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.     

Antifriction and Wear Characteristics of Electrolessly-Deposited Ni–P with PTFE Composites

This aim of this study was to investigate the tribological properties of a self-lubricating Ni–P–polyfluorotetraethylene (PTFE) composite coating prepared by the electroless plating method. The effects of PTFE contents in the coating, load and rotation speed on the tribological behaviors were evaluated using a ring-on-disk wear machine. The results show that there was a distinct decrease in the average value of the friction coefficient from 0.33 to 0.12 at 70 N with an increase in PTFE content from 4.2 to 15.2 wt%. The coating of Ni–P–4.2 wt% PTFE had good antifriction and wear properties at a load of 30–70 N, and that of Ni–P–10.6 wt% PTFE had passable wear resistance and better antifriction at <50 N. Antifriction and wear mechanisms of Ni–P–PTFE are discussed in detail based on the results from micrograph and element analyses of the worn surface, subsurface stratum and wear debris analysis by scanning electronic microscopy (SEM), and energy-dispersive X-ray analysis (EDAX), respectively. The lubricating film (LF) generated during wear played a key role in the antifriction effect, which in turn was dependent on the integrity and thickness of the film determined by the PTFE concentration and wear conditions. The formation, fracture, and delamination course of the LF during wear were also analyzed and characterized.     

Coupled Effect of Filler Content and Countersurface Roughness on PTFE Nanocomposite Wear Resistance

In tests of PTFE with 2.9% volume content alpha-phase alumina nanoparticles (40 or 80 nm) in sliding reciprocation against polished steel, wear rates of ~10⁻⁷ mm³/Nm were measured which is four orders-of-magnitude lower than unfilled PTFE and two orders-of-magnitude lower than with microparticles (0.5 or 20 μm) of more conventional filler size. This was similar to that previously reported in unidirectional sliding, and did not vary greatly with stroke of reciprocation. For a microfilled PTFE, the wear rate gradually increased towards that of unfilled PTFE as filler content was reduced, whereas nanofilled PTFE maintained relatively constant ~10⁻⁷ mm³/Nm to filler contents as low as 0.18% before reverting towards the rapid wear rate of unfilled PTFE. Lightly filled nanocomposites depend upon low countersurface roughness to maintain such low wear rate, and with increasing roughness the wear rate was found to transition at a critical value to a wear rate of ~10⁻⁵ mm³/Nm. Nanocomposites with higher filler contents were able to retain the low wear rates against rougher countersurfaces, as the critical roughness at which this wear resistance was lost tended to increase with the square of the filler content. Upon encountering extremely high countersurface roughness in the range R _a = 6–8 μm, nanocomposites at each filler content eventually increased in wear rate to ~10⁻⁴ mm³/Nm. The steel countersurface did not appear to play an important role in the extreme wear resistance of these alumina nanofilled PTFE composites, as comparable performance was also displayed against alumina countersurfaces.     

Tribological Behavior of PTFE Composites Filled with PEEK and Nano-Al2O3

In this study, the tribological properties of polytetrafluoroethylene (PTFE) composites filled with polyetheretherketone (PEEK) and nano-Al₂O₃ particles were studied using a block-on-ring wear tester. The tribological performance of the composites was affected by the experimental parameters (sliding speed, normal load, and environmental temperature) and the composites achieved a high-speed sliding friction state. The results showed that the PEEK and nano-Al₂O₃ particles significantly improved the wear resistance of the PTFE composites. In addition, the nano-Al₂O₃ particles increased the hardness of the composites and enhanced the mechanical properties to enable applications in a wider range of industrial fields. The effects of the sliding speed and normal load on the tribological properties were more significant than that of the environmental temperature. In addition, the entire wear process was divided into three stages (the initial wear stage, severe wear transition stage, and ultralow stable wear stage), according to the evolution of the tribological characteristics (wear rate, morphology of the worn surface and transfer film, and wear debris morphology).     

High Temperature Tribological Characteristics of Fe–Mo-based Self-Lubricating Composites

Fe–Mo-based self-lubricating composites were prepared by a powder metallurgical hot-pressing method. The tribological properties of Fe–Mo-based composites with varied CaF₂ contents at high temperature were evaluated, and the effect of glaze films on the friction and wear characteristics of composites were analyzed. The results show that the introduction of CaF₂ into Fe–Mo alloys improved the mechanical properties, and the best tribological properties of Fe–Mo–CaF₂ composites were achieved at the CaF₂ content of 8 wt% at both room temperature and 600 °C. The worn surface of Fe–Mo–CaF₂ composite at 600 °C is characterized to plastic deformation and slight scuffing, and the improved tribological properties are attributed to the formation of lubricious glaze film that composed of high-temperature lubricants CaMoO₄ and CaF₂ on the worn surface of the composites.     

