Friction and wear of copper/lead and aluminium/tin filled polyamide coatings

The friction and wear of steel pins coated with filled polyamides and loaded against a rotating cylinder of bearing steel were tested under dry, lubricated, and abrasive contaminated conditions. The filler materials were copper/lead and aluminium/tin powders. The test results show a significant reduction in friction with the Cu/Pb filled polyamides (8 wt.% Cu, 12 wt.% Pb, and 80 wt.% PA6). The Al/Sn filled polyamides (3 wt.% Al, 2 wt.% Sn, and 95 wt.% PA6) showed the best wear resistance, accompanied by an increase in the coefficient of friction.     

热喷涂MoS2/PA(聚酰胺)复合涂层的摩擦学性能及磨损机理研究

利用热喷涂技术在45钢上制备了MoS2／PA(聚酰胺)复合涂层，考察了不同填料含量复合涂层的摩擦磨损性能，采用SEM分析涂层及对偶磨损表面形貌，并探讨了填料对复合涂层摩擦磨损性能的影响机制。结果表明：填料含量大于39／6时，虽然摩擦因数较小，但磨损率很大，且大于纯PA涂层的磨损率；当填料含量小于3％时，涂层摩擦学性能有所提高。     

Friction and Wear of Polyamide 66 With Different Weight Average Molar Mass

The friction and wear of monolithic polyamide 66 (PA66) and a PA66 composite reinforced with short glass fibers were examined using a block-on-ring friction tester with particular focus on the effect of weight average molar mass (M _w) of PA66. The amount of glass fibers in the composite and the molecular weight strongly affected the friction level and wear rate because it altered the shear strength and adhesion of PA66. In the case of the glass fiber-reinforced PA66 composites, the improvement of the tribological property was attributed to the increased softening temperature of the composite and reduced material transfer to the counter surface. From this study, the optimum composite having the improved wear resistance with the low friction level was achieved with the lower M _w PA66 containing 40 vol.% glass fibers.     

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.     

Tribological Investigation of MC PA6 Reinforced by Boron Nitride of Single Layer

Monomer casting polyamide 6 (MC PA6)/boron nitride of single layer (SBN) nanocomposites were successfully synthesized by in situ ring-opening polymerization. SBN was prepared by sonication assisted with solution beforehand. Studies on frictional and wear performance of the nanocomposites were carried out on a block-on-ring tester. The results showed that the nanocomposites had lower wear rates and friction coefficients in comparison with neat MC PA6. The incorporation of 0.25 wt% SBN into MC PA6 significantly reduced wear and friction under dry sliding; however, with further increasing the SBN loading, both wear rate and friction coefficient began to increase. The SEM micrographs of the worn surface revealed their friction and wear mechanisms. Pure MCPA6 was characterized by severe lamellar spalling with adhesive wear being the major wear form which caused high friction and wear. The wear modes of the nanocomposites became mainly abrasive wear with lower content of SBN and displayed fatigue wear with higher content of SBN. The morphology of a uniform transfer film on the counterpart ring and fine wear debris for the nanocomposites corresponded to the improved tribological performance.     

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.     

Ionic liquids as lubricants of polystyrene and polyamide 6-steel contacts. Preparation and properties of new polymer-ionic liquid dispersions

Room-temperature ionic liquids (ILs) have been used as external lubricants in polystyrene (PS) and polyamide 6 (PA6)-steel contacts and as internal lubricants in new polymer-IL dispersions. 1−C _n H_2n+1−3−CH₃-imidazolium X⁻ [X=BF₄; n=2 (IL1), 6 (IL2), 8 (IL3). X=PF₆; n=6 (IL4). X=CF₃SO₃; n=2 (IL5). X=(4−CH₃C₆H₄SO₃); n=2 (IL6)] ionic liquids give low friction and extremely mild wear in PS/AISI 316L stainless steel contacts, independently of IL composition. For AISI 52100 steel pins a tribocorrosion reaction produces FeF₂ and increases friction. PS+IL1 (1; 1.35; 3 wt.% IL1) dispersions show lower dry friction and wear against AISI 52100 as IL1 proportion increases, but the lowest friction, with a one order of magnitude reduction with respect to PS, is reached for PS+1%IL1 once the skin layer has been worn out. Increasing IL1 content to 10 wt.% produces an heterogeneous material with non-uniform IL distribution. IL4 reduces friction and wear in PA6+3%IL4 dispersions against AISI 316L, although the lowest values are obtained with IL4 as external lubricant. The cryofracture surfaces of the polymers have been examined and the thermal stability of the polymers in the presence of ILs has been determined.     

