In-flight Oxidation of MCrAlY Particles During High Velocity Air-Fuel Spraying: A Numerical Study

Oxygen present in the High Velocity Air-Fuel (HVAF) process can react with the in-flight metallic particles and cause their oxidation. A grown brittle oxide shell on MCrAlY micro-size particles can reduce their deposition efficiency and impair the coating final deposited properties/structure.

In the current study, the oxide growth of MCrAlY particles, where M stands for Ni and Co, during their flight in the HVAF process has been modeled using the Lagrangian particle tracking scheme. A comprehensive theoretical oxide layer growth background is presented and included in the model. The oxidation model includes the Mott-Cabrera theory for very thin film function of the particle surrounding temperature and oxygen partial pressure. The very thin film regime, applicable under a limiting thickness, is defined based on a strong electric field across the oxide layer. However, the voltage across the oxide giving rise to a uniform field is independent of the oxide thickness and leads to a linear growth rate. As the electric field decreases, the oxidation rate is determined by the thermal diffusion.

The obtained results provide a correlation between HVAF process parameters and surface oxidation phenomena while offering a clear description of different oxidation stage