Superlubricity behaviors of Nitinol 60 alloy under oil lubrication

The tribological tests were performed using Nitinol 60 alloy pin sliding over GCr15 steel disc in the tribometer system. Four kinds of oils were experimentally investigated as lubrication oils for lubricating Nitinol 60 alloy in the boundary lubrication regime. The experimental results were compared with a reference dry friction. It was found that Nitinol 60 alloy can be lubricated significantly and has shown remarkable lubrication performance. A superlubricity behavior of Nitinol 60 alloy was observed under castor oil lubrication. An ultra-low coefficient of friction of Nitinol 60 alloy about 0.008 between Nitinol 60 alloy and GCr15 steel was obtained under castor oil lubrication condition after a running-in period. Accordingly, the present study is focused on the lubrication behaviors of castor oil as potential lubrication oil for Nitinol 60 alloy. In the presence of castor oil, coefficient of friction is kept at 0.008 at steady state, corresponding to so-called superlubricity regime （when sliding is then approaching pure rolling）. The mechanism of superlubricity is attributed to the triboformed OH-terminated surfaces from friction-induced dissociation of castor oil and the boundary lubrication films formed on the contact surface due to high polarity and long chain of castor oil allowing strong interactions with the lubricated surfaces.

Effects of Fatty Acids on Low-Sulfur Diesel Lubricity:Experimental Investigation, DFT Calculation and MD Simulation

The continuous reduction in sulfur content of fuels would lead to diesel fuel with poor lubricity which could re- sult in engine pump failure. In the present work, fatty acids were adopted as lubricity additives to low-sulfur diesel fuel. It was attempted to correlate the molecular structures of fatty acids, such as carbon chain length, degree of saturation and hy- droxylation, to their lubricity enhancement, which was evaluated by the High-Frequency Reciprocating Rig （HFRR） meth- od. The efficiency order was supported by the density functional theory （DFT） calculations and the molecular dynamics （MD） simulations. The lubricity enhancing properties of fatty acids are mainly determined by the cohesive energy of adsorbed films furmed on iron surface. The greater the cohesive energy, the more efficiently the fatty acid would enhance the lubricity of low-sulfur diesel fuel.

Experimental and Molecular Dynamics Simulations for Investigating the Effect of FattyAcid and Its Derivatives on Low Sulfur Diesel Lubricity

In this work,fatty acid and its derivatives were adopted as lubricity additives for low sulfur diesel.Tribological evaluation obtained from the High-Frequency Reciprocating Rig(HFRR)apparatus showed that the lubricating performance of the additives increased in the following order:stearic acid>glycol monopalmitate>stearyl alcohol>ethyl palmitate>cetyl ethyl ether.The adsorption behavior of the additives on Fe(110)surface and Fe2O3(001)surface was investigated by molecular dynamics(MD)simulations to verify their lubricity performance.The results suggested that adsorption energies of the additives on Fe(110)surface are determined by the van der Waals forces,while adsorptions on Fe2O3(001)surface are significantly attributed to the electrostatic attractive forces.Higher values of adsorption energy of the additives on Fe2O3(001)surface indicate that the additive has more efficient lubricity enhancing properties.

Superlubricity of a Mixed Aqueous Solution

A super-low friction coefficient of 0.0028 is measured under a pressure of 300MPa when the friction pair(the silicon nitride ball sliding on the silicate glass)is lubricated by the mixed aqueous solution of glycerol and boric acid.The morphorlogies of the hydroxylated glass plate are observed by an atomic force microscope(AFM)in deionized water,glycerol,boric acid and their mixed aqueous solution.Bonding peaks of the retained liquids adhered on the surface of the sliding track are detected by an infrared spectrum apparatus and a Raman spectrum apparatus.The mechanism of the superlubricity of the glycerol and boric acid mixed aqueous solution is discussed.It is deduced that the formation of the lubricant film has enough strength to support higher loads,the hydration effect offering the super lower shear resistance.

