Friction and wear properties of in-situ synthesized Al_2O_3 reinforced aluminum composites

Al-5%Si-AI2O3 composites were prepared by powder metallurgy and in-situ reactive synthesis technology. Friction and wear properties of Al-5%Si-Al2O3 composites were studied using an M-2000 wear tester. The effects of load, sliding speed and long time continuous friction on friction and wear properties of Al-5%Si-Al2O3 composites were investigated, respectively. Wear surface and wear mechanism of Al-5%Si-Al2O3 composites were studied by Quanta 200 FE-SEM. Results showed that with load increasing, wear loss and coefficient of friction increased. With sliding speed going up, the surface temperature of sample made the rate of the producing of oxidation layer increase, while wear loss and coefficient of friction decreased. With the sliding distance increasing, coefficient of friction increased because the adhesive wear mechanism occurred in the initial stage, then formation and destruction of the oxide layer on the surface of the sample tended to a dynamic equilibrium, the surface state of the sample was relatively stable and so did the coefficient of friction. The experiment shows that the main wear mechanism of Al-5%Si-Al2O3 composites includes abrasive wear, adhesive wear and oxidation wear.

Dry Friction and Wear Characteristics of Impregnated Graphite in a Corrosive Environment

Tribological properties of impregnated graphite are greatly influenced by preparation technology and working conditions and it’s highly susceptible to corrosion environmental impacts,but the experimental research about it are few.In this paper,three kinds of impregnated graphite samples are prepared with different degree of graphitization,the tribological properties of these samples in the dry friction environment and in a corrosive environment are analyzed and contrasted.The tribo-test results show that the friction coefficient of samples is reduced and the amount of wear of samples increase when the graphitization degree of samples increases in dry friction condition.While in a corrosive environment（samples are soaked N2O4）,the friction coefficient and amount of wear are changed little if the graphitization degree of samples are low.If the degree of graphitization increase,the friction coefficient and amount of wear of samples increase too,the amount of wear is 2 to 3 times as the samples tested in the non-corrosive environment under pv value of 30MPa？m/s.The impregnated graphite,which friction coefficient is stable and graphitization degree is in mid level,such#2,is more appropriate to have a work in the corrosion conditions.In this paper,preparation and tribological properties especially in corrosive environment of the impregnated graphite is studied,the research conclusion can provide an experimental and theoretical basis for the selection and process improvement of graphite materials,and also provide some important design parameters for contact seal works in a corrosive environment.

Friction and Wear Performances of Cathodic Arc Ion Plated TiAlSiN Coating under Oil Lubricated Condition

TiAlSiN coating was deposited on H13 hot work mould steel using cathodic arc ion plating（CAIP）. The surface-interface morphologies and phases of the obtained coating were analyzed using field emission scanning electron microscopy（FESEM） and X-ray diffraction（XRD）, respectively, and the morphologies, distributions of chemical elements and profiles of worn tracks were also researched using scanning electron microscopy（SEM）, energy disperse spectroscopy（EDS）, and optical microscope（OM）, respectively. The friction-wear performances of TiAlSiN coating under oil lubricated and dry fiction conditions were investigated, and the wear mechanisms of TiAlSiN coating were discussed. The experimental results show that the coating is primarily composed of（Ti, Al）N, AlTiN, and TiN hard phases, Si_3N_4 exists between the（Ti, Al）N crystal grains, increasing the coating microhardness to 3200 HV. The TiAlSiN coating has excellent performances of reducing friction and wear resistance, the average coefficient of friction（COF） of TiAlSiN coating under oil lubricated condition is only 0.05, lowered than the average COF of 0.211 under dry friction condition, the wear rate decreases by about 81.2% compared with that under dry friction condition. The wear mechanism of TiAlSiN coating under oil lubricated and dry friction conditions is composed of abrasive wear, fatigue wear, and abrasive wear, respectively. The internal friction of oil lubrication is a main factor of decreasing fatigue wear.

