To address the problems of the difficult processing and internal microstructure disorder of porous bearing cages, Polyetheretherketone (PEEK) porous self-lubricating bearing cage material was ...prepared based on a fused deposition molding (FDM) process, and the porous samples were heat-treated on this basis, the research was carried out around the synergistic design of the material preparation, microstructure, and tribological properties. The results show that the pore size of the PEEK porous material prepared by the FDM process meets the requirements of the porous bearing cage; the samples with higher porosity also have higher oil content, and all the samples show high oil retention. Under dry friction conditions, the higher the porosity of the porous material, the larger the friction coefficient, and the friction coefficients of each sample after heat treatment show the same pattern; under starved lubrication conditions, the friction coefficient of the porous PEEK material decreased significantly compared to the compact PEEK material, showing a better self-lubrication effect, and the porous samples reached the best self-lubrication effect after heat treatment. The optimal process parameters were 60% mass fraction of NaCl, 40% mass fraction of PEEK, and the applied heat treatment process.
Carbon fabric reinforced phenolic-based composites (CF/PF composites) often act a potential alternative to traditional materials which currently used in machine elements such as self-lubricating ...bearing, high-performance gears, and movable sealed. In the present study, the CNTs@MoS.sub.2 hybrids were synthesized by hydrothermal method, which were used as additives for their optimal wear resistance and lubricating properties in order to enhance the tribological properties of CF/PF composites. We found that the CF/PF composites with varying contents of CNTs@MoS.sub.2 hybrids showed improved self-lubricating properties under different sliding conditions, and the friction coefficient decreased as the content of additives increased. Nevertheless, the doping of 1 wt% hybrids decreased the wear resistance of CF/PF composites due to the occurrence of severe abrasive wear caused by peeling off of matrix in relatively large volume. However, with the contents of hybrids increased to 2 wt% and 4 wt%, the CF/PF composites exhibited improved wear resistance. The mechanism of wear resistance could be attributed to the excellent mechanical properties of CNTs and strong interfacial bonding force between hybrids and matrix as well as the formation of MoS.sub.2 transfer film on the surface of counterpart.
The recent rise of 2D materials has extended the opportunities of tuning a variety of properties. Tribo-corrosion, the complex synergy between mechanical wear and chemical corrosion, poses ...significant challenges across numerous industries where materials are subjected to both tribological stressing and corrosive environments. This intricate interplay often leads to accelerated material degradation and failure. This review critically assesses the current state of utilizing 2D nanomaterials to enhance tribo-corrosion and -oxidation behavior. The paper summarizes the fundamental knowledge about tribo-corrosion and -oxidation mechanisms before assessing the key contributions of 2D materials, including graphene, transition metal chalcogenides, hexagonal boron nitride, MXenes, and black phosphorous, regarding the resulting friction and wear behavior. The protective roles of these nanomaterials against corrosion and oxidation are investigated, highlighting their potential in mitigating material degradation. Furthermore, we delve into the nuanced interplay between mechanical and corrosive factors in the specific application of 2D materials for tribo-corrosion and -oxidation protection. The synthesis of key findings underscores the advancements achieved through integrating 2D nanomaterials. An outlook for future research directions is provided, identifying unexplored avenues, and proposing strategies to propel the field forward. This analysis aims at guiding future investigations and developments at the dynamic intersection of 2D nanomaterials, tribo-corrosion, and -oxidation protection.
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•Various 2D materials reportedly boost the tribo-corrosion and -oxidation resistance.•Review covers graphene, chalcogenides, boron nitride, MXenes and black phosphorous.•Exploration of the interplay between wear and corrosion/oxidation.•Guidance for future research in 2D nanomaterials for tribo-corrosion protection.
PS400 is a multi-component alloy developed by NASA and intended for high temperature bearing applications. This study reports on four mating surfaces, namely bulk 4130 steel, diamond-like carbon ...(DLC), polycrystalline diamond, and molybdenum boride cobalt chrome coatings sliding against PS400 coating, and the best performing tribopair at 25 and 500 °C was identified. The temperature range and sliding speeds simulate extreme conditions for low-speed space-related applications, such as bearings on landing probes for future missions to Venus. PS400 vs. DLC showed low friction and excellent wear resistance up to 500 °C. DLC provided good lubrication at 25 °C, whereas at 500 °C oxide glazes transferred on DLC, maintaining low friction. The worn surfaces and the transfer films were analyzed using different analytical techniques.
