Formation Of Tribochemical Film Research Articles

Tribological Behavior of Si3N4/Ni Composite With Tree-Trunk Ring Structure Under High-Humidity Environment

To achieve the coordination of mechanical properties and tribological performance of ceramic-based materials, a novel Si3N4/Ni composite with a tree-trunk ring structure was developed in this study. Furthermore, the tribological properties of the Si3N4/Ni composite were investigated in a high-humidity environment. The results showed that when the Si3N4/Ni composite disc slid against the Si3N4 pin, a continuous water layer formed on the wear surface of the composite disc due to their good hydrophilicity and the action of gravity. The water layer inhibits the abrasive wear and promotes the formation of tribochemical film. Under the combined effect of the water layer and tribochemical film, the sliding pair exhibited excellent tribological properties (a low coefficient of friction (COF) of 0.05 and wear rate on the order of 10−6 mm3/Nm). However, when the Si3N4/Ni composite pin slid against the Si3N4 disc, due to poorer hydrophilicity and the negative effect of gravity, the sliding pair presented a worse tribological performance.

Superlubricity of PTFE triggered by green ionic liquids

Polytetrafluoroethylene (PTFE) is in the limelight due to its self-lubricating properties and outstanding corrosion resistance. Nevertheless, it suffers from severe adhesive and abrasive wear, resulting in barriers to the achievement of robust superlubricity and reliability of moving parts. Herein, two green protic ionic liquids (ILs) are synthesized using alkyl amine and carboxylic acids with long molecular chains, which are applied in PTFE/steel tribo-pair, showing a robust superlubricity under high contact pressure. Compared with conventional lubricating oils (PAO8, PAO10 and PEG400), as-prepared ILs show the lowest coefficients of friction less than 0.008, and the lowest wear volume of PTFE with the adhesive and abrasive wear of PTFE significantly inhibited. The excellent lubricating performance attributes to the thick and dense Stern layer as well as the formation of tribo-chemical film. This work, for the first time, achieves superlubricity on soft material substrates and guides the lubricants design for PTFE tribological applications.

Optimization of natural polymer additives towards tribological behavioural of bio-oil extracted from peel waste of musa aluminata balbisiana

Bio oil has been given a serious consideration as alternative replacing synthetic lubricant as it is biodegradable, eco-friendly, and obtained from non-conventional energy resources. Following that, this paper study the tribological potentials of peel waste of Musa Aluminata Balbisiana (MBS) oil extract with the addition of natural polymer additives of ethyl acetate (EC) and ethylene vinyl acetate (EVA). The tribological behavior of MBS oil was tested using pin-on-disc tribometer at different loads following American Society for Testing and Materials,ASTM G99-05. In this method, the hemisphere pin was loaded with a normal load varied from 20 N to 100 N at varied temperatures of 27 °C, 40 °C and 100 °C. It was found that the optimum performance in producing the lowest coefficient of friction of MBS oil + EC is 0.5% EC, 40 °C sliding temperature, and 80 N applied load meanwhile the optimum performance of MBS oil + EVA is at 4.0% EV, 100 °C sliding temperature, and 80 N applied load. These results were attributed to the formation of tribo-chemical film which existed as protective layer on sliding surface which act to prevent metal to metal contacted each other’s hence contributed to the favor of frictional reduction. Hence, it can be said that MBS oil has the potentials as an alternative bio-oil in the future.

Effect of additives on a surface textured piston ring–cylinder liner system

ABSTRACTLaser texturing of the surface is a known approach to improve the tribological performance of mechanical systems. Many studies focused on optimising surface texture parameters for the piston-ring cylinder liner (PRCL) system. However, little attention is given to explore the effect of the textured surface on additive film formation. In the present work, the effect of a laser textured surface on the formation of additives tribochemical films and its impact on the tribological performance of PRCL system is studied. Commercially available steel piston ring and grey cast iron cylinder liner are used as samples to carry out the experiments using linear reciprocating tribometer. Experiments are carried out at 75 N load, 0.1 Hz frequency and 80°C temperature, using polyalphaolefin as base oil mixed with different additives. It is found that dimples are interfering in the formation of tribo-chemical films. However, the hydrodynamic effect of dimples is contributing to the improvement of lubrication performance even in the presence of additives.

