Sliding tribological behavior of AlCrN coating

The sliding tribological behavior of the PVD AlCrN coating against Si₃N₄ ball have been investigated by using the CETR multi-functional UMT-2 test system under two sliding conditions (bidirectional and unidirectional). Reciprocating sliding tests (bidirectional) were performed under varied normal loads (5, 10 and 20 N) at sliding velocity of 0.48 m/min. Ball-on-disc tests (unidirectional) were performed at varied sliding velocities (0.48 and 5 m/min) under normal load of 5 N. The wear scars of the coating were evaluated by surface profilometer, scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDX), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), and the sliding wear mechanism of the coating was consequently discussed. The results showed that AlCrN coating had excellent anti-abrasion properties. Both the normal load in reciprocating sliding test and the sliding velocity in ball-on-disc test had significant influence on the sliding tribological behavior of the AlCrN coating. The combination of abrasion and oxidation was the main sliding wear mechanism for the AlCrN coating. The wear resistant and thermally stable oxides formed by the tribo-chemical reactions of chromium and aluminum protected the AlCrN coating against wear admirably.     

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。     

Tribological Behavior of TiAlN,AlTiN, and AlCrN Coatings at Boundary Lubricating Condition

In this study, ~?3.5 µm thick multilayer titanium alumina nitride (TiAlN), alumina titanium nitride (AlTiN), and alumina chromium nitride (AlCrN) coatings were deposited on the H13 steel surface by cathodic arc physical vapor deposition (CAPVD) method. The tribological performance of the coatings was evaluated by a tribometer at boundary lubrication condition. Then, coating surfaces were observed by optical microscope, optical profilometer, and atomic force microscope to evaluate the morphological changes, wear volumes, and tribofilm thickness. Also, scanning electron microscopy (energy dispersive X-ray) and X-ray photoelectron spectrometry analyses were applied to coating surfaces for the tribochemical evolution of the tribofilm. Results showed that AlCrN coating performed the best tribological behavior at boundary lubricated condition, when compared to TiAlN and AlTiN coatings and it can be used as a wear resistant cam tappet coating in internal combustion engines.     

磨料粒度对表面微织构纯钛干摩擦性能的影响

为了提高钛及钛合金钻具在超深钻探、深海钻探和外太空钻探工程中的减摩抗磨性能。利用激光表面加工技术在工业纯钛（TA2）表面制备了不同参数的点阵微织构。采用MS-T3000摩擦磨损试验机测试了微织构钛合金在不同粒度模拟月壤作用下的摩擦学性能。利用扫描电子显微镜和能谱分析仪分析磨痕形貌及元素含量。研究结果表明：当磨料粒度小于微织构点阵的直径时,磨料压入微织构点阵里,磨料具有滚动和滑动两种运动方式。当粒度大于微织构点阵的直径时,磨料不能完全压入微织构点阵里,磨料对微织构TA2表面产生了滑动犁削作用。由于两种磨料磨损的作用机理不同,同等条件下,小粒度的磨料作用下的微织构TA2的摩擦因数和磨损率较大粒度磨粒作用下的最大减少量分别为50%和53%。考虑磨料粒度与微结构的匹配性,可以大大降低摩擦减少磨损。     