Experimental and Molecular Simulations for Evaluating the Effect of Lubricity Improvers on the Property of Jet Fuel

Since the 1990 s, the kerosene fuel(code: JP-8) had been applied in the ground equipment provided with direct injection compression ignition engines in the U.S. Army, resulting in increased occurrence of injection pump failures. Anti-wear additives must be used in the single fuel due to its poor lubricity. In the present work, lubricity improvers were selected on the basis of molecular simulation theoretically and these agents were evaluated to improve the lubricity of jet fuel using the high frequency reciprocating rig(HFRR) apparatus and the ball-on-cylinder lubricity evaluator(BOCLE). It was revealed that dimer acid with higher value of adsorption energy on the Fe(110) plane surface had more efficient lubricity promoting properties than that of naphthenic acid. The experimental results suggested that the dimer acid had a better tribological behavior compared with that of naphthenic acid used as lubricity improver of jet fuel. And addition of anti-wear additives at a dosage of 15 μg/g was able to promote the lubricity of jet fuel to a required level on BOCLE, while a higher concentration over 80 μg/g was needed to improve the lubricity to a demanded value of diesel on HFRR.

Lubricity of Rare Earth Compounds in Oil

The lubricities of fifteen rare earth compounds of lanthanum, praseodymium, samarium, europium and gadolinium are evaluated on a four ball tester and compared with that of ZDDP(Zinc Dialkyldithiophosphate). Results show that some of rare earth compounds provide much better lubricities than ZDDP, and the hexagonal type of rare earth metal compounds exhibit better lubricites than the body centered cubic type of metal compounds.

Scalable preparation of functionalized graphite nanoplatelets via magnetic grinding as lubricity-enhanced additive

Graphite nanoplatelets were prepared by a novel magnetic-grinding method using self-made equipments. Under a variant magnetic field, magnetic needles collided at a high rotating speed and exfoliated pristine graphite into graphite nanoplatelets with high efficiency. The obtained graphite nanoplatelets are highly crystalline, and the thickness is less than 10 nm. Moreover, the surface area could reached 738.1 m^2/g with a grinding time of 4 h. Silanized graphite nanoplatelets can disperse well in SG 15W-40 engine oil and serve as lubricant additive. Tribological results indicate that the friction coefficient and wear-scar of the friction pairs are lower than 76% and 41%, respectively, by adding 1.5‰(mass fraction) of silanized graphite nanoplatelets. Notably, the functionalized graphite nanoplatelets can realize large-scale production and commercial application.

Liquid superlubricity of lubricants containing hydroxyl groups and their aqueous solution under rolling/sliding conditions

Macroscale rolling/sliding conditions are in the superlubricity,a little-studied topic so far.The purpose of this paper is to examine the formation of elastohydrodynamic lubrication(EHL)films by water-based lubricants(glycerol and polyethylene glycol(PEG)),providing superlubricous friction.Experiments were carried out on an optical ball-on-disc tribometer under rolling/sliding conditions.The film thickness was measured by the thin film colorimetric interferometry,and the viscosity of liquids was measured by rotational and high-pressure falling body viscometers.The results show that tribochemical reactions are not the mandatory reason for friction to reach the superlubricity level when using the water-based lubricants.The studied liquids themselves are almost Newtonian.With the addition of water,the signs of shear thinning behavior disappear even more.Suitable conditions for this type of lubricant can be predicted using the known Hamrock–Dowson equations.An anomaly in the thickness of the lubricants was observed as an abrupt change at certain conditions.The more PEG there is in the lubricant,the higher the thickness at the beginning of the jump.

Combination of diketone and PAO to achieve macroscale oil-based superlubricity at relative high contact pressures

1-(4-ethylphenyl)-nonane-1,3-dione(0206)is an oil-soluble liquid molecule with rod-like structure.In this study,the chelate(0206-Fe)with octahedral structure was prepared by the reaction of ferric chloride and 1,3-diketone.The experimental results show that when using 0206 and a mixed solution containing 60%0206-Fe and 40%0206(0206-Fe(60%))as lubricants of the steel friction pairs,superlubricity can be achieved(0.007,0.006).But their wear scar diameters(WSD)were very large(532µm,370µm),which resulted in the pressure of only 44.3 and 61.8 MPa in the contact areas of the friction pairs.When 0206-Fe(60%)was mixed with PAO6,it was found that the friction coefficient(COF)decreased with increase of 0206-Fe(60%)in the solution.When the ratio of 0206-Fe(60%)to PAO6 was 8:2(PAO6(20%)),it exhibited better comprehensive tribological properties(232.3 MPa).Subsequent studies have shown that reducing the viscosity of the base oil in the mixed solution helped to reduce COF and increased WSD.Considering the COF,contact pressure,and running-in time,it was found that the mixed lubricant(Oil3(20%))prepared by the base oil with a viscosity of 19.7 mPa·s(Oil3)and 0206-Fe(60%)exhibited the best tribological properties(0.007,161.4 MPa,3,100 s).