Oil-soluble ionic liquids as antiwear and extreme pressure additives in poly-\u03b1-olefin for steel/steel contacts

To enhance the lubricating and extreme pressure (EP) performance of base oils, two types of oil-soluble ionic liquids (ILs) with similar anion albeit dissimilar cations were synthesized. The physical properties of the prepared ILs were measured. The anticorrosion properties of ILs were assessed by conducting corrosion tests on steel discs and copper strips, which revealed the remarkable anticorrosion properties of the ILs in comparison with those of the commercial additive zinc dialkyldithiophosphate (ZDDP). The tribological properties of the two ILs as additives for poly-α-olefin-10 (PAO10) with various mass concentrations were investigated. The tribological test results indicate that these ILs as additives are capable of reducing friction and wear of sliding contacts remarkably as well as enhance the EP performance of blank PAO10. Under similar test conditions, these IL additives exhibit higher lubricating and anti-wear (AW) performances than those of ZDDP based additive package in PAO10. Subsequently, X-ray photoelectron spectroscopy (XPS) and energy dispersive spectrometer (EDS) were conducted to study the lubricating mechanism of the two ILs. The results indicate that the formation of tribochemical film plays the most crucial role in enhancing the lubricating and AW behavior of the mixture lubricants.

Understanding evolution of tribo-chemical interfaces during boundary lubrication in manufacturing

Boundary lubrication during manufacturing processes especially at spindles, gears, machining interfaces, and other areas is an aggressive tribological condition resulting in the loss of energy, materials, and overall productivity. Nano-engineered lubricants have been explored to address lubrication challenges at nano/microscopic interfaces. However, lubrication mechanism at nano/microscopic interfaces is not fully understood. This paper reports investigation on tribo-chemical lubricant film formation mechanism using techniques of four-ball tribometer, SEM/EDS, Raman spectroscopy, and TEM to understand morphology, chemistry, and structure at interfaces as lubrication progresses over time. It was found that tribo-chemical film formation showed adaptive characteristics during lubrication for progressive surface protection.

Ionic Grease Lubricants: Protic [Triethanolamine][Oleic Acid] and Aprotic [Choline][Oleic Acid

Ionic liquid lubricants or lubricant additives have been studied intensively over past decades. However, ionic grease serving as lubricant has rarely been investigated so far. In this work, novel protic [triethanolamine][oleic acid] and aprotic [choline][oleic acid] ionic greases are successfully synthesized. These ionic greases can be directly used as lubricants without adding thickeners or other additives. Their distinct thermal and rheological properties are investigated and are well-correlated to their tribological properties. It is revealed that aprotic ionic grease shows superior temperature- and pressure-tolerant lubrication properties over those of protic ionic grease. The lubrication mechanism is studied, and it reveals that strong physical adsorption of ionic grease onto friction surface plays a dominating role for promoted lubrication instead of tribo-chemical film formation.

Effect of laser surface texturing (LST) on tribochemical films dynamics and friction and wear performance

Surface texturing or topographical design is one of the primary techniques to control friction and wear performance of surfaces in tribological contact. Laser surface texturing (LST), whereby a laser beam is used to produce regular arrays of dimples on a surface, has been demonstrated to reduce friction in conformal lubricated contacts. Friction and wear behavior under boundary lubrication is also known to be dependent on the formation and durability of the tribochemical film formed from lubricant additives. In this paper, the effects of LST on the formation and durability of tribochemical films and its consequent impacts on friction and wear behavior in various lubrication regimes were evaluated. Friction and wear tests that cycled through different lubrication regimes were conducted with both polished and LST treated surfaces using a synthetic lubricant with and without model additives of ZDDP and MoDTC mixture. In the base oil without additives, LST produced noticeable reduction in friction in all lubrication regimes. However, with low-friction model additives, friction was higher in tests with LST due to significant differences in the tribochemical film formation in the polished and LST surfaces, as well as the sliding counterface. Continuous tribo-films were formed on ball conterface rubbed against polished surfaces while the films were streaky and discontinuous in ball rubbed against LST surfaces. LST produced more wear on the ball counterface in both base and additized oils. No measurable wear was observed in both the polished and LST flat specimens.

