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.

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.

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.

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.

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.

Graphite-based solid lubricant for high-temperature lubrication

High-temperature solid lubricants play a significant role in the hot metal forming process.However,preparing high-temperature solid lubricant is formidably challenging due to the stern working conditions.Here we successfully develop a new type of eco-friendly high-temperature graphite-based solid lubricant by using amorphous silica dioxide,aluminum dihydrogen phosphate,and solid lubricant graphite.The solid lubricating coating exhibits excellent tribological properties with a very low friction coefficient and good wear protection for workpiece at high temperature under the air atmosphere.An array of analytical techniques reveals the existence of solid lubricant graphite in the lubricating coating after the high-temperature friction test.A synergistic effect between the protective surface film and the solid lubricant graphite is proposed to account for such superior lubricating performance.This work highlights the synergistic effect between the protection layer and the lubricant graphite and further provides the insight in designing the high-temperature solid lubricant.

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.

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.

Influence of addition of Gr_p/Al_2O_(3p )with SiC_p on wear properties of aluminum alloy 6061-T6 hybrid composites via friction stir processing

Aluminum alloy base surface hybrid composites were fabricated by incorporating with mixture of （SiC＋Gr） and （SiC＋Al2O3） particles of 20 μm in average size on an aluminum alloy 6061-T6 plate using friction stir processing （FSP）. Microstructures of both the surface hybrid composites revealed that SiC, Gr and Al2O3 are uniformly dispersed in the nugget zone （NZ）. It was observed that the addition of Gr particles rather than Al2O3 particles with SiC particles, decreases the microhardness but immensely increases the dry sliding wear resistance of aluminum alloy 6061-T6 surface hybrid composite. The observed microhardness and wear properties are correlated with microstructures and worn micrographs.

Influence of sulfides on the tribological properties of composites produced by pulse electric current sintering

Self-lubricating A1203-15wt% ZrO2 composites with sulfides, such as molybdenum disulfide （MoS2） and tungsten disulfide （WSz） serving as solid lubricants, were fabricated by using the pulse electric current sintering （PECS） technique. The coefficient of friction （COF） of the A1203-15wt% ZrO2 composite without/with sulfides was in the range of 0.37-0.48 and 0.27-0.49, respectively. As the amoant of sul- fides increased, the COF and the wear rate decreased. The reduction in COF and wear rate of the sulfide-containing composite is caused by a reduction in shear stresses between the specimen and the tribological medium due to the formation of a lubricating film resulting from the lamellar structure of sulfides located on the worn surface.

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.

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.

Effect of Counterface Material on Friction and Wear Behavior of Ni-Cr-W-Al-Ti-MoS_2 Composites

Ni-Cr-W-Al-Ti-MoS2 self-lubricating composites were prepared through the powder metallurgy （P/M） method. Their friction properties were investigated by a pin-on-disk tribometer in the range from the room temperature to 600 ℃. Alumina, silicon nitride and nickel-iron-sulfide alloys were selected as the counterface materials. Results indicate that the lowest friction coefficients under 0.22 can be obtained at 600℃ when rubbed against alumina. When rubbed against nickel-iron-sulfide alloys, are presented the lowest wear rates in the magnitude of 10^-6 mm^3/N-m, one order of magnitude lower than those when rubbed against ceramics. In the case of three rubbing pairs, the wear rates of the composite containing MoS2 present themselves inversely proportional to friction coefficients. With alumina ceramics used as a counterface, transfer films and glaze layers will form on the contact surface playing a main role in lubrication at high temperatures. However, when silicon nitride and nickel-iron-sulfide alloy are used, the lubricating transfer films appear not to be prominent.

Effects of h-BN content on properties of Ni-Cr/h-BN composite

Ni-Cr/h-BN self-lubricating composities were prepared by powder metallurgy (P/M) method.The effects of hexagonal boron nitride (h-BN) content on the mechanical and tribological properties of the Ni-Cr/h-BN composites were investigated.The corresponding frictional models were established to analyze the formation of the lubricant h-BN films on the surfaces of the Ni-Cr/h-BN composites.The results show that,when the content of h-BN increases from 5% to 15% (mass fraction),the bending strength of the Ni-Cr/h-BN composite decreases from 96.670 MPa to 17.319 MPa,and the hardness (HB) decreases from 33 to 14.The friction coefficient of the Ni-Cr/h-BN composite decreases firstly from 0.385 to 0.216,and then increases to 0.284,while the wear rate decreases firstly from 4.14×10-9 kg/(N·m) to 1.35×10-9 kg/(N·m),then increases to 2.36×10-9 kg/(N·m).The best comprehensive mechanical and tribological properties can be obtained between 10% and 12% h-BN addition.

