Tribological Properties Of La-Ti Doped WS₂-Based Lubricating Films Deposited By Magnetron Sputtering

WS₂ film has hexagonal structure,which is easy to shear slip between molecular layers and has good antifriction performance.However,the pure WS₂ film has poor compactness and is prone to oxidation reaction,which leads to its unstable properties.The structure of WS₂ film can be effectively improved by selecting the special coating method to prepare the metal doped WS₂-based composite film,and then the lubricating film with excellent friction and wear performance can be obtained.In this paper,WS₂ films,Ti/WS₂ composite films and La-Ti/WS₂ composite films were prepared by magnetron sputtering.The micromorphology,composition and structure of the films were characterized by using scanning electron microscope(SEM),energy dispersive spectrometer(EDS)and X-ray diffraction(XRD).The mechanical properties,friction coefficient and wear rate of the films were measured by using nano indentation tester,friction and wear tester and white light interference three-dimensional profilometer.The effects of La and La-Ti doping on the tribological properties of WS₂-based composite films were studied,the wear mechanism of WS₂-based lubricating films were studied by analyzing the characteristics of wear scar morphology.The microstructure of WS₂-based lubricating films with different process parameters were studied.With the increase of argon flow rate,the deposition rate and grain size of the films first increased and then slightly decreased,the S/W ratio first increased and then decreased,and the compactness first decreased and then increased.With the increase of deposition pressure,the deposition rate and grain size of the films first decreased and then increased,the S/W ratio and the compactness first increased and then decreased.With the increase of sputtering power of Ti target or La-Ti target,the deposition rate and grain size of Ti/WS₂ and La-Ti/WS₂ composite films decreased,the S/W ratio first decreased and then increased,the compactness improved obviously,and the dominant orientation growth of WS₂ (101)crystal surface disappeared gradually.Compared with pure WS₂ films and Ti/WS₂ composite films,the doping of rare earth element La can effectively refined the grain size of La-Ti/WS₂ composite films,the structure compactness of the films were significantly improved,and the S/W ratio of the films were greatly reduced,The growth of WS₂loose columnar crystal structure was inhibited,the dominant orientation of(002)base surface easy to slip was formed.The mechanical properties of WS₂-based lubricating films with different process parameters were studied.With the increase of argon flow rate,the hardness,modulus of elasticity,H/E and H³/E²ratio of the films first decreased and then increased.With the increase of deposition pressure,the hardness,modulus of elasticity,H/E and H³/E²ratio of the films first increased and then decreased.With the increase of sputtering power of Ti target or La-Ti target,the hardness,modulus of elasticity,H/E and H³/E² ratio of Ti/WS₂ and La-Ti/WS₂composite films showed an overall upward trend.Compared with pure WS₂ films and Ti/WS₂ composite films,the doping of rare earth element La had obvious fine grain strengthening effect.La-Ti/WS₂ composite films showed higher microhardness and good elastic-plastic deformation resistance.The friction and wear properties of WS₂-based lubricating films with different process parameters were studied.With the increase of argon flow rate,the friction coefficient and wear of the films first increased and then decreased.With the increase of deposition pressure,the friction coefficient and wear of the films first decreased and then increased.With the increase of sputtering power of Ti target or La-Ti target,the friction coefficient and wear of Ti/WS₂ and La-Ti/WS₂ composite films first decreased and then increased.When the argon flow rate was 40sccm,the deposition pressure was1.2pa and the sputtering power of La-Ti target was 20W,the friction coefficient of La-Ti/WS₂composite film was 0.084,and the wear rate was as low as 5.47×10^-9mm³/N·m,compared with the pure WS₂ film and Ti/WS₂composite film,the wear rate was reduced by about two orders of magnitude,and the friction state was more stable.La-Ti/WS₂composite films showed more excellent low friction and wear resistance.With the process parameters of the argon flow rate was 40 sccm,the deposition pressure was 1.2 pa and the sputtering power of Ti target or La-Ti target were 20W,there were no obvious furrows and peeling marks on the worn surface of La-Ti/WS₂ composite film,the wear characteristics was mild wear;There were obvious peeling signs on the worn surface of Ti/WS₂ composite film,the wear characteristics was serious delamination wear;There were more and deeper furrows and no obvious peeling marks on the worn surface of pure WS₂ film,the wear characteristics was obvious abrasive wear.