Friction and wear behavior of thin-film ceramic coatings under lubricated sliding contact

Thin film ceramic coatings are increasingly being used in lubricated tribological components. Unfortunately, lubricants formulated with functional additives such as anti-wear and friction modifiers, are usually designed to interact with ferrous material to form tribochemical surface films. When these lubricants are applied to coated surfaces, the effectiveness of the additives is still largely unknown. In this study, we evaluated the friction and wear behavior of several commercially available thin-film ceramic coatings when lubricated with unformulated and fully formulated synthetic oils to assess the impact of lubricant on such coatings. A variety of behaviors were observed for different coatings which can be explained in terms of the differences in tribochemical film formation and properties on the coatings surfaces.

Comparison Friction and Wear Properties of Overbased Calcium Sulfonate Complex Grease and Polyurea Grease

The friction and wear properties of the overbased calcium sulfonate complex grease and polyurea grease were evaluated using an Optimol SRV reciprocating friction and wear tester under the boundary lubrication conditions. The morphologies of the worn surfaces of the AISI 52100 steel discs were observed using a scanning electron microscope (SEM). In addition, the elemental compositions and chemical states of several typical elements on the worn surfaces of the AISI 52100 steel discs were examined by means of X-ray photoelectron spectroscopy (XPS). The results show that the overbased calcium sulfonate complex greases and polyurea grease have stable friction coefficients as low as 0.10-0.11. The calcium sulfonate complex grease has better wear resistance properties than polyurea grease, polyurea grease has better reducing friction properties than calcium sulfonate complex grease, According to the XPS analyses, it is considered that the formation of tribochemical films led to lower friction coefficient and high wear resistance.

Study of tribo-chemical lubricant film formation during application of nanolubricants in minimum quantity lubrication (MQL) grinding

This paper presents the study of mechanism of nanolubricant impingement in minimum quantity lubrication grinding. To study the role of nanolubricants (a new class of advanced lubricants integrating multicomponent chemistries) during workpiece-tool interaction, surface-grinding tests were performed on ductile iron workpieces using an aluminium oxide wheel under varied infeed conditions. The process performance in terms of force ratio, specific energy, and G-ratio has shown substantial improvement when using nanolubricant. Formation of tribo-chemical films of Mo–S–P chemistry complex on the workpiece surface was identified as the mechanism responsible for these improvements.

Tribological Behavior of Si3N4-hBN Ceramic Materials without Lubrication under Different Test Modes

Unlubricated tribological behaviors of silicon nitride–boron nitride (Si 3 N 4 -hBN) composites were investigated with two test modes in air by using a pin-on-disc tribometer. Under upper-disc-on-bottom-pin test mode, the addition of hBN to Si 3 N 4 resulted in a significant decrease of the friction coefficient, from 0.54 for Si 3 N 4 against Si 3 N 4 to 0.19 for Si 3 N 4 -20% hBN against Si 3 N 4 . The surface analysis indicated that a tribochemical film consisting of SiO2 and H 3 BO 3 was formed on the wear surfaces. The formation of tribochemical film might be attributed to the embedment of wear debris into the spalling pits on the wear surfaces of Si 3 N 4 -hBN specimen. The wear debris reacted with moisture in air, and the resultant tribochemical film lubricated the wear surfaces. Under upper-pin-on-bottom-disc test mode, the wear mechanism was dominated by abrasive wear, and no tribochemical products could be detected on the wear surfaces. A slight decrease of the friction coefficient, from 0.85 for Si 3 N 4 /Si 3 N 4 to 0.56 for Si 3 N 4 /Si 3 N 4 -30% hBN, was obtained, which might be attributed to the layered structure of hBN.

Comparing Tribochemical Film Formation and Durability at Steel and CrN Coating Interface in Boundary Lubrication

