Tribological properties of carbon nanotube-doped carbon/carbon composites

Carbon nanotube (CNT)-doped carbon/carbon (C/C) composites were fabricated by the chemical vapor infiltration (CVI) method to investigate the effect of CNTs on tribological properties of C/C composites. CNTs, which had been synthesized by catalytic pyrolysis of hydrocarbons, were added to carbon fiber formed preforms before CVI process. Ring-on-block-type wear tests were performed to evaluate the frictional properties of CNT-doped C/C composites. Results show that CNTs can not only increase wear resistance of C/C composites but also maintain stable friction coefficients under different loads. Polarized light microscopy, X-ray diffraction, scanning electron microscopy and Raman spectroscopy analyses demonstrate that favorable effects of CNTs on tribological properties of C/C composites have been achieved indirectly by altering microstructure of pyrocarbons and directly by serving as high-strength lubricative frictional media at the same time. Electron dispersive spectroscopy (EDS) analyses verify the existence of adhesive wear mechanism in both pure C/C composites and CNT-doped C/C composites albeit the two-body abrasive mechanism dominates in pure C/C composites.     

Effect of Carbon Nanotube Addition on Tribological Behavior of UHMWPE

Carbon nanotubes (CNTs) were added to Ultra-high molecular weight polyethylene (UHMWPE) to improve the tribological properties of UHMWPE. CNTs which have a diameter of about 10–50 nm, while their length is about 3–5 nm were produced by the catalytic decomposition of acetylene gas using a tube furnace. Ball-on-disc-type wear tests were performed to evaluate the tribological performance of UHMWPE composites reinforced with CNTs. The results showed that addition of carbon nanotube up to 0.5 wt% lowered wear loss significantly and increased friction coefficient slightly. Also through the scanning electron microscope (SEM), the surfaces of UHMWPE were observed and analyzed to discuss the tribological behavior of CNT added UHMWPE.     

Tribological Behavior of Carbon-Nanotube-Filled PTFE Composites

Carbon nanotube/polytetrafluoroethylene (CNT/PTFE) composites with different volume fractions were prepared and their friction and wear properties were investigated using a ring-on-block under dry conditions. It was found that CNTs signifi-cantly increased the wear resistance of PTFE composites and decreased their coefficient of friction. PTFE composites with 15–20 vol.% CNTs exhibited very high wear resistance. The significant improvements in the tribological properties of CNT/PTFE composites are attributed to the super-strong mechanical properties and the very high aspect ratio of CNTs. The CNTs greatly reinforce the structure of the PTFE-based composites and thereby greatly reduce the adhesive and plough wear of CNT/PTFE composites. The CNTs are released from the composite during sliding and transferred to the interface of the friction couples. They thus serve as spacers, preventing direct contact between the mating surfaces and thereby reducing both wear rate and friction coefficient.     

Effects of carbon fillers on the tribological and mechanical properties of an epoxy-based polymer (SU-8)

SU-8, an epoxy-based negative photoresist polymer, is highly suitable for making micro-electro-mechanical systems (MEMS) structures. Despite fabrication advantages, its bulk mechanical and tribological properties are the main limitations for application as MEMS material. Carbon filler materials such as graphene, graphite and multi-walled carbon nanotube (MWCNT) are added to SU-8 for tribological and mechanical property enhancements. SU-8/(5 wt%) graphite composite has performed better for the steady-state coefficient of friction at all loads including for the speed effect. SU-8/(5 wt%) MWCNT has shown excellent wear resistance. At 10 wt% graphite content, SU-8/graphite is superior in tribological performance to other composites tested.     

预制体添加BN对炭/炭复合材料性能的影响

在炭纤维预制体中添加六方氮化硼(h-BN),采用等温化学气相渗透(CVI)和超高压沥青浸渍/碳化混合工艺制备了炭/炭(C/C)复合材料。研究了材料的组织结构和力学性能,采用XD-MSM定转速摩擦试验机对材料的摩擦磨损性能进行了测试;分析了h-BN含量对摩擦磨损性能的影响。实验表明:预制体添加h-BN可以明显降低材料的摩擦系数,稳定材料的摩擦磨损性能。其中以9wt%时,材料的摩擦磨损性能最佳。     

Friction and Wear Properties of 3D Carbon/Silicon Carbide Composites Prepared by Liquid Silicon Infiltration

Carbon/silicon carbide (C/SiC) composites were prepared by a liquid silicon infiltration (LSI) process and their microstructure and friction and wear properties studied. The matrices of the C/C green bodies were found to be reinforced with dense carbon fiber bundles hanging together. The density of the composites before and after the LSI process was 1.25 and 1.94 g/cm³, respectively. However, the open porosity of C/SiC composites was about 16% due to the opening of closed pores during the machining process. The C/SiC composites exhibited excellent tribological properties in the dry condition, with an average coefficient of friction (COF) and wear rate of about 0.29 and 16.15 μg/m MPa, respectively. In comparison, the average COF was about 0.13 in the moist condition, with a wear rate of 5.87 μg/m MPa. The main wear mechanism of the C/SiC composites was worn particles and debris with a high degree of hardness, producing a plough effect on the friction surface in the dry condition and an adhesive effect in the moist condition.     

