Study On The Micro Tribological Properties And Solid Lubrication Properties Of MXene

As an emerging two-dimensional material,MXene is widely used in the field of high-efficiency solid lubricants due to its excellent mechanical properties,chemical stability,weak interlayer forces and excellent electrical and thermal conductivity.Its solid lubricating properties help to enhance the reliability of mechanical parts,extend service life and reduce energy consumption.In this paper,the micro tribological properties and micro mechanisms of MXenes with different structures of Ti₃C₂and Nb₂C at the micro scale under different environments were studied by atomic force microscopy and surface analysis technology including temperature module.On this basis,the solid lubricating properties of two MXenes with different structures were studied,and their anti-friction and anti-wear mechanisms were revealed.The main research contents and conclusions of this paper are as follows:（1）Multilayer Ti₃C₂nanosheet samples were prepared by hydrofluoric acid etching.The characterization results show that the Al atomic layer has been successfully removed,and the Ti₃C₂nanosheets are typical accordion-shaped,with uniform thickness,clear edges,smooth surface,and a complete lattice structure.（2）The surface micro tribological properties and micro mechanisms of Ti₃C₂and Nb₂C under constant temperature and humidity were studied.（1）The experimental study of the surface micro tribology of multilayer MXene with two structures under different loads and speeds was carried out.The results show that the surface friction of the multilayer MXenes of both structures increases linearly with the increase of the load,because the increase of the load directly leads to the increase of the contact area between the probe and the sample.In addition,the surface friction of multilayer MXene is less affected by the probe sliding speed.（2）The surface micro tribological experiments of multilayer MXene with two structures under the same load and speed were carried out.The results show that the surface friction of Ti₃C₂is always greater than that of Nb₂C.This is due to the fact that the dipole moment and polarity of Ti₃C₂are larger than those of Nb₂C when the surface ends of the MXenes of both structures are-O or-OH.（3）The surface micro tribological experiments of MXene with two structures and different layers under different loads and speeds were carried out.The results show that the micro tribological properties of MXene are closely related to the number of layers.The surface micro friction force decreases with the increase of the number of layers within 1-4 layers,but remains stable above 4 layers.This phenomenon is caused by the wrinkling effect of the material.（3）The surface micro tribological properties and micro mechanisms of Ti₃C₂and Nb₂C under different temperature and humidity were studied.（1）The experimental study of the surface micro tribology of multilayer MXene with two structures at different temperatures was carried out.The results show that the micro-friction force on the MXene surface of both structures decreases significantly with the increase of temperature.This is because when the temperature rises,the lattice oxygen content on the surface of the sample increases,resulting in a decrease in the polarity of the material surface.At the same time,the possibility of sliding atoms jumping from the original position to the adjacent position with minimum potential energy also increases.（2）The surface micro tribological experimental study of single-layer and multi-layer MXene at different temperatures was carried out.The results show that when the temperature increases,the decreasing trend of the surface micro-friction of single-layer MXene is more obvious than that of multilayer.This is because the thermal conductivity of the MXene surface is greatly affected by the number of sample layers.The friction of the material is affected by a combination of thermal conductivity changes due to the number of layers and the wrinkling effect.（3）The surface micro tribological experiments of multilayer MXene with two structures under different humidity were carried out.The results show that the micro friction force on the surface of the sample is less affected by the environmental humidity.The reason is that the MXene surfaces of both structures have good hydrophobicity.（4）The surface micro tribological properties and micro mechanisms of Ti₃C₂and Nb₂C aged at room temperature and high temperature were studied.（1）The experimental study on the surface micro tribology of MXene with two structures after aging in deionized water at room temperature was carried out.The results show that the aging of the two structures of MXenes in deionized water is very slow.Only physical adsorption occurred within 12 hours,and the microscopic friction force on the surface changed little.When the aging time reached 9 months,chemical adsorption occurred on the surface of the samples,and the surface micro friction force increased significantly.（2）The surface micro tribological experimental study of MXene with two structures after high temperature aging was carried out.The results show that after high temperature aging,defects and cracks were formed on the surface of MXene of both structures.Lattice defects cause an increase in the sliding energy barrier,and cracks increase the out-of-plane deformation during sliding,resulting in more energy dissipation during friction.In addition,Ti₃C₂is more severely aged than Nb₂C,with greater depth and extent of defects.（5）The friction and wear characteristics and mechanisms of Ti₃C₂and Nb₂C solid lubricant coatings under dry friction conditions were studied.The experimental results show that both solid lubricating coatings can reduce the friction coefficient under different loads and rotational speeds.The wear reduction effect of Nb₂C solid lubricant coating is better than that of Ti₃C₂solid lubricant coating.The weak van der Waals force between the two solid lubricating coating materials is the main wear reduction mechanism.MXene nanosheets are deposited on the defects of the friction interface to increase the contact area and inhibit the adhesive wear between the interfaces as its main anti-wear mechanism.