One of the main challenges that engine oil manufacturers are now facing is to reduce friction losses while at the same time increasing the durability of engine components. New materials are being used for engine components, alongside and to replace conventional ferrous materials. More components are being coated with low friction and highly durable coatings. Lubricants are required to lubricate these surfaces as effectively as conventional materials, with no environmental impact. Knowing that the additive package in today’s lubricants is optimised for lubricating conventional ferrous materials it is of paramount importance to understand how effective the current additives are in lubricating non-ferrous materials.The aim of the current paper is to understand the formation and durability of tribofilms on a Chromium Nitride (CrN) coating formed from two conventional additives; Zinc Dialkyldithiophosphate (ZDDP) and Molybdenum Dialkyl Dithiocarbamate (MoDTC) additives. Tribofilm formation was studied by testing model lubricants containing ZDDP and MoDTC additives on the CrN coating in boundary lubrication, taking the performance on a ferrous system as a reference. The durability was assessed by assessing the tribocouple friction performance in base oil once the tribofilm was formed. Wear scars were fully chemically characterised using X-ray Photoelectron Spectroscopy (XPS). The study shows that the chemical nature of the tribofilms formed on steel and CrN is similar. In both materials, tribofilms were shown to have comparable durability. The factors which affect tribofilm durability and formation, and the reason why ferrous systems and CrN show similarities are discussed.

Surface topography and tribology of cast iron in boundary lubrication

This work aims to study and understand the influence of the surface topography on wear of grey cast iron used for heavy duty diesel engine cylinder liners. A micro-alloyed grey cast iron was tested with different surface topographies. These were polished surfaces, honed surfaces (with two different honing parameters) and three model surfaces with well defined grooves on a polished specimen. Reciprocating friction tests using a steel ball rubbing against a flat or a cylindrical sample (extracted from a cylinder liner) were carried out on a Cameron Plint test rig. A commercial synthetic oil for diesel engine was used as the lubricant. The friction coefficient and the electrical contact resistance were measured during the tests. The wear volume of the cylinder liner part was also measured at the end of the test. The influence of the surface topography on the tribochemical film formation and on the wear behaviour of cast iron was established. Surfaces exhibiting lots of surface asperities had the highest wear, mainly due to delayed formation of protective tribochemical film. In our test conditions, the spacing between the grooves on model specimens had no influence on the wear behaviour of the cast iron specimens.

Influence of Material Nature and Surface Texturing on Wear of Heavy-Duty Diesel Engine Cylinder Liners

The aim of this work is to study the influence of the material (chemical composition and mechanical properties) and the surface texturing on wear of heavy-duty diesel engine cylinder liners. Three kinds of lamellar grey cast iron have been studied: a classical grey cast iron, a surface-quenched grey cast iron, and a micro-alloyed grey cast iron. Honed samples have been tested with different surface roughness parameters. Reciprocating friction tests with the configuration “sphere against a piece of cylinder liner” in lubricated contact have been carried out on a Cameron-Plint test rig. The friction coefficient and the electrical contact resistance were measured during the test. The tribochemical film formation on the wear scars has been studied after different test durations (during and after the running-in stage). The wear volume of the cylinder and the sphere has been determined. Surface heat treatment and phosphorus eutectics can improve the tribochemical film formation and the wear resistance of cylinder liners. Moreover, the surface topography has an important influence; a flat surface with deep valleys shows a better wear resistance than a surface with lots of asperities.

Pressure Dependence of ZnDTP Tribochemical Film Formation: A Combinatorial Approach

Combinatorial testing has been performed on zinc dialkyldithiophosphate (ZnDTP)-containing lubricants, to investigate the effects of contact pressure on the formation of tribochemical films. Contact pressures ranging from 25 to 500 MPa were applied in ball-on-disc tribotests with oscillating load. Both the ball and the disc were investigated by means of small-area and imaging X-ray photoelectron spectroscopy (XPS). The thickness and the composition of the reaction layer were estimated from the XPS data. The thickness of the reaction layer in the tribologically stressed areas of the ball and of the disc increased with both temperature and contact pressure. The reaction layer mainly consisted of short-chain poly(thio)phosphates, shorter chains being observed at higher contact pressures. At high pressures, the presence of a thick, high-toughness short-chain poly(thio)phosphate layer can explain the lower friction and dimensional wear coefficients observed. On the ball, similar anti-wear film formation mechanisms were observed as on the disc, zinc sulphide being deposited in the post-contact region.

