Effects of lubricants on friction and wear of Ti(CN)/1045 steel sliding pairs

The friction and wear properties of Ti(CN)/1045 steel rubbing pairs were investigated under dry and lubricated conditions by using a pin-on-disk tribometer. The selected speed range was 0.8 to 3.2 m/s and the load range was 58.8 to 235.2 N. Distilled water and a mineral oil (no additives) were used for lubrication, respectively. The wear of Ti(CN) ceramic under dry conditions was caused mainly by adhesion between the rubbing surfaces and the microfracture of Ti(CN). With the load and speed increasing, the adhesion and diffusion between rubbing surfaces increased and resulted in wear increasement of Ti(CN). Because of the brittleness of ceramics, the microfracture wear of Ti(CN) increased rapidly when the load was raised to some high values. The lubricating and cooling effects of the lubricants could improve the frict on and wear. Compared with water, oil was much better in improving the tribological properties. The analysis results obtained from XPS and AES examinations showed that ferrous oxide was produced on the wear scars, which could reduce the adhesion between the rubbing surfaces to some extent. The lubricating effects of the oil under boundary lubrication conditions were attributed to the formation of carbon films on the rubbing surfaces.     

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.     

T8钢/Al2O3陶瓷副极压抗磨减摩添加剂的协同效应研究

利用Falex摩擦磨损机考察了T8钢/Al_2O_3。陶瓷摩擦副在油性剂T451与极压抗磨剂T306作用下的摩擦学性能:用扫描电子显微镜(SEM)观察试销表面磨损状态;采用俄歇电子能谱仪分析了摩擦表面元素化学成分。结果表明:T8钢/Al_2O_3陶瓷摩擦副在T451、T306复配作用下表现出良好的减摩抗磨协同作用;随着T451质量分数的增加,其减摩抗磨性能增强,而随着T306质量分数的增加,其减摩抗磨性能减弱。在已完成的试验方案中,最佳的复配比例为:2％T451 1％T306。AES分析表明T451与T306复配时产生协同作用的主要原因为油性剂T451的存在使T8钢试销摩擦表面形成厚的富磷层。在文中的试验条件下,T8钢/Al_2O_3摩擦副的磨损形式为磨料磨损和摩擦化学(腐蚀)磨损。     

Slurry abrasion response of surface engineered Ti6Al4VELI

Titanium alloys, by virtue of their outstanding combination of properties, continue to evolve as direct replacements for steels in offshore production systems to meet the challenging offshore application conditions. However, the wider use of titanium and its alloys is frequently retarded by their reputation for poor tribological behaviour. It is because of this simple engineering scenario that comparative tribological behaviour of surface engineered Ti6Al4VELI in abrasive slurry has been evaluated to identify treatments capable of improving its wear behaviour. To best simulate potential application conditions, sliding wear tests were carried out using a block-on-wheel test configuration in abrasive mud slurry. The wear volumes lost from the surface engineered Ti6Al4VELI test blocks ranged from negligibly small for substrates plasma sprayed with either WC–Co, Ni–Cr or Mo, to approximately twice that measured for a steel test block in the cases of untreated, shot peened, electroless Ni plated and anodised Ti6Al4VELI. Hard chrome plated material and thermochemically treated material demonstrated a certain degree of wear, which however, was significantly less than that found for the steel block.     

Examination of tribological properties of plasma surface layer using special test equipment

The hardness, adhesion, and tribological behaviour of magnetron-deposited coatings (TiN and (Ti,Al)N) have been determined and related to microstructure composition. To enhance the adhesion of the coating, plasma nitriding of substrates was employed. Wear behaviour, coefficient of friction and contact temperature were measured using computerised data acquisition and processing. The bonding force between the coated samples and counter material was monitored and controlled by newly designed and constructed equipment, to keep a constant level of load during sliding. With the new hardware and software, it was possible to monitor on-line the development of the wear process. The hardware consisted of PC computer, piezoelectric transducer, sensors with high sensitivity, microprocessor-controlled measuring system, AD/DA transformer, and multichannel plotter. The wear zone morphology and characteristics of the surface layer structure and other important properties were investigated using scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD). Energy dispersive X-ray analysis (EDAX) of the wear scars on pins provided essential information on the wear characteristics. Based on the results, the correlations between the mechanical properties, the surface structure, and tribological characteristics are explained.     

