Wear resistance of amorphous-crystalline detonation coatings with solid lubricant additive in vacuum

Detonation amorphous-crystalline coatings Zr–Si–B that additionally contain solid lubricant additive as an anti-friction component in the form of the dispersed molybdenum disulfide have been developed. The high wear resistance of coatings that contain molybdenum disulfide has been noted. In a study of the surface layer, photomicrographs of friction surfaces on which activation processes take place have been used in electron diffraction analysis. The wear resistance of the coatings has been established, which enabled the creation of separating juvenile thin film surface of an object that represented the product of oxygen-free structures based on chemical elements of intermetallic phases included in the coating composition.     

Study of the Performance of Copper Coatings Formed by Electroplating and Deformation Cladding with a Flexible Tool

The results of comparative tests of copper coatings formed by electroplating and deformation cladding with a flexible tool (DGFT) under ultimate loads that cause breakage and burrs have been presented. The number of cycles of lateral bending that cause the copper coating to peel and the sample to break, as well as coefficient of sliding friction and the wear of samples during the friction of a lubricant-free spherical indenter on the flat surface of the copper-plated steel disks with substrate hardnesses of 20, 50, and 70 HRC, have been accepted as the performance standards. During the peeling test under bending, it has been found that cladded coatings were not peeled off from the basic material, even in the case when experimental samples were broken, and the peeling of coating in the samples with galvanic coatings has been observed on half of the first bending cycle. Based on the results of the tribotechnical tests, it has been found that copper coatings formed using the above technologies contribute mainly to a reduction in the coefficient of sliding friction on friction surfaces compared to samples without coatings. However, under loads that cause burrs, galvanic coatings have smaller values of the coefficient of sliding friction compared to cladded coatings.     

Tribological performances of ZDDP and ashless triphenyl phosphorothionate (TPPT) as lubricant additives on Ti–N and Ti–Al–N coated steel surfaces

Abstract

In recent years, there has been much attention on the effects of lubricant additives on the friction and wear properties of surface coatings. However, little research has been conducted to investigate the influence of antiwear additives on the tribological performances of titanium nitride (Ti–N) and titanium aluminium nitride (Ti–Al–N) coatings. It has been reported that introducing aluminium into Ti–N coatings enhanced their oxidation resistance. In this study utilising a pin on cylinder tribometer, lubricants containing zinc dialkyl dithiophosphate (ZDDP) or a more environmentally friendly alternative, ashless triphenyl phosphorothionate (TPPT), were used. Experimental results revealed that ZDDP and TPPT helped to reduce wear on both coatings through the formation of a tribofilm, although it was also found that both additives increased the friction coefficient on both surfaces. Based on overall findings, this paper suggests the use of TPPT as a suitable ZDDP replacement for providing wear protection on Ti–N and Ti–Al–N coatings.     

Some Environmental Factors Affecting Surface Coating Formation with Lubricating Oil Additives

Dynamic friction and static immersion tests in which oil temperature was varied and dynamic friction tests in which load was varied have been run on steel balls with oil blends containing seven commercial additives. Analyses of the ball surfaces by X-ray fluorescence have shown that significant surface coating formation is initiated at calculated surface temperatures of from 250 to 350 F for most of the additives studied. Although the surface coating “thickness” generally increased with temperature, the rate of increase was generally different for the static and dynamic tests. Both surface temperature and mechanical shearing appear to influence the reactions responsible for the surface coatings. Used oil analyses showed that base oil oxidation, additive decomposition, and, in some cases, sludge formation became detectible at temperatures corresponding to the start of significant surface coating formation. The results suggest that in situ polymerization may be an important phenomenon occurring on rubbing surfaces.     

