Oil-lubricated Conditions Research Articles

The effect of temperature on the tribological mechanisms and reactivity of hydrogenated, amorphous diamond-like carbon coatings under oil-lubricated conditions

In this work we present the wear and friction behaviour of boundary-lubricated, hydrogenated, amorphous, diamond-like carbon coatings (a-C:H), in self-mated a-C:H/a-C:H contacts, at three different testing temperatures: 20, 80, 150 °C. We present results from Auger electron spectroscopy, X-ray photoelectron spectroscopy and Raman analyses relating to the chemical and structural changes in the diamond-like carbon coatings during sliding in the presence of mineral oil, with and without additives. We show, that chemical reactions between the a-C:H coatings and the oil additives take place, which are dependent on the temperature, on the presence of additives and the type of additives used. At high temperatures the extreme pressure additive interacts with the diamond-like carbon surface and forms a tribochemical layer with a four-times lower sulphur/phosphorous ratio than the additive formulation. In the absence of additives, however, graphitisation of the coating occurs under these conditions, which results in high-wear and low-friction behaviour. Another result from this study is that a-C:H coatings can oxidise during room-temperature experiments, suggesting that some interactions and adsorptions are also possible at lower temperatures.

Effect of surfactant on the electrodeposition and wear resistance of Ni–Al 2O 3 composite coatings

Ni–Al 2O 3 composite coatings were electrodeposited from a Watts-type bath containing particles in suspension, which were dispersed with the aid of a cationic surfactant hexadecylpyridinium bromide (HPB). The effects of the surfactant on the zeta potential, co-deposition and distribution of Al 2O 3 particles in nickel matrix, and tribological properties of composite coatings were investigated. Experimental results showed that the addition of HPB could improve the amount of co-deposited Al 2O 3 particles, reduce the agglomeration of particles and achieve a more uniform distribution of Al 2O 3 particles in the nickel matrix. The wear resistance of the composite coatings increased with increasing concentration of HPB up to a certain optimum of 150 mg l −1, beyond which a decreasing trend of wear resistance was observed under dry sliding and oil-lubricated conditions. This is probably due to the increased brittleness of metal matrix when the concentration of surfactant exceeded the optimum.

The tribological performance of DLC coatings under oil-lubricated fretting conditions

Whether or not the process of fretting occurs is to a large extent dependent on the coefficient of friction, because the coefficient of friction directly affects the amount of shear stress. As a result, the key factor when it comes to reducing the amount of fretting damage is to reduce the coefficient of friction. Various surface coatings, and especially hard, diamond-like carbon (DLC) coatings, are known to be able to produce surfaces with a low level of friction. Despite some such attempts in the past, which did not result in major improvements, the developments and improvements in DLC coatings in recent years suggest the need for a re-evaluation of these coatings for fretting applications. Another way to reduce the amount of friction in mechanical components is to apply lubricants, and recent studies on the lubrication of DLC coatings suggest that this combination could be very successful in preventing failures under boundary-lubrication conditions. Therefore, in this work we present the results of friction and wear measurements from three types of fretting contacts: steel/steel, steel/DLC and DLC/DLC. Boundary oil-lubrication conditions were investigated and a wide range of displacement amplitudes, i.e., from 25 to 500 μm, were selected to assess the fretting and sliding behaviours. The results show a significant difference between the fretting and sliding regimes. In the fretting regime, the DLC-containing contacts, and especially the self-mated DLC/DLC contacts, performed much better than the steel/steel contacts, and significantly reduced both the wear (a 3–10 times reduction with steel/DLC and DLC/DLC) and the friction (a more-than-two-times reduction with DLC/DLC). In the sliding regime, the lubrication effects governed the tribological performance, making the results for all three material combinations very similar.

