Effect Of LaF₃/CeF₃ On The Friction Transfer And Interface Microstructure Of PTFE-Based Composites

The friction and wear properties of PTFE modified by rare earth compounds have been reported.Most of them are single addition of one rare earth compound.There is little research on the effect of two rare earth compounds on the tribological properties of PTFE.In this paper,lanthanum fluoride（LaF₃）and cerium fluoride（CeF₃）were used as functional fillers and graphite as basic fillers to prepare PTFE-based composites.The transfer film formed on the surface of PTFE-based composites was mainly studied.The change of thickness and coverage of transfer film and the effect of LaF₃/CeF₃ on the microstructure of friction interface of PTFE-based composites were discussed.In this paper,the change of thickness and coverage of transfer film under different contents and working conditions was studied,and the friction coefficient and wear rate of transfer film and PTFE-based composite were correlated.In addition,the effect of LaF₃/CeF₃ on the friction interface microstructure of PTFE-based composites was investigated from the aspects of molecular weight change of wear debris,element analysis and wear surface morphology.In this paper,the main conclusions are as follows:1.Effect of different factors on friction transfer of PTFE-based composites（1）Effect of LaF₃/CeF₃ content:LaF₃/CeF₃ can reduce the thickness of transfer film and improve the coverage of transfer film.When the thickness of the transfer film is in the range of 1.4μm to 2.0μm,the coverage of the transfer film is concentrated in the range of 30%to 65%,and the friction coefficient and wear rate of the composite are relatively low.（2）Effect of working conditions:As the load increases,the coverage and thickness of the transfer film gradually increase.When the load reaches 1.0 MPa,the coverage of the transfer film exceeds 50%,and the increase rate slows down.The thickness and coverage of the transfer film also show an increasing trend as the sliding speed increases.2.Effect of different factors on tribological properties of PTFE-based composites（1）Effect of LaF₃/CeF₃ content:Compared with LaF₃or CeF₃ single addition,LaF₃and CeF₃ are added into PTFE composites together with a content of 0.6 Vol%,the reduce-friction and anti-wear effect on the PTFE-based composites is the best.（2）Effect of working conditions:The friction coefficient of PTFE-based composites first decreases and then increases with the increase of load,and the wear rate increases with the increase of load.Under the experimental conditions,when the applied load exceeds 1.0 MPa,the friction coefficient and wear rate of the composite material increase sharply,indicating that the PTFE composite material is not suitable for application under high load conditions.When the sliding speed is between 0.2 m/s and0.6 m/s,due to the formation of the transfer film,the friction coefficient and wear rate of the composite material increase slowly,but when the sliding speed exceeds 0.6 m/s,the friction coefficient of the composite material and the wear rate increases sharply.3.Effect of LaF₃/CeF₃ on friction interface microstructure of PTFE-based composites.（1）The addition of LaF₃/CeF₃ delayed the decrease of the molecular weight of the wear debris,stabilized the transfer film,and improved the interfacial adhesion between the transfer film and the counterface.（2）Rare earth elements react with the end group of broken chain of PTFE to form rare earth coordination bond.The binding force between filler and PTFE-based is stronger,which shows that the wear surface of S6 is smoother and the cracks are reduced.（3）It is found that rare earth fluoride exists on the worn surface of the sample by XPS analysis,which is helpful to improve the interfacial adhesion between the transfer film and the counterface and reduce the wear.