Numerical Analysis of Quasicrystal Particle Behavior in the High-Velocity Oxygen Fuel (HVOF) Process

The in-flight behavior of quasicrystal (QC) particles during the high-velocity oxygen fuel (HVOF) process across four distinct operational settings was analyzed using computational fluid dynamics (CFD) simulations. A three-dimensional two-way coupled Eulerian-Lagrangian approach was used to simulate the process. The gas phase was modeled by solving equations governing mass, momentum, energy, and species, alongside the shear stress transport (SST) k-omega turbulence model, while the oxygen-propylene premixed combustion was simulated using the eddy dissipation model. Following the gas flow modeling, the trajectory and thermal evolution of QC particles were tracked within the computational domain, utilizing accurate correlations for drag coefficient and Nusselt number that cover a wide range of Mach, Knudsen, and Reynolds numbers. The analysis revealed that large particles do not melt due to their mass and the low thermal conductivity of QC materials. These particles typically attain impact velocities around 400 m/s. In contrast, smaller particles with diameters less than 20-25 mu m reach temperatures of 1200 degrees C or higher, transitioning into a molten state with impact velocities reaching approximately 600 m/s. Moreover, it was found that approaching stoichiometric conditions with reduced mass flow rates of QC powder resulted in elevated particle temperatures and velocities upon impact, consequently leading to a reduction in porosity. To verify this finding, experiments were conducted under varying oxygen-to-fuel ratios and powder loadings, with subsequent measurement of the coating porosity. An in-flight particle diagnostic system was also used to assess the particle velocity. The numerical study agrees closely with the experimental observations.