Some aspects of improving abrasive resistance

A survey of literature on the structural and phase strengthening of alloys and steel is presented. Methods of strengthening such as mechanical riveting and expanding the length of intergrain boundaries do not increase abrasive wear resistance to hard particle attack. Alloying to increase the interatomic bond forces does not increase abrasive wear resistance. Thus there is a close connection between the modulus of normal elasticity of different metals and the wear resistance.The sharp decrease in dislocation mobility at the brittle transition temperature increases abrasive wear resistance. For a high carbon steel the resistance increases by a factor of 2.5.Increased resistance to attack by abrasive particles (by a factor of 2) can be achieved by preliminary friction treatment of the steel surface (especially by dry frictional contact against low carbon steel) because of the complex phase and structural transformations in the material of the surface that is subjected to frictional contact.     

Improvement of wear resistance of quenched structural steel by nanostructuring frictional treatment

The paper deals with the study of the structure, deformation hardening, and wear resistance under abrasive and sliding friction of quenched structural steel 50 (0.51% of C), which is subjected to frictional treatment by a hard alloy indenter. The resistance of a steel surface layer hardened by frictional treatment to mechanical effects is estimated using the kinetic indentation method. It is shown that frictional treatment yields a considerable increase in the wear resistance of quenched medium-carbon steel tested in pairs with flint and corundum, as well as under the conditions of adhesive wear and boundary friction, due to the hampering of the processes of microcutting, seizure, and plastic deformation. This is favored by the higher resistance of the nanostructured layer to residual deformation during contact loading.     

Lubrication of Solids at High Temperatures

This paper deals with recent work applicable to the problems of high-temperature lubrication carried out in the Laboratory of Physics and Chemistry of Solids, University of Cambridge, England. Three main aspects are considered (a) friction of lamellar solids, (b) lubrication from the gas phase (c) frictional properties of hard metals at high temperatures.     

氧化铜填充双马来酰亚胺摩擦学性能的研究

双马来酰亚胺树脂（简称BMI）是一种耐热性优于酚醛树脂耐高温工程塑料,但存在摩擦系数不稳定,与对偶材料发生较严重的粘着磨损问题。本文选择氧化铜作为摩擦调节剂,研究了氧化铜粉的用量对双马来酰亚胺与硬铝的滑动摩擦磨损性能的影响。并借助于扫描电镜分析了氧化铜提高双马来酰亚胺和铝环耐磨性的作用机理。试验结果表明：氧化铜不仅可以增加BMI的摩擦系数,改善其磨擦特性,使摩擦稳定,而且还可以提高摩擦副的耐磨性,随氧化铜用量增加,滑动副的摩擦系数和耐磨性均增加。摩擦表面的形貌分析表明：氧化铜加入到双马来酰亚胺中可以促使BMI在对偶铝环表面形成牢固的转移膜,转移膜减小了铝环的磨损,同时抑制了BMI复合材料的磨损。     

Low load multiple scratch tests of ceramics and hard metals

Abrasion is caused by the repeated scratching of materials by individual particles in an abrasive, often under fairly light loads. This process has been simulated by carrying out scratch tests on a range of ceramics and hard metals. An array of different scratches was carried out on each sample with a different number of repeats along the same track for each scratch. The magnitude of the damage was measured by the width of the scratches. The frictional force between the indenter and test sample was also measured.

Although the width of single pass scratches in some of the harder materials was smaller than in softer materials, in multiple pass scratches, the final widths of scratches in some of the harder materials were greater than in the softer materials. This was due to differences in the contribution of fracture in the development of damage in multiple pass scratches.

It was found that fracture was a predominant form of damage to both hard metals and ceramics. In the case of the hard metals the fracture was on a fine scale, but with the ceramics fracture occurred on a larger scale, often removing large fragments of material.

These results, and the results of the friction measurements are correlated with the results of a microstructural examination of the mechanisms that occurred. They are also compared with a microstructural assessment of the early stages of wear in the abrasion of these materials.     

The effect of lubricants on deep drawability of zinc-coated steel sheets

The effect of lubricants on deep drawability was studied for two types of zinc-coated steel sheets on a high-speed deep-drawing machine. The drawability of galvannealed steel sheet, GA, at low speeds is significantly improved by friction modifiers, due to reduction in frictional forces around the die radius. In contrast to the results for GA, double layered steel, GAE, which has an Fe-rich alloy coating on the top, and is superior to GA in terms of drawability, is insensitive to changes in the additives. This is mainly because the hardness of the upper coating layer of GAE decreases frictional resistance through a decline in the boundary contact area.     

The wear of ultrafine WC–Co hard metals

The wear performance of ultrafine-grained tungsten carbide–cobalt (WC–Co) hard metals during three-body abrasion and particle erosion has been evaluated and compared to that of similar conventional coarser grained hard metals. The tungsten carbide grain size varied between 0.5 and 3 μm with cobalt contents ranging from 6 to 15%. Silica particles were used in both forms of testing. Erosion was carried out at 60 ms⁻¹ at an impact angle of 75° and abrasion at a velocity of 0.5 ms⁻¹ and a load of 50 N.

