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.     

The machinability and tribological characteristics of aluminum alloys with improved elevated temperature properties using rapidly solidified powder

In this investigation the tribological characteristics of rapidly solidified Al–8Fe–4Ce with improved elevated temperature properties were studied. Such characteristics were compared with cast aluminum–silicon alloy and cast zinc–aluminum alloy. These materials included Al–13Si, Zn–35Al, Zn–35Al–Si, Zn–35Al–3.75Si and Zn–35Al–5.8Si. The wear rates of all materials were tested on a crossed-cylinders wear machine against 440C stainless steel counterface lapped by random abrasion using diamond paste to the desired average surface roughness. The effects of sliding distance on both the worn volume and the coefficient of friction were examined. The aluminum–iron–cerium alloy (Al–8Fe–4Ce) showed the lowest wear rate. The experiments were then extended on this material to examine the effect of varying the applied load and sliding speed on its wear rate. It was found that increasing the applied load increased the wear rate while it was slightly sensitive to the change in sliding speed. As the wear results showed that the Al–8Fe–4Ce alloy has the lowest wear rates, its machinability during turning operation was studied. Statistically-based experimental design (response surface methodology) using central composite second-order rotatable design technique was used to improve the experimentation design without loss of accuracy of the results. The interaction of cutting parameters (cutting speed, feed rate and depth of cut) was examined and their effect on the average surface roughness was reported. It was found that employing a combination of high cutting speed and small depth of cut with small feed rate causes a significant reduction in R_a. The data were represented in three-dimensional and contour graphs for selecting the appropriate machining conditions required to achieve desired values of surface roughness.     

Effect of copper content on the mechanical and sliding wear properties of monotectoid-based zinc-aluminium-copper alloys

One binary zinc-aluminium monotectoid and five ternary zinc-aluminium-copper alloys were produced by permanent mould casting. Their wear properties were examined using a block-on-ring test machine. Hardness, tensile strength and percentage elongation of the alloys were also determined and microhardness of aluminium-rich α phase was measured.It was observed that the hardness of the alloys increased continuously with increasing copper content up to 5%. Their tensile strength also increased with increasing copper content up to 2%, but above this level the strength decreased as the copper content increased further. Microhardness of the aluminium-rich α phase was also affected by the copper content in a manner similar to that of the tensile strength. It was found that the wear loss of the alloys decreased with increasing copper content and reached a minimum at 2% Cu for a sliding distance of 700 km. However, the coefficient of friction and temperature due to frictional heating were found to be generally less for the copper containing alloys than the one without the element. The effect of copper on the wear behaviour of the alloys was explained in terms of their microstructure, hardness, tensile strength, percentage elongation and microhardness of the α phase.     

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.     

Microstructure and tribological behaviour of nitrocarburizing-quenching duplex treated steel

This paper explores salt bath nitrocarburizing and nitrocarburizing-quenching duplex treatment technologies. For comparison, a quenching-tempering treatment was also conducted. By means of metallographic examination, microhardness tests and X-ray diffraction analysis, the microstructures, phase structures, surface hardnesses and hardness profiles of 1045 steel treated by several techniques were investigated. The ball-on-block and ring-on-block apparatuses were employed to investigate the friction coefficient and wear-resistance respectively. The surface roughness was also measured by a profilometer. The experimental results indicate that a higher sub-surface hardness and a superior hardness profile are obtained by nitrocarburizing-quenching duplex process. This in turn improves the wear-resistance and fatigue strength, although the surface hardness is somewhat lower compared with that obtained by nitrocarburizing. It also demonstrates that the -phase formed on the steel surface has significant effects on reducing friction and improving wear-resistance. X-ray diffraction analysis shows that the phases at the nitrocarburized specimen surface are mainly -compound [Fe₃(N,C)] and small amounts of Fe₄N(γ′) and Fe_2–3(N,C). While the phases at the nitrocarburized-quenched specimen surface are very different from those at the nitrocarburized specimen. In this case, the -compound has decomposed almost completely and the nitrogen and carbon diffuse to the γ-Fe at the temperature of quenching to form the supersaturated solid solution which will become martensite containing nitrogen and carbon along with retained austenite after subsequent water cooling.     

