Microstructural, mechanical and thermal properties of Al2O3/CYSZ functionally graded thermal barrier coatings

In this study, CYSZ/Al2O3 ceramic TBCs were produced in double layered and FGed design having 4, 8 and 12 layers by high-velocity oxy-fuel and atmospheric plasma spraying processes. Microstructural, mechanical and thermal properties of the TBCs were evaluated. The thickness of metallic bonding layer and ceramic top coat were measured as 100 ± 30 μm and 250 ± 80 μm, respectively. Thermal conductivity value of the coating having 8 layered CYSZ/Al2O3 functionally graded design (0.82 W/m·K) were lowest compared to CYSZ/Al2O3 double layered (1.32 W/m·K) and CYSZ single layered (1.44 W/m·K) designs at 835 °C. Thermal cycle performance and bonding strength of the CYSZ/Al2O3 FGed TBCs were superior to those of single layered CYSZ and double layered CYSZ/Al2O3 coatings. Phase transformation from γ-Al2O3 to α-Al2O3 was observed after the thermal cycle test.