Comparison between metallic and ceramic splats: Influence of viscosity and kinetic energy on the particle flattening

Plasma-sprayed coating properties are strongly linked to the real contacts between layered splats, defects created by splashing of melted particles and inclusion of unmolten ones, and pores and cracks formed during coating generation. In this paper, the impact, flattening and solidification of millimetre- and micrometre-sized ceramic (alumina) and metallic (Ni5Al) drops or droplets onto a smooth 304 L stainless steel (Ra = 0.06 μm) substrate have been studied to understand the impact phenomena and respond to the following questions:- dimensionless numbers must be considered and how do they compare at both scales? experiments developed to compare droplets (plasma-sprayed) and drops (free-falling) differ? e flattening behaviours comparable at both scales? been shown that for droplets (40 μm in diameter) the thickness of the liquid flow boundary layer between flattening droplets and substrate plays a more important role than with drops. It must also be pointed out that with the metal drops or droplets, solidification at their surface can occur, thus modifying the matter flattening. The flattening process depends strongly upon the substrate temperature and the modification of its wettability. Finally, it has been shown that the flattening velocity is strongly linked to the amounts of adsorbates and condensates existing on the substrate, according to heat treatments prior to spraying.