Abrasive wear of Al‐SiC composites

The two‐ and three‐body abrasion of aluminium matrix composites, reinforced with silicon carbide particles, have been investigated. The metal matrix composites were fabricated by a powder metallurgy route involving a final hot extrusion step. Air atomised aluminium powder Al 1100 was used as matrix and α‐SiC_p as reinforcement with mean sizes of 10, 27 and 43 μm; in the proportions of 5, 10 and 20 vol.%. Using a pin‐on‐disc apparatus and a wet monolayer tester, two‐ and three‐body abrasion tests were carried out respectively against silicon carbide and alumina abrasives with four different grit sizes. The microstructural characterizations were performed using light microscopy. The dominant wear mechanisms were identified using scanning electron microscopy. The influence of type of the abrasive particles on wear resistance and dominating wear mechanisms was reported. Relationships between size and volume fraction of the SiC_p reinforcement and wear resistance were discussed. It was shown that SiC_p particles reinforcement increases the abrasion resistance against all the abrasives used. This increase was generally higher against alumina than against silicon carbide abrasives.     

Optimization of tribological parameters in abrasive wear mode of carbon-epoxy hybrid composites

Abrasive wear performance of fabric reinforced composites filled with functional fillers is influenced by the properties of the constituents. This work is focused on identifying the factors such as filler type, filler loading, grit size of SiC paper, normal applied load and sliding distance on two-body abrasive wear behaviour of the hybrid composites. Abrasive wear tests were carried on carbon fabric reinforced epoxy composite (C-E) filled with filler alumina (Al₂O₃) and molybdenum disulphide (MoS₂) separately in different proportions, using pin-on-disc apparatus. The experiments were planned according to Taguchi L18 orthogonal array by considering five factors, one at two levels and the remaining at three levels, affecting the abrasion process. Grey relational analysis (GRA) was employed to optimize the tribological parameters having multiple-response. Analysis of variance (ANOVA) was employed to determine the significance of factors influencing wear. Also, the comparative specific wear rates of all the composites under dry sliding and two-body abrasive wear were discussed. The analysis showed that the filler loading, grit size and filler type are the most significant factors in controlling the specific wear rate of the C-E composite. Optimal combination of the process parameters for multi performance characteristics of the composite under study is the set with filler type as MoS₂, filler loading of 10 wt.%, grit size 320, load of 15 N and sliding distance of 30 m. Further, the optimal parameter setting for minimum specific wear rate, coefficient of friction and maximum hardness were corroborated with the help of scanning electron micrographs.     

Experimental investigation of hardfaced martensitic steel under slurry abrasion conditions

Wear by slurry abrasion is a potential problem in engineering components subjected to particulate flow. The life of the components under slurry abrasive wear situations is primarily decided by operating conditions and the materials properties. Martensitic steels are widely used for abrasion resistant applications. The present work reports slurry abrasion response of hardfacing martensitic steel under a wide range of experimental conditions. The response data is generated using systematic and simultaneous variation of test parameters. The experiments were performed using silica sand slurry with different slurry concentration, particle size, sliding distance and load. The results of the investigation suggest that slurry concentration had relatively stronger effect than normal load. The wear volume loss exhibited an increasing trend with increasing severity of test parameters. An empirical equation is proposed to describe the interactive effect of the test parameters, abrasive particle properties and material property. SEM (Scanning Electron Microscope) studies revealed different morphology of the worn surfaces which was attributed to mild to severe slurry abrasion test conditions.     

Abrasion predictions for Francis turbines based on liquid–solid two-phase fluid simulations

The runner blades and guide vanes of Francis turbines are worn by sediment in the flow. However, there are few studies about abrasion of the runner blade and guide vane for normal turbine operating conditions. This study investigated the relation between the wear rates on the surfaces of the runner blade and guide vane and the sediment concentration, and analyzed the distribution of the wear rates for normal turbine operating condition. An Eulerian–Lagrangian Computational Fluid Dynamics (CFD) procedure was used to simulate steady liquid–solid two-phase flow for various operating conditions. The Finnie model was then used to predict the abrasion. The conditions leading to abrasion in the inner flow passage components of a Francis turbine are clarified through analysis of the abrasion conditions for the runner blades and guide vanes. Field tests and simulations show that the relative wear rate on the runner blades and guide vanes increases with increasing sediment concentration, and the maximum wear on the runner blades occurs in a small opening region with the maximum increasing as the head increases. The maximum wear on the guide vanes occurs at the maximum output and the relative wear rate on the runner blades is much greater than that on the guide vanes. There is no good data, so the relative wear rates on the runner blades and the guide vanes can only be obtained numerically. Thus actual wear rates cannot be given and are beyond the scope of this paper. This paper shows the abrasion characteristics on the runner blades and guide vanes with sediment flow and provides reference data for predicting the abrasion conditions in the flow passage components of a Francis turbine.     

