The abrasive wear resistance of TIC and (Ti,W)C-reinforced Fe–17Mn austenitic steel matrix composites

Pin-on-disc dry sliding wear tests have been carried out to study the wear behaviour of 10 vol% TiC and (Ti,W)C-reinforced Fe–17Mn austenitic steel matrix composites. The composites have been synthesized in situ by means of conventional melting and casting route. It has been observed that the abrasive wear resistance of the composites is higher than that of their unreinforced Fe–17Mn austenitic steel. Compared with the TiC-reinforced composite, the abrasive wear resistance of the (Ti,W)C-reinforced composite is better. The abrasive wear resistance and coefficient of friction of both reinforced and unreinforced materials decrease as the load increases.     

Tribological Behavior of Composites Based on ZA-27 Alloy Reinforced with Graphite Particles

The objective of this investigation is to assess the influence of graphite reinforcement on tribological behavior of ZA-27 alloy. The composite with 2 wt% of graphite particles was produced by the compocasting procedure. Tribological properties of unreinforced alloy and composite were studied, using block-on-disk tribometer, under dry and lubricated sliding conditions at different specific loads and sliding speeds. The worn surfaces of the samples were examined by the scanning electron microscopy (SEM). The obtained results revealed that ZA-27/graphite composite specimens exhibited significantly lower wear rate and coefficient of friction than the matrix alloy specimens in all the combinations of applied loads (F _n ) and sliding speeds (v) in dry and lubricated tests. The positive tribological effects of graphite reinforcement of ZA-27 in dry sliding tests were provided by the tribo-induced graphite film on the contact surface of composite. In test conditions, characterized by the small graphite content and modest sliding speeds and applied loads, nonuniform tribo-induced graphite films were formed leading to the increase of the friction coefficient and wear rate, with increase of the sliding speed and applied load. In conditions of lubricated sliding, the very fine graphite particles formed in the contact interface mix with the lubricating oil forming the emulsion with improved tribological characteristics. Smeared graphite decreased the negative influence of F _n on tribological response of composites, what is manifested by the mild regime of the boundary lubrication, as well as by realization of the mixed lubrication at lower values of the v/F _n ratio, with respect to the matrix alloy.     

聚苯酯填充聚四氟乙烯复合材料摩擦学行为研究

采用聚苯酯（Ekonol）、Ekonol／PAB纤维增强聚四氟乙烯（PTFE）制备利用转移膜润滑的摩擦副材料，并研究了两组材料在于摩擦条件下与9Cr18轴承钢对摩时的摩擦学性能；运用扫描电镜分析了两组材料磨损表面形貌和磨损机理。结果表明：随着Ekonol含量的增大，Ekonol填充PTFE复合材料的摩擦因数逐渐增大，当Ekonol质量分数超过25％时摩擦因数略有下降，磨损方式由以犁削磨损为主转变为以疲劳磨损为主；而Ekonol／PAB纤维填充门FE复合材料的摩擦因数，随Ekonol含量的增大而增大，磨损方式由以粘着磨损为主转变为以疲劳磨损为主。Ekonol／PAB纤维填充PTFE复合材料的摩擦学性能优于Ekonol填充PTFE复合材料。     

Dry sliding wear of fly ash particle reinforced A356 Al composites

In the present study aluminium alloy (A356) composites containing 6 and 12 vol. % of fly ash particles have been fabricated. The dry sliding wear behaviour of unreinforced alloy and composites are studied using Pin-On-Disc machine at a load of 10, 20, 50, 65 and 80 N at a constant sliding velocity of 1 m/s. Results show that the dry sliding wear resistance of Al-fly ash composite is almost similar to that of Al₂O₃ and SiC reinforced Al-alloy. Composites exhibit better wear resistance compared to unreinforced alloy up to a load of 80 N. Fly ash particle size and its volume fraction significantly affect the wear and friction properties of composites. Microscopic examination of the worn surfaces, subsurfaces and debris has been done. At high loads (>50 N), where fly ash particles act as load bearing constituents, the wear resistance of A356 Al alloy reinforced with narrow size range (53–106 μm) fly ash particles were superior to that of the composite having the same volume fraction of particles in the wide size range (0.5–400 μm).     

Enhancement of abrasive wear resistance in consolidated Al matrix composites via extrusion process

Abstract

The present study addresses the dry wear behaviour of aluminium matrix composites under different sliding speeds and applied loads. Values of the friction coefficient of the matrix alloy and composite materials were in expected range for light metals in dry sliding conditions. The higher coefficient of friction was the consequence of established contact between hard SiC particles and the counter body material. The rough and smooth regions are distinguished on the worn surface of the composites similar to the unreinforced Al alloy. Plastic deformation occurred when the applied specific load was higher than the critical value. The high shear stresses on the sliding surface cause initiation and propagation of the cracks in the subsurface, leading to the loss of material from the worn surface in the form of flakes. The debrises of the composites at low wear rate comprise a mixture of the fine particles and small shiny metallic plate-like flakes and are associated with the formation of more iron rich layers on the contact surfaces.     

