Numerical Simulation Study of Particle Deposition Behavior of NiCoCrAlY by High Velocity Oxy-Fuel Spraying

In the face of the strong demand for high efficiency and high performance of aviation components, surface coating technology is developing rapidly. The coating deposition at the macro level is essentially the particle impact stacking at the micro level. At present, most of the research on the deposition behavior of sprayed particles focuses on the deformation of single particles in cold spraying, ignoring the deposition changes of multiple particles in complex thermal-fluid-solid coupling process such as high velocity oxy-fuel spraying. In this work, a random multi-particle impact model had been established by Coupled Eulerian Lagrangian method and Johnson-Cook material equation, and the independent effects of the main deposition parameters (the impact velocity of particle, the impact temperature of particle, substrate preheating temperature, surface frictional coefficient) on the porosity of NiCoCrAlY coating and the residual compressive stress of GH4169 substrate during high velocity oxy-fuel spraying were studied. Based on the velocity level within the spraying particle system before deposition, the effects of different collision degrees caused by the difference of particle collision velocity and the number of collision points on the coating quality were carried out. It was found out that most of the kinetic energy of the deposition system was converted into plastic dissipation energy and internal energy for particle deformation and heating. With the increasement of particle impact velocity and particle impact temperature, the flattening deformation of the particles had become more sufficient, and the porosity of the coating tended to gradually decrease. In order to form a continuous layered microstructure, the impact temperature of the particles should not be too high (not more than 1 300 K) to ensure the effective and moderate deformation of the particles. Changing the substrate preheating temperature and frictional coefficient of the substrate played little effect on the porosity of the coating. The residual compressive stress of the substrate was most affected by the particle impact velocity. The reduction of velocity led to the decrease of impact depth, at the same time, the average stress value was declined. When there were few velocity levels in the particle system before deposition (one layer speed or two layer speeds), the larger the difference of particle collision velocity, the greater the degree of collision, the more conducive to the formation of eutectic between particles, and the lower the porosity of the coating. Then the velocity levels increased gradually, the number of impact points became larger, and the porosity initially decreased and then increased, and excessive collision caused particle scattering. In the end, screening the particles before deposition was recommended as a practical solution to obtain the medium velocity level of the particle system as the appropriate degree of particle collision was helpful to improve the density of the coating.