Determination of the Friction Coefficient in the Flat Strip Drawing Test

Current work is focused on the influence of friction in deep drawing process. Friction measurements were also conducted using a modified tribotester based on strip sliding between tools. Four different tool surfaces were tested under similar contact conditions regarding contact area, normal pressure, sliding speed, lubricant and surface characteristics to calculate the friction coefficient between the tool surface and a high strength low alloy steel sheet HSLA 380. The results showed that friction coefficient varies over a wide range with different lubricating conditions and different sliding velocities. For some sliding velocities, the coefficient of friction is stable and low, while for others it is unstable and higher. Results of the experiments reveal that this novel tribotester is a very useful tool to evaluate and compare the friction between steel sheet and tool surfaces in alloyed steel for cold working applications. The outcomes have only small dispersion within the different test series, which indicates a stable process with good repeatability. The test method enables comparison of different surface finishes and treatments, lubricants and coatings in terms of friction and galling under conditions similar to those found in sheet metal forming processes. The four different types of surfaces considered for this study were grinded, polished, nitrided and quenched/tempered. The main difference among the tested tools in this work was the surface roughness, which was found to have a strong influence on friction.

Effect of Variation of the Coefficient of Friction on the Temperature at the Level of the Fault Lips

Earth’s crust is an anisotropic and purely heterogeneous medium, which is justified by existence of different discontinuities;our study aims to show the effect of the variation of coefficient of friction on the evolution of temperature and its impact on seismic forecasting. In this work, we are model in 2D the variation of thermal energy and temperature produced by friction at the level of fault lip as function of depth of the seismic focus and at different value of time. Earthquakes are born when the energy accumulated by friction at the level of fault is suddenly released causing damage, sometimes noticeable on the surface of earth (macroseisms), and sometimes not at all noticeable on the surface of earth (microseisms), then energy which occurs before is important to forecasting earthquake. Assuming that coefficient of friction is variable, our results have enabled us to highlight the fact that, the greater the coefficient of friction, more the temperature increases, although the temperature profile increase over time but not linearly reflecting the presence of different asperities and discontinuities zone;slip generated at the level of fault occur a variation of temperature on specific points called roughness in common agreement with the literature. A large part of energy produced by friction is dissipated in heat causing a local increases in temperature which a very short duration and called flash contact temperature, and that despite the fact that the temperature evolved in time and space, it all converged towards a perfectly distinguishable fixed point.

Current state-of-the-art review of footwear–ground friction

The most important role of footwear is to ensure safe,functional walking,and foot protection.For the proper functionality of not only the work shoes,the anti-slip behavior of the shoe under various conditions and environments plays an important role in the prevention of slips,trips,falls,and consequent injuries.This article is intended to review the current understanding of the frictional mechanisms between shoe outsoles and various counterfaces that impact the evaluation of outsole slipperiness.Current research focuses on the mechanisms driving outsole friction on different ground surfaces or the definition and description of parameters that influence outsole friction.Subsequently,the review discusses the effect of various surface contaminants on footwear friction.Lastly,challenges and outlooks in the field of footwear outsoles are briefly mentioned.

AFM probe with the U-shaped cross-sectional cantilever for measuring the ultra-low coefficient of friction of 10^(–6)

Accurately measuring the coefficient of friction(COF)is the fundamental prerequisite of superlubricity research.This study aimed to reduce the COF measurement resolutionΔμof atomic force microscopy(AFM).Based on the theoretical model,a distinctive strategy was adopted to reduceΔμby optimizing the cantilever’s cross-section of the AFM probe,inspired by civil engineering.Δμcan be reduced by decreasing the width of the horizontal side wR and the wall thickness t and increasing the width of the vertical side wH.Moreover,the I-shape demonstrates the highest reduction inΔμ,followed by the U-shape.Considering the processability,the AFM probe with the U-shaped cross-sectional cantilever was investigated further,and the dimensions are 35μm wR,3.5μm wH,0.5μm t,50μm l(cantilever length),and 23μm htip(tip height).The finite element analysis results confirm its reliability.After being fabricated and calibrated,the AFM probe achieves the minimalΔμof 1.9×10^(–6)under the maximum normal force so far.Additionally,the friction detection capability of the fabricated AFM probe improves by 78 times compared to the commercial tipless-force modulation mode(TL-FM)AFM probe with the conventional solid rectangular cross-sectional cantilever.This study provides a powerful tool for measuring 10^(–6)COF.

