Wear and frictional performance of polymeric composites aged in various solutions

The aim of the present work is to investigate the effect of aging process on the wear and frictional characteristics of polyester composites based on oil palm fibres. Prepared samples of treated oil palm fibre reinforced polyester (T-OPRP) composite were immersed in different types of solutions (i.e. water, salt water, diesel, petrol and engine oil) for three years. The samples were then tested on a Pin on disc (POD) machine subjected to a polished stainless steel counterface under dry adhesive wear at different sliding distances (0-6.72 km). Scanning electron microscopy (SEM) was used to observe the damage features on the worn surfaces. Results revealed that aging process has pronounced influence on the adhesive wear and frictional behaviour of the T-OPRP composite. Immersing the samples in water and salt water demonstrated poorest wear performance as compared to the ones immersed in engine oil and diesel. This was mainly due to the higher viscosities of engine oil and diesel solutions as compared to the rest.     

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.     

Polyester composite based on betelnut fibre for tribological applications

A polyester composite based on betelnut fibres was fabricated and its adhesive wear and frictional performance studied using a block on disk machine at different applied loads and sliding distances at 2.8 m/s sliding velocity under dry/wet contact conditions. SEM was used to study worn surface morphology. The results revealed that betelnut fibre reinforced polyester (BFRP) composite had better wear and frictional performance under wet contact condition compared to dry. The wear mechanism of the BFRP composite was predominated by micro and macro-cracks in the polyester regions and debonding of fibres.     

Tribological behaviour of PTFE modified cotton polyester composites

Abstract

An attempt on modification of tribological behaviour of cotton polyester composite was done with polytetrafluoroethylene (PTFE). PTFE modified polyester–cotton composites were developed and studied for their friction and sliding wear behaviour at different applied loads. The sliding wear tests of composites were conducted against EN-31 steel counter face. The coefficient of friction μ as well as the sliding wear rate of cotton–polyester composites reduced significantly on addition of PTFE. The reduction in wear rate of PTFE modified polyester–cotton composite has been discussed with the help of SEM observations of worn surfaces and coefficient of friction.     

The Tribological Behaviour of Fe–28Al–5Cr/TiC Under Liquid Paraffine Lubrication

The tribological behaviour of Fe–28Al–5Cr and its composites containing 15, 25 and 50 wt% TiC (corresponding to 19.3, 31.2 and 57.6 vol%), produced by hot-pressing process, was investigated under liquid paraffine lubrication against an AISI 52100 steel ball in ambient environment at varied applied loads and sliding speeds. It was found that the wear resistance increased and friction coefficient decreased with increasing of TiC content. The coefficients of friction are in the range of 0.09–0.14 at the given testing conditions. The wear rates of all the materials except the 50% composite are on the order of 10⁻⁶–10⁻⁵ mm³ m⁻¹, the wear rate for the 50% composite is too low to quantify under the two sliding conditions, (50 N, 0.04 m/s) and (100 N, 0.02 m/s). The wear rates of all the materials increase as applied load increases and the increasing extent diminishes with the increase of TiC content, but first increase slightly and then nearly remains steadiness with increasing sliding speed. The 50 wt% composite has wear resistance about 7–20 times better than pure Fe–28Al–5Cr at different sliding parameters. The enhanced wear resistance by TiC addition is attributed to the high hardness of the composites, as well as support of the oil lubrication film/layer by the hard TiC phase. The worn surfaces of all the materials are analyzed by a scanning electron microscope. The dominant wear mechanism of the Fe–28Al–5Cr and 15% composite is grooving and flaking-off, but those of the 25 and 50% composites are mainly shallow grooving.     

