Sstudy On Functional Nanostructure Tuning Tribological Performance Of Polymer-metal Pair

Irreversible friction-related energy dissipation is posing ever-mounting challenges for today’s moving mechanical assemblies since a large portion of energy is spent to overcome friction in increasing transportation and other industrial activities.Moving mechanical interfaces are lubricated commonly with liquid or/and solid lubricants for combating friction and wear-related energy and material losses.Liquid lubricants delivered onto the friction interfaces separate the contact due to hydrodynamic fluid films and protective boundary reaction layers.However,liquid lubricants usually contain environmentally harmful additives.Solid lubricants are applied in forms of thin films using physical and chemical vapor deposition techniques.When the thin films are worn out,their lubrication effectiveness loses.It is highly desirable to develop durable self-lubrication moving systems,so that further maintenance is not required and adverse environmental impact is avoided.Polymer composites are playing an increasingly important role in moving components,e.g.bearings,liners and washers,of aerospace,petrochemical industry field due to their excellcnet properties such as good self-lubrication and stronger desifnability.Further incorporation of nanoparticles into the conventional polymer composites can greatly improve the tribological performances of the composites according to the previous research.It can be deemed the relation of self-lubrication properties of nanocomposites with growth of tribofilms on friction interface.Nanoparticles released on the interface facilitate tribofilm obtaining well-suited shearing and lasting wear life.In some cases,it is prohibited to add any additives to reduce friction and wear of moving mechanism in order to reduce environmental poolution.It is expected to establish tribofilm with better tribological properties under harsh dry friction conditions by optimizing the reasonable design and coupling of nanoparticles filler.Therefore,it is the key to realize the function design of tribofilm to in-depth and comprehensive reveal the influence mechanism of the physical and chemical properties of nanoparticles on the structure and properties of the tribofilm and synergistic mechanism of different nanoparticles.This work focus on the key of in-depth study on the formation mechanism of tribofilm,adjustment of tribofilm’nanostructure,design and preparation of new self-lubricating materials under heavy pressure and high speed dry friction tconditions.The effect of reinforcing fibers,fillers and nanoparticles on tribological properties of traditional polymer composites was investigated to optimize design of tribofilm’nanostructure.Tubular MWCNTs were introduced into regulate the interface friction chemistry and physics of the friction pair and construct high-performance tribofilms.By coupling hard nanoparticles with MWCNTs,high performance tribofilm were rapidly generated at dry friction interface and extremely friction and wear were obtained.The main research contents and conclusions are as follows:(1)The effects of different properties of nanoparticles on tribological behavior of polymer composites under harsh dry friction conditions were studied.The influence mechanism and evolution mechanism of different nanoparticles on the structure and properties of tribofilms were investigated.Nano-Si O2,nano-Al2O3 and nano-Zr O2 particles in the composites were sintered into dense tribofilms with other wear materials at the friction interface.It not only reduces the running time of composites,but also improves the bearing capacity of friction interface.Different hard nanoparticles have significant effects on improving tribological properties of composites and greatly reducing friction coefficient and wear rate.When polymer nanocomposites slide on the steel surface,the results show that tribofilm with high adhesion and lubrication properties forms on the steel surface,which can mitigate or prevent direct scratch of friction pair.Nanoparticles in polymer nanocomposites are released into friction interface and mixed with other wear particles,dense and functional tribofilms are formed by friction sintering.Rigid nanoparticles improve low-carrying of tribofilms.Our work demonstrated the feasibility of filling nanoparticles into traditional polymer composites to adjust nanostructure and function of tribofilms on friction interface,providing a strategy for development of new highly wear self-lubricating materials.(2)The effect of MWCNTs on tribological properties of polymer composites were emphatically investigated,and wear rate of polymer composites was reduced to 80% by adding 3 vol.% MWCNTs into polymer composites.First principle(DFM)calculations show that O atoms or ions in air environment could destroy the C-C skeleton of CNTs and facilitate transformation of CNTs into graphitized nano-carbon.These results provide direct evidence for existence of graphitized nano-carbon in tribofilms.Insertion of graphitized nano-carbon into tribofilms significantly enhances toughness and elasticity of tribofilms,which are able to withstand severe interface friction(heavy load and high speed),while additing MWCNTs significantly reduce wear rate of composites.(3)The effect of coupling MWCNTs and nano Zr O2 on tribological behavior of polymer composites is studied under heavy load and high speed dry friction.Mechanism of interaction between nanoparticles and MWCNTs on formation and structure of solid tribofilms at friction interface.Coupling of 3 vol.% nanoparticles Zr O2 and MWCNTs significantly reduces friction coefficient and wear rate of polymer composites to 72% and 89%,respectively.It is found that incorporation of nanoparticles and MWCNTs into solid tribofilms at friction interface significantly improve shear and high toughness of tribofilms.At the same time,Zr O2 nanoparticles are released into friction interface and formed a chemical chelate on the metal surface.Sintered Zr O2 nanoparticles in solid tribofilms could bear heavy load during friction process.MWCNTs are influenced by O atoms or ions in air environment to form graphitized nano-carbon at friction interface.Embedding of graphitized nano-carbon into tribofilms reduces shear force and high toughness of friction pair materials.High performance tribofilms can significantly reduce the friction coefficient(0.08)and wear rate(4.5×10-8 mm3/Nm)of nanocomposites,which is higher than the previously known polymer composites.