Research progress on rolling superlubricity in solid lubricants

Superlubricity is an ideal lubrication state where friction nearly vanishes between contact interfaces. It has become one of the most important research topics and approaches owing to its significance in reducing energy consumption and preventing device failures. As an efficient and universal lubricating principle capable of achieving superlubricity, rolling lubrication has attracted widespread attention in recent years. In this review, the theoretical concept of rolling lubrication and the experimental research progress of spherical/scroll structures are summarized. The review focuses on the possibility of achieving rolling lubrication using spherical/scroll structures(such as spherical fullerenes, carbon nanotubes, and formed and constructed spherical/scroll structures). The challenges in achieving rolling lubrication are summarized, and the possibility of molecular rolling lubrication,as well as its potential applications in superlubrication, are discussed.

A novel polyionic liquid with lubricity and viscosity-increasing dual functionalities as the additive in aqueous lubrication system

The polyionic liquid poly-PEGMA-r-METAC(PPM)with quaternary ammonium has been synthesized and evaluated as additive in aqueous lubricating fluids.The rheological behavior of aqueous lubricating fluids with PPM has been characterized to confirm PPM’s function as a viscosity modifier.The tribological behavior of aqueous lubricating fluids with PPM has been investigated on SRV-V and MTM testing machines.It was found that PPM has excellent viscosity-increasing,lubricating,and anti-wear properties as an additive for aqueous,which can be attributed to the ability of PPM to form the protective film and boundary tribofilm generated from complex tribochemical reaction on rubbing surface.The obtained PPM with dual functions of anti-corrosion additives and viscosity index improver can play an important role in diverse lubrication regimes.

Experimental study on boundary lubricity of superficial area of articular cartilage and synovial fluid

The boundary lubrication mechanism at the articulating surface of natural synovial joints has been the subject of much discussion in tribology.In this study,to elucidate the lubricating function of the superficial area of articular cartilage and synovial fluid(SF),cartilage specimens were processed with four different treatments:gentle and severe washing with detergent,incubation in NaCl solution,and trypsin digestion to selectively remove certain constituents from the cartilage surface.Subsequently,the frictional characteristics were examined in phosphate-buffered saline(PBS)and SF against glass.Angularly reciprocating sliding tests with a spherical glass probe and square articular cartilage specimens were performed at low contact loads in the mN range to extract the frictional behavior in the superficial area of the cartilage specimens.Meanwhile,the cartilage surface was observed to confirm the effects of treatments on the morphology of the cartilage surface using a fluorescence microscope and water-immersion methods.The coefficient of friction(COF)of the prepared cartilage specimens was varied from 0.05 to over 0.3 in PBS.However,a certain group of cartilage specimens exhibited a low COF of less than 0.1 with limited variation.For the low COF group of specimens,all four treatments increased the COF in PBS to different extents,and fluorescence microscopy revealed that the integrity of the cartilage surface was deteriorated by treatments.This means that the intact cartilage surface had lubricating constituents to maintain low friction,and the removal of such constituents resulted in the loss of the intrinsic boundary lubricity of the cartilage surface.The variation in the COF of the cartilage specimens was suppressed in SF because it had a clear boundary lubrication effect on the cartilage surface.The lubricating effect of SF could be confirmed even after degenerative treatment.

Achieving macroscale superlubricity with ultra-short running-in period by using polyethylene glycol-tannic acid complex green lubricant

Superlubricating materials can greatly reduce the energy consumed and economic losses by unnecessary friction.However,a long pre-running-in period is indispensable for achieving superlubricity;this leads to severe wear on the surface of friction pairs and has become one of the important factors in the wear of superlubricating materials.In this study,a polyethylene glycol-tannic acid complex green liquid lubricant(PEG10000-TA)was designed to achieve macroscale superlubricity with an ultrashort running-in period of 9 s under a contact pressure of up to 410 MPa,and the wear rate was only 1.19×10^(–8)mm^(3)·N^(−1)·m^(−1).This is the shortest running-in time required to achieve superlubricity in Si_(3)N_(4)/glass(SiO_(2)).The results show that the strong hydrogen bonds between PEG and TA molecules can significantly reduce the time required for the tribochemical reaction,allowing the lubricating material to reach the state of superlubrication rapidly.Furthermore,the strong hydrogen bond can share a large load while fixing free water molecules in the contact zone to reduce shear interaction.These findings will help advance the use of liquid superlubricity technology in industrial and biomedical.

