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Copyright of Lubrication Engineering (0254-0150) is the property of Editorial Office of LUBRICATION ENGINEERING and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The stability of the graphite seal device is a key factor for the normal operation of aero engines. However, conventional graphite exhibits poor comprehensive performance due to its porous structure, which limits its application at high temperatures. Therefore, in this paper, phosphate was used to impregnated graphite pores, and the interaction between the friction, wear, and oxidation of phosphate-impregnated graphite against superalloy at high temperatures was studied through pin-on-disk friction tests. The results revealed that the coefficient of friction (COF) of matrix graphite fluctuated greatly, from 0.07 to 0.17, in the range of 100 °C to 500 °C, while the COF of impregnated graphite was stable, at around 0.13, from 100 °C to 500 °C. The wear rates of the two types of graphite were close from 20 °C to 300 °C, while the wear rate of the impregnated graphite was significantly lower than that of the matrix graphite at higher temperatures, from 400 °C and 500 °C. The reason was that the impregnated phosphate reacted with graphite at a high temperature, forming the inert site which helped to inhibit the oxidation and maintain the mechanical properties of the impregnated graphite at high temperatures. In addition, the impregnated graphite could maintain better integrity of the contact surface and reduce the inclusion of large hard metal oxides, thus effectively reducing the abrasive wear of the disk. Therefore, the wear depth of the superalloy disk samples with impregnated graphite was significantly lower than that of the matrix graphite. The results promote the application of phosphate-impregnated graphite under the high temperature conditions of aero engines. [ABSTRACT FROM AUTHOR]

The gas–liquid miscible backflow pumping seal (G-LMBPHS) is a non-contact mechanical seal that is suitable for high-speed bearing chambers. However, the tribological properties and wear mechanisms of the frictional pair of G-LMBPHS in an oil–air environment have not yet been comprehensively studied. In this study, the tribological properties of six frictional pairs, consisting of three hard materials (18Cr2Ni4WA, Al2O3 coating, and Cr2O3 coating) and two soft materials (metal-impregnated graphite [Metal-IG] and resin-impregnated graphite [Resin-IG]), were analyzed using a disc-on-disc tribometer. An oil–air environment was created using a minimal quantity lubrication (MQL) system and a closed chamber. The results show that the COF of the four frictional pairs consisting of two coatings and two graphites decreases gradually with increasing rotational speed, and the frictional pairs composed of Al2O3 coating and Resin-IG and Cr2O3 coating and Resin-IG have the lowest COF between 0.022 and 0.03. Therefore, the frictional pairs of G-LMBPHS are in a mixed lubrication condition. The lubricant in the oil–air environment is adsorbed and stored in pits on the surface of graphite and coatings, enhancing the hydrodynamic effect of the spiral grooves and reducing the COF by up to 45%. Metal-IG has better wear resistance than Resin-IG, and the frictional pair consisting of Cr2O3 coating and Metal-IG has the lightest wear. This study provides an important basis for the selection of G-LMBPHS frictional pairs in oil–air environments. [ABSTRACT FROM AUTHOR]

Copyright of Lubrication Engineering (0254-0150) is the property of Editorial Office of LUBRICATION ENGINEERING and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The gas–liquid miscible backflow pumping seal (G-LMBPHS) is a non-contact mechanical seal that is suitable for high-speed bearing chambers. However, the tribological properties and wear mechanisms of the frictional pair of G-LMBPHS in an oil–air environment have not yet been comprehensively studied. In this study, the tribological properties of six frictional pairs, consisting of three hard materials (18Cr2Ni4WA, Al2O3 coating, and Cr2O3 coating) and two soft materials (metal-impregnated graphite [Metal-IG] and resin-impregnated graphite [Resin-IG]), were analyzed using a disc-on-disc tribometer. An oil–air environment was created using a minimal quantity lubrication (MQL) system and a closed chamber. The results show that the COF of the four frictional pairs consisting of two coatings and two graphites decreases gradually with increasing rotational speed, and the frictional pairs composed of Al2O3 coating and Resin-IG and Cr2O3 coating and Resin-IG have the lowest COF between 0.022 and 0.03. Therefore, the frictional pairs of G-LMBPHS are in a mixed lubrication condition. The lubricant in the oil–air environment is adsorbed and stored in pits on the surface of graphite and coatings, enhancing the hydrodynamic effect of the spiral grooves and reducing the COF by up to 45%. Metal-IG has better wear resistance than Resin-IG, and the frictional pair consisting of Cr2O3 coating and Metal-IG has the lightest wear. This study provides an important basis for the selection of G-LMBPHS frictional pairs in oil–air environments.