Friction and wear of carbon nanohorn-containing polyimide composites

Polyimide (PI)-based composites containing single-wall carbon nanohorn aggregate (NH) were fabricated using the spark plasma sintering (SPS) process. For comparison, composites with carbon nanotube (NT) and traditional graphite (Gr) were also fabricated. The NH was produced using CO₂ laser vaporization and a graphite target and the NT was produced by a chemical synthesis method. We evaluated the friction and wear properties of the PI-based composites with a reciprocating friction tester in air using an AISI 304 mating ball. NH drastically decreased the wear of PI-based composites; the specific wear rate of composite with NH of only 5 wt% was of the order of 10⁻⁸ mm³/Nm, which was two orders of magnitude less than that of PI alone. The wear reduction ability of NT seemed to be slightly inferior to that of NH, although it was considerably better than that of Gr. NH and NT lowered the friction of composites. The friction coefficient of composite with 10 wt% NH was less than 0.25, although it was slightly higher than that of composite with 10 wt% Gr. There was no clear difference in the friction reduction effect of NH and NT. The further addition of Gr to composites with NH or NT rather deteriorated the antiwear property of composites, although the friction coefficient was slightly reduced. The transferred materials existed on the friction surface of the mating ball, sliding against composites with three types of carbon filler. These transferred materials seemed to correlate with the low friction and wear properties of composites.     

Influence of matrix carbon texture on the temperature field of carbon/carbon composites during braking

The friction, wear and thermal properties and temperature fields of three C/C composites with different matrix carbon textures were investigated in simulations of normal landing condition for aircraft brake disks. Temperature fields were also simulated using a finite element method. The matrix carbon textures had important influence on temperature fields. The sample with rough laminar pyrolytic carbon is the best choice for airplane brake disk due to its excellent friction, wear and thermal properties and lower temperature at the friction interface and thermal gradient by contrast with the samples with resin-derived carbon and smooth laminar pyrolytic carbon.     

Mechanical and tribological properties of carbon fabric composites filled with several nano-particulates

The carbon fabric composites filled with the particulates of nano-SiO₂, nano-TiO₂, and nano-CaCO₃, respectively, were prepared by dip-coating of the carbon fabric in a phenolic resin containing the particulates to be incorporated and the successive curing. The friction and wear behaviors of the resulting carbon fabric composites sliding against AISI-1045 steel in a pin-on-disc configuration were evaluated on a Xuanwu-III high temperature friction and wear tester. The tensile strength and adhesion strength of the filled carbon fabric composites were determined on a DY35 universal materials test machine. The morphologies of the worn surfaces of the unfilled and filled carbon fabric composites and the transfer films on the counterpart steel pins were analyzed by means of scanning electron microscopy, and the elemental plane distributions on the transfer films were analyzed with an energy dispersive X-ray analyzer (EDAX). It was found that the nano-particles as the fillers contributed to significantly improve the mechanical properties and wear-resistance of the carbon fabric. Nano-CaCO₃ as the filler was the most effective in increasing the wear-resistance, while nano-SiO₂ was the most effective in increasing the friction-reducing ability and mechanical properties. This was because the nano-particulates as the fillers contributed to enhance the bonding strength between the carbon fabric and the adhesive resin. Moreover, the friction and wear properties of the carbon fabric composites were closely dependent on the characteristics of the transfer films formed on the counterpart steel pin surfaces and on the environmental temperature as well. Namely, the differences in the wear-resistance of various filled carbon fabric composites were related to the differences of their transfer films on the counterpart steel pin surface. The wear rates of the composites at elevated temperature above 180 °C were much larger than that below 180 °C, which was attributed to the degradation and decomposition of the adhesive resin at excessively elevated temperature.     