Structural and chemical study of C/C composites before and after braking tests

The oxygen, nitrogen, and hydrogen contents of three kinds of C/C composites used for brake discs, before and after braking tests, have been measured by a combustion-infrared method. The morphologies of wear debris have been observed by SEM, and the relationships between their oxygen, nitrogen, and hydrogen contents and crystal structures and friction properties have been established. The results have shown that the oxygen, nitrogen, and hydrogen contents of the C/C composites are mainly determined by structural defects, and are independent of the degree of anisotropy; the greater the number of lattice defects, the higher the contents of oxygen, nitrogen, and hydrogen. Oxygen, nitrogen, and hydrogen were desorbed during the braking tests, but they were re-adsorbed on the friction surface and wear debris in greater amounts after braking. The oxygen content directly affects the friction behavior; the greater the amount of oxygen desorbed, the greater the increase in friction coefficient, that is, the worse the stability of friction.     

Tribological properties of composite multilayer coating

Abstract

The use of surface coatings is emerging as one of the most important approaches in reducing friction and wear in various tribological applications. Even though single layer coatings have a wide range of applications, the performance of the single layer alone may not always be adequate to meet the desired tribological property requirements. Hence, coatings consisting of multilayers to meet different property requirements in demanding applications are required. In this study, the tribological properties of a graded composite multilayer coating, with a specific layer sequence of MoS₂/Ti–MoS₂/TiBN–TiBN–TiB₂–Ti deposited on tool steel substrate, have been investigated at temperatures of 40 and 400°C respectively. The experimental results from the tests at 40°C have shown that the friction coefficient value ranges between 0·02 and 0·034. It was found that the deposition parameters influenced the friction and durability of the coatings. Higher substrate bias was found to result in higher friction, and the coating deposited at high substrate bias and low N₂ flow showed the lowest durability. The friction coefficient and durability of the coatings were found to be highly dependent on temperature. At high temperature, the friction coefficient increases almost threefold, and the durability decreases significantly.     

Friction and wear behaviors of MoS2/Zr coated HSS in sliding wear and in drilling processes

MoS2 metal composite coatings have been successful used in dry turning, but its suitability for dry drilling has not been yet established. Therefore, it is necessary to study the friction and wear behaviors of MoS2/Zr coated HSS in sliding wear and in drilling processes. In the present study, MoS2/Zr composite coatings are deposited on the surface of W6Mo5Cr4V2 high speed steel(HSS). Microstructural and fundamental properties of these coatings are examined. Ball-on-disc sliding wear tests on the coated discs are carried out, and the drilling performance of the coated drills is tested. Test results show that the MoS2/Zr composite coatings exhibit decreases friction coefficient to that of the uncoated HSS in sliding wear tests. Energy dispersive X-ray(EDX) analysis on the wear surface indicates that there is a transfer layer formed on the counterpart ball during sliding wear processes, which contributes to the decreasing of the friction coefficient between the sliding couple. Drilling tests indicate that the MoS2/Zr coated drills show better cutting performance compared to the uncoated HSS drills, coating delamination and abrasive are found to be the main flank and rake wear mode of the coated drills. The proposed research founds the base of the application of MoS2 metal composite coatings on dry drilling.     

The Effect of DLC Coating Thickness on Elstohydrodynamic Friction

The application of surface coatings has been shown to reduce friction in elastohydrodynamic lubrication (EHL), not only in the mixed and boundary regime when asperity interactions occur, but also in the full film regime. Several studies suggest that the full film friction reduction is due to a violation of the no-slip boundary condition and thus slip is taking place between the solid and the liquid. Another hypothesis proposes that the full film friction reduction is due to the low thermal conductivity of diamond-like carbon (DLC) coatings. In this work, two DLC coatings with the same composition, but different thicknesses, are investigated with uncoated steel specimens as a reference, all with the same surface roughness. Friction tests in a ball-on-disk machine show that both coatings reduce friction compared to the uncoated reference case in full film EHL. The thicker coating is significantly more effective at reducing friction than the thinner one at a maximum friction reduction of 41 % compared to 29 % for the thinner coating. Moreover, contact angle measurements, surface energy measurements, and spreading parameter calculations show no statistically significant differences between the two coatings, suggesting that the friction reduction capabilities of coatings in full film EHL cannot be described by solid–liquid interactions alone. The difference in friction reduction between the specimens in this work is mainly attributed to different thermal properties.     

