Lubrication Mechanism of Micro/Nano-particles on Sialon

The tribological properties of Sialon sliding against AISI52100 steel ball under the lubrication of solid particle additives, as micro-borate particle and nano-PbS particle, were evaluated by a SRV ball-on-disc test rig. The chemical composition of the worn surface was characterized by X-ray photoelectron spectroscopy (XPS). The morphologies of the worn surfaces of Sialon were analyzed by scanning electron microscopy (SEM). The results show that the particles can reduce the friction coefficient of the pairs and the wear volume of Sialon significantly. The wear resistance of micro-borate is superior to that of nano-PbS while the friction-reducing ability of PbS is better than that of borate. According to the XPS and SEM results, the wear resistance of PbS is mainly depended on the tribochemical film mainly composed of PbSO 4, which deposited on the worn surface with good bonding strength. No tribochemical reaction or deposited film was detected or observed on the worn surface of Sialon under the lubrication of borate, indicating that the possible physically deposited film generated from micro particle can also greatly reduce the wear volume of Sialon, though the friction reducing ability of which is inferior to that of nano PbS particle.

Effect of applied load on transition behavior of wear mechanism in Cu-15Ni-8Sn alloy under oil lubrication

Tribological behavior of Cu-15Ni-8Sn(mass fraction, %) alloy against GCr15 ring under various loads was investigated on a ring-on-block tester in oil lubrication. The results showed that the wear rate increased slowly from 1.7×10^(-7) to 9.8× 10^(-7) mm^3/mm under the load lower than 300 N, and then increased dramatically to the climax of 216×10^(-7) mm^3/mm under the load over 300 N, which indicated the transition of wear mechanism with the increase of applied load. The wear mechanism mainly was plastic deformation and abrasive wear under the load less than 300 N. As the applied load was more than 300 N, the wear mechanism of Cu-15Ni-8Sn alloy primarily was delamination wear. Besides, the transition can also be confirmed from the different morphologies of worn surface, subsurface and wear debris. It is distinctly indicated that the appearance of flaky debris at the applied load over 300 N may be a critical point for the change of wear mechanism.

Synthesis and Lubrication of Phosphorylcholine Derivative

The monomer of phosphorylcholine derivative, O-(5-（2-methacryloxy）-3, 3-dimethyl-3-azapentyl)-O’-（ω-hydroxy-octyl）-phosphatequaternary ammonium salt, was designed and synthesized successfully. It was characterized by the spectra ofHNMR and Mass spectra （ESI+）, and every signal was assigned. Then the lubricating characteristics of the phosphorylcholinederivative were investigated on the tribological setup of ball-oh-flat. The Ultra-High Molecular Weight Polyethylene（UHMWPE） flat was rotated against a stainless steel ball with 6 mm diameter. The load was 2.3 N, which corresponded to amaximal Hertz contact pressure of 29 MPa. Water, phosphorylcholine derivative, and Acrylic Acid （AA） solution were used aslubricants, respectively. Compared with AA, the phosphorylcholine derivative shows significant lubrication. It can be stronglyhydrated under water due to the charged segment in chemical structure. The thick water layers within the chains serves asboundary lubricants, and this is thought to be the molecular origins of lubricating behavior.

MATHEMATICAL PROGRAMMING ANALYSIS OF BILINEAR RHEOLOGICAL LUBRICATION MECHANICS

Bilinear theological lubrication mechanics provides an important basis for the designs of re- cently developed electrorheological(ER)'smart'journal bearings and those lubricated by mixed fluid-solid lubri- cants.But there is not yet a reliable and efficient numerical method for such a problem of non-Newtonian flu- id mechanics.In the present paper,a finite element method(FEM)together with mat hematical programming solution is successfully used to solve such a problem.A reliable and generalized numerical method for the designs of electrorheological 'smart' journal bearings and the bearings lubricated by mixed fluid- solid lubri- cant is presented.

The Effect and Mechanism of Nano-Cu Lubricating Additives on the Electroless Deposited Ni-W-P Coating

The coating and deposition process with excellent anti wear and suitable for industrial application were developed, and the optimum bath composition and process were obtained by studying the influence of the bath composition, temperature and pH value on the deposition rate and the plating solution stability. Moreover, the tribological properties of nano-Cu lubricating additives and electroless deposited Ni-W-P coating as well as their synergistic effect are researched using ring-block abrasion testing machine and energy dispersive spectrometer. Research results show that Ni-W-P alloy coating and nano-Cu lubricating additive have excellent synergistic effect, e g, the wear resistance of Ni-W-P alloy coating （with heat treatment and the oil with nano-Cu additives） has increased hundreds times than 45 steel as the metal substrate with the basic oil, and zero wear is achieved, which breaks through the bottleneck of previous separate research of the above-mentioned two aspects.

