Particle motion and modes of wear in the dry sand–rubber wheel abrasion test

In the dry sand–rubber wheel test, the particles are free to move between the wheel and testpiece. The particles may either roll as they pass through the contact, or they may temporarily embed in the rubber wheel and groove the sample; the motion of the particles will govern the modes of deformation of the sample and thus the dominant mechanisms of wear. In experiments concerning the abrasion of a range of steels with widely varying hardnesses, it has been shown that the motion of the particles through the contact depends not only upon the details of the testing conditions (for example particle feedrate, particle size and shape, applied load) but also upon the testpiece material properties themselves, such as hardness. Such a dependence upon testpiece material properties is a cause for concern for those who use the test, and indicates that observations of the mechanisms of wear are an essential part of this test methodology. Particle rolling through the contact is favoured by low applied loads and low testpiece hardness whereas particle sliding through the contact is favoured by high applied loads and high testpiece hardness. The wear coefficients in situations where particle sliding (grooving) occurs are not significantly higher than those for situations where particle rolling occurs and it is argued that this is associated with the way in which grooving particles orient themselves with respect to the testpiece as they pass through the contact. This is in contrast to fixed-particle grooving abrasion (such as might be observed in tests using abrasive papers), and as such, it is argued that what is commonly termed two-body abrasion should be subcategorised into “fixed-particle grooving abrasion” and “free-particle grooving abrasion”. The paper then proceeds to provide an analysis of the motion of particles in the dry sand-rubber wheel abrasion test, and seeks to understand the mechanics controlling their motion, and thus the dependence of particle motion upon external factors, focussing on the effects of testpiece hardness and applied load. The effect of hardness on particle rotation is well predicted by the model, but the effect of the applied load on particle motion observed experimentally is opposite to that which is predicted by the model. The shortcomings of the model are discussed, and the model has been qualitatively modified to account for this discrepancy. The modifications centre around the significant changes in rubber wheel–particle contact geometry as the applied load is changed; such changes are difficult to model analytically due to the large strains associated with such a contact, and it is suggested that finite element modelling may be required to fully understand and model the complex contacts occurring in this simple and widely employed test method.     

Some observations on two-body abrasive wear

Pin-on-disc-type two-body abrasion tests were carried out on five metals with seven particle sizes over a range of loads, lengths of travel and sliding speeds. The familiar results that two-body abrasive wear is proportional to load and to distance travelled were confirmed. The “size effect”, in which particles below about 100 μm produce progressively less wear, was shown to be independent of load, sliding speed and prior cold working. Increasing the sliding speed from 1 to about 100 mm s^?1 produced an increase in wear resistance of about 50% for AISI 1020 steel. An increase in velocity above 100 mm s^?1 had little effect on the wear resistance. Plots of the wear resistance against the hardness of the annealed metal showed significant deviations from the linear relationship reported in the literature. The result is influenced by both sliding velocity and particle size.     

Wear of Unlubricated Steel Surfaces in Sliding Contact

Observations have been made of the wear from an SAE 1113 steel pin specimen rubbing on a SAE 113 steel disk in a normal laboratory atmosphere in relation to normal load (0.5–10.4 lbf), slidinq speed (21–188 ft/sec), sliding distance and track history. As a function of sliding distance, three regions are observed; (i) initial severe wear, (ii) mild wear resultinq from the formation of oxide layers on both the pin specimen and transferred particles adhering to the track, (iii) a milder wear, due to the attainment of a uniform track condition. The wear rate measured in (ii) is observed to be proportional to normal load for constant (normal load)^1/2 × (sliding speed) provided that the magnitude of this parameter is insufficient to cause periodic removal of the surface film. This conclusion is shown to be compatible with earlier theoretical predictions when the presence of an oxide layer was pre-supposed. Unlike the coefficient of friction which is primarily determined by the pin surface condition only, the pin wear rate depends on the conditions of both the pin and track surface.     

