Friction and sliding wear of UHMWPE modified cotton fibre reinforced polyester composites

Ultrahigh molecular weight polyethylene (UHMWPE) modified polyester-cotton composites were developed and studied for friction and sliding wear behaviour at different applied loads and UHMWPE concentrations. Sliding wear tests were conducted by using pin-on-disc apparatus. Composites in the form of the pin were tested against EN-24 steel disc. The specific wear rate of polyester reduced on reinforcement of cotton and on addition of UHMWPE. The coefficient of friction of polyester resin increased on cotton reinforcement and reduced significantly on addition of UHMWPE in cotton polyester composite. The composites exhibited reductions in specific wear rate against the normal load in the specimens those containing 7.41 or higher volume percent of UHMWPE. The significant reduction in wear rate of UHMWPE modified polyester-cotton composite has been discussed with the help of SEM observations of worn surfaces and coefficient of friction. The addition of 14.19 vol.% UHMWPE in polyester resin brought down the value of μ to nearly half to that of polyester resin and 1/3rd of cotton polyester composite.     

Friction and wear behaviour of electron beam modified PTFE filled EPDM compounds

The friction and wear of non-modified and electron beam modified polytetrafluoroethylene (PTFE) filled ethylene–propylene–diene–monomer (EPDM) rubber investigated with the help of pin on disk tribometer showed different behaviour during the sliding contact with hard spherical steel-ball. The friction coefficient (μ) and specific wear rate (k) of modified PTFE filled EPDM increased with an absorbed dose of PTFE powder while non-modified PTFE filled EPDM showed the lowest μ and k values. This variation in friction and wear behaviour of PTFE filled EPDM compounds is caused by the influence of radiation induced chemical changes in PTFE powder on the radical initiated peroxide crosslinking. It results from the lower crosslinking efficiency and consequently in the deterioration of the bulk properties. The electron modification of PTFE powder reduces the hardness (modulus) and increases the energy dissipation (tan delta) of compounds. Beside other factors, these variations in bulk properties have been shown to have deleterious effects on the friction and wear properties of electron beam modified PTFE filled EPDM.     

Replacing of glass fibres with seed oil palm fibres for tribopolymeric composites

Abstract

In the current study, the possibility of replacing woven glass fibres (WGFs) with seed oil palm fibres (SOPFs) as reinforcements for tribopolymeric composites is investigated. Mainly, two different polyester composites based on woven glass reinforced polyester (WGRP) and seed oil palm reinforced polyester (SOPRP) are developed. Different volume fractions (25, 35, and 45 vol.-%) of SOPFs were considered. The experiments were performed using a block on disc (BOD) machine and the tests were conducted under dry contact condition against smooth stainless steel counterface at 2˙8 m s^–1 sliding velocity, 20 N applied load for different sliding distances (up to 5 km). The wear mechanism was categorised using a Scanning Electron Microscope (SEM). The results revealed that the steady state was reached after 4 km sliding distance for both WGRP and SOPRP composites. Seed oil palm reinforced polyester composites showed very high friction coefficient compared to WGRP. 35 vol.-% SOPRP composite exhibited a promising wear result, i.e. SOPFs are possible to replace WGFs in polymeric composites reinforcements whereas the wear resistance of the synthetic and natural composite were almost the same. The wear mechanisms for SOPRP composites were predominated by microcracks, deformation and pulledout of fibres while in the WGRP composite, abrasive nature was observed.     

Dry sliding wear behaviour of PTFE filled with glass and bronze particles

Abstract

The wear behaviour of polytetrafluroethylene (PTFE) filled with 25% glass and 40% bronze particles was studied on a pin on disc test rig. Solid lubricant composite materials were prepared by compression moulding technique. The wear parameters considered for the study were applied load, sliding speed and sliding distance. The experimental results indicate that the weight loss increases with increasing load, sliding speed and sliding distance, as expected. Sliding distance has more effect on weight loss followed by applied load. The 40% bronze+PTFE composite exhibits better wear resistance compared to other types. The dominant interactive wear mechanisms during sliding of PTFE and its composites are discussed in this paper.     

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.     

