Effect of Gd₂O₃ on the microstructure and thermal properties of nanostructured thermal barrier coatings fabricated by air plasma spraying

The nanostructured 4–8 mol% Gd₂O₃−4.5 mol% Y₂O₃-ZrO₂ (4–8 mol% GdYSZ) coatings were developed by the atmospheric plasma spraying technique. The microstructure and thermal properties of plasma-sprayed 4–8 mol% GdYSZ coatings were investigated. The experimental results indicate that typical microstructure of the as-sprayed coatings were consisted of melted zones, nano-zones, splats, nano-pores, high-volume spheroidal pores and micro-cracks. The porosity of the 4, 6 and 8 mol% GdYSZ coatings was about 9.3%, 11.7% and 13.3%, respectively. It was observed that the addition of gadolinia to the nano-YSZ could significantly reduce the thermal conductivity of nano-YSZ. The thermal conductivity of GdYSZ decreased with increasing Gd₂O₃ addition. And the reduction in thermal conductivity is mainly attributed to the addition of Gd₂O₃, which results in the increase in oxygen vacancies, lattice distortion and porosity.