Tribological Behaviour of Polymeric Coatings: II. SCF‐Reinforced PEEK Nanocomposite Systems

This paper focuses on coatings based on poly(ether ether ketone) (PEEK) applied to metal substrates and their tribological investigation. Short carbon fibres (SCF), graphite, and 300 nm titanium dioxide (TiO₂) and zinc sulphide (ZnS) particles were used as filler materials for the PEEK. These filler materials and their combinations were found to have a significant influence on the tribological behaviour of the corresponding PEEK compounds. One of the compounds (PEEK6) was found, especially at higher temperatures and under higher normal loads, to be a good coating material showing superior tribological behaviour. For PEEK6, a specific wear rate and a coefficient of friction (COF) lower than those for the best commercially available PEEK compound (PEEK4) were measured. For specific test parameters, PEEK6 showed a COF of less than 0.1. The tribological results were also compared with those of a conventional sliding bearing material based on poly(vinylidene fluoride) (PVDF).     

Tribological properties of few-layer graphene oxide sheets as oil-based lubricant additives

The performance of a lubricant largely depends on the additives it involves. However, currently used additives cause severe pollution if they are burned and exhausted. Therefore, it is necessary to develop a new generation of green additives. Graphene oxide (GO) consists of only C, H and O and thus is considered to be environmentally friendly. So the tribological properties of the few-layer GO sheet as an additive in hydrocarbon base oil are investigated systematically. It is found that, with the addition of GO sheets, both the coefficient of friction (COF) and wear are decreased and the working temperature range of the lubricant is expanded in the positive direction. Moreover, GO sheets has better performance under higher sliding speed and the optimized concentration of GO sheets is determined to be 0.5wt%. After rubbing, GO is detected on the wear scars through Raman spectroscopy. And it is believed that, during the rubbing, GO sheets adhere to the sliding surfaces, behaving like protective films and preventing the sliding surfaces from contacting with each other directly. This paper proves that the GO sheet is an effective lubricant additive, illuminates the lubrication mechanism, and provides some critical parameters for the practical application of GO sheets in lubrication.     

碳酸酯对Ti6Al4V/钢摩擦副摩擦磨损性能的影响

采用SRV型微动摩擦磨损实验机分别考察了Ti6Al4V-钢摩擦副在2种碳酸酯润滑下的摩擦磨损性能,并利用扫描电子显微镜和X射线光电子能谱仪分析了Ti6Al4V磨斑表面形貌和典型元素的化学状态。结果表明,2种碳酸酯作为Ti6Al4V/钢摩擦副的润滑剂所表现出的减摩抗磨和承载能力优于其相对应的脂肪醇;载荷和频率明显影响Ti6Al4V/钢摩擦副在碳酸酯润滑下的摩擦磨损行为;碳酸二-2-乙基己酯所表现出的减摩抗磨和承载能力明显优于碳酸二辛酯;2种碳酸酯对Ti6Al4V/钢摩擦副的润滑机制为在Ti6Al4V磨损表面形成吸附膜,从而起到减摩抗磨的作用。     

Surface behaviour of as-Cast Al–Fe intermetallic composites

In order to produce energy-efficient material for tribological applications, Al–Fe inter-metallic composites have been produced by liquid metallurgy route. Iron content of the composites varies from 1.67 to 11.2 wt.%. These composites have been tested for their wear properties at different parameters. Debris and wear tracks have been studied in detail to see the surface effects during dry sliding and have been correlated to wear properties. Observations show that low loads and sliding velocities are dominated by oxidative debris and largely covered wear track surface with smooth oxide layer is observed. Whereas metallic debris dominates at higher loads and sliding velocities and highly deformed wear track surface with deep grooves and gross delamination were observed. Further, wear rate is seen to increase continuously with load whereas with sliding velocity it attains a minima after initial decrease and then increases continuously. Low solubility of iron supports the formation of FeAl₃ and an increase in hardness from 95 to 179 VHN continuously improves the wear resistance with increase in percentage iron.     

Effects of Normal Load,Sliding Speed,and Surface Roughness on Tribological Properties of Niobium under Dry and Wet Conditions

The effects of normal load, sliding speed, and surface roughness on the friction and wear of high-purity niobium (Nb) during sliding without and with an introduction of water were systematically investigated. Increasing the normal load or sliding speed decreased the friction of the Nb under the both dry and wet conditions because the increased wear of the Nb decreased the interfacial shear strength between the steel ball and Nb by promoting the surface roughening and the production of wear debris. However, the Nb tested at the lowest sliding speed under the lowest normal load with water exhibited the lowest friction and wear due to the formation of oxide layer on the wear track. The friction and wear of the Nb tested under the dry condition decreased with increased surface roughness because the higher interfacial shear strength between the steel ball and smoother Nb resulted in the earlier breakdown of the native oxide layer and direct contact between the steel ball and Nb. However, increasing the surface roughness of the Nb increased its friction and wear under wet conditions, probably due to the easier breakdown of the oxide layer that formed on the rougher surface during sliding. The tribological results clearly showed that the introduction of water during sliding had a significant influence on the tribological properties of the Nb.     

