Study On High-Temperature And High-Speed Wear Mechanism Of Graphite Seal Pair In Aeroengine

As a typical dynamic seal technology,the graphite seal pair comprises a graphite seal ring and a dual metal ring rotating relative to it,and the excellent anti-friction performance of graphite is used to achieve sealing,mainly used in the aircraft engine spindle,gear box and accessories.With the development of aero-engines towards high temperature and high speed,graphite seal pairs that can be used in harsher environments are urgently needed.Therefore,it is of great application value to study the tribological behavior of new graphite under corresponding harsh working conditions.In this paper,zinc phosphate impregnated graphite（ZPIG）and antimony/zinc phosphate co-impregnated graphite（AZPIG）were taken as the research object,matrix graphite（ZMG）used for impregnating ZPIG and matrix graphite（AZMG）used for impregnating AZPIG were taken as the reference object,and nickel base superalloy GH4169 was selected as the friction counterpart material;the friction and wear properties of four kinds of graphite from 20℃ to 500℃ were investigated by high temperature pin-on-disk tests,with emphasis on the mechanism of interaction between friction and oxidation on lubrication and wear.The effects of load and velocity（50 N100 N,10 m/s-40 m/s）on the tribological properties of graphite were investigated by high speed ring-on-block tests,and the relationship between the structure evolution of graphite friction surface and the coefficient of friction and wear depth was revealed.The wear loss,friction surface morphology and composition of graphite and friction pair,and the structural evolution of graphite friction surface and graphite friction transfer film were characterized and analyzed by SEM,EDS,ultra-depth threedimensional microscope,white light interferometer,Raman spectrometer and X-ray photoelectron spectrometer.The main conclusions are as follows:（1）Under dry friction conditions,the coefficient of friction of the seal pair tends to decrease with the increase of temperature,while the wear loss of graphite tends to increase.The oxidation of graphite at high temperature greatly promotes the wear,and the damage mechanism is mainly the abrasive wear of furrow.（2）Zinc phosphate as the impregnating agent reacts with graphite at high temperature（400℃-500℃）to generate C-O-P inert site,which prevents oxygen from intruding into the graphite along the friction surface pores,inhibits the mechanical property attenuation caused by oxidation of graphite,and improves the hightemperature wear resistance of graphite.At the same time,the zinc phosphate further ensures the integrity of the graphite surface,so that the large volume and irregular shape of metal oxide abrasive debris are difficult to embed on the graphite surface,reduce the three-body abrasive wear in the friction process,reduce the damage to the friction pair 4169 alloy,and is conducive to extending the life of the graphite seal pair.（3）Antimony was used as impregnating agent to form a metal skeleton in graphite.The better supporting effect enhanced the mechanical properties of graphite and improved the density of graphite,which made the abrasive particles on the surface of the co-impregnated graphite are finer and the damage to the friction pair 4169 alloy is less.At high temperature,some of the antimony is oxidized to Sb₂O₃ with lubricating effect,which promotes the co-impregnated graphite to keep very low coefficient of friction（0.05）at high temperature,and improves the high temperature lubricity of graphite.（4）Zinc phosphate and antimony as impregnant play a role in keeping the friction surface of graphite and the regularity of the friction transfer film,which makes the process curve of the coefficient of friction of the two kinds of impregnated graphite stable at different temperatures.Meanwhile,the coefficient of friction stability is higher between 100℃ and 500 ℃.（5）Under the condition of high-speed oil lubrication,the coefficient of friction of seal pair tends to decrease with the increase of speed and load,and the wear loss of graphite tends to increase.The damage mechanism is abrasive wear,which is manifested as furrow with accompanying spalling pit.The coefficient of friction of the seal pair is closely related to the state of the oil film at the friction interface.The pores of ZPIG are large,and the oil film thickness increases with the increase of the speed,and the friction coefficient decreases.AZPIG has small pores,and the oil film thickness decreases and the friction coefficient increases with the increase of velocity.