The Friction and Wear Properties of the Spherical Plain Bearings with Self-lubricating Composite Liner in Oscillatory Movement

A test method based on the condition simulation and a friction and wear test machine featuring in oscillatory movement were set up for self-lubricating spherical plain bearings (SPB). In the machine the condition parameters such as load, angle and frequency of oscillation and number of test cycles can be properly controlled. The data relating to the tribological properties of the bearing, in terms of friction coefficient, linear wear amount, temperature near friction surface and applied load, can be monitored and recorded simultaneously during test process by a computerized measuring system of the machine. Efforts were made to improve the measurement technology of the friction coefficient in oscillating motion. In result, a well-designed bearing torque mechanism was developed, which could reveal the relation between the friction coefficient and the displacement of oscillating angle in any defined cycle while the curve of friction coefficient vs number of testing cycles was continuously plotted. The tribological properties and service life of four kinds of the bearings, i.e, the sampleⅠ-Ⅳ with different self-lubricating composite liners, including three kinds of polytetrafluoroethylene (PTFE) fiber weave/epoxy resin composite liners and a PTFE plastic/copper grid composite liner, were evaluated by testing, and the wear mechanisms of the liner materials were analyzed.

Wear and mechanical characterization of Mg-Gr self-lubricating composite fabricated by mechanical alloying

In this research,the wear and mechanical responses of pure magnesium-graphite(Mg-Gr)composite have been investigated aiming to get the optimum composition of reinforcement.The composite materials were fabricated by mechanical alloying.The percentage of graphite reinforcement was chosen as 3,5,7 and 10 wt.%to identify its potential for self-lubricating property under dry sliding conditions.The mechanical properties including hardness,tensile strength and flexural strength of the composites and the base material were tested.The wear tests were conducted by using a pin-on-disc tribometer.The results show that the mechanical properties decrease with increasing graphite content as compared to that of the base material.The wear rate and average coefficient of friction decrease with the addition of graphite and was found to be minimum at 5 wt.%graphite reinforcement.The addition of 5 wt.%graphite in the composite exhibits superior wear properties as compared to that of the matrix material and other compositions of the Mg-Gr composites.

Tribological Behavior of Ni-based Self-lubricating Composites with the Addition of Ti3SiC2 and Ag2W2O7

The tribological properties of Nickel-based composites containing Ti3SiC2 and Ag2W2O7 fabricated by spark plasma sintering against Si3N4 balls were investigated using a ball-on-disk tribometer from room temperature to 600℃. The tribolayers formed on the friction surface and their effects on the tribological properties of composites at different temperatures were discussed based on the worn surface characterization. The results show that Ag2W2O7 is decomposed into metallic silver and CrWO4 during the high-temperature fabrication process. The composite with the addition of 20 wt% Ti3SiC2 and 5 wt% Ag2W2O7 exhibits a friction coefficient of 0.33-0.49 and a wear rate of 7.07x 10~5-9.89x 10~5 mm3/(Nm) over a wide temperature range from room temperature to 600℃. The excellent tribological properties at a wide temperature range are attributed to the formation of a glaze layer at low temperature and a tribooxide layer at high temperature, which can provide a low shearing strength for the synergistic effects of Ag and tribooxides.

Microstructure and properties of HVOF sprayed Ni-based submicron WS_2/CaF_2 self-lubricating composite coating

Ni-based submicron WS2/CaF2 self-lubricating composite coatings were produced on carbon steel substrate by high velocity oxygen fuel(HVOF) spray processing, and the microstructure and mechanical properties of the coatings were investigated. Non-uniform microstructure characterized by some pores and microcracks is observed in the produced composite coatings, which leads to low microhardness value, low adhesive strength and low frictional coefficient. For Ni45-5%CaF2-10%WS2 (mass fraction) and Ni45-10%CaF2-5%WS2 (mass fraction) coatings, under the test condition of load 40 N and speed 2 m/s, the friction coefficients obtained at room temperature are in the range of 0.35-0.48 and 0.31-0.41, respectively. The friction coefficients of two kinds of coatings increase to 0.4-0.63 and 0.35-0.46, respectively, at the test speed of 1 m/s. And the Ni45-10%CaF2-5%WS2 coating presents the minimum friction coefficient of 0.32-0.38 and good anti-wear properties at 400 ℃.