Minimum quantity lubrication machining of aeronautical materials using carbon group nanolubricant: From mechanisms to application

It is an inevitable trend of sustainable manufacturing to replace flood and dry machining with minimum quantity lubrication(MQL)technology.Nevertheless,for aeronautical difficult-tomachine materials,MQL couldn’t meet the high demand of cooling and lubrication due to high heat generation during machining.Nano-biolubricants,especially non-toxic carbon group nano-enhancers(CGNs)are used,can solve this technical bottleneck.However,the machining mechanisms under lubrication of CGNs are unclear at complex interface between tool and workpiece,which characterized by high temperature,pressure,and speed,limited its application in factories and necessitates in-depth understanding.To fill this gap,this study concentrates on the comprehensive quantitative assessment of tribological characteristics based on force,tool wear,chip,and surface integrity in titanium alloy and nickel alloy machining and attempts to answer mechanisms systematically.First,to establish evaluation standard,the cutting mechanisms and performance improvement behavior covering antifriction,antiwear,tool failure,material removal,and surface formation of MQL were revealed.Second,the unique film formation and lubrication behaviors of CGNs in MQL turning,milling,and grinding are concluded.The influence law of molecular structure and micromorphology of CGNs was also answered and optimized options were recommended by considering diverse boundary conditions.Finally,in view of CGNs limitations in MQL,the future development direction is proposed,which needs to be improved in thermal stability of lubricant,activity of CGNs,controllable atomization and transportation methods,and intelligent formation of processing technology solutions.

Effect of nickel-plated graphite on microstructure and properties of matrix for Fe-based diamond tools

Nickel-plated graphite particles and unmodified graphite particles with different contents were added to the Fe-based diamond composites.The basic properties of those specimens were measured,including relative density,hardness,bending strength,abrasion ratio and holding force coefficient.And also,SEM,XRD and EDS were used to carry out microstructure characterization,phase analysis and element distribution of these specimens.The results show that nickel plating effectively improves the surface wettability of graphite particles.And it is determined that an element diffusion zone is formed on the transition interface between the nickel-plated graphite and the matrix materials,effectively enhancing the interfacial bonding strength.Also,the pores and cracks in the matrix generated by adding the graphite particles are reduced after nickel plating.Thus,the loss of basic properties of the specimens is restrained.But it is found the higher the graphite content is,the weaker the positive effect of nickel plating is.In addition,it is revealed that nickel plating plays a conducive part in the formation of graphite lubricants on the working surface,and nickel-plated graphites can slow down the thermal corrosion of the diamond particles inside the high-temperature sintered specimens.

Study on Tribology Performance of Different Lubricant Additives under Atmospheric Pressure and High Vacuum Conditions

By using PAO-10 as the base oil, the tribological behavior of 11 additives under high vacuum condition was evaluated. By adopting some surface analytical instruments, such as scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS) and X-ray photoelectron spectroscopy(XPS), the tribological mechanisms of these additives were studied. In air, O_2 can react with metal to form metal oxide that can protect the surfaces of rubbing pair during the tribological tests. According to the theory of the competitive adsorption, the function of some active elements is weakened. In a vacuum environment, the additives contributed more to the lubrication performance. The sulfur-containing additives could react with Fe to produce Fe Sx and "M—C" bonds("M" represents metal). They both had contributions to the lubrication. As for the phosphorus-containing additives, they only generated the phosphates during the tests. When the sulfur and phosphorus-containing additives were applied, the generated phosphates and Fe Sx had the primary contribution to the lubrication performance during the tests.

A Simple Way to Prepare Silicon Carbide Reinforced Graphite Composite Lubricating Materials

SiC reinforced graphite composites were prepared via introducing carbide silicon into the natural graphite flakes（NGF） by hot-pressing process. Their physical and mechanical properties, including density, open porosity, flexural strength, and friction behavior were investigated. The addition of 30vol% Si C increased the bending strength of composites materials to 127 MPa, 2 times higher than 60 MPa of commercial pure graphite block. What was particularly interesting was that the as-obtained graphite composite with 30vol% Si C kept the same low friction coefficient of about 0.1 as pure graphite, and the wear resistance of composites increased.

