Exploring the Friction and Wear Properties of Silver Coatings on 718 Alloy

Fasteners of 718 alloys are used to set up connection between each support and other components for ITER system, metal-based Ag solid lubricant coating is widely used as an anti-seizure lubricant coating due to its strong low-temperature shear resistance. But the poor adhesion to the steel surfaces has been a critical restriction for applying the silver coatings to the practical machine elements. In this work, an 8-μm silver self-lubricating coating was deposited on the surface of 718 alloy by the method of magnetron sputtering. The coating was uniform, dense and consistent. The wear mechanism was investigated by analyzing the friction and wear properties of the coating. Stress is one of the important impacts on the friction coefficient, the results showed that it first increased and then decreased with the increase of pressure at room temperature and under vacuum. Temperature exerted an effect on the silver self-lubricating coating. A study was conducted under vacuum on the friction and wear performance of the coating at 300 K, 225 K, 155 K, and 77 K, respectively. The results showed that the wear mechanism and wear state varied under various low-temperature conditions, with the severity of wear reaching the maximum only at 225 K. Through the same silver coating process, the washer of superbolt was improved by silver coating treatment.

Molecular Dynamics Simulation on Friction and Thermal Properties of FCC Copper in Nanoscale Sliding Contacts

In nanoscale sliding contact,adhesion effects and adhesive force are predominant,and high friction force will be produced.Friction energy is mainly converted into heat,and the heat will make nanomaterials become soft to affect friction behaviors,so it is important to investigate the friction and thermal properties of the nanoscale sliding contacts.A model of a nanoscale sliding contact between a rigid cylindrical tip and an FCC copper substrate is developed by molecular dynamics simulation.The thermal properties of the substrate and the friction behaviors are studied at different sliding velocities and different tip radii.The results show that at a low sliding velocity,the friction force fluctuation is mainly caused by material melting⁃solidification,while at a high sliding velocity the material melting is a main factor for the friction reduction.The average friction forces increase at initial phase and then decrease with increasing sliding velocity,and the average temperature of the substrate increases as sliding velocity increases.Increasing tip radius significantly increases the temperature,while the coupled effects of tip radius and temperature rise make friction force increase slightly.

Lyapunov exponent and dimension of the strange attractor of elastic frictional system

In this paper, we have calculated the spectrum of Lyapunov exponent of the strange attractor for a single degree of freedom in elastic system with a two-state variable friction law via the method advanced by Wolf. The system is expressed by the following dimensionless equation:where,and f are dimensionless state variable, logarithm slip velocity and frictional stress, respectively;β1,β2,ρ,and K are dimensionless system parameters.The state of this system is chaotic when dimensionless parameters are β1=1. 00, β2=0. 84, ρ=0. 048, =0. 198 85, K=0. 0685.The Lyapunov exponent spectrum of its strange attractor has been calculated as follows:λ1=0. 0179, λ2=0, λ3=-0. 1578The dimension of this strange attractor has also been calculated as DL=D0=2.11where DL and D0 denote Lyapunov dimension and Kolmogorov dimension respectively.

Morphology,Bending Property and Secondary Structure Estimation of Dog Hair

The morphology, bending property and secondary structure estimation of dog hair were investigated by scanning electron microscope( SEM),fiber compression bending analyzer,fiber frictional coefficient tester and Fourier transform infrared spectroscopy( FTIR). The SEM micrograph of hair indicated guard hair( GH),intermediate hair( IH) and underhair( UH) from dog hair fibers displayed considerable differences in the diameter,length,scale shape and medulla. In addition,the bending property of fibers were related to the diameter of fibers and the percentage and structure of medulla. The UH had the greatest frictional coefficient,while the guard hair had the largest bending rigidity in three kinds of hairs. The analysis of amide I region implied that there was an apparent variety in the secondary structure of hairs,mainly the percentage of α-helix and β-pleated sheet and β-turn structure. The X-ray diffraction results showed that the crystallinity of the UH was the lowest in the three kinds of fibers. The tensile behaviors of dog hair also indicated that the increase of β-pleated and β-turn structure caused the increase of the breaking strength.

