Yinping Ye

Structure, Mechanical, and Tribological Properties of MoS2/a-C:H Composite Films

A series of hydrogenated amorphous carbon (a-C:H) films doped with molybdenum disulfide (MoS2) were deposited by medium frequency unbalanced magnetron sputtering with mixed Ar/CH4 gases of different volume ratios as the source gases. The effects of Ar/CH4 ratio on morphology, microstructure, mechanical, and tribological properties of the MoS2/a-C:H composite films were investigated. Results show that the content of MoS2 in the as-deposited films decreases with the decreasing Ar/CH4 ratio, and the highest Ar/CH4 ratio favors the formation of nanostructured films. Besides, the hardness and internal stress of the composite films first decrease and then increase with decreasing Ar/CH4 ratio. Furthermore, the film deposited at the highest Ar/CH4 ratio exhibits excellent antiwear ability in all test environments and shows promising potential as a solid lubricating film in aviation and space industries.

Preparation and properties of MoS2/a-C films for space tribology

MoS2/a-C composite films with various (Mo+S)/C ratios were deposited by medium frequency unbalanced magnetron sputtering. The effects of MoS2 doping on the microstructure, mechanical and vacuum tribological properties of the films were investigated. Results show that the sp2 carbon content in the film increases with increasing (Mo+S)/C ratio from 0 to 0.19, and MoS2 nanocrystallines are formed in film as (Mo+S)/C ratio increased to 0.07. Consequently, the composite film exhibits decreasing hardness (from 5.2 to 2.5?GPa) and elastic modulus (from 116 to 24?GPa). As the (Mo+S)/C ratio increases from 0 to 0.19, the friction coefficient of the films decreases from 0.18 to 0.008 and sliding time increases from 3?s to more than 3600?s in vacuum. This is mainly attributed to that the films with higher (Mo+S)/C ratios (at least 0.12) are inclined to form the lamellar MoS2 with low shear strength on the counterface. Furthermore, the composite film with (Mo+S)/C ratio of 0.12 has been investigated in various test environments (air, N2, vacuum). The average friction coefficient is lower than 0.035 and it exhibits little sensitivity to the test environment. However, the highest and lowest wear rate (about 4???10?7?mm3?Nm?1 and 0.8???10?7?mm3?Nm?1) are obtained in vacuum and N2, respectively. The environment dependence of the tribological behaviours is related with the lattice orientation of MoS2 crystalline and the graphitization degree of the film.

Influence of Polyfluo-Wax on the Friction and Wear Behavior of Polyimide/Epoxy Resin–Molybdenum Disulfide Bonded Solid Lubricant Coating

ABSTRACT Polyimide/Epoxy resin–molybdenum disulfide bonded solid lubricant coatings (denoted as PI/EP-MoS2) were prepared. The influence of polyfluo-wax (denoted as PFW) on the microhardness and friction and wear behavior of as-prepared PI/EP-MoS2 lubricant coating was measured using a microhardness tester and a reciprocating ball-on-disc tribometer, respectively. The worn surfaces of the lubricant coatings were observed with a scanning electron microscope, and their wear rate was determined with a Micro XAM surface mapping microscope. Moreover, the transfer films formed on the counterpart steel ball surfaces were analyzed by X-ray photoelectron spectroscopy. Results indicate that the incorporation of a proper content of PFW filler is effective at improving the antifriction performance of the PI/EP-MoS2 lubricant coating while maintaining better wear resistance. Moreover, the friction coefficient of the lubricant coating decreases with increasing content of PFW from 2 to 10%, and the one with a filler content over 6% PFW has a steady friction coefficient of 0.07. The improvement in the antifriction performance of the lubricant coating with the incorporation of the PFW filler is attributed to the excellent lubricity of homogeneously distributed PFW.

Microstructure, Tribological Behavior, and Corrosion-Resistant Performance of Bonded MOS2 Solid Lubricating Film Filled with Nano-LaF3

The anti-friction and wear-resistant performances of bonded MoS2 solid lubricating films filled with nano-LaF3 filler were investigated under in drying wear conditions, the corrosion-resistant performances of bonded lubricating films was evaluated according to ASTM-B117, and the characteristics of the bonded lubricating films were examined by TEM and elemental x-ray map. The wear-resistant performance of the bonded lubricating films filled with nano-LaF3 filler increases with increasing content of nano-LaF3 filler within a content range between 0 and 5 wt%, whereas the bonded lubricating films filled with 0.5–1 wt% micro-LaF3 filler exhibit the better wear-resistant performances. The incorporation of both nano-LaF3 and micro-LaF3 filler leads the increase of the coefficient of friction of the bonded lubricating films. The LaF3 filler can improve the corrosion-resistant performance of the bonded MoS2 solid lubricating films, whereas the incorporation of nano-LaF3 filler is more effective to improve the corrosion-resistant performance of the bonded lubricating films than micro-LaF3 filler. The improvement in the wear-resistant and corrosion-resistant performances of the bonded lubricating films by the incorporation of the nano-LaF3 filler is attributed to the strengthened interfacial bonding among the nano-LaF3 and the MoS2 lubricant and the polymeric matrix. However, a too high mass fraction of the nano-LaF3 filler in the bonded lubricating films will increase surface and interface defects, and lead the worsening of corrosion-resistant performance of the bonded lubricating films.

