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In thermal spraying, molten YSZ (Yttria Stabilized Zirconia) drop impact is crucial to the understanding of formation of splats and hence coatings. However, existing studies hardly cast attention to the possible rebounding dynamics when successive molten YSZ drops impinge onto newly solidified splats whose temperature is still high so that freezing may be delayed. This work uses a newly developed numerical model based on the conservative level set method to probe into the rebounding dynamics of YSZ drops in practical thermal spraying conditions. The free-energy-based surface tension model in the phase field method was introduced to avoid the computing of curvature, which is however necessary in the continuum surface tension model. The projection method was invoked to solve the Navier–Stokes equations. The model was validated against an experiment of drop impact with rebounding, showing reasonable agreement. Moreover, the model was applied to both dense and hollow YSZ drop impact, with the details of fluid flow being analyzed. The maximum spread factor was found in agreement with existing scaling laws. [ABSTRACT FROM AUTHOR]

In the drop-on-demand 3D printing technique, molten drop impact is crucial to the understanding of the formation of the building block of a part. However, existing studies cast less due attention to the rebounding dynamics of molten drops. This paper thus develops a phase field method to that end. The model consists of the Cahn-Hilliard equation, coupled with the Navier-Stokes equation to track the evolving liquid-gas interface. A heat source is added to the energy balance equation to distinguish between solid and fluid. The model is discretized using a finite difference method on a semi-staggered grid, and is paralleled based on the shared memory parallelism, OpenMP. The model was first compared with an experiment before being applied to various impacts. The agreement is reasonable. Typical impacts in 3D printing conditions were considered. The major findings are that the Tin drop rebounds off the substrate with a dimpled bottom when the impact velocity is 1 m/s, but with a rounded one when the impact velocity is reduced by half, and that the dimpled bottom is caused by an entrapped bubble during the receding process. Besides, effect of solidification on drop rebounding was examined as well. [ABSTRACT FROM AUTHOR]