Research progresses of nanomaterials as lubricant additives

Friction and wear are unavoidable in mechanical movement.The use of lubricants with nano-additives can effectively reduce friction and wear,which is of great significance to saving energy and protecting the environment.At present,great progress has been made in the scientific research and industrial application of nano-additives for lubricants.This paper mainly introduces the types of nano-additives for lubricants(such as carbon nanomaterials,nano-metals,nano-oxides,sulfides,complexes,polymers,etc.),the tribological properties of lubricants with different components of nano-additives,and the lubrication mechanisms of the nano-additives(including tribofilm formation,rolling ball bearing effect,repairing effect,polishing effect,and synergistic effect).It also deals with the dispersion of nano-additives in lubricants and the influences of their particle size and microstructure on the tribological properties of lubricants.This review outlines the performance requirements of nano-additives in different lubrication states,discusses the use of nano-additives in challenging working conditions,and identifies various industrial oil nano-additives with reference to the appropriate options in diverse working environments.Furthermore,the existing problems of nano-additives and their application prospects are summarized.This review,hopefully,would help to shed light on the design and synthesis of novel high-performance nano-additives and promote their application in engineering.

MXenes in tribology:Current status and perspectives

MXenes are an emerging class of new two-dimensional materials, which have been widely used in energy storage,catalysis, sensing, biology, and other fields due to their unique structure and properties. The distinct structure,low shear resistance, and easy-to-modify ability endow MXenes with particularly superior lubrication potentials.This review highlights the research status and applications of MXenes lubrication categorized into solid lubricants, lubricant additives, and reinforcement phase parts, summaries the influencing factors and lubricationmechanisms of MXenes lubrication, points out some unexplored research fields and unsettled questions, and thenputs forwards possible solutions and prospects for the future research. The lubrication advances and potentials ofMXenes are fully verified. Predictably, the emerging MXenes lubricants will exhibit remarkable applicationprospects in advanced manufacturing such as machining industries, automotive industries, micro/nanoelectromechanical systems, and spacecraft components.

Structural engineering design of carbon dots for lubrication

Carbon dots(CDs)have opened up a new field of carbon nanomaterials and successively attracted increasing attention since their discovery in 2004.Owing to their ultrasmall size,tunable surface functional groups,excellent dispersibility,attractive stability,low toxicity,environmental friendliness,facile synthesis and low-cost precursors,CDs have been developed as green and promising frictionreducing and anti-wear materials in lubrication science,applied to energy conservation and extension of mechanical service life in recent years.However,there are few reviews focusing on the application of CDs in the important field of lubrication.In this review,we comprehensively summarize the development of CDs in lubrication for the first time.Firstly,three strategies for structural engineering design of CDs to improve their tribological characteristics are fully analyzed,in terms of size and shape control,surface modification and heteroatom doping.Secondly,the advance in lubrication application of CDs,including CDs as additives for lubricants,greases,gel and magnetorheological fluids as well as CDs as lubricating coatings,is systematically highlighted.Thirdly,the lubricating mechanisms of CDs as additives are introduced in detail.Furthermore,the remaining major challenges and opportunities for CDs in lubrication field are discussed and outlined.

Insights into the tribological behavior of choline chloride-urea and choline chloride-thiourea deep eutectic solvents

Deep eutectic solvents(DESs)have been considered as novel and economic alternatives to traditional lubricants because of their similar physicochemical performance.In this study,choline chloride(ChCl)DESs were successfully synthesized via hydrogen-bonding networks of urea and thiourea as the hydrogen bond donors(HBDs).The as-synthesized ChCl-urea and ChCl-thiourea DESs had excellent thermal stability and displayed good lubrication between steel/steel tribo-pairs.The friction coefficient and wear rate of ChCl-thiourea DES were 50.1%and 80.6%,respectively,lower than those of ChCl-urea DES for GCr15/45 steel tribo-pairs.However,for GCr15/Q45 steel,ChCl-urea DES decreased the wear rate by 85.0%in comparison to ChCl-thiourea DES.Under ChCl-thiourea DES lubrication,the tribo-chemical reaction film composed of FeS formed at the interfaces and contributed to low friction and wear.However,under high von Mises stress,the film could not be stably retained and serious wear was obtained through direct contact of friction pairs.This illustrated that the evolution of the tribo-chemical reaction film was responsible for the anti-friction and anti-wearproperties of the DESs.

