Tribological behaviours of PA/UHMWPE blend under dry and lubricating condition

Dry-sliding and lubricated friction and wear behaviours of polyamide (PA) and ultra-high molecular weight polyethylene (UHMWPE) blend were studied using a pin-on-disc method (polymer pin sliding against a stainless steel disc) at room environment. The tribological performance of PA and UHMWPE were also investigated for the purpose of comparison. The worn surfaces were examined using a scanning electron microscope (SEM) and optical microscope. It was observed that PA specimen demonstrated highest friction coefficient, UHMWPE the lowest in both dry-sliding and lubricated sliding test. The friction of PA could be sufficiently decreased by blending with UHMWPE. Statistical analysis suggested the relationship between the wear volume loss and the sliding distance could be expressed by a linear model for dry-sliding, while a logarithmic model was determined for lubricated sliding. The difference in wear modes between both sliding series suggested that there was change in the mode of material removal process. The lower wear rate in lubricated sliding was attributed to the elastohydrodynamic or partial elastohydrodynamic lubrication through the development of a continuous lubricant film between the polymer and the counterface, while the high wear rate of the specimens, in dry-sliding test, was mainly caused by fatigue process due to the repeated action of tearing and crack-propagation.     

Dry sliding wear behaviour of polyamide 66 and polycarbonate composites

A study has been made of the reciprocating dry sliding wear behaviour of polyamide 66 and polycarbonate containing glass fibres, ultra high molecular weight polyethylene (UHMWPE) and polytetrafluoroethylene (PTFE/2% Si oil). Studies have been conducted at sliding loads of 2 kg and 10 kg at an average velocity of 0.33 m s⁻¹ against a hardened stainless steel counterface with a surface roughness of 0.3 μm.It has been shown that additions of 10–15% of filler/reinforcement lead to greatly improved sliding wear behaviour. PTFE/2% Si oil filled polyamide 66 has been shown to have the best overall wear performance whilst the high glass filled variants of polyamide 66 and polycarbonate have the best combination of wear resistance and mechanical strength. These findings are discussed with reference to composite constitution and properties, thermal effects and counterface interactions. Explanations are advanced to account for the differences in behaviour inter alia the composite materials.     

Tribological Behavior of UHMWPE Reinforced with Graphene Oxide Nanosheets

In this article, a series of graphene oxide (GO)/ultrahigh molecular weight polyethylene (UHMWPE) composites are successfully fabricated through an optimized toluene-assisted mixing followed by hot-pressing. The mechanical and tribological properties of pure UHMWPE and the GO/UHMWPE composites are investigated using a micro-hardness tester and a high speed reciprocating friction testing machine. Also, the wear surfaces of GO/UHMWPE composites are observed by a scanning electron microscope (SEM), to analyze the tribological behavior of the GO/UHMWPE composites. The results show that, when the content of GO nanosheets is up to 1.0 wt%, both the hardness and wear resistance of the composites are improved significantly, while the friction coefficient increases lightly. After adding GO, the tribological behavior of the GO/UHMWPE composites transforms from fatigue wear to abrasive wear associated with the generation of a transfer layer on the contact surface, which efficiently reduced the wear rate of the GO/UHMWPE composites.     

Effect of compatibilizer on the transfer and tribological behaviors of PA46/HDPE polyblends

The effect of compatibilizer HDPE-g-MAH of different contents on the transfer and tribological behaviors of PA46/HDPE polyblends was investigated, using a ring-on-block wear tester. All the polyblends showed friction as low as HDPE of 0.20. The wear of the polyblends was reduced when the compatibilizer ranged from 1 to 5 wt.%, showing a minimum value as 1/7 of that of PA46 when the concentration of the compatibilizer was 5 wt.%. Scanning electronic microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) analyses were used to examine the worn surface and the physical state of the acid-eroded transfer films on the counterface. It was found that the physical bonding between PA46 and HDPE phases became stronger due to the better compatibility of the polyblends. The strengthened physical bonding might decrease the peel-back process of the dispersed HDPE particles from the polyblend, enhance the adhesion between the transfer film and the counterface, and ultimately decreased the wear. The formation of a transfer film on the counterface was hardly detectable, which was the primary reason for the relatively high wear of the polyblend with excess compatibilizer.     

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.     

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.     