Monitoring of Wear Characteristics of TiN and TiAlN Coatings at Long Sliding Distances

TiN and TiAlN thin hard coatings have been widely applied on machine components and cutting tools to increase their wear resistance. These coatings have different wear behaviors, and determination of their wear characteristics in high-temperature and high-speed applications has great importance in the selection of suitable coating material to application. In this article, the wear behavior of single-layer TiN and TiAlN coatings was investigated at higher sliding speed and higher sliding distances than those in the literature. The coatings were deposited on AISI D2 cold-worked tool steel substrates using a magnetron sputtering system. The wear tests were performed at a sliding speed of 45 cm/s using a ball-on-disc method, and the wear area was investigated at seven different sliding distances (36–1,416 m). An Al₂O₃ ball was used as the counterpart material. The wear evolution was monitored using a confocal optical microscope and surface profilometer after each sliding test. The coefficient of friction and coefficient of wear were recorded with increasing sliding distance. It was found that the wear rate of the TiAlN coating decreases with sliding distance and it is much lower than that of TiN coating at longer sliding distance. This is due to the Al₂O₃ film formation at high temperature in the contact zone. Both coatings give similar coefficient of friction data during sliding with a slight increase in that of the TiAlN coating at high sliding distances due to the increasing alumina formation. When considering all results, the TiAlN coating is more suitable for hard machining applications.     

The respective role of oxygen and water vapor on the tribology of hydrogenated diamond-like carbon coatings

The tribological behavior of diamond-like carbon coatings (DLC) strongly depends on the chemical nature of the test environment. The present study proposes to explore the influence of water vapor and oxygen on the friction behavior of a hydrogenated DLC coating exhibiting ultralow friction in ultrahigh vacuum (friction coefficient below 0.01). Using a UHV tribometer, reciprocating pin-on-flat friction tests were performed in progressively increasing or decreasing partial pressures of pure oxygen and pure water vapor. The maximum gaseous pressures of oxygen and water vapor were 60 hPa and 25 hPa (1 hPa = 100 Pa), respectively, the second value corresponding to a relative humidity (RH) of 100% at room temperature. It was found that, for the pressure range explored, oxygen does not change the ultralow friction behavior of DLC observed in UHV. Conversely, water vapor drastically changes the friction coefficient at pressures above 0.5 hPa (RH = 2%), from about 0.01 to more than 0.1. Electron energy loss spectroscopy and in situ Auger electron spectroscopy have been performed to elucidate the friction mechanisms responsible for the tribological behaviors observed with the two different gaseous environments. In all cases no significant oxidation has been observed either inside the wear scars or in the wear debris particles. Ultralow friction is systematically associated with a homogeneous carbon-based transfer film. The higher friction observed at partial pressure of water vapor higher than 0.5 hPa, is associated with a thinner transfer film. Consequently friction seems to be controlled by the transfer film whose kinetics of formation strongly depends on the partial pressure of water vapor. This revised version was published online in August 2006 with corrections to the Cover Date.     

Mechanisms of friction of bicomponent coatings of thermodynamically incompatible metals produced using vapor condensation on cryogenic surfaces

Comparative tribotests of bicomponent Al–Pb and Al–Sn coatings produced using the codeposition of the metals from the vapor phase on glass substrates having room temperature and cooled to–100°С have been carried out. It has been found that changes in the mechanisms of the friction of the cryogenic coatings are related to conditions of their condensation. If the dimensions of the structure units of the coatings are similar, the tribological characteristics of these coatings are inversely proportional to the strength and the adhesion of their components. The most fusible metals are recommended for use as the solid-lubricating component of the coatings, since they have lower strength and surface energy.     

