Shot Peening and Solid Lubricating on Ti6 Al4 V Fretting Fatigue

The effects of three factors i.e. compressive residual stress, surface roughness and microstructure hardening in shot peened surface on fretting fatigue (FF) were evaluated. The results show that the residual stress and the surface roughness are predominant FF with the rectangular contact pad. Two kinds of commercial lubricants for post peening coating can not improve the FF resistance, since their processing reduce the compressive residual stress.

Low-cost solid FeS lubricant as a possible alternative to MoS2 for producing Fe-based friction materials

Three reaction systems of MoS_2-Fe, FeS -Fe, and Fe S-Fe-Mo were designed to investigate the use of FeS as an alternative to MoS_2 for producing Fe-based friction materials. Samples were prepared by powder metallurgy, and their phase compositions, microstructures, mechanical properties, and friction performance were characterized. The results showed that MoS_2 reacts with the matrix to produce iron-sulfides and Mo when sintered at 1050°C. Iron-sulfides produced in the MoS_2-Fe system were distributed uniformly and continuously in the matrix, leading to optimal mechanical properties and the lowest coefficient of friction among the systems studied. The lubricity observed was hypothesized to originate from the iron-sulfides produced. The Fe S-Fe-Mo system showed a phase composition, porosity, and density similar to those of the MoS_2-Fe system, but an uneven distribution of iron-sulfides and Mo in this system resulted in less-optimal mechanical properties. Finally, the Fe S-Fe system showed the poorest mechanical properties among the systems studied because of the lack of Mo reinforcement. In friction tests, the formation of a sulfide layer contributed to a decrease in coefficient of friction（COF） in all of the samples.

Solid FeS lubricant: a possible alternative to MoS2 for Cu–Fe-based friction materials

Molybdenum disulfide(MoS_2) is one of the most commonly used solid lubricants for Cu–Fe-based friction materials. Nevertheless, MoS_2 reacts with metal matrices to produce metal sulfides(e.g., FeS) and Mo during sintering, and the lubricity of the composite may be related to the generation of FeS. Herein, the use of FeS as an alternative to MoS_2 for producing Cu–Fe-based friction materials was investigated. According to the reaction principle of thermodynamics, two composites—one with MoS_2(Fe–Cu–MoS_2 sample) and the other with FeS(FeS–Cu_2S–Cu–Fe–Mo sample), were prepared and their friction behaviors and mechanical properties were compared. The results showed that MoS_2 reacted with the Cu–Fe matrix to produce FeS, metallic ternary sulfides, and Mo when sintered at 1050°C. The MoS_2–Cu–Fe and FeS–Cu_2S–Cu–Fe–Mo samples thereby exhibited similar characteristics with respect to phase composition, density, hardness, and tribological behaviors. Micrographs of the worn surfaces revealed that the stable friction regime for both composites stemmed from the iron sulfides friction layers rather than from the molybdenum sulfides layers.

High temperature tribological behaviors of aluminum matrix composites reinforced with solid lubricant particles

The AA6061-10 wt.%B4 C mono composite, AA6061-10 wt.%B4 C-Gr(Gr: graphite) hybrid composites containing 2.5, 5, and 7.5 wt.% Gr particles, and AA6061-10 wt.%B4 C-Mo S2 hybrid composites containing 2.5, 5, and 7.5 wt.% Mo S2 particles were fabricated through stir casting. The dry sliding tribological behaviors of the mono composite and hybrid composites were studied as a function of temperature on high temperature pin-on-disc tribotester against EN 31 counterface. The wear rate and friction coefficient of the Gr-reinforced and Mo S2-reinforced hybrid composites decreased in the temperature range of 30-100 ℃ due to the combined lubrication offered by the wear protective layer and its solid lubricant phase. Scanning electron microscopy(SEM) observation of the worn pin surface revealed severe adhesion, delamination, and abrasion wear mechanisms at temperatures of 150, 200, and 250 ℃, respectively. At 150 ℃, transmission electron microscopy(TEM) observation of the hybrid composites revealed the formation of deformation bands due to severe plastic deformation and fine crystalline structure due to dynamic recrystallization.

STUDY ON THE LUBRICATION FACTOR OF INVOLUTE SPUR GEARS

Based on a lot of numerical solutions to the problems of the thermalnon-Newtonian elastohydrodynamic lubrication and some fatigue tests with rollers, the lubricationfactor of involute spur gears (called gear for short) is investigated. The results suggest that gearlubrication effects bear close relations to a dimensionless parameter D which is syntheticallydetermined by gearing rotational speed, load, material, dimension and lubricant viscosity. When D<=8, the gear fatigue life increases as the lubricant viscosity is increased; When D>8, however, thelife decreases with the viscosity addition, which is in marked contrast to the lubrication factorZ_L recommended by the International Standard for Computing Cylindrical Gear Strength. At the end, aset of formulae for calculating gear lubrication factors suitable for different working conditionsare advanced.

