Abstract
Low pressure plasma spraying (LPPS) is well established as coating process for the deposition of TBC systems for industrial gas turbines as well as aero applications under industrial standards. With the extension to LPPS Thin Film process, the operating conditions can vary in a wide range from only a few mbar up to typically 200 mbar which imposes different characteristics of the corresponding spray conditions and resulting coating properties. The flexibility of this process allows for subsequent coating of different layers for bond and top coat of a complex TBC system by using only a single TS technology. This simplifies the operational needs for industrial production and offers the potential of increased technological and economical benefits. Depending on the process conditions a broad variety of different TBC layers, multi-layer systems including bond coats & diffusion barriers, dense, porous or graded YSZ layers as well as EB-PVD like layers with columnar microstructure, can be realized using the LPPS-TF technology. Proper adjustment of spraying conditions and suited material selection allows controlling the grade of “columnarity” of the layer. Thermal cycling as well as GE erosion tests have been used to characterize and benchmark the coating quality. Transfer of such coatings onto real turbine blade has demonstrated that all substrate areas could be coated with a columnar TBC structure up to a thickness of about 250 microns. This offers the possibility either to develop coatings with optimized performance or of comparable quality at reduced production costs when compared to established vapour deposition techniques like EB-PVD. This paper presents an overview on the development of various TBC systems such as multi-layers or columnar structures by using the LPPS Thin Film technology.