Effect of rare earths on mechanical and tribological properties of carbon fibers reinforced PTFE composite

The effect of a rare earth (RE) surface treatment on the mechanical and tribological properties of carbon fiber (CF) reinforced polytetrafluoroethylene (PTFE) composites was experimentally investigated. The tensile properties of the CF reinforced PTFE (CF/PTFE) composites treated with air oxidation and RE modifier were superior to those of untreated CF/PTFE composites, while RE treatment was most effective in promoting the tensile strength and strain at break of the CF/PTFE composite. The bending strength of the RE treated CF/PTFE composite was improved by about 16% compared with that of untreated composites, while 2% improvement was achieved by air oxidation. Under oil-lubricated conditions, RE treatment was more effective than air oxidation to reduce the friction coefficient and wear of PTFE composite. RE treatment effectively improved the interfacial adhesion between CF and PTFE. The strong interfacial coupling of the composite made CF not easy to detach from the PTFE matrix, and prevented the rubbing-off of PTFE, accordingly improved the friction and wear properties of the composite.

Preparation and tribological properties of the carbon nanotubes–Ni–P composite coating

A method to prepare the carbon nanotubes (CNTs)–Ni–P composite coating with different mass content of CNTs on the surface of 45 # steel by electroless plating was proposed. The transmission electron microscopy (TEM) and the scanning electron microscopy (SEM) were used to observe the appearance of the as-prepared CNTs and the CNTs–Ni–P composite coating, and then the roughness of the coating surface was also analyzed by atomic force microscopy (AFM). Furthermore, the wear and friction behavior of the CNTs–Ni–P composite coating were investigated under oil-lubricated condition, Due to the self-lubrication property and the unique antifriction structure, CNTs can greatly improve the wear resistance of the CNTs–Ni–P composite coating, where the wear resistance of the CNTs–Ni–P composite coating is optimized with the intermediate mass content of 2 kg/m 3 CNTs.

On the friction and wear behavior of PTFE composite filled with rare earths treated carbon fibers under oil-lubricated condition

Carbon fibers (CF) were surface treated with air-oxidation, air-oxidation followed by rare earths (RE) treatment and RE treatment, respectively. The friction and wear properties of the polytetrafluoroethylene (PTFE) composites filled with differently surface treated carbon fibers, sliding against GCr15 steel under oil lubrication, were investigated on a reciprocating ball-on-disk UMT-2MT tribometer. The worn surfaces of the PTFE composites were examined using a scanning electron microscopy (SEM). Experimental results revealed that surface treatment of carbon fibers reduced the wear of CF-reinforced PTFE composites. Among all the treatments to carbon fibers, RE treatment was the most effective and lowest friction and wear rate of CF-reinforced PTFE composite was exhibited, owing to the effective improvement of the interfacial adhesion between the carbon fibers and PTFE matrix.

Wear characteristics of carbon-phenolic woven composites mixed with nano-particles

The friction and wear characteristics of carbon fiber phenolic composites are important because carbon fiber phenolic composites are increasingly employed in journal bearing materials. Since the friction and wear characteristics of phenolic composites have been mainly investigated under dry sliding conditions, in this work, wear characteristics were experimentally investigated both under dry sliding and oil-lubrication conditions. Nano-size particles were mixed in the surface layers of the composite specimens to improve their wear characteristics. From the observation of morphology of failed composite, a wear stage of carbon-phenolic composite is proposed.

Bias-graded deposition of diamond-like carbon for tribological applications

Hydrogen-free diamond-like carbon coatings of thickness 1.5 μm were deposited on 440C stainless steel substrates and silicon wafers via DC magnetron sputtering of graphite target at power density of 10.5 W/cm 2. RF bias voltage was applied in the range of −20 to −150 V in two configurations: constant bias and bias-graded. The structure, surface topography, hardness and tribological behavior of these coatings were investigated. The surface roughness ( R a) of the coating decreased from 5.8 to 3.4 nm as bias voltage increased. Results from nanoindentation showed that the hardness of the coatings deposited at high bias voltage reached at 30 GPa and toughness (plasticity during indentation deformation) from approximately 50 to 60%. The hardness of the coating deposited with bias-graded configuration was comparable to the coatings deposited at high bias voltage but the toughness and adhesion strength were significantly improved. Ball-on-disc tribotests were carried out under dry, water- and oil-lubrication conditions. The result showed that the bias-graded coating had a very low coefficient of friction (down to 0.07 in oil). Furthermore, after 2.5 km sliding against alumina and steel (6 mm in diameter) at a high load of 10 N with and without lubrication, no sign of damage was observed on the wear track. Bias-graded sputtering deposition is an appropriate technique to combine the hardness, toughness and adhesion strength into one coating for demanding tribological applications.