Review of engineered tribological interfaces for improved boundary lubrication

Recent advances in smart surface engineering and coating technologies offer unique possibilities for better controlling friction and wear under boundary or marginally lubricated rolling, sliding or rotating contact conditions. Specifically, such coatings can be tailored to meet the increasingly multi-functional application needs of future engine systems by enabling them to operate in lower viscosity oils with reduced sulfur and phosphorous. Using these technologies, researchers have already pioneered the development of a variety of nano-composite and super-hard coatings providing longer tool life in demanding machining and manufacturing applications. The same technologies can also be used in the design and development of novel coating architectures providing lower friction and wear under boundary-lubricated sliding conditions. For example, such coatings can be tailored in a very special way that while one of the phases can favorably react with certain additives in engine oils to result in an ideal chemical boundary film; the other phases can provide super-hardness and hence resists wear and scuffing. Because of their very dense microstructure and high chemical inertness, these coatings can also provide superior protection against oxidation and corrosive attacks in aggressive environments. The use of solid lubricant coatings may also improve the tribological properties of sliding contact interfaces under boundary lubricated sliding conditions. When fluid and boundary films fails or is broken down, such coatings can carry the load and act as a back-up lubricant. Other smart surface technologies such as laser texturing and/or dimpling, laser-glazing and -shotpeening have also become very popular in recent years. In particular, laser texturing of control or coated surfaces have opened up new possibilities for further manipulation of the lubrication regimes in classical Stribeck diagrams. Controlling dimple size, shape, orientation, and density, researchers were able to modify both the width and the height of the boundary lubrication regimes and thus achieve lower friction and wear at sliding and rotating contact interfaces. Overall, smart surface engineering and coating technologies have matured over the years and they now become an integral part of advanced machining and manufacturing applications. They can also be used to meet the increasingly stringent and multi-functional application needs of demanding tribological applications. In this paper, selected examples of recently developed novel surface engineering and coating technologies are introduced, and the fundamental tribological mechanisms that control their friction and wear behavior under boundary lubrication regimes are presented.     

Tribological properties of flame sprayed Fe–Ni–RE alloy coatings under reciprocating sliding

Fe–Ni–RE self-fluxing alloy powders were flame sprayed onto 1045 carbon steel. The tribological properties of Fe–Ni–RE alloy coatings under dry sliding against SAE52100 steel at ambient conditions were studied on an Optimol SRV oscillating friction and wear tester in a ball-on-disc contact configuration. Effects of load and sliding speed on tribological properties of the Fe–Ni–RE coatings were investigated. The worn surfaces of the Fe–Ni–RE alloy coatings were examined with a scanning electron microscopy(SEM) and an energy-dispersive spectroscopy(EDS). It was found that the Fe–Ni–RE alloy coatings had better wear resistance than the SAE52100 steel. An adhered oxide debris layer was formed on the worn surface in friction. Area of the friction layer varied with variety of sliding speed, but did not vary with load. The oxide layer contributed to decreased wear, but increased friction. Wear rate of the material increased with the load, but dramatically decreased at first and then slightly decreased the sliding speed. The friction coefficient of the material was 0.40-0.58, and decreased slightly with the load, but increased with sliding speed at first, and then tended to be a constant value. Wear mechanism of the coatings was oxidation wear and a large amount of counterpart material was transferred to the coatings.     

激光织构和碳基薄膜复合处理提高钛合金摩擦学性能研究

在重载滑动干摩擦条件下，对比不同织构密度的钛合金表面的摩擦学性能；在耐磨性最好的织构密度钛合金表面再制备碳基薄膜，并与直接在钛合金表面制备的碳基薄膜的摩擦学性能进行对比。结果表明：3种低织构密度条件下，TC4钛合金的摩擦因数减小、磨损率降低；随着织构密度的增大，钛合金材料的摩擦因数变化极小，磨损率有所增加；在织构密度5.95%的钛合金表面制备的碳基薄膜，因织构微凹处产生的小微湍流，减少了摩擦阻力，使得其摩擦因数相比直接在钛合金表面制备的碳基薄膜的摩擦因数有所减小。织构化碳基薄膜的磨损率比钛合金的磨损率降低了99.31%，比直接在钛合金表面制备碳基薄膜的磨损率也降低了约60%，这是因为高接触应力摩擦过程中触发石墨化转变，被磨损的石墨化颗粒碎片嵌入织构微凹中，抑制了摩擦接触界面的磨损行为。     

Assessment and application of TiB2 coating in sliding pair under lubrication conditions