聚丙烯、炭黑和碳纤维共混填充超高分子量聚乙烯复合材料的力学和摩擦磨损性能

采用模压成型的方式制备超高分子量聚乙烯(UHMWPE)复合材料,通过AG-1型电子万能实验机和MM-200型摩擦磨损试验机分别研究填料对复合材料力学性能和摩擦磨损性能的影响,采用光学显微镜分析复合材料磨损表面的形貌。结果表明:聚丙烯(PP)和无机填料炭黑(CB)或CB与碳纤维(CF)混杂填料的加入使UHMWPE复合材料的拉伸强度降低,弯曲模量和硬度增加,其中UHMWPE/PP/CB/CF复合材料的弯曲模量和硬度增幅大于UHM-WPE/PP/CB复合材料。填料的加入可改善UHMWPE复合材料的摩擦磨损性能,当填料的质量分数为5%时,UHMWPE复合材料的摩擦磨损性能最好,且UHMWPE/PP/CB/CF复合材料的耐磨性能优于UHMWPE/PP/CB复合材料。与UHM-WPE相比,UHMWPE/PP/CB/CF复合材料的摩擦因数和磨痕宽度分别下降了10%和44%,UHMWPE/PP/CB复合材料则分别下降了12%和42%。光学显微镜观察表明填料的加入大大改善了UHMWPE的磨粒磨损,复合材料表面以较浅的犁沟磨损为主要特征。     

Wear behaviour of carbon nanotube reinforced epoxy resin composites

This paper deals with the effect of a multi-walled carbon nanotube (MWCNT) reinforcement on the wear behaviour of Epoxy (EP) composites. Firstly, various dispersion methods were compared. Secondly, the optimum CNT amount was evaluated. In a third step, dry lubricants were added to the optimised EP/CNT composite. Finally, the influence of the steel counterpart (martensitic bearing steel 100Cr6 and austenitic stainless steel X5CrNi18-10) was studied. The preparation method was found to have a decisive effect on the wear behaviour of the composite. A pre-treatment of the CNTs in concentrated nitric acid proved beneficial. Even more important was the mixing method. A dual asymmetric centrifuge delivered so good wear results that the pre-treatment could be skipped. The optimum CNT content was at about 1 wt%, regardless of the preparation method. The lowest wear rates were found after addition of 10 wt% graphite. MoS₂ proved to be less effective and Polytetrafluorethylene (PTFE) even increased the wear. The wear rates against the unalloyed martensitic steel were far higher than against austenitic stainless steel.     

On the friction and wear behavior of PTFE composite filled with rare earths treated carbon fibers under oil-lubricated condition

Carbon fibers (CF) were surface treated with air-oxidation, air-oxidation followed by rare earths (RE) treatment and RE treatment, respectively. The friction and wear properties of the polytetrafluoroethylene (PTFE) composites filled with differently surface treated carbon fibers, sliding against GCr15 steel under oil lubrication, were investigated on a reciprocating ball-on-disk UMT-2MT tribometer. The worn surfaces of the PTFE composites were examined using a scanning electron microscopy (SEM). Experimental results revealed that surface treatment of carbon fibers reduced the wear of CF-reinforced PTFE composites. Among all the treatments to carbon fibers, RE treatment was the most effective and lowest friction and wear rate of CF-reinforced PTFE composite was exhibited, owing to the effective improvement of the interfacial adhesion between the carbon fibers and PTFE matrix.     

巴基管的润滑性能研究

本文实验研究了镍－磷－巴基管复合镀层的润滑性能，结果表明：巴基管复合镀层具有优良的减摩，耐磨特性，说明巴基管是一种性能优异的固体润滑材料。     

载荷对激光选区烧结Cf/SiC复合材料摩擦磨损性能的影响

通过激光选区烧结技术和液相渗硅工艺制备了碳纤维增强碳化硅（Cf/SiC）复合材料。试样组织由C、SiC和Si三相组成,其密度和弯曲强度分别为2.89±0.01 g/cm3和237±9.8 MPa。采用UMT TriboLab多功能摩擦磨损试验机研究了Cf/SiC复合材料在不同载荷(10 N, 30 N, 50 N和70 N)条件下的摩擦学特性。研究结果表明：载荷较小(10 N)时,Cf/SiC复合材料的磨损由微凸起和SiC硬质点造成,磨损机制为磨粒磨损;载荷为30 N时,复合材料的摩擦磨损综合性能最好,其平均摩擦因数为0.564,磨损率低(5.24×10-7 cm3/（N·m）),主要磨损机制为犁削形成的磨粒磨损和黏结磨损。载荷增大到70N时,材料磨损严重,磨粒脱落形成凹坑,产生裂纹,其磨损率(8.68×10-7 cm3/（N·m）)高,磨损机制主要为脆性剥落。     

电刷镀镍/碳纳米管复合纳米镀层的结构与磨损性能

用含碳纳米管的快速镍电刷镀液制备了镍/碳纳米管复合纳米镀层,研究了热处理温度和镀液中碳纳米管含量对镀层平均晶粒尺寸、结构、力学性能及耐磨性能的影响。结果表明,镀层的晶粒大小随热处理温度的升高是先降低而后增大的;同样碳纳米管的加入对镍刷镀层的平均晶粒尺寸和微结构有显著的影响。镀层的硬度和耐磨性与镀层的平均晶粒尺寸有非常好的对应关系。热处理和碳纳米管的强化作用可导致镀层晶粒细化和结构致密化,从而有效地改善了镀层的力学性能和耐磨性能。     

