Superior Anti-wear Properties Research Articles

The deposition properties of tetrahedral amorphous carbon coatings deposited on piston ring: Molecular dynamics simulation

The tetrahedral amorphous carbon (ta-C) coatings are deposited on piston rings to improve the tribological property of the piston ring-cylinder liner system of the internal combustion engines. The deposition parameters are optimized by molecular dynamics simulation to reduce the cost of coatings’ fabrication. The ta-C coatings with higher sp3 fraction, lower friction coefficient, and superior anti-wear properties are achieved by optimizing the incident energy and substrate temperature of carbon atoms. The second nearest-neighbor modified embedded-atom method potential and Tersoff potential are used to describe the interatomic interactions. The effects of the incident energy of the carbon atoms and substrate temperature on the deposition properties of the ta-C coatings are discussed. The numerical results show that the ta-C coatings with high sp3 fraction, high density, and good interface mixing are obtained, and the deposition properties of the ta-C coatings are improved.

TiO2 and CeO2 nanoparticles as lithium complex grease additives for enhanced lubricity

PurposeThis paper aims to improve the tribological properties of lithium complex greases using nanoparticles to investigate the tribological behavior of single additives (nano-TiO2 or nano-CeO2) and composite additives (nano-TiO2–CeO2) in lithium complex greases and to analyze the mechanism of their influence using a variety of characterization tools.Design/methodology/approachThe morphology and microstructure of the nanoparticles were characterized by scanning electron microscopy and an X-ray diffractometer. The tribological properties of different nanoparticles, as well as compounded nanoparticles as greases, were evaluated. Average friction coefficients and wear diameters were analyzed. Scanning electron microscopy and three-dimensional topography were used to analyze the surface topography of worn steel balls. The elements present on the worn steel balls’ surface were analyzed using energy-dispersive spectroscopy and X-ray photoelectron spectroscopy.FindingsThe results showed that the coefficient of friction (COF) of grease with all three nanoparticles added was low. The grease-containing composite nanoparticles exhibited a lower COF and superior anti-wear properties. The sample displayed its optimal tribological performance when the ratio of TiO2 to CeO2 was 6:4, resulting in a 30.5% reduction in the COF and a 29.2% decrease in wear spot diameter compared to the original grease. Additionally, the roughness of the worn spot surface and the maximum depth of the wear mark were significantly reduced.Originality/valueThe main innovation of this study is the first mixing of nano-TiO2 and nano-CeO2 with different sizes and properties as compound lithium grease additives to significantly enhance the anti-wear and friction reduction properties of this grease. The results of friction experiments with a single additive are used as a basis to explore the synergistic lubrication mechanism of the compounded nanoparticles. This innovative approach provides a new reference and direction for future research and development of grease additives.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-09-2023-0291/

Simultaneous fabrication of Ti-MoS2 self-lubricating coatings and gradient structures to improve the wear resistance of AZ91D alloys

Magnesium alloys are essential for lightweight manufacturing. Nevertheless, defects such as low hardness and poor wear resistance severely restrict their further applications. Ultrasonic impact treatment (UIT) was used to simultaneously fabricate surface Ti-MoS2 self-lubricating coatings and interior gradient structures on AZ91D magnesium alloy for the first time. The surface morphology and microstructure were investigated, the tribological properties were evaluated at various normal loads, and the formation principles and anti-wear mechanisms of coatings and gradient structures were revealed. The findings indicate that the coatings present a particle-stacking microstructure. The gradient structures were characterized by grain, dislocation, and hardness distribution from greater to lesser along the depth direction. At all loads, the UIT samples exhibited superior anti-wear properties. Compared to untreated samples, the UIT sample's wear volume at 5 N, 15 N, and 25 N loads was reduced by 89.78 %, 84.23 %, and 43.88 %, respectively. The wear surface analysis indicates that the Ti-MoS2 coatings effectively enhance the lubricity of friction surfaces. Additionally, gradient structure works when the coatings fail and reduces the shear deformation, further reducing wear. This work presents a new method for fabricating simultaneously surface coatings and interior gradient structures using UIT, contributing to improving the anti-wear properties of magnesium alloys and enhancing their utilization in lightweight manufacturing fields.