Impregnated graphite has attracted considerable attention and has been widely used as an ideal sealing material in many fields. However, the service environment often contains vibrations, which can easily lead to severe fretting wear and leakage. In this study, the fretting friction and wear properties of resin-impregnated graphite and antimony-impregnated graphite were investigated. The results revealed that only gross slipping regime (GSR) occurred for two impregnated graphite. For resin-impregnated graphite, both abrasive and adhesive wear were discovered. Yet slight fatigue wear occurred on the worn surface of antimony-impregnated graphite at higher cyclic contact stress. The significant properties of the impregnated graphite can be attributed to a transfer film, which uniformly and stably adsorbs on the contact interfaces. This study provides an important basis for matching the industrial applicability of graphite-based modified sealing materials. • The fretting friction and wear characteristics of different impregnated graphite were comparatively investigated. • Only gross slipping regime (GSR) occurred for two impregnated graphite. • Abrasive and adhesive wear were the major mechanisms for resin-impregnated graphite. • Slight fatigue wear occurred on the worn surface of antimony-impregnated graphite at higher cyclic contact stresses. • The significant properties of the impregnated graphite can be attributed to a transfer film on the contact interface. [ABSTRACT FROM AUTHOR]

Abstract Impregnated graphite has attracted considerable attention and has been widely used as an ideal friction material in many fields. However, the influence of the friction temperature on its tribological properties has not been clearly studied; furthermore, the evolution mechanism of transferred tribofilm is unknown. In this study, the tribological properties of impregnated graphite were investigated at different friction temperatures, and the evolution of the carbon-based tribofilm was also determined. The results revealed that the tribological properties significantly improved with an increase in friction temperature. The friction coefficient and wear depth of impregnated graphite reduced by 68% and 75%, respectively, at a high temperature of 160 °C compared with those of non-impregnated graphite. The significant properties of the impregnated graphite can be attributed to a transferred carbon-based tribofilm with an ordered structure induced by the friction temperature, which uniformly and stably adsorbs on friction interfaces. This study provides an important basis for designing graphite-based friction materials with improved properties suited for industrial applications.

The frictional performance between impregnated graphite materials and YG-8 cemented carbide is investigated on a self-developed rotating-type tribometer. The test configuration is a cemented carbide plate rotating against the graphite surface. Three types of concave-type textures, including linear grooves, circular dimples and isosceles triangular dimples, are fabricated by laser process on the graphite surfaces to improve the tribological properties. The test environments include dry condition and water lubrication. The corresponding friction coefficients, surface micrographs of graphite samples and cemented carbide plates are analyzed. To reveal the underlying mechanism of the frictional modification effect under water lubrication, the formation of graphite transfer film on cemented carbide plates, the water contact angles of graphite surface and the hydrodynamic effect are further discussed. It is verified that the introduction of textures on graphite surfaces can significantly improve the tribological performance of water-lubricated graphite materials.

The frictional performance of the shaft-end graphite seal rings plays a critical role in determining the maintenance-free duration of aircraft integrated drive generators, and significantly depends on the types of graphite materials used. In this study, three types of graphite materials, including epoxy resin, metal antimony and furan resin impregnated ones, were selected for evaluation using a rotating-type tribometer. The frictional test configuration involved an actual graphite seal ring sliding against the surface of a 12Cr2Ni4A disc under the lubrication of 4050 high-temperature synthetic aerospace lubricating oil, which was highly consistent with the practical operational conditions. The frictional performance of the three different impregnated graphite seal rings, including coefficient of friction, two-dimensional (2D)/three-dimensional (3D) morphologies of wear marks and wear rate of ring mass, were quantitatively analyzed and compared. The experimental results indicated that the metal antimony-impregnated graphite seal ring behaved with the smallest coefficient of friction among the three seal rings. 2D and 3D surface roughness parameters of the metal antimony impregnated graphite seal are the smallest. The wear rate of the seal ring’s mass is only approximately 22% of that of furan resin impregnated seal ring. The corresponding investigations demonstrated that the currently employed epoxy resin-impregnated graphite seal rings could be replaced by new candidates with better frictional performance to improve the service life.

