Full-Cycle Numerical Modeling and Experimental Study of Random Multiparticle Impact in High-Velocity Air-Fuel Spraying of Titanium Alloys

High-velocity air-fuel (HVAF) spraying can form dense corrosion- and wear-resistant coatings on the surface of TC18 titanium alloy, solving the problem of protecting aircraft landing gear surfaces. In this study, the combustion reaction and discrete phase models for HVAF spraying of WC-12Co powder were established on the basis of computational fluid dynamics. In addition, the evolution law of flame temperature and velocity during spraying was revealed, and the influence of powder particle size and sphericity on particle flight characteristics was investigated. In view of the randomness of the shape distribution and spatial position of the powder particles, a three-dimensional multi-particle full-cycle random polycrystalline impact model has been established based on coupled Eulerian–Lagrangian and Voronoi methods. The evolution laws of the temperature, strain, and stress fields during particle impact have been determined. Calculations showed that the maximum velocity of the spray flame is 1504 m/s, and the maximum temperature is 1960 K. The size and shape of powder particles affect their velocity and temperature, and the velocity of particles with a small diameter and low sphericity (β) is high. The temperature of ellipsoidal particles with β ≤ 0.6 is significantly lower than that of spherical particles with β ≤ 1.0. Due to the introduction of grain inhomogeneity, the stress distribution of the heterogeneous substrate exhibited significant dispersion. The Mises stress of the grains inside the substrate was positively correlated with the microhardness of the material. This study may provide theoretical guidance for optimizing thermal spray processes.