Assessment of the tribological performance of glass fibre reinforced polyamide 6 under harsh abrasive environments

High-performance thermoplastics exhibit significant potential to substitute metals in various applications, primarily due to their remarkable tribological, thermal and mechanical characteristics. Nevertheless, their characteristics require further refinement. This research aims to assess and compare the influence of distinct material types on the tribological characteristics of Polyamide 6 composites, as well as their reliance on the PV factor, which is the result of the velocity and pressure product.In the current research, the friction and wear performances of polyamide 6 (PA6) reinforced with glass fibres were examined in adverse PV factors till materials failed. Twin screw extrusion and subsequent injection moulding procedures were utilised to process the materials. The tribo-performance of the materials was assessed in ambient conditions using a pin-on-disc abrasive configuration. The morphological analysis of the abraded surfaces was conducted through field emission scanning electron microscopy (FESEM), and the plausible wear mechanisms contributing to wear are explained. Furthermore, the materials were thoroughly characterised for their tribological, mechanical and physical behaviours.The wear behaviour depended mainly on operating parameters and composition. PA6 proved to be beneficial till moderate PV conditions but not for harsh operating environments as compared to PA6 reinforced with 25% by volume of glass fibres (PA625GF). PA625GF showed PVlimit value of 1.04 MPa m/s which was decisively superior to PA6 (0.78 MPa m/s). Additionally, under a load of 50 N, PA625GF could sustain a higher speed of 800 rpm as compared to PA6 (600 rpm). The results showed that under all testing conditions glass fibres can minimise the coefficient of friction. Under low PV settings, the specific wear rate of PA625GF was remarkably reduced owing to the presence of glass fibres, reflecting superior anti-wear properties. Notably, the wear resistance of PA6 was considerably improved by glass fibres, particularly under high PV conditions, resulting in a PVlimit of 1.04 MPa m/s. The enhancement in PVlimit was attributed to the protective function of the fibres on the matrix and their superior mechanical properties. PA625GF proved to be tribo-potential materials in abrasive wear mode under extreme conditions in terms of low specific wear rate (8.484 ×10−3 mm3/N.m) and PVsafe value (0.78 MPa*m/s). This study is expected to pave the way for the development of novel self-lubrication composite materials for harsh service environments.

Diamond-like carbon films prepared by a low temperature periodic process for application in ventricular assist devices.

Due to the poor tribological properties of titanium (Ti) and its alloy Ti6Al4V (commonly used for ventricular assist devices manufacturing), diamond-like carbon (DLC) films with excellent anti-wear properties are pursued to improve the wear resistance of Ti and its alloys. Considering the effect of temperature on magnets inside pump impellers and workpiece deformation, DLC films are preferred to be prepared under low temperature. In this study, DLC films were prepared on Ti6Al4V alloys by periodic and continuous processes, and the corresponding maximum deposition temperature was 85 and 154°C, respectively. The periodic DLC films exhibited the feature of columnar structure, and the surface hillocks were less uniform than that of continuous DLC films. The periodic DLC films possessed more sp3 -bonded structures, and the accessorial sp3 -bonding mainly existed in the form of CH. Compared to continuous DLC films, the periodic DLC films had lower residual stress and better adhesion with Ti6Al4V substrates. Both DLC films could effectively reduce the friction coefficient and wear rate of Ti6Al4V alloys both in air and fetal bovine serum (FBS), and the periodic DLC films exhibited superior anti-wear properties to that of continuous DLC films in FBS. Haemocompatibility evaluation revealed that both DLC films presented similar levels of more human platelet adhesion and activation as compared with that of bare Ti6Al4V. However, both DLC films significantly prolonged plasma clotting time in comparison to bare Ti6Al4V. This study demonstrates the potential of low-temperature DLC films as wear-resistant surface modification for VADs.