Corrosion and wear behaviors of ferrous powder thermal spray coatings on aluminum alloy

Atmospheric plasma spray coating was performed on a cast AA383 Aluminum alloy plate, and this process formed a 170-μm thick spray coating layer by using tentative Fe–C powders with nickel added (up to 14 mass%) or without supplementary nickel. Hardness test, microstructure observation, corrosion and wear tests in engine oil with or without sulfuric acid water solutions added were performed as well. The corrosion performance was dependent upon the nickel content. On the contrary, the wear resistance testing under two engine oil lubrication conditions (with or without sulfuric acid water solution) showed the different tendency instead.

Wear and friction of a new wear-resistant material: TiNi-based composites

The equiatomic TiNi alloy exhibits an excellent wear resistance benefiting from its pseudoelasticity. The wear behavior of TiNi alloy was expected to improve further if hard particles were embedded in the alloy. The hard-phase particles may withstand the external load and the pseudoelastic matrix can absorb impact energy and accommodate a relatively large strain. TiNi-based composites, reinforced, respectively, with TiC and TiN particles were developed by using a vacuum sintering process. Sliding wear of the composites was evaluated. It was demonstrated that the composite exhibited an enhanced wear resistance with a considerable room for further improvement. Friction of the composites against steel under an oil-lubrication condition was also investigated. The correlation between the mechanical properties and wear and friction of the composites is discussed.

High temperature phase transformations under fretting conditions

Different and sometimes contradictory assessments of the importance of thermal and mechanical effects on tribochemical reactions in fretting have been reported in the literature. In our study of fretting wear between steel and silicon nitride ceramics, tribochemical reactions were determined to play the critical role under both non-lubricated and oil-lubricated conditions. Various possible effects on the resulting tribological interfaces are discussed based on the experimental evidence of microstructural changes, phase transformations, various thermodynamic and flash temperature calculations, and interaction couple experiments in which chemical wear was isolated by controlled mechanical and thermal parameters. It is shown here that a very high temperature must be considered as the most important factor influencing in tribochemical reactions and various phase transformations, even under conditions which are usually considered to be low speed–low temperature conditions.

Effects of lubricating-oil additives on the friction and wear properties of polymers and their composites sliding against steel under oil-lubricated conditions

Effects of lubricating-oil additives on the friction and wear properties of polymers and their composites sliding against steel under oil-lubricated conditions

Effects of lubricating-oil additives on the friction and wear properties of polymers and their composites sliding against steel under oil-lubricated conditions

The effects of lubricating-oil additive zinc dialkyldithiophosphate (ZDDP) on the friction and wear properties of polymers and their composites sliding against GCr15 bearing steel were studied by using an MHK-500 ring-on-block wear tester (Timken wear tester). Then the frictional surfaces of the friction pairs were examined by using electron probe microanalysis (EPMA). Experimental results show that the ZDDP contained in liquid paraffin has little effect on the friction coefficients of the polyimide (PI) or polyamide 66 (PA66) against GCr15 bearing steel friction pairs compared with that under the lubrication of liquid paraffin, but it slightly reduces the friction coefficients of polytetrafluoroethylene (PTFE) or its composites against GCr15 bearing steel friction pairs. Under lubrication of liquid paraffin containing 2 wt % ZDDP, the ZDDP film absorbed on the frictional surfaces of the PTFE composites–GCr15 bearing steel friction pairs exhibits obvious antiwear properties; it greatly reduces the wear of pure PTFE and the PTFE composites filled with Pb, PbO, and MoS2; and the wear of the PTFE composites can be reduced by one order of magnitude compared with that under lubrication of pure liquid paraffin. Meanwhile, the inorganic fillers Pb, PbO, and MoS2 contained in PTFE have little effect on the absorption of ZDDP to the frictional surfaces, so they have little effect on the friction coefficients of the PTFE composites–GCr15 bearing steel friction pairs under the lubrication of liquid paraffin containing 2 wt % ZDDP. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1240–1247, 2000

