Alumina Splat Investigation: Visualization of Impact and Study of Splat / Substrate Interface for Micrometer and Millimeter Sized Drops

Coating adhesion mainly depends on real contact between first splats and substrate. Unfortunately, the study of a single micrometer sized splat interface, resulting from the thermal and dynamic behaviours occurring in a few microseconds, is complex and unpredictable. In order to overcome problems due to time and dimension scales, many previous works were devoted to the flattening of millimeter sized drops. But, according to difficulties in producing millimeter sized ceramics drops, most works dealed with metals or alloys.

The aim of this work is to analyse the effect of substrate surface chemistry (oxidation, atom diffusion …) on a single alumina drop flattening. For that, a technique of millimeter sized free falling alumina drop with different impact velocities (rotating crucible heated by transferred arc) has been developed and a fast camera (4000 image/s) has been used to follow the drop flattening. This system allows first studding the interface phenomena (such as desorption of absorbates and condensates, and liquid drop / substrate wettability) and then, investigating the effects, at impact, of the kinetic energy of the flattening drop. Finally, these results have been compared with those obtained with micrometer sized droplets plasma sprayed.