A review of recent advances of ionic liquids as lubricants for tribological and thermal applications

The novel characteristics of ionic liquids (ILs) led to an improved tribological and thermal performance. This article discusses current progress in developing ILs as neat lubricants or additives in lube oils, with a focus on ILs chemistry, synthesis, miscibility, and other relevant rheological, thermal, and tribological properties at macro to nanoscales. This article also introduces a review of lubrication mechanisms based on the tribofilm formed on the rubbing interfaces owing to tribochemical reactions among the ILs, base oil, and solid bodies, which shows key insights into anti-wear properties. ILs exhibited superior anti-wear properties compared to fully formulated oils. Notably, there was no symmetry between the friction results of ILs and their wear counterpart. Furthermore, the main challenges to further improve ILs performance for tribological applications are highlighted. Eventually, prospects for ILs tribology are suggested, which will guide the development and synthesis of ILs-based lubricants for tribological applications.

Nanoscale viscosity of triboreactive interfaces

It has been long speculated that the good antiwear properties of the nano-thin triboreactive interfaces might have a rheological origin that can greatly influence their friction, lubrication and antiwear characteristics, which account for nearly one quarter of the worldwide total energy consumption. However, the measurement of the nanoscale viscosity of such tribological interfaces is still a challenging task. This is mainly due to their ultralow thickness, i.e. typically < 150 nm, high viscosity and reactivity, which make the currently used bulk, interfacial or micro-gap rheological techniques inadequate. Here we demonstrate two methods, i.e. creep and squeeze flow, that can be used to quantify the viscosity of triboreactive films in-situ as they form and ex-situ after formation. Films generated from the zinc and ashless dialkyldithiophosphate (ZDDP and DDP) antiwear additives were analysed as model systems because of their industrial and academic importance. The results confirm that the formed tribofilms behave as molten glass with an average viscosity ranging from 2 × 1 0 11 to 7 × 1 0 12 Pa s. During its formation, the molten glass showed rich intrinsic rheological properties that allowed them to maintain local order on the nanoscale through the motion and reconfiguration of single and multiple patches within the formed film, which can significantly predetermine its superior antiwear properties. The findings of this study open future opportunities for optimizing the nano-flowable glass to efficiently control the lubrication of tomorrow’s engines without the need of any environmentally harmful oil additives. • Triboreactive films behave as molten glass with rich intrinsic rheological properties. • Local order at the nanoscale predetermines the friction and wear performance. • Nano-flowable glasses are the key to efficient lubrication in tomorrow’s engines. • Single asperity AFM is fully capable of probing the flowability of surfaces nano-patches for energy harvesting and other applications.

Influence of Complex SiF62− Ions on the PEO Coatings Formed on Mg–Al6–Zn1 Alloy for Enhanced Wear and Corrosion Protection

The present study was carried out to explore the effect of SiF62− incorporation and concentration on the plasma electrolytic oxidation (PEO) coatings formed on AZ61 Mg alloy. The coatings were prepared using electrolyte solution with various concentration of Na2SiF6 (0.0–0.7 g/L). Highly compact coatings with minimum porosity were obtained for an optimum concentration of Na2SiF6 ~0.3 g/L added into the electrolyte. The highest corrosion resistance, ~2.04 × 105 Ω·cm2, was obtained for 0.3 g/L of Na2SiF6, in addition to its superior anti-wear properties. However, it was found from the scanning electron microscope (SEM) image analysis that increasing concentration above 0.3 g/L, could cause severe breakdown in the inner layers, and thus the said coatings could not withstand effectively against wear and corrosion.