Tribological behaviours of an ion sulphurisation layer on steels

A sulphide layer with a certain thickness was made on the surface of 1045 and 52100 steels by means of a low temperature ion sulphurisation process. Tribological behaviours of the sulphide layers were investigated on a SRV reciprocating wear tester under dry and paraffin oil lubrication conditions. SEM equipped with EDX was used to analyse the morphologies and compositions of wear scars and wear debris. Sulphide layers showed remarkable friction-reducing effects and obvious wear-resistance. With the increase in thickness of the sulphide layer, its operational period was extended, but its friction coefficient was unchanged greatly. Under the same experimental conditions, the operational period of the sulphide layer on 52100 steel was longer than that on 1045 steel, and the wear-resistance of the former was better. The wear mechanism of the sulphurised surface is discussed.

Friction and wear behavior of PTFE composites filled with rare earth compounds under oil-lubricated conditions

Polytetrafluoroethylene (PTFE)-based composites, filled with CeO 2 , CeF 3 , and La 2 O 3 in volume contents of 5, 10, 15, 20, and 30%, were prepared. Then, the friction and wear behavior of these PTFE composites sliding against GCr15 bearing steel under both dry and liquid paraffin-lubricated conditions was evaluated using an MHK-500 ring-on-block wear tester. Finally, the worn surfaces and the transfer films of these PTFE composites were investigated using a scanning electron microscope (SEM) and an optical microscope. Experimental results showed that filling CeO 2 , CeF 3 , and La 2 O 3 into PTFE can reduce the wear of the PTFE composites by 1-2 orders of magnitude. When the content of CeO 2 in PTFE is 15%, the friction and wear properties of the CeO 2 -filled PTFE composite are the best. Meanwhile, when the content of La 2 O 3 in PTFE is between 15 and 20%, the PTFE composite filled with La 2 O 3 exhibits excellent friction and wear-reducing properties. However, the friction coefficient of the CeF 3 -filled PTFE composite increases but its wear decreases with increase in the content of CeF 3 from 5 to 30%. The friction and wear-reducing properties of CeO 2 -, CeF 3 -, and La 2 O 3 -filled PTFE composites can be greatly improved by lubrication with liquid paraffin, but the limit loads of the PTFE composites decrease with increase in the content of CeO 2 , CeF 3 , and La 2 O 3 in PTFE (from 5 to 30%) under the same conditions. Investigations of worn surfaces show that the interaction between liquid paraffin and the CeO 2 -, CeF 3 -, and La 2 O 3 -filled PTFE composites, especially the absorption of liquid paraffin into the microdefects of the PTFE composites, creates some cracks on the worn surfaces of the PTFE composites and that the creation and development of the cracks reduces the mechanical strength and the load-supporting capacity of the PTFE composites. However, with increase of the content of CeO 2 , CeF 3 , and La 2 O 3 in the PTFE, the microdefects in the PTFE composites also increase, which would lead to increase in the number of the cracks on the worn surfaces of the PTFE composites under load and, so, in turn, lead to the reduction of the limit loads of the CeO 2 -, CeF 3 -, and La 2 O 3 -filled PTFE composites under lubrication with liquid paraffin.

Friction and wear characteristics of ceramic particle filled polytetrafluoroethylene composites under oil-lubricated conditions

