Study of Abrasive Wear Volume Map for PTFE and PTFE Composites

The potential of this work is based on consideration of wear volume map for the evaluation of abrasive wear performance of polytetrafluoroethylene (PTFE) and PTFE composites. The fillers used in the composite are 25% bronze, 35% graphite and 17% glass fibre glass (GFR). The influence of filler materials, abrasion surface roughness and applied load values on abrasive wear performance of PTFE and PTFE composites were studied and evaluated. Experimental abrasive wear tests were carried out at atmospheric condition on pin-on-disc wear tribometer. Tests were performed under 4, 6, 8 and 10 N load values, travelling speed of 1 m/sec and abrasion surface roughness values of 5, 20 and 45 μm. Wear volume maps were obtained and the results showed that the lowest wear volume rate for PTFE is reached using GFR filler. Furthermore, the results also showed that the higher is the applied load and the roughness of the abrasion surface, the higher is the wear rate. Finally it is also concluded that abrasive wear process mechanism include ploughing and cutting mechanisms.     

Stress‐dependent fatigue mechanisms of CrC–NiCr coatings in rolling contact

The rolling contact fatigue (RCF) behaviour of the plasma‐sprayed CrC–NiCr cermet coatings under different tribological conditions of contact stress was investigated. Four sets of fatigue life data of coatings were characterized by Weibull distributions. The failure modes of the coatings were classified on the basis of worn surface observations of the failed coatings. Results showed that the failure mode of the coating was related to the magnitude of contact stress. The RCF life data of the coatings tested at high contact stresses exhibited high scattering, because the bimodal distribution of the fatigue life data was seen in the Weibull plot. Generally, when the contact stress was relatively low, the coatings were prone to fail in spalling and cohesive delamination. However, at high contact stress, the coatings often failed due to interfacial delamination. At different contact stress levels, the maximum shear stress amplitude was the main reason for the generation of spall and delamination.     

Wear behaviour and rolling contact fatigue life of Ti/TiN/DLC multilayer films fabricated on bearing steel by PIIID

In order to improve the friction and wear behaviours and rolling contact fatigue (RCF) life of bearing steel materials, Ti/TiN/DLC (diamond-like carbon) multilayer hard films were fabricated onto AISI52100 bearing steel surface by plasma immersion ion implantation and deposition (PIIID) technique. The micro-Raman spectroscopy analysis confirms that the surface film layer possess the characteristic of diamond-like carbon, and it is composed of a mixture of amorphous and crystalline phases, with a variable ratio of sp²/sp³ carbon bonds. Atomic force microscope (AFM) reveals that the multilayer films have extremely smooth area, excellent adhesion, high uniformity and efficiency of space filling over large areas. The nanohardness (H) and elastic modulus (E) measurement indicates that the H and E of DLC multilayer films is about 32 GPa and 410 GPa, increases by 190.9% and 86.4%. The friction and wear behaviours and RCF life of DLC multilayer films specimen have also been investigated by ball-on-disc and three-ball-rod fatigue testers. Results show that the friction coefficient against AISI52100 steel ball decreases from 0.92 to 0.25, the longest wear life increases nearly by 22 times. In addition, wear tracks of the PIIID samples as well as wear tracks of the sliding steel ball were analyzed with the help of optical microscopy and scanning electron microscopy (SEM). The L₁₀, L₅₀, L_a and mean RCF life L of treated bearing samples, in 90% confidence level, increases by 10.1, 4.2, 3.5 and 3.4 times, respectively. Compared with the bearing steel substrate, the RCF life scatter extent of Ti/TiN/DLC multilayer films sample is improved obviously.     

Wear of coatings in wool-severing applications

Various surface treatments; including thermally sprayed ceramic coatings, titanium nitride (TiN) deposited by physical vapour deposition and nitrogen implantation processes, have been applied to combs and cutters that are used for wool severence. A series of laboratory and field tests have been carried out to evaluate the relative merits of the different treatments.     

PTFE/金属自润滑复合材料的磨损性能研究

用MM-200磨损试验机对纯PTFE板料、3层复合材料(DU)及钉板型复合材料的工作层在干摩擦定载荷条件下的磨损性能进行了研究;用SEM对磨损试样表面和磨屑形貌进行观察和分析.结果表明:铜和PTFE的复合能提高PTFE的耐磨性并改变其磨屑的形成机理;铜钉板取代传统的平钢板,不仅提高了材料的承载能力,也大大提高了材料的耐磨性能;在干摩擦条件下,纯PTFE板料主要发生粘着磨损和微凸体刨切,3层复合材料主要是磨粒磨损,钉板型复合材料的磨损机理是粘着磨损和磨粒磨损共同作用.     