Experimental Study on Grinding Force of Electrostatic Coated Grinding Wheel

In order to deal with the hard machining of TC4 alloy,coated graphite on grinding wheel surface by electrostatic device is proposed in this paper.This paper mainly completed the design of graphite electrostatic spraying grinding wheel device,force experimental analysis of grinding TC4 alloy with coated graphite grinding wheel,and summary of the influence of different grinding speeds and grinding depths on grinding force and grinding force ratio.The experimental results show that the lubrication coating can reduce the grinding force and grinding force ratio in the process of grinding TC4 alloy with graphite powder-coated wheel under electrostatic field force,compared to dry grinding with the uncoated wheel.

Tribological properties of transition metal di-chalcogenide based lubricant coatings

Transition metal di-chalcogenides MX2 （X= S, Se, Te; and M = W, Mo, Nb, Ta） are one kind of solid lubricant materials that have been widely used in industry. The lubricant properties of such lubricant coatings are dependent not only on microstructure, orientation, morphology, and composition of the coatings, but also on the substrate, the interface between substrate and lubricant coatings, and the specific application environment. In this review, the effects of parameters on tribological properties of such kind of lubricant coatings were summarized. By comparing advantages and disadvantages of those coatings, the special treatments such as doping, structural modulation and post-treatment were suggested, aiming to improve the tribologicai performance under severe test conditions （e.g. high temperature, oxidizing atmosphere or humid condition）.

Tribologically induced nanostructural evolution of carbon materials: A new perspective

Carbon-based solid lubricants are excellent options to reduce friction and wear,especially with the carbon capability to adopt different allotropes forms.On the macroscale,these materials are sheared on the contact along with debris and contaminants to form tribolayers that govern the tribosystem performance.Using a recently developed advanced Raman analysis on the tribolayers,it was possible to quantify the contactinduced defects in the crystalline structure of a wide range of allotropes of carbon-based solid lubricants,from graphite and carbide-derived carbon particles to multi-layer graphene and carbon nanotubes.In addition,these materials were tested under various dry sliding conditions,with different geometries,topographies,and solid-lubricant application strategies.Regardless of the initial tribosystem conditions and allotrope level of atomic ordering,there is a remarkable trend of increasing the point and line defects density until a specific saturation limit in the same order of magnitude for all the materials tested.

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.

Improving surface integrity when drilling CFRPs and Ti-6Al-4V using sustainable lubricated liquid carbon dioxide

In the quest for decreasing fuel consumption and resulting gas emissions in the aeronautic sector,lightweight materials such as Carbon Fiber Reinforced Polymers(CFRPs)and Ti-6Al-4V alloys are being used.These materials,with excellent weight-to-strength ratios,are widely used for structural applications in aircraft manufacturing.To date,several studies have been published showing that the use of metalworking fluids(MWFs),special tool geometries,or advanced machining techniques is required to ensure a surface quality that meets aerospace component standards.Conventional MWFs pose a number of environmental and worker health hazards and also degrade the mechanical properties of CFRPs due to water absorption in the composite.Therefore,a transition to more environmentally friendly cooling/lubrication techniques that prevent moisture problems in the composite is needed.This research shows that lubricated LCO_(2) is a viable option to improve the quality of drilled CFRP and titanium aerospace components compared to dry machining,while maintaining clean work areas.The results show that the best combination of tool geometry and cooling conditions for machining both materials is drilling with Brad point drills and lubricated LCO_(2).Drilling under these conditions resulted in a 90%improvement in fiber pullout volume compared to dry machined CFRP holes.In addition,a 33% reduction in burr height and a 15% improvement in surface roughness were observed compared to dry drilling of titanium.

Cooling and lubrication techniques in grinding:A state-of-the-art review,applications,and sustainability assessment

Grinding technology is an essential manufacturing operation,in particular,when a component with a superfinishing and an ultra-resolution is yearned.Meeting the required strict quality checklist with maintaining a high level of productivity and sustainability is a substantive issue.The recent paper outlines the lubrication and cooling technologies and mediums that are used for grinding.Furthermore,it provides a basis for a critical assessment of the different lubrication/cooling techniques in terms of machining outputs,environmental impact,hygiene effect,etc.Meanwhile,the paper put light on the sustainability of different cooling/lubrication strategies.The sustainability of machining aims to get the product with the best accuracy and surface quality,minimum energy consumption,low environmental impact,reasonable economy,and minimum effect on worker’s health.The paper revealed that despite some cooling/lubrication mediums like mineral oils and semisynthetic,afford sufficient lubrication or cooling,they have a significant negative impact on the environment and public health.On the other hand,emulsions can overcome environmental problems but the economy and the energy consumption during grinding are still a matter of concern.Biodegradable and vegetable oils are considered eco-friendly oils,but they suffer from a lack of thermal stability which affects their ability of efficiently cooling.Using the cooling medium with the lowest amount can achieve the goal of the economy but it may be reflected negatively on the machinability.Furthermore,cryogenic lubrication doesn’t provide sufficient lubrication to reduce friction and hence energy consumption.The research described in the paper is such a comprehensive compilation of knowledge regarding the machinability and machining performance under different cooling and lubrication systems that it will aid the next generation of scientists in identifying current advancements as well as potential future directions of research on ecological aspects of machining for sustainability.