The tribological behaviour of electroless Ni-P-Gr-SiC composite

The tribological behaviour and wear mechanism of Ni-P-Gr (graphite)-SiC (manufactured by electroless plating) is surveyed in this paper. The worn surface, wear debris and the compositional changes that take place during wear were characterized using scanning electron microscopy (SEM) and energy-dispersive analysis of X-ray (EDAX). By comparison with Ni-P-Gr and Ni-P-SiC, the results indicate that hybrid Ni-P-Gr-SiC composite presented well anti-friction and wear resistance which is resulted from a graphite-rich mechanical mixed layer (GRMML) formed on the contact surface. Hard SiC particles mixed with GRMML played a load-bearing role at high load when relative motion occurs. After heat treatment at 400 °C for 1 h, the wear rate of the hybrid composite decreased with an increase in microhardness. During sliding, the temperature of the hybrid composite occured less change than Ni-P-SiC coating and further guaranteed the stable state of the whole wear process.     

Effect of crosslinking on tribological behavior of tung oil-based polymers

In this study, the tribological properties of tung oil-based polymers synthesized by the cationic copolymerization of tung oil with divinylbenzene and styrene are evaluated as a function of crosslinking density. Tribological measurements were performed using a ball-on-flat reciprocating microtribometer on samples with three crosslinking densities of 20%, 30% and 40% by weight of the crosslinking agent. Friction and wear characteristics during dry sliding were evaluated using a spherical (1.2 mm radius) silicon nitride probe as well as a conical (100 μm radius, 90° cone angle) diamond probe. Microscale friction behavior was evaluated from single strokes at ramped normal loads, whereas wear experiments were evaluated from 100 to 500 reciprocating cycles at fixed normal loads. Elastic modulus and hardness information were evaluated using nanoindentation tests. Scanning electron microscopy of wear tracks was used to elucidate deformation mechanisms in the various samples. All samples showed friction coefficients ranging from 0.06 to 0.49. It was found that a higher crosslinking density resulted in lower abrasive wear due to increased hardness. These results provide some insight into the friction and wear behavior of tung oil-based polymers.     

Friction and wear behaviour of sintered steels submitted to sliding and abrasion tests

Fe–C–Mo and Fe–C–Cr steels were sintered by PM processes carried out using different values of temperature and pressure, leading to different microstructures and density values. Flat specimens were submitted to tribological tests in order to evaluate their behaviour under both dry sliding and abrasive wear conditions. A flat-on-cylinder tribometer was used for the sliding tests, while a micro-scale ball cratering device was used for the abrasion tests. The dry sliding wear resistance of the PM steels was mainly influenced by the composition and sintering conditions. In this regard, the best behavior was observed for the more hardenable Fe–C–Mo steels with higher Mo content, sintered under conditions giving rise to bainitic microstructures. A determining role was also played by the porosity content and pore shape: reduction in porosity (obtained by increasing the sintering temperature and the compacting pressure), as well as an increase in pore roundness, led to a significant improvement in the resistance to sliding wear. A mild oxidative wear regime were observed for all the sintered steels under relatively low values of the applied load, while an increase of the applied load led to a delamination wear regime. The resistance to abrasive wear was low for all the tested steels, irrespective of composition and sintering cycle.     

Effect of saliva viscosity on tribological behaviour of tooth enamel

Employing a special device simulating conditions of the masticatory process, two series tests were conducted involving studies of the tribological behaviour of enamel subjected to two- and three-body tests at different saliva viscosities.The studies showed no significant influences of saliva viscosity on the mean of the friction coefficient. However, below 2.08 mPa s the coefficient was unstable, i.e. scatter was observed. Both higher wear rate and higher scatter were observed for viscosities below of 1.68 mPa s. Comparing the wear results of the three- and two-body tests, no significant differences were obtained for viscosities above 1.68 mPa s, although for lower viscosities the wear rate in the presence of abrasive particles was higher than that obtained with pure saliva.Two regions with different tribological behaviour of enamel were observed in relation to saliva viscosity; the region with stable and low values of the tribological parameters beyond some threshold value, and the other with higher mean values of tribological parameters and their scattering. The author suggests that different concentrations of proteins are possible at the same low saliva viscosity, thus there are qualitatively different interactions between enamel surface and saliva components resulting in different lubrication regimes.     