Wear properties of UHMWPE/aromatic thermosetting copolyester blends in unlubricated sliding

To improve the wear resistance of ultrahigh molecular weight polyethylene (UHMWPE), blends of UHMWPE, and an aromatic thermosetting copolyester (ATSP) (50/50, v/v) were developed, taking advantage of the crosslinked structure and good wear resistance of ATSP. As a compatibilizer, poly(ethylene-co-acrylic acid) (PEA) was added into the blends with its contents changing from 0 to 20% (w/w). Dynamometer wear tests (sliding against stainless steel surface with contact pressure ranging from 600 to 2500 kPa) showed that the UHMWPE/ATSP blend with 10% PEA had lower wear rate than the UHMWPE sample. The improved wear resistance resulted from the change of the wear mechanism. Scanning electron microscopy (SEM) images of the worn surfaces revealed that the presence of ATSP and PEA would prevent the lamellar alignment in the UHMWPE phase and adding PEA effectively enhanced the interaction between UHMWPE and ATSP.     

Pre-Polishing the Metal Counterface of Metal–UHMWPE Wear Pair with Filler-Filled UHMWPE Composites to Generate Counterface Changes for an Effective Reduction in Pure UHMWPE Wear

Ultra-high molecular weight polyethylene (UHMWPE) is well known for high-wear-resistance applications. Its long-chained easy sliding molecules and semi-crystalline structures enable the polymer’s great wear resistance. UHMWPE composites made for higher wear resistance study have been analyzed in this paper. Pure UHMWPE, 1 wt% CNT UHMWPE, 1 wt% PEEK UHMWPE, 1 wt% alumina (nano)–UHMWPE composites were made to be tested against metal disk on pin-on-disk tribometer. The metal disk surface conditions were found to have significant influence on the UHMWPE–polymer wear than the composite itself. This result indicates a simple and industrial applicable method that involves transfer film on the counterface to reduce polymer wear for metal–polymer wear pair applications.     

Surface Morphology Studies in Polymer-Graphite/Epoxy Sliding

Ultrahigh-molecular-weight polyethylene (UHMWPE) and polycarbonate pins were slid dry against continuous graphite fiber/epoxy plates in reciprocating multiple-pass wear tests for different values of virgin surface roughness, fiber orientation, and load. Scanning electron photomicrographs of the polymer wear surfaces were combined with three-dimensional graphs of wear rate versus virgin surface roughness and fiber orientation. The types of surface damage observed for UHMWPE at both an 8.9- and 35.6-N load were mild plastic deformation, fatigue of loose particles, and light abrasive cutting. The types of surface damage observed for polycarbonate at either load were massive abrasive plowing and plastic flow of material. The wear debris of UHMWPE consisted of rolled, cut, or extruded particles; for polycarbonate, clumps of transferred plateaus of polymer. The unit pressure times velocity (PV) limit for polycarbonate was reached when samples were slid against the most abrasive counterface transverse to the graphite fibers.     

Antifriction nanocomposites based on chemically modified UHMWPE. Part 1. Mechanical and tribological properties of chemically modified UHMWPE

The mechanical and tribological properties of chemically modified UHMWPE are studied. X-ray diffraction analysis, IR spectroscopy, scanning differential calorimetry, and electron emission are used to study the permolecular structure and friction surface of polymers with different amounts of copolymers UHMWPE and LDPE grafted with maleic anhydride. Addition of grafted UHMWPE is shown to have no effect on the viscoelastic properties of the polymer-polymer composite, while the addition of grafted LDPE noticeably improves its performance (ductility, plasticity) while retaining its strength. Chemical modification of UHMWPE significantly improves its wear resistance (two to three times), which is due to the features of polymer crystallization and the formation of a permolecular structure.     

Adhesive wear and frictional characteristics of UHMWPE and HDPE sliding against different counterfaces under dry contact condition

Abstract

The current work evaluates the wear and frictional performance of ultrahigh molecular weight polyethylene (UHMWPE) and high density polyethylene (HDPE) sliding against different metal counterfaces, stainless steel(SS), mild steel (MS) and aluminium (Al), under dry contact condition. The experiments were conducted using pin on disc machine at different sliding distances (0–40·32 km), 15 N applied load and 2·8 m s^–1 sliding velocity. Interface temperatures and frictional forces were measured simultaneously during the sliding, while specific wear rates were determined for every 1·68 km sliding distance. Based on the optical microscopy of the worn surface and wear track, frictional and wear results were analysed and discussed. The experimental results showed that the type of counterface material significantly influences both frictional and wear performances of the selected polymers. This was mainly due to the film transfer characteristics. Higher temperature and friction coefficient for UHMWPE and HDPE were evident when sliding took place against Al counterface. Sliding the polymers against stainless steel showed low friction coefficients compared to other counterfaces.     