Influence of chemical composition and microstructure of gray cast iron on wear of heavy duty diesel engines cylinder liners

This work aims to study the influence of the chemical composition and the microstructure of gray cast iron on wear of heavy duty diesel engines cylinder liners. Two kinds of lamellar gray cast iron are studied: a classical gray cast iron and a micro-alloyed gray cast iron. Polished samples are tested. Reciprocating friction tests with the configuration steel ball against a flat sample, extracted from a cylinder liner, in lubricated contact are carried out on a Cameron Plint test rig (with commercial synthetic oil for diesel engines of the type 5W30). The friction coefficient and the electrical contact resistance are measured during all tests. The tribochemical film formation on the wear scars of the samples and the steel ball is studied after different friction periods. The wear volume evolution of the cylinder liner part and the steel ball are determined. The influence of the presence of hard phosphorous eutectics on the tribochemical film formation and on the wear behavior of cast iron is identified. After tribochemical film formation, the wear rate decreases considerably for all the samples. The micro-alloyed cast iron shows a better wear resistance than the “classical” cast iron. However, no tribofilm is formed on hard phosphorous eutectics and carbides.

Low-friction behaviour of boundary-lubricated diamond-like carbon coatings containing tungsten

It is generally accepted and well described that the mechanism by which extreme-pressure (EP) and antiwear (AW) additives reduce the friction and wear of metallic surfaces under boundary lubrication is the formation of tribochemical films. Although investigations of diamond-like carbon (DLC)-coated surfaces showed improved tribological properties when lubricated by additivated oil, the mechanism responsible is not fully understood. Therefore, the aim of the investigation was to determine the mechanism responsible for the low-friction behaviour of W-containing DLC coatings when lubricated with polyalphaolefin (PAO) oil containing EP or AW additives and to obtain some further understanding to this important area. The results of the present investigation clearly show that low-friction behaviour of boundary-lubricated W-DLC coatings is governed by formation of WS 2-containing tribofilms on the steel countersurface or exposed steel substrate, which reduce friction by up to 50%.

Formation of tribochemical films and white layers on self-mated bearing steel surfaces in boundary lubricated sliding contact

Formation of tribochemical layers and microstructural surface alterations during mild reciprocating sliding wear of AISI 52100 steel were studied under boundary lubricated conditions using a non-additive hydrocarbon lubricant. At the onset of relative motion no friction-induced chemical processes could be detected due to the protecting natural oxide film on the contacting steel surfaces. After a few sliding cycles, chromium carbides were pulled out of the ball surface leading to removal of the protecting layers and to the initiation of fast tribochemical reactions on the contact area. After about 1000 sliding cycles, so-called white layers developed on the ball surface showing greater carbon contents and hardness than the bulk material. This white layer formation could be attributed to high local pressures and subsequent grooving of the surface by wear debris. It was shown that the lubricant acted as a carbon donor owing to the adsorption of cracked hydrocarbon molecules on the steel surface. Adsorbed carbon atoms diffused into the bulk material and promoted the mechanically-induced phase transformation to the white layers.

An investigation on component and formation of tribochemical film in Si 3N4-white iron sliding pair lubricated with distilled water

A tribofilm was formed during wear tests of a Si 3N 4-white iron pair lubricated with distilled water. In order to clarify the formation of the film, the wear tests for Si 3N 4-white iron pair with different sliding distances were carried out on a ring-block tester, using distilled water as lubricant. The worn surfaces of white iron specimens were observed under SEM. Furthermore, the component and structure of the film were analyzed by using AES, XPS, FTIR and XRD. From the investigation, the following results are presented. During the wear tests of Si 3N 4-white iron pair lubricated with distilled water, the oxidation and hydrolysis of Si 3N 4 occur on the wearing surfaces, and a tribochemical film, which mainly consists of silica gel, is formed on the wearing surface. The reason for the film formation is that the carbides in cast iron spall off during the wearing tests and the spalling pits are left on the wearing surface of the white iron. Then, the debris of Si 3N 4 or its oxidized product are embedded into the pits, and are further oxidized and hydrolyzed. The products of reactions are concentrated in the pits and polycondensed into silica gel, and a silica gel film is formed on the wearing surface. The film protects both Si 3N 4 and white iron, and makes the paired surfaces smooth. Therefore, the friction coefficient of the pair is down to 0·02, and the wear rates of Si 3N 4 and iron are near zero. However, because the resultants of oxidation and hydrolysis of Si 3N 4 can not be enriched on the wearing surface of carbon steel to form an effective tribofilm, both friction coefficient and wear rate of Si 3N 4-carbon steel pair lubricated with distilled water are still high in value.