Metathesized castor oil acylated derivatives: lubricants base stocks with low pour points and superior anti-wear properties

Castor (Ricinus communis) oil containing ricinoleic acid 89% was self-metathesized in the presence of Grubbs’ second generation catalyst (0.025 mmol), followed by epoxidation and insitu hydroxylation using Prilezhaev dihydroxylation method to obtain hydroxylated derivatives in 93% yields. MALDI study has shown that the metathesized products comprised of a mixture of monomer, dimer and trimer metathesized products. The hydroxylated derivatives were acylated using acetic, propionic, butyric and hexanoic anhydrides in 85–90% yields. The acylated base stocks being highly branched and of high molecular weights exhibited very low pour points (− 30 to − 40 °C) and broad viscosity ranges 45.5 cSt to 60.0 cSt at 40 °C, high viscosity indices (165–191), excellent anti-wear properties (0.52–0.69 mm), good thermal and oxidative stabilities along with high load carrying capacities (165–184 kg) suitable for multi-range industrial applications. These base stocks can be used with the addition of minimum additives during the formulation.

On the Transient Decomposition and Reaction Kinetics of Zinc Dialkyldithiophosphate.

Despite the ubiquitous use of the zinc dialkyldithiophosphate (ZDDP) as an antiwear additive, no complete information is yet available on its exact decomposition reactions and kinetics to form triboreactive protective films on contacting surfaces. This hinders the replacement of ZDDP with more environmentally friendly additives of similar antiwear capabilities. Using a multitechnique approach, this study shows that before the formation of a phosphate-rich protective film, the decomposition of ZDDP proceeds by forming intermediate zinc sulfide and sulfate species, which can be mechanically mixed with the iron oxides on the rubbing steel surfaces. The mixed sulfur-oxide layer can play different vital roles including binding the subsequently formed phosphate layers with the metal surface. These layers consist mainly of zinc thiophosphate of initially short chains, which are formed due to the excess concentration of metal oxide on the surface. As the concentration of the oxide decreases in the subsequent layers, the short chains start to polymerize into longer ones. The polymerization process follows first-order reaction kinetics with two distinctive phases. The first one is a fast transient burst phase near the steel surface, whereas the second phase dominates the formation process of the layers away from the substrate and is characterized by slow kinetics. The findings of this study provide new insights into the decomposition mechanisms of the currently most widely used antiwear additive and open future opportunities to find green alternatives with similar superior antiwear properties.

Microtribological behavior of Mo and W nanoparticle/graphene composites

This work examines the tribological behavior of two novel graphene composites (Mo and W nanoparticles grafted onto graphene platelets) under boundary lubrication. While similar composites have been studied in past literature, the grafted nanomaterials Mo and W have not been tested before. Such composites benefit both from the friction reduction properties of graphene and the increased load capacity provided by nanoparticles. Their application as a potential antiwear lubricant additive was investigated. Both composites were blended into a mineral base oil. Graphene and neat oil were also tested to serve as controls. By DLS characterization, these dispersions were found to be stable over the testing duration. Tribological behavior was studied using a custom microtribometer via ramped load and cyclic tests for friction and wear, respectively. Results demonstrated a similar reduction in friction with the addition of each additive while the composites provided superior antiwear properties in comparison to the base oil and graphene alone.

The Effect of the Chemical Structures of Synthetic Hydrocarbon Oils on Their Tribochemical Decomposition

Under boundary lubrication conditions, the formation of a highly active nascent surface can catalyze the decomposition of lubricant oils. Extreme pressure additives can reduce this decomposition but have undesirable environmental impacts, and so it is necessary to develop eco-friendly lubricants. The following study investigated the effects of the chemical structures of hydrocarbon oils on their tribochemical decomposition by comparing an alkyldiphenylether (ADE) to a multialkylated cyclopentane. The analysis of gaseous decomposition products via mass spectrometry during the application of friction showed that the multialkylated cyclopentane decomposed after an induction period of 1.95 km while the ADE did not degrade, even at a distance of 57.5 km, under the same mechanical contact conditions, and exhibited superior anti-wear properties. However, a high concentration of the ADE was necessary to extend the induction period for lubricant decomposition when it was used as an additive. Although the ADE showed high stability in response to friction, it was prone to decomposition once a nascent steel surface was formed. These decomposition characteristics of the ADE are closely related to its chemical structure, because the ether group in the ADE molecule preferentially adsorbs on metal oxide surfaces, forming a dense and robust film. In contrast, the weak bonding between adjacent alkyl groups reduces the shear strength at the interface. Both the benzene and alkyl groups of ADE molecules were found to detach, followed by the further rupture of C–C, C–H, and C–O bonds, catalyzed by active sites on the nascent surface such as surface defects.

