Removal mechanism of NiTi alloy by ultrasonic assisted polishing based on molecular dynamics simulation

NiTi alloy has been widely used in mechanical and electronic, aerospace, energy and transportation, petrochemical industry and various biomedicine fields due to its unique super elasticity and shape memory effect. The traditional polishing method of NiTi alloy has the problems of poor consistency of polishing quality and low efficiency, especially for some NiTi alloy with complex shapes, the traditional mechanical contact method is difficult to polish its inner surface. For some NiTi alloys prepared by additive manufacturing, due to the existence of "step effect" and "spherodizing effect", there are unmelted powder particles on the surface, and it also needs to be polished. However, it is necessary not to destroy the original structure shape and performance, but also to achieve high efficiency, high quality and consistent polishing, so it is a technical problem. Its polishing process is still unclear, and the polishing effect needs to be improved. Therefore, in this paper, molecular dynamics method was used to study the polishing process of ultrasonic vibration diamond abrasive particles on NiTi alloy. The influences of ultrasonic vibration frequency, ultrasonic amplitude and temperature on polishing force, average friction coefficient, surface morphology, structural evolution and dislocation distribution were studied, and the microscopic material removal mechanism was revealed. The results indicate that as the ultrasonic frequency increases, the number of normal force fluctuations increases, and the elastic and plastic deformation during the scratching process also increases. With the increase of ultrasonic amplitude, the average friction coefficient decreases, and the adoption of larger vibration amplitude is conducive to the scratching process, and the average friction coefficient will increase when the temperature increases, which is not conducive to the polishing process.