Low friction of superslippery and superlubricity:A review

The issues regarding energy dissipation and component damage caused by the interface friction between a friction pair attract enormous attention to friction reduction.The key-enabling technique to realize friction reduction is the use of lubricants.The lubricants smooth the contact interfaces,achieving an ultralow friction contact,which is called superslippery or superlubricity.At present,superslippery and superlubricity are two isolated research topics.There is a lack of unified definition on superslippery and superlubricity from the viewpoint of tribology.Herein,this review aims at exploring the differences and relations between superslippery and superlubricity from their origin and application scenarios.Meanwhile,the challenges for developing superslippery surface and superlubricity surface are discussed.In addition,perspectives on the interactive development of these two surfaces are presented.We hope that our discussion can provide guidance for designing superslippery or superlubricity surfaces by using varies drag-reduction technologies.

Astonishingly distinct lubricity difference between the ionic liquid modified carbon nanoparticles grafted by anion and cation moieties

The astonishingly distinct lubricity difference between the ionic liquid modified carbon nanoparticles grafted by anion and cation moieties(A-g-CNPs and C-g-CNPs)was well established as additives of polyethylene glycol(PEG200).The peripheral anion moieties and positively charged inner parts of C-g-CNPs could successively absorb onto the friction interfaces by electrostatic interactions to form the organic-inorganic electric double layer structures,tremendously boosting the lubricity of PEG200.Contrarily,the preferentially electrostatic adsorption of negatively charged inner parts but repulsion of the peripheral cation moieties determined the weak embedded stability of A-g-CNPs between the friction interfaces,even impairing the lubricity of PEG200.This work can offer solidly experimental and theoretical guidance for designing and developing the high-performance nanoadditives modified by ionic molecules.

Rheology and lubricity characteristics study at different temperatures using synthesized SnO_(2) nanoparticles in KCl free bentonite water base mud

Drilling mud is a major concerning element due to its high operational and economic impact on the drilling process.Various additives are introduced to enhance the efficiency of drilling fluid,but none of them could perfectly achieve their proposed efficacy in drilling operations.Researchers conceived several nanoparticles(NPs)in drilling fluid to dissolve this issue.In a singular instance,commercial tin oxide(SnO_(2))nanoparticles were utilized to analyze the influence of NPs on the rheological and filtration properties of inorganic KCl salt-based drilling fluid.However,the effect of SnO_(2) NPs on mud lubricity characteristics is not studied previously.However,due to the hazardous behavior of KCl,its use is very limited.Thus,we consider a KCl-free bentonite water-based mud to avoid any environmental damages from drilling operations.We also use SnO_(2) NPs that is synthesized in our laboratory by co-precipitation method.In addition to rheological and filtration properties,we also investigate the effect of NPs on mud's lubricity that was not considered in the previous study.Drilling fluid properties are measured at five different NPs concentrations of 0.10,0.25,0.50,0.75&1.0 wt%,and at six different temperatures of 30,40,50,60,70,and 80°C,while filtration properties are measured using API low-pressure low temperature(LPLT)condition.The addition of 0.1 wt%SnO_(2) NPs increases plastic viscosity,yield point,10 s gel strength,and 10 min gel strength by 10%,63%,20%,and 14%,respectively.The maximum reduction in lubricity coefficient is found to be 14%at NPs concentration of 1.0 wt%.The NPs concentration of 0.5 wt%yielded a reduction in fluid loss and mud cake thickness by 8.1%and 34%,respectively.The study suggests that SnO_(2) NPs can be employed as an additive to improve the rheology,lubricity,and filtration properties of KCl-free bentonite water-based drilling mud.

Superlubricity on the nanometer scale

The transition from atomic stick-slip to continuous sliding has been observed in a number of ways.If extended contacts are moved in different directions,so-called structural lubricity is observed when the two surface lattices are non-matching.Alternatively,a“superlubric”state of motion can be achieved if the normal force is reduced below a certain threshold,the temperature is increased,or the contact is actuated mechanically.These processes have been partially demonstrated using atomic force microscopy,and they can be theoretically understood by proper modifications of the Prandtl−Tomlinson model.

