Tribological Properties Of Ptfe Blended With Nickel-phosphorus And Peek

Polymer self-lubricating materials have the characteristics of light weight,high strength,superb corrosion resistance,and excellent tribological properties,thus they have been widely used in industries,aerospace,and other application fields.Among them,polytetrafluoroethylene（PTFE）has an excellent anti-friction performance,but pristine PTFE’s drawbacks of weak load-bearing capacity and poor wear resistance limit its application in some fields.Therefore,the strategy by modifying PTFE matrix to improve its wear and friction reduction performance is an important issue in the research field of polymer self-lubricating materials.The approach of filling modification can effectively improve the mechanical and tribological properties of PTFE,but unfortunately,it may be accompanied by a loss of friction reduction of the composites.Accordingly,it is practical significance for extending the application range of PTFE to seek novel fillers to strength the anti-wear and friction reduction properties of PTFE,study the impacts of the fillers on the tribological properties of PTFE,and explore the internal interaction mechanisms.Electroless nickel-phosphorus（Ni-P）alloy plating as a coating material has the features of high hardness,chemical stability and friction resistance,and has been widely applicated in the industrial field.When PTFE particles are loaded into the Ni-P coating as a friction reducing and enhancing component,the Ni-P composite coating exhibits good friction reducing and wear resistance.However,the impact and mechanism of Ni-P as a reinforcing material on the tribological properties of PTFE matrix are still unclear,and it is necessary to conduct tribological research on Ni-P/PTFE composite materials.In addition,it has shown that filling with polyetheretherketone（PEEK）in the PTFE matrix can effectively improve the tribological properties of PTFE composites,indicating that PEEK is a high-performance PTFE reinforcement material.In view of the outstanding tribological performance of electroless Ni-P alloy and PEEK,it is necessary to study the tribological properties of blending the two fillers into PTFE matrix and explore the internal friction and wear mechanisms,which can provide guidance for the development of novel PTFE self-lubricating composite materials.Firstly,three kinds of Ni-P particles in micrometer level were fabricated following the electroless plating method;after filling the Ni-P particles in PTFE matrix,Ni-P/PTFE composites were obtained;co-doping Ni-P and PEEK in PTFE matrix,Ni-P/PEEK/PTFE composites were also prepared.The microstructure,physical components,and phase structures of Ni-P and PTFE composites were analyzed and studied.The analysis results show that the Ni-P particles in PTFE matrix mainly exist in crystalline Ni phase and Ni₃P phase with high hardness.Forthurmore,PEEK is enriched in PTFE matrix and forms a network structure,while the co-introduction of Ni-P particles leads to the refinement of the PEEK enrichment zone.Secondly,the effects of Ni-P particles with different concentrations of P element on the mechanical,thermal and tribological properties of Ni-P/PTFE composites were studied.The results showed that Ni-P particles can effectively improve the mechanical properties of PTFE composite materials,increase the crystallinity of PTFE,and have an effect of simultaneous friction and wear reduction.Ni-HP particles with high content of P can effectively improve the mechanical,wear and friction reduction properties of PTFE composites.The Ni-P/PTFE composite filling with 20 wt.%of Ni-HP possesses the lowest friction coefficient and wear rate,which are attributed to the ability of the composite to form a fine-quality transfer film during the friction process,and the Ni-P filler in the PTFE matrix bears compressive loads and effectively hinders the wide range sliding of PTFE molecular chains.Additionally,the effects of co-doping of Ni-HP and PEEK on the mechanical and tribological properties of PTFE composites were analyzed.Comparing with the PEEK/PTFE composites,the results indicate that the mechanical and anti-wear properties of PTFE composites co-doped with Ni-P and PEEK are further enhanced,but their friction properties are compromised with the increase of the Ni-HP and PEEK additions.The analysis of the microscopic surfaces and transfer films found that the Ni-P particles,and also the oxygen-containing compounds of Fe which were scratched off the steel balls’surfaces during the worn processes,were adhered and aggregated on the PEEK surface in the worn zone of the composites.These findings can cause an increase of the actual contace area,and are not conducive to the formation of high-quality PTFE transfer films,resulting in a decrease in the self-lubricity performance of the composites.Finally,theoretical models of friction pairs of PTFE-Fe and Ni-P/PTFE-Fe were established respectively,and molecular dynamics simulation was implemented.The friction processes between polymer composites and Fe atom layers were simulated at a molecular level.The results show that the adsorption of Ni-P on PTFE can impose restrictions on the slippage of PTFE molecular chains in the matrix.The microscopic analysis results such as the atomic temperature and velocity distribution,and relative atomic concentration during the friction processes indicate that Ni-P applicated as friction reinforcement filler can improve the wear resistance and anti-friction properties of PTFE composites.Furthermore,the models of friction pairs of PEEK/PTFE-Fe and Ni-P/PEEK/PTFE-Fe were built respectively and the friction processes were simulated.The results indicaties that Ni-P filled in the composites causes an increase in the interaction energy,relative atomic concentration,and temperature of the friction interface,leading to the aggregation and adhesion of polymer molecular chains at the interface,and an increment in the friction coefficient is occoured.The tribological mechanism of the composites were reavealed.