On dry sliding friction and wear behaviour of PEEK and PEEK/SiC-composite coatings

In this work, polyetheretherketone (PEEK) and PEEK/SiC-composite coatings were deposited on Al substrates using a printing technique to improve their surfaces performance. The objective of this work was to investigate coatings friction and wear behaviour. Especially, the effect of sliding velocity and applied load on coatings friction coefficient and wear rate was evaluated in range of 0.2-1.4 m/s and 1-9 N, respectively. Compared to Al substrate, the coated samples exhibit excellent friction coefficient and wear rate. For PEEK coating, under an applied load of 1 N, the increase in sliding velocity can result in decreasing of friction coefficient at a cost of wear resistance. Under a load of 9 N, however, PEEK coating exhibits the highest friction coefficient and wear rate at an intermediate velocity. These influences appear to be mainly ascribed to the influence of contact temperature of the two relative sliding parts. In most test conditions, the composite coating exhibits better wear resistance and a little higher friction coefficient. SiC reinforcement in composite coating plays a combined role. First of all, it might lead to energy dissipation for activation of fracture occurred on the interface of PEEK and the powders. Moreover, it can reduce coating ploughs and the adhesion between the two relative sliding parts.     

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

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

On sliding friction and wear of polyetheretherketone (PEEK) composites at elevated temperatures

The friction and wear behaviour of polyetheretherketone (PEEK) composites, incorporating different amounts of short carbon fibres with different surface treatments, was studied under dry sliding conditions against smooth steel on a pin-on-disc apparatus at different temperatures. Wear of the composites was reduced considerably in all cases, but, whatever the surface treatment, wear increased with increasing temperature for all proportions off fibres. For minimum friction coefficient there was an optimum proportion of fibre volume fraction of about 10 vol.%. The effect of the fibre surface treatment was not significant for the tribological behaviour of the PEEK composites. To predict wear performance, a wear model proposed by Friedrich and Voss seemed to work properly, and, furthermore, a friction model was developed to predict the friction behaviour of PEEK composites with short carbon fibres.     

Influence of the countermaterial on the dry sliding friction and wear behaviour of low temperature carburized AISI316L steel

Low temperature carburising (LTC) allows a significant hardness increase, with a consequent increase in wear resistance, without deteriorating corrosion behaviour. However, wear resistance strongly depends on contact conditions, therefore this work focuses on the dry sliding behaviour of LTC-treated AISI316L austenitic stainless steel against several countermaterials (AISI316L, LTC-treated AISI316L, hard chromium or plasma-sprayed Al₂O₃–TiO₂). LTC produced a hardened surface layer (C-supersaturated expanded austenite), which improved corrosion resistance in NaCl 3.5% and increased wear resistance, to an extent which depends on both normal load and countermaterial. The best results were obtained when at least one of the contacting bodies was LTC-treated, because this condition led to mild tribo-oxidative wear. However, LTC did not improve the behaviour in terms of friction.     

Effect of temperature on friction and wear of prehardened tool steel during sliding against 22MnB5 steel

Abstract

Mechanical components in tribological systems exposed to elevated temperatures are gaining increased attention since more and more systems are designed to operate under extreme conditions. In hot metal forming, the effect of temperature on friction and wear is especially important since it is directly related to process economy (tool wear) and quality of the produced parts (friction between tool and workpiece). This study is therefore focused on fundamental understanding pertaining to the tribological characteristics of prehardened hot work tool steel during sliding against 22MnB5 boron steel. The tribological tests were carried out using a high temperature reciprocating sliding friction and wear tester under a normal load of 31 N (corresponding to a contact pressure of 10 MPa), a sliding speed of 0·2 m s^?1 and temperatures ranging from 40°C to 800°C. It was found that friction coefficient and specific wear rate decreased at elevated temperature because of formation of compacted wear debris layers on the surfaces.     