Tribological behaviour of new chemically bonded PTFE polyamide compounds

Topic of the study is the formation of new PTFE polyamide materials by reactive extrusion. The new type of formed PTFE polyamide compound shows very good material properties. Recently it has been revealed that carboxylic acid groups exhibit a very high reactivity under polyamide melting conditions. PTFE micro powders functionalized by carboxylic acid groups are the base for the block copolymer formation in polyamide melts under defined process conditions. Such functionalized micro powders are formed from virgin PTFE by electron irradiation in the presence of oxygen. These new PTFE polyamide materials can be processed easily using commercial (common) process equipment like twin-screw extruders and injection molding. Many experimental investigations have been performed under dry sliding friction on PA 6, PA 6.6 and PA 12 compounds with PTFE weight portions between 3.3 and 50%. They show low coefficients of friction and low specific wear rates. The wear resistance of newly developed PTFE polyamide compounds is comparable with commercially available mechanically or physically produced PTFE and PEAK compounds.     

Large‐scale specimen testing on friction and wear of pure and internally lubricated cast polyamides

Due to the casting process for nylons, their composition can easily be modified to cover a wide range of mechanical properties and applications, especially as large wear surfaces in, for example, crane guidances. Presently, selection tests for working conditions up to 40MPa are presented on pure Na‐catalysed polyamides, oil‐filled polyamides with homogeneous oil dispersions and holes in the surface containing oil lubricant and two types of thermoplastic solid‐lubricated polyamides. Pure polyamides are, however, prone to high and unstable sliding at pressures as low as 10MPa with brittle fracture and lumpy transfer. Oil lubrication is not able to remove the sliding instabilities as oil supply to the sliding interface is controlled by migration effects that are restricted by deformation and thermal softening or melting of the polyamide matrix. Although friction and wear are lower and more stable for samples with oil supplied through lubricating holes, additional running‐in phenomena are attributed to a relatively thick transfer film that is brittle and easily peels off. A continuous thick molten film or island‐like deposition occurs on the polyamide surface. Solid lubricants are able to stabilize friction and lower wear down to the formation of a thin and coherent transfer film. However, increasing the amount of lubricants induces lower mechanical properties and higher deformation of the test samples. The differences in transfer behaviour are discussed with reference to optical microscopy and calculations of bulk and flash temperatures. Copyright © 2006 John Wiley & Sons, Ltd.     

Effect of rubber on tribological behaviors of polyamide 66 under dry and water lubricated sliding

The friction and wear behaviors of polyamide 66 (PA 66) and rubber-filled PA 66 (PA 66/SEBS-g-MA) composites were investigated on a block-on-wheel model friction and wear tester under dry sliding and water lubricating conditions. In order to further understand the wear mechanisms, the worn surfaces and scraps of samples were analyzed by scanning electron microscopy (SEM) and differential scanning calorimeter (DSC). The experimental results indicated that the wear mass loss and the friction coefficient of PA 66 decreased with the addition of rubber particles. The friction coefficients of PA 66 and PA 66/SEBS-g-MA composites under water lubricating condition are lower than those under dry sliding condition, but the wear mass losses are higher than those under dry sliding condition. The main wear mechanisms under dry sliding condition are the plastic deformation and mechanical microploughing. Whereas the main wear mechanisms under water lubricating condition are the mechanical microploughing and abrasive wear.     

The repeatability of friction and wear results obtained from unlubricated reciprocating sliding tests

Laboratory tests can help in the analysis of tribological failures of elements, and improve tribo‐systems by choosing appropriate materials. In order to characterise the friction and wear behaviour of candidate materials, various different test methods have been developed in the past and are still in use. One such method is the reciprocating sliding of a ball against a disc. In the work reported here, the repeatability of friction and wear results was evaluated with ten tests under identical conditions with a steel (100Cr6) or alumina (Al₂O₃) ball against a steel (100Cr6) disc under unlubricated conditions at room temperature. The influence of ambient humidity on friction and wear behaviour was determined in three additional tests in dry and in moist air, respectively. The repeatability of friction coefficient in normal air was better than 5% for alumina/100Cr6 and 12% for 100Cr6/100Cr6, while the repeatability of volumetric wear was slightly better than 10% for alumina/steel, and slightly worse than 10% for steel/steel. For both couples the coefficient of friction is lowest in moist air and about 50% higher in dry air. The coefficient of wear is also least in moist air and higher by a factor of 3(5) in dry air for tests with a 100Cr6 (alumina) ball.     