Effect of vacuum annealing on the microstructure and tribological behavior of hydrogenated amorphous carbon films prepared by magnetron sputtering

Hydrogenated amorphous carbon films (a-C:H) were prepared on silicon and steel substrates by medium frequency unbalanced magnetron sputtering with argon (Ar) and methane (CH4) as the source gases. The effect of annealing temperature in vacuum on the microstructure as well as mechanical properties and tribological behavior of as-prepared a-C:H films were investigated. The friction and wear behaviors of the films in different environments (vacuum, N2, and air) were evaluated with a pin-on-disk tribometer; and their sliding lifetime in vacuum was discussed in relation to friction and wear mechanisms. Results show that annealing in vacuum at a low temperature of up to 200 ℃ causes little change in the microstructure and hardness of a-C:H films but reduces their internal stress and surface roughness to some extent. These annealed films exhibit excellent antiwear ability in all test environments and show promising potential as a kind of space lubricants. The film begins to release hydrogen and increases the content of graphite-like structure at about 300 ℃. As a result, a-C:H films annealed above 200 ℃ have increased surface roughness as well as reduced hardness, internal stress, and wear resistance in all test environments.

Mechanical and tribological properties of Cr/Cr2O3 multilayer films

Cr/Cr2O3 multilayer and single-layer films were deposited through multiple arc ion plating technique. The influence of modulation ratio on the mechanical and tribological properties was also investigated. Results show that the multilayer design of Cr/Cr2O3 films could improve the toughness of films, but a certain degree of hardness loss is also observed. The hardness and adherence strength are improved with the increase of Cr2O3 layer thickness. Furthermore, alternating layers of ductile soft metals and hard ceramics could suppress the propagation of microcracks and brittle fracture. However, the decrease of modulation ratio could causes a decline in the mechanical properties. The film with appropriate modulation ratio (Cr2O3:Cr ratio 10:1) exhibits better comprehensive properties than other films, this film also exhibits an excellent wear resistance with a high load of 10 N. Consequently, the wear life is improved from 6 m of the single-layer Cr2O3 film to 835 m of the multilayer film.

Effect of Chemisorptions on Wetting Property in TiO Nanosheet Film

TiO nanosheet films were fabricated by magnetron sputtering and followed with the direct in situ hydrothermal method. Without UV irriadiation, the TiO nanosheet surface showed a wetting property of superhydrophilicity. However, after chemisorptions using a self-assembled monolayer of n-CF3(CF2)7CH2CH2Si(OC2H5)3, the wetting property of the film can be changed from superhydrophilicity to superhydrophobicity. Based on the FESEM, XRD, XPS analysis, the mechanism of the wetting bahavior was proposed.

The Tribological Characteristics of Polyimide Bonded Solid Lubricating Films under Different Lubrication Conditions

In this paper, the tribological behaviors of polyimide bonded PTFE solid lubricating film and polyimide bonded MoS2 solid lubricating film under dry sliding and under lubrication of kerosene oil, diesel fuel, paraffin liquid and lubrication oil were investigated by using a ring-on-block wear tester. The results show that the anti-friction and wear-resistance properties of both lubricating films are greatly improved under oil lubrication conditions as compared with the dry friction condition; the friction coefficients of both lubricating films under different oil lubrications keep steady-state value with 0.08; but both lubricating films under different oil lubrications reveal the different wear-resistance properties, such as the best wear-resistance properties under diesel fuel, followed by paraffin liquid, lubrication oil and kerosene oil; the differences in the wear-resistance properties of the lubricating films under different lubrication conditions are mainly ascribed to the influence of the oil’s characteristics, especially boiling point and viscosity.

The tribological properties of a pure iron surface modified by Cr ion implantation

Abstract The friction and wear behaviour of a pure iron specimen modified by Cr+ implantation under lubrication conditions were investigated. The results indicate that wear properties of the specimen modified by Cr+ implantation in various doses are significantly different under conditions of lubrication with various additives, and depend on the amount of Cr+ implantation. Auger electron spectroscopy and X-ray photo-electron spectroscopy analysis of the worn surfaces shows that Cr+ implantation alters the interaction between the rubbing surface and additives. The composition of the surface films formed on the rubbing surface depends on the Cr content in the surface layer of the specimen, and governs the tribological behaviour of implanted specimens.