Five kinds of polytetrafluoroethylene (PTFE)-based composites were prepared: PTFE, PTFE + 30 vol % SiC, PTFE + 30 vol % Si3N4, PTFE + 30 vol % BN, and PTFE + 30 vol % B2O3. The friction and wear properties of these ceramic particle filled PTFE composites sliding against GCr15 bearing steel under both dry and liquid paraffin lubricated conditions were studied by using an MHK-500 ring-block wear tester. The worn surfaces and the transfer films formed on the surface of the GCr15 bearing steel of these PTFE composites were investigated by using a scanning electron microscope (SEM)and an optical microscope, respectively. The experimental results show that the ceramic particles of SiC, Si3N4, BN, and B2O3 can greatly reduce the wear of the PTFE composites; the wear-reducing action of Si3N4 is the most effective, that of SiC is the next most effective, then the BN, and that of B2O3 is the worst. We found that B2O3 reduces the friction coefficient of the PTFE composite but SiC, Si3N4, and BN increase the friction coefficients of the PTFE composites. However, the friction and wear properties of the ceramic particle filled PTFE composites can be greatly improved by lubrication with liquid paraffin, and the friction coefficients of the PTFE composites can be decreased by 1 order of magnitude. Under lubrication of liquid paraffin the friction coefficients of these ceramic particle filled PTFE composites decrease with an increase of load, but the wear of the PTFE composites increases with a load increase. The variations of the friction coefficients with load for these ceramic particle filled PTFE composites under lubrication of liquid paraffin can be properly described by the relationship between the friction coefficient (μ) and the simplified Sommerfeld variable N/P as given here. The investigations of the frictional surfaces show that the ceramic particles SiC, Si3N4, BN, and B2O3 enhance the adhesion of the transfer films of the PTFE composites to the surface of GCr15 bearing steel, so they greatly reduce the wear of the PTFE composites. However, the transfer of the PTFE composites onto the surface of the GCr15 bearing steel can be greatly reduced by lubrication with liquid paraffin, but the transfer still takes place. Meanwhile, the interactions between the liquid paraffin and the PTFE composites, especially the absorption of liquid paraffin into the surface layers of the PTFE composites, create some cracks on the worn surfaces of the ceramic particle filled PTFE composites; the creation and development of these cracks reduces the load-supporting capacity of the PTFE composites. This leads to the deterioration of the friction and wear properties of the PTFE composites under higher loads in liquid paraffin lubrication. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2611–2619, 1999

Friction and wear characteristics of metal sulfides and graphite-filled PTFE composites under dry and oil-lubricated conditions

Five kinds of polytetrafluoroethylene (PTFE)-based composites, pure PTFE, PTFE + 30(v)% MoS2, PTFE + 30(v)% PbS, PTFE + 30(v)% CuS, and PTFE + 30(v)% graphite (GR) composites, were first prepared. Then the friction and wear properties of these PTFE composites, sliding against GCr15-bearing steel under both dry and liquid paraffin-lubricated conditions, were studied by using an MHK-500 ring-on-block wear tester. Finally, the worn surfaces and the transfer films of the PTFE composites formed on the surface of GCr15 bearing steel were investigated by using a scanning electron microscope (SEM) and an optical microscope, respectively. Experimental results show that filling with MoS2, PbS, CuS, or graphite to PTFE can reduce the wear of the PTFE composites by two orders of magnitude compared to that of pure PTFE under dry friction conditions. However, the friction and wear-reducing properties of these PTFE composites can be greatly improved by lubrication with liquid paraffin. Investigations of transfer films show that MoS2, PbS, CuS, and graphite promote the transfer of the PTFE composites onto the surface of GCr15-bearing steel under dry friction conditions, but the transfer of the PTFE composites onto the surface of GCr15-bearing steel can be greatly reduced by lubrication with liquid paraffin. SEM examinations of worn surfaces show that with lubrication of liquid paraffin, the creation and development of the cracks occurred on the worn surfaces of the PTFE composites under load, which reduces the load-supporting capacity of the PTFE composites. This would lead to the deterioration of the friction and wear properties of the PTFE composites under higher loads (>600N). © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 751–761, 1999

Application of the Compressive Force Method to the Angle Control Method of Bolt Tightening.

In this study, the new angle control method to reduce the scatter band of clamping forces has been developed. The present method simultaneously loads a bolt with torque and compressive force, and measures torque and angle. The friction coefficients, the snug point and the spring constants of the bolted joint can be accurately evaluated during tightening process. Thus, the scatter band of clamping force in the elastic-region can be reduced within the error of 10% under oil free or lubricated conditions by the present method. The present method have high reliability and never loss tightening efficiency. It is possible to apply the present method to the plastic region tightening.