The wear resistance of the ultrafine grades was found to be at least double that of the closest conventional fine grained hard metals. These increases in wear performance are considerably higher than any corresponding increase in hardness which is, at most, 25% and is not achieved at the expense of fracture toughness which is maintained at a similar level to that of conventional fine grained hard metals. The increase in wear resistance coincides with a change in the mechanism of material removal. Sub-micron materials experience ductile deformation and bulk removal of material whilst coarser grades display more localised response with extensive fragmentation of the WC grains.     

Metal transfer in the frictional contact of a rough hard surface

The frictional behaviour between a hard rough surface and a soft smooth surface was examined under lubricated and unlubricated conditions. Transfer of soft metal to hard asperities in contact with it caused significant changes in the shape, size and height distributions of the asperities. Thus metal transfer reduced the effect of the initial surface roughness of the hard metal on friction.     

硬夹层中含裂纹的非均质焊接接头的COD研究

本文将焊缝中含有裂纹的高匹配焊接接头或HAZ硬化区中含有裂纹的焊接接头以及过渡层较硬且其中含有裂纹的异种金属焊接接头简化为硬夹层中含有裂纹的非均质中心裂纹板,裂纹平行于硬夹层与软区的分界。用弹塑性有限元方法和云纹实验应运地这种模型的应变场、断裂参量COD等进行了研究。研究结果表明,材料的不均匀性对COD的影响是不可忽略的,特别当名义应力或名义应变较高时更是如此。COD随硬夹层宽度的增加而减小。     

Finite element analysis of the effect of interfacial roughness and adhesion strength on the local delamination of hard coating under sliding contact

The interfacial roughness and the adhesion strength are very important for making a high-quality coating for friction and wear applications. In order to obtain a quantitative understanding concerning the effect of the two factors on the local delamination of hard coatings, finite element analyses concerning the maximum shear stress in a hard coating with various kinds of interfacial roughness and adhesion strength were made under low and high frictional conditions. As a result, local delamination maps for the identification of the local delamination of hard coatings were obtained as a function of the shear strength ratio of coating to substrate and the ratio of coating thickness to half-contact width. Also, the critical contact pressure required to produce local delamination of hard coatings is given.     

斜直井中考虑摩擦时钻柱的正弦屈曲分析

提出了在斜直井中钻柱正弦屈曲分析时对摩擦阻力的处理方法,给出了考虑摩擦阻力时的屈曲平衡方程,建立了相应的微分求积法列式,用微分求积法时平衡方程直接求解。在力学模型中考虑了摩擦因数、重力线密度、钻柱长度和井斜角对临界载荷的影响,并将数值计算结果与实验数据进行了比较。分析表明,提出的在钻柱正弦屈曲分析时对摩擦阻力的处理方法是正确有效的,能够为实验结果提供理论分析基础;在同等条件下,钻柱正弦屈曲临界载荷随摩擦因数的增加而增大;钻柱越长,摩擦阻力对临界载荷的影响越大,在一定程度上,摩擦可以增加钻柱的稳定性。     

Magnetic and eddy-current testing of hardened constructional steel subjected to combined strain-thermal treatment

The potentialities of magnetic and eddy-current methods for testing a structural state, wear resistance, and mechanical properties of steel 50 (0.51 wt. % C) subjected to quenching from 850°C, nanostructurizing frictional treatment with a hard alloy indenter, and tempering at the temperatures of 100–600°C are studied. It is shown that the structural state of constructional steel 50 that is subjected to combined strain-thermal treatment can be tested using the eddy-current method upon low temperature (to 250°C) tempering and in the tempering temperature range of 250–450°C, the coercitimetric method and based on the maximum permeability in the temperature range of 100–350°C, based on the residual magnetic induction for major and minor magnetic hysteresis loops in the temperature ranges of 100–400°C and 250–600°C, respectively, and based on the specific resistivity in the temperature range of 100–300°C. Correlations between electromagnetic parameters and hardness, mechanical properties, wear intensity under the conditions of dry frictional that point to the possibility of using eddy-current and magnetic testing of the quality of optimized strain-thermal treatment, which provides a good complex of wear resistance and mechanical characteristics of constructional steel, were established.     

Frictional hardening and softening of steel 52100 during dry sliding

The behavior of frictional hardening and softening of steel 52100 with different microstructures during dry sliding was studied based on dynamic metallographic analysis. It was demonstrated that such frictional behavior significantly affected wear resistance of the steel. The results showed that anti-softening microstructures exhibited a rather better wear resistance; the difference in the wear resistance of various steels with different microstructures was caused by the difference in the energy consumption in surface layers during wear. These results indicate that the original structures and properties of steels should not be taken as the only criterion for judging the wear resistance. It is necessary to consider the influence of dynamic microstructural changes under specific wear conditions in order to evaluate the wear resistance.     