Torsional Wear Behavior of MC Nylon Composites Reinforced with GF: Effect of Angular Displacement

The torsional wear behavior of monomer cast nylon (MC nylon) composites reinforced with glass fiber was studied with a self-made torsional friction tester. The worn surface of MC nylon composites was investigated with a scanning electron microscope. The worn surface of the steel disk was observed with a 3-D profiler. The experimental results indicated that the shape of torque–angular displacement (T–θ) curves changed from elliptic shape to quasi-parallelogram with the angular displacement increased from 5° to 30°. The serious wear characterized with a deep groove occurred at the position of about 1.5–4 mm radius of contact zone on the steel surface. The mass of MC nylon samples increased after torsional wear test. The torsional contact area can be divided into three zones: (a) a central stick zone, (b) an intermediate mixed-slipping annulus, and (c) a peripheral sliding annulus. The most serious wear occurred in the intermediate annulus because of the higher contact stress and mixed slip regime. The main wear mechanism of MC nylon samples was adhesive wear and abrasive wear. Plastic deformation of asperities was the character in the central zone. Slight adhesive wear was the main wear mechanism in the peripheral annulus.     

Influence of Plasma Treatment on Carbon Fabric for Enhancing Abrasive Wear Properties of Polyetherimide Composites

Interfacial adhesion between matrix and fiber plays a crucial role in controlling performance properties of composites. Carbon fibers have major constraint of chemical inertness and hence limited adhesion with the matrix. Surface treatment of fibers is the best solution of the problem. In this work, cold remote nitrogen oxygen plasma (CRNOP) was used for surface treatment. Twill weave carbon fabric (CF) (55–58 vol%) was used with and without plasma treatment with varying content of oxygen (0–1%) in nitrogen plasma to develop composites with Polyetherimide (PEI) matrix. The composites were developed by compression molding and assessed for mechanical and tribological (abrasive wear mode) properties. Improvement in tensile strength, flexural strength, and interlaminar shear strength (ILSS) was observed in composites due to treatment. Similarly, improvement in wear resistance (W _R) and reduction in friction coefficient (μ) were observed in treated fabric composites when slid against silicon carbide (SiC) abrasive paper under varying loads. A correlation between wear resistance and tensile strength was slightly better than that in Lancaster–Ratner plot indicating that ultimate tensile strength (S) and elongation to break (e) were contributing to control the W _R of the composites. It was concluded that enhanced adhesion of fibers with matrix was responsible for improvement in performance properties of composites, as evident from SEM, Fourier Transform Infrared spectroscopy-Attenuated Total Reflectance (FTIR-ATR) technique.     

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.     

Influence of Internal Lubricants (PTFE and Silicon Oil) in Short Carbon Fibre-Reinforced Polyimide Composites on Performance Properties

Short carbon fibre-reinforced thermoplastic polyimides (30 wt%) often show high and unstable coefficients of friction. In this study, the effects of internal lubrication by polytetrafluoroethylene (PTFE) (15 wt%) or silicon oil (15 wt%) have been investigated using a reciprocating cylinder-on-plate test under 50–100 N normal loads and 0.3–1.2 m/s sliding velocities. The sliding mechanisms are discussed by considering mechanical and thermochemical modifications. The PTFE additives provide lowest coefficients of friction completely stabilising after a transition from mechanically into thermally controlled sliding at 120 °C. The sliding mechanisms and homogeneous transfer films are mainly controlled by plasticisation rather than easy-shear of its lamellar structure that is hindered by fibre reinforcement. Thermoplastic lubricants decrease the mechanical strength and therefore cause deformation and highest wear rates under 200 N. Internal oil lubricants do not reduce coefficients of friction at mild to intermediate normal loads and sliding velocities, while they become most efficient at severe sliding conditions, augmenting the pv-limit. While coefficients of friction match uniquely to the pv-conditions, the wear rates are mainly influenced by the load level: the lowest wear rates are provided by PTFE at low to intermediate pv-conditions and by oil lubricants under high normal loads.     