The aim of the present work is to determine the influence of TiB₂ coating on the friction parameters in sliding pairs under lubricated friction conditions. The TiB₂ coating deposited on modified surface layers of ring specimens made of AISI 5045 steel was matched under test conditions with counterparts made from SAE-783 and SAE-48 bearing alloys. Tested sliding pairs were lubricated with 5 W/40 Lotos synthetic engine oil. Tribological properties of the TiB₂ coating were measured using a block-on-ring tribometer. The applied modification technology of the surface layer of steel allowed for obtaining construction material with pre-determined tribological characteristics required for the elements of sliding pairs in lubricated contact. The results showed differences in the wear of bearing alloys, as a result of the interaction between co-operating surface layers and of the physiochemical changes of their surfaces, induced by external forces. Friction resistance and temperature in the friction area in the pair with TiB₂ coating and the SAE-783 bearing alloy are considerably higher than in the pair with the SAE-48 bearing alloy. The SAE-48 bearing alloy is subjected to more intensive wear processes in contact with the TiB₂ coating than the SAE-783 bearing alloy.     

Surface texturing by pulsed Nd:YAG laser

Introducing specific textures on a tribological surface can contribute to friction reduction in sliding contacts. In the present paper, a pulsed Nd:YAG laser emitting at 1064 nm, was used against 100Cr6 steel samples in order to produce well-defined surface micro-pores, which can act as lubricant reservoirs, micro-hydrodynamic bearings as well as traps for wear debris. Due to the high flexibility of the laser system, structural features such as shape, size, density and depth can be varied easily by changing the laser parameters. To optimize the parameters of the laser surface texturing process, an investigation was performed using different pulse numbers, various pulse energies and two different modes (single- and multi-mode). The microtextures were characterized with optical microscopy, scanning electron microscopy (SEM) and by topography techniques. The relationship between the laser processing parameters and qualitative and quantitative profile of the micro-pores was studied. Tribological testing of laser textured surfaces was performed in a low frequency–long displacement reciprocating sliding wear tester under boundary lubrication and results compared to un-textured case. Tribological comparison of textured, textured and lapped, and untextured surfaces shows only minimal influence of texturing for contact conditions investigated.     

Tribological behaviour of DLC coatings compared to different materials used in hip joint prostheses

The goal of the study carried out in the laboratory was to quantify the wear and the friction of two materials used for the manufacturing of hip prostheses. Tests used had to obtain in a short time the tribological behaviour laws of the materials. Tests on a hip simulator have been excluded because their cost and their duration were too high for a program of preliminary development of new materials.

To amplify wear phenomena, dry friction tests were carried out for two configurations: ball-on-disc and pin-on-disc. The influence of the contact pressure at constant sliding velocity on the wear of materials has been clearly shown.

Results obtained with several different tested materials (stainless steel/UHMWPE, stainless steel+DLC coating/UHMWPE, stainless steel+DLC coating/stainless steel+DLC coating, titanium alloy+DLC coating/UHMWPE, titanium alloy+DLC coating/titanium alloy+DLC coating, zirconium dioxide/UHMWPE, alumina/UHMWPE, alumina/alumina) have shown the superiority of DLC coatings. Promising results obtained during this study are in the validation stage on a hip simulator.     

Tribological properties of selected PVD coatings when slid against ductile materials

In this paper, a physical vapour deposited (PVD) deposited TiB₂ coating is compared in dry sliding with commercial PVD titanium nitride (TiN), titanium aluminium nitride (TiAlN) and titanium carbonitirde (TiCN) as to frictional properties and tendency of counter material pick-up. The aim is to investigate if the superior behaviour of the TiB₂ coating experienced in severe sliding applications against aluminium alloys can be extended to other materials with a similarly poor tribological characteristics.A new tribological test for sliding contact has been used. The test configuration involves two crossed elongated cylindrical test specimens which are forced to slide axially against each other at a constant sliding speed and a gradually increasing normal load, while recording the friction. The evaluation is performed by correlating the friction history with the width, topography and composition of the sliding tracks as detected by optical and scanning electron microscopy.Coated cemented carbide (CC) test cylinders have been slid against cylinders of a Ti alloy (Ti–6Al–4V), an Al alloy (Al 7075) and Inconel 718. It was shown that the TiB₂ surface displayed superior friction and anti-sticking properties, when tested against the aluminium alloy. Against the Ti and Inconel alloys no major difference between the coatings could be found. Instead, it is concluded that the friction coefficient is determined by the plastic properties of the counter material since a complete transfer layer instantly builds up on the coating.It proved possible to estimate the friction force from the width of the sliding tracks, the Vickers hardness of the counter material and simple plastic considerations. This estimation also verifies the unexpectedly low friction of all coatings against the Ti alloy.     