Thick rutile layer on titanium for tribological applications

In the present work, efforts have been made to oxidise the titanium surface, followed by very slow cooling to produce a thick and adherent oxide layer. The response of titanium to oxidation at various temperatures and timings has been investigated, in terms of layer thickness, phase evolution, surface morphology, oxide layer–substrate adhesion, hardness and tribological characteristics. A variety of experimental and analytical techniques, including X-ray diffraction, field-emission scanning electron microscopy, scanning electron microscopy, micro-hardness and tribological testing, have been used to characterise the resultant thermal oxidised surfaces. The results showed that a thick oxide layer with rutile TiO₂ and oxygen diffused Ti structure can be produced, which exhibited excellent adhesion with the titanium substrate, low friction and superior wear resistance during pin-on-disc sliding tests and thus good potential for tribological applications.     

Effects of Nd:YAG Laser Surface Treatment on Tribological Properties of Cold-Sprayed Ti-6Al-4V Coatings Tested against 100Cr6 Steel under Dry Condition

The surfaces of cold-sprayed Ti-6Al-4V (Ti64) coatings were laser irradiated with different laser powers of 50–200 W to study the effects of Nd:YAG laser surface treatment on their tribological properties. The hardness of the laser-treated Ti64 coatings became higher with higher laser power due to the more rapid cooling caused by a larger temperature difference between the coating temperature and room temperature. The wear of the laser-treated Ti64 coatings tested against 6-mm 100Cr6 steel balls under dry condition at room temperature decreased with increased laser power as a result of their increased surface wear resistance associated with their increased surface hardness. It could be concluded that the laser surface treatment of the cold-sprayed Ti64 coatings improved their surface wear resistance compared to that of the untreated Ti64 coatings.     

HIP-Si3N4陶瓷/45#钢副干摩擦和水润滑下摩擦学性能

利用MPX-2000型盘销式摩擦磨损试验机考察了HIP—Si3N4陶瓷／45^#钢副在干摩擦和水润滑下的摩擦磨损性能；用扫描电子显微镜观察了试件表面的磨损状态；采用X射线电子能谱仪分析了摩擦表面的化学成分：结果表明：干摩擦条件下，HIP—Si3N4陶瓷的磨损速率比45^#钢小，45^#钢发生粘着磨损，HIP—Si3N4陶瓷发生了脆性断裂和脱落；水润滑条件下，摩擦表面产生了Si(OH)4反应膜，降低了磨损，主要是化学腐蚀磨损。     

QPQ表面改性层和镀铬层干摩擦状态下磨损特性的研究

在M-2000型摩擦磨损试验机上,对QPQ表面改性层和镀铬层干摩擦状态下的滑动摩擦特性进行对比试验研究,在扫描电子显微镜下观察磨痕的微观形貌,分析2种处理层的磨损机制。结果表明,在磨合阶段,QPQ表面改性层的磨损量较镀铬层的大,而在稳定磨损阶段,QPQ表面改性层的磨损率和摩擦因数均小于镀铬层;在磨合阶段,QPQ表面改性层的磨损机制主要为轻微的磨粒磨损和黏着磨损,镀铬层主要为严重的磨粒磨损,而在稳定磨损阶段,QPQ表面改性层的磨损机制主要为氧化磨损,镀铬层主要为黏着磨损。     

Modelling sliding wear: From dry to wet environments

Corrosive species in various forms exist widely in the environment and can significantly affect wear behaviour of materials, usually accelerating wear. Under conditions where the environments are seemingly non-deleterious in terms of corrosivity, some species from the environment can still affect the tribological behaviour of materials. It is thus extremely important to recognise the roles of reactive species in affecting the tribological processes and to understand the processes of tribo-corrosion interactions. In this paper, the mechanisms of wear debris generation and the roles of reactive species in the generation of wear debris during sliding wear in gaseous or aqueous environments are discussed. The effect of environment on the development of wear-protective layers is described. Based on the proposed mechanisms, mathematical models for sliding wear in both dry and aqueous environments are outlined, and the validity of the models is assessed against experimental data in sliding conditions.     