Dry sliding wear characteristics of some industrial polymers against steel counterface

In this investigation, the influence of test speed and applied pressure values on the friction and wear behaviour of polyamide 66 (PA 66), polyoxymethylene (POM), ultrahigh molecular weight polyethylene (UHMWPE), 30% glass fibre reinforced polyphenylene-sulfide (PPS+30%GFR) and aliphatic polyketone (APK) polymers were studied. Friction and wear tests of PA 66, POM, UHMWPE, PPS+30%GFR and APK versus AISI D2 steel were carried out at dry condition on a pin-on-disc arrangement. Tribological tests were performed at room temperature at different pressures (0.35–1.05 MPa) and sliding speeds (0.5–2.0 m/s). The results showed that, for all polymers used in this investigation, the coefficient of friction decreases linearly with the increase in pressure. The specific wear rate for UHMWPE, PPS+30%GFR and APK were in the order of 10⁻⁵ mm³/N m, while the wear rate value for PA 66 was in the order of 10⁻⁶ mm³/N m. In addition to this, the wear rate value for POM was in the order of 10⁻³ mm³/N m. Furthermore, as the results of this investigation, the wear rate showed very little sensitivity to the applied pressures and test speed.     

Effect of counterface on the tribology of UHMWPE in the presence of proteins

Artificial joints in orthopedics occupy a principal position owing to the increase in number of cases suffering from arthritis and associated diseases in addition to impairment caused by accidents. In this work, one of the most commonly used joint material, i.e. ultrahigh molecular weight polyethylene (UHMWPE), was tested against the duplex stainless steels instead of the conventional 316 L stainless steel. The UHMWPE was found to exhibit the lowest friction coefficient and wear rates when lubricated with water followed by globulin and glucose. The friction coefficient in the presence of egg albumen was higher along with high wear rates recorded. Post-test evaluation of surface roughness and wear scar/track analysis was performed to identify the wear mechanisms. Worn surfaces were analyzed using a differential scanning calorimeter for changes in crystallinity with sliding. The specimens tested under lubricated conditions with glucose, egg albumen and globulin indicated the presence of reaction products on the worn surface. Adhesive and corrosive wear mechanisms were the predominant modes of wear identified on the polymer samples. The wear tracks indicated that the proteins did react with the counterface material forming a thin deposit on them. Low temperature nitriding of the duplex stainless steel counterfaces were performed and the UHMWPE specimens were tested under similar conditions against the nitrided surfaces. Low temperature nitriding of the counterface did result in improved tribological behavior of UHMWPE and the corrosive effects were minimal.     

Fretting Wear Behavior of UHMWPE—Influence of Load and Stroke

In this study, the tribological behavior of ultra-high-molecular-weight polyethylene (UHMWPE) against a GCr 15 steel ball during fretting wear conditions was investigated using an oscillating reciprocating tribometer. The aim of this study was to characterize the critical value of normal load and stroke corresponding to this transition in UHMWPE worn surface at room temperature. Results showed that there existed a critical value of load or stroke at fixed condition. The friction coefficient and wear volume loss of UHMWPE at or near the critical values of load and stroke exhibited extreme changes. Based on observation of the worn surface by scanning electron microscopy (SEM) and 3D surface profiler measurements, it can be found that damage to the worn surface can be linked to the contact load and stroke. In addition, results showed that during the process of fretting wear under different load or stroke conditions, the gross slip regime dominated throughout the whole test period.     

The influence of polymer composition on the wear of the metal surface during fretting of steel on polymer

The effects of the nature of the polymer on the amount of metal wear during fretting of steel on polymers in laboratory air have been studied under a range of loads (130–330 g), amplitudes (3–10 μm) and frequencies (30–60 Hz).A number of polymers can cause damage to the metal, which takes the form of adhesive transfer of α-Fe₂O₃ particles to the polymer surface. The amount of metal wear depends on the polymer counterface and, under a given set of experimental conditions, increases in the order polytetrafluoroethylene (PTFE) and polyethylene, polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene (PCTFE), polysulphone, Polyvinylchloride (PVC), polymethylmethacrylate (PMMA), polycarbonate, nylon 66. No metal wear occurs when the counterface is PTFE and only occurs with polyethylene when the amplitude is greater than 7 μm. These differences are explained in terms of the adhesive properties of the polymers, as determined by their surface energetics. Wear of the polymer during fretting takes the form of fibre formation for polysulphone, PVC, polycarbonate, nylon 66 and, to a small extent, polyethylene, while it takes the form of a transfer of a polymer film to the metal for PTFE and PVDF. No polymer wear occurs for PCTFE or PMMA.     