Modeling and prediction of tribological properties of copper/aluminum-graphite self-lubricating composites using machine learning algorithms

The tribological properties of self-lubricating composites are influenced by many variables and complex mechanisms.Data-driven methods,including machine learning(ML)algorithms,can yield a better comprehensive understanding of complex problems under the influence of multiple parameters,typically for how tribological performances and material properties correlate.Correlation of friction coefficients and wear rates of copper/aluminum-graphite(Cu/Al-graphite)self-lubricating composites with their inherent material properties(composition,lubricant content,particle size,processing process,and interfacial bonding strength)and the variables related to the testing method(normal load,sliding speed,and sliding distance)were analyzed using traditional approaches,followed by modeling and prediction of tribological properties through five different ML algorithms,namely support vector machine(SVM),K-Nearest neighbor(KNN),random forest(RF),eXtreme gradient boosting(XGBoost),and least-squares boosting(LSBoost),based on the tribology experimental data.Results demonstrated that ML models could satisfactorily predict friction coefficient and wear rate from the material properties and testing method variables data.Herein,the LSBoost model based on the integrated learning algorithm presented the best prediction performance for friction coefficients and wear rates,with R^(2) of 0.9219 and 0.9243,respectively.Feature importance analysis also revealed that the content of graphite and the hardness of the matrix have the greatest influence on the friction coefficients,and the normal load,the content of graphite,and the hardness of the matrix influence the wear rates the most.

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.

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.

In-situ preparation of robust self-lubricating composite coating from thermally sprayed ceramic template

The self-lubricating ceramic coatings that can control friction and wear have attracted researchers’widespread attention.However,the poor interfacial bonding between lubricants and ceramics and the deterioration of mechanical properties due to a tribological design limit their practical applications.Here,a robust self-lubricating coating was fabricated by an in-situ synthesis of MoS_(2)/C within inherent defects of thermally sprayed yttria-stabilized zirconia(YSZ)coatings.The edge-pinning by noncoherent endows hybrid coatings with excellent interfacial strength,increasing their hardness(HV)and cohesive strength.Furthermore,owing to the formation of a well-covered robust lubricating film at a frictional interface,a coefficient of friction(COF)can be reduced by 79.6%to 0.15,and a specific wear rate(W)drops from 1.36×10^(−3) to 6.27×10^(−7) mm^(3)·N^(−1)·m^(−1).Combining outstanding mechanical properties and tribological performance,the hybrid coating exhibits great application potential in controlling friction and wear.Importantly,this strategy of introducing the target materials into the inherent defects of the raw materials to improve the relevant properties opens new avenues for the design and preparation of composite materials.

Friction of metal-matrix self-lubricating composites: Relationships among lubricant content, lubricating film coverage, and friction coefficient

Metal-matrix self-lubricating composites can exhibit excellent tribological properties owing to the release of solid lubricant from the matrix and the formation of a lubricating film on the tribosurface.The coverage of the lubricating film on a worn surface significantly influences the sliding process.However,it is difficult to quantify the film coverage owing to the thin and discontinuous character of the lubricating film and the high roughness of the worn surface.A quantitative characterization of the lubricating film coverage based on X-ray photoelectron spectroscopy(XPS)analysis was developed in this study.The friction tests of Cu-MoS2 composites with a MoS2 content of 0-40 vol%were conducted,and the worn surfaces of the composites were observed and analyzed.Further,the influence of the MoS2 volume content on the coverage of the lubricating film on the worn surface was investigated.The relationships among the volume fraction of the lubricant,coverage of the lubricating film,and the friction coefficient were established.The friction model for the metal matrix self-lubricating composites was developed and verified to facilitate the composition design and friction coefficient prediction of self-lubricating composites.

Friction and wear properties of Cu-based self-lubricating composites in air and vacuum conditions

Cu-based self-lubricating materials containing two different solid lubricants （graphite and MoSs） were fabricated by P/M hot pressing techniques. Physical and mechan- ical properties of the samples were examined. The effects of graphite and MoSs contents on friction coefficient and wear rate were investigated by a ring-on-disc wear machine in air and vacuum conditions, respectively. Tribo-films formed on the worn surfaces were characterized by scanning electron microscopy （SEM） and X-ray photo- electron spectroscopy （XPS）. The results indicated that density, hardness and bending strength all increased with the increasing content of MoS2, while the relative density was opposite. Sample B containing 15 vol. pct graphite and 15 vol. pct MoS2 pos- sessed superior tribological properties both in air and vacuum conditions. However, the tribo-films formed on the worn surfaces of the sample B were greatly discrepant in composition at different testing conditions. In air, the volume ratio of MoS2 and graphite in the tribo-films is 0.31：1 whereas the ratio in vacuum is 1.07：1.

