Multiscale mechanics of yttria film formation during plasma spray coating

In this study, we proposed a multiscale analysis method that integrates the direct simulation Monte Carlo (DSMC) method and all-atom molecular dynamics (MD) simulation to comprehend the process of unsteady plasma spray coating of yttria nanoparticles (YNPs) on an alumina substrate. The correlation between the increase in the powder feed rate and growth mechanism of the film microstructure was obtained by solving the collisions of the sprayed YNPs and corresponding spatial trajectories. The results showed that higher powder feed rates form a wider spray cone angle, and a reduction in spray distance increased the probability of powder impinging normal to the substrate. This also explained the changes in the interfacial adhesion and hardness of the films with the powder feed rate and spray distance observed in the experiments. In particular, vertically incident YNPs not only constituted the densest bulk layer, but also contributed to strong adhesion by increasing the probability of generating Y-O-Al binding structures at the interface. The findings were the first to examine the complexity of chemo-mechanical behavior between spatial particle trajectories and facing material, thus throwing light on an important factor in the quality of sprayed ceramic coatings.