Microstructures and mechanical properties of electroplated Cu-Bi coatings

Electroplating has been used to produce Cu-Bi coatings. The crystal structure and lattice parameters of Cu in Cu-Bi composite coating were measured and compared with Cu coating. The mechanical properties of the coatings were also studied. It was found that the deposition parameters have significant effect on the mechanical properties of the Cu-Bi coatings. The microhardness has been improved from HVso165 of Cu coating to HVs0 250 of Cu-Bi composite coating prepared at 50 mA/cm2 for 20 min. Correspondingly, wear resistance of the Cu-Bi composite coating has also been enhanced significantly.

Tribological behavior of self lubricating Cu/MoS_2 composites fabricated by powder metallurgy

The effects of MoS2 content on microstructure, density, hardness and wear resistance of pure copper were studied. Copper-based composites containing 0-10%（mass fraction） MoS2 particles were fabricated by mechanical milling and hot pressing from pure copper and MoS2 powders. Wear resistance was evaluated in dry sliding condition using a pin on disk configuration at a constant sliding speed of 0.2 m/s. Hardness measurements showed a critical MoS2 content of 2.5% at which a hardness peak was attained. Regardless of the applied normal load, the lowest coefficient of friction and wear loss were attained for Cu/2.5 MoS2 composite. While coefficient of friction decreased when the applied normal load was raised from 1 to 4 N at any reinforcement content, the wear volume increased with increasing normal load. SEM micrographs from the worn surfaces and debris revealed that the wear mechanism was changed from mainly adhesion in pure copper to a combination of abrasion and delamination in Cu/MoS2 composites.

Dry sliding wear behavior of an extruded Mg-Dy-Zn alloy with long period stacking ordered phase

The dry sliding wear behavior of extruded Mg-2Dy-0.5Zn alloy(at.%)was investigated using a pin-on-disk configuration.The friction coefficient and wear rate were measured within a load range 20-760 N at a sliding velocity of 0.785 m/s.Microstructure and wear surface of alloy were examined using scanning electron microscopy.The mechanical properties of alloy were tested at room and elevated temperatures.Five wear mechanisms,namely abrasion,oxidation,delamination,thermal softening and melting dominated the whole wear behavior with increasing applied load.The extruded Mg-2Dy-0.5Zn alloy exhibited the better wear resistance as compared with as-cast Mg_(97)Zn_(1)Y_(2) alloy under the given conditions through contact surface temperature analysis.The improved wear resistance was mainly related to fine grain size,good thermal stability of long period stacking order(LPSO)phase and excellent higher-temperature mechanical properties.

Investigation of dry sliding wear properties of multi-directional forged Mg-Zn alloys

Effect of multi-directional forging(MDF)on wear properties of Mg-Zn alloys(with 2,4,and 6wt%Zn)is investigated.Dry sliding wear test was performed using pin on disk machine on MDF processed and homogenized samples.Wear behavior of samples was analyzed at loads of ION and 20 N,with sliding distances of 2000m and 4000m,at a sliding velocity of 3m/s.Microstructures of worn samples were observed under scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),and x-ray diffraction(XRD)and the results were analyzed.Mechanical properties were evaluated using microhardness test.After 5 passes of MDF,the average grain size was found to be 30±4p m,22±3 pm,and 18±3 pm,in Mg-2%Zn,Mg-4%Zn,and Mg-6%Zn alloys,respectively,with significant improvement in hardness in all cases.Wear resistance was improved after MDF processing,as well as,with increment in Zn content in Mg alloy.However,it decreased when the load and the sliding distance increased.Worn surface exhibited ploughing,delamination,plastic deformation,and wear debris along sliding direction,and abrasive wear was found to be the main mechanism.

Comparative study on pullout behaviour of pressure grouted soil nails from field and laboratory tests

Pullout resistance of a soil nail is a critical parameter in design and analysis for geotechnical engineers. Due to the complexity of field conditions, the pullout behaviour of cement grouted soil nail in field is not well investigated. In this work, a number of field pullout tests of pressure grouted soil nails were conducted to estimate the pullout resistance of soil nails. The effective bond lengths of field soil nails were accurately controlled by a new grouting packer system. Typical field test results and the related comparison with typical laboratory test results reveal that the apparent coefficient of friction （ACF） decreases with the increase of overburden soil pressure when grouting pressure is constant, but increases almost linearly with the increase of grouting pressure when overburden pressure （soil depth） is unchanged. Water contents of soil samples at soil nail surfaces show obvious reductions compared with the results of soil samples from drillholes. After soil nails were completely pulled out of the ground, surface conditions of the soil nails and surrounding soil were examined. It is found that the water content values of the soil at the soil/nail interfaces decrease substantially compared with those of soil samples extracted from drillholes. In addition, all soil nails expand significantly in the diametrical direction after being pulled out of ground, indicating that the pressurized cement grout compacts the soil and penetrates into soil voids, leading to a corresponding shift of failure surface into surrounding soil mass significantly.