High Temperature Oxidation and Tribological Behaviors of NiCrAl-Graphite Self-Lubricating Composites

Nickel-graphite self-lubricating composites are a promising candidate to be used in turbine constructions that are usually exposed to high temperature oxidation and wear.However,the high-temperature stability of graphite as well as the effect that the oxide scale will play on the following wear process are still yet in debate.In this work,oxidation behavior of a NiCrAl-graphite composite and the subsequent friction and wear performances were studied.Results indicate that graphite is stable in the composites after oxidation at T≤400℃ for 300 h,which contributes synergistically with the thin oxide film to self-lubrication.The friction coefficient is below 0.20 and the wear rate is~1.43×10^(-5) mm³ N-1 m-1.The composite has the highest friction coefficient and wear rate when it was suffered from the high temperature oxidation at 500℃.Once it was oxidized at 600℃,a glaze layer would develop during the subsequent sliding.It plays a positive role in improving tribological properties though in the absence of lubricant phase of graphite,with to be exactly the friction coefficient and wear rate reduced by 13%and 21%,respectively,in comparison with the case of oxidation at 500℃.

Improving high-temperature wear resistance of NiCr matrix self-lubricating composites by controlling oxidation and surface texturing

Self-lubricating composites(SLCs)are widely used in the fields of aerospace and marine,but the conventional NiCr matrix SLCs with sulfide as solid lubricant often suffer from low wear resistance at high temperatures.In view of its high affinity with oxygen and also the high oxidation rate,appropriate amount of nano Ti was added to NiCr-WS_(2)composites prepared by spark plasma sintering(SPS)to adjust the oxidation behavior and surface texture.When exposed to high temperature,Ti was preferentially oxidized in comparison to Ni and Cr,resulting in abundant TiO_(2)protrusions and microdimples on the surface,i.e.in situ surface texturing.Besides,TiO_(2)was of high chemical activity and readily to react with other oxide debris during high temperature sliding process to form compounds of NiTiO_(3)and CrTi_(2)O_(5).The high chemical activity of oxide debris that was conducive to sintering,combining with the special surface texture that stores as many wear debris as possible,promoted the rapid formation of a protective glaze layer on the sliding surface.The NiCr-WS_(2)-Ti composite exhibited low friction coefficient but high wear resistance at elevated temperatures.Especially at 800℃,it presented a wear rate of as low as(2.1±0.3)×10^(-5)mm^3N-1m^(-1),accounting for only 2.7%of that of NiCr-WS_(2)composite.

Development and application of novel high‐efficiency composite ultrafine cement grouts for roadway in fractured surrounding rocks

The fractured surrounding rocks of roadways pose major challenges to safe mining.Grouting has often been used to reinforce the surrounding rocks to mitigate the safety risks associated with fractured rocks.The aim of this study is to develop highly efficient composite ultrafine cement(CUC)grouts to reinforce the roadway in fractured surrounding rocks.The materials used are ultrafine cement(UC),ultrafine fly ash(UF),ultrafine slag(US),and additives(superplasticizer[SUP],aluminate ultrafine expansion agent[AUA],gypsum,and retarder).The fluidity,bleeding,shrinkage,setting time,chemical composition,microstructure,degree of hydration,and mechanical property of grouting materials were evaluated in this study.Also,a suitable and effective CUC grout mixture was used to reinforce the roadway in the fractured surrounding rock.The results have shown that the addition of UF and US reduces the plastic viscosity of CUC,and the best fluidity can be obtained by adding 40%UF and 10%US.Since UC and UF particles are small,the pozzolanic effect of UF promotes the hydration reaction,which is conductive to the stability of CUC grouts.In addition,fine particles of UC,UF,and US can effectively fill the pores,while the volumetric expansion of AUA and gypsum decreases the pores and thus affects the microstructure of the solidified grout.The compressive test results have shown that the addition of specific amounts of UF and US can ameliorate the mechanical properties of CUC grouts.Finally,the CUC22‐8 grout was used to reinforce the No.20322 belt roadway.The results of numerical simulation and field monitoring have indicated that grouting can efficaciously reinforce the surrounding rock of the roadway.In this research,high‐performance CUC grouts were developed for surrounding rock reinforcement of underground engineering by utilizing UC and some additives.