Impregnated graphite has attracted considerable attention and has been widely used as an ideal friction material in many fields. However, the influence of the friction temperature on its tribological properties has not been clearly studied; furthermore, the evolution mechanism of transferred tribofilm is unknown. In this study, the tribological properties of impregnated graphite were investigated at different friction temperatures, and the evolution of the carbon-based tribofilm was also determined. The results revealed that the tribological properties significantly improved with an increase in friction temperature. The friction coefficient and wear depth of impregnated graphite reduced by 68% and 75%, respectively, at a high temperature of 160 °C compared with those of non-impregnated graphite. The significant properties of the impregnated graphite can be attributed to a transferred carbon-based tribofilm with an ordered structure induced by the friction temperature, which uniformly and stably adsorbs on friction interfaces. This study provides an important basis for designing graphite-based friction materials with improved properties suited for industrial applications. [ABSTRACT FROM AUTHOR]

Graphite-based composites are well recognized as ideal functional materials in mechanical seals, bearings of canned pumps, and electrical contact systems because of their outstanding self-lubricating ability, thermostability, and chemical stability. Working in harsh conditions is a huge challenge for the graphite materials, and their tribological properties and wear mechanisms are not well studied. In this study, the tribological performance of metal-impregnated graphite, resin-impregnated graphite, and non-metal-impregnated graphite under high temperature and high load are studied using a ball-on-disc tribometer. The results show that the metal-impregnated graphite (Metal-IG) has a stable friction regime and exhibits better anti-friction and anti-wear properties than that of resin-impregnated graphite (Resin-IG) and non-impregnated graphite (Non-IG) under extreme pressure (200~350 MPa) and high temperature (100–350 °C). The Metal-IG and Resin-IG can reduce the wear depth by 60% and 80%, respectively, when compared with Non-IG substrate. The impregnated materials (metal or resin) can enhance the strength of the graphite matrix and improve the formation of graphite tribofilm on the counterpart surfaces. Friction-induced structural ordering of graphite and slight oxidation of metal in the formed mechanically mixed layer is also beneficial for friction and wear reduction. This study demonstrates the tribological characteristics of impregnated graphite under harsh conditions and provides the experimental basis for the advanced usage of high-reliability and self-lubrication graphite composites.

Novel superconducting tilting pad bearing can realize the compound of superconducting magnetic force and hydrodynamic fluid-film force in liquid rocket engine and possesses the advantages of larger bearing capacity and higher stiffness. The indispensable small operational clearance for the bearing would possibly cause rubbing phenomena between superconducting stator and magnet rotor under impact loads. Three Y1.8Ba2.4Cu3.4Ox bulk superconductors with different crystal domains are used to study the dry friction coefficients between superconductor and neodymium iron boron (NdFeB) magnet with nickel coating. In order to improve the fundamental tribological performance of the novel bearing, upper surface of modified superconducting tilting pad is covered by thin impregnated graphite and the nickel coating of magnet is replaced by chromium coating. Pin-on-disc experimental results indicate that the antifriction design method is effective and safe for liquid rocket engine. This study can promote the application process of novel superconducting bearing in a new generation of liquid rocket engine in China. [ABSTRACT FROM AUTHOR]