Wear and microstructural studies of alloy sintered steels

Abstract

Crossed cylinder abrasive wear tests were carried out on alloy sintered steels T15, M2, and M42. The test parameters necessary for reproducible and reliable wear data have been studied. These parameters include applied load, time of test, abrasive grit size, speed of abrasion, and hardness of test specimen. Use has been made of the hypothesis of Archard to relate the test parameters to the wear rates found for these steels. Results show that Archard's hypothesis of abrasive wear holds for the conditions used in the test. The wear rates determined using this test method were found to be comparable to those observed in the use of these steels in industry and, therefore; it is considered that this method could be used to predict wear behaviour in service conditions. Using a replica technique on the polished and etched surfaces of these steels, it has been possible to make an assessment of the carbide size and distribution, both as number per cent and volume per cent. Examination of the microstructures of these steels showed a uniform distribution of carbide with a maximum size of 8 μm in a hardened and tempered steel matrix. The importance of microstructure in the characterisation of the wear behaviour of these alloy steels is discussed.

MST/1369     

Structural, mechanical, and tribological properties of fluorinated mesoporous silica films: Effect of functional moiety and surfactant template concentrations

Thin organo-functional coatings are inherently weak and can be easily damaged and their functional properties degraded by wear. Encapsulating organo-functional moieties into surfactant-templated ceramic coatings has the possibility of extending the functional lifetime of such materials. This study examines the effects of functional silane and surfactant template concentrations on the structural, mechanical, and tribological properties of hydrophobic silica films. Fluorinated silica films were synthesized via sol-gel co-condensation of tetraethoxysilane and a perfluoropolyether silane, templated with PEO₁₀₆PPO₇₀PEO₁₀₆ surfactant (Pluronic F127), and coated on glass substrates. The results show that the increasing concentrations of fluorinated silane and surfactant template generally improve hydrophobicity of films worn by abrasion. However, surfactant templating creates void spaces which are detrimental to the mechanical properties of the material, as was determined by nitrogen adsorption porosimetry and nanoindentation. Tribological results from atomic force microscopy suggest that the low-friction surface generated by encapsulation of fluorosilane moieties grafted to internal surfaces mitigates to some extent the detrimental effect of film porosity on hardness and wear resistance.     

Effect of aging on the abrasive wear properties of AlMgSi1 alloy

In this paper, the wear performance of the aged AlMgSi1 alloy was investigated. Great improvements in mechanical properties of Al alloys can be achieved by suitable solution treatment and aging operations. A pin-on-disk wear machine was designed and developed for abrasive wear tests. The wear resistance was evaluated using a pin-on-disk wear testing method with a SiC abrasive paper counterface. The variation of wear volume is presented as a function of applied normal load, abrasive grit size and sliding distance for running speed. Mass losses were measured within a load range of 6.45–11 N, a sliding velocity range of 0.078–0.338 m/s and abrasive grit size of 5–30 μm. The effects of different sliding speeds and loads on wear resistance and surface roughness were also examined. It was measured amounts of mass loss and examined worn surfaces. Metal microscope was used to study the microstructures of the wear scars. Natural aged specimen observed maximum wear resistance.     

Mechanisms and causes of wear in tooth enamel: implications for hominin diets

The wear of teeth is a major factor limiting mammalian lifespans in the wild. One method of describing worn surfaces, dental microwear texture analysis, has proved powerful for reconstructing the diets of extinct vertebrates, but has yielded unexpected results in early hominins. In particular, although australopiths exhibit derived craniodental features interpreted as adaptations for eating hard foods, most do not exhibit microwear signals indicative of this diet. However, no experiments have yet demonstrated the fundamental mechanisms and causes of this wear. Here, we report nanowear experiments where individual dust particles, phytoliths and enamel chips were slid across a flat enamel surface. Microwear features produced were influenced strongly by interacting mechanical properties and particle geometry. Quartz dust was a rigid abrasive, capable of fracturing and removing enamel pieces. By contrast, phytoliths and enamel chips deformed during sliding, forming U-shaped grooves or flat troughs in enamel, without tissue loss. Other plant tissues seem too soft to mark enamel, acting as particle transporters. We conclude that dust has overwhelming importance as a wear agent and that dietary signals preserved in dental microwear are indirect. Nanowear studies should resolve controversies over adaptive trends in mammals like enamel thickening or hypsodonty that delay functional dental loss.     

