Abstract
High demands for higher turbine efficiency bring attention to newer and more advanced insulating materials for the high temperature components in the turbine. Yttrium aluminum garnet (YAG) has shown good insulating properties in the previous published research, such as higher temperature limitation and better resistance to calcium–magnesium–alumina–silicate environmental contaminant penetration than the more conventional yttria-stabilized zirconia systems. Whereas in literature, coatings of YAG are typically prepared by solution deposition processes, in the present work YAG powder has been prepared for more conventional thermal spraying methods. The goal is to show the potential YAG powders have as a thermal barrier coating. Different approaches for obtaining a successful deposition and a good coating have been explored. Small-sized industrial-supplied powder and larger in-house-made powder have been compared, emphasizing the importance of energy used for deposition and crystallinity in the final coating. Highly crystalline material has successfully been produced with F4 atmospheric plasma spray system without post-treatment or substrate heating.
Highlights
Thermal barrier coatings (TBC) in the form we most commonly know them, or ‘‘the current era’’ as Miller (Ref 1) referred to, have been around since the middle of the 1970s
The well-known system consisting of an yttria-stabilized zirconia (YSZ) insulating top coating and a NiCrAlY metallic bond coat developed by the NASA Lewis Research Centre in Cleveland by Stecura and Leibert (Ref 2, 3) is to the current day one of the most used TBC systems
Electron-beam physical vapor deposition (EB-PVD) for producing YSZ is known to be a method for producing high-quality columnar structures, often used for the high thermo-mechanically loaded blades of aero engines (Ref 4)
Summary
Thermal barrier coatings (TBC) in the form we most commonly know them, or ‘‘the current era’’ as Miller (Ref 1) referred to, have been around since the middle of the 1970s. The well-known system consisting of an yttria-stabilized zirconia (YSZ) insulating top coating and a NiCrAlY metallic bond coat developed by the NASA Lewis Research Centre in Cleveland by Stecura and Leibert (Ref 2, 3) is to the current day one of the most used TBC systems. The columnar structure is favored in all TBCs due to the structure allowing some deformation in the ceramic layer due to thermal expansion in the substrate. The thermal stress is limited allowing the ceramic layer to deform rather than causing delamination. Vertical cracking in homogenous ceramic layers is desired when TBCs are produced with atmospheric plasma spraying (APS), which was the original deposition technique used by Stecura and Leibert
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