiC composites. For the B₄C-SiC composite with 5 wt% PCS added, a flexural strength of 319±12 MPa, and an elastic modulus of 402±18 GPa can be achieved, which is 23% and 15% higher than those of the composite without PCS addition, respectively. While, with the higher content of PCS addition, the mechanical properties of the composites are decreased drastically due to the large amount of residual Si agglomeration in the composites. The reaction mechanisms as well as their microstructure evolution processes correlated with the mechanical properties of the reaction bonded B₄C-SiC composites are further discussed in our work.     

The effects of high-temperature annealing on microstructure and performance of Cf/C-SiC composites modified by FeSi2

FeSi₂ modified C/C-SiC composites (C/C-SiC-FeSi₂) are fabricated by chemical vapor infiltration (CVI) combined with reactive melt infiltration (RMI) with FeSi75 alloy. The effects of high-temperature annealing (1600?°C, 1650?°C, 1700?°C) on the microstructure and performance of C/C-SiC-FeSi₂ are investigated. With the elevation of annealing temperature, the porosity of the composites and the content of SiC increase due to the evaporation of liquid Si and the further reaction of Si and C. The mechanical performance gradually decreases due to the catalytic graphitization of the carbon fiber, the high porosity and the thermal residual stress (TRS) caused by thermal mismatch of different phases. The coefficient of thermal expansion and thermal diffusivity slightly decrease with increasing annealing temperature for the increase of porosity. However, the friction performance of the heat treated materials at high braking speed are greatly improved attributing to the increase of SiC content and the capturing and storage function of pores on hard particles.     

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.     

Effect of high-temperature heat treatment on the microstructure and mechanical behavior of PIP-based C/C-SiC composites with SiC filler

C/C-SiC composites were fabricated by a combined process of chemical vapor deposition (CVD), slurry infiltration(SI), and precursor infiltration and pyrolysis (PIP). The microstructure and mechanical behavior were investigated for the dense C/C-SiC composites before and after high-temperature heat treatment. The results indicated that the sintering of the SiC matrix and the migration of the SiC matrix/fiber bundles weak interface occurred after high-temperature heat treatment at 1900 ℃. The SiC sintering resulted in an increase in the flexural strength of the C/C-SiC composites from 298.9 ± 35.0 MPa to 411.1 ± 57.3 MPa. The migration of the weak interface changed the direction of crack propagation, making the fracture toughness of the C/C-SiC composites decrease from 13.3 ± 1.7 MPa⋅m ^1/2 to 9.02 ± 1.5 MPa⋅m ^1/2.     

Microstructure and tribological behaviors of C/C–BN composites fabricated by chemical vapor infiltration

In this paper carbon fiber reinforced carbon–boron nitride binary matrix composites (C/C–BN) were prepared by chemical vapor infiltration (CVI). The infiltration of BN in the CVI process was controlled by the diffusion of BCl₃, and BN matrix was distributed homogeneously in the porous carbon fiber reinforced carbon matrix composites (C/C) due to the good infiltration ability of BN. The as-received C/C–BN composites were composed of 92 vol% C and 8 vol% BN. Both the friction coefficient and wear rate of C/C composites decreased significantly by the incorporation of BN. After heat-treated at 1600 °C, the interlayer spacing of CVI BN decreased to 3.36 Å, and CVI BN with high crystalline degree displayed the excellent lubricating effect, leading to the decrease of friction coefficient and wear rate. The improvement of the tribological properties also was partially attributed to the improved oxidation resistance and the formation of friction film by the incorporation of BN matrix.     

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.     

Effect of mono and hybrid ceramic reinforcement particles on the tribological behavior of the AZ31 matrix surface composites developed by friction stir processing

The effects of the size and morphology of the reinforcement particles on hardness and tribological behaviors of the AZ31 Mg alloy matrix composites were studied. Different ceramic compounds, including boron carbide (B₄C), tungsten carbide (WC), and Zirconia (ZrO₂) were selected as the reinforcement materials for developing mono composites. The average sizes of the B₄C, WC, and ZrO₂ particles were about 150 μm, 5 μm, and 35 nm, respectively. Besides, hybrid reinforcements composed of the B₄C + ZrO₂ and WC + ZrO₂ powders were employed to develop hybrid composites. All the composite were fabricated using the friction stir processing (FSP) technique. Investigating the microstructure of the composites by secondary electron microscopy (SEM) analysis showed a homogenous distribution of the reinforcement particles in the AZ31 Mg alloy matrix. Microhardness measurements revealed that the hardness of AZ31/ZrO₂ nanocomposite is about 120% higher than that of AZ31 base metal. According to the results of the dry sliding wear tests, the AZ31/B₄C and AZ31/ZrO₂ composites had a maximum wear resistance and a minimum friction coefficient average, respectively. Combining the B₄C and WC reinforcements with the ZrO₂ nanoparticles caused an improvement in wear resistance and friction performances of the hybrid composites. SEM observations of the worn surfaces and debris resulted from wearing of the samples after 500 m sliding distance under the normal load of 10 N, revealed that the severe and mild abrasive mechanisms are dominant.     

