Abstract
Low Pressure Plasma Spraying (LPPS) is nowadays a well-established thermal spray process with a broad variety of important applications for functional surface coatings. The operating pressure for LPPS processes can vary in a wide range from typically 200 mbar down to only a few mbar. This leads to unconventional properties of the plasma jet, in terms of supersonic flow with strong shock structure at moderate pressure, towards rarefaction and frozen flow at very low pressure. In order to optimize and control the spray processes for specific applications, it is necessary to understand the underlying physical mechanisms. However, so far only limited knowledge has been established on the plasma jet properties and its interaction with the spray particles in LPPS conditions. We present several experimental investigations to characterize plasma spray processes under various pressure conditions. Measured plasma jet properties using a dedicated enthalpy probe system and imaging are combined with IR-pyrometry and velocimetry on the particles (DPV2000) to further improve the understanding of the plasma particle interactions. These results, along with spray deposit characterization, can be used to optimize the coating properties and explore further potential applications.
