This work investigates the effect of calcium-magnesium aluminosilicate (CMAS) deposits on thermal barrier coatings. CMAS infiltration was achieved by means of a cement tape containing synthetic glass powder. The tape was placed on coating surfaces and melted in a tube furnace or with a flame burner. The resulting coating failures were investigated by examining thermomechanical and thermochemical interactions between the coatings and aluminosilicate deposits. It was found that the porous nature of thermal spray TBCs makes them vulnerable to CMAS attack even before discernible chemical reactions start. Possible mitigation approaches are proposed for improving coating life under such conditions.

The most advanced thermal barrier coating (TBC) systems for aircraft engine and power generation hot section components consist of EBPVD applied yttria stabilized zirconia and platinum modified diffusion aluminide bond coating. Thermally-sprayed ceramic and MCrAlY bond coatings, however, are still used extensively for combustors and power generation blades and vanes. This paper highlights the key features of plasma spray and HVOF, diffusion aluminizing and EBPVD coating processes. The coating characteristics of thermally sprayed MCrAlY bondcoat as well as low density and dense vertically cracked (DVC) Zircoat TBC are described. Essential features of a typical EBPVD TBC coating system, consisting of a diffusion aluminide and a columnar TBC, are also presented. The major coating cost elements such as material, equipment and processing are explained for the different technologies, with a performance and cost comparison given for selected examples.

This study on ceramic thermal barrier coatings (TBCs) presents baseline thermal conductivity data on as-deposited 7-8 wt.% YSZ and a paired-cluster rare-earth oxide doped YSZ, prepared using air plasma spray (APS). The thermal diffusivity for each coating was measured up to 1100°C using the laser flash method, and from these values, the thermal conductivity was calculated. The maximum benefit for thermal conductivity reduction in TBCs with a (GdO 2 , Yb 2 O 3 )-doped YSZ composition was highest for APS dense, vertically macrocracked microstructures, whereas in the case of low density APS TBCs, the reduction in conductivity was found to be more strongly influenced by horizontally-oriented, sub-critical defects and porosity within the coating microstructure.