Achieving superlubricity in DLC films by controlling bulk, surface, and tribochemistry

Superlubricity refers to a sliding regime in which contacting surfaces move over one another without generating much adhesion or friction[1].From a practical application point of view,this will be the most ideal tribological situation for many moving mechanical systems mainly because friction consumes large amounts of energy and causes greenhouse gas emissions[2].Superlubric sliding can also improve performance and durability of these systems.In this paper,we attempt to provide an overview of how controlled or targeted bulk,surface,or tribochemistry can lead to superlubricity in diamond-like carbon(DLC)films.Specifically,we show that how providing hydrogen into bulk and near surface regions as well as to sliding contact interfaces of DLC films can lead to super-low friction and wear.Incorporation of hydrogen into bulk DLC or near surface regions can be done during deposition or through hydrogen plasma treatment after the deposition.Hydrogen can also be fed into the sliding contact interfaces of DLCs during tribological testing to reduce friction.Due to favorable tribochemical interactions,these interfaces become very rich in hydrogen and thus provide super-low friction after a brief run-in period.Regardless of the method used,when sliding surfaces of DLC films are enriched in hydrogen,they then provide some of the lowest friction coefficients(i.e.,down to 0.001).Time-of-flight secondary ion mass spectrometer(TOF-SIMS)is used to gather evidence on the extent and nature of tribochemical interactions with hydrogen.Based on the tribological and surface analytical findings,we provide a mechanistic model for the critical role of hydrogen on superlubricity of DLC films.

Nanolubricant additives: A review

Using nanoadditives in lubricants is one of the most effective ways to control friction and wear,which is of great significance for energy conservation,emission reduction,and environmental protection.With the scientific and technological development,great advances have been made in nanolubricant additives in the scientific research and industrial applications.This review summarizes the categories of nanolubricant additives and illustrates the tribological properties of these additives.Based on the component elements of nanomaterials,nanolubricant additives can be divided into three types:nanometal-based,nanocarbon-based,and nanocomposite-based additives.The dispersion stabilities of additives in lubricants are also discussed in the review systematically.Various affecting factors and effective dispersion methods have been investigated in detail.Moreover,the review summarizes the lubrication mechanisms of nanolubricant additives including tribofilm formation,micro-bearing effect,self-repair performance,and synergistic effect.In addition,the challenges and prospects of nanolubricant additives are proposed,which guides the design and synthesis of novel additives with significant lubrication and antiwear properties in the future.

Black phosphorus quantum dots: A new-type of water-based high-efficiency lubricant additive

Black phosphorus quantum dots(BPQDs),obtained via a typical solution-based top-down method,were used as water-based lubricant additives.BPQDs exhibited remarkable friction reduction and anti-wear properties even at the ultra-low concentration of 0.005 wt%,which reduced the friction coefficient and wear volume of the base liquid by 32.3%and 56.4%,respectively.In addition,the load-supporting capacity of the base liquid increased from 120 N to over 300 N.BPQDs-based additives exhibited a relatively long lifetime at a relatively high load of 80 N.The performance of BPQDs considerably exceeded that of the BP;this may be attributed to their small and uniform particle size,good dispersion stability in water,and high reactivity at the frictional surfaces.The results of the surface wear resistance analysis demonstrated that a robust tribochemical film with a thickness of approximately 90 nm was formed on the rubbing surface lubricated with 0.005 wt%of BPQDs dispersion.Moreover,the film served as a direct evidence of the excellent tribological performance of BPQDs.

Effects of magnetic ionic liquid as a lubricant on the friction and wear behavior of a steel-steel sliding contact under elevated temperatures

A magnetic ionic liquid(abridged as MIL)[C_(6)mim]_(5)[Dy(SCN)_(8)]was prepared and used as the magnetic lubricant of a steel-steel sliding pair.The tribological properties of the as-prepared MIL were evaluated with a commercially obtained magnetic fluid lubricant(abridged as MF;the mixture of dioctyl sebacate and Fe_(3)O_(4),denoted as DIOS-Fe_3O_4)as a control.The lubrication mechanisms of the two types of magnetic lubricants were discussed in relation to worn surface analyses by SEM-EDS,XPS,and profilometry,as well as measurement of the electric contact resistance of the rubbed steel surfaces.The results revealed that the MIL exhibits better friction-reducing and antiwear performances than the as-received MF under varying test temperatures and loads.This is because the MIL participates in tribochemical reactions during the sliding process,and forms a boundary lubrication film composed of Dy_(2)O_(3),FeS,FeSO_(4),nitrogen-containing organics,and thioether on the rubbed disk surface,thereby reducing the friction and wear of the frictional pair.However,the MF is unable to form a lubricating film on the surface of the rubbed steel at 25°C,though it can form a boundary film consisting of Fe_(3)O_(4) and a small amount of organics under high temperature.Furthermore,the excessive Fe_(3)O_(4) particulates that accumulate in the sliding zone may lead to enhanced abrasive wear of the sliding pair.