Tribological studies of coated pistons sliding against cylinder liners under laboratory test conditions

The presence of coatings and surface topography play an important role in the tribological performance of sliding components. Depending on the coating used, it is possible to reduce friction and/or reduce wear. However, although there may be low friction and wear‐resistant coatings suitable for use in pistons, some coatings may hinder the tribological performance by changing the lubrication regime or by preventing additives from their intended function through chemical mechanisms. In this work, piston skirt segments extracted from a commercial aluminium alloy piston were coated with a diamond‐like carbon (DLC) coating, a graphite–resin coating or a nickel–polytetrafluoroethylene (Ni–PTFE) coating and were tribologically tested using a reciprocating laboratory test rig against commercial grey cast iron liner segments. The tribological tests used commercial synthetic motor oil at a temperature of 120 °C with a 20 mm stroke length at a reciprocating frequency of 2 Hz. Results showed that the graphite–resin coating, although it may serve as a good break‐in coating, wears rapidly. The Ni–PTFE coating showed friction reduction, whereas the DLC coating wore off quickly due to its small thickness. Furthermore, the higher hardness of the DLC coating relative to the cast iron liner surface led to pronounced changes on the liner counterface by polishing. In contrast with the uncoated piston skirt segments, all of the coatings prevented the formation of a visible tribochemical film on the cast iron surface. Copyright © 2012 John Wiley & Sons, Ltd.     

硅酸盐粉体作为润滑油添加剂在金属磨损表面成膜机制

在润滑油中添加蛇纹石硅酸盐粉体,采用MM-200摩擦磨损试验机研究了45#钢-45#钢摩擦副磨损表面的自修复陶瓷膜层形成机制,借助SEM及EDAX测试分析自修复陶瓷膜层的表面形貌及表面成分组成。结果表明摩擦能量对硅酸盐添加剂在磨损表面形成自修复膜层有很大的影响:自修复膜层为氧化物陶瓷材料,主要成分来自于硅酸盐添加剂。在低载荷300 N时,摩擦因数减小,硅酸盐添加剂不能转移到磨损表面,不能形成自修复膜层,仅仅起到减磨作用。下试样的失重随磨损时间增加而增加;在试验时间为20 h时,试样失重达到最大值,随后试样的失重反而减小。在载荷为600 N、900 N,试验时间30 h摩擦磨损后,在金属表面形成自修复保护膜,磨损表面比较平整光滑,无明显的片层剥落和犁沟,摩擦发生在自修复陶瓷材料之间,摩擦因数增加。硅酸盐添加剂在机械剪切作用下变形,在金属的磨损表面上铺展,并且在摩擦磨损过程中不断向摩擦表面转移,形成了均匀光滑的自修复膜层。自修复膜层隔离了金属摩擦表面的直接接触,摩擦磨损发生在自修复膜层之间,有效地降低了金属的磨损。     

高能离子源清洗对AlCrN刀具涂层结构及性能的影响

采用自主研发的离子源增强多弧离子镀设备,研究涂层沉积前不同清洗工艺对基材表面粗糙度以及所制备的AlCrN涂层的表面形貌、硬度、膜基结合力、摩擦磨损和切削性能的影响。研究结果表明,高能Ar⁺清洗可以更有效清洁基材表面。与传统弧源清洗技术相比,经高能离子源清洗后的基体表面粗糙度降低,沉积态涂层的表面粗糙度更低。相比于传统弧源清洗工艺,高能Ar⁺清洗可以显著提高膜基结合强度,达到48.7 N,摩擦因数和磨损率均降低,涂层刀具寿命提高了3倍。     

Tribological properties of combined molybdenum coatings formed by electric-spark alloying on stainless steel

To improve the operational properties of the parts of machines made of quenched stainless steel 30X13, the surface were hardened by electric-spark alloying (ESA) with combined coatings (molybdenum + chromium and molybdenum + bronze). The results of investigations showed the correlation between the wear resistance of coatings and their hardness. It has been noted that the roughness of all alloyed coatings after tribological tests lowered, while the roughness of unalloyed surface of steel 30X13 increased. The smallest coefficient of friction has been established for samples alloyed with the molybdenum + bronze combined coating.     