The Friction Wear Properties and Application of Thermoplastic Polyester Elastomer and Polyoxymethylene

The experiment of injection molding, Dais-simulating test, morphological structure investigation(Scanning Electron Microscopy, SEM),X-ray photoelectron spectroscopy(XPS)were performed on mini-automobile spherical seat which was made of thermoplastic polyester elastomer(TPEE)and oiled polyoxymethylene(POM),respectively. The friction-wear properties between the frictionl pair of polymer spherical seat and metallic(iron)spherical pin were studied. The test results indicate that the antifriction property of TPEE is superior to that of POM, while its surface chemical effect is inferior to that of POM.

Constitutive Model of Friction Stir Weld with Consideration of its Inhomogeneous Mechanical Properties

In practical engineering, finite element（FE） modeling for weld seam is commonly simplified by neglecting its inhomogeneous mechanical properties. This will cause a significant loss in accuracy of FE forming analysis, in particular, for friction stir welded（FSW） blanks due to the large width and good formability of its weld seam. The inhomogeneous mechanical properties across weld seam need to be well characterized for an accurate FE analysis. Based on a similar AA5182 FSW blank, the metallographic observation and micro-Vickers hardness analysis upon the weld cross-section are performed to identify the interfaces of different sub-zones, i.e., heat affected zone（HAZ）, thermal-mechanically affected zone（TMAZ） and weld nugget（WN）. Based on the rule of mixture and hardness distribution, a constitutive model is established for each sub-zone to characterize the inhomogeneous mechanical properties across the weld seam. Uniaxial tensile tests of the AA5182 FSW blank are performed with the aid of digital image correlation（DIC） techniques. Experimental local stress-strain curves are obtained for different weld sub-zones. The experimental results show good agreement with those derived from the constitutive models, which demonstrates the feasibility and accuracy of these models. The proposed research gives an accurate characterization of inhomogeneous mechanical properties across the weld seam produced by FSW, which provides solutions for improving the FE simulation accuracy of FSW sheet forming.

Effects of different friction stir welding conditions on the microstructure and mechanical properties of copper plates

Friction stir welding is a new and innovative welding method used to fuse materials. In this welding method, the heat generated by friction and plastic flow causes significant changes in the microstructure of the material, which leads to local changes in the mechanical properties of the weld. In this study, the effects of various welding parameters such as the rotational and traverse speeds of the tool on the microstructural and mechanical properties of copper plates were investigated; additionally, Charpy tests were performed on copper plates for the first time. Also, the effect of the number of welding passes on the aforementioned properties has not been investigated in previous studies. The results indicated that better welds with superior properties are produced when less heat is transferred to the workpiece during the welding process. It was also found that although the properties of the stir zone improved with an increasing number of weld passes, the properties of its weakest zone, the heat-affected zone, deteriorated.

Effect of micro-dimple patterns on capillary pull-off force and friction force of silicon surface

A microtribometer is used to measure and compare pull-off forces and friction forces exerted on （a） micro-dimpled silicon surfaces, （b） bare silicon surfaces, and （c） octadecyltrichlorosilane （OTS） treated silicon surfaces at different relative humidity （RH） levels separately. It is found that above a critical RH level, the capillary pull-off force increases abruptly and that the micro-dimple textured surface has a lower critical RH value as well as a higher pull-off force value than the other two surfaces. A micro topography parameter, namely sidewall area ratio, is found to play a major role in controlling the capillary pull-off force. Furthermore, micro-dimpled silicon surface is also proved to be not sensitive to variation in RH level, and can realize a stable and decreased friction coefficient compared with un-textured silicon surfaces. The reservoir-like function of micro dimples is considered to weaken or avoid the breakage effect of liquid bridges at different RH levels, thereby maintaining a stable frictional behaviour.