Abrasive wear performance of carbon fabric reinforced polyetherimide composites: Influence of content and orientation of fabric

Dry abrasive wear performance of five plain weave carbon fabric (CF) reinforced Polyetherimide (PEI) composites, developed with increasing CF contents (in the step of 10 vol%) is reported in this paper. It was observed that composite reinforced with 65 vol% CF (IP₆₅) exhibited the best tensile and shear strength and closely followed the leader (IP₇₅) in flexural strength. IP₆₅ when abraded against silicon carbide paper showed highest wear resistance (W_R) and lowest friction coefficient (μ) among all composites. The composites IP₈₅ and IP₄₀ containing highest and lowest amount of CF respectively showed least enhancement in strength properties and poorest wear performance. Parallel studies on the influence of fabric orientation with respect to the sliding plane and direction, on W_R showed that when CF was oriented parallel to the sliding plane, it had poorest wear resistance. The performance improved for the composites when fabric was oriented normal to the plane. The parallel or anti-parallel orientation of warp or weft fibers with respect to sliding direction showed marginal changes in friction and wear performance. Wear mechanisms were suggested and strongly supported by worn surface analysis using SEM.Efforts were also done to investigate the wear-property correlation. It was observed that the W_R was directly proportional to the product of interlaminar shear strength (I_s) and elastic modulus (E). Fairly good linearity was shown for specific wear rate (K₀) as a function of factor (μP/I_sE) where μ is coefficient of friction and P is the normal pressure (N/mm²).     

Tribological Characteristics of Rubber-Based Friction Materials

This article deals with the rubber-based friction materials (RBFMs) which can be used in brake system. The physico-mechanical and tribological properties of a series of fiber filled RBFMs containing steel wool and aramid pulp at different concentrations along with a fiber-free reference material were characterized. Rubber–glass transition induced at higher sliding velocities was identified based on the friction fade behavior of the RBFMs. The rubber–glass transition which is inherently originated by viscoelastic response of polymeric binder was found to be influential on the tribological properties of the RBFMs. It was revealed that steel wool increased coefficient of friction (COF) and improved friction recovery behavior at low volume percent (7.5 vol.%) but it aggravated the COF at high concentration of steel wool (15 vol.%) and severe sliding conditions because of harsh abrasive mechanism. Aramid pulp improved the fade behavior at high sliding velocities and increased COF due to formation of sticky contact patches. It was revealed that steel wool increased the wear rate while aramid pulp did not affect the wear rate significantly, contrary to the increase in the friction coefficient of RBFM. SEM analysis was proved to be useful in correlating the wear rates of composites to the topographical changes on the worn surfaces.     

Friction and wear of polyphenylene sulfide composites filled with micro and nano CuO particles in water-lubricated sliding

The tribological behavior of polyphenylene sulfide (PPS) composites filled with micro and nano CuO particles in water-lubricated sliding condition were studied. Pin-on-disk sliding tests were performed against a steel counterface of surface roughness 0.09–0.11 μm. The lubrication regimes were established from friction data corresponding to various combinations of loads and sliding speeds. Later experiments were performed using the sliding speed of 0.5 m/s and contact pressure of 1.95 MPa, which corresponded to boundary lubrication regime. Micro CuO particles as the filler were effective in reducing the wear of PPS but nano CuO particles did not reduce wear. The steady state wear rate of PPS-30 vol.% micro CuO composite was about 10% of that of unfilled PPS and the coefficient of friction in this case was the lowest. The examination of the topography of worn pin surfaces of nano CuO-filled PPS by SEM revealed grooving features indicating three-body abrasion. The transfer films formed on the counterfaces during sliding were studied by optical microscopy and AFM. The wear behavior of the composites in water-lubricated sliding is explained using the characteristics of worn pin surfaces and transfer films on the counterface.     

