Comprehensive Evaluation of Thermal Cycling, Corrosion, and Thermomechanical Resistance of Multilayer Yttria-Stabilized Zirconia/Gadolinium Zirconate Coatings Obtained by High-Velocity Oxygen-Fuel and Atmospheric Plasma Spraying

This study aimed to evaluate how two hydrogen flow rates during atmospheric plasma spraying of the gadolinium zirconate (GZO) top layer are associated with the microstructure and high-temperature performance of multilayer nickel–chromium–aluminum–yttrium (NiCrAlY)/yttria-stabilized zirconia (YSZ)/GZO thermal barrier coatings. Coatings produced at 1.5 and 1.8 L/min were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction with Rietveld refinement, thermomechanical analysis, calcium–magnesium–alumino–silicate (CMAS) hot-corrosion testing, and thermal cycling. Increasing the hydrogen flow rate was accompanied by increases in GZO thickness from 313.48 to 467.57 μm and porosity from 0.89 ± 0.11% to 1.25 ± 0.05%. CMAS penetration depths were 41.22 ± 4.18 μm for GZO1 and 60.44 ± 4.82 μm for GZO2. After 300 thermal cycles, GZO1 retained greater structural integrity, whereas GZO2 exhibited cracking and local spallation. Rietveld refinement indicated predominant pyrochlore in GZO1 and a larger defect-fluorite contribution in GZO2 after cycling. These results demonstrate that processing-related microstructural differences are associated with coating durability. Among the two investigated conditions, GZO1 showed better overall performance, indicating its potential for further development of thermal barrier coatings for high-temperature applications.