Thermal cycling tests of APS and SPS TBC systems on additively manufactured samples with cooling holes

In the field of aerospace engineering, the efficiency of cooling mechanisms in high-temperature turbine airfoils and combustion chamber walls of jet engines is of great significance. The utilization of cooling holes and thermal barrier coating systems (TBCs) is crucial in protecting these components from the effects of high-temperature combustion gases. Additive Layer Manufacturing (ALM) techniques have emerged as a promising method for the fabrication of more efficient cooling holes with sophisticated geometries. In this study, ALM button samples with and without cooling holes were coated with High-Velocity Oxygen Fuel (HVOF) CoNiCrAlY bond coats and partially Yttria-stabilized zirconia (YSZ) top coats. The top coats were prepared by either suspension plasma spraying (SPS) or atmospheric plasma spraying (APS), using non-90° spraying angles to avoid spraying directly into the cooling holes. Subsequent to this, the samples were exposed to thermal cycling in a furnace at 1100 °C, with the objective of comparing their lifetimes and failure mechanisms. The results indicated that the lifetime of the coatings was comparable when applied to samples with and without cooling holes, as well as when using APS and SPS. Stress concentrations that emerge at the complex hole structure appeared to be not critical for the lifetime under cyclic isothermal conditions, although they can influence the direction of preferred crack propagation.