Tribological Behaviour of SiC Particle Reinforced Al–Si Alloy

The purpose of this study is to explore the effect of SiC reinforcement along with immiscible element addition in spray formed Al–Si base alloy. The investigation is done for four different compositions, i.e., Al–Si base alloy, Al–Si/SiC, Al–Si–5Sn/SiC and Al–Si–10Sn/SiC composite. The dry sliding wear properties of base alloy and composites were investigated against EN 31 steel at five different normal loads (14.7, 24.5, 34.3, 44.1 and 53.9 N). The tests were carried out in dry sliding conditions with a sliding speed of 1.6 ms⁻¹ over pin-on-disc tribometer. Each composition is tested at four different temperatures 50, 75, 100 and 150 °C. To determine the wear mechanism, the worn surfaces of the samples were examined using scanning electron microscope (SEM). The composites emerge to be better wear resistant material than base alloy especially at higher loads. The optimum wear reduction was obtained in Al–Si–10Sn/SiC composite at all the different normal loads and temperatures.     

An investigation on worn surfaces of chopped glass fibre reinforced polyester through SEM observations

The wear mechanisms of chopped strand mat (CSM) glass fibre reinforced polyester (CGRP) composite subjected to dry sliding against smooth stainless steel counterface (R_a=0.06 μm) were studied using a pin-on-disc technique. The effects of normal load (30-90 N), sliding velocity (2.8-3.9 m/s) and sliding distance (0.7-3.5 km) on friction and wear behaviour of the CGRP composite in two different CSM orientations (parallel and anti-parallel) were measured. The worn surfaces of the CGRP composite specimens for each specific test condition were examined using scanning electron microscopy (SEM).Sliding in P-orientation exhibited lower friction coefficient at lower load and higher speed compared to AP-orientation. Meanwhile, sliding in AP-orientation exhibited (15%) less friction coefficient at higher load compared to P-orientation. At higher range of all tested parameters, AP-orientation exhibited less mass loss (16%) compared to the P-orientation.Interestingly, SEM observations showed various wear mechanisms that predominated by abrasive nature. Damage of different features in the matrix and CSM glass fibre associated with higher values of load, speed, and sliding distance such as micro- and macro-cracks in the matrix, interface separation, fibre debonding and fracture, and different sizes of fractured fibres were evident.     

Tribological Properties of Spark-Plasma-Sintered ZrO2(Y2O3)–Al2O3–Ba x Sr1?x SO4 (x?=?0.25, 0.5, 0.75) Composites at Elevated Temperature

Self-lubricating ZrO₂(Y₂O₃)–Al₂O₃–Ba _x Sr_1−x SO₄ (x = 0.25, 0.5, 0.75) composites have been fabricated by spark plasma sintering (SPS) method. The tribological properties have been evaluated using a high-temperature friction and wear tester at room temperature and 760 °C in dry sliding against alumina ball. The composites exhibit distinct improvements in effectively reducing friction and wear, as compared to the unmodified ZrO₂(Y₂O₃)–Al₂O₃ ceramics. The ZrO₂(Y₂O₃)–Al₂O₃–Ba _x Sr_1−x SO₄ (x = 0.25, 0.5, 0.75) composites have great low and stable friction coefficients of less than 0.15 and wear rates in the order of 10^− 6mm³/Nm at 760 °C. Delamination is considered as the dominating wear mechanism of the composites at room temperature. At elevated temperature, the formation and effective spreading of Ba _x Sr_1−x SO₄ (x = 0.25, 0.5, 0.75) lubricating films during sliding play an important role in the reduction of the friction and wear.     

Friction and Wear Behavior of Ultra-High Molecular Weight Polyethylene Sliding Against GCr15 Steel and Electroless Ni–P Alloy Coating Under the Lubrication of Seawater