润滑油添加剂对聚合物及其复合材料摩擦磨损性能的影响

利用MHK-500型环-块磨损试验机研究了二烷基二硫代磷酸锌(ZDDP)对几种聚合物及其复合材料-金属摩擦副油润滑摩擦磨损性能的影响。结果表明,液体石蜡中的ZDDP对尼龙66(PA66)及聚酰亚胺(PI)-GCr15轴承钢摩擦副的摩擦系数影响不大,但却使聚四氟乙烯(PTEE)及其复合材料-GCr15轴承钢摩擦副的摩擦系数略有降低。PTEE及其复合材料-GCr15轴承钢摩擦副表面的ZDDP吸附膜具有一定的抗磨作用,它大幅度降低了Pb、PbO及MoS     

Tribological characterization of thin hard coatings by reciprocating sliding tests

Thin hard coatings on metal or ceramic surfaces offer a large spectrum of improvements of the friction and/or wear behaviour of tribosystems. The development of coatings and the tailoring of their properties require test methods providing information about their friction and wear behaviour. A new wear test standard (ASTM) is under development for the evaluation of friction and wear quantities for sliding motions using the reciprocating sliding mode. The applicability of this test method to coated specimens was checked by testing uncoated and coated steel specimens in contact with alumina balls, whereby lower loads were used than in the ASTM proposal for bulk materials. Additionally, the influence of the relative humidity of the surrounding air at room temperature on friction and wear results was examined.     

Tribological properties of short glass fiber reinforced polyamide 12 sliding on medium carbon steel

The friction and wear of short glass fiber reinforced polyamide 12 (PA12) were investigated. The behavior of the fibers on a sliding surface and their effect on the friction and wear were studied in terms of the amount and orientation of the fibers in the composite. Results showed that the friction level and wear resistance were strongly affected by the fiber content, and glass fiber patches produced on the sliding surface played important roles in the wear resistance of the composite. The optimum fiber content for the best wear resistance of the PA12 composite was approximately 30 wt.% and higher fiber contents had no added effect on the wear amount. The applied load also strongly affected the wear resistance due to the increase in temperature at the sliding interface, and an increase in rapid wear was observed when the interface temperature increased above the glass transition temperature of PA12. On the other hand, the fiber orientation had less effect on the friction and wear of the composite compared to the fiber content and applied load. Based on the behavior of glass fibers on the sliding surface and wear debris analysis, the wear mechanism of the PA12 composite is discussed.     

Combination of DLC coatings and EP additives for improved tribological behaviour of boundary lubricated surfaces

The aim of the present investigation was to obtain some further understanding of the mechanism responsible for low-friction behaviour of W-containing DLC coatings (W-DLC) when lubricated with EP additivated oil. Boundary lubricated wear and friction tests were performed under reciprocating sliding motion using a high frequency test rig and a contact pressure of 1.5 GPa. Additionally, some of the tests were performed in a load-scanning reciprocating test rig, with the contact pressure being in the range from 2.4 to 5.6 GPa. The influence of concentration of a sulphur-based EP additive on the friction behaviour was investigated.This investigation showed that W-DLC coatings greatly improve the tribological properties of boundary-lubricated surfaces, especially when pairing coated and uncoated steel surfaces. The improved tribological behaviour was found to be governed by the gradual formation of a WS₂ type tribofilm on the steel counter-face or on revealed steel substrate. The friction level depends on the additive concentration.     

Reducing the effect of three-body abrasive wear by adding polymeric powder to lubricating grease

The present paper reports on work aimed at improving the abrasive wear resistance of surfaces lubricated with contaminated greases. The intended improvement can be achieved by reducing the effect of wear occurring between the abrasive particles and the rubbing surfaces. Different polymeric thickeners in powder form, such as high-density polyethylene (HDPE), low-density polyethylene (LDPE), polyvinylchloride (PVC), polyamide (PA6) and polymethylmethacrylate (PMMA), were added to lithiumbased grease. The wear resistance and the coefficient of friction of cylindrical steel specimens were examined using a cross-pin test machine. The test machine provides concentrated contact under mixed lubrication conditions. Wear was measured on the stationary test specimen by the wear scar diameter, using an optical microscope, with an accuracy of ±1 μm. The frictional torque generated between the rubbing surfaces was measured using a full bridge strain gauge measuring cell attached to the stationary test specimen holder. The experiments were performed using clean and contaminated lubricating greases to which Air Cleaner Fine Test Dust (SCFTD) was added to the greases at a concentration of 10 wt.%. The results show that the effect of the abrasive contaminants can be reduced by the addition of polymeric powders. However, the addition of polymer to lubricating grease at relatively high concentration (more than 35 wt.%) has no effect on the antiwear action of the lithium grease. Further, the addition of polymeric powder with a particle size relatively greater than that of the contaminant can be considered as a useful method of eliminating the cutting process of the three-body abrasive mechanism introduced by the presence of the hard contaminant particles.     