Influence of microstructure of HC CoCrMo biomedical alloys on the corrosion and wear behaviour in simulated body fluids

The corrosion and tribological behaviour of an as-cast High Carbon CoCrMo alloy subjected to different thermal treatments in simulated body fluids has been analyzed by electrochemical techniques. After the microstructural characterization of the alloy, the samples were studied electrochemically and tribo-electrochemically. Thermal treatments influence the corrosion behaviour, passive dissolution and tribological response. An increase of grain boundaries accelerates the anodic reaction in all solutions. A higher carbide volume fraction generates a lower wear-rate. Microscopic observation by means of Optical and SEM microscopy showed that presence of proteins modified the debris behaviour. In non-protein containing solutions particles are dispersed away from the track while in protein solutions particles tend to agglomerate and sediment around the wear track.     

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.     

Effect of surface structure on frictional behaviour of a tongue/palate tribological system

The effect of surface structure on the friction and lubrication properties of a model tribological system representing the tongue/palate contact was investigated under dry conditions and in the presence of oil and aqueous solution having the same viscosity at mouth temperature. To this end, several soft silicone surfaces with well-defined surface structures, based on hemisphere pillars of different dimensions in the sub-millimetre range, were fabricated by a moulding technique in order to cover the different scales roughness of the human tongue. The friction experiments were performed on a reciprocating motion sliding tribometer involving contact between a relatively hard ball (steel or PCTFE) representing the palate and one of the soft silicone surfaces simulating the tongue. Test conditions were designed to represent those encountered in the mouth when thin films of food residues coat the oral mucosa surfaces. The results show that the frictional behaviour of the investigated model tribosystem is strongly affected by the topographical structure of the contacting surfaces. Under dry conditions, the coefficient of friction decreases significantly with increase of hemispherical pillar density. For lubricated surfaces, higher pillars with an optimal high density increase the friction coefficient. Further, it was observed that a minimal wetting of at least one contacting surface is essential for establishing effective lubrication.     

Sliding friction and wear of magnesium alloy AZ91D produced by two different methods

Alloy AZ91D is a leading magnesium alloy used for structural applications. It contains aluminum and zinc as principal alloying elements. This alloy is normally die-cast, but recent developments in semi-solid injection molding (Thixomolding^®), which offers certain processing advantages, produces a slightly different microstructure than die-casting, and it was of interest to determine whether the two processing routes would measurably affect the friction and wear of AZ91D. The present work involved ambient air, room temperature testing of die-cast (DC) and Thixomolded^® (ThM) AZ91D, in both unidirectional and reciprocating sliding motion, using stainless steel type 440C as the counterface. After running-in, the average sliding friction coefficients in both types of test fell into the range of 0.29–0.35, irrespective of processing method. The formation of a built-up edge raised the friction slightly in unidirectional tests compared with reciprocating tests. The average wear rate of the ThM alloys in reciprocating sliding was approximately 25% lower than that for DC alloys. However, the wear rates of the magnesium specimens in unidirectional sliding were comparable for DC and ThM materials. Owing to the transfer of magnesium, there was no measurable wear on the stainless steel 440C balls. The wear mechanism during sliding involves the formation of thin, narrow shards along the edges of wear grooves which break off to produce loose particles.     

AZ91D镁合金在水介质下的冲击磨损特性研究

研究了AZ91D镁合金在冲击载荷和去离子水介质综合作用下的磨损特性.结果表明,镁合金表面冲击斑深度及面积随冲击次数的增加而增加;冲击磨损初期,损伤的主要形式为塑性变形及粘着磨损,随着表面塑性耗竭,微观疲劳裂纹产生;磨损后期,水介质的腐蚀作用明显,加速了材料表面的损失.     