Sliding Wear of Electrically Conductive ZrO<Subscript>2</Subscript>−WC Composites Against WC–Co Cemented Carbide

ZrO₂-based composites with WC addition can be successfully machined by electrical discharge machining (EDM) in demineralised water. ZrO₂ composites with 40 vol.% WC were produced from nanocrystalline and micrometre sized WC starting powders in order to compare their tribological behaviour. Friction and wear data are obtained on wire-EDM’ed ZrO₂–WC composite flats sliding against a WC–Co cemented carbide pin using a small-scale pin-on-plate testing rig. Correlations between wear volume, wear rate and friction coefficient on the one hand and material properties and test conditions on the other hand were elucidated. The experimental results revealed that the grain size of the electro-conductive WC-phase exhibits a strong influence on the friction and wear behaviour of the ZrO₂-based 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.     

The friction and wear of electroless Ni–P matrix with PTFE and/or SiC particles composite

In this paper, the friction behaviour and wear mechanism of electroless Ni–P matrix with PTFE and/or SiC particles composite coating are investigated by virtue of ring-on-disk wear machine at a high load of 150 N. The worn surface, wear debris and the composition changes after wear were characterized using scanning electron microscopy (SEM) and energy-dispersive analysis of X-ray (EDAX). By comparison with Ni–P and Ni–P–SiC coatings, the results indicated that the combination of a PTFE-rich mechanical mixed layer (PRMML) formed on the worn surface and hard SiC were responsible for the good tribological properties of the hybrid Ni–P–PTFE–SiC composites at high load. After heat treatment at 400 °C for 1 h, the wear rate of Ni–P matrix composites decreased with corresponding increase in microhardness. During sliding, an obvious decrease in the temperature rise with PTFE addition was attributed to the good anti-friction of PTFE.     

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.     

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 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.     

On dry sliding friction and wear behavior of PPESK filled with PTFE and graphite

Novel poly(phthalazinone ether sulfone ketone) (PPESK) resins have become of great interest in applications such as bearing and slider materials. In this paper, dry sliding wear of polytetrafluoroethylene (PTFE) and graphite-filled PPESK composites against polished steel counterparts were investigated on a block-on-ring apparatus at the same sliding velocities and different loads. The results indicated that the addition of 5–25 wt% PTFE and 5–30 wt% graphite contribute to an obvious improvement of tribological performance of PPESK at room temperature. Worn surfaces were investigated using a scanning electron microscope (SEM). As a result, the friction coefficient and wear rate of the PPESK composites decreased gradually with addition of fillers. A moderately low friction coefficient and specific wear rate were reached when the filler contents were above 20 wt%. The mechanical properties of PPESK composites were also investigated. The tensile and impact strength of PPESK composites decrease slightly as the addition of fillers contents were below 15 wt%.     

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

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

Novel polytetrafluoroethylene (PTFE) composites with newly developed Tribaloy alloy additive for sliding bearings

A group of novel polytetrafluoroethylene (PTFE)-based composite materials are developed for sliding bearing applications. The reinforcements include the newly developed T-401 Tribaloy alloy, which possesses better ductility compared to conventional Tribaloy alloys, spherical bronze particles, chopped carbon fibers and milled graphite. The specimens are fabricated with the compression moulding technique under different preforming and sintering cycles. The mechanical and tribological properties as well as corrosion resistance of the new composites are investigated. It is demonstrated that these properties are influenced by the type of fillers and the content level of fillers. The wear resistances of all the developed PTFE composites are much higher than that of pure PTFE with very low coefficients of friction. Among the developed composites, the mixture of 40% PTFE + 15% T-401 + 45% bronze exhibits the best combination of properties.     

