Understanding of Spray Coating Adhesion Through the Formation of a Single Lamella

Plasma spraying involves the total or partial melting of micrometer sized particles, flattening of the particles in about one microsecond onto a substrate to build a coating by layering the resulting solidified splats. The coating adhesion is essential and depends mainly on the behaviour of first lamellae in contact with the substrate. But in the plasma spray process about 10 8 particles/s impact onto the substrate, and thus it is difficult to understand the role of the different spray parameters onto the coating adhesion. In order to get a better understanding of phenomena involved, it is necessary to study the formation of a single lamella. An experimental set-up has been designed to study this process and is composed of a fast (50 ns) two-colour pyrometer and an imaging system, comprising two fast (1-10 μs) CCD cameras triggered by the velocity signal of the particle in flight prior to its impact. This work is focused on alumina particles flattening onto stainless steel (304L) substrates preheated at different temperatures during different times.