Influence of structural depth of laser-patterned steel surfaces on the solid lubricity of carbon nanoparticle coatings

Carbon nanoparticle coatings on laser-patterned stainless-steel surfaces present a solid lubrication system where the pattern's recessions act as lubricant-retaining reservoirs.This study investigates the influence of the structural depth of line patterns coated with multi-walled carbon nanotubes(CNTs)and carbon onions(COs)on their respective potential to reduce friction and wear.Direct laser interference patterning(DLIP)with a pulse duration of 12 ps is used to create line patterns with three different structural depths at a periodicity of 3.5μm on AISI 304 steel platelets.Subsequently,electrophoretic deposition(EPD)is applied to form homogeneous carbon nanoparticle coatings on the patterned platelets.Tribological ball-on-disc experiments are conducted on the as-described surfaces with an alumina counter body at a load of 100 mN.The results show that the shallower the coated structure,the lower its coefficient of friction(COF),regardless of the particle type.Thereby,with a minimum of just below 0.20,CNTs reach lower COF values than COs over most of the testing period.The resulting wear tracks are characterized by scanning electron microscopy,transmission electron microscopy,and energy-dispersive X-ray spectroscopy.During friction testing,the CNTs remain in contact,and the immediate proximity,whereas the CO coating is largely removed.Regardless of structural depth,no oxidation occurs on CNT-coated surfaces,whereas minor oxidation is detected on CO-coated wear tracks.

Synthetic polymers:A review of applications in drilling fluids

With the growth of deep drilling and the complexity of the well profile,the requirements for a more complete and efficient exploitation of productive formations increase,which increases the risk of various complications.Currently,reagents based on modified natural polymers(which are naturally occurring compounds)and synthetic polymers(SPs)which are polymeric compounds created industrially,are widely used to prevent emerging complications in the drilling process.However,compared to modified natural polymers,SPs form a family of high-molecular-weight compounds that are fully synthesized by undergoing chemical polymerization reactions.SPs provide substantial flexibility in their design.Moreover,their size and chemical composition can be adjusted to provide properties for nearly all the functional objectives of drilling fluids.They can be classified based on chemical ingredients,type of reaction,and their responses to heating.However,some of SPs,due to their structural characteristics,have a high cost,a poor temperature and salt resistance in drilling fluids,and degradation begins when the temperature reaches 130℃.These drawbacks prevent SP use in some medium and deep wells.Thus,this review addresses the historical development,the characteristics,manufacturing methods,classification,and the applications of SPs in drilling fluids.The contributions of SPs as additives to drilling fluids to enhance rheology,filtrate generation,carrying of cuttings,fluid lubricity,and clay/shale stability are explained in detail.The mechanisms,impacts,and advances achieved when SPs are added to drilling fluids are also described.The typical challenges encountered by SPs when deployed in drilling fluids and their advantages and drawbacks are also discussed.Economic issues also impact the applications of SPs in drilling fluids.Consequently,the cost of the most relevant SPs,and the monomers used in their synthesis,are assessed.Environmental impacts of SPs when deployed in drilling fluids,and their manufacturing processes are identified,together with advances in SP-treatment methods aimed at reducing those impacts.Recommendations for required future research addressing SP property and performance gaps are provided.

Nanotribological studies using nanoparticle manipulation: Principles and application to structural lubricity

The term“structural lubricity”denotes a fundamental concept where the friction between two atomically flat surfaces is reduced due to lattice mismatch at the interface.Under favorable circumstances,its effect may cause a contact to experience ultra-low friction,which is why it is also referred to as“superlubricity”.While the basic principle is intriguingly simple,the experimental analysis of structural lubricity has been challenging.One of the main reasons for this predicament is that the tool most frequently used in nanotribology,the friction force microscope,is not well suited to analyse the friction of extended nanocontacts.To overcome this deficiency,substantial efforts have been directed in recent years towards establishing nanoparticle manipulation techniques,where the friction of nanoparticles sliding on a substrate is measured,as an alternative approach to nanotribological research.By choosing appropriate nanoparticles and substrates,interfaces exhibiting the characteristics needed for the occurrence of structural lubricity can be created.As a consequence,nanoparticle manipulation experiments such as in this review represent a unique opportunity to study the physical conditions and processes necessary to establish structural lubricity,thereby opening a path to exploit this effect in technological applications.