Diamond jet hybrid HVOF thermal spray: Rule-based modeling of coating microstructure

This paper focuses on the computational modeling and simulation of the microstructure of coatings produced by an industrial high-velocity oxygen-fuel (HVOF) thermal spray process (Diamond Jet hybrid gun, Sulzer Metco, Westbury, NY). On the basis of an understanding of the coating structure and mechanisms of pore formation inside of the coating obtained from experimental studies, a stochastic simulation procedure is used to explore the evolution of the microstructure of the coatings. In the coating growth model, the velocity, temperature, and degree of melting of the particles hitting the substrate are determined by a previously developed mathematical model (first article of this series) describing gas and particle behavior, and the complex characteristics of the thermally sprayed coatings are captured by applying certain basic rules that encapsulate the main physical features of the deposition process. In addition to providing useful insight into pore formation and coating growth, the model is used to make a comprehensive parametric analysis, which allows us to systematically characterize the influence of operating conditions, such as the gas flow rate and spray distance, as well as the effect of particle size, on the particle melting behavior, coating porosity, surface roughness, and deposition efficiency. A comparison of simulation results and experimental studies shows that the proposed model can reasonably predict the relationship between the macroscopic processing conditions and the coating microstructure.