High-temperature friction and wear behaviour of different tool steels during sliding against Al–Si-coated high-strength steel

The recent years have witnessed an increasing usage of high-strength steels as structural reinforcements and in energy-absorbing systems in automobile applications due to their favourable high-strength-to-weight ratios. Owing to poor formability, complex-shaped high-strength steel components are invariably produced through hot-metal forming. The high-strength steel sheets are in some instances used with an Al–Si-coating with a view to prevent scaling of components during hot-metal forming. However, friction and wear characteristics of Al–Si-coated high-strength steel during interaction with different tool steels have not yet been investigated. With this in view, friction and wear behaviours of different tool steels sliding against Al–Si-coated high-strength steel at elevated temperatures have been investigated by using a high-temperature version of the Optimol SRV reciprocating friction and wear tester at temperatures of 40, 400 and 800 °C. In these studies both temperature ramp tests with continuously increasing temperature from 40 to 800 °C and constant temperature tests at 40, 400 and 800 °C, have been conducted. The results have shown that both the friction and wear of tool steel/Al–Si-coated high-strength steel pairs are temperature dependent. Friction decreased with increasing temperature whereas wear of the tool steel increased with temperature. On the other hand, the Al–Si-coated high-strength steel showed significantly lower wear rates at 800 °C as compared to those at 40 and 400 °C. The Al–Si-coated surface undergoes some interesting morphological changes when exposed to elevated temperatures and these changes may affect the friction and wear characteristics. The mechanisms of these changes and their influence on the tribological process are unclear and further studies are necessary to fully explain these mechanisms.     

Friction and dry sliding wear behaviour of cermets

The friction and wear behaviour of cermets/steel rubbing pairs were investigated. Friction and wear tests were carried out using three different crèmets on the base of tungsten, titanium and chromium carbides under dry sliding conditions against steel disk (0.45% C). Sliding wear tests were carried out using modified block-on-ring equipment at a sliding speed of 2.2 m/s and normal load 40 N.It is shown that wear resistance and coefficient of friction depend on the type and chemical composition of the cermets. The WC–Co cermets have the highest wear resistance. The wear rate of WC–Co and TiC–NiMo cermets increased with increasing binder content in the cermets. The wear of Cr₃C₂–Ni cermets is more complicated and depends on the composition of cermets. The wear of WC–Co cermets is caused mainly by preferential removal of the cobalt binder, followed by fracture of the intergranular boundaries and fragmentation of the carbide grains. The main wear mechanism in the TiC–NiMo cermets is polishing (micro-abrasion) and adhesion, resulting in a low wear rate. The main wear mechanism of Cr₃C₂–Ni cermets involves thermal cracking and fatigue-related crushing of large carbide grains and carbide framework and also adhesion.     

Effect of cryogenic treatment on the tribological behaviour of H11 hot die steel dry sliding against D3 steel

The tribological behaviour, hardness and microstructural characteristics of vacuum and cryogenically treated AISI H11 steel at varied soaking temperature (?154 and ?184 °C) for specific time period (6, 21 and 36 h) have been examined in this research work. The influence of selected parameters on the tribological behaviour have been studied at five levels of varying sliding velocities (0.628–1.885 m/s) and normal loads (60–140 N) through block–on–ring dry sliding wear test against hardened and tempered AISI D3 tool steel (counter face). The experiments are designed based on full factorial response surface methodology. The responses (wear rate, average coefficient of friction and maximum contact temperature) are analyzed based on plotted graphs. The results reveal that 21 h at ?184 °C for H11steel is the optimal soak time to have the lowest wear rate. The sliding speed influences the wear rate more in comparison to load. Wear debris have shape of metallic plate. Carbide particles appeared to delaminate from the sample surface due to subsurface cracks and plastic deformation. The augmentation of apparent and bulk hardness number and wear resistance ascribed to the increase in number of fine globular secondary carbide and improved morphology of matrix microstructure of cryogenic-treated sample. It is also observed that cryogenic treatment reduces the retained austenite content to near zero.     

Friction and dry sliding wear behavior of carbon and glass fabric reinforced vinyl ester composites

Friction and dry sliding wear behavior of glass and carbon fabric reinforced vinyl ester composites have been presented. The results show that the coefficient of friction and wear rate increased with increase in load/sliding velocity and depends on type of fabric reinforcement and temperature at the interphase. The excellent tribological characteristics were obtained with carbon fiber in vinyl ester. It is believed that a thin film formed on counterface was seems to be effective in improving the tribological characteristics. The worn surfaces examined through SEM, showed higher levels of broken glass fiber in vinyl ester compared to carbon-vinyl ester composites.     

