Vapor Phase Deposition Using a Plasma Spray Process

Abstract

Abstract Plasma spray – physical vapor deposition (PS-PVD) is a low pressure plasma spray technology to deposit coatings out of the vapor phase. PS-PVD is part of the family of new hybrid processes recently developed by Sulzer Metco AG (Switzerland) on the basis of the well established low pressure plasma spraying (LPPS) technology. Included in this new process family are plasma spray - chemical vapor deposition (PS-CVD) and plasma spray - thin film (PS-TF) processes. In comparison to conventional vacuum plasma spraying (VPS) and low pressure plasma spraying (LPPS), these new processes use a high energy plasma gun operated at a work pressure below 2 mbar. This leads to unconventional plasma jet characteristics which can be used to obtain specific and unique coatings. An important new feature of PS-PVD is the possibility to deposit a coating not only by melting the feed stock material which builds up a layer from liquid splats but also by vaporizing the injected material. Therefore, the PS-PVD process fills the gap between the conventional physical vapor deposition (PVD) technologies and standard thermal spray processes. The possibility to vaporize feedstock material and to produce layers out of the vapor phase results in new and unique coating microstructures. The properties of such coatings are superior to those of thermal spray and EB-PVD coatings. In contrast to EB-PVD, PS-PVD incorporates the vaporized coating material into a supersonic plasma plume. Due to the forced gas stream of the plasma jet, complex shaped parts like multi-airfoil turbine vanes can be coated homogeneously with columnar thermal barrier coatings using PS-PVD. This paper reports on the progress made by Sulzer Metco to develop a thermal spray process to produce coatings out of the vapor phase.