含硫镍基合金与YJ2硬质合金对偶的高温摩擦特征分析

本文研究了通过热压法制备得到的含硫镍基合金与YJ2硬质合金对偶的摩擦特征。结果表明：在高温摩擦过程中，材料中的硫化物共晶体是主要的润滑组元，摩擦面的温度对其润滑效果有较大的影响；材料与YJ2对偶时的摩擦系数随着温度变化有所不同，但是磨损率都随着温度升高而增大，其高温下磨损形式主要为磨粒磨损和氧化磨损；YJ2硬质合金表面生成的氧化物对材料减摩性能有很大影响。     

多纤维增强重型汽车制动器摩擦材料的摩擦磨损性能研究

采用芳纶浆粕、玻璃纤维、硅灰石纤维和钛酸钾晶须多纤维混杂增强制备重型汽车制动器摩擦材料.利用XD-MSM型定速摩擦试验机,考察了摩擦材料的摩擦系数和磨损率随温度变化的情况,并且通过扫描电镜观察了摩擦材料在不同温度下磨损后的表面形貌,分析其摩擦磨损机理.研究结果表明,所研制的摩擦材料具有足够的机械性能和优异的摩擦磨损性能,热衰退小、恢复性能好、耐磨损,可满足重型汽车制动性能的要求.材料在中高温下主要是磨粒磨损和热疲劳磨损,同时伴随着粘着磨损.     

Two-body abrasion wear mechanism of super bainitic steel

The abrasion wear resistance and wear mechanism of super bainitic steel austempered at different temperatures and time have been investigated by two-body abrasion testings, scanning electron microscopy, X-ray diffraction, transformation electron microscopy and electron backscattering diffraction. The results show that the two-body abrasion wear mechanism is predominantly micro-ploughing abrasion, and the wear resistance is decreased with increasing isothermal temperature which is attributed to the decreased hardness caused by a higher retained austenite content and the coarsening of the microstructure. The sample austempered at 230°C for 2?h with the higher amount of retained austenite and lower carbon concentration exhibits excellent wear resistance, and the transformation induced plasticity effect is observed during wear process which is beneficial for the improving of hardness and wear resistance.     

Nano-Scratching resistance of high-chromium white cast iron and its correlation with wear of cBN tool in machining

In this paper, a nano-scratch testing approach was used to measure and evaluate the abrasion wear resistance of high-chromium white cast irons in order to understand the wear mechanism in the interaction between the high-chromium white cast iron and the cBN cutting tool during the machining process. Scratch testing was performed on a nanoindentation instrument using a diamond indenter as the scratch tool. Linear multi-pass scratches in the same path were made on pre-worn surfaces of test materials. The correlation of the scratching resistance and tool wear measured from the machining is presented by the flank wear and maximum scratch depth. The appearance of the cutting edge on a cBN tool suggests that the abrasion wear is mainly related with a combined effect of the carbides and the matrix during machining the high-chromium white cast iron.     

Wear of ceramic particle-reinforced metal-matrix composites

Pin-on-disc dry sliding tests were carried out to study the wear mechanisms in a range of metal-matrix composites. 6061-aluminium alloys reinforced with 10 and 20 vol% SiC and Al₂O₃ particles were used as pin materials, and a mild steel disc was used as a counterface. A transition from mild wear to severe wear was found for the present composites; the wear rate increased by a factor of 10². The effects of the ceramic particles on the transition load and wear with varying normal pressure were thoroughly investigated. Three wear mechanisms were identified: abrasion in the running-in period, oxidation during steady wear at low load levels, and adhesion at high loads. A higher particle volume fraction raised the transition load but increased the wear rate in the abrasion and adhesion regimes. Increase of particle size was more effective than increase of volume fraction to prolong the transition from mild wear to adhesive wear. The reasons for different wear mechanisms were determined by analyses of the worn surfaces and wear debris.     

玉米植株中的植硅石及其纳米SiO2的制备

以玉米植株为原料制备了纳米结构SiO₂. 通过常温混酸浸泡等手段在玉米植株中观察到了微米级植硅石,并以植硅石为原料,通过煅烧、硝酸煮沸等方法制备了纳米级SiO₂;运用X射线粉末衍射（XRD）、光学显微镜、透射电子显微镜（TEM）、扫描电子显微镜（SEM）、电子能谱（EDS）、红外光谱(IR)等手段对样品进行了表征. 结果表明,玉米茎表皮和叶中植硅石均为哑铃形,前者沿木质素导管方向顺向排列,后者为横向排列;经硝酸煮沸煅烧后,植硅石可以形成103nm左右的SiO₂球,并随着煅烧温度的升高,纳米球逐渐交联.     