Low temperature tribology at the B. Verkin Institute for Low Temperature Physics & Engineering (historical review)

This review presents the history of creation and evolution of the Tribology Laboratory at Special Research & Development Bureau of the B. Verkin Institute for Low Temperature Physics & Engineering. It describes the low temperature tribometers designed at the laboratory, gives our understanding of the processes of protective secondary structure formation during friction providing higher wear resistance of materials under extreme frictional stressing conditions, reports the main results on the analysis of friction and wear in metals and alloys, solid lubricants and coatings and other engineering materials at low temperatures in vacuum and in low-pressure gases and also in various cryogenic liquids (liquid nitrogen, liquid hydrogen, liquid helium).     

压力测试平台在燃料泵送系统中的应用

针对燃料泵送系统存在的水击压力过大、气液分离不足以及汽蚀等问题，采用压力传感器和数字信号采集系统建立燃料泵送系统压力测试平台。根据测得的压力信号，对燃料枪关闭瞬间流量、管长、溢流阀调定压力以及主阀弹簧刚度对水击效应引起的峰值压力的影响进行研究，并通过频率分析方法和小波分析方法较精确地获得系统的气液分离值和临界汽蚀压力点。该测试平台不仅能实时可靠地对系统压力进行定量诊断与识别，同时还可以为燃料泵送系统的性能优化提供依据。     

Computation of wear in artificial heart valves.

In order to assist with the prognosis of wear processes in low profile disc heart valves, an approximate haemodynamic theory has been used for the determination of opening and closing dynamics of these valves, together with the most developed theory to date of frictional fatigue. The heart valve element wear was defined by solving the contact problem, which takes account of changes to the contact surface form as a consequence of wear. Calculated values are compared with in vivo wear data for artificial heart valves. The proposed model for estimating wear in artificial heart valves allows an optimization to be made of the wear resistance in available designs and to predict the wear resistance of artificial heart valves at the design stage.     

Kinetic frictional behaviour of alumino-silicate ceramics

The frictional behaviour was experimentally investigated of alumino-silicate ceramics (3Al₂O₃, 2SiO₂) rubbing against a hard steel surface under static and kinetic friction conditions. Tests were carried out on a pin-on-disc machine under both dry and wet contact conditions. Results showed that the frictional behaviour under either static or kinetic conditions was highly dependent on the ceramic body phase transformation which in turn was controlled by the firing temperature during ceramic processing and treatment. Lower friction values were evident when using specimens of ceramic bodies containing a high mullite crystalline phase, which are attained at high firing temperatures. Both the running speed and applied loads had insignificant effects at high loads.During kinetic friction tests lower frictional values were displayed than for static friction tests under wet contact conditions, and under dry conditions when using high mullite ceramic bodies. For specimens of ceramics fired at relatively low temperatures, kinetic friction tests produced higher frictional values than static friction tests.     

非金属硬脆材料加工技术的最新进展

综述了近年国内外非金属硬脆材料加工技术的发展和最新研究成果,主要包括在传统磨削技术基础上发展起来的先进磨削技术,加热、超声和摩擦化学反应等辅助能量加工技术,以及激光、等离子、电火花、磨料水射流等高能束加工技术,展望了超精密加工技术的发展前景,旨在为促进我国的非金属硬脆材料优质、高效、低成本加工技术的快速发展提供借鉴。     

ANALYSIS ON THERMAL ELASTO-PLASTIC ASPERITY CONTACTS OF LAYERED MEDIA

A thermal elasto-plastic asperity contact model is investigated, which takes into account the steady-state heat transfer and the asperity distortion due to thermal elasto-plastic deformations. A hard coating and a soft coating are applied to study the correlations between contact area and contact pressure, average gap and contact pressure, coating thickness and contours of the contact stress distribution, etc. The effects of material properties, coating thickness, frictional coefficient, and the heat input combinations on the stress distribution are investigated and discussed. The frictional heat input increases the maximum value of yon Mises stress. Finally, the appropriate thickness of the hard coating is also discussed. To protect the substrate, one can choose hard coating and the thickness of that is suggested that can be hc=70 Rm.     

Surface wear characteristics of some hard carbons

The surface resistance to damage of homogeneous hard carbons such as glassy low temperature isotropic pyrolytic (LTI) and Ceraphite carbons have been determined by the falling abrasive particle test using SiC grit. Surfaces prepared from within the bulk of the glassy carbon specimens exhibit wear resistance proportional to their microindentation hardness but material near their virgin surfaces shows a lower resistance to this low velocity impact wear. Both pure and silicon-alloyed LTI carbons and Ceraphite material show considerably greater wear than the bulk glassy carbons of the same hardness. However, all of the hard carbons exhibit much greater surface damage resistance than other materials of comparable hardness such as mild steel or soda-lime glass. Microscopic surface examination indicates that brittle fracture is the main wear mode of the hard carbons in this test and the results are interpreted in terms of the microstructural features and characteristic elasticity properties of these solids.