Effects of Sinusoidal Vibration of Crystallization Roller on Composite Microstructure of Ti/Al Laminated Composites by Twin-Roll Casting

A new,innovative vibration cast-rolling technology of “electromagnetic stirring+dendrite breaking+asynchronous rolling” was proposed with the adoption of sinusoidal vibration of crystallization roller to prepare Ti/Al laminated composites,and the effect of sinusoidal vibration of crystallization roller on composite microstructure was investigated in detail.The results show that the metallurgical bonding of titanium and aluminum is realized by mesh interweaving and mosaic meshing,instead of transition bonding by forming metal compound layer.The meshing depth between titanium and aluminum layers (6.6μm) of cast-rolling materials with strong vibration of crystallization roller (amplitude 0.87 mm,vibration frequency 25 Hz) is doubled compared with that of traditional cast-rolling materials (3.1μm),and the composite interfacial strength(27.0 N/mm) is twice as high as that of traditional cast-rolling materials (14.9 N/mm).This is because with the action of high-speed superposition of strong tension along the rolling direction,strong pressure along the width direction and rolling force,the composite linearity evolves from "straight line" with traditional casting-rolling to "curved line",and the depth and number of cracks in the interface increases greatly compared with those with traditional cast-rolling,which leads to the deep expansion of the meshing area between interfacial layers and promotes the stable enhancement of composite quality.

Rational design and synthesis of Cr_(1-x)Te/Ag_(2)Te composites for solid-state thermoelectromagnetic cooling near room temperature

Materials with both large magnetocaloric response and high thermoelectric performance are of vital importance for all-solid-state thermoelectromagnetic cooling.These two properties,however,hardly coexist in single phase materials except previously reported hexagonal Cr_(1-x)Te half metal where a relatively high magnetic entropy change(-△S_(M))of~2.4 J·kg^(-1)·K^(-1)@5 T and a moderate thermoelectric figure of merit(ZT)of~1.2×10^(-2)@300 K are simultaneously recorded.Herein we aim to increase the thermoelectric performance of Cr_(1-x)Te by compositing with semiconducting Ag_(2)Te.It is discovered that the in-situ synthesis of Cr_(1-x)Te/Ag_(2)Te composites by reacting their constitute elements above melting temperatures is unsuccessful because of strong phase competition.Specifically,at elevated temperatures(T>800 K),Cr_(1-x)Te has a much lower deformation energy than Ag_(2)Te and tends to become more Cr-deficient by capturing Te from Ag_(2)Te.Therefore,Ag is insufficiently reacted and as a metal it deteriorates ZT.We then rationalize the synthesis of Cr_(1-x)Te/Ag_(2)Te composites by ex-situ mix of the pre-prepared Cr_(1-x)Te and Ag_(2)Te binary compounds followed by densification at a low sintering temperature of 573 K under a pressure of 3.5 GPa.We show that by compositing with 7 mol%Ag_(2)Te,the Seebeck coefficient of Cr_(1-x)Te is largely increased while the lattice thermal conductivity is considerably reduced,leading to 72%improvement of ZT.By comparison,-△S_(M)is only slightly reduced by 10%in the composite.Our work demonstrates the potential of Cr_(1-x)Te/Ag_(2)Te composites for thermoelectromagnetic cooling.

Experimental Investigation of the Anisotropic Thermal Conductivity of C/SiC Composite Thin Slab

Fiber-reinforced composites possess anisotropic mechanical and heat transfer properties due to their anisotropic fibers and structure distribution.In C/Si C composites,the out-of-plane thermal conductivity has mainly been studied,whereas the in-plane thermal conductivity has received less attention due to their limited thickness.

