The impact and solidification history of individual YSZ particles has been the subject of many experimental and theoretical studies. Yet it is customary to assume that solidification occurs at the equilibrium temperature. Furthermore, the diffusion of the solute (yttria) in the liquid phase during solidification of a splat has not been considered. Using our model, we study non-equilibrium effects during the rapid solidification of a molten YSZ particle, by solving the so-called hyperbolic equations for heat and mass transfer. The hyperbolic model predicts the interface undercooling (due to thermal and solutal effects) and velocity as a function of time, as well as the yttria redistribution within the solid phase. Results are then compared to corresponding ones that we obtained from a parabolic model, in order to assess the extent to which YSZ solidification is influenced by non-equilibrium effects. Results indicate that these effects are limited to the early part of the solidification process when undercooling is most significant. At this stage, the interface velocity is unsteady, and solute redistribution is most evident. As solidification decelerates, the non-equilibrium effects wane and solidification can then be properly modeled as an equilibrium process.

We used a three-dimensional model of droplet impact and solidification to simulate the effect of surface roughness on the impact dynamics and the splat shape of an alumina droplet impinging onto a substrate. The substrate surface was patterned by a regular array of cubes spaced at an interval twice their size. Three different cube sizes were considered, and the results were compared to the case of droplet impact onto a smooth substrate. To understand the effect of solidification on the droplet impact dynamics and splat morphology, the simulations were run with and without considering solidification. Comparing the results, we have concluded that solidification plays a major role in determining splat shape on a rough surface. We also present results of the distribution of voids between the splat and the substrate.

This paper presents results regarding the influence of the spray angle on the spray shape. Simulations of the liquid dynamics of the impact of Ni particles, which were the characteristic of both HVOF and DC plasma conditions, are carried out. The results show that the splashes stretch with decreasing spray angle and confirm previous experimental observations to the effect that the splash area varies little with the spray angle. In addition, the results indicate that more than 90% of the material is applied "behind" the point of impact, even at spray angle is equal to 45 degree. Paper includes a German-language abstract.

Various models exist of the 2D impact of a molten thermal spray particle onto a flat solid surface. Such models, however, cannot be used to examine 3D effects such as the asymmetric splashing and breakup which are common under thermal spray conditions. The focus of the present work is on such effects. A 3D model of droplet impact has been developed which predicts splashing and the subsequent formation of small satellite droplets. The model is a 3D version of RIPPLE (LA12007- MS), an Eulerian fixed-grid finite volume code utilizing a volume tracking algorithm to track the droplet free surface. Simulations are presented of the impact and splashing of a molten tin droplet, and the results compared with photographs. A simple model, based on Rayleigh-Taylor instability theory, yields an estimate of the number of satellite droplets which form during impact. Finally, a simulation of droplet impact under thermal spray conditions demonstrates breakup, although in the form of a corona which separates from the bulk of the fluid.