Observation of contact phenomena in glass/metal systems

Microscopic observation of the wetting of glass sessile drops on platinum has revealed the presence of glassy droplets in the vicinity of the wetting edge. A study of the droplets has Clarified the deposition process and the influence of the platinum grain structure on their nucleation and growth, and has allowed comment to be made on the mode of grainboundary movement during grain growth.     

Characterization of WC/Co coatings on metal substrates

In the present work, WC/Co coatings were obtained by electro-thermal explosion directional spraying technology. The performances including microstructure, elements distribution, hardness, elastic modulus and wear resistance of the coatings were investigated by means of SEM, EDAX, nano-indentation test, friction and wear test, respectively. Results show that WC/Co coatings are characterized by compact construction, good bond, high hardness and elastic modulus. The WC/Co coatings also have outstanding wear resistance.     

Wear and friction of aramid fibre and PTFE filled composites

The most widespread reinforcements and lubricants used for wear applications include polytetrafluoroethylene (PTFE), silicone, glass fibre, carbon fibre and aramid fibre. Of these, PTFE and aramid fibre play a key role in the production and performance of a huge variety of seal components. This article describes work undertaken at LNP Engineering Plastics to optimise the aramid fibre loadings in systems with and without PTFE. Mechanical properties, tribological performance and cost were all considered, and in addition the transfer film formed when these composites are wearing was examined.     

Application of thin-film interference coatings in infrared reflection spectroscopy of organic samples in contact with thin metal films

A thin dielectric IR-transparent interlayer is introduced between an IR-transparent medium of incidence and a thin metal film. The interlayer increases the intensity of light on the metal/sample interface at certain wavenumbers. By computations, the reflectivities of the system "calcium fluoride (CaF)-germanium (Ge)-gold (Au) sample" are analyzed as a function of incidence angle and Ge layer thickness. Absorbance spectra with acetonitrile as a sample are recorded for different angles of incidence and polarizations and compared to computations. A characteristic feature of the absorbance spectra is the occurrence of interference fringes distributed between 1000 and 6000?cm(-1), i.e., over the complete mid-IR wavelength range into the near-IR. These fringes could be used in analytical spectroscopy.     

金属/Hg1-xMnxTe接触的I-V特性研究

分别采用溅射和蒸发镀膜法在Hg1-xMnxTe试样表面形成了Au/Hg1-xMnxTe和Al/Hg1-xMnxTe接触,并用Aligent4155c I-V测试仪对其I-V特性进行了测量,随后对试样在10%NH4F:10%H2O2:H2O中进行了钝化处理,并对处理后的试样再次进行了I-V测量,对于测试结果用热电子发射-扩散理论进行了分析.结果表明:Au与Hg1-xMnxTe形成了良好的欧姆接触,而Al与Hg1-xMnxTe形成了具有整流特性的肖特基接触,其肖特基势垒的理论推算值为0.38eV.钝化处理后的试样,其表面漏电现象明显降低,Au/Hg1-xMnxTe接触的电流下降幅度在0.1V时最大,为76.1%;而Al/Hg1-xMnxTe接触在0.2V时最大,为93.2%.随着偏压的进一步增大,两种接触的电流减小的幅度都逐渐变小.     

Wear of metal by rubber

Rates of wear have been determined for steel and bronze scrapers sliding over rubber surfaces. The wear rates were found to depend strongly upon the particular elastomer used, varying by orders of magnitude even though the other ingredients in the compound and the physical properties of the rubber were largely unchanged. In the absence of oxygen the metal scrapers were found to wear away much faster in general; by a factor of 5 to 50 times, depending upon the elastomer. Butyl rubber was anomalous in this respect, however, causing three times greater wear in air than in nitrogen. These diverse observations are attributed to the direct attack upon metals of free radical species generated by mechanical rupture of elastomer molecules during abrasion. The rate of metal wear is closely correlated with the stability of polymeric radicals formed in this way. When the radical is highly reactive it is thought to take part primarily in internal reactions and thus cause little wear of the scraper. On the other hand, relatively stable polymer radicals appear to attack metals vigorously.     