The friction and wear behavior of ultra-high molecular weight polyethylene (UHMWPE) sliding against GCr15 steel and electroless Ni-P alloy coating under the lubrication of seawater was investigated and compared with that under dry sliding and lubrication of pure water and 3.5 wt.% NaCl solution, respectively. It was found that under the lubrication of aqueous medium, the friction and wear behavior of UHMWPE mainly depended on the corrosion of counterface and the lubricating effect of the medium. Because of serious corrosion of counterface by the medium, the wear rates of UHMWPE sliding against GCr15 under the lubrication of seawater and NaCl solution were much larger than that under other conditions, and such a kind of wear closely related to the corrosion of counterface can be reckoned as indirect corrosive wear. However, when sliding against corrosion-resistant Ni–P alloy under the lubrication of seawater, the lowest coefficient of friction and wear rate of UHMWPE were obtained, owing to superior lubricating effect of seawater. Moreover, periodic ripple patterns were observed on the worn surfaces of UHMWPE sliding against GCr15 under the lubrication of seawater and NaCl solution, which were ascribed to the intelligent reconstruction of surface microstructure of UHMWPE upon large plowing effect of the counterface asperities. Based on scanning electron microscopic (SEM) and three-dimensional (3D) profile analyses of the worn surfaces of UHMWPE, a stick–slip dynamic mechanism was proposed to illustrate the pattern abrasion of UHMWPE. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Tribological Behaviour of Orthopaedic Ti-13Nb-13Zr and Ti-6Al-4V Alloys

The aim of this study is to compare the tribological behaviour of novel orthopaedic implant alloy Ti-13Nb-13Zr with that of the standard Ti-6Al-4V ELI alloy, available in four different microstructural conditions produced by variations in the heat treatments. The friction and wear tests were performed by using a block-on-disc tribometer in Ringer’s solution at ambient temperature with a normal load of 20–60 N and sliding speed of 0.26–1.0 m/s. It was found that variations in microstructures produced significant variations in the wear resistance of Ti-6Al-4V ELI alloy. The wear losses of materials solution treated (ST) above the β transus temperature are significantly lower compared with those of materials ST in the (α + β) phase field and are almost insensitive to applied load and sliding speed. Wear loss of the (α + β) ST Ti-6Al-4V ELI alloy continuously increased as applied load was increased and was highest at the highest sliding speed. The Ti-6Al-4V ELI alloy in all microstructural conditions possesses a much better wear resistance than cold-rolled Ti-13Nb-13Zr alloy. Friction results and morphology of worn surfaces showed that the observed behaviour is attributed to the predominant wear damage mechanism.     

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.     

Design of Low Wear Polymer Composites

Multifunctional tribological coatings rely on combinations of materials to improve properties, such as lubricity and wear resistance. For example, some polymer composites exhibit favorable tribological performance as solid lubricants. Here, classical molecular dynamics simulations are used to investigate the tribological behaviors of a mixed system of polyethylene (PE) sliding over polytetrafluoroethylene (PTFE) with the results compared with the sliding of the relevant homogeneous systems. In particular, oriented cross-linked PTFE and PE surfaces are slid in several relative sliding directions such that the surface chains are in-registry or out-of-registry and at various applied normal loads. The simulation results quantify the ways in which the mixed PTFE–PE system behaves differently than either of the homogeneous systems due to the lack of interlocking phases at the interface. These findings are compared with experimental production of polyetheretherketone (PEEK)–PTFE composites that have unusually low wear rates of 7.0 × 10⁻⁸ mm³/Nm, coupled with a steady, low friction coefficient of μ = 0.11 for over two million sliding cycles. The simulation results explain the atomic-scale origins of the frictional properties of this composite.     

Effect of Tribofilm Formation on the Dry Sliding Friction and Wear Properties of Magnetron Sputtered TiAlCrYN Coatings

Nano-structured TiAlCrYN coatings, grown by unbalanced magnetron sputtering on various steel substrates, exhibited friction coefficients 0.6–0.8 and wear coefficients 10⁻¹⁶–10⁻¹⁵ m³ N⁻¹ m⁻¹ in dry sliding wear tests. This article reports comprehensive worn surface analyses using SEM, TEM, EDX, EELS and Raman spectroscopy. A ~80 nm thick tribofilm formed on the TiAlCrYN worn surface was found to have dense amorphous structure and homogeneous oxide composition of Cr_0.39Al_0.19Ti_0.20Y_0.01O_0.21. Viscous flow of the amorphous tribofilm was dominant in causing the high friction coefficient observed. The coatings showed combined wear mechanisms of tribo-oxidation and nano-scale delamination.