Tribological properties of hydrogenated amorphous carbon under dry and lubricated conditions

Abstract Diamond-like carbon (DLC) coatings are considered as potential surface coatings for many engineering applications including gears and engine parts. It is important to know whether conventional extreme pressure (EP) additive-containing oil can work with DLCs and provide tribological performance as effective as they provide on steel surfaces. This study examines the friction and wear properties of hydrogenated amorphous carbon (a-C:H) under dry, base oil (BO)- and fully formulated gear oil (FF)-lubricated conditions. Pronounced graphitisation occurs due to rubbing under dry condition and provides low friction but promotes wear. However, BO and FF greatly suppress graphitisation and wear. Tribofilms formed from FF in a-C:H/steel contact appear to exhibit superior antiwear properties than those formed in steel/steel contact.

An XPS Study on the Composition of Zinc Dialkyl Dithiophosphate Tribofilms and Their Effect on Camshaft Lobe Wear

In this study, various zinc dialkyl dithiophosphate (ZDDP)-derived tribofilms were analyzed with X-ray photoelectron spectroscopy (XPS) to determine the relationship between tribofilm chemical composition and wear severity. Samples were generated on camshaft lobes from engine tests conducted at different oil temperatures, and wear depths were measured with a surface profilometer. Tribofilm specimens were analyzed by XPS to assess changes in film chemistry as a function of wear severity. Tribofilms present on all camshaft lobes were found to contain polyphosphate glass of various chain lengths. Long-chain polyphosphates were observed on low wear tracks, whereas short-chain polyphosphates were found on more severe wear tracks. Variations in polyphosphate chain length are also apparent at different wear depths along a low wear track. The presence of long-chain polyphosphates on low wear tracks was indicative of their superior antiwear properties, whereas the occurrence of short-chain polyphosphates on more pronounced wear tracks was indicative of their inferior antiwear properties.

Al2O3-nanodiamond composite coatings with high durability and hydrophobicity prepared by aerosol deposition

We attempted the room-temperature fabrication of Al2O3-based nanodiamond (ND) composite coating films on glass substrates by an aerosol deposition (AD) process to improve the anti-scratch and anti-smudge properties of the films. Submicron Al2O3 powder capable of fabricating transparent hard coating films was used as a base material for the starting powders, and ND treated by 1H,1H,2H,2H-perfluorooctyltriethoxysilane (PFOTES) was added to the Al2O3 to increase the hydrophobicity and anti-wear properties. The ND powder treated by PFOTES was mixed with the Al2O3 powder by ball milling to ratios of 0.01wt.%, 0.03wt.%, and 0.05wt.% ND. The water contact angle (CA) of the Al2O3-ND composite coating films was increased as the ND ratio increased, and the maximum water CA among all the films was 110°. In contrast to the water CA, the Al2O3-ND composite coating films showed low transmittance values of below 50% at a wavelength of 550nm due to the strong agglomeration of ND. To prevent the agglomeration of ND, the starting powders were mixed by attrition milling. As a result, Al2O3-ND composite coating films were produced that showed high transmittance values of close to 80%, even though the starting powder included 1.0wt.% ND. In addition, the Al2O3-ND composite coating films had a high water CA of 109° and superior anti-wear properties compared to those of glass substrates.

2105 微粒子ピーニングによって創成された傾斜組成材料の摩擦摩耗特性における熱処理の効果(テクスチャリングと低摩擦(2),一般講演)

The present study describes the effect of heat treatment of functional graded material fabricated by fine particle peening treatment that is one of the surface modifications. Fine tungsten carbide particles accompanied with steel beads were penetrated on the target alloy steel surface by peening. Heat treatment was applied after the peening to melt and infiltrate of the penetrated tungsten carbide into the alloy steel. Results of indentation measurements showed that an applicable heat treatment was effective to improve the hardness. A thrust type rolling contact experiment was also applied to the modified surface, superior anti wear properties were found in the heat treated specimen.

