Abstract
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.