Wear properties of Saffil/Al,Saffil/Al2O3/Al and Saffil/SiC/Al hybrid metal matrix composites

The purpose of this study is to investigate the wear properties of Saffil/Al, Saffil/Al₂O₃/Al and Saffil/SiC/Al hybrid metal matrix composites (MMCs) fabricated by squeeze casting method. Wear tests were done on a pin-on-disk friction and wear tester under both dry and lubricated conditions. The wear properties of the three composites were evaluated in many respects. The effects of Saffil fibers, Al₂O₃ particles and SiC particles on the wear behavior of the composites were elucidated. Wear mechanisms were analyzed by observing the worn surfaces of the composites. The variation of coefficient of friction (COF) during the wear process was recorded by using a computer. Under dry sliding condition, Saffil/SiC/Al showed the best wear resistance under high temperature and high load, while the wear resistances of Saffil/Al and Saffil/Al₂O₃/Al were very similar. Under dry sliding condition, the dominant wear mechanism was abrasive wear under mild load and room temperature, and the dominant wear mechanism changed to adhesive wear as load or temperature increased. Molten wear occurred at high temperature. Compared with the dry sliding condition, all three composites showed excellent wear resistance when lubricated by liquid paraffin. Under lubricated condition, Saffil/Al showed the best wear resistance among them, and its COF value was the smallest. The dominant wear mechanism of the composites under lubricated condition was microploughing, but microcracking also occurred to them to different extents.     

Friction and wear properties of bronze–graphite composite under water lubrication

Bronze–graphite composite was prepared using powder metallurgy. The friction and wear behaviors of the resulting composites in dry- and water-lubricated sliding against a stainless steel were comparatively investigated on an MM-200 friction and wear tester in a ring-on-block contact configuration. The wear mechanisms of the bronze–graphite composite were discussed based on examination of the worn surface morphologies of both the composite block and the stainless steel ring by means of scanning electron microscopy equipped with an energy dispersion spectrometry and on determination of some typical elements on the worn surfaces by means of X-ray photoelectron spectroscopy. It was found that the friction coefficient was higher under water lubrication than that under dry sliding and it showed margined change with increasing load under the both sliding conditions. A considerably decreased wear rate of the bronze–graphite composite was registered under water-lubricated sliding than under dry sliding, though it rose significantly at a relatively higher load. This was attributed to the hindered transfer of the composite onto the counterpart steel surface under water-lubricated sliding and the cooling effect of the water as a lubricant, while its stronger transfer onto the steel surface accounted for its higher wear rate under dry sliding. Thus, the bronze–graphite composite with much better wear-resistance under water-lubricated sliding than under dry sliding against the stainless steel could be a potential candidate as the tribo-material in aqueous environment.     

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.     

纳米和微米SiO2颗粒对PPESK复合材料摩擦学性能的影响

用热压成型法制备了纳米、微米SiO2填充聚醚砜酮(PPESK)复合材料，考察了复合材料的硬度和抗弯强度，并研究了干摩擦条件下纳米、微米SiO2颗粒对复合材料摩擦磨损性能的影响，用扫描电镜观察分析了复合材料磨损表面形貌及磨损机理。结果表明：干摩擦条件下，纳米SiO2填充PPESK主要是轻微的磨粒磨损；而微米SiO2填充PPESK主要是严重的磨粒磨损。     

Coefficient of Friction Measurements for Thermoplastics and Fibre Composites Under Low Sliding Velocity and High Pressure

Friction materials for typical brake applications are normally designed considering thermal stability as the major performance criterion. There are, however, brake applications with very limited sliding velocities, where the generated heat is insignificant. In such cases it is possible that friction materials which are untypical for brake applications, like thermoplastics and fibre composites, can offer superior performance in terms of braking torque, wear resistance and cost than typical brake linings. In this paper coefficient of friction measurements for various thermoplastic and fibre composite materials running against a steel surface are presented. All tests were carried out on a pin-on-disc test-rig in reciprocating operation at a fixed sliding speed and various pressure levels for both dry and grease lubricated conditions. Moreover, a generic theoretical framework is introduced in order to interpret the changes of friction observed during the running-in phase.     