PTFE基复合材料海水润滑下的摩擦学性能研究

研究碳纤维/聚四氟乙烯（CF/PTFE）、玻璃纤维/聚四氟乙烯（GF/PTFE）复合材料与氮化硅陶瓷配副在海水环境下的摩擦学性能与润滑机制,分析滑动速度对摩擦副海水润滑性能的影响规律。结果表明：在海水润滑条件下,随着滑动速度的增加,PTFE、CF/PTFE、GF/PTFE材料与Si3N4陶瓷配副时的摩擦学性能均有明显改善,摩擦因数与磨损率均呈显著降低的趋势,其中CF/PTFE复合材料表现出更为优异的摩擦学性能,在1 000 r/min滑动速度下摩擦因数低至0.026。磨损表面表征结果表明,在海水润滑条件下,PTFE基复合材料在摩擦过程中由于摩擦化学反应生成了润滑膜,可为摩擦副提供良好的润滑和减磨作用,从而减少摩擦磨损行为的发生。     

Adhesive Wear Performance of T-OPRP and UT-OPRP Composites

In the current work, the effects of treating the oil palm fibres on the tribological performance of polyester composite were studied against polished stainless steel counterface using Block-on-Ring (BOR) technique under dry contact condition. Wear and friction characteristics of treated and untreated oil palm fibre reinforced polyester (T-OPRP and UT-OPRP) composites were evaluated at different sliding distances (0.85–5 km), sliding velocities (1.7–3.9 m/s) and applied loads (30–100 N). SEM observations were performed on the worn surfaces of the composites to examine the damage features. Specific wear rate (Ws), friction coefficient and interface temperature results were presented against the operating parameters. The results revealed that test parameters significantly influenced the wear performance of the composites. Both treated and untreated oil palm fibres enhanced the wear and frictional performance of polyester composites. T-OPRP showed less Ws by about 11% compared to UT-OPRP. This was due to the better interfacial adhesion offered by the treated fibres. The SEM observation made on UT-OPRP worn surface showed debonding and bending of fibres, and fragmentation and deformation on the resinous regions. Meanwhile, T-OPRP composite showed less damages compared to UT-OPRP, where no sign of fibres debonding was observed.     

Dry Sliding Friction and Wear Characteristics of Cu-Sn Alloy Containing Molybdenum Disulfide

The wear and sliding friction response of a hybrid copper metal matrix composite reinforced with 10 wt% of tin (Sn) and soft solid lubricant (1, 5, and 7 wt% of MoS₂) fabricated by a powder metallurgy route was investigated. The influence of the percentages of reinforcement, load, sliding speed, and sliding distance on both the wear and friction coefficient were studied. The wear test with an experimental plan of six loads (5–30 N) and five sliding speeds (0.5–2.5 m/s) was conducted on a pin-on-disc machine to record loss in mass due to wear for two total sliding distances of 1,000 and 2,000 m. The results showed that the specific wear rate of the composites increased at room temperature with sliding distance and decreased with load. The wear resistance of the hybrid composite containing 7 wt% MoS₂ was superior to that of the other composites. It was also observed that the specific wear rates of the composites decreased with the addition of MoS₂. The 7 wt% MoS₂ composites exhibited a very low coefficient of friction of 0.35. The hardness of the composite increased as the weight percentage of MoS₂ increased. The wear and friction coefficient were mainly influenced by both the percentage of reinforcement and the load applied. Wear morphology was also studied using scanning electron microscopy and energy-dispersive X-ray analysis.     

A study on friction and wear characteristics of nanometer Al2O3 /PEEK composites under the dry sliding condition

The friction and wear properties of the polyetheretherketone (PEEK) based composites filled with 5 mass% nanometer or micron Al₂O₃ with or without 10 mass% polytetrafluroethylene (PTFE) against the medium carbon steel (AISI 1045 steel) ring under the dry sliding condition at Amsler wear tester were examined. A constant sliding velocity of 0.42 m s⁻¹ and a load of 196 N were used in all experiments. The average diameter 250 μm PEEK powders, the 15 or 90 nm Al₂O₃ nano-particles or 500 nm Al₂O₃ particles and/or the PTFE fine powders of diameter 50 μm were mechanically mixed in alcohol, and then the block composite specimens were prepared by the heat compression moulding. The homogeneously dispersion of the Al₂O₃ nano-particles in PEEK matrix of the prepared composites was analyzed by the atomic force microscopy (AFM). The wear testing results showed that nanometer and micron Al₂O₃ reduced the wear coefficient of PEEK composites without PTFE effectively, but not reduced the friction coefficient. The filling of 10 mass% PTFE into pure PEEK resulted in a decrease of the friction coefficient and the wear coefficient of the filled composite simultaneously. However, when 10 mass% PTFE was filled into Al₂O₃/ PEEK composites, the friction coefficient was decreased and the wear coefficient increased. The worn scars on the tested composite specimen surfaces and steel ring surfaces were observed by scanning electron microscopy (SEM). A thin, uniform, and tenacious transferred film on the surface of the steel rings against the PEEK composites filled with 5 mass% 15 nm Al₂O₃ particles but without PTFE was formed. The components of the transferred films were detected by energy dispersive spectrometry (EDS). The results indicated that the nanometer Al₂O₃ as the filler, together with PEEK matrix, transferred to the counterpart ring surface during the sliding friction and wear. Therefore, the ability of Al₂O₃ to improve the wear resistant behaviors is closely related to the ability to improve the characteristics of the transfer film.     