Tribological Behavior of Carbon-Nanotube-Filled PTFE Composites

Carbon nanotube/polytetrafluoroethylene (CNT/PTFE) composites with different volume fractions were prepared and their friction and wear properties were investigated using a ring-on-block under dry conditions. It was found that CNTs signifi-cantly increased the wear resistance of PTFE composites and decreased their coefficient of friction. PTFE composites with 15–20 vol.% CNTs exhibited very high wear resistance. The significant improvements in the tribological properties of CNT/PTFE composites are attributed to the super-strong mechanical properties and the very high aspect ratio of CNTs. The CNTs greatly reinforce the structure of the PTFE-based composites and thereby greatly reduce the adhesive and plough wear of CNT/PTFE composites. The CNTs are released from the composite during sliding and transferred to the interface of the friction couples. They thus serve as spacers, preventing direct contact between the mating surfaces and thereby reducing both wear rate and friction coefficient.     

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.     

A study on tribological behaviour of transfer films of PTFE/bronze composites

Transfer films of PTFE/bronze composites with 5–30% volume content of bronze were prepared using a RFT friction and wear tester on surface of AISI-1045 steel bar by different sliding time (5–60 min). Tribological properties of these transfer films were studied using a DFPM reciprocating tribometer in a point contacting configuration under normal loads of 0.5, 1.0, 2.0 and 3.0 N. Thickness and surface morphology of the transfer films were investigated. It was found thickness of the transfer films slightly increased along with the increase of bronze content of corresponding composites. Increased sliding time of transfer film preparation is helpful to form transfer film with better ductibility and continuity, but sliding time almost has no effect on tribological properties of the transfer film. Higher bronze content in the composite improved tribological properties of the corresponding transfer film, i.e., reduced friction coefficient and prolonged wear life. All these transfer films are sensitive to load change. Their wear life becomes shorter along with the increase of load. SEM image of the worn surface show fatigue wear and adhesion wear have happened on the transfer film during the friction process. The author believe bronze in the transfer film effectively partaked in shear force applied on the transfer film and its good ductibility helped to improve tribological properties of the transfer films.     

PTFE基复合材料海水润滑下的摩擦学性能研究

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

Tribological behavior of graphite-containing nickel-based composite as function of temperature,load and counterface

Nickel-based graphite-containing composites were prepared by powder metallurgy method. Their mechanical properties at room temperature and friction and wear properties from room temperature to 600 °C were investigated by a pin-on-disk tribometer with alumina, silicon nitride and nickel-based alloy as counterfaces. The effects of graphite addition amount, temperature, load, sliding speed and counterface materials on the tribological properties were discussed. The micro-structure and worn surface morphologies were analyzed by scanning electron microscope (SEM) attached with energy dispersive spectroscopy (EDS). The results show that the composites are mainly consisted of nickel-based solid solution, free graphite and carbide formed during hot pressing. The friction and wear properties of composites are all improved by adding 6–12 wt.% graphite while the anti-bending and tensile strength as well as hardness decrease after adding graphite. The friction coefficients from room temperature to 600 °C decrease with the increase of load, sliding speed while the wear rates increase with the increasing temperature, sliding speed. The lower friction coefficients and wear rates are obtained when the composite rubs against nickel-based alloy containing molybdenum disulfide. Friction coefficients of graphite-containing composites from room temperature to 600 °C are about 0.4 while wear rates are in the magnitude of 10^?5 mm³/(N m). At high temperature, the graphite is not effective in lubrication due to the oxidation and the shield of ‘glaze’ layer formed by compacting back-transferred wear particles. EDS analysis of worn surface shows that the oxides of nickel and molybdenum play the main role of lubrication instead of graphite at the temperature above 400 °C.     

Microstructural and Tribological Properties of A356 Al–Si Alloy Reinforced with Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Particles

In the present study, the effect of the Al₂O₃ particles (average size of 12 μm, 3 and 10 wt.%) reinforcement on the microstructure and tribological properties of Al–Si alloy (A356) was investigated. Composites were produced by applying compocasting process. Tribological properties of unreinforced alloy and composites were studied, using pin-on-disc tribometer, under dry sliding conditions at different specific loads and sliding speed of 1 m/s. Microhardness measurements, optical microscope and scanning electron microscope were used for microstructural characterization and investigation of worn surfaces and wear debris. During compocasting of A356 alloy, a transformation from a typical dendritic primary α phase to a non-dendritic rosette-like structure occurred. Composites exhibited better wear resistance compared with unreinforced alloy. Presence of 3 wt.% Al₂O₃ particles in the composite material affected the wear resistance only at specific loads up to 1 MPa. The wear rate of composite with 10 wt.% Al₂O₃ particles was nearly two order of the magnitude lower than the wear rate of the matrix alloy. Dominant wear mechanism for all materials was adhesion, with others mechanisms: oxidation, abrasion and delamination as minor ones.