The study of tribological properties of laser‐textured surface of 2024 aluminium alloy under boundary lubrication

The tribological property of aluminium alloy is critical for its reliable operation in practical applications. In this paper, the tribological performance of laser‐textured 2024 aluminium alloy is studied in unidirectional sliding tests under boundary lubrication. The dimples were produced on the aluminium alloy surface by using a pulse Nd : YAG laser. The topographical microstructures of these laser‐induced textures were characterised by optical and scanning electron microscopy. In comparison with untextured surfaces, a significant improvement in friction behaviour was observed for the textured surfaces. The influences of dimples density on the tribological properties were investigated. Two types of oil with different viscosities were evaluated as lubricants. It was found that the beneficial effects of laser surface texturing are more pronounced at higher speed and load with higher viscosity oil. The optimum dimples density of 8.5% was found to have a lower friction coefficient. On basis of the experimental results, the mechanism of friction reduction and anti‐wear is proposed. Copyright © 2012 John Wiley & Sons, Ltd.     

Effect of chemical structure of borates on the tribological characteristics of magnesium alloy during sliding

Effects of four borates with different chemical structure on the tribological properties of magnesium alloy in sliding contact with bearing steel were investigated under boundary lubrication using a Timken type tester. It was shown that the borate without active element is not effective at reducing the friction and wear of magnesium alloy, and the borates containing nitrogen, sulfur and chlorine are effective at improving the tribological properties of magnesium alloy. Different active elements have different action characteristics at improving the tribological properties of magnesium alloy. The rubbed surfaces were investigated using Scanning Electron Microscopy (SEM) and X-ray Photoelectron Spectroscopy (XPS), the wear mechanisms were also proposed.     

Tribological Properties of Lubricating Films on the Al-Si Alloy Surface via Laser Surface Texturing

Dimpled textures were prepared by using a pulse solid laser on the surface of Al-Si alloy. The combination of laser surface texturing (LST) and MoS₂ solid lubricant as well as their tribological properties were investigated in this article. The obtained friction and wear data were critically analyzed to investigate how the parameters of texture influence the tribological performance of Al-Si alloy. Furthermore, morphological investigations of the transfer layers on the worn surfaces were performed and the wear mechanisms are discussed. The results show that the combination of LST and solid lubricant improves the tribological characteristics of Al-Si alloy. The friction coefficient of Al-Si alloy: steel friction pairs can be reduced to 0.15 under dry friction. The lubrication mechanism is attributed to a synergetic effect of providing solid lubricant and traps wear debris in the dimples. It was found that the optimum density of structure was 37% for excellent tribological properties.     

Enhanced wear resistance of Ti-5Al-2Nb-1Ta orthopaedic alloy by nitrogen ion implantation

The tribological properties of nitrogen implanted Ti-5Al-2Nb-1Ta orthopaedic alloy was studied by performing lubricated pin on disc tests against ultra high molecular weight polyethylene pins. The results were interpreted on the basis of friction coefficient, wear volume loss and by characterising the wear debris to understand the wear mechanism. The results indicated a decrease in wear rate for implanted samples. Detailed investigations of the dose dependence on wear performance were carried out. The friction and wear data show a clear transition in wear modes between implanted and unimplanted alloys. The wear debris confirms the presence of titanium oxide and titanium oxynitride phases for untreated and nitrogen implanted alloy.     