Wear resistance and anti-sticking properties of duplex treated forming tool steel

The aim of this work was to investigate the potential of using hard physical vapour deposition (PVD) coatings on forming tools, as well as to determine the influence of plasma nitriding on the load-carrying capacity and wear resistance of coated tool surfaces. A load-scanning test rig was used for evaluation, where duplex treated cold work tool steel samples were loaded against soft austenitic stainless steel and hardened ball bearing steel, respectively. Four different coatings (TiN, TiB₂, TaC and DLC) and two substrate treatments (hardening and plasma nitriding in two different gas mixtures) were included.Plasma nitriding alone significantly improved the friction, wear, and anti-sticking properties of the tool steel. PVD coating, and especially PVD coating of nitrided tool steel further improved the performance. Therefore, from the point of view of tool life as well as work peace surface quality, the DLC coating with its excellent anti-sticking properties and sufficiently good wear resistance represent the best solution for forming tool applications of austenitic stainless steel.     

Friction and wear measurements of laser-sintered and coated parts

The aim of this research is the investigation of surface properties, the measurements of friction coefficient and wear rate of laser-sintered and coated parts. The industrial background of this research is to prove applicability of laser-sintered prototype tools for injection moulding of fibre-reinforced polymers, furthermore to increase the wear resistance of unalloyed steel tools by laser coatings. The materials of the test specimens were laser-sintered phosphorous bronze and unalloyed steel. For increase of wear resistance we used hard Co-based and glassy-like Fe-based (FeB) coatings. As counter bodies we used polymers reinforced with short carbon and glass fibres. The laboratory model tests of selective laser-sintered parts were carried out on a pin-on-disk machine. In case of coated parts—with higher wear resistance—we used a cylinder-on-cylinder tribometer. The tribological properties were determined at different load and temperature conditions. The results of the investigation show that the friction coefficient and wear resistance of laser treated surfaces are good. The coefficient of friction of coated specimens is slightly less, but the wear rate is significantly less.     

Tribological Properties of DLC Coatings in Helium

The aim of this research work was to investigate tribological properties of low-friction DLC coatings when operating in helium atmosphere. Two commercial DLC coatings (a-C:H and Me-C:H) were included in the investigation and compared to reference PTFE-based coatings, normally used on components operating in helium. Coatings were deposited on hardened 100Cr6 bearing steel discs and tested against uncoated steel balls in low-load pin-on-disc contact configuration. Investigation was focused on the effect of substrate roughness (R _a ?=?0.05?C0.2???m) and contact conditions, including contact pressure (150?C350?MPa) and sliding speed (0.2?C0.4?m/s) on the coefficient of friction of DLC coatings operating in helium. Results of this investigation show that for low-load sliding contact DLC coatings provide low friction in helium atmosphere, similar to soft PTFE-based coatings. At the same time DLC coatings investigated were found to substantially reduce wear of the coated surface. However, while the wear of the coated part has been more or less eliminated, application of DLC coating prolongs running-in and increases wear of the steel counter-part. Furthermore, also in helium atmosphere tribolgical behaviour of DLC coatings showed dependence on the coating type and contact conditions.     

Friction of Undulated Surfaces Coated with MoS2 by Pulsed Laser Deposition

Solid lubricants such as molybdenum disulfide can provide very low friction, but their effectiveness especially in the geometrically constrained sliding pairs is limited by plowing of coated surfaces by wear particles. Even in the presence of solid lubricants wear particles cause higher friction by plowing the interface. To minimize plowing, undulated surfaces with microgrooves perpendicular to the sliding direction can be used to trap wear particles. Smooth and undulated stainless steel surfaces were coated with molybdenum disulfide by pulsed laser deposition (PLD) and friction tested. Under identical test conditions, the friction coefficient of coated undulated surfaces is between 20–40 percent lower than that of coated smooth surfaces. The friction coefficient of undulated uncoated surfaces is about 100–350 percent less than that of smooth uncoated surfaces. Moreover, the entrapment of wear particles at the interfaces of geometrically constrained bearings may lead to seizure even when bearing surfaces are coated with solid lubricants. The use of undulated surf aces on these sliding systems has shown improved operating time and a reduced maintenance cycle.