Controlling the wettability of surfaces is imperative for the tribology behavior during the friction and wear, especially in aqueous environment. In this work, fiber laser treatment of impregnated graphite was used to achieve a bidirectional wettability transition. The treated surfaces were characterized using scanning electron microscopy, 3D confocal surface topography analysis, Raman spectroscopy, and Fourier transform infrared (FTIR) spectroscopy. The surface treated by a low–energy laser became hydrophobic (increase of contact angle from 73.6° to 131.6°) and the surface treated by a high–energy laser became more hydrophilic (decrease of contact angle to 6.7°). Examination of the morphology indicated that with increasing laser energy, the roughness increased and the surface changed from a flocculent to scaly structure. Analysis of the energy spectra revealed an increase of oxygen content on the hydrophilic surface. In addition, Raman spectra analysis indicated a positive correlation between graphite ordering and the contact angle. The FTIR results demonstrated the existence of hydrocarbon on the hydrophobic surface. After ultraviolet/O 3 cleaning, the contact angle of the hydrophobic surface decreased to 37°; however, the contact angle of the surface which did not be treated by laser hardly changed. Based on these results, it was concluded that the wettability transition was caused by the changes in surface morphology and chemical composition. [ABSTRACT FROM AUTHOR]

The friction and wear behaviors of graphite impregnated with inorganic salts against stainless steel in the ring-on-ring friction pairs are studied by experiments and simulation. As the load increases, the friction coefficient decreases and the wear rate of graphite increases, respectively. The worn surface of impregnated graphite shows two different styles of worn taper angle after tests. When the load increases, the taper angle near the inner diameter of contact area increases. Meanwhile, some impregnations of graphite break into pieces and these pieces migrate along the diameter outward in the surface of friction pair. Furthermore, in the cases of severe wear, the accumulation of impregnations causes a reverse taper angle near the outer diameter of contact area. [ABSTRACT FROM AUTHOR]

Tribological properties of impregnated graphite are greatly influenced by preparation technology and working conditions and it's highly susceptible to corrosion environmental impacts, but the experimental research about it are few. In this paper, three kinds of impregnated graphite samples are prepared with different degree of graphitization, the tribological properties of these samples in the dry friction environment and in a corrosive environment are analyzed and contrasted. The tribo-test results show that the friction coefficient of samples is reduced and the amount of wear of samples increase when the graphitization degree of samples increases in dry friction condition. While in a corrosive environment (samples are soaked NO), the friction coefficient and amount of wear are changed little if the graphitization degree of samples are low. If the degree of graphitization increase, the friction coefficient and amount of wear of samples increase too, the amount of wear is 2 to 3 times as the samples tested in the non-corrosive environment under pv value of 30 MPa · m/s. The impregnated graphite, which friction coefficient is stable and graphitization degree is in mid level, such #2, is more appropriate to have a work in the corrosion conditions. In this paper, preparation and tribological properties especially in corrosive environment of the impregnated graphite is studied, the research conclusion can provide an experimental and theoretical basis for the selection and process improvement of graphite materials, and also provide some important design parameters for contact seal works in a corrosive environment. [ABSTRACT FROM AUTHOR]

Graphite-based composites are well recognized as ideal functional materials in mechanical seals, bearings of canned pumps, and electrical contact systems because of their outstanding self-lubricating ability, thermostability, and chemical stability. Working in harsh conditions is a huge challenge for the graphite materials, and their tribological properties and wear mechanisms are not well studied. In this study, the tribological performance of metal-impregnated graphite, resin-impregnated graphite, and non-metal-impregnated graphite under high temperature and high load are studied using a ball-on-disc tribometer. The results show that the metal-impregnated graphite (Metal-IG) has a stable friction regime and exhibits better anti-friction and anti-wear properties than that of resin-impregnated graphite (Resin-IG) and non-impregnated graphite (Non-IG) under extreme pressure (200~350 MPa) and high temperature (100–350 ℃). The Metal-IG and Resin-IG can reduce the wear depth by 60% and 80%, respectively, when compared with Non-IG substrate. The impregnated materials (metal or resin) can enhance the strength of the graphite matrix and improve the formation of graphite tribofilm on the counterpart surfaces. Friction-induced structural ordering of graphite and slight oxidation of metal in the formed mechanically mixed layer is also beneficial for friction and wear reduction. This study demonstrates the tribological characteristics of impregnated graphite under harsh conditions and provides the experimental basis for the advanced usage of high-reliability and self-lubrication graphite composites. [ABSTRACT FROM AUTHOR]