The effects of load and substrate hardness on the development and maintenance of wear-protective layers during sliding at elevated temperatures

Transitions to low wear rates often occur during sliding between contacting metal surfaces, due to the establishment of high-resistance load-bearing layers. Such layers are developed from compaction of wear debris particles, with adhesion between the particles being an important factor in determining whether the layers are maintained, leading to wear protection, or break down, leading to abrasive wear. They are formed more easily and retained more effectively at higher temperatures, due to increased sintering and adhesion between the debris particles and to enhanced oxidation of these particles. This paper presents the results of a study of the reciprocating sliding wear and friction of dissimilar combinations of pin and disc steel specimens (high-speed steel and high-chrome steel pins and carbon steel discs) at temperatures of 500–600°C, with emphasis on the influence of load and substrate hardness on the development and maintenance of such wear-protective particulate layers. Complex relationships occur between the effects of increased load in producing larger debris particles, in decreasing the critical particle size for establishing the layers and in decreasing the separation between the sliding surfaces, and the effects of hardness of the substrates on the sizes and amounts of wear particles and on the topographies of the wear scars. The relationships are complicated further by oxidation and sintering of debris particles, leading to development of oxide or oxide-containing ‘glaze’ surfaces, and subsequent breakdown of the layers during sliding.     

不同摩擦副条件下Ti-6Al-4V合金的微磨粒磨损行为

采用TE66微磨粒磨损实验机对医用Ti-6Al-4V钛合金在不同摩擦副条件下的微磨粒磨损行为进行研究,考察滑行距离、载荷对其微磨粒磨损的影响,通过观察磨斑形貌,分析其磨损机制。研究结果表明:Ti-6Al-4V合金的磨损量随滑移距离和载荷增加而增加,磨损率则相反,并且硬度较高的Si3N4陶瓷球对合金造成的磨损量和磨损率均低于ZrO2陶瓷球;在不同摩擦副条件下,随着滑行距离和载荷的增加,Ti-6Al-4V合金的磨损机制均由三体磨损转变为二三体混合磨损,所不同的是与Si3N4陶瓷球对摩时合金的混合磨损区域要少于与ZrO2陶瓷球对摩时。     

氮化硅陶瓷球研磨去除机制试验与仿真研究

为研究研磨过程中氮化硅陶瓷球的材料去除形式及磨损行为,结合陶瓷材料动态压痕断裂力学理论,进行陶瓷球研磨加工试验,采用超景深三维显微镜和扫描电镜对研磨后陶瓷球表面进行观察,同时建立单颗金刚石磨粒冲击作用有限元模型并进行仿真研究。试验结果表明:氮化硅陶瓷球表面材料去除以脆性断裂去除和粉末化去除为主,陶瓷球表面残留有大量贝壳状缺陷和呈簇状随机分布的粉末化材料区域;研磨过程中,陶瓷球表面存在擦伤、划伤和凹坑等缺陷;磨粒冲击作用时,表面材料会受微切削作用产生破碎去除,同时也会受挤压作用产生脆性断裂去除,当磨粒以滚动方式作用在陶瓷球表面时,陶瓷球表面更容易形成粉末化去除,且材料去除率更高。仿真结果表明:各磨粒冲击作用方式产生的最大等效应力由大到小的顺序为滚动磨粒变切深、滚动磨粒定切深、磨粒挤压、滑动磨粒定切深,其中,滚动磨粒变切深产生的亚表面裂纹最深。     