Efficient stress evaluation of stationary viscoelastic rolling contact problems using the boundary element method: Application to viscoelastic coatings

The present work is a contribution towards the development of a new and novel technique to evaluate the contact stresses between linear-viscoelastic cylinders under stationary rolling contact loading. A two-dimensional numerical model is considered using a reference system fixed to the contact zone and including the effects of Coulomb friction between the rolling cylinders. The contact stresses are determined by solving a non-linear system of equations coming from the combination of the discretized boundary element viscoelastic equations and the fulfillment of the contact conditions, expressed using projection functions. The results obtained for viscoelastic rollers are compared with those from other authors for different rolling velocities, showing good agreement and consistency. Finally, some results for viscoelastic coatings are presented and commented.     

混杂填料增强PTFE复合材料的摩擦磨损性能

利用M-2000型摩擦磨损试验机考察了载荷以及纳米TiO2/SiO2与玻璃纤维的混合填料对PTFE复合材料摩擦磨损性能的影响,用扫描电子显微镜观察了复合材料磨损后的表面形貌.结果表明:纳米材料与玻璃纤维的协同作用显著改善了材料的摩擦磨损性能,其中纳米TiO2与玻纤填充复合材料的耐磨性较好,磨损量降低了2～3个数量级,其磨损机制是低载荷下为磨粒磨损.高载荷下为疲劳磨损;纳米SiO2与玻纤填充复合材料的摩擦系数与PTFE相近,磨损机制是低载荷下为磨粒磨损,高载荷下为粘着磨损和表面微犁削磨损.     

Elastic stresses between curved bodies in rolling contact

An outline of the development of the elastic theory of contact stresses is presented. The literature is discussed in some detail, and equations for the sub-surface stresses are given for several important cases. The effects of surface shear stresses associated with tangential forces and rolling with spin are also considered.     

纳米蒙脱石填充PTFE和UHMWPE的摩擦磨损性能

用纳米蒙脱石(nano-MMT)对聚四氟乙烯(PTFE)和超高分子量聚乙烯(UHWMPE)进行填充改性,在往复式滑动摩擦试验机上进行摩擦磨损实验,用扫描电镜观察了材料摩擦表面形貌.结果表明:nano-MMT可以提高PTFE和UHWMPE材料的耐磨性,而PTFE基和UHWMPE基复合材料的摩擦系数无明显增大.与UHMWPE相比,nano-MMT更能提高PTFE基材料的耐磨性;nano-MMT/PTFE复合材料比nano-MMT/UHMWPE复合材料具有更低的摩擦系数和更好的导热性;纯PTFE、纯UHWMPE和10%nano-MMT/PTFE复合材料磨损机理主要为粘着和犁沟效应,而10%nano-MMT/UHWMPE复合材料表现为犁沟和疲劳机制.     

Plasma-assisted deposition of metal and metal oxide coatings

A combination of physical vapour deposition and plasma-assisted chemical vapour deposition techniques were used to deposit Cu-, Ni- and Sn-rich SnO/SnO2 coatings on metal and ceramic substrates. Cu and Ni were deposited on Al alloy 6061 substrates and Ni deposition was also performed on glass microscope slides and commercially pure alumina substrates. Sn-rich SnO/SnO2, on the other hand, was coated on stainless steel and pure Cu substrates. A direct-current plasma system was used to deposit the pure metals in vacuum with a resistively heated tungsten boat that was coated with alumina. All samples were sputtered for 20 min in an argon:hydrogen (1:1) atmosphere at a pressure of 300 mTorr. To reduce contamination and oxidation of both substrates and deposited layers, Cu and Ni coatings were made with argon:hydrogen (2:1) carrier gas. Sn-rich tin oxide coatings were deposited in a pure argon atmosphere (no hydrogen) to allow for the oxidation of Sn deposits on the stainless steel and copper substrates. Investigations of coated surfaces by scanning electron microscopy and X-ray diffraction showed coatings to be smooth, continuous and pure. Deposition rates showed this application to provide a very high rate when compared with chemical vapour deposition and metal–organic chemical vapour deposition techniques. Scratch tests results prove good attachment of the coatings to their respective substrates. © 1998 Chapman & Hall