The effect of fiber oxidation on the tribological behavior of 3D-braided carbon fiber/nylon composites

To investigate the influence of carbon fiber oxidation on the tribological behavior of the 3D-braided carbon fiber/nylon composites (C_3D/MCN), C_3D/MCN composites were prepared. The characteristics of carbon fibers with different conditions were characterized. The mechanical property, friction and wear tests of the composites with untreated and treated carbon fabric were performed and the worn surface morphology and wear debris were analysed. The results show that the specific surface area of the treated carbon fiber was far higher than that of the untreated carbon fiber and there formed a functional group of –CO on the carbon fiber surface after air oxidation. The flexural strength, flexural modulus and shear strength of C_3D/MCN composites with oxidized carbon fiber fabric were improved. The friction coefficient and wear rate of C_3D/MCN composites with oxidized carbon fiber fabric were apparently lower than that with untreated carbon fiber fabric. In conclusion, the surface treatment favored the improvement of the higher interface strength and so had good effect on improving the tribological properties of the composites.     

Influence of pitch air-blowing and thermal treatment on the microstructure and mechanical properties of carbon/carbon composites

This paper discusses the optimization of pitch properties as a matrix precursor of C/C composites by subjecting the pitches to different pretreatments to promote polymerization of the molecular components of pitch, which could improve carbon yield and density of the resultant carbon materials. Two series of pitches were prepared by air-blowing of impregnating coal-tar pitches at temperatures between 523 and 573 K, and thermal treatment at temperatures between 673 and 703 K, in an inert atmosphere. Effects of pitch treatments on resultant coke texture and porosity were monitored by polarized light microscopy. Unidirectional laminar composites were prepared using the original and treated pitches and commercial PAN-based carbon fibres. Effects of pitch treatments on the main microstructural features of composites are determined by scanning electron microscopy and polarized light microscopy, and related to the mechanical properties of composites. Results show an improvement of the mechanical properties of composites in both series, particularly for pitch treatments at 523 K/air in the air-blown series, and at 698 K–5 h in the thermally treated one.     

固体润滑剂对碳纤维增强尼龙复合材料摩擦学性能的影响

分别制备了PTFE／碳纤维、MoS2／碳纤维混杂增强的尼龙66复合材料，用MM-2000型摩擦磨损试验机评价其摩擦磨损性能，用SEM和XPS分析了磨损表面。结果表明：PTFE／碳纤维混杂增强可以明显改善尼龙复合材料摩擦学性能；MoS2／碳纤维混杂增强没有改善复合材料的摩擦学性能；MoS2在摩擦过程中氧化生成的MoO3充当了摩擦副之间的磨粒，其磨损机理推测为粘着和磨粒磨损的综合作用。     

炭黑/双马来酰亚胺复合材料的性能研究

采用浇铸成型法制备了炭黑填充双马来酰亚胺(BM I-BA)复合材料,研究了炭黑的填充量对复合材料力学性能和摩擦学性能的影响。在M-200型磨损机上测试该复合材料的摩擦学性能,利用扫描电镜(SEM)观察了摩擦副的表面形貌。结果表明:炭黑能够有效提高复合材料的力学性能和摩擦学性能。当炭黑的添加量为4.0wt%时,复合材料的综合力学性能最好;当炭黑的的添加量为6.0wt%时,复合材料的耐磨性能最好。SEM显示复合材料主要是粘着磨损,能在对磨环上形成薄而连续均匀的转移膜,而BM-BA树脂主要发生的是疲劳磨损,并伴有塑性变形。     

矿渣微粉填充树脂基复合材料力学性能和摩擦学性能研究

为了充分利用废弃材料研发绿色制动片,在树脂基复合材料中加入不同颗粒度的矿渣微粉作为无机填料,用热压成型的方法配制试样,并对试样的力学性能和摩擦磨损性能进行试验。研究结果表明：在复合材料中加入矿渣微粉作为无机填料,摩擦系数高于未掺样且更稳定,试样摩擦系数随掺量增加而增大。增加矿渣微粉后复合材料的磨损率均有明显降低,200目掺量为30％的试样具有较好的综合性能。两种粒径试样的硬度均高于未掺试样,冲击强度略有下降,仍高于标准较多。磨损形式由未掺样的严重的粘着磨损转变为有掺样轻微的磨粒磨损和粘着磨损。