Environmental dependence of ultra-low wear behavior of polytetrafluoroethylene (PTFE) and alumina composites suggests tribochemical mechanisms

Composites of polytetrafluoroethylene (PTFE) and alpha phase alumina produce wear rates that can be nearly five orders of magnitude less than the wear rates of virgin PTFE. The mechanism for this reduction in wear cannot be explained solely by mechanical effects. The influences of oxygen and humidity on the tribological performance of both unfilled PTFE and PTFE/alumina composites were studied. The wear rate of PTFE/alumina composites is dependent on the humidity of the environment; this dependence suggests a tribochemical mechanism is responsible for the ultra-low wear behavior of these PTFE/alumina composites.     

Surface characterization of polytetrafluoroethylene (PTFE) transfer films during rolling-sliding tribology tests using X-ray photoelectron spectroscopy

A disk-on-disk Amsler wear tester simulating the rolling-sliding motion and high pressure during wheel/rail contact, was used to study the wear performance of PTFE including its film transfer and material flow properties. The chemical composition of the transfer film formed on the wheel-disk surface at various test stages were analyzed by X-ray photoelectron spectroscopy (XPS). The friction curve of the PTFE films obtained on the Amsler can be divided into three regions, according to the friction level and disk surface morphology. Initially, there is a rapid increase of friction coefficient which is presumably accompanied by a fast material transfer from pre-coated rail-disk to the wheel-disk surfaces. In the second region, the friction remains stable throughout and the XPS results show the presence of PTFE on the wheel-disk surface which confirms a transfer of material between the two contact surfaces. In addition, the splitting of F 1s and C 1s photoelectron peaks of PTFE, as a result of a discrepancy in surface charging, suggests that the transfer film exists in two forms: thick patch and thin film. With an increase in rolling cycles, the thick patches become thinner, as well as its coverage reduces. By contrast, the thin film gains both in thickness and coverage. Using a simple model, the thin film is calculated to be only a few nanometers thick. At the beginning of the third region, only a thin film is left on the surface. Additional rolling leads to a rapid rise in friction and the transfer film thickness continues to decrease. The evidence supports the removal of PTFE out of the contact zone, and a high friction coefficient (μ = 0.6) is reached at the end of the test indicating an un-lubricated metal-metal contact. No major tribochemical reaction of PTFE is observed during this study.     

Dry sliding wear behaviour of cast high strength aluminium alloy (Al–Zn–Mg) and hard particle composites

This paper describes the results of dry sliding wear tests of aluminium alloy (Al–Zn–Mg) and aluminium (Al–Zn–Mg)–10, 15 and 25 wt.% SiCp composite was examined under varying applied pressure (0.2 to 2.0 MPa) at a fixed sliding speed of 3.35 m/s. The sliding wear behaviour was studied using pin-on-disc apparatus against EN32 steel counter surface, giving emphasis on the parameters such as coefficient of friction, rise in temperature, wear and seizure resistance as a function of sliding distance and applied pressure. It was observed that the wear rate of the alloy was noted to be significantly higher than that of the composite and is suppressed further due to addition of silicon carbide particles. The temperature rise near the contacting surfaces and the coefficient of friction followed reversed trend. Detailed studies of wear surfaces and subsurface deformation have been carried out. The wear mechanism was studied through worn surfaces and microscopic examination of the developed wear tracks. The wear mechanism strongly dictated by the formation and stability of oxide layer, mechanically mixed layer (MML) and subsurface deformation and cracking. The overall results indicate that the aluminium alloy–silicon carbide particle composite could be considered as an excellent material where high strength and wear resistance are of prime importance.     

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.     

Film-forming mechanisms for self-lubricating radial spherical plain bearings with hybrid PTFE/aramid fabric liners modified by ultrasonic

PTFE/aramid woven fabric liners were modified by ultrasonic. With self-made wear tester, tribological properties of the self-lubricating radial spherical plain bearings with modified and unmodified liners over swivel times were investigated. With scanning electron microscope and energy disperse spectroscopy, the film-forming mechanisms were analyzed. Results show: ultrasonic modification can improve tribological performances of the liners. Through ultrasonic modification, continuous and stable PTFE transfer films which had better wear resistance formed in a shorter time. Bearings with modified liners occurred slight adhesive wear, while the bearings with unmodified liners occurred serious adhesive wear and abrasive wear during the test process.     

