Tribo‐investigation of PEEK‐short carbon fibre composites in severe testing conditions

A series of composites of polyetheretherketone (PEEK) containing short carbon fibre (CF) in the range of 0–30% (w/w) was developed. Their wear behaviour in low amplitude oscillating wear (LAOW) mode was studied under various operating parameters such as load and temperature. The LAOW mode was studied in ball‐on‐plate configuration against steel (100 Cr 6) at ambient temperature and at 100°C. In this mode, the coefficient of friction (µ), specific wear rate (Ko) and limiting loading pressure‐sliding speed (PV) values were investigated. It was observed that with increase in %CF, the wear performance and utility of PEEK (limiting PV value) improved significantly. Thirty percent CF was best performing composite in all aspects. The µ, however, was hardly influenced with the inclusion of CF or variation in operating parameters. The same composites were also evaluated in abrasive wear mode to study the influence of severe operating conditions on wear and friction performance. In this wear mode, the CF‐filled composites showed poorer wear resistance than did neat PEEK. The specific wear rate was correlated with strength properties and it was observed that these composites closely followed the predictions of the Ratner–Lancaster plot. Scanning electron microscopy was used to examine the microstructural features of worn surfaces. Copyright © 2007 John Wiley & Sons, Ltd.     

Recent advances in polymer composites' tribology

An overview is given on the friction and wear properties of high temperature resistant polymers, in particular polyetheretherketone (PEEK), under various testing conditions against smooth steel counterparts. The effects of internal lubricants, especially polytetrafluoroethylene (PTFE), and short fibre reinforcements (glass vs. carbon) are outlined. In addition, results of sliding wear experiments with continuous glass, carbon or aramid fibre-polymer matrix composites against steel were used to develop a hypothetical model composite with optimum wear resistance.     

Solid particle erosion of unidirectional fibre reinforced thermoplastic composites

In the present study, the solid particle erosion behaviour of neat PEEK matrix and unidirectional glass fibre (GF) and carbon fibre (CF) reinforced polyetheretherketone (PEEK) and polyetherketoneketone (PEKK) composites has been studied. The erosion experiments have been carried out by using silica sand particles (200 ± 50 μm) as an erodent. Steady state erosion rates of these composites have been evaluated at different impact angles and impact velocities. The neat PEEK exhibited peak erosion rate at 30° impingement angle whereas the composites exhibited a semi-ductile behaviour with peak erosion rate at 60° impact angle. The erosion rate of the glass fibre reinforced composites was higher than that of the carbon fibre reinforced composites. The results show that the fibre orientation has a significant influence on erosion rate only at lower impact angles. The erosion rate of the composites was higher when the particles impact perpendicular to the fibre direction than parallel to the fibres. The morphology of eroded surfaces was observed under scanning electron microscope and damage mechanisms were discussed.     

模拟矿井环境下的PEEK/SiO2/CF-MoS2复合材料摩擦行为研究*

为改善聚醚醚酮（PEEK）在矿井工况下的摩擦性能,选用纳米二氧化硅（SiO2）、二硫化钼（MoS2）和短切碳纤维（CF）为增强填料制备PEEK/SiO2/CF-MoS2复合材料,并探究PEEK/SiO2/CF-MoS2复合材料在不同工况条件下的滑动与滚动摩擦学性能;通过模拟滚轮罐耳在矿井环境下的运行方式,分析其磨损形貌和磨损机制。结果表明：PEEK/SiO2/CF-MoS2复合材料在不同载荷条件下均具有良好的减摩和耐磨特性;滑动摩擦在水介质工况下及滚动摩擦在干摩擦工况下,复合材料的摩擦因数和磨损率最低,其磨损机制均以磨粒磨损为主。与矿井常用的聚氨酯材料的对比,PEEK/SiO2/CF-MoS2复合材料的摩擦学性能更为优异。     

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.     