Research on material design and high-temperature friction and wear properties of new graphitic steel

To solve the problem of the severe mismatch between the product and roll materials in the preliminary rolling line,a new graphitic steel material was designed,its microstructure and high-temperature friction and wear properties were investigated.Moreover,the feasibility of replacing semi-steel with this new material in the V1 stand roll was studied herein.The results show that the graphitic steel matrix is strengthened by silicon and nickel elements.The presence of spherical graphite also provides self-lubrication and heat conduction and prevents the propagation of cracks.Carbides in the appropriate amount and size strengthen the matrix,reduce the cracking effect of the matrix,and are not easily broken,thereby reducing high-temperature abrasive wear.Under the same hightemperature friction and wear conditions,compared with semi-steel,the wear-scar surface of graphitic steel exhibits less wear-scar depth and wear volume,a smaller friction coefficient,reduced oxide layer thickness,and fewer instances of peeling and microcracks.Therefore,the newly designed graphitic steel has higher wear resistance and hot-crack resistance than semi-steel,which makes it feasible for use in replacing semi-steel as a new V1 frame roll material in the blooming mill.

Analysis on Tribological Properties of Potentially New Friction Material with Response Surface Method

The tribological properties of newly developed friction material were evaluated by statistical analysis of the major affecting factors.The material for investigation was non-metallic friction material synergistically reinforced with aramid fibre and CaSO 4 whisker,which was developed for hoisting applications in coal mine.The response surface method（RSM）was employed to analyze the material performances affected by the independent and interactive effect of the factors under the normal working condition and severe working condition,respectively.Results showed that under the normal working condition,the newly developed material exhibited stable tribological properties which were insensitive to the test conditions.While under the severe working condition,the sliding velocity was the most dominant factor affecting the friction coefficient.Additionally,compared to the commercially available material,the modified material showed superior wear resistance and thermal stability.

FABRICATION AND AFM/FFM STUDIES OF C_(60)-CONTAINING POLYELECTROLYTE SELF-ASSEMBLED FILMS

An initial investigation on the roughness and frictional properties of the self-assembled thin films from polyelectrolytes is presented. Star-shaped C-60-Poly(styrene-maleic anhydride) was successful prepared. The multilayer thin films have been fabricated on mica with diazoresin as the cationic polyelectrolyte and hydrolyzed star-shaped C-60-poly(styrene-maleic anhydride) as the anionic polyelectrolyte via self-assembly technique. The crosslinking structure of the films is formed from the conversion of ionic bond to covalent bond after UV irradiation. AFM/FFM investigations provide insights into the roughness and frictional properties on a microscale. The roughness depends strongly on the number of film layers in the case of C-60-containing films. The frictional forces of the films exhibited a well behaved non-linear relationship in response to the change of applied load. It supports the prediction of enhanced load-bearing property Of C60-containing thin films.

Impact Wear Properties of Metal-Plastic Multilayer Composites Filled with Glass Fiber Treated with Rare Earth Element Surface Modifier

The friction and wear properties of metal-plastic multilayer composites filled with glass fiber, which is treated with rare earth element surface modifier, under impact load and dry friction conditions were investigated. Experimental results show that the metal-plastic multilayer composite filled with glass fiber exhibits excellent friction and impact wear properties when using rare earth elements as surface modifier for the surface treatment of glass fiber.

Effect of Rare Earths-Treated Glass Fiber on Impact Wear-Resistance of Metal-Plastic Multilayer Composites

The friction and wear properties under impact load and dry friction conditions of metal-plastic multilayer composites filled with glass fiber, treated with rare earth elements, were investigated. The worn surfaces were observed and analyzed by scanning electron microscopy (SEM). It shows that applying rare earth elements surface modifier to treat the glass fiber surface can enhance the interfacial adhesion between the glass fiber and polytetrafluoroethylene (PTFE), as well as promote the interface properties of the composites. This helps to form a uniformly distributed and high adhesive transfer film on the counterface and abate the friction between the composite and the counterface. As a result, the wear of composite is greatly reduced. The composite exhibits excellent friction properties and impact wear-resistance.