Impact of Viscoelasticity on the Tribological Behavior of PTFE Composites for Valve Seals Application

In this article, we studied and explored the impact of viscoelasticity on the friction and wear behavior of pure polytetrafluoroethylene (PTFE), carbon–graphite PTFE composite, and glass fiber–MoS₂ PTFE composite. Tests were carried out using a specific reciprocating tribometer for valve seal application. The worn surfaces of the PTFE composites and the transfer films formed on the counterface were examined with a scanning electron microscope (SEM). Experimental results revealed that the addition of filler materials was effective in reducing the wear volume in all composites studied. In addition, the friction coefficient and wear resistance showed high sensitivity to the viscoelastic behavior of the PTFE seal. SEM investigation showed that the incorporation of particulate fillers into the PTFE matrix could dramatically reduce and stabilize the transfer films to the counterface, so they largely decreased the wear of the PTFE composites.     

Sliding wear behavior of planar random zinc-alloy matrix composites

The friction and wear behavior of planar random zinc-alloy matrix composites reinforced by discontinuous carbon fibres under dry sliding and lubricated sliding conditions has been investigated using a block-on-ring apparatus. The effects of fibre volume fractions and loads on the sliding wear resistance of the zinc-alloy matrix composites were studied. Experiments were performed within a load range of 50–300 N at a constant sliding velocity of 0.8 m s⁻¹. The composites with different volume fractions of carbon fibres (0–30%) were used as the block specimens, and a medium-carbon steel used as the ring specimen. Increasing the carbon fibre volume fraction significantly decreased the coefficient of friction and wear rates of both the composites and the medium-carbon steel under dry sliding conditions. Under lubricated sliding conditions, however, increasing the carbon fibre volume fraction substantially increased the coefficient of friction, and slightly increased the wear of the medium-carbon steel, while reducing the wear of the composite.Under dry sliding conditions, an increasing load increased not only the wear rates of both the composite and the unreinforced zinc alloy, but also those of their corresponding steel rings. However, the rate of increase of wear with increasing load for both the composite and its corresponding steel ring was much smaller than for the unreinforced zinc alloy and its corresponding steel ring. The coefficient of friction under dry sliding conditions appeared to be constant as load increased within a load range of 50–150 N for both the composite and the unreinforced zinc alloy, but increased at the higher loads. Under any load the coefficient of friction of the composite was lower than half that of the unreinforced zinc alloy under dry sliding conditions.     

Effect of fiber orientation on friction and wear of fiber reinforced polymeric composites

The friction and wear behavior of composites (i.e. uniaxially oriented graphite fiber-epoxy, Kevlar fiber-epoxy and biaxially oriented glass fiber-MoS₂-polytetrafluoroethylene (PTFE)) was investigated as a function of varying fiber orientations with respect to the sliding direction. In graphite fiber-epoxy composites, both wear and friction coefficients were minimum when the orientation of the fibers was normal to the sliding surface. In Kevlar-epoxy composites when the fibers were oriented normal to the surface and the sliding direction, the wear rate was also minimum but the friction coefficient was the highest. In glass fiber-MoS₂-PTFE composites wear was minimum when the largest fraction of fibers was oriented normal to the sliding surface.     

Enhancement of abrasive wear resistance in consolidated Al matrix composites via extrusion process

Abstract

The present study addresses the dry wear behaviour of aluminium matrix composites under different sliding speeds and applied loads. Values of the friction coefficient of the matrix alloy and composite materials were in expected range for light metals in dry sliding conditions. The higher coefficient of friction was the consequence of established contact between hard SiC particles and the counter body material. The rough and smooth regions are distinguished on the worn surface of the composites similar to the unreinforced Al alloy. Plastic deformation occurred when the applied specific load was higher than the critical value. The high shear stresses on the sliding surface cause initiation and propagation of the cracks in the subsurface, leading to the loss of material from the worn surface in the form of flakes. The debrises of the composites at low wear rate comprise a mixture of the fine particles and small shiny metallic plate-like flakes and are associated with the formation of more iron rich layers on the contact surfaces.     