Using parallel scratches to simulate abrasive wear

Abrasive wear is currently classified according to different particle dynamics: (a) the sliding of active particles on the sample surface and (b) the rolling of abrasive particles between the surfaces. In this paper, instrumented laboratory tests are used to present a new methodology for the simulation of abrasive wear. The rolling of the abrasives is represented by a sequence of indentations, and the sliding of the active particle by a sequence of scratches. A new piece of equipment was especially developed to reproduce the action of an abrasive particle. Two high resolution sliders drive the sample horizontally while the indenter is moved vertically by another slider. Besides this, a high resolution piezoelectric translator is used to control the indenter movement while a 3D load cell controls the intensity of the process. A worn surface produced in a rubber wheel abrasive wear test was used as the reference for the simulation. Its topography was assessed by using laser interferometry and scanning electron microscopy and showed that the prevailing wear mechanism was parallel scratches. The results showed that the superimposition of scratches is the basis which makes it possible to correlate topographical parameters of the reference to the controlling variables used in the simulation. A special method to describe the average depth of the scratches in function of the distance between them (superimposition) was developed. Wear occurs when superimposition is greater than 80%. The average depth of the scratches increased according to an elevation in the degree of superimposition and to the augmentation of normal load. This simulation methodology produced a surface topographically and morphologically similar to that of the reference.     

金刚石刀具材料粒度、磨削砂轮粒度与刃口质量的关系

聚晶金刚石(PCD)刀具由于其自身的高硬度、高耐磨性的特征,使得刃磨加工极易出现崩刃——呈锯齿状刃口的典型缺陷,因此其机械磨削加工较其它刀具材料来看难度更大。本文针对金刚石刀具常用的加工方式——金刚石砂轮机械刃磨展开试验,主要针对金刚石刀片自身材料颗粒度与磨削砂轮粒度这两方面进行研究。通过收集数据,分析对比,研究金刚石材料颗粒度、磨削砂轮粒度对刀具最终刃口质量的影响。     

Wear of CBN Tools in Ultra-Precision Machining of STAVAX

CBN cutting tools are widely used in ultra-precision machining of STAVAX (specialized stainless steel) mould inserts for injection moulding of optical lenses. This paper will report on experiments carried out to investigate the wear of CBN tools with different grain sizes and various CBN/TiN ratios in ultra-precision machining of STAVAX. The tool-wear characteristics were observed to be greatly dependent on the tool type, hardness of the STAVAX and cutting parameters used. In the machining of STAVAX with a hardness of 55 HRC, fine-scale cavities were formed on the rake face and as such the surface damage acted like a chip breaker resulting in formation of cracks. While the flank faces of all tool types showed a similar wear resistance, it was observed that a combination of a higher percentage of TiN binder and smaller grain size led to greater wear resistance on the rake face. It was found that the formation of cracks on the rake faces could be prevented by means of either increasing the cutting speed or reducing the hardness of the machined workpiece.     

Abrasive wear and its application to digger teeth

Abrasive wear is receiving increased attention particularly as its economic importance is appreciated. Low alloy carbon steels are widely used in the heat treated condition to resist abrasion and, in particular, are used for digger teeth. Little information is available in the literature on field or service wear studies and it was necessary, therefore, to carry out field studies in parallel with a laboratory wear investigation.A particular feature of the field study is the realization that significant wear occurs by rubbing to produce smooth surfaces and surface transformation, as well as wear by cutting and micro-chipping.A laboratory investigation based upon two-body pin-on-disc testing has been used to investigate the wear of a wide range of experimental steels, a manganese steel and a commercial digger tooth steel for comparison. Wear is directly proportional to the load and inversely related to hardness, but not to sliding distance because of the degradation of the abrasive paper. Abrasion increases with harder abrasives and increased abrasive particle size.The analysis of these results, although important from a wear mechanism point of view, shows that there is currently a lack of direct correlation between the field and laboratory studies because of the different surface features developed. Further investigations are proceeding to improve this correlation.     

The wear of high density polyethylene sliding against steel surfaces

The wear of high density polyethylene sliding against steel surfaces was studied with a pin-on-disc machine. The disc surfaces were finished by a turning operation on a lathe, changing the cutting conditions and tool geometries so as to provide varying surface finishes and different numbers of asperity peaks per unit distance. Optical and scanning electron microscopy were used to study the wear particles and the transfer films. It is found that a polymer film composed of layers about 500–1000 Å thick is formed on the metallic surfaces with sharp asperities. The size of the polymer wear particles decreases with increasing number of asperity peaks per unit distance and with decreasing asperity angle. The steady state wear rate increases rapidly with increasing polymer wear particle size. The wear for polymermetal sliding occurs by the mechanism of abrasion.     