Mechanical and friction properties of aluminum and titanium reinforced Ni-based self-lubricating composite

Ni-20Cr powders mixed with tungsten,aluminum,titanium,and different contents of molybdenum disulfides were hot-pressed in graphite mould by powder metallurgy method. Their tribological properties from room temperature to 600 ℃ and mechanical properties at atmosphere were tested. The results show that the hardness and anti-bending strength of composites increase by more than 20% when containing 6%(mass fraction) MoS2. But when molybdenum disulfide content exceeds 6%,the hardness and anti-bending strength will decrease gradually. The addition of MoS2 is favored to the reduction of friction coefficient of composite. The friction coefficient of composite decreases with the increase of molybdenum disulfide until the percentage of lubricant reaches 12%. In excess of this value,the friction coefficient value starts to ascend. The wear rates of composite with molybdenum disulfide are one order of magnitude lower than the alloy without lubricant. When the addition amount of MoS2 is in the range of 6% and 12%,the wear rates keep at the resemble level.

Microstructure and preparation of nano S-W-S new solid lubrication system

The method for preparing a new solid lubrication system of nano S W S was presented. The microstructure of the S W S nano cluster was investigated using TEM and XRD. The system is a mixture clusters of both monocrystal and polycrystal of layered hexagonal structure with one tungsten atom linking with two sulphur atoms, and the week Van der Waals’ force bonding together the different layers. The changes of electronic structure were studied with XPS. The hybridization of different electronic shell orbitals of the sulphur atom in the nano cluster is regarded as the quantum size effect. The clusters are found to be of a closed spherical structure without any dangling bond. [

Calculation of flash temperature for hybrid ceramic ball bearing lubricated with solid

The scuffing behavior of hybrid ceramic bearing lubricated with solid is greatly affected by the contact flash temperature. Formulas are dedused using Lee’s asperity flash temperature method, to calculate the flash temperature of ball bearing lubricated with solid. The maximum flash temperature is calculated for hybrid ceramic ball bearings. The results show that under given conditions, the flash temperature of inner race is higher than that of outer race, the flash temperature of the hybrid ceramic bearing is sensitive to the load, rotational speed and race curvature. The flash temperature of inner race at 20 000 r/min is 66 9% more than that that at 11 000 r/min, and with the load changing from 1.1 kN to 2 kN, the flash temperature inner race goes up to 165 7%. Very common for high speed ball bearings, when curvature coefficients of both inner and outer race change from 0 515 to 0 56, the inner race flash temperature decreases from 421 446℃ to 56 2℃.

Phase Representation and Property Determination of Raw Materials of Solid Lubricant

The composition, microstructure, mechanical and frictional properties of PTFE and its fillers were represented and analyzed by XRD, SEM, DSC, XPS and large-scale polarizing microscope. The results show that PTFE has a flocculent structure with high melt temperature and decomposition temperature, big contact angle and crystallinity, and low surface hardness, compression strength, friction coefficient, wearing capacity and surface energy. Cooling rate influenced the friction coefficient and wear resistance. Graphite and molybdenum disulfide have a flake structure, and molybdenum disulfide has a big contact angle and low surface energy. Copper powder has a globular structure and its chief component is Cu-Pb alloy, and there is a loose layer on the surface. Carbon fiber has a rod structure and there are C=O and C-O-C polar groups on the skeleton surface. The decreasing order of water absorption capacity is graphite, carbon fiber, molybdenum disulfide, PTFE and copper powder.

Nano K_2Ti_4O_9 Whisker Enhanced Solid Lubrication Coating for Cutting Application

In order to decrease cutting fluid and improve environment, the cutting fluid was replaced by solid lubricant. Four kinds of solid lubricants were tested on a high temperature friction tester, from which nano K 2Ti 4O 9 whisker enhanced solid lubrication film was chosen. It was coated on the surface of cutters and tested on a CA6140 lathe. At the rate of 400r/min, the wear of the tool flank with solid lubrication film is 1/6 of that without the film, and it is even lower than that using cutting fluid. With the increase of cutting speed, the wear of the tool flank with solid lubrication film is still lower than that without film, but it is higher than that using cutting fluid. Surface analyses by AFM, SEM and EDX reveal that the solid lubrication film can prevent Fe element of chips from diffusing the cutter surface; adhesion of the cutter and chips is abated and the wear of the tool flank is obviously decreased.

Improvement of Drill Performance in Metal Cutting Using MoST Solid Lubricant Coatings

Coated tools are widely used in today’s metal cutting industries and have significantly improved machining productivity through reducing operation costs and time. This paper presents the results of a systematic study of the performance of HSS drills coated with CrTiAIN and drills with a top solid lubricant coating of MoST?. The tests were performed on a Haas vertical machining centre under wet and dry cutting conditions to machine through holes in medium carbon steel workpieces. The feed force and torque were recorded throughout some of the tests using a force dynamometer, while the tool wear was monitored and measured. It was found that MoST? coatings even under accelerated conditions improve the tool life significantly based on their unique properties and very low friction.