The friction and wear properties of nanometre SiO2 filled polyetheretherketone

Nanometre SiO₂ filled-polyetheretherketone (PEEK) composite blocks with different filler proportions were prepared by compression moulding. Their friction and wear properties were investigated on a block-on-ring machine by running a plain carbon steel (AISI 1045 steel) ring against the composite block. The morphologies of the wear traces and the transfer film were observed by scanning electron microscopy (SEM). It was found that nanometre SiO₂ filled-PEEK exhibited considerably lower friction coefficient and wear rate in comparison with pure PEEK. The lowest wear rate was obtained with the composite containing 7.5 wt.% SiO₂. The SEM pictures of the wear traces indicated that with the frictional couple of carbon steel ring/composite block (fillec with 7.5 wt.% filler), a thin, uniform, and tenacious transfer film was formed on the ring surface. It was inferred that the transfer film contributed largely to the decreased friction coefficient and wear rate of the filled PEEK composites.     

Wear of PEEK composites related to their mechanical performances

A series of polyetheretherketone-based composites was investigated, blended with different contents of polytetrafluoroethylene and/or graphite, and reinforced with various amounts of short carbon fibres. The mixture of the PEEK with various fillers was achieved by twin-screw-extruders. Thereafter, the composites were finally manufactured using an injection moulding machine. Testing of the tribological properties of the PEEK composites was carried out on a block-on-ring apparatus. The dependence of mechanical properties, e.g. Charpy impact resistance, fracture toughness, flexural modulus and strength, on various filler contents of these composites was also investigated, which is believed to be of help towards a better understanding of the steps on how to improve the composite’s wear resistance.     

聚合物填充聚四氟乙烯复合材料的摩擦磨损性能

采用机械共混-冷压成型-烧结的工艺制备了PEEK、PPS填充PTFE基粘弹．摩擦型阻尼材料，用环-块式磨损试验机研究了在干摩擦条件下的摩擦磨损性能；用扫描电子显微镜观察磨损表面形貌和内部组织结构。结果表明：混合填充PEEK和PPS时，2种填充物的比例对材料的摩擦因数影响不大，当二者含量相近时，摩擦因数最大；填充物对磨损性能的影响与对摩擦因数的相同；随着PEEK含量的增加和PPS含量的减少，材料的磨损方式由疲劳剥落磨损为主转变为犁削、粘着磨损；PTFE含量的增加，使得复合材料的摩擦因数减小，而磨损有所增大。综合考虑认为，PTFE与适当比例的PEEK／PPS混合填充，具有合适的摩擦因数和较好的耐磨性，能够满足特殊工况下阻尼材料的需要。     

PEEK基自润滑复合材料的摩擦学研究和应用

聚醚醚酮(PEEK)基自润滑复合材料具有摩擦因数低、耐磨性好等特点,可以在无润滑、高温、潮湿、污染、腐蚀等恶劣环境下使用。本文综述了对聚醚醚酮(PEEK)基复合材料摩擦学研究的新进展,讨论了纤维增强、无机填充、有机共混改性以及温度、对偶和介质、固体润滑剂等对PEEK基复合材料摩擦学性能的影响,介绍了PEEK基复合材料在人工关节假体材料方面的应用,指出PEEK摩擦复合材料今后的研究方向,以期扩大PEEK复合材料的摩擦学工程应用。     

均匀设计法在聚醚醚酮复合材料摩擦学特性试验中的应用研究

采用均匀设计法设计了CF/SiO2/PTFE/PEEK复合材料,并模压成型;在摩擦磨损试验机上研究了PEEK复合材料的摩擦学特性,应用回归分析法对其摩擦学特性试验数据进行了分析,得到了摩擦学特性参数的回归公式。结果表明,均匀设计法应用于PEEK复合材料的摩擦学特性研究是可行的,能有效预测复合材料的摩擦学特性参数,回归分析结果与复合材料的摩擦磨损试验数据相吻合。     

Correlation of the tribological behaviors with the mechanical properties of poly-ether-ether-ketones (PEEKs) with different molecular weights and their fiber filled composites

