Molecular Dynamics Simulation Of The Effect Of Process Parameters On Ni/Fe Metal Thermal Spraying

Thermal spraying technology is an important and complex surface treatment technology,which can strengthen,modify,repair the surface of mechanical parts and give the surface new functions.It is widely used in aerospace,weapons and other fields.However,there are still technical thermal spray coating porosity,structural defects,substrate and coating binding strength is poor,seriously affect the performance of the coating,limiting the application of thermal spray technology.Therefore,it is very important to establish the relationship among chemical properties,microstructure and function of the coating by adjusting the process parameters of thermal spraying.But,due to some limitations,experimental observation and detection techniques cannot continuously characterize the interface bonding at atomic scale.However,the molecular dynamics method can not only obtain the information of velocity,position and energy of atoms,but also track the motion state and trajectory of each atom,intuitively observe the microstructure evolution and analyze the interface bonding mechanism.In this paper,based on molecular dynamics,the effects of different process parameters and surface structure on cluster flattening,substrate structure and bonding strength in thermal spraying process were studied,which made up for the lack of test method,and expounded the formation mechanism of thermal spraying coating.The main work includes the following aspects.1.The melting point and melting temperature of Ni clusters with different sizes was studied.The process of nano thermal spraying was described in detail.Through CNA analysis,at the initial stage of spraying substrate,the impact force reached the disorder of substrate atoms lattice,and the extruded substrate atoms showed "mountain" shape,and then the substrate was repaired due to the elastic recovery and lattice reconstruction of substrate atoms.The atomic trajectories in the spraying process were observed,and the atoms had good fluidity due to little hindrance in the diffusion of the outer layer of the clusters.At the same time,the cluster flattening ratio was analyzed and the tensile testing model was established to evaluate the thermal spraying effect.2.The effects of different process parameters(spray speed,cluster size,cluster temperature and spray angle)on the thermal spraying of Ni clusters on Fe substrate were studied.The morphology of clusters,sub surface damage of substrate and the bonding strength of substrate/cluster were analyzed.The mechanism of critical spraying velocity,cluster size,temperature and incident angle are discussed.The results show that the effects of various process parameters are not independent of each other,but need to be considered comprehensively.3.The rough substrate surface was established and the influence of surface structure on thermal spraying process was compared and analyzed.The effects of columnar rough surface and smooth surface on cluster flattening,substrate defect evolution,stress distribution,coating substrate bonding mechanism and bonding strength were analyzed.The mechanism of improving the bonding strength between the rough interface and the coating and the mechanical properties during the spraying process are explained.