Thermal diagnostics of friction in sliding bearings with account for propagation of heat and movement of shaft

A method for the thermal diagnostics of friction in a sliding bearing is considered for the case when a three-dimensional mathematical model of the thermal process taking into account the motion of the shaft is used. Basic relations for restoring the specific power of the frictional heat generation in the friction zone of the bearing using temperature data and results of computational experiments are presented, which show the stability of a solution of the corresponding inverse boundary problem to errors of the temperature data.     

Calculation of Stribeck curves for (water) lubricated journal bearings

This paper describes a mixed elastohydrodynamic lubrication (EHL) model for finite length elastic journal bearings. The finite element method was employed to discretise the coupled system of 2D–3D Reynolds-structure equations and to compute Stribeck curves at constant load. As underrelaxation strategies have been found to be insufficient for an iterative solution of this problem, artificial dynamics have been added to the numerical structure equations in order to solve for stationary solutions of the fluid–structure problem. An ideal plastic asperity contact model together with an effective film thickness formulation according to Chengwei and Linqing was employed in order to compute the contact pressure in mixed lubrication. The method presented in this paper is applied to a typical water lubricated journal bearing problem. Computed Stribeck curves are presented and the numerical performance of the method is evaluated.     

PTFE/铜网复合材料衬垫自润滑关节轴承的试验研究

建立了自润滑关节轴承的摆动工况模拟试验方法和试验装置，试验评价了PTFE／铜网复合材料衬垫的关节轴承在不同载荷条件下无油润滑的摩擦磨损性能。结果表明：随着载荷自20kN增大至40kN，该轴承摩擦系数和线磨损量均有所增大，摩擦状态也发生了变化；40kN载荷已达到或超过该衬垫关节轴承的承载极限。     

Analysis of tapered land aerostatic bearings for combined radial and thrust loads (yates' configuration)

In this paper the analysis of tapered land aerostatic Yates' bearings for supporting combined radial and thrust loads is presented. Air flow in the journal and thrust bearings is expressed in terms of the Reynolds equation and the Navier-Stokes equations respectively. The pressure distributions in the bearing clearance are obtained by solving these equations using a finite difference numerical technique. The effects of various design and operational parameters on the performance of the combined journal and thrust bearing are reported. In conclusion, guidelines for the optimal design of such bearings are suggested.     

Novel Technologies for Compact Electron Linear Accelerators (Review)

Instruments and Experimental Techniques - This paper reviews new technologies that make it possible to implement such modern principles of development and creation of applied linear electron...     

Effect of heat treatment on the sliding wear behaviour of aluminium alloy (Al–Zn–Mg) hard particle composite

Effect of heat treatment on the sliding wear behaviour of aluminium alloy hard particle composite was studied under varying applied load and sliding speed, giving emphasis on the parameters such as wear rate, temperature rise, coefficient of friction and seizure pressure. Hardness is improved due to heat treatment irrespective of the material. Maximum hardness is noted when the materials are aged for 6 h. These facts have been discussed on the basis of nature of worn surface produced after wear. In the present investigation, aging time has been varied from 4 to 10 h at a regular increment of 2 h.     

Turning titanium metal matrix composites (Ti-MMCs) with carbide and CBN inserts

Despite excellent mechanical and physical features of titanium metal matrix composite (Ti-MMC), hard and abrasive ceramic particles within the matrix structure, as well as high price, may lead to severe difficulties on machining and machinability of Ti-MMCs. Review of literature denotes that only limited studies are available on machining Ti-MMCs with commercial cutting tools under various cutting conditions and cutting tools/inserts. Furthermore, limited studies are available on machinability attributes of Ti-MMC under various cutting conditions used. Therefore, to remedy the lack of knowledge observed, this work intends to report turning Ti-MMCs with carbide, and cubic boron nitride (CBN) inserts under various cutting conditions. The mean values of surface roughness (R_a) and directional cutting forces, as well as flank wear (V_B) were studied as the machinability attributes. The microstructural evaluations were conducted to discover the wear modes. Furthermore, the statistical tools were used to present the factors governing machining attributes studied. Adhesion, abrasion, and oxidation were observed as the principle wear modes on the flank sides of the tested inserts. According to experimental results and statistical analysis, the R_a and V_B could be controlled by cutting parameters only when CBN inserts were used. Despite the inset used, factors governing both responses were not identical. Although average cutting forces were directly affected by cutting parameters used, however, the relatively low correlation of determination (R²) of directional cutting forces can be attributed to effects of cutting speed, elevated temperature in the cutting zone as well as rapid tool wear which are all correlated to others.     