Co- and post-seismic slip analysis of the 2017 M_(W)7.3 Sarpol Zahab earthquake using Sentinel-1 data

The M_(w)7.3 Sarpol Zahab earthquake that occurred in the Zagros Fold-Thrust Belt(ZFTB) of Iran on November 12,2017 is the largest earthquake instrumentally recorded in the region.This earthquake provides an opportunity to investigate the slip behaviour and frictional properties of the fault,which is significant for assessing future seismic potential.In this study,we use Sentinel-1 images to map the coand post-seismic deformation to invert for the fault slip.The result indicates that most of the coseismic slip is buried in the depth range of 11-17 km,and the maximum slip is about 3.8 m at a depth of 15 km.The coseismic slip induces an increase of Coulomb stress in the unruptured area of the seismogenic fault plane,driving the afterslip.Based on the stress-driven afterslip,we obtain a frictional parameter of(ab)=(0.001-0.002) for the updip afterslip zone and(a-b)=0.0002 for the downdip afterslip zone in the framework of rate-and-state friction.The constitutive parameter(a-b) of the fault is very small,suggesting that the fault segments are close to velocity-neutral and may experience coseismic rupture.

Effect of Sintering Temperature and Hydrophobic Treatment on the Microstructure and Properties of Copper-Graphite Composites

Copper-graphite composites were prepared by spark plasma sintering(SPS)using coppercoated graphite powder.Hydrophobic surfaces were successfully constructed by chemical etching and surface treatment.The density,metallographic structure,microstructure,Shore hardness,resistivity,water contact angle,and friction/wear properties of the composites were investigated using the Archimedes drainage method,a metallographic microscope,a scanning electron microscope,a hardness tester,a resistometer,a surface science tester,and a friction tester.The results showed that the relative density and Shore hardness of the copper-graphite composites increased slightly from 90.04%and 56 HSD to 92.66%and 59 HSD,respectively,when the sintering temperature increased from 700 to 900℃.The copper and graphite phases in the copper-graphite composites were uniformly distributed with a continuous and network-like structure at various sintering temperatures.The interface between the copper and graphite was in good condition,without any obvious cracks or voids.The optimum process for hydrophobic surface construction included etching with a 1 mol/L K_(2)Cr_(2)O_(7)-H_(2)SO_(4)solution for 1 min,and soaking in a 0.09 mol/L cetylbenzene sulfonic acid alcohol solution for 1 h.The contact angle of the copper-graphite composite reached 130°.Hydrophobic treatment was beneficial for reducing the friction coefficient(from 0.18-0.19 to 0.13-0.15)and the wear rate(from 4.1-6.2×10^(-3)to 1.1-2.1×10^(-3)mm^(3)/(N·m)),demonstrating obvious antifriction and wear-resisting properties.The resistivities of the hydrophobic-treated samples increased slightly,from(4-8)×10^(-7)Ω·m to(5-15)×10^(-7)Ω·m,meeting the resistivity requirements of copper-graphite composite pantograph sliders and current receiver sliders in actual working conditions.

Friction and wear properties of PM cam materials with different boron contents

In this study,effects of B addition on the sintering densification,microstructure,hardness,friction and wear properties of sintered Fe-2.4C-4Cr-1Mo-0.5P-0.7Si-2.5Cu(in wt%)were investigated.In spite of the decreased sintered density,the addition of B changes the phase composition of the materials and their ratio.Moreover,hardness of either the matrix or the liquid solidification structure dramatically increases.These changes in micro structure result in higher friction coefficient and lower wear loss.It is observed that the addition of0.1 wt%B offers the optimum friction and wear properties with a running-in period of only 30 s and wear volume loss of 0.006 mm^(3) under the testing conditions.Such friction and wear properties are superior to those of the other two widely used cam materials,cast iron and 45 steel.

