Research On The Molecular Dynamics Of The Nano-scale Friction And Wear Mechanism Of TiC-reinforced Ni-based Composites

With the increasing demand for special materials in modern technology,nickel matrix composites are widely used in various industries because of their excellent high temperature mechanical properties.However,this material often fails due to frictional wear during extreme service,so it is important to study the origin and mechanism of wear of this material.For a long time,most of the studies on the frictional wear mechanism have been conducted by experimental means,but it is difficult to dynamically observe the details of atomic motion in all directions due to the limitation of testing equipment and experimental cost,and it is impossible to explain the frictional wear mechanism of nickel matrix composites in essence.Molecular dynamics simulation,as a scientific algorithm,has been proven to be a powerful tool to effectively study materials at the microscopic level.It can start from the basic units that constitute the material,analyze the movement of atoms at the nanometer level,reveal the reinforcement mechanism and interface structure of the reinforcement,and clarify the friction and wear mechanism of nickel matrix composites.In this paper,by establishing an accurate basic model of TiC/Ni based composites,the study of the tribological behavior of TiC/Ni based composites at the nanoscale,the frictional wear characteristics and the strengthening mechanism of the reinforcement TiC from the viewpoint of the friction mode(repeated circumferential friction,fixed load linear friction)and the TiC phase distribution characteristics has been carried out.The main work is reflected in the following aspects.(1)The process of repeated friction of TiC/Ni based composites by grinding balls was investigated comprehensively in terms of friction force,wear rate,atomic displacement,internal defect evolution and temperature.It is found that: when the action of the grinding ball on the workpiece is transferred to the TiC phase,the friction force extremes appear,the number of atoms with large displacement in the workpiece is small,the atoms show a tendency to bypass the displacement of the TiC phase,the TiC assumes the external action energy leading to an increase in temperature and a discontinuity in the temperature distribution of the workpiece.During repeated friction processes,the large structural defects generated by initial friction events are decomposed into small structural defects or stable laminar dislocation tetrahedral structures leading to the formation of dislocation entanglement which improves the overall wear resistance of the workpiece,the temperature of the TiC increases rapidly,and the temperature difference compared to the substrate gradually increases.(2)The deformation behavior of the grinding balls from the contact with the workpiece material until the compaction process was investigated.The results show that the variation of the tangential and normal forces is related to the relative positions of the grinding ball and the TiC phase,with large fluctuations in the frictional force when the grinding ball is located above the TiC phase,shallow depth of the abrasion marks and low wear rate when the normal force appears to be extremely large.The presence of TiC phase during friction impedes the development and extension of defects,leading to dislocation entanglement and improving the wear resistance of the workpiece.It was also found that the internal atomic motion guided by the carbonized phase was related to the position of the grinding ball relative to the reinforced phase,and when the grinding ball was at different positions relative to the reinforced phase,the reinforced phase produced a tendency to rotate in different directions,which in turn affected the deformation of the whole workpiece.(3)The influence of the distribution characteristics of TiC phase on the tribological properties of the nickel matrix was simulated and discussed.MD models with different TiC phase depths and radii were established.It is found that TiC phase with large radius and small depth distribution is prone to local stress concentration,forming high dislocation density regions,causing interaction between dislocations,forming obstacles to dislocation movement,and enhancing the deformation resistance of the workpiece.It is also found that the presence of TiC phase changes the stress state inside the workpiece,making the TiC phase and surrounding nickel atoms into a high-temperature state,but the workpiece atoms below the TiC phase always exist in a low-temperature state,which has a good thermal insulation effect and improves the high-temperature performance of the material.The combination of nickel matrix composites and molecular dynamics technology can provide new perspectives and breakthroughs in the research of nickel matrix composites,which can better utilize the advantages of nickel matrix composites and develop higher performance products more effectively.