Phosphoryl tris(diethanolamide) (DAP) — A new additive for water-based and ethylene-glycol-based hydraulic fluids and lubricants

A new additive to improve the lubricating properties and rolling contact fatigue resistance of non-flammable water-based and ethylene-glycol-based hydraulic fluids is described. Results of sliding and rolling four ball tests and full-scale pump tests are given.     

一种新的简便实用的供毛细管电泳与电感耦合等离子体质谱联用的接口

介绍了一种由德国GKSS研究中心A.Prange和D.Schaumloffel设计再经他们与美国CETAC公司联合，进一步开发成功的供毛细管电泳（CE）和电感耦合等离子体质谱（ICP-MS）联用的商品化的接口-CEI-100的性能和应用。本文的目的是开拓国内的ICP-MS在元素化学形态分析方面的应用。     

滑块型直线驱动并（混）联机构新型驱动装置及其变胞性研究

提出将钢丝伺服驱动作为并（混）联机构的驱动方式,该驱动方式是一种新型的具有较高精度的直线驱动方式,其原理为：通过伺服电机驱动使钢丝绳规则有序地缠绕在卷筒上并拖动滑块平台实现较长距离的往复直线运动。设计了一种单轴钢丝绳伺服精密直线驱动装置,介绍了其结构组成和工作原理,建立了其运动学计算模型;同时还研究了滑块型直线驱动并（...     

Microstructural and wear behavior of hypoeutectic Al-Si alloy (LM25) grain refined and modified with Al-Ti-C-Sr master alloy

Present article reports the microstructure and wear behavior of grain refined and modified Al-7Si-0.3Mg (LM25) alloy. Combined grain refinement and modification is achieved by inoculating LM25 melt with various inoculation levels (0.2, 0.5 and 1.0 wt%) of a novel Al base master alloy containing Ti, C and Sr (synthesized in the authors’ laboratory) at 720 °C. The wear resistance of LM25 alloy improves with the addition of this master alloy up to 0.5 wt%. It is observed that α-Al cell size and morphology of the eutectic silicon of LM25 alloy have significant effect on the wear resistance of the alloy.     

中高密度钨镍合金粉末注射成形(MIM)工艺参数的优化

在丰庆FC-80型注塑机上,用粉末装载量为53vol%的90W-7Ni-3Fe喂料成形打印座.用正交实验的方法研究了"射胶"面板上"射一"的压力、速度、时间之间的关系及其最优工艺参数组合.实验结果表明,在喂料温度为120℃,保压压力和保压时间分别为40bar和3s的实验条件下,"射一"的压力、速度、时间之间存在着显著的交互作用,压力和时间、压力和速度的交互作用大于任一因素的单独作用,我们对这种交互作用做了定性的描述.实验条件下的最优工艺参数组合为压力120bar,速度20%,时间6s.     

In Vacuo Tribological Behavior of Polytetrafluoroethylene (PTFE) and Alumina Nanocomposites: The Importance of Water for Ultralow Wear

Polytetrafluoroethylene (PTFE) is widely regarded as an excellent candidate for solid lubrication in vacuum. However, it is often precluded from many practical applications due to its intrinsically high wear rate. Over the past decade, it has been discovered that small loading fractions of alumina nanofillers can increase the wear resistance of PTFE by three to four orders of magnitude. This dramatic increase in wear resistance has in turn prompted numerous tribological studies to examine the robustness of this performance. In this study, the wear and friction behavior of unfilled PTFE and PTFE and alumina nanocomposites were evaluated under a broad range of vacuum environments from 760 to 4 × 10^?6 Torr. The nanocomposites of PTFE/alumina showed a dramatic increase in wear of over two orders of magnitude at the highest vacuum conditions. There appears to be an optimal vacuum environment around 1–10 Torr, in which these samples achieved the lowest wear rates of approximately 2.5 × 10^?7 mm³/(Nm).