Preparation of Ni-Cr/BN self-lubricating composites by active sintering process

A Ni-Cr/BN composite was produced by a active sintering process. The powder of nickel carbonyl,Cr2O3 and C were used as the original materials,and a hexagonal BN(h-BN) powder was added as a solid lubricant. The influence of sintering temperature,heating rate and holding time on the properties of Ni-Cr/BN were studied. The composition and microstructure of Ni-Cr/BN were analysed by X-ray diffraction(XRD) and the optical microscopy(OM). The frictional behavior and hardness were measured with ring-block friction testing machine and Brinell hardness tester respectively. The results show that Ni-Cr is the matrix and a low-melting eutectic compound is the bonding phase in the composite. The porosity reaches 48% and the value of hardness reaches HB18 when the composite is fabricated at 1 100 ℃ for 1 h. Its wear rate is 7.44×10-5 g/min,and the average friction coefficient is 0.266. These properties make such composite suitable for use as self-lubricating material.

Lubrication properties of silver-palladium alloy prepared by ion plating method for high temperature stud bolt

As a solid lubricant, silver-palladium (Ag-Pd) alloy coating was investigated for the application to high temperature stud bolt. A glue layer nickel (Ni) film was deposited on the surface of the hex bolt sample and then Ag-Pd alloy coating was performed on it using ion plating method. The friction coefficient of Ag-Pd alloy film coated bolt was lower than that of N-5000 oil coated bolt by the result of axial force measurement. The cyclic test of heat treatment was conducted to evaluate the durability of Ag-Pd alloy film coated bolt. In a cycle, sample was assembled into the block using torque wrench, followed by heating and disassembling. It was not successful to disassemble the N-5000 oil coated bolt from the block after only one cycle. However, the Ag-Pd alloy film coated bolt was able to be disassembled softly till 12 cycles.

A MIXED LUBRICATION MODEL MODIFIED BY SURFACES' FRACTAL CHARACTERISTICS

Fractal characteristics are introduced into solving lubrication problems. Based on the analysis of the relationship between roughness and engineering surfaces' fractal characteristics and by introducing fractal parameters into the mixed lubrication equation, the relationship between flow factors and fractal dimensions is analyzed. The results show that the pressure flow factors' values increase, while the shear flow factor decreases, with the increasing length to width ratio of a representative asperity γ at the same fractal dimension. It can be also found that these factors experience more irregular and significant variations and show the higher resolution and the local optimal and the worst fractal dimensions, by a fractal dimension D , compared with the oil film thickness to roughness ratio h/R q . As an example of application of the model to solve the lubrication of the piston skirt in an engine, the frictional force and the load capacity of the oil film in a cylinder were analyzed. The results reveal that the oil film frictional force and the load capacity fluctuate with increasing fractal dimension, showing big values at the small D and smaller ones and slightly variable in the range of bigger one, at the same crank angle.

Effects of boundary slippage on thin-film lubricationbetween two nonparallel plane plates

Hydrodynamic lubrications between two plane plates with an intersection angle θ have been investigated us- ing the boundary slippage theory, and relations are obtained between dimensionless pressures and coordinate x, between bearing capacity, friction force, friction coefficient and di- mensionless slipping size factor. The results show that bear- ing capacity of two plane plates without boundary slippage significantly increases with increasing intersection angle θ when 0 〈 θ 〈 1°, whereas decreases with increasing in- tersection angle 0 when θ 〉 1°. The results also show that negative pressure occurs in fluid entrance region and bearing capacity decreases, and friction force and friction coefficient increase with the increase of dimensionless slipping size fac- tor.

Topology optimization of AISI 4140 steel with surface texture filled by multi-solid lubricants for enhancing tribological properties

Wind power gears will be excessively worn due to lubrication failure during operation.Herein,the tribological properties of rubbing pairs are improved by filling solid lubricants into surface texture.In texture design,three types of topological textures(Circle(C),Hexagon(H),and Circle/Hexagon(CH))were obtained by cell topology optimization,and then three cases with 20%,30%,and 40%density were designed for each texture.Next,SnAgCu and TiC were deposited in texture of AISI 4140 steel(AS)to obtain 9 kinds of self-lubricating surfaces.Among them,AS with 30%CH density(AS-CH30)exhibits excellent mechanical and tribological properties.Compared with AS-C and AS-H,the maximum equivalent stress of AS-CH was decreased by 10.86%and 5.37%,respectively.Friction coefficient and wear rate of AS-CH30 were 79.68%and 78%lower than those of AS.The excellent tribological performances of AS-CH30 can be attributed to the synergistic effect of topological surface and solid lubricants.Topological surface can not only reduce fluctuation of equivalent stress,but also promote the stored lubricants to be easily transferred at the contact interface to form a 200 nm lubricating film containing solid lubricants(mainly),oxides and wear debris.