The effect of fibre reinforcement on the friction and wear of polyamide 66 under dry rolling–sliding contact

An investigation into the effect of fibre reinforcement on the friction and wear of PA66 in rolling–sliding contact is reported. Three types of short fibre—aramid, carbon and glass—were examined with the composites running against identical materials in a twin disc machine. It was found that the aramid-fibre reinforcement did not significantly alter the friction of the matrix material. However, both the carbon-fibre and glass-fibre reinforcement reduced the coefficient of friction substantially. Wear of the aramid- and carbon-fibre composites was essentially linear with time and generally around ten times greater than that of the unreinforced material. The wear of the glass-fibre composite was complex with an initial period where the wear rate was similar to that of the unreinforced material. After a significant depth of wear had occurred the wear rate changed to a value similar to, but slightly higher than, that of the other reinforced materials.It appears that one of the major benefits of introducing fibre reinforcement, particularly glass, is that it reduces the coefficient of friction and hence allows the material to be used for higher duties without exceeding the softening point of the matrix. This increase in duty is, however, at the expense of an increased wear rate and shorter component life.     

Investigations on the influence of graphite filler on dry sliding wear and abrasive wear behaviour of carbon fabric reinforced epoxy composites

In this experimental study, the dry sliding wear and two-body abrasive wear behaviour of graphite filled carbon fabric reinforced epoxy composites were investigated. Carbon fabric reinforced epoxy composite was used as a reference material. Sliding wear experiments were conducted using a pin-on-disc wear tester under dry contact condition. Mass loss was determined as a function of sliding velocity for loads of 25, 50, 75, and 100 N at a constant sliding distance of 6000 m. Two-body abrasive wear experiments were performed under multi-pass condition using silicon carbide (SiC) of 150 and 320 grit abrasive papers. The effects of abrading distance and different loads have been studied. Abrasive wear volume and specific wear rate as a function of applied normal load and abrading distance were also determined.The results show that in dry sliding wear situations, for increased load and sliding velocity, higher wear loss was recorded. The excellent wear characteristics were obtained with carbon-epoxy containing graphite as filler. Especially, 10 wt.% of graphite in carbon-epoxy gave a low wear rate. A graphite surface film formed on the counterface was confirmed to be effective in improving the wear characteristics of graphite filled carbon-epoxy composites. In case of two-body abrasive wear, the wear volume increases with increasing load/abrading distance. Experimental results showed the type of counterface (hardened steel disc and SiC paper) material greatly influences the wear behaviour of the composites. Wear mechanisms of the composites were investigated using scanning electron microscopy. Wear of carbon-epoxy composite was found to be mainly due to a microcracking and fiber fracture mechanisms. It was found that the microcracking mechanism had been caused by progressive surface damage. Further, it was also noticed that carbon-epoxy composite wear is reduced to a greater extent by addition of the graphite filler, in which wear was dominated by microplowing/microcutting mechanisms instead of microcracking.     

Effect of grain refinement and modification on the dry sliding wear behaviour of eutectic Al-Si alloys

The present study deals with an investigation of dry sliding wear behaviour of grain refined and or modified eutectic (Al-12Si) Al-Si alloy by using a Pin-On-Disc machine. The indigenously developed Al-1Ti-3B and Al-10Sr master alloys were used as grain refiner and modifier for the grain refinement of α-Al dendrites and modification of eutectic Si, respectively. Various parameters have been studied such as alloy composition, sliding speed, sliding distance and normal pressure. The cast alloys, master alloys and worn surfaces were characterized by SEM/EDX microanalysis. Results suggest that, the wear resistance of eutectic Al-Si alloys increases with the addition of grain refiner (Al-1Ti-3B) and or modifier (Al-10Sr). Further, the worn surface studies show that adhesive wear was observed in Al-12Si alloy in the absence of grain refiner and modifier. However, an abrasive and oxidative wear was observed when the grain refiner and modifier are added to the same alloy. Commercially available LM-6 (12.5%Si) alloy was used for comparison.     