Epoxy, ZnO, and PTFE nanocomposite: friction and wear optimization

To lower the friction coefficient and increase the wear resistance of epoxy, nanoparticles of zinc oxide and polytetrafluoroethylene (PTFE) were added in small volume percents to an epoxy matrix. Tribological testing of the samples in this study was completed on a linear reciprocating tribometer with a 250 N normal load and a 50.8 mm/s sliding speed. Several samples were made and tested following a modified Simplex Method optimization procedure in order to find a volume percent for optimized wear resistance and friction coefficient. The sample with the optimum wear rate consisted of 1 volume percent of zinc oxide nanoparticles and 14.5 volume percent of PTFE nanoparticles. It had a wear rate of k = 1.79 × 10⁻⁷ mm³/Nm; 400× more wear resistant than neat epoxy. The sample with the optimum friction coefficient consisted of 3.5 volume percent of zinc oxide nanoparticles and 14.5 volume percent of PTFE nanoparticles and had a friction coefficient of μ = 0.113, which is almost a 7× decrease in friction coefficient from neat epoxy.     

表面改性硅灰石纤维填充PTFE复合材料的摩擦学性能

用KH550硅烷偶联剂表面改性的硅灰石纤维(WF)填充PTFE,在MPX-2000型磨损试验机上研究复合材料的摩擦磨损性能,并与经典的炭纤维(CF)填充PTFE复合材料进行比较。采用SEM对磨损面和对偶面进行分析。结果表明:较高载荷(200和300 N)下复合材料摩擦因数随WF含量变化的幅度不大,较稳定地维持在较低值;细小尺寸WF填充PTFE复合材料的耐磨性能较好,在WF质量分数为10%时,复合材料的磨损量只有相同含量CF填充PT-FE复合材料的81%;细小尺寸WF填充PTFE复合材料的磨损面较为平整,存在轻微黏着磨损,其对偶面转移膜平整光滑、结构致密;而CF/PTFE复合材料磨损面存在许多裸露和碎断的CF,犁削和磨粒磨损是主要的磨损形式。     

Friction and wear characteristics of lead and its compounds filled polytetrafluoroethylene composites under oil lubricated conditions

The friction and wear properties of Pb, PbO, Pb₃O₄, or PbS filled polytetrafluoroethylene (PTFE) composites sliding against GCr15 bearing steel under both dry and liquid paraffin lubricated conditions were studied by using an MHK-500 ring-block wear tester. The worn surfaces and the transfer films of these PTFE composites formed on the surface of GCr15 bearing steel were then investigated by using a scanning electron microscope (SEM) and an optical microscope, respectively. Experimental results show that filling Pb, PbO, Pb₃O₄ or PbS to PTFE can greatly reduce the wear of the PTFE composites, but the wear reducing action of Pb₃O₄ is the most effective. Meanwhile, PbS increases the friction coefficient of the PTFE composite, but Pb and Pb₃O₄ reduce the friction coefficients of the PTFE composites. However, the friction and wear properties of lead or its compounds filled PTFE composites can be greatly improved by lubrication with liquid paraffin, and the friction coefficients of the PTFE composites can be decreased by one order of magnitude. Optical microscope investigation of transfer films shows that Pb, PbO, Pb₃O₄ and PbS enhance the adhesion of the transfer films to the surface of GCr15 bearing steel, so they greatly reduce the wear of the PTFE composites. However, the transfer of the PTFE composites onto the surface of GCr15 bearing steel can be greatly reduced by lubrication with liquid paraffin, but the transfer still takes place. SEM examination of worn surfaces shows that the interaction between liquid paraffin and the PTFE composites creates some cracks on the worn surfaces of the PTFE composites; the creation and development of the cracks reduces the load-carrying capacity of the PTFE composites, and this leads to deterioration of the friction and wear properties of the PTFE composites filled with lead or its compounds under higher loads in liquid paraffin lubrication.     

Friction and wear behavior of hybrid glass/PTFE fabric composite reinforced with surface modified nanometer ZnO