Investigation into sliding wear performance of zinc-based alloy reinforced with SiC particles in dry and lubricated conditions

The objective of the present investigation was to assess the influence of SiC particle dispersion in the alloy matrix, applied load, and the presence of oil and oil plus graphite lubricants on the wear behaviour of a zinc-based alloy. Sliding wear performance of the zinc-based alloy and its composite containing SiC particles has been investigated in dry and lubricated conditions. Base oil or mixtures of the base oil with different percentages of graphite were used for creating the lubricated conditions. Results show a large improvement in wear resistance of the zinc-based alloy after reinforcement with SiC particles. The lubrication improved the wear resistance and friction behaviour of both the reinforced and base alloys. It was also observed that there exists an optimum concentration of graphite particles in the lubricant mixture that leads to the best wear performance. The composite experienced higher frictional heating and friction coefficient than the matrix alloy in all the cases except oil lubricated conditions; a mixed trend was noticed in the latter case. The wear rate and frictional heating increased with load while friction coefficient was affected in an opposite manner. Test duration influenced the frictional heating and friction coefficient of the samples in a mixed manner.Examination of worn surfaces revealed a change of predominating wear mechanisms from severe ploughing and/or abrasive wear for base alloy to delamination wear for the reinforced material under dry sliding conditions. The presence of the lubricant increased the contribution of adhesive wear component while reducing the severity of abrasion. This was attributed to the generation of more stable lubricant films on the contacting surfaces. Cross-sections of worn surfaces indicated substantial wear-induced plastic deformation, thereby suggesting adhesive wear to be a predominant wear mechanism in this study. The debris particles revealed deformed flakes and machining chips signifying the involvement of adhesion and abrasion modes of wear respectively.     

压渗法制备陶瓷网络复合材料摩擦行为研究

提出了三维陶瓷网络(骨架)增强金属基复合材料的新构思,设计和制备了一种新型的三维陶瓷网络(骨架)增强铝合金复合材料,研究了其在干摩擦状态下的滑动摩擦磨损行为。结果表明,基体铝合金在重载时产生严重粘着磨损,磨损层发生软化和塑性流动,而复合材料中的陶瓷颗粒暴露于磨损表面并起承载作用,从而保护基体小发生严重磨损。与基体合金相比,复合材料摩擦因数平稳而较低,且耐磨性提高6倍左右。     

Tribological properties of metal-plastic multilayer composites under oil lubricated conditions

Three kinds of metal-plastic multilayer composites, which were composed of a steel backing, a middle layer of sintered porous bronze and a surface layer of polytetrafluoroethylene (PTFE) filled by Pb or Cu₂O powders, were prepared. The friction and wear properties as well as the limiting pressure times velocity (PV) values of these metal-plastic multilayer composites sliding against 45 carbon steel under both dry and oil lubricated conditions were evaluated on a MPV-1500 friction tester with a steel axis rotating on a journal bearing. The worn surfaces of these metal-plastic multilayer composites and the transfer films formed on the surface of steel axis were examined by electron probe microscopy analysis (EPMA). Experimental results show that filling of Pb to PTFE reduces the friction coefficient and wear of the composite, while filling of Cu₂O to PTFE increases the friction coefficient but decreases the wear of the composite. The friction and wear properties as well as the limiting PV values of these metal-plastic multilayer composites can be greatly improved with the oil lubrication. EPMA investigations show that Pb and Cu₂O fillers preferentially transfer onto the surfaces of steel axis, which may enhance or deteriorate the adhesion between transfer films and steel surfaces. Meanwhile the transfer of these metal-plastic multilayer composites onto the steel surface can be greatly reduced with oil lubrication, which results in the remarkable decrease of the wear of these metal-plastic multilayer composites.     

配副材料对碳纤维增强环氧树脂复合材料摩擦学性能的影响

采用铺层/热压烧结的方法制备交叉铺层的碳纤维增强环氧树脂复合材料,探究配副材料及载荷对铺层材料摩擦学性能的影响,并探讨复合材料的磨损机制。结果表明:随着载荷的增加,复合材料的摩擦因数逐渐降低,磨损率则逐渐增加;在研究的载荷下,复合材料与轴承钢配副时摩擦因数较低,而与Si₃N₄和Al₂O₃陶瓷球配副时润滑性能较差;在低载荷下复合材料与轴承钢配副时磨损率较高,高载荷下则相反。磨损表面形貌分析显示:当施加的载荷较低时,磨损表面形貌主要为犁沟及少量裂纹,磨损机制主要为磨粒磨损;当载荷较高时,高的接触应力使磨损表面产生了大量裂纹并伴随树脂基体脱落,磨损机制由磨粒磨损转变为疲劳磨损。     

Wear behaviour of AE42+20% saffil Mg-MMC

The wear behaviour of AE42 magnesium alloy and AE42+20% saffil short fibre composite is investigated in dry sliding condition using a pin-on-disc set-up in the load range of 5–40 N with sliding speeds of 0.838, 1.676 and 2.513 m/s for a constant sliding distance of 2.5 km. In case of both the alloy and the composite wear rate increases with increasing loads and the wear rate of the composite is lower at lower loads. At all sliding speeds, a crossover in wear rate is observed with the increase in load, i.e., above a certain load the wear rate of the composite becomes greater than that of the alloy, and the crossover shifts to lower loads with increase in the sliding speed. Severe sub-surface plastic deformation and fibre breakage are found to be the dominant mechanism for the unreinforced alloy and the composite, respectively.     

