Xue Qunji

Study of the wear of filled polytetrafluoroethylene

Abstract The friction and wear behaviour of polytetrafluoroethylene (PTFE)-based composites filled by incorporating a metallic (stainless steel or copper) net with inorganic fillers was studied by rubbing composite pins against a mild steel block on a reciprocating tester. The mechanism of the load-supporting action of the fillers in reducing wear was verified and the process of formation of smaller wear debris was also discussed. It was found that the wear rate of the composites filled with a stainless steel net incorporating graphite is more than 300 times lower than that of pure PTFE.

Investigation of adhesion wear of filled polytetrafluoroethylene by ESCA, AES and XRD

Abstract In this paper more than 15 polytetrafluoroethylene (PTFE)-based composites incorporated by metal powders or metal oxides were studied by rubbing against smooth surfaces of steel, aluminium and copper on a reciprocating tester. Experiments based on sliding a pure PTFE pin against different metal blocks showed that the wear rate of pure PTFE does not change with the chemical properties of the counterface. Similar results have been obtained when pins of composite or pure PTFE are alternately rubbed against the same track of the block. The experimental results show that wear rate of PTFE-based composites filled by metal powders or metal oxides are lower than the wear rate of pure PTFE by a factor of about 1000 and the frictional properties of these composites are nearly the same as those of pure PTFE. The wear behaviour of pure PTFE was not affected by chemical activity of the counterface and a layer of transfer film of PTFE-based composites preferentially transferred onto the frictional track. X-ray diffraction (XRD) analysis showed that these metal powders disrupt the banded structure of PTFE and decrease its wear rate. Electron spectroscopy for chemical analysis of the frictional tracks on the metallic blocks suggested that chemical reaction of PTFE with zinc in the PTFE-based composite filled with zinc occurred under the experimental conditions. This reaction between PTFE and zinc was found to promote the preferential transfer of zinc from the composite to the counterface, resulting in a great reduction in the wear rate of the composite. Auger electron spectroscopy (AES) and its depth profiling analyses across the tracks on the blocks showed that a transferred film of pure PTFE may be formed on top of the transferred layer of PTFE-based composites on the metallic blocks but the transferred layer of the composites does not reduce the wear rate of pure PTFE.

A study of S-(1H-benzotriazol-1-yl)methyl N,N-dialkyldithiocarbamates as novel multifunctional oil additives

Abstract The load-carrying capacity, friction reduction and antiwear properties of two benzotriazole derivatives containing the R 2 NC(=S)S- group, added in liquid paraffin under boundary lubrication conditions were evaluated using a Seta-Shell Four-ball lubrication machine and an optimal SRV tester. Their anticorrosive and antioxidative properties, and thermal stabilities were also examined. The results when compared with those of zinc butyloctyldithiophosphate (ZDDP) show that the two novel compounds possess an excellent load-carrying capacity similar to ZDDP and better antiwear and antioxidative properties than ZDDP. Besides that, they have good anticorrosive properties and high thermal stabilities. The rubbed surfaces were investigated using X-ray photoelectron spectroscopy, Auger electron spectroscopy and electron probe microanalysis analytical tools. The extreme-pressure, antiwear and antioxidative mechanisms were discussed.

ESCA study on tribochemical characteristics of filled PTFE

Abstract ESCA analyses were performed on the frictional tracks on metal blocks covered with the transfer films of PTFE-based composites containing zinc, copper, and lead powders. Results show that the tribochemical reactions between PTFE and an aluminum or an iron counterface as well as between PTFE and zinc filler were found to occur under experimental conditions. Compounds of iron or aluminum fluoride were detected at the interface between the transfer film and the steel or aluminum substrate when PTFE composite pins rub against a steel or an aluminum counterface. This means that a chemical reaction between them has occurred. But the formation of a chemical bond between the transfer film of the composite and the substrate is not the real reason why metallic fillers reduce the wear of the PTFE, because the chemical reaction can also be detected when a pure PTFE pin rubs against a steel or an aluminum disk under these test conditions. The consumption of fluorine in PTFE at the interface between the films and the substrate is much more serious than that on the surface of the transfer films. It was found that the chemical reaction of the PTFE to the steel or aluminum substrate is by means of the fluorinc atom and not the carbon atom in the PTFE.