Friction and wear of carbon steel near T1-transition under dry sliding

The wear phenomenon of metals under dry sliding is, generally, divided into two modes of severe and mild wear. A discontinuous transition between the wear modes often takes place in a certain load range. The T₁-transition is usually observed at lower levels of load or sliding velocity. There is a great difference in wear rate between severe and mild wear. This indicates that the occurrence of severe wear should be avoided, especially in the field of machine design to prevent energy loss, occurrence of noise and vibration, and life reduction of machines and their components. Therefore, it is important for machine designers to know the relationship between friction and wear and the difference in properties of the wear surfaces in the two wear modes. In this study, wear tests of 0.35% C steel in contact with itself under constant load were conducted in moist air at various contact loads under dry sliding. The friction and wear were measured continuously throughout each test. After the tests, the relationship between friction and wear and the difference in properties of the wear surfaces were investigated in each wear mode. From the results, the upper and lower critical loads (P_acr and P_Acr) appeared between severe and mild wear. The phenomenon of zero wear has been newly found in the early period at very low loads. The zero wear continued for a long sliding distance and then changes to mild wear. The critical load between zero wear and mild wear is defined as P_zerowear. The load was changed once in a step-wise manner from low to high levels in process of test. Since the rubbing history under mild wear condition at the low load in the first stage affected the properties of wear surface, the wear mode at the high load in the second stage changed from ‘mild wear’ to ‘quasi-mild wear’ having a low rate. From the relationship between sliding distance necessary for the appearance of quasi-mild wear and contact load in the first stage, the boundary curve between severe wear and quasi-mild wear in the second stage is hyperbolic. This curve gradually approaches P_zerowear with decreasing contact load. Thus, P_zerowear is one of the important critical loads for elucidating the test results under varying load.     

Friction and wear behaviour of stainless steel rubbing against copper-impregnated metallized carbon

A series of experimental tests were carried out using stainless steel rubbing against copper-impregnated metallized carbon under electrical current on a pin-on-disc test rig. The test parameters include the sliding speed of 60-100 km/h, normal force of 40-80 N and electrical current of 0-50 A. During testing, the friction coefficient and wear volume were recorded. The topography of worn surfaces was also observed with SEM. The cross sectional profiles of worn surfaces of stainless steel were measured with Ambios profiler. The result displays that electrical current, normal load and sliding speed have a distinct effect on the friction and wear behaviour of stainless steel rubbing against copper-impregnated metallized carbon. Without electric current, the friction coefficient is largest but the wear volume of copper-impregnated metallized carbon is lowest. With increasing electric current, the friction coefficient decreases while the wear volume of copper-impregnated metallized carbon increases. Through the whole test, it is found that the wear loss of stainless steel was light. The wear of copper-impregnated metallized carbon becomes severe when electrical current or sliding speed is high. When the electrical current or sliding speed is high, arc ablation is a dominant wear mechanism of copper-impregnated metallized carbon.     

Effect of pH on wear and friction of silicon nitride sliding against alumina in water

The influence of the pH in water lubricated sliding contacts was evaluated in terms of friction and wear. The experiments were carried out using a ball-on-disc setup. Si₃N₄ balls and Al₂O₃ discs were tested at temperature of (22±2) °C, sliding speed of (1.00±0.03) m/s and normal load of (54.25±0.17) N. Eight types of water with pHs varying from 3 to 12 were used as lubricant. The running-in period, friction coefficient and wear-volume were shown to be nearly independent of the initial pH values within the DLVO range (4≤pH≤10), since at these range the water׳s pH tends to the same value (7.6±0.3) during the test. Superlubricity could be reached with negligible wear by properly setting the electrochemical properties and operating conditions of the tribosystem.     

Tribological behaviour of colloidally processed sialon ceramics sliding against steel under dry conditions

Advanced structural ceramics are presently used in several tribological applications such as precision instrument bearings, water pumps, automotive engine parts and cutting tools inserts. In the present work, the tribological behaviours of colloidally processed and pressureless sintered sialon ceramics with different phases ( and ) have been studied, aiming at increasing the industrial applications of sialon ceramics. The friction and wear behaviour of sialon ceramics against steel DIN-Ck45K were investigated using a pin-on-disk tribometer under dry conditions. Scanning electron microscopy (SEM), and energy dispersion spectroscopy (EDS) were used to analyse the worn surfaces of the sialon ceramics. Under the conditions used, sialon ceramics exhibited a typical mild wear (10^-6 mm³ N^-1 m^-1) and the dominant wear mechanisms present were adhesive and abrasion. The results confirmed that colloidal processing and pressureless sintering are effective methods to prepare wear resistant sialon ceramic components.     