Tribological study of a novel borate ester containing dialkylthiophosphate group as multifunctional additive

PurposeAs multifunctional additives, ZDDP, which provides excellent oxidation resistance and superior antiwear properties, has been used widely in lubricants, however, it shows oppositional effect with friction modifiers when used together. In this paper, an attempt is made to find a novel kind of borate ester which can be used as potential substitute for ZDDP.Design/methodology/approachA novel borate ester containing dialkylthiophosphate group was prepared and characterized. Its tribological properties as an additive in synthetic ester were evaluated using a four‐ball tribometer and antioxidative ability tested by pressurized differential scanning calorimetry (PDSC). Thermal degradation tests were conducted to identify its thermal stabilities using thermogravimetric analyzer (TGA). The worn surface of the steel ball was investigated by X‐ray photoelectron spectroscopy (XPS) and the antiwear mechanism of the additive was preliminarily discussed.FindingsResults show the additive possesses outstanding loading‐carrying and friction‐reducing properties, compared with ZDDP, and can improve antiwear properties of the base oil dramatically. Moreover, it also has excellent antioxidation performance and thermal stability.Originality/valueThis paper provides a multifunctional ashless additive which possesses excellent tribological properties, and gives another selection for industrial applications in which ZDDP is needed.

High-Precision Cutting of Titanium Aluminide Intermetallic Compounds.

The purpose of this study is to obtain a high-precision surface in titanium aluminide intermetallic compounds. The wear mechanisms of tools and the formation mechanism of surface defects are investigated with the cutting experiment using the various types of tools. The results obtained from this study are as follows: All tools are damaged with streaky abrasive type wear due to lamellar structure of workpiece. The sintered tools which mean polycrystalline diamond tool and cemented carbide tool are accompanied with falling off of diamond or tungsten carbide particle from tool surface. In the case of diamond tools, polycrystalline type is superior to single-crystalline type at flank wear and surface roughness. In the case of sintered tools, the tools made of small diamond or tungsten carbide particle have superior anti-wear properties. The surface defects whose shape are long and narrow are formed along the layer direction of lamellar structure. These are tearing off by cutting edge due to the growth of crack in layer or on layer boundary.

Function and performance of silicone copolymers: 1. Syntheses of polysiloxane containing copolymers and their absorption phenomena under extreme pressure

Two types of multifunctional copolymers containing siliconized-acrylate monomer (SAM) were synthesized: copolymer SNS (containing SAM, stearyl acrylate and N,N-dimethylaminoethyl acrylate monomers) and copolymer SAS (containing SAM, stearyl acrylate and an amine salt of acrylic acid). Their structures were confirmed by 1H nuclear magnetic resonance, and their adsorption behaviours on metal surface were characterized by electron spectroscopy for chemical analysis. It was found that both synthesized copolymers were good viscosity index improvers and have superior anti-wear properties when used in boundary lubrication conditions. Scanning electron microscopy results indicated that these two copolymers formed significantly thick adsorption layers compared with conventional anti-wearing agents, and the chemisorption occurred more in the case of the SAS additive in the case of the SNS.

Antiwear behaviour of cyclic phosphorus compounds: Comparison with zinc O, O-dialkylphosphorodithioate

The purpose of the present study is to examine the antiwear properties of some cyclic phosphates and phosphites and to compare them with a noncyclic phosphite and a commonly used oil additive zinc O, O-diisooctylphosphorodithioate (ZnDTP). A number of cyclic phosphates and phosphites were tested on a four-ball machine using various temperatures, loads, speeds and base oils. It was observed that cyclic phosphites possess better antiwear properties than cyclic phosphates. Of the phosphites, the compound containing sulphur was more effective than the corresponding molecule with oxygen in place of sulphur and it gave better results. This superior performance was observed in base oils A, B and C. In comparison with ZnDTP, this compound possesses significantly superior antiwear properties at high temperatures and loads.