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.

Nano-tribological behavior of graphene nanoplatelet-reinforced magnesium matrix nanocomposites

The corrosion resistance and wear resistance of metallic biomaterials are critically important for orthopedic hard-tissue replacement applications because the lack of such properties not only adversely affects their mechanical integrity but also allows the release of wear debris into the human body.In this study,the potential of zirconium(Zr)as an alloying element and graphene nanoplatelets(GNPs)as a nano-reinforcement material were investigated in relation to improving the tribological performance of pure magnesium(Mg).The GNPs-reinforced Mg matrix nanocomposites(MNCs)were fabricated using powder metallurgy.Results indicate that additions of 0.5 wt.%Zr and0.1 wt.%GNPs to Mg matrices significantly improved the wear resistance by 89%and 92%at 200μN load,60%and 80%at 100μN load,and 94%and 93%at 50μN load,respectively,as compared to the wear resistance of pure Mg.The wear depth and coefficient of friction of the MNC containing 0.5 wt.%Zr and 0.1 wt.%GNPs(Mg0.5 Zr0.1 GNPs MNC)were considerably reduced as compared to pure Mg and Mg0.5 Zr.Our results demonstrate that the Mg0.5 Zr0.1 GNPs MNC is promising for orthopedic applications in relation to its excellent tribological performance.

Pullout behavior of polymeric strip in compacted dry granular soil under cyclic tensile load conditions

Assessment of the reinforcement behavior of soil under cyclic and monotonic loads is of great impor- tance in the safe design of mechanically stabilized earth walls, In this article, the method of conducting a multistage pullout （MSP） test on the polymeric strip （PS） is presented, The post-cyclic behavior of the reinforcement can be evaluated using a large-scale pullout apparatus adopting MSP test and one-stage pullout （OSP） test procedures, This research investigates the effects of various factors including load amplitude, load frequency, number of load cycles and vertical effective stress on the peak apparent coefficient of friction mobilized at the soil-PS interface and the pullout resistance of the PS buried in dry sandy soil. The results illustrate that changing the cyclic tensile load frequency from 0,1 Hz to 0,5 Hz does not affect the pullout resistance. Moreover, the influence of increasing the number of load cycles from 30 to 250 on the peak pullout resistance is negligible. Finally, the effect of increasing the cyclic tensile load amplitude from 20% to 40% on the monotonic pullout resistance can be ignored. The peak apparent coefficient of friction mobilized at the soil-PS interface under monotonic and cyclic load conditions decreases with the increase in vertical effective stress.

Enhancement of wear resistance of Ti–6Al–4V alloy by picosecond laser surface micro texturing process

A pulsed,picosecond Nd:YAG laser with a wavelength of 532 nm is used to texture the surface of grade 5 titanium alloy(Ti–6Al–4V)for minimizing its wear rate.The wear properties of the base samples and laser surface textured samples are analyzed by conducting wear tests under a sliding condition using pin-on-disk equipment.The wear tests are conducted based on the Box–Benhken design,and the interaction of the process parameters is analyzed using response surface methodology.The wear analysis is conducted by varying the load,rotating speed of the disc,and track diameter at room temperature with a sliding distance of 1500 m.The results demonstrate that the laser textured surfaces exhibited a lower coefficient of friction and good anti-wear properties as compared with the non-textured surfaces.A regression model is developed for the wear analysis of titanium alloy using the analysis of variance technique.It is also observed from the analysis that the applied load and sliding distance are the parameters that have the greatest effect on the wear behavior followed by the wear track diameter.The optimum operating conditions have been suggested based on the results obtained from the numerical optimization approach.

