Alumina Splat investigation : visualization of impact and splat/substrate interface for millimiter sized drops
Résumé
Coating adhesion-cohesion is strongly linked to the real contact between splats and substrate and between themselves. Unfortunately, the study of a single micrometer-sized splat interface, resulting from flattening and solidification processes and dynamic behaviors, all occurring in a few microseconds, is extremely complex. To overcome problems due to time and dimension scales, many previous works were devoted to the flattening of millimeter-sized drops. However, because of difficulties in producing millimeter- sized ceramic fully melted drops, most works were devoted to metals or alloys. The aim of this work is to present the development of a setup to understand the effect of substrate surface chemistry (oxidation, atom diffusion, etc.) on the flattening of a single millimeter-sized alumina drop. Thus, a new technique to produce such drops with different impact velocities has been developed. It consists in a rotating crucible heated by a transferred arc and a piston controlling substrate velocity and thus drop velocity relative to it. A fast camera (4000 image/s) that combines temperature evolution with a fast pyrometer (4000 Hz), allows following the drop flattening. This system enables the study of interface phenomena (such as desorption of adsorbates and condensates, and liquid drop/substrate wettability) and investigate the effects, at impact, of the kinetic energy or the Weber number of the flattening drop.