Tribology characteristics of magnesium alloy AZ31B and its composites

In this paper, wear characteristics of magnesium alloy, AZ31B, and its nano-composites, AZ31B/nano-Al₂O_3, processed by the disintegrated melt deposition technique are investigated. The experiments were carried out using a pin-on-disk configuration against a steel disk counterface under different sliding speeds of 1, 3, 5, 7 and 10 m/s for 10 N normal load, and 1, 3 and 5 m/s for 30 N normal load. The worn samples and wear debris were then examined under a field emission scanning electron microscopy equipped with an energy dispersive spectrometer to reveal its wear features. The wear test results show that the wear rates of the composites are gradually reduced over the sliding speed range for both normal loads. The composite wear rates are higher than that of the alloy at low speeds and lower when sliding speed further increased. The coefficient of friction results of both the alloy and composites are in the range of 0.25–0.45 and reaches minimums at 5 m/s under 10 N and 3 m/s under 30 N load. Microstructural characterization results established different dominant mechanisms at different sliding speeds, namely, abrasion, delamination, oxidation, adhesion and thermal softening and melting. An experimental wear map was then constructed.     

Tribological behaviour of carbon and low alloy steels: effect of mechanical properties and test conditions

Abstract

In this paper, the effects of mechanical properties and test conditions on the tribological behaviour of ISO C45 carbon steel and ISO 42CrMo4 low alloy steel were studied. The tribological tests were carried out, without lubrication, on a reciprocating friction tester. Cylinder on flat contact configuration was adopted. The results showed that there is no obvious relationship between the mechanical properties and the friction ones. However, the variation in the coefficient of friction depends on the test conditions. In contrary to normal load, the effect of sliding speed on the coefficient of friction is not the same for the two steel nuances. The tribological properties are dependent, however, on the nature of wear debris.     

Effect of rare earth on microstructure and carbides in WC-Fe composite coating

WC-Fe composite coatings were prepared on IC45/080A47 steel substrates by argon arc cladding technique. Minute amounts of La were added into the coating, and the microstructure was investigated to find the relation to rare earth. Results show that RE does not change the categories of phases, and the main components remain α-Fe, Fe₃W₃C, WC and W₂C. However, the distribution of carbide particles is optimised. It reduces the agglomeration and bridging in the cladding layer's structure, makes the particles distribute homogeneously and restrains the dissolution of WC and the formation of fishbone shaped dendritic carbides. It promotes the formation of granular carbide and refines grains. It also reserves the WC particles in the composite coating and improves the average hardness and wear resistance.     

Effect of plasma treatment of Kevlar fabric on the tribological behavior of Kevlar fabric/phenolic composites

Pure and plasma-treated Kevlar fabrics were used to prepare Kevlar fabric/phenolic composites by consecutive dipping of the fabric in phenolic adhesive resin. The friction and wear performance of the resulting composites has been evaluated in a pin-on-disk wear tester at various dry-sliding conditions. The surface changes occurring on Kevlar fibers treated with air-plasma were analyzed by using X-ray photoelectron spectroscope (XPS), Fourier transform infrared spectroscope (FT-IR) and scanning electron microscope (SEM). Moreover, the impact of air-plasma treatment time and power on the friction and wear behavior of Kevlar fabric/phenolic composites composed of the air-plasma-treated Kevlar fabrics was systematically studied. It was found that plasma treatment can significantly improve the tribological performance of the prepared Kevlar fabric/phenolic composites; the best performance was after a plasma treatment at 50 W for 15 min. The plasma treatment generates oxygenic and nitrogenous groups on the surface of the fabric, coupled with an increase of the surface roughness, strengthening the bond between the Kevlar fabric and phenolic adhesive resin and hence improving the tribological properties of the Kevlar fabric/phenolic composites.     

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.     

Vacuum tribological behaviour of self‐lubricating quasicrystalline composite coatings

High‐temperature‐resistant self‐lubricating coatings are needed in space vehicles for components that operate at high temperatures and/or under vacuum. Thick composite lubricant coatings containing quasicrystalline alloys as the hard phase for wear resistance can be deposited by a thermal spray technique. The coatings also contain lubricating materials (silver and BaF₂ CaF2 eutectic) and NiCr as the tough component. This paper describes the vacuum tribological properties of TH103, a coating of this type, with a very good microstructural quality. The coating was deposited by high‐velocity oxygen fuel spraying and tested under vacuum using a pin‐on‐disc tribometer. Different loads, linear speeds, and pin materials were studied. The pin scars and disc wear tracks were characterised using a combination of scanning electron microscopy and energy dispersive spectrometry. A minimum mean steady friction coefficient of 0.32 was obtained when employing an X750 Ni superalloy pin in vacuum conditions under 10 N load and 15 cm/s linear speed, showing moderate wear of the disc and low wear of the pin.