Tribological Behavior of Electrodeposited Ni-Fe Multilayer Coating

In the present study, the sliding wear behavior of pulse-electrodeposited multilayer Ni-Fe coatings as a function of pulse parameters including frequency and duty cycle has been studied using pin-on-disc tests against an Al₂O₃ counterbody. Sliding wear was investigated with respect to the coefficient of friction (COF), worn surfaces, wear rate, and wear debris. The results of COF with sliding distance revealed a two-region state. At the start of the test the COF was higher, which was due to high stress at the contact region and the occurrence of delamination wear. Then the COF was collapsed as a result of pin penetration and decreased stress at the contact region. The intensity of delamination is decreased at the later stage. The wear resistance of multilayer coatings is increased with increasing frequency and decreasing duty cycles as a consequence of grain refinement and hardness enhancement.     

Mechanical and Tribological Properties of Ca/P-Doped Titanium Dioxide Layer Produced by Plasma Electrolytic Oxidation: Effects of Applied Voltage and Heat Treatment

Plasma electrolytic oxidation (PEO) is a technique that produces a hard oxide layer on the titanium surface where its properties can be tailored by changing the process parameters or by a posterior heat treatment (HT). In this work, a TiO₂ layer with different crystallinity was produced by PEO with different applied voltages (250 to 400 V) and post-HT at 600°C. Our aim was to evaluate the influence of the PEO voltage and HT on the mechanical and tribological properties of anodized Ti. There is an increase in pore size, oxide thickness, and Ca/P ratio for the oxide layer with the applied voltage during the PEO process. X-ray diffraction (XRD) results indicated an increase in the crystalline rutile phase in the oxide layer with voltage and HT. Nanoindentation shows an increase in the oxide hardness and elastic modulus with increased voltage and HT, leading to an improvement in the wear resistance.     

Ti6Al4V/WC-Co干摩擦性能研究

利用Optimal SRV高温摩擦磨损试验机,研究干摩擦条件下钛合金(Ti6Al4V)对硬质合金(WC-Co)的摩擦学性能.研究了载荷、温度与滑动速度对摩擦过程的影响,通过磨损区微观形貌表征分析了磨损机理.结果表明:Ti6Al4V与WC-Co的摩擦系数波动剧烈,产生了严重的黏滑摩擦,且随着载荷、温度与滑动速度的增加,黏...     

Characterization of wear scar surfaces using combined three-dimensional topographic analysis and contact resistance measurements

In this paper, a technique for the quantitative characterization of wear scar surfaces, using combined three-dimensional topographical analysis and contact resistance measurements, is introduced. Parameters for the characterization of wear surfaces, developed during sliding of pin-on-disk specimens in oxygen at high temperature, such as wear volume, roughness, average wear depth on the disk specimen, surface coverage by wear-protective oxide layers and their distributions over the wear surface, are presented and calculated. Such analyses provide more effective data for the analysis of wear processes and wear mechanisms.This method has been applied to the analysis of dry reciprocating sliding wear of a nickel-base alloy, N80A, at temperatures to 600°C. It was found that there was usually a difference between the wear rates of the pin and the disk. This difference increased with increase in temperature, the wear of the pin being much less than that of the disk at the higher temperatures. Although the total wear of both the pin and the disk decreased considerably with increase in temperature, the damage to the disk, judged by the wear depth of the scar, was much higher at elevated temperatures than at low temperatures. The roughnesses of the wear surfaces generally increased with increase in temperature. Less than 50% coverage of the scar surfaces by wear-protective oxide layers was sufficient for the severe-to-mild wear transition. However, the distribution of the wear-protective layers over the wear surfaces was non-uniform. Most of them were concentrated near the centre of the scar, along the sliding direction, under the present conditions. These features of the wear scar surfaces were mainly related to the adhesion and compaction of wear debris particles onto the wear surfaces, leading to development of the wear-protective layers at the various temperatures.     

Friction and wear behaviour of partially stabilised zirconia in reduced pressure atmospheres containing organic compounds: Potential for process lubrication of ceramics

Friction and wear tests were used to evaluate a partially stabilised zirconia (PSZ) disc rubbing against a PSZ pin in a high-vacuum sliding tester. The surrounding atmosphere contained an organic compound vapour (either benzene, acetone, methane or methanol) at a reduced pressure. In order to understand the mechanism of the tribochemical reaction, the sliding conditions, velocity, and load were varied. During the sliding test, the friction coefficient, surface electrostatic voltage, and adsorption behaviour were measured dynamically. After the sliding test, the worn surfaces were analysed with EPMA and TOF-SIMS to characterise the components and the molecular weight of the reaction products. The formation of sticky reaction products was observed on the sliding surface in benzene and acetone vapours. These products acted as lubricants, reducing the friction coefficients and wear rates. Analysis suggested that such sticky reaction products contained molecules up to 1000 atomic mass units (AMU).