Deformation and solidification process of a super–cooled droplet impacting on the substrate under plasma spraying conditions

To date, many modelling efforts related to the deformation and solidication processes of a droplet impacting on the substrate under plasma spraying conditions have been reported. However, to the authors’ knowledge, no modelling effort has dealt with the super-cooling effects on the deformation and solidification processes, though much evidence of super-coolingeffects has been reported. In this paper, we will show the first results derived from our recent modelling efforts for thecase of Al2O3 droplets, which clearly show the strong effects of the super-cooling conditions on the deformation and solidification processes. For example, we predict a significant decrease in deformation degree — defined as the ratio of droplet to splat diameters — to less than 2.0, and also a faster solidification front velocity of up to 5 m/s. Although the small deformation degree is clearly caused by the larger value of viscosity under super-cooled conditions, therapid solidification is eventually caused by the super-cooling. The model did not predict a dendritic growth, but it clearly suggested that plasma sprayed particles are not all but may be actually in super-cooled state, and any modelling efforts should include the super-cooling effects.