Investigations on the Deposition and the Efficiency of a Multilayer High Temperature Coating System for Gas Turbine Blades

The content of this work is the development and investigation of a high temperature coating system for gas turbine blades. On a single crystal CMSX4 substrate a thin CVD layer of alpha-alumina was deposited as a diffusion barrier coating. As a protection against high-temperature corrosion it was covered with a PVD NiCoCrAlY layer, which also performs as a bond-coat for the following thermal barrier coating deposited by Atmospheric Plasma Spraying. The surface preparation techniques and coating parameters for the multilayer coating were optimized with respect to the bonding mechanisms of the different deposition techniques. The samples were annealed at 1100°C for 100 h under a neutral atmosphere. Furthermore thermocycle experiments were carried out to investigate thermocycle behaviour. The coating system proved its efficiency: no cracks were observed except vertical segmentation cracks in the TBC, all layers showed good adhesion and the diffusion barrier remained intact suppressing any noticeable diffusion of Al, Cr, Ta, Re, W and Ti.