Sliding wear behaviour of aluminum syntactic foam: A comparison with Al-10 wt% SiC composites

The sliding wear behaviour of cenosphere-filled aluminum syntactic foam (ASF) has been studied in comparison with that of 10 wt% SiC particle reinforced aluminum matrix composite (AMC) at a load of 3 kg and varying sliding speeds under dry and lubricated conditions using a pin-on disc test apparatus. The tribological responses such as the wear rate, the coefficient of friction and the frictional heating were investigated. The wear surfaces and subsurfaces were studied for understanding the wear mechanism. It was noted that the coefficient of friction, the wear rate, and the temperature rise for ASF are less than that for AMC in both dry and lubricated conditions. The craters (vis-à-vis exposed cenospheres) play an important role in the wear mechanism for ASF.     

The effect of phosphating on the friction and wear properties of grey cast iron

The friction and wear resistance of two commercial manganese phosphate coatings have been evaluated. Grey cast iron wear pins were treated by the two processes and were tested by sliding against a steel disc, under both lubricated and dry sliding wear conditions.Phosphating increases the sliding distance to scuffing as well as the scuffing load, whilst marginally reducing the coefficient of friction. No advantage was found in phosphating dry sliding surfaces.Phosphating reduces the likelihood of adhesive wear in marginal or poorly lubricated sliding couples. The choice of phosphate coating is primarily dependent on the surface finish of the sliding counterface; thin coatings are suitable if the counterface is smooth but thicker coatings are superior against rougher surfaces.     

Dry sliding friction and casing wear behavior of PCD reinforced WC matrix composites

The friction and casing wear properties of PCD reinforced WC matrix composites were investigated using a cylinder-on-ring wear-testing machine against N80 casing steel counterface under dry sliding conditions. The results indicate that the friction and casing wear rate of PCD reinforced WC matrix composites are the lowest among the materials. As the applied load and sliding speed steadily increase, the friction coefficients of PCD reinforced WC matrix composites decrease. In addition, the casing wear rates increase with increasing load, but decline with sliding velocity. The dominant wear mechanism of the PCD composite is the micro-cutting wear, accompanied by adhesive wear.     

Effect of nanoparticles on the tribological behaviour of short carbon fibre reinforced poly(etherimide) composites

The tribological behaviour of nano-TiO₂ particle filled polyetherimide (PEI) composites, reinforced additionally with short carbon fibre (SCF) and lubricated internally with graphite flakes, was investigated. The wear tests were conducted on a pin-on-disc apparatus, using composite pins against polished steel counterparts under dry sliding conditions, different contact pressures and various sliding velocities. It was found that the conventional fillers, i.e. SCF and graphite flakes, could remarkably improve both the wear resistance and the load-carrying capacity. With the addition of nano-TiO₂, the frictional coefficient and the contact temperature of the composite were further reduced, especially under high pv (the product of the normal pressure, p, and the sliding velocity, v) conditions. Based on microscopic observations of worn surfaces and transfer films on the counterparts, possible wear mechanisms were discussed.     

Friction and wear properties of metal powder filled PTFE composites under oil lubricated conditions

Four kinds of polytetrafluoroethylene (PTFE)-based composite, pure PTFE, PTFE+30vol.%Cu, PTFE+30vol.%Pb and PTFE+30vol.%Ni composite, were prepared. The friction and wear properties of these metal powder filled PTFE composites sliding against GCr15 bearing steel under both dry and lubricated conditions were studied using an MHK-500 ring-block wear tester. The worn surfaces of the PTFE composites and the transfer films formed on the surface of GCr15 bearing steel were examined using scanning electron microscopy (SEM) and optical microscopy respectively. Experimental results show that the friction and wear properties of the PTFE composites can be greatly improved by liquid paraffin lubrication. The wear of these PTFE composites can be decreased by at least 1 to 2 orders of magnitude compared with that under dry friction conditions, while the friction coefficients can be decreased by 1 order of magnitude, SEM and optical microscopy investigations of the rubbing surfaces show that metal fillers of Cu, Pb and Ni not only raise the load carrying capacity of the PTFE composites, but also promote transfer of the PTFE composites onto the counterfaces, so they greatly reduce the wear of the PTFE composites. However, the transfer of these PTFE composites onto the counterfaces can be greatly reduced by liquid paraffin lubrication, but transfer still takes place.