By using computational fluid dynamics (CFD) to numerically model the high-velocity oxygen fuel thermal spraying process, the velocity and temperature of particles at the moment of impact with the substrate can be calculated, thereby predicting the microstructure and properties of the coating. However, the discrete phase model, the current mainstream model for calculating particle velocity and temperature in thermal spraying, neglects the effect of inter-particle collisions during their flight, leading to discrepancies between the predicted particle distribution at impact and experimental results. Therefore, it is necessary to consider the influence of inter-particle collisions on their flight characteristics, establish a model for particle velocity and temperature distribution during thermal spraying, and analyze the impact of flight characteristics on deposition behaviors.
In this study, a combined Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) model was developed to simulate the flight behavior of WC-10Co4Cr particles during the high-velocity oxygen fuel thermal spraying process. Through experiments and finite element analysis, the velocity and temperature distribution characteristics of particles during flight, as well as their deposition behaviors upon impact with the substrate, are studied. Subsequently, the model is applied to investigate the flight behavior of particles of different sizes. By combining measurements of the particle state during thermal spraying and the height distribution of the coating, the effects of particle size distribution on flight and deposition behaviors are analyzed.
In DEM, most particles are still distributed near the center line, and only a few particles are far away from the center line due to the collision between particles, and the main particles are small particles. The average impact velocity of particles calculated using the DEM model is 658 m/s, with an error of 3.9%. The calculated average temperature is 1 697 K, with an error of 3.3%. The model provides more accurate results for the average velocity of small particles compared with experimental values, but its predictions for large particles are less accurate. The DEM calculations show that the average impact velocities of small, medium, and large particles are 683 m/s, 630 m/s, and 587 m/s, respectively, with errors of 3.8%, 6.7%, and 8.0%. The DEM model is more accurate in predicting the temperature of large particles, with average temperature for the three different particle sizes being 1 659 K, 1 720 K, and 1 666 K, with errors of 6.5%, 0.9%, and 0.5%, respectively. Due to the influence of the initial velocity of the particles, the particles deviate from the center point in the Y direction. The larger the particle size, the greater the offset distance. In DEM, due to the trajectory changes caused by particle collision, the velocity, temperature and particle size distribution of particles do not show obvious differentiation in the Y direction. Under the same spraying conditions, the width and thickness of the coating deposited by large particles are both smaller than those deposited by small particles and mixed-size particles, indicating that the velocity and temperature of large particles are not conducive to deposition. In conclusion, CFD-DEM can effectively calculate the flight behavior of WC-10Co4Cr particles in a high-velocity oxygen fuel flow field, analyze the impact position and velocity and temperature of particles upon collision with the substrate, and predict the deposition state of particles.
Key words
HVOF /
tungsten carbide /
computational fluid dynamics /
discrete element method /
multi-particles /
numerical simulation
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Funding
National Key Research and Development Program of China (2023YFB4302400)
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