TRIBOLOGY ISSUES IN MACHINING

Machining is the process of shaping materials into useful articles by removing the unwanted material. In traditional machining processes such as in cutting and grinding, the unwanted material is removed by mechanical means using a cutting tool. Since the tool makes contact with the workpiece and either the tool, the workpiece, or both are in motion, tribology (i.e., the study of rubbing or sliding) becomes an important issue. Tribology has a crucial and significant role as an enabling technology, since tool wear is a major problem in the production of reliable and cost-effective products. This paper reviews recently published articles related to the wear of cutting tools and grinding wheels. These papers are classified into such areas as the wear process, measurement of wear, reduction of wear through the use of different cutting tools and abrasive materials, strategies used to monitor wear during machining and grinding, and in-process control of machining to compensate for tool wear.     

Wear study of Ni–WC composite coating modified with CeO2

In the present investigation, Ni–WC composite powder was modified with the addition of CeO₂ in order to form a new composition of Ni–WC–CeO₂. The Ni–WC and Ni–WC–CeO₂ compositions were used for coating deposition by high-velocity oxy-fuel (HVOF) spraying process so as to study the effect of CeO₂ addition on microstructure, distribution of various elements, hardness, formation of new phases, and abrasive wear behavior. Further, the effect of load, abrasive size, sliding distance, and temperature on abrasive wear behavior of these HVOF-sprayed coatings was investigated by response surface methodology. To investigate the abrasive wear behavior of HVOF-sprayed coatings four factors such as load, abrasive size (size in micrometers), sliding distance (meters), and temperature (°C) with three levels of each factor were investigated. Analysis of variance was carried out to determine the significant factors and interactions. Investigation showed that the load, abrasive size, and sliding distance were the main significant factors while load and abrasive size, load and sliding distance, abrasive size and sliding distance were the main significant interactions. Thus an abrasive wear model was developed in terms of main factors and their significant interactions. The validity of the model was evaluated by conducting experiments under different wear conditions. A comparison of modeled and experimental results showed 4–9% error. The abrasive wear resistance of coatings increases with the addition of CeO₂. This is due to increase in hardness with the addition of CeO₂ in Ni–WC coatings.     

The role of triboparticulates in dry sliding wear

In this paper, wear processes and mechanisms for wear transitions with sliding time and temperature during sliding of a nickel-based alloy, N80A, in oxygen at temperatures to 250°C are discussed. Transitions in wear from high rates to low rates with sliding time were always observed at all the temperatures investigated. The transitions in wear were usually accompanied by transitions in contact resistance between the rubbing surfaces from nearly zero to positive high values. It was found that wear debris particles were heavily involved in the wear processes. The transitions in wear and contact resistance with sliding time mainly resulted from the development of wear-protective layers following the compaction of wear debris particles on the rubbing surfaces. The adhesion of triboparticulates to each other and to the rubbing surfaces played an important role in the rapid decrease in wear rate with sliding time and with increase in temperature. Processes involved in the development of the wear-protective particle layers and mechanisms for the wear transitions have been described on the basis of experimental observations. The importance of triboparticulates in wear and its implications for wear protection are discussed.     

Tribological behavior of microwave processed copper–nanographite composites

Excellent properties offered by nanographite particles are exploited as a reinforcement to the copper matrix. The effects of graphite particle size, spatial distribution, normal load and sliding speed on the friction and wear performance of microwave sintered copper metal matrix composites were studied using a pin-on-disc tribometer. Copper–nanographite composites show higher wear resistance and low coefficient of friction compared to copper–graphite composites. High surface area of nanographite particles embedded in copper matrix exhibited high adherent graphite tribo-layer at the contact surface. Formed graphite layer reduces the sub-surface deformation of the composite by way of reduced frictional force.     