Nano-ZnO was successfully grafted with 2,4-toluenediisocyanate (TDI) and β-aminoethyltrimethoxylsilane (OB551) to avoid the agglomeration of nano-ZnO in composite. The hybrid glass/PTFE fabric composites reinforced with the untreated, OB551 and TDI modified nano-ZnO, respectively, were prepared by dip-coating of the hybrid fabric in a phenolic adhesive resin containing the nanoparticles to be incorporated and the successive curing. The friction and wear behaviors of various nano-ZnO reinforced hybrid glass/PTFE fabric composites sliding against AISI-1045 steel in a pin-on-disk configuration were evaluated on a Xuanwu-III high-temperature friction and wear tester, with the unfilled one as a reference. The morphologies of the worn surfaces of the composites and of the counterpart pins were analyzed using scanning electron microscopy. In addition, FTIR spectrum was taken to characterize the untreated and treated nano-ZnO. It is found that the untreated and treated nano-ZnO reinforced hybrid glass/PTFE fabric composites exhibit improved wear resistance and friction-reduction in comparison with the unfilled one. The TDI modified nano-ZnO reinforced composite can obtain the best friction and wear performance under different applied load; followed by the OB551 modified nano-ZnO reinforced one. Sliding conditions, such as environmental temperature and lubricating condition, significantly affect the tribo-performances of the unfilled and filled hybrid glass/PTFE fabric composites.     

聚苯酯填充聚四氟乙烯复合材料摩擦学行为研究

采用聚苯酯（Ekonol）、Ekonol／PAB纤维增强聚四氟乙烯（PTFE）制备利用转移膜润滑的摩擦副材料，并研究了两组材料在于摩擦条件下与9Cr18轴承钢对摩时的摩擦学性能；运用扫描电镜分析了两组材料磨损表面形貌和磨损机理。结果表明：随着Ekonol含量的增大，Ekonol填充PTFE复合材料的摩擦因数逐渐增大，当Ekonol质量分数超过25％时摩擦因数略有下降，磨损方式由以犁削磨损为主转变为以疲劳磨损为主；而Ekonol／PAB纤维填充门FE复合材料的摩擦因数，随Ekonol含量的增大而增大，磨损方式由以粘着磨损为主转变为以疲劳磨损为主。Ekonol／PAB纤维填充PTFE复合材料的摩擦学性能优于Ekonol填充PTFE复合材料。     

Wear-Resistant PTFE/SiO2 Nanoparticle Composite Films

Polytetrafluoroethylene (PTFE) is a polymer that is well known for its exceptional tribological properties and, as such, it is commonly used to reduce the coefficient of friction between surfaces. In recent years it has also been established that by incorporating nanoparticle fillers in PTFE, it is possible to extend the polymer's life by reducing its wear rate. Although much study has been placed on bulk PTFE, very little study has been focused on thin films. This article demonstrates that SiO ₂ nanoparticles can be used as a filler to significantly reduce the wear of PTFE thin films while also maintaining a low coefficient of friction. The wear resistance and coefficient of friction of PTFE/SiO ₂ composite films on stainless steel substrates were tested using a linear reciprocating tribometer and compared to pure PTFE films and bare stainless steel to evaluate the benefit of incorporating the SiO ₂ filler in the film. The composite films showed a significant improvement in wear resistance when compared to pure PTFE films. The coefficient of friction for the composite film remained low and stable during a 50 g normal load friction test for a duration of approximately 300 cycles, whereas that of PTFE showed an increasing trend at onset. In addition, of 1.7 and 3.3 wt% SiO ₂ concentrations in solution, 3.3 wt% SiO ₂ showed better performance, with a much higher wear resistance than that of 1.7% SiO ₂ after being subjected to a 1,000-cycle abrasive wear test.     

Tribological behavior of Cu20%Nb and Cu15%Cr in situ composites under dry sliding conditions

The tribological behavior of Cu20%Nb and Cu15%Cr in situ composites was studied on a pin-on-disk tester. Composite pins were slid against a hardened AISI 52100 steel disk under dry ambient conditions. Comparison of coefficient of friction, wear rate and bulk temperature was made between the two composites in terms of effects of normal pressure and sliding speed. Microstructural changes in the composites due to sliding were studied and correlated with the change of tribological behavior. The wear rate increased with increasing normal pressure and decreased with increasing sliding speed in the studied range of normal pressure (0.06–0.56 MPa) and sliding speed (2.50–5.83 m s⁻¹) for both composites. Cu20%Nb showed a much better wear resistance and a lower coefficient of friction than Cu15%Cr. The coefficient of friction slightly increased for Cu20%Nb and slightly decreased for Cu15%Cr with increasing normal pressure. The coefficient of friction for both composites decreased with increasing sliding speed. The bulk temperature was higher and subsurface deformation layer thickness was larger for Cu15%Cr than for Cu20%Nb. Both of them increased with increasing normal pressure and sliding speed. Scanning electron microscopy analysis showed plastic deformation flow on the wear surface at an early stage for both composites. However, the formation of a surface film led Cu20%Nb composite to reach a steady state much sooner and therefore to have a lower wear rate than Cu15%Cr.