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•PS400 coating vs. DLC coating exhibited low friction and zero wear at 25 °C and 500 °C.•Excellent lubrication performance of DLC at low temperature.•PS400 glazed oxides transferred on DLC at high temperature.•Graphitized DLC survived 500 °C tribotesting
The preparation of a series of dispersible nano-SiO
2 by surface-modification in situ was described in this paper. It is found that some silane coupling agents can be combined with nano-SiO
2 by ...covalent bonds, which change the nanoparticle's surface properties and make nano-SiO
2 disperse well and steadily in many organic mediums. The structure of nanoparticles was characterized by transmission electron microscopy (TEM), infrared spectrum (IR), X-ray photoelectron spectra (XPS) and thermogravimetric analysis (TG). The dispersivity of these nanoparticles in organic solvents was measured by light transmittance. Considering such superior dispersion in oily solvents and very small size, we primarily investigated their tribological behaviors as additive in lubricant on wear testers. The results show that they can evidently increase anti-wear ability and reduce the friction coefficient of lubricant.
•In-situ TiC and Ti5Si3 particles can enhance the corrosion and tribocorrosion resistance of the composites.•The composite with 5 vol% Ti3SiC2 exhibits the highest corrosion and tribocorrosion ...resistance.•The corrosion and tribocorrosion mechanisms of the composites are discussed.
To explore whether in-situ (TiC + Ti5Si3)/TC4 composites with network structure have simultaneously excellent corrosion and tribocorrosion resistance, the corrosion and tribocorrosion properties of the composites were studied. In-situ TiC and Ti5Si3 particles can effectively enhance the corrosion and tribocorrosion properties of the composites. The composite with 5 vol% Ti3SiC2 exhibits the highest corrosion and tribocorrosion resistance. Grain refinement and the effect of TiC and Ti5Si3 are important factors in enhancing the corrosion and tribocorrosion resistance of the composites.
The interaction between soil and geotextile is essential for the performance of reinforced soil. This study reveals the microscopic mechanism of interface shear between sand and geotextile based on ...the discrete element method (DEM). The surface characteristics of geotextile are simulated by overlapped particles. The micromechanical parameters of sand, geotextile, and interface are calibrated effectively using laboratory test results. Three types of shear tests on the sand-geotextile interface are simulated; namely, interface direct shear test (IDST), double-sided interface shear test (D_IST), and interface direct shear test with periodic boundary (PBST). For IDST, the results show that the thickness of shear band is 2.4--3.0 times the average particle diameter (D.sub.50); the contact force, percentage of sliding contact, and contact normal anisotropy inside the shear band are larger than those outside the shear band, whereas the coordination number is smaller inside the shear band. The mechanical response of D_IST is similar to that of IDST. However, D_IST has a shear band thickness of 3.0D.sub.50, and greater coordination number, percentage of sliding contact, and contact normal anisotropy. The results of PBST indicate that the peak stress and the shear band no longer appear without boundary constraint and the contact distribution is uniform.
The tribological behavior of cutting is a decisive factor in changing the production cycle, cost, and quality of parts. Minimum quantity lubrication (MQL) based on environmentally friendly ...biolubricants can convert contact conditions in cutting zones, but it cannot meet the manufacturing requirements of difficult-to-machine materials in the continuous friction turning process. Under the boundary conditions of high temperature, high cutting speed, and high pressure at the tool–workpiece interface, the scientific issue of performance enhancement remains unclear and thus has been the focus of academic and industry research. Moreover, under the continuous cutting boundary condition, technology enhancement as a development trend has not yet been systematically reviewed. Wetting, friction reduction, and heat transfer mechanisms have also not yet been investigated. In this study, the cooling lubrication mechanism and technical iteration motivation of MQL were initially analyzed. Subsequently, a quantized comparative assessment of cutting force, cutting temperature, tool wear, and surface quality under enhanced environmentally friendly lubrication turning, including parts enhanced by nanoparticles, cryogenic medium, ultrasonic vibration, and textured tools, was performed. The technical performance, parameter optimization, and mechanism of enhanced MQL were comprehensively studied, and the development stages of biolubricant MQL turning (MQLT) were fully reviewed. Finally, the development trend of the theory and application of MQLT for difficult-to-machine materials was prospected. This study may be used by scientists to deeply understand the mechanism, tribological behavior, and development trend of lubrication in relation to continuous cutting.
In order to seal the void defects in CrN coatings so as to enhance its mechanical and tribological properties, the electrochemical polarization treatment at different over-potentials was employed. ...The results showed that the maximum content of oxygen was increased by 1.22 at% after electrochemical polarization treatment, but the crystal structure of CrN(111) and Cr2N(002) for CrN coatings remained stable. The formation of a little chromium oxides as expected sealed the CrN coatings pores, and therefore lowered its porosity from 16.79 % to 12.28 %. As a result, the maximum hardness was increased by 20.3 %. Moreover, the wear resistance of CrN coatings was enhanced by 29.9 % whilst the friction coefficient was reduced by 25.2 % at the over-potential of 70 mV.
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•As a destructive test, electrochemical polarization was the first time used as a repair method to seal coatings defects.•The porosity of CrN coatings was reduced from 16.79 % to 12.28 % after electrochemical polarization treatment.•The hardness and wear resistance of CrN coatings were enhanced by 20.3 % and 29.9 % after electrochemical polarization.