Effect of tribochemical reaction of polytetrafluoroethylene transferred film with substrates on its wear behaviour

Abstract X-ray photoelectron spectroscopy analyses of carbon steel, aluminium and copper blocks covered by polytetrafluoroethylene (PTFE) transferred film were performed. The tribochemical reactions of the PTFE transferred film with iron and aluminium were detected and no reaction was found for the system of PTFE and copper. When the tribochemical reactivity between PTFE and metals was compared with the wear rates of PTFE rubbing against these metal surfaces, it is concluded that no effect of the reactivity on the wear behaviour of PTFE was found. This appears to indicate that the PTFE transferred films were detached from the middle layer of the films and not from the interface between the films and substrate during the rubbing process.

Surface modification of PTFE by 60Co γ‐ray irradiation

Surface carboxyl groups were formed during the 60Co γ-ray irradiation of poly(tetrafluoroethylene) (PTFE) in air. Fourier transform infrared spectroscopy enables the detection of surface carboxyl groups. The contact angles were used to calculate the dispersive and polar components of the surface free energy according to a two-liquid method. The γ-ray irradiation of PTFE mainly caused degradation of the polymer. The concentration of carboxyl groups, the wettability, the friction, and the dispersive and polar components of the surface energy and the crystallinity on PTFE surface were increased, while the particle size of PTFE decreased with increasing irradiation dose. A highly modified PTFE was used to reduce the aqueous liquid repellent properties of PTFE. A 20 kGy dose for modified PTFE surface was suitable in air additivity in antifriction, anticorrosion, antifouling, lubrication, and noise reduction coatings.

Friction and wear characteristics of p-containing antiwear and extreme pressure additives in the sliding of steel against aluminum alloy

The tribological properties of P-containing antiwear (AW) and extreme pressure (EP) additives in the sliding of steel against aluminum alloy were investigated by Optimol SRV tester. It was found that phosphates reduces the friction coefficient of base stock. However, all P-containing AW and EP additives produce larger wear volume than base stock. The relationship between tribological properties of the additives and their chemical reactivity with aluminum was also found. The acting mechanism of P-containing additives in the lubricated aluminum-on-steel system was proposed.

Tribochemical investigation of tungsten carbide/titanium alloy tribo-couples under aqueous lubrication

The present paper deals with the fundamental understanding on the tribochemical mechanism of tungsten carbide (WC) coating and titanium alloy tribo-couples system. The tribological experiments were performed with a Timken-type tester. Water containing water-soluble additives was employed as the lubricating media. The rubbed surfaces of the carbide coating were characterized with scanning electric microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Significant titanium transfer was observed. Results of XPS analyses show that the interfacial layers formed consist of multiple oxides which suggests that oxidative reactions predominate in frictional processes under aqueous lubrication. It is proposed that the oxide layer is responsible for the tribological behavior because it controls the diffusive and adhesive wear.

Effects of additives on friction and wear behaviour of Cr2O3 coatings

Abstract The effects of several lubricating oil additives on the friction and wear properties of Cr 2 O 3 coatings were studied using a block-on-ring tester under ambient conditions. The results show that, compared with the base oil, oleic acid, glycol oleate and dibutyl phosphite have a friction-reducing function but sulphurized olefin does not; a remarkable wear resistance is observed for dibutyl phosphite and oleic acid but not for glycol oleate and sulphurized olefin. The concentration of these additives has a great influence on the wear behaviour of the Cr 2 O 3 coating but little influence on the friction behaviour. Analytical results of X-ray photoelectron spectroscopy show that the antiwear action of dibutyl phosphite is due to the formation of tribochemical reaction films on the rubbing surface and that the wear-increasing action of sulphurized olefin may be related to the physical adsorption of this additive and its decomposed products on the rubbing surfaces.

Tribochemical mechanisms of Si3N4 with additives

Abstract The effects of several extreme pressure additives on the wear behaviour of silicon nitride (Si 3 N 4 ) were investigated using a reciprocating wear tester; the tribochemical reaction mechanisms of Si 3 N 4 with these additives were studied by means of scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The wear tests show that the additives have different antiwear functions compared with n -tetradecane in the order tridodecyl borate ≈ tributyl phosphate (TBP) 3 N 4 oxidizes and forms crystalline SiO 2 . ZDDP, sulphurized olefin and chlorinated paraffin are effective in antiwear action, because of the formation of tribochemical reaction products obtained from the reaction with SiO 2 , while TBP and tridodecyl borate have little antiwear function because of their physical adsorption on the rubbing surfaces.