Friction and wear characteristics of copper and its compound-filled PTFE composites under oil-lubricated conditions

Four kinds of polytetrafluoroethylene (PTFE)-based composites, such as pure PTFE, PTFE + 30(v)%Cu, PTFE + 30(v)%Cu2O, and PTFE + 30(v)%CuS composite, were prepared. Then the friction and wear properties of the PTFE composites filled with Cu, Cu2O, or CuS sliding against GCr15-bearing steel under both dry and liquid paraffin-lubricated conditions were studied by using an MHK-500 ring-block wear tester. Finally, the worn surfaces and the transfer films of these PTFE composites formed on the surface of GCr15-bearing steel were investigated by using a scanning electron microscope (SEM) and an optical microscope, respectively. Experimental results show that the antiwear properties of these PTFE composites can be greatly improved by filling Cu, Cu2O, or CuS to PTFE, and the wear of these PTFE composites can be decreased by two orders of magnitude compared to that of pure PTFE under dry friction conditions. Meanwhile, CuS increases the friction coefficient of the PTFE composite, but Cu and Cu2O reduce the friction coefficients of the PTFE composites. However, the friction and wear properties of Cu, Cu2O, or CuS-filled PTFE composites can be greatly improved by lubrication with liquid paraffin. The friction coefficients of these PTFE composites can be decreased by one order of magnitude compared to those under dry friction conditions, while the wear of these PTFE composites can be decreased by one to two orders of magnitude. The PTFE + 30(v)%Cu composite exhibits excellent friction and wear-reducing properties under higher loads in liquid paraffin-lubricated conditions, so the PTFE + 30(v)%Cu composite is much more suitable for application under oil-lubricated conditions in practice. Optical microscope investigation of transfer films shows that Cu, Cu2O, and CuS enhance the adhesion of the transfer films to the surface of GCr15-bearing steel, so they greatly reduce the wear of the PTFE composites. However, the transfer of the PTFE composites onto the surface of GCr15-bearing steel can be greatly reduced by lubrication with liquid paraffin, but the transfer still takes place. SEM examination of worn surfaces shows that the interaction between liquid paraffin and the PTFE composites, especially the absorption of liquid paraffin into the surface layers of the PTFE composites, creates some cracks on the worn surfaces of Cu2O or CuS-filled PTFE composites, the creation and development of the cracks reduces the load-carrying capacity of the PTFE composites; this leads to the deterioration of the friction and wear properties of the PTFE composites under higher loads in liquid paraffin lubrication. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1455–1464, 1998

Friction and wear properties in dry, water- and oil-lubricated DLC against alumina and DLC against steel contacts

Diamond-like carbon (DLC) films can be divided into two major categories according to their hydrogen content. These categories have similarities in tribological performance, but the films also behave in a different manner in different tribological conditions. The results of amorphous hydrogenated carbon films (a-C:H) and hydrogen-free hard carbon films (a-C) are reported in this study. The a-C:H films were deposited using the radio frequency (rf) plasma technique, and the hydrogen-free hard carbon films using pulsed vacuum arc. The coatings were characterized and investigated with respect to their tribological performance in dry (50% RH), water-lubricated and oil-lubricated slow sliding conditions (0.004 m s −1). The a-C and a-C:H films had a low friction coefficient in dry sliding conditions (0.15 to 0.22), which was further decreased by 10–40% under boundary lubrication. The a-C:H(Ti) films exhibited good self-lubricating properties (0.10) in dry sliding conditions and the a-C films had the lowest friction coefficient in water- (0.03) and oil-lubricated (0.08) conditions. The hydrogen-free hard carbon films showed excellent wear resistance in dry, water- and oil-lubricated conditions, but hydrogenated a-C:H films suffered from severe wear in aqueous conditions. The performance of a-C:H films could be improved by titanium alloying. In dry sliding conditions, the tribolayer formation of DLC films influenced the friction and wear performance, but in oil-lubricated conditions boundary lubrication layers were formed, which governed the tribological mechanisms in the contact.