正硅酸乙酯为无机组分前驱体的聚碳酸酯耐磨涂层

以正硅酸乙酯(TEOS)作为无机组分的前驱体,甲基三甲氧基硅烷(MTMS)水解聚合产物作为有机组分,通过溶胶-凝胶法在聚碳酸酯(PC)表面形成耐磨涂层。红外光谱分析表明该涂层具有Si—O—Si的交联网络结构。研究了MTMS和TEOS的摩尔比对涂层的光学性能、硬度、附着力和耐磨性能的影响。结果表明,当MTMS和TEOS的摩尔比为2∶1时,涂层的综合性能达到最优,该涂层在经历500次耐磨试验后的雾度为12.69%,而纯PC的雾度增至42.38%。采用SEM和TEM分析了MTMS/TEOS具有优异耐磨性能的原因在于该涂层具有纳米SiO2粒子分散于有机基体的微观结构。     

Abrasive wear of individual grits in diamond rollers and sticks and its relation to the overall tool wear in dressing operations

Abrasive wear of individual grits in diamond dressing tools during the dressing of abrasive wheels is studied. The wear rate is assessed analytically allowing for mechanical-statistical and temperature characteristics of the grit operation in dressing with rollers and sticks, as well as for the temperature-induced variations of the diamond hardness. A relationship is established between wear of individual grits and that of the diamond-containing layer as a whole.     

Microstructural examination of service exposed coal mill liner material

This study mainly focuses the microstructural characterisation of the service exposed coal liner. These liners are generally referred to as bull ring segments in the bowl mill of coal pulveriser systems. The failed bull ring segment was collected from a coal-fired power plant of Kolaghat thermal plant, West Bengal, India. The crack that has been observed in the middle of the liner was observed under SEM and detailed microstructural studies are made for the liner material. The hardness measurements are made and XRD is carried out to identify the phases present in the sample. The results suggest that the material confirms to high chromium cast iron and microstructural studies reveal that the cracks are mainly due to the heavy service exposed conditions where lumps of coal and silica sand falling on these liners causing severe impact and abrasion conditions. High abrasive studies on the liner material are carried out and it showed that increasing the abrasive size as well as load is responsible for higher wear loss. The results suggest that prolonged exposure to abrasion conditions results in the progressive removal of the matrix material and due to various phase transformations from austenite to martensite introduces surface volume changes and causes the generation of cracks and further lead to failure of the component.     

Tribological evaluation of high-speed steels with a regulated carbide phase

Wear resistance of a commercial steel and titanium–niobium high-speed steels with a regulated carbide phase was evaluated by employing a micro-scale abrasive wear test with alumina particles. The worn volumes and corresponding wear coefficients were the lowest for the new non-ledeburitic grades containing titanium, then the two niobium grades, the conventional (both wrought and by powder metallurgy) steels exhibited the worse wear resistance. Fractography SEM observations together with energy-dispersive X-ray (EDX) chemical analysis revealed the decisive role of the steels' MC particles in the wear process. These carbides influenced the abrasion by stoppage of the wear scars and/or changing their trajectories. Directional and nondirectional abrasion modes in the steels tested using alumina and carborundum abrasives were found and are discussed.     

Verfestigung und Verschleißverhalten von weißen Gußeisen bei abrasiver Beanspruchung

Work Hardening and Abrasion Resistance of White Cast Irons White cast irons are frequently used against abrasive wear under extreme loading conditions. The microsructure and the mechanical properties of these alloys play an important role to control their wear rates. Regarding the mechanical properties, it has been reported that the bulk hardness alone is not enough to describe the wear behaviour. Generally, it has been shown that the work hardening induced by the wear process has an essential effect on the abrasion resistance. In this investigation, using a pin abrasion test, the wear behaviour of Ni-Hard 4 and high chromium white cast irons has been studied. The results of this study contribute to discuss the correlation mechanisms between work hardening and abrasive wear behaviour.     

Wear Behaviour of CTC/FeCrCSi Composite

To bring the excellent abrasion-resistant po-tential of carbide into full play,composites of casttungsten carbide(CTC)grains based on mainlyplate martensite and high Cr,W white cast iron aremade on substrate of grey iron by cast-in-placehardfacing process.Results of high-stresstwo-body and three-body abrasion show that:(1)Base alloy microstructures have overwhelmingdominating effects on abrasion resistances of thecomposites in two-body and especially three-bodyabrasion systems.(2)All composites have very ex-cellent abrasion-resistances which increase drasti-cally with the increase of CTC grain size.In case ofthe same CTC grain size,composite based onmartensite white cast iron is much morewear-resistant than that based on mainly platemartensite although the volume fraction of CTCgrains in the latter is considerably larger than thatin the former.In three-body abrasion system,loadhas little effect on wear rate for composites basedon martensite white cast iron,but wear rate ofconventional wear-resistant materials increaseslinearly in a very steep slope as the nominal stressincreases.