The tribological behaviors of three poly-ether-ether-ketones (PEEKs) with different molecular weights and their SCF (short carbon fiber)/graphite/PTFE (polytetrafluoroethylene) filled composites were examined using a block-on-ring apparatus under dry sliding conditions. Tensile tests, hardness measurements and dynamic mechanical thermal analysis (DMTA) of the PEEK based materials were also performed. The tribological behaviors of PEEK based materials were correlated with their mechanical properties and the tribological mechanisms were discussed based on scanning electron microscope (SEM) inspections of worn surfaces and wear debris. Under a low apparent pressure, a high material ductility seems to reduce the wear rate of pure PEEK through alleviating the microcutting effect exerted by the protruding regions of the counterpart. Under a high pressure, however, a high stiffness seems to improve the wear resistance of pure PEEK by reducing the plastic flow occurring in the PEEK surface layer. After incorporating SCF/graphite/PTFE fillers, the wear rate of PEEK was decreased significantly. Thinning and cracking of SCF are supposed to be the important factors determining the tribological behaviors of the composites.     

Solid particle erosion of unidirectional carbon fibre reinforced polyetheretherketone composites

The solid particle erosion behaviour of unidirectional carbon fibre (CF) reinforced polyetheretherketone (PEEK) composites has been characterised. The erosion rates of these composites have been evaluated at different impingement angles (15–90°) and at three different fibre orientations (0, 45, and 90°). The particles used for the erosion measurements were steel balls with diameter of 300–500 μm and impact velocities of 45 and 85 m/s. The unidirectional CF reinforced PEEK composites showed semi-ductile erosion behaviour, with maximum erosion rate at 60° impingement angle. The fibre orientations had a significant influence on erosion rate. The morphology of eroded surfaces was examined by using scanning electron microscopy (SEM). Possible erosion mechanisms are discussed.     

Self-Lubricating PTFE-Based Composites with Black Phosphorus Nanosheets

Black phosphorus (BP), a newly emerging two-dimensional material, has recently received considerable attention. Our recent work suggested that BP nanosheets exhibit extraordinary mechanical and lubrication properties. In the present work, the tribological properties of polyetheretherketone (PEEK)/polytetrafluoroethylene (PTFE) and carbon fiber (CF)/PTFE composites with BP nanosheets have been investigated. The morphologies and surface element distribution of the worn tracks of the tribopair surfaces were examined by different analytical techniques. The results show that the coefficients of friction (COFs) of both the PEEK/PTFE and CF/PTFE composites decreased dramatically after the addition of BP nanosheets, and the minimum COF of the composite was 0.04, which was a quarter of that of the PTFE composite without BP nanosheets. After BP nanosheets were added into the composites, the wear rate of the PTFE/PEEK composite decreased dramatically, while that of the CF/PTFE composite increased significantly with the increase in the filler concentration. The analysis of the lubrication mechanism of the PTFE composite with BP nanosheets suggested that BP nanosheets could be constantly supplied into the contact area and gradually formed a BP film composed of phosphorus oxide and phosphoric acid on the counterpart surface instead of the formation of PTFE transfer film. The formed BP transfer film promoted the friction reduction and the disappearance of the adhesive wear.     

Tribological Behaviour of Polymeric Coatings: II. SCF‐Reinforced PEEK Nanocomposite Systems

This paper focuses on coatings based on poly(ether ether ketone) (PEEK) applied to metal substrates and their tribological investigation. Short carbon fibres (SCF), graphite, and 300 nm titanium dioxide (TiO₂) and zinc sulphide (ZnS) particles were used as filler materials for the PEEK. These filler materials and their combinations were found to have a significant influence on the tribological behaviour of the corresponding PEEK compounds. One of the compounds (PEEK6) was found, especially at higher temperatures and under higher normal loads, to be a good coating material showing superior tribological behaviour. For PEEK6, a specific wear rate and a coefficient of friction (COF) lower than those for the best commercially available PEEK compound (PEEK4) were measured. For specific test parameters, PEEK6 showed a COF of less than 0.1. The tribological results were also compared with those of a conventional sliding bearing material based on poly(vinylidene fluoride) (PVDF).     

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.     