Effects of supply of fine oxide particles onto rubbing steel surfaces on severe–mild wear transition and oxide film formation

This study is the first to show a quantitative condition required for the establishment of severe–mild wear transition with sliding distance, by studying the effects of supply of Fe₂O₃ particles onto rubbing steel surfaces on the transition and oxide film formation process. The supply of fine Fe₂O₃ particles was found to accelerate the wear transition, and the sliding distance at which the transition occurs was found to increase with particle diameter and applied load. Oxide films are produced on the rubbing surfaces by sintering of the supplied Fe₂O₃ oxide particles. At the severe–mild wear transition, the relative area of oxide films is the same for all diameters of supplied Fe₂O₃ particles. This finding suggests that the transition occurs when the relative area of oxide films reaches a specific value, which is proportional to the area of real contact.     

铁谱磨粒图像的计算机纹理分析

利用计算机图像处理技术，采用灰度共生矩阵方法提取典型磨粒图像的纹理特征参数，作为判断机械设备故障机理的判据之一。通过正常、滑动、切削、疲劳磨粒灰度共生矩阵纹理分析，得到熵、能量、惯性矩等参数的范围。     

Tribological Behavior of Micrometer- and Submicrometer-Size Cenosphere Particulate-Filled Glass Fiber–Reinforced Vinylester Composites Under Dry and Water-Lubricated Sliding Conditions

In this work, the tribological behavior of micrometer and submicrometer cenosphere particulate–filled E-glass fiber–reinforced vinylester composites have been investigated on a pin-on-disc tester under dry sliding and water-lubricated sliding conditions. Three different uniform sizes of cenosphere particles (2 μm, 900 nm, 400 nm) were used as fillers in the glass fiber–reinforced vinylester composites. The weight fraction of cenosphere particles has been varied in the ranges from 5, 10, 15, to 20 wt%. The experimental results show that all of the composites exhibited lower coefficient of friction and lower wear resistance under water-lubricated sliding conditions than under dry sliding. It has been noted that the submicrometer size (400 nm) cenosphere particulates as fillers contributed significantly to improve the wear resistance. It has also been noted that 10 wt% of the cenosphere particles is the most effective in reducing the wear rate and coefficient of friction. Effects of various wear parameters such as applied normal loads, sliding speeds, particle size, and particle content on the tribological behavior were also discussed. In order to understand the wear mechanism, the morphologies of the worn surface were analyzed by means of scanning electron microscopy (SEM) for composite specimens under both dry and water-lubricated sliding conditions.     

The preparation and tribology of spherical nanometric particles of diantimony trioxide SbOx(OH)y

Spherical diantimony trioxide SbO_x(OH)_y with a particle size of 30–70 nm has been prepared using a technique known as ‘ethanol supercritical fluid drying’. The tribological properties of an SN500 oil containing these nanometric particles were measured using a four-ball and block-on-ring tribotester. The wear resistance and load-carrying capacity of the oil were higher, and its friction coefficient lower, than that of the base oil. An excessive nanometric particles content was found to be disadvantageous to the load-carrying capacity of the oil. The spherical nanometric diantimony trioxide appears to work by deposition on the rubbing surfaces and through the rolling action of the spherical particles.     

Effect of the Normal Load on the Release of Aerosol Wear Particles During Abrasion

A study highlighting the aspect of the generation of aerosol wear particles during abrasion is presented. The substrate chosen is a masonry brick which is reinforced with TiO₂ nanoparticles. This is done using a pin on plate arrangement. The material removal mechanism via fracturing is first understood. The parameter chosen for the study is the normal load. The formed aerosols are then characterized by their number concentration, particle size distribution, individual particle shape, size and chemical composition. Having irregular shapes, the aerosol wear particles have unimodal size distributions with 5–7 % (in mass) of Ti content. The size mode increases with the increase in normal load. However, at higher normal loads, while there is an unexpected increase in the wear mass, the maximum concentration of the aerosol particles saturates. During the whole study, no free nanoparticles of TiO₂ were found.