Role of nanoparticles in achieving macroscale superlubricity of graphene/nano-SiO_(2) particle composites

Recent studies have reported that adding nanoparticles to graphene enables macroscale superlubricity to be achieved.This study focuses on the role of nanoparticles in achieving superlubricity.First,because graphene nanoscrolls can be formed with nanoparticles as seeds under shear force,the applied load(or shear force)is adjusted to manipulate the formation of graphene nanoscrolls and to reveal the relationship between graphene-nanoscroll formation and superlubricating performance.Second,the load-carrying role of spherical nano-SiO_(2)particles during the friction process is verified by comparison with an elaborately designed fullerene that possesses a hollow-structured graphene nanoscroll.Results indicate that the incorporated nano-SiO_(2)particles have two roles in promoting the formation of graphene nanoscrolls and exhibiting load-carrying capacity to support macroscale forces for achieving macroscale superlubricity.Finally,macroscale superlubricity(friction coefficient:0.006–0.008)can be achieved under a properly tuned applied load(2.0 N)using a simple material system in which a graphene/nano-SiO_(2)particle composite coating slides against a steel counterpart ball without a decorated diamond-like carbon film.The approach described in this study could be of significance in engineering.

Tribological performance of various metal-doped carbon dots as water-based lubricant additives and their potential application as additives of poly(ethylene glycol)

Advances in nano-lubricant additives are vital to the pursuit of energy efficiency and sustainable development.Carbon dots(CDs)have been widely investigated in the domain of lubricant additives owing to their extraordinary tribological properties,in particular,their friction-reducing and anti-wear properties.Metal-doped CDs are a new type of CDs,and their friction-reducing and anti-wear properties are attracting increasing attention.Therefore,a series of CDs doped with various divalent metal ions have been successfully synthesized via one-pot pyrolysis.The tribological properties of the synthesized CDs as water-based lubricant additives are in the following order:Zn-CDs>Cu-CDs>>Mg-CDs>Fe-CDs>U-CDs.Specifically,adding 1.0 wt%of Zn-CDs into water-based lubricant results in 62.5%friction and 81.8%wear reduction.Meanwhile,the load-carrying capacity of the water-based lubricant increases from 120 N to at least 500 N.Zn-CDs as an additive have long service life.Additionally,anion-tuned Zn-CDs fabricated via anion exchange exhibit promise as lubricant additives for poly(ethylene glycol).Based on the results of wear scar surface analyses,it is discovered that tribochemical films,primarily composed of iron oxides,nitrides,metal carbonates,zinc oxides,zinc carbonates,organic compounds,and embedded carbon cores,formed on the rubbing surfaces with a thickness of approximately 270 nm when Zn-CDs are used as additives.This film combined with the“ball-bearing”and third-particle effects of Zn-CDs contributed to excellent lubrication performance.

Characterizing a lubricant additive for 1,3,4-tri-(2-octyldodecyl) cyclopentane: Computational study and experimental verification

In order to increase the life of spacecraft, it is important to improve the comprehensive lubrication performance. Multiple alkylated cyclopentane (MAC) lubricants are presently gaining wide acceptance for actual space applications; adding extreme pressure additive is a strategy to improve lubrication performance. In this study, taking 1,3,4-tri-(2-octyldodecyl) cyclopentane as base oil, tricresol phosphate (traditional additive) and tri-(2-octyldodecyl) phosphate (developmental additive) have been screened computationally for compatibility, shear film forming and energy dissipation. Theoretical results indicate that (a) tricresol phosphate additive is not suited for addition to 1,3,4-tri-(2-octyldodecyl) cyclopentane lubricant due to limited compatibility; (b) tri-(2-octyldodecyl) phosphate is an excellent lubricant additive due to its perfect compatibility, ease of forming a shear film on the surface of friction pairs, higher strength, and low energy dissipation; and (c) lubrication occurs through the solid-liquid composite lubrication mechanism. These theoretical results were confirmed experimentally.