Effects of ABS-g-MAH on the properties of Nylon 6/ABS alloy

The alloy of Nylon 6/acrylonitrile-butadiene-styrene (ABS) was used for a compatibilizer to generate the maleic anhydride (ABS-g-MAH),in which the proportion of PA6/ABS is 90/10.The results of the mech...     

Sliding wear behaviour of ion implanted ultra high molecular weight polyethylene against a surface modified titanium alloy Ti-6Al-4V

A study has been made of the sliding wear behaviour of untreated and ion implanted ultra high molecular weight polyethylene (UHMWPE) against a surface modified titanium alloy (Ti-6Al-4V) using a pin on disc apparatus. It was found that the presence of water lubrication and a very smooth counterface was necessary to maintain low wear rates of the UHMWPE. A ‘zero wear’ effect was observed when nitrogen implanted UHMWPE was tested against very smooth counterfaces (R_a ≈ 0.03 μm) of either surface oxidized or nitrogen implanted Ti-6Al-4V under water lubrication. The enhanced mechanical and physical properties of the surface treated materials are believed to be responsible for the improved wear performance.     

Improved wear resistance of ultra-high molecular weight polyethylene by plasma immersion ion implantation

Surface modification of ultra-high molecular weight polyethylene (UHMWPE) has been explored using the novel non-line-of-slight plasma immersion ion implantation (PIII) with nitrogen. The modified surfaces were characterised by SEM and a Nano Test 600 testing machine. The tribological behaviour of PIII treated UHMWPE sliding against AISI 316L stainless steel counterfaces was evaluated using a pin-on-disc tribometer under water lubricated conditions. The experimental results show that PIII is a very promising surface engineering technique to improve such surface mechanical properties as surface hardness and elastic modulus of UHMWPE. As a result, the wear resistance of UHMWPE was significantly enhanced by a factor of three following PIII treatment, as compared with untreated material. It was found that the significantly improved wear resistance of PIII treated UHMWPE can be mainly attributed to ion bombardment induced cross-linking, and thus surface hardening.     

The effect of counterface surface roughness on the wear of UHMWPE in water and oil-in-water emulsion

The South African gold mining industry is at present involved in a programme whereby the hydraulic stoping machinery currently operating on a water-based fluid will be modified to run on mine service water. The wear of the UHMWPE seals is an area of particular concern. This paper examines the effect of type of lubricant and counterface surface roughness on the wear of UHMWPE. A reciprocating sliding wear rig was used with UHMWPE sliding against AISI 431 at an average speed of 0.25 m/s. The contact pressure was 10 N/mm². Tests were conducted in water and in a 5% oil-in water emulsion (5:95). The surface roughness of the steel was varied in the range 0.1–1.0 μm (centreline average). The results of the tests in water showed that the logarithm of the specific wear rate is proportional to the surface roughness. The results of the tests in 5:95 showed that there is a significant transition in specific wear rate at a surface roughness of approximately 0.35 μm. At surface roughness less than 0.35 μm the specific wear rate in 5:95 is considerably lower than the specific wear rate in water, while at surface roughness greater than 0.35 μm the specific wear rate in 5:95 approaches that in water. However, SEM examination of the surfaces from both series of tests showed that, irrespective of lubricant, there was a change in the mode of material removal at a surface roughness of approximately 0.35 μm. The wear mechanisms are discussed as a function of type of lubricant and surface roughness. It is believed that the topography of the counterface is responsible for the change in the mode of material removal.     

Optimization on wear performance of UHMWPE composites using response surface methodology

This study examined the wear characteristics of ultra-high molecular weight polyethylene (UHMWPE) reinforced with talc particles. Analysis of variance (ANOVA) was used to construct empirical models to show the connection between control factors (filler loading, load and sliding speed) and responses (wear rate and average coefficient of friction (COF)) of UHMWPE. Response Surface Methodology (RSM) was employed to project the optimization of the control variables in order to reduce the wear of UHMWPE. It was discovered that the rate of wear and the average COF of UHMWPE could be minimized by the inclusion of talc. The SEM analyses of the worn surfaces and transfer films indicated that the degree of wear on the surface of the UHMWPE was reduced.