Experimental determination of static and dynamic coefficients of sliding friction of epilam-coated materials

The effect of the method for depositing epilam coatings on materials on the static and dynamic coefficients of sliding friction is experimentally studied. Experiments were carried out using the pin-on-plate arrangement under dry friction conditions at a constant velocity of sliding under pressures of 0.5–5 MPa. It has been found that, for a like friction pair made from the 14Kh17N2 steel, the deposition of epilam coatings on materials reduces the coefficients of friction, but the wear resistance of the coated materials changes only slightly because the epilam film has a molecular-layer thickness. Thermovacuum tests carried out at T = 350°C under a pressure of 10^?6 Torr have shown the loss of the antifriction properties of the materials covered with the 6SFK-180-05 epilam.     

Comparative friction characteristics of high-entropy mononitride coatings

The tribotechnical characteristics of nitride coatings in a pair with a diamond on air have been determined. The friction has been applied in the range of velocities of 6–16 mm/s and loads on diamond in the range of 1.5–5.5 N. A decrease in the friction for all nitride coatings under study with a decrease in the slip velocity has been determined. The intensity of periodic wear of nitride coatings decreases with growth in the load and varies from 1.6 × 10^–6 to 5.3 × 10^–6. High-entropy nitride coating possesses higher tribotechnical characteristics relative to mononitride coatings.     

Extreme Pressure Lubricant Additives Interacting on the Surface of Steel- and Tungsten Carbide–Doped Diamond-Like Carbon

Certain diamond-like carbon (DLC) coatings offer excellent tribological properties under both dry and oil-lubricated sliding conditions. However, the underlying mechanisms under lubricated conditions are generally not fully understood, especially when performance depends on strong tribochemical interactions with lubricant additives. The aim of the present work is to explore the friction and wear performance of steel and tungsten carbide (WC)-doped DLC (WC-DLC) surfaces in the presence of different types of extreme pressure (EP) and nitrogen–sulfur-based (NS) additives. Tribological tests were performed on a ball-on-disc test rig, and X-ray photoelectron spectroscopy (XPS) was used for physical and chemical characterization of the tribofilms. It was observed that EP and NS additives significantly reduced the wear of WC-DLC surfaces in comparison with tests conducted on steel surfaces. XPS indicated that the additive interactions on the WC-DLC surface formed a distinctive tribofilm that promoted better friction and wear performance. The higher concentration of carbon compounds and lower concentration of oxygen compounds in the tribofilm significantly improved friction and wear characteristics.     

Features of triboformation of the steel surface layer using lubricating materials modified with nanodispersed β-sialon

The results of triboengineering tests have revealed the effectiveness of β-sialon nanodispersed particles as an additive to lubricating materials oiling heavily loaded friction units. The method of X-ray structural analysis has established that use of β-sialon as an additive leads to the appearance of steel structures in the surface layer distinct in having a larger parameter of the crystalline lattice, reduced relative mean quadratic micro-deformation, and sparser dislocations, ensuring better triboengineering characteristics of friction couples. The main tribological effect of β-sialon in the lubricating material is that the mechanical energy of deformation converts into the chemical energy of formation of a new structure—an ordered surface layer.     

Ni-P-MoS2自润滑复合镀层的研究

在钢铁材料的基体上沉积了N i-P-MoS2复合镀层,借助于SEM、XRD、热分析仪、显微硬度计、磨损试验机等设备对镀层的表面形貌、成分、结构、硬度以及摩擦磨损性能进行了分析。结果表明:MoS2粒子的加入不影响基质金属N i-P合金的结构和晶化转变,N i-P-MoS2复合镀层无论在干摩擦状态还是油摩擦状态均具有较N i-P镀层低的摩擦因数,但是2种状态下磨损失重都很大,因而它是一种具有优异减摩性能的复合镀层。