Tribological behaviors of hierarchical porous PEEK composites with mesoporous titanium oxide whisker

Hierarchical porous PEEK self-lubricating composites were prepared by mold-leaching and vacuum melting process under high temperature. The tribological behaviors were investigated for the porous PEEK composite and the porous composite after incorporating micro-porogen (NaCl) and mesoporous titanium oxide whiskers. If only micro-porogen was incorporated, the lowest steady state specific wear rate was observed for PEEK composites filled with 30% NaCl. Based on this porous PEEK composite, the effects of mesoporous titanium oxide whiskers and non-perforated titanium oxide whiskers on the friction and wear properties of PEEK composites were studied. Results showed that nano-micro porous PEEK composites with 30 wt% micro-porogen and 5 wt% mesoporous titanium oxide whiskers reached the lowest friction coefficient and specific wear rate, which were recorded as 0.0194 and 2.135×10^–16 m³/Nm under the load of 200 N. Compared with 15 wt% carbon fiber-reinforced PEEK composite which is widely used in industry, the wear resistance of the designed hierarchical porous PEEK composite increased by 41 times, showing outstanding wear resistance.     

Fretting Wear Study of PEEK-Based Composites for Bio-implant Application

The failure caused by fretting wear is a key issue in orthopedic applications as well as other engineering applications. In this study, fretting wear tests were conducted on poly (ether ether ketone) (PEEK), glass fiber reinforced PEEK (GFRPEEK) and carbon fiber reinforced PEEK (CFRPEEK), respectively. Surface characterizations of tested specimens were performed using XRD, microhardness tester, 3D white-light interfering profilometry, SEM and optical microscopy to analyze their wear features. The obtained results showed that the fibers increased the microhardness values and reduced the friction coefficients and wear rates of PEEK-based composites. The fretting regimes of PEEK, GFRPEEK and CFRPEEK were gross slip. The fretting wear mechanisms of those PEEK composites were dominated by abrasive wear, adhesive wear and delamination. CFRPEEK has demonstrated superior fretting wear characteristics, and hence, is a potential bio-implant material for applications such as artificial joints.     

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.     

Effect of reinforcement coatings on the dry sliding wear behaviour of aluminium/SiC particles/carbon fibres hybrid composites

Dry sliding wear of an AA 6061 alloy reinforced with both modified SiC particles and metal coated carbon fibres has been studied. SiC particles were used to increase the hardness of the composite while short carbon fibres are supposed to act as a solid lubricant. SiC particles were coated with a silica layer deposited through a sol–gel procedure to increase the processability of the composite and to enhance the particle–matrix interfacial resistance. The metallic coatings on carbon fibres were made of copper or nickel phosphorus which was deposited through an electroless process. The metallic coatings favoured the wetting of the fibres during processing and then dissolved in the aluminium matrix forming intermetallic compounds that increased its hardness. Wear behaviour of AA 6061–20%SiC and AA 6061–20%SiC–2%C was compared with that of the composites with the same reinforcement content but using coated particles and fibres. The influence that the modification of the matrix because of the incorporation of coatings on the reinforcements had on the mild wear behaviour was investigated. The wear resistance of the composites increased when carbon fibres were added as secondary reinforcement and when coated reinforcements were used.     

Microfriction of various phases in a carbon fiber, polytetrafluoroethylene, graphite and polyetheretherketone composite blend as measured by atomic force microscopy

Atomic force microscopy and friction force microscopy have been used to conduct microfriction studies on short carbon fiber reinforced PEEK/PTFE composite blends. The relative micro-scale coefficients of friction of different filler particles (PTFE, CF in normal and anti-plane orientation, and graphite) have been compared with the matrix PEEK. The order of the nanoscopic coefficients of friction was: carbon fiber in normal orientation>carbon fiber in plane orientation>PEEK matrix>graphite flake>carbon fiber in parallel orientation>PTFE particle. Additional microhardness studies resulted in qualitative hardness comparisons of the various phases. Their order of the form: carbon fibers PEEK and graphite>PTFE also reflects the contribution of the various phases to the wear resistance of the composite blend. The latter can be estimated from the AFM-topography traces of the polished composite surfaces.