Mechanical properties and frictional resistance of Al composites reinforced with Ti3C2Tx MXene

Two-dimensional(2D)Ti3C2Tx MXene is an attractive additive not only used in base oil due to its low friction coefficient,but also used in composites due to its high aspect ratio and rich surface functional groups.So far there has been intense research into polymer matrix composites reinforced with Ti3C2Tx,Here we report on the use of 2D Ti3C2Tx to enhance the mechanical and frictional properties of Al matrix composites.Ti3C2Tx/Al composites were designed and prepared by pre s sureless sintering followed by hot extrusion technique.The prepared composites exhibit a homogeneous distribution of Ti3C2Tx.The Vickers hardness and the tensile strength continuously increase with increasing Ti3C2Tx content.A hardness of 0.52 GPa and a tensile strength of 148 MPa were achieved in the 3 wt%Ti3C2Tx/Al composite.The frictional properties of pure Al and the Ti3C2Tx/Al composite were comparably studied under dry sliding.A low friction coefficient of 0.2,twice lower than that of pure Al,was achieved in the 3 wt%Ti3C2Tx/Al composite.Ti3C2Tx acting as a solid lubricant reduces the abrasive wear in the composite,improving the frictional properties of Al matrix composites.

Effects of fibrous fillers on friction and wear properties of polytetrafluoroethylene composites under dry or wet conditions

The friction and wear behavior and mechanism as well as the mechanical properties of polytetrafluoroethylene （PTFE） composites filled with potassium titanate whiskers （PTW） and short carbon fibers （CF） under dry, wet and alkaline conditions were investigated. Experiments indicated that owing to appropriate cooling and boundary lubricating effects, the filled PTFE composites showed much lower frictional coefficient and better wear resistance under alkaline than dry and wet sliding conditions. The wear resistance of carbon-fiber-filled PTFE was much better than that of potassium titanate-whisker-filled PTFE composites in water. Results also showed that the transfer film on counterpart rings was significantly hindered by water and alkali. Hydrophilic-filler-reinforced PTFE composites yield higher wear rate when sliding under water.

Fabrication of large-bulk ultrafine grained 6061 aluminum alloy by rolling and low-heat-input friction stir welding

In this study, the ultrafine grained （UFG） 6061 Al alloys fabricated by cold rolling were friction stir welded （FSW） with different rotation rates under both air cooling and rapid cooling in water. Low-heat-input parameters of 400 rpm rotation rate in water （400-Water） could effectively inhibit the coarsening of recrystallized grains, reduce the precipitation rate, and retain more dislocations of the UFG 6061 Al parent metal. 400-Water joint showed high lowest-hardness value, narrow low-hardness zone, and high tensile strength, attributing to the effect of dislocation, grain boundary, solid-solution, and precipitation hardening. This work provides an effective strategy to fabricate large-sized bulk UFG AI alloy by cold rolling with large deformation and low-heat-input FSW.

Effect of friction stir processed microstructure on tensile properties of an Al-Zn-Mg-Sc alloy upon subsequent aging heat treatment

An as-cast Al-Zn-Mg-Sc alloy was friction stir processed varying tool related parameters, yielding microstructures with different grain sizes （0.68, 1.8 and 5.5 μm）. Significant increases in room temperature ductility were obtained in these materials with reasonable enhancement in strength. It is demonstrated that the type of microstructure produced by friction stir processing （FSP） has a significant influence on the choice of post-FSP heat treatment design for achieving improved tensile properties. It is also found that the ultrafine grained FSP material could not achieve the desired high strength during the post-FSP heat treatment without grain coarsening, whereas the micro-grained FSP materials could reach such strength levels （〉560 MPa） under conventional age hardening heat treatment conditions.