Improving tribological and thermal properties of Al alloy using CNTs and Nb nanopowder via SPS for power transmission conductor

This study aimed at improving the tribological and thermal properties of Al alloy using CNTs and Nb nanopowder as reinforcements and spark plasma sintering(SPS)as the fabrication method.The SPS was conducted at 630℃,30 MPa,10 min,and 200℃/min.The tribology test was run with ball-on-disc tribometer using steel ball as the counter body.And the thermal test was processed with thermogravimetric analyzer(TGA)and laser flash apparatus(LFA).Results showed that the addition of 8 wt.%CNTs and 8 wt.%Nb reinforcements respectively decreased the coefficient of friction(COF)of the composite by 79%.The wear volume of the composite was decreased by 23%,and so was the wear rate.However,the thermal conductivity of the composite was equally improved by 44%.The tribology improvement was stimulated by a C film generated by CNTs and a protective Nb2O5 formed by Nb nanopowder.The thermal conductivity was improved by the grain refining property of Nb and the high thermal conductivity of CNTs.Therefore,these results indicated that Al-CNTs-Nb composite is a robust material for high transmission conductor capable of reducing sag and ensuring the durability of the composite.

Characterization and Tribological Performance of Titanium Nitrides in Situ Grown on Ti6Al4V Alloy by Glow Discharge Plasma Nitriding

Titanium(Ti)nitrides were in situ grown on Ti6Al4V alloy(TA)using a glow discharge plasma nitriding(GDPN).The morphology,chemical composition,phase and mechanical property of the obtained nitrided TA were analyzed using a scanning electron microscope(SEM),energy dispersive spectroscope(EDS),X-ray diffraction(XRD),and nanoindentation tester,respectively.The tribological performances of un-nitrided and nitrided TAs were evaluated using a ball-on-plate wear tester,and the wear mechanism was also discussed in detail.The results show that the nitrided layer with the compound and diffusion layers is formed on the nitrided TA,which is composed of δ-TiN and a-Ti phases.The nanohardness and elastic modulus of nitrided TA are 6.05 and 143.13 GPa,respectively,higher than those of un-nitrided TA.The friction reduction and anti-wear performances of nitrided TA are better than those of un-nitrided TA,and the wear mechanism is primary abrasive wear,accompanying with adhesive wear,which is attributed to the formation of Ti nitrides with the high nanohardness and elastic modulus.

Evaluation of Contact Pressure in Bending under Tension Test by a Pressure Sensitive Film

The contact pressure acting on the sheet/tools interface has been studied because of growing the concern about the wear of tools. Recent studies make use of numerical simulation software to evaluate and correlate this pressure with the friction and wear generated. Since there are many studies that determine the coefficient of friction in sheet metal forming by bending under tension (BUT) test, the contact pressure between the pin and the sheet was measured using a film that has the ability to record the applied pressure. The vertical force applied to pin was also measured. The results indicate that the vertical force is more accurate to set the contact pressure that using equations predetermined. It was also observed that the contact area between the sheet and the pin is always smaller than the area calculated geometrically. The friction coefficient was determined for the BUT test through several equations proposed by various authors in order to check if there is much variation between the results. It was observed that the friction coefficient showed little variation for each equation, and each one can be used. The material used was the commercially pure aluminum, alloy Al1100.

Tribological behaviors between commercial pure titanium sheet and tools in warm forming

The tribological conditions between tools and sheet are the major factors affecting the product quality,forming limits and service life of tools in thin-walled titanium components warm forming.Using the orthogonal design based twist compression test in the temperature range of 25-300 °C,the significant factors affecting the coefficient of friction（Co F） and the influencing rules in CP-3 titanium sheet warm forming are clarified and discussed by changing tribological conditions such as tool material,lubrication,temperature and normal pressure.The results show that the significant factors affecting the Co F are lubrication,surface roughness,tool material,sliding velocity,normal pressure and temperature;compared with unlubricated condition,the graphite and Mo S2 greatly improve the friction condition and the maximum reduction of the Co F is 0.318;the Co Fs of Cr12 Mo V/CP-3 and QAl10-3-1.5/CP-3 tribo-pairs show a similar tendency：the Co Fs increase with increasing surface roughness and sliding velocity,and increase firstly then decrease with increasing normal pressure and temperature.