Tribological Dependence of the High-Performance Ferrous-Based Coating on Different Coating Counterparts in Engine Oil

A ferrous-based coating with significant chromium was fabricated on aluminum alloy substrate using a plasma spray technique. The tribological performance of the as-fabricated ferrous-based coating sliding against different coatings including Cr, CrN, TiN, and diamond-like carbon (DLC) in an engine oil environment were comparatively studied. Results showed that the high hardness of the sprayed ferrous-based coating was achieved due to the dispersion strengthening effect of Cr₇C₃ phase embedded in the austenite matrix. The ferrous-based coating exhibited low friction coefficients when coupled with these four coating counterparts, which could be attributed to the boundary lubricating effect of engine oil. However, both friction and wear of the ferrous-based coating were different when sliding against these different coating counterparts, which might be closely related to the surface roughness, self-lubricating effect, and mechanical properties of the coupled coatings. Ferrous-based coating sliding against CrN and DLC coatings exhibited good tribological performance in engine oil. The best coating counterpart for the ferrous-based coating in an engine was DLC coating.     

Friction and wear behavior of Ni-P coated Si3N4 reinforced Al6061 composites

Al6061 matrix composite reinforced with nickel coated silicon nitride particles were manufactured by liquid metallurgy route. Microstructure and tribological properties of both matrix alloy and developed composites have been evaluated. Dry sliding friction and wear tests were carried out using pin on disk type machine over a load range of 20-100 N and sliding velocities of range 0.31-1.57 m/s. Results revealed that, nickel coated silicon nitride particles are uniformly distributed through out the matrix alloy. Al6061-Ni-P-Si₃N₄ composite exhibited lower coefficient of friction and wear rate compared to matrix alloy. The coefficient of friction of both matrix alloy and developed composite decreased with increase in load up to 80 N. Beyond this, with further increase in the load, the coefficient of friction increased slightly. However, with increase in sliding velocity coefficient of friction of both matrix alloy and developed composite increases continuously. Wear rates of both matrix alloy and developed composites increased with increase in both load and sliding velocity. Worn surfaces and wear debris was examined using scanning electron microscopy (SEM) for possible wear mechanisms. Energy dispersive spectroscope (EDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscope (XPS) techniques were used to identify the oxides formed on the worn surfaces and wear debris.     

镍基合金喷熔层摩擦学行为与机制的研究

采用热喷熔工艺制备了两种镍基合金喷熔层,并选用高锰钢、不锈钢作为对比材料,研究了镍基合金喷熔层的摩擦磨损性能。研究结果表明：镍基合金喷熔层具有良好的耐磨损性能和较低的摩擦系数。镍含量对喷熔层的摩擦学性能有显著影响,高镍含量的镍基合金,其耐磨性能明显优于低镍含量的镍基合金。在低速轻载条件下,镍基合金喷熔层的磨损机理为微观犁削;高速重载时,表现为粘着磨损和磨料磨损,其中高镍含量的喷熔层表面形成了致密的转移膜,有效地降低了磨损率。     

The Tribological Behavior of a Ti-46Al-2Cr-2Nb Alloy Under Liquid Paraffine Lubrication

The tribological behavior of a Ti-46Al-2Cr-2Nb alloy prepared by hot-pressed sintering was investigated under liquid paraffine lubrication against AISI 52100 steel ball in ambient environment and at varying loads and sliding speeds. For comparison, the tribological behavior of a common Ti-6Al-4V alloy was also examined under the same testing conditions. The worn surfaces of the two alloys were analyzed using a scanning electron microscope. The friction coefficient of the Ti-46Al-2Cr-2Nb alloy in the range of 0.13–0.18 was significantly lower than that of the Ti-6Al-4V alloy (0.4–0.5), but comparable to that under dry sliding, which indicated that TiAl intermetallics could be more effectively lubricated by liquid paraffine than titanium alloys. Applied load and sliding speed have little effect on the friction coefficient of the Ti-46Al-2Cr-2Nb alloy. The wear rate of the Ti-46Al-2Cr-2Nb alloy was about 45–120 times lower than that of Ti-6Al-4V alloy owing to Ti-6Al-4V alloy could not be lubricated effectively. The wear rate of the Ti-46Al-2Cr-2Nb alloy increased with increasing applied load, but decreased slightly at first and then increased with increasing sliding speed. The wear mechanism of the Ti-46Al-2Cr-2Nb intermetallics under liquid paraffine lubrication was dominated by main plowing and slight flaking-off, but that of the Ti-6Al-4V alloy was plastic deformation and severe delamination.