Effects of BN on the Mechanical and Thermal Properties of PP/BN Composites

In order to explore the thermal conductivity of polypropylene(PP)/hexagonal boron nitride(BN) composites,PP composites filled with different proportions of BN were prepared through extrution compounding,injection moulding and compression moulding.The composites were filled with BN particles of 5 and 20 μm respectively,and their mass fractions in composites were considered.Percentage of BN was varied from 0 to 25wt% in steps of 5wt%.The effects of BN filler on mechanical properties of the composites were evaluated.The thermal behaviors were studied using DSC and TGA,and the thermal conductivity was also investigated by Laser Flash Device and the Model of 3D Heat Conduction respectively.The experimental results show that impact strength of PP/BN can be enhanced with the addition of BN,but that composites exhibit lower breaking elongation & tensile strength when compared to unfilled ones.It is found that mass fraction of BN influenced the final thermal stability and degree of crystallization of PP matrix,the degree of crystallization of PP with 15wt% of 20 μm BN can be improved by 25% than neat PP.Meanwhile,crystallization temperatures of PP composites are elevated by about 10 ℃.The thermal conductivity results demonstrate that the maximum value of the thermal conductivity is achieved from PP/BN with 20wt% of 20 μm BN,higher than that of pure PP by 95.65%,close to the simulation one.

Influence of Mass Ratio of Resin and Stabilizer on Mechanical Properties of Mo Fiber-reinforced Granite Polymer Composite

Because inferior mechanical strength of granite polymer composite(GPC)has become the main drawback limiting its application and popularization,Mo fibers were added into(GPC)to improve its mechanical strength.Mechanical properties of matrix materials with different mass ratio of resin and stabilizer(MRRS)were investigated systematically.The influences of MRRS on interface bonding strength of Mo fiber-matrix,wettability and mechanical strength of GPC were discussed,respectively,and the theoretical calculation result of MRRS k was obtained,with the optimal value of k=4.When k=4,tensile strength,tensile strain and fracture stress of the cured resin achieve the maximum values.But for k=7,the corresponding values reach the minimum.With the increase of MRRS k,surface free energy of the cured resin first increases and then decreases,while contact angles between Mo sample and matrix have displayed the opposite trend.Wettability of resin to Mo fiber is the best at k=4.Pulling load of Mo fiber and interface bonding strength appear the maximum at k=4,followed by k=5,k=3 the third,and k=7 the minimum.When k=4,mechanical properties of Mo fiber-reinforced GPC are optimal,which is consistent with the result of theoretical calculation.This study is of great significance to get better component formulas of Mo fiber reinforced GPC and to improve its application in machine tools.

Comparison among the UECM Model, and the Composite Model in Forecasting Malaysian Imports

For more than a century, forecasting models have been crucial in a variety of fields. Models can offer the most accurate forecasting outcomes if error terms are normally distributed. Finding a good statistical model for time series predicting imports in Malaysia is the main target of this study. The decision made during this study mostly addresses the unrestricted error correction model (UECM), and composite model (Combined regression—ARIMA). The imports of Malaysia from the first quarter of 1991 to the third quarter of 2022 are employed in this study’s quarterly time series data. The forecasting outcomes of the current study demonstrated that the composite model offered more probabilistic data, which improved forecasting the volume of Malaysia’s imports. The composite model, and the UECM model in this study are linear models based on responses to Malaysia’s imports. Future studies might compare the performance of linear and nonlinear models in forecasting.

Gypsum-based Silica Gel Humidity-controlling Composite Materials:Preparation,Characterization,and Performance

Gypsum was used as substrate,and silica gel was mixed into substrate at a certain mass ratio to prepare humidity-controlling composites;moreover,the moisture absorption and desorption properties of gypsum-based composites were compared with adding different silica gel particle size and proportion.The morphological characteristics,the isothermal equilibrium moisture content curve,moisture absorption and desorption rate,moisture absorption and desorption stability,and humidity-conditioning performance were tested and analyzed.The experimental results show that,compared with pure-gypsum,the surface structure of the gypsum-based composites is relatively loose,the quantity,density and aperture of the pores in the structure increase.The absorption and desorption capacity increase along with the increase of silica gel particle size and silica gel proportion.When 3 mm silica gel particle size is added with a mass ratio of 40%,the maximum equilibrium moisture content of humidity-controlling composites is 0.161 g/g at 98% relative humidity(RH),3.22 times that of pure-gypsum.The moisture absorption and desorption rates are increased,the equilibrium moisture absorption and desorption rates are 2.68 times and 1.61 times that of pure-gypsum at 58.5% RH,respectively.The gypsum-based composites have a good stability,which has better timely response to dynamic humidity changes and can effectively regulate indoor humidity under natural conditions.