Study on high-temperature composite properties of fluorosilicone rubber with nano-Sb2O3

This article studied the influence of nano-Sb₂O₃ on the high-temperature composite performance of fluorosilicone rubber (FVMQ). FVMQ with 4% mass of nano-Sb₂O₃ content was prepared by mechanical blending method. The friction properties of FVMQ and Sb₂O₃/FVMQ composites at different temperatures were analyzed by means of three-dimensional profilometer and scanning electron microscopy. The results showed that nano-Sb₂O₃ can enhance the matrix strength of FVMQ, and this effect was obvious at high temperature. The elongation of Sb₂O₃/FVMQ composites was increased by 10.7% at 25°C. The tear strength of Sb₂O₃/FVMQ composites was increased by 53.1%. While the friction coefficient and the wear amount, respectively, were decreased by 20 and 48.53% at 200°C. Sb₂O₃/FVMQ composite showed excellent anti-wear, antifriction, anti-tear, and other characteristics in the high-temperature test. The enhancement of the cross-linking density of matrix caused by adding Sb₂O₃ into FVMQ can lead to the softening of rubber, and the type of wear changed from abrasive wear to adhesive wear. Thus, the composite showed good wear resistance.     

High density carbon fiber/boron nitride matrix composites: Fabrication of composites with exceptional wear resistance

This paper describes the fabrication of high density (ρ ∼ 1.75 g/cc) composites containing a hybrid (carbon and boron nitride), or complete boron nitride matrix. The composites were reinforced with either chopped or 3D needled carbon fibers. The boron nitride was introduced via liquid infiltration of a borazine oligomer that can exhibit liquid crystallinity. The processing scheme was developed for the chopped carbon fiber/boron nitride matrix composites (C/BN) and later applied to the 3D carbon fiber reinforced/boron nitride matrix composites (3D C/BN). The hybrid matrix composites were produced by infiltrating the borazine oligomer into a low density 3D needled C/C composite to yield 3D C/C-BN. In addition to achieving high densities, the processing scheme yielded d₀₀₂ spacings of 3.35 Å, which afforded boron nitride with excellent hydrolytic stability. The friction and wear properties of the composites were explored over the entire energy spectrum for aircraft braking using an inertial brake dynamometer. The C/BN composites outperformed both the previously reported C/C-BN and chopped fiber reinforced C/C. The high density 3D C/BN performed as well as both the 3D C/C and the C/BN. The 3D C/C-BN provided outstanding wear resistance, incurring nearly zero wear across the entire testing spectrum. The coefficient of friction was relatively stable with respect to energy level, varying from 0.2 to 0.3.     

Self-lubricating behavior caused by tribo-oxidation of Ti3SiC2/Cu composites in a wide temperature range

Ti₃SiC₂/Cu composite, a new wide temperature range intelligent lubricating functional material, was fulfilled, for mechanical equipment components, by Spark Plasma Sintering process. The microstructure, composition and mechanical properties of the Ti₃SiC₂/Cu composites (TSC-Cu) were investigated. Additionally, the friction and wear behaviors of TSC-Cu sliding against Inconel 718 were conducted on a pin-on-disk configuration at a sliding speed of 0.5 m/s under a load of 5 N at 25–800 °C. For comparison, the tribological property of polycrystalline Ti₃SiC₂/Inconel 718 was measured in an identical condition. The worn surface of TSC-Cu was analyzed by SEM, EDS and XPS, respectively. The results indicated that TSC-Cu consisted of Ti₃SiC₂, TiC and Cu₃Si. It was worth noting that the as-formed Cu₃Si uniformly distributed along the grain boundary of Ti₃SiC₂. As for mechanical property, the addition of Cu increased the hardness, compressive strength of TSC-Cu but lowered its flexural strength. Compared with polycrystalline Ti₃SiC₂, the average friction coefficient of TSC-Cu was higher at 25–400 °C whereas it was lower at 600 °C and 800 °C. The lower friction coefficient was owing to the cooperative lubricating characteristic of tribo-oxidation films containing TiO₂, SiO₂ and CuO. Furthermore, the wear rate of TSC-Cu was absolutely lower than that of polycrystalline Ti₃SiC₂, which resulted from the effective surface strengthening effect of the as-formed hard TiC product. Moreover, the wear mechanism of the composite changed from three-body abrasion wear to adhesion wear and tribo-oxidation wear, with the temperature increasing from RT to 800 °C.     

Effect of CVI SiC content on ablation and mechanism of C/C-SiC-ZrC-Cu composites

C/C-SiC-ZrC-Cu composites were fabricated by chemical vapor infiltration, precursor infiltration-pyrolysis and vacuum-pressure infiltration methods. During Cu infiltration, the Cu_6·69Si and Cu₃Si new phases are generated through reaction between SiC and molten Cu. The formed Cu_6·69Si, Cu₃Si, ZrC and SiC phases can improve the wettability and interface combination between Cu and the doped carbon matrix. The ablation tests demonstrate that the CVI SiC content significantly affects the structure of protective oxide layer, and induces inverse effects in ablation center at 2500 ^°C and 3000 ^°C. The relatively high CVI SiC content enhances the ablation resistance of composites at 2500 ^°C, but increases the linear ablation rate at 3000 ^°C due to the excessive evaporation and mechanical denudation. During ablation, the formed Si-Zr-C-O layer underneath ablation center and the Si-Cu-C-O layer on transition or marginal areas can prevent carbon matrix from serious oxidation. After ablation for 20 s, the C/C-SiC-ZrC-Cu composites with high CVI SiC content display the best anti-ablation property at 2500 ^°C, and the ablation rates are 3.5 ± 0.1 μm/s and 3.4 ± 0.1 mg/s.