Unlubricated sliding and rolling wear of thermoplastic dynamic vulcanizates (Santoprene) against steel

The friction, sliding and rolling wear characteristics of thermoplastic dynamic vulcanizates (TPV; Santoprene^® grades), composed of polypropylene (PP), ethylene/propylene/diene rubber (EPDM) and extender oil, were studied against steel counterparts in dry condition. The composition and basic mechanical properties of the TPV of various hardness (Shore A = 60°, 70° and 80°) were evaluated. The wear performance of the TPVs was investigated in different tribotests, viz. pin-on-plate (POP), cylinder-on-plate (fretting) and rolling ball-on-plate (RBOP), whereby “plate” was always the rubber. From the above tests the coefficient of friction (COF) and specific wear rate were determined. It was established that with increasing hardness usually both COF and the specific wear rate were reduced. Values of the COF and wear rate depended strongly on the configuration and testing parameters of the related tribotests. The wear mechanisms were concluded by inspecting the worn surfaces by white light profilometry and scanning electron microscopy (SEM), respectively, and discussed.     

Effect of the microstructure of thermally sprayed coatings on friction and wear response under lubricated and dry sliding conditions

Five thermally sprayed coatings, considered for application in earth moving vehicle undercarriage components, undergoing consecutively lubricated and dry sliding wear, were prepared and investigated. Four different wear tests were employed to reveal the factors controlling the wear response under different contact conditions. An approach considering the local and overall strength of the coating in connection with the knowledge of contact stresses helped to understand the major wear modes under specific contact conditions for the materials tested. The testing illustrated that in situations with lower contact stresses the contact response of the coating may not be directly related to the intersplat binding strength and hardness, but rather to the local splat properties. It has been shown that a porous structure although limiting the wear resistance of nickel aluminum coating in dry under high contact stress may be beneficial in quasi-lubricated sliding. High local splat hardness measured for the molybdenum carbide coatings appeared to be crucial for its enhanced wear resistance. The testing configuration ‘rotating ring on flat’ newly employed in this study has been proven to be a highly reproducible and efficient way of wear testing for thermal spray coatings.     

The friction and sliding wear of unlubricated 316 stainless steel at room temperature in air

The friction and reciprocating wear of unlubricated type 316 austenitic stainless steel on itself was investigated in air at room temperature in the load range 8–50 N. The wear kinetics were followed by intermittently collecting and weighing the wear debris. A model of the wear process was developed in terms of the interaction of asperities to form adhesive transfer platelets which agglomerate to layered prows. It is postulated that wear debris is subsequently produced by prow breakdown. This occurs by two main modes: at low loads to fine particles and at high loads prows are flattened to thin flakes which fracture at the prow-matrix interface, possibly by a fatigue mechanism. There is evidence to suggest that the rate-limiting step is located at a stage prior to prow formation.     

Effect of sliding speed on friction and wear behaviour of nanocrystalline nickel tested in an argon atmosphere

The sliding speed dependence of the coefficient of friction (COF) and wear rate (W) of a nanocrystalline (nc) Ni with a grain size of 15 ± 3 nm and a hardness of 5.09 ± 0.11 GPa was compared to that of a microcrystalline (mc) Ni with a grain size of 20 ± 5 μm and a hardness of 1.20 ± 0.05 GPa. The sliding wear tests were performed in an argon environment under a constant normal load of 2 N using three different sliding speeds of 0.2 × 10⁻², 0.8 × 10⁻² and 3.0 × 10⁻² m/s. The lesser wear damage in the nc Ni at any given speed was attributed to its higher hardness and its greater elastic depth recovery ratio compared to the mc Ni. The mc Ni's COFs and wear rates were independent of the sliding speed over the relatively small range used. However, the same small increase in sliding speed caused an 86% reduction in the nc Ni's wear rate, from 3.44 × 10⁻³ to 0.47 × 10⁻³ mm³/m, and a 31% increase in its COF, from 0.49 ± 0.05 to 0.64 ± 0.06. A modified Archard equation was proposed to predict wear rates of Ni as a function of grain size and sliding speed. Increasing the sliding speed made it increasingly difficult for surface damage by plastic deformation to occur in the nc Ni, because the grain-boundary-induced deformation mechanisms are more difficult to operate at higher strain rates. At the highest speed, the smallest amount of debris was generated, which was not sufficient to form protective tribolayers leading to a high COF value.