Study on the preparation and fretting behavior of bonded oriented MoS_(2)solid lubricant coating

The bonded MoS_(2)solid lubricant coating is an effective measure to mitigate the fretting wear of AISI 1045 steel.In this work,the amino functionalized MoS_(2)was protonated with acetic acid to make the MoS_(2)positively charged.The directional arrangement of protonated MoS2 in the coating was achieved by electrophoretic deposition under the electric field force.The bonded directionally aligned MoS_(2)solid lubricant coating showed high adaptability to various loads and excellent lubrication performance under all three working conditions.At a load of 10 N,the friction coefficient and wear volume of the coating with 5 wt%protonated MoS_(2)decreased by 20.0%and 37.2%compared to the pure epoxy coating,respectively,and by 0.07%and 16.8%than the randomly arranged MoS_(2)sample,respectively.The remarkable lubricating properties of MoS_(2)with directional alignment were attributed to its effective load-bearing and mechanical support,barrier effect on longitudinal extension of cracks,and the formation of a continuous and uniform transfer film.

Novel Blasting-Like Lubricating Process for Cold Extrusion

A blasting-like lubricating process(combination of shot blasting and lubricating processes)is proposed.In this process,the specimens to be treated,alloy shots,and solid lubricating powder are rotated together in a roller.The surface pockets formed due to the impact by the shots can store lubricants,and the lubricant can also adhere to the specimen surface by hitting.The effects of process parameters,including rolling time,rotational speed,mass of alloy shots,and the diameter of shots,on the surface topography of the steel specimen are investigated using 13 experimental schemes.The distribution ratio and average depth of surface pockets on the defined areas of the specimen are quantitatively analyzed.Four selected schemes with the MoS_(2) solid lubricating powder are further carried out to lubricate the cylindrical billets,and the lubricating effect is evaluated using the steady combined forward and backward extrusion test.The indicated friction factor of the novel blasting-like process is smaller than that of the conventional phosphate-soap coating process.

Investigation of tribological characteristics of nickel alloybased solid-lubricating composites at elevated temperatures under vacuum

The development of a high‐performance solid‐lubricating composite with excellent self‐lubricity over a broad temperature range in vacuum is significant to solve the frictional problems of spatial mechanisms.In this study,the vacuum tribological behaviors of nickel‐matrix/Ag/(Ca,Ba)F2/graphite(0–2 wt%)composites were studied from 25 to 800°C.The results show that the synergistic effects of solid lubricants can significantly improve the tribological properties of the composites in vacuum,with the graphite content contributing considerably.For 2 wt%graphite,a low friction coefficient(0.14–0.25)and the lowest wear rate((0.12–4.78)×10^(-5) mm^(3)∙N^(-1)∙m^(-1))were observed in vacuum over the entire testing temperature range.Moreover,the wear mechanisms were clarified via analysis of the chemical composition and morphologies of the sliding surfaces.

Fluid-solid Interaction Model for Hydraulic Reciprocating O-ring Seals

Elastohydrodynamic lubrication characteristics of hydraulic reciprocating seals have significant effects on sealing and tribology performances of hydraulic actuators, especially in high parameter hydraulic systems. Only elastic deformations of hydraulic reciprocating seals were discussed, and hydrodynamic effects were neglected in many studies. The physical process of the fluid-solid interaction effect did not be clearly presented in the existing fluid-solid interaction models for hydraulic reciprocating O-ring seals, and few of these models had been simultaneously validated through experiments. By exploring the physical process of the fluid-solid interaction effect of the hydraulic reciprocating O-ring seal, a numerical fluid-solid interaction model consisting of fluid lubrication, contact mechanics, asperity contact and elastic deformation analyses is constructed with an iterative procedure. With the SRV friction and wear tester, the experiments are performed to investigate the elastohydrodynamic lubrication characteristics of the O-ring seal. The regularity of the friction coefficient varying with the speed of reciprocating motion is obtained in the mixed lubrication condition. The experimental result is used to validate the fluid-solid interaction model. Based on the model, The elastohydrodynamic lubrication characteristics of the hydraulic reciprocating O-ring seal are presented respectively in the dry friction, mixed lubrication and full film lubrication conditions, including of the contact pressure, film thickness, friction coefficient, liquid film pressure and viscous shear stress in the sealing zone. The proposed numerical fluid-solid interaction model can be effectively used to analyze the operation characteristics of the hydraulic reciprocating O-ring seal, and can also be widely used to study other hydraulic reciprocating seals.