Tribological Properties Of Two-Dimensional Nano Material Mo₂C Reinforced Polyimide Composites

With the rapid development of industry,friction and wear has become one of the main factors of energy loss and mechanical failure.Polymer friction materials have the advantages of light weight,high specific strength,high specific modulus,fatigue resistance,corrosion resistance and good self-lubricating properties.Polyimide（PI）is one of the organic polymer materials with the best comprehensive properties,but as a high-performance self-lubricating and wear-resistant material,pure PI still has some problems,such as high friction coefficient and poor wear resistance.The thermal,mechanical and tribological properties of the materials can be significantly improved by adding a small amount of nano-materials.As a new two-dimensional nano-material,transition metal carbon/nitride MXene shows good properties in the mechanical and tribological applications of polymer composites.In this paper,the preparation of two-dimensional transition metal carbide MXene and the research progress of its composites were introduced,and Mo₂C/polyimide（Mo₂C/PI）composites were prepared with Mo₂C as reinforcement and polyimide（PI）.The effects of Mo₂C nano-fillers on the tribological properties of PI under dry friction under wide temperature range were studied.The main studies include:（1）Firstly,Mo₂C MXene were prepared by etching method with Mo₂Ga₂C and hydrofluoric acid solution,and its phase and micro-morphology were characterized.The results show that the prepared Mo₂C is a two-dimensional nano-lamellar structure,and the thickness of the sheet is about 200nm;there are many oxygen-containing polar groups on the surface of Mo₂C,which is electronegative.PEI surface modified Mo₂C nanomaterials were prepared by electrostatic interaction.（2）Mo₂C/PI polymer nanocomposites were prepared by liquid phase mixing and molding method.The cross-sectional microstructure of the composites was analyzed by SEM,and the effects of Mo₂C on the thermal properties and hardness of PI matrix were studied.The results show that Mo₂C is uniformly dispersed in PI matrix and has a good bonding interface.The addition of Mo₂C can effectively improve the thermal properties and hardness of Mo₂C/PI composites,but the glass transition temperature and storage modulus decreased.The tribological properties of polyimide and Mo₂C/polyimide composites were investigated by high temperature friction and wear tester.The results showed that the tribological properties of polyimide were significantly improved with the addition of Mo₂C,and the friction coefficient and wear rate decreased significantly with the increase of Mo₂C concentration.（3）Mo₂C was introduced into polyamide acid prepared by 4.4-diaminodiphenyl ether（ODA）and pyromellitic dianhydride（PMDA）by in-situ polymerization,and Mo₂C/PI thin were prepared by thermal imidization of PAA.The strength,modulus and toughness of PI matrix were enhanced by the addition of Mo₂C.In the surface friction test,the PI composite with 1.0wt%Mo₂C has the lowest friction coefficient and wear rate,which is 11%and 75%lower than that of pure PI,respectively.It is found that the layered structure of two-dimensional crystal Mo₂C can effectively improve the anti-friction and anti-wear performance of the composites.The uniform dispersion of Mo₂C in the matrix and the increase of mechanical and thermal properties of the composite enhance the lubricity and load-bearing capacity of the film.The microstructure analysis of the worn surface shows that the friction mechanism of the composite coating is composed of fatigue wear and adhesive wear.There are 40 figures,8 tables and 105 references.