Processing and characterization of CYSZ/Al2O3 and CYSZ/Al2O3 + YSZ multilayered thermal barrier coatings

CYSZ/Al2O3 and CYSZ/Al2O3 + YSZ multilayer ceramic coatings were produced in 4, 8 and 12 layered with a total thickness of ~ 400 μm by high-velocity oxy-fuel (HVOF) and atmospheric plasma spraying (APS) processes. Microstructure, thermal and mechanical properties were evaluated. The thickness of metallic bonding layer and total thickness of ceramic top layer were measured as 100 ± 10 μm and 400 ± 20 μm, respectively. Porosity levels of multilayer coatings were observed between 6 and 13%. Thermal conductivity values of the CYSZ/Al2O3 and CYSZ/Al2O3 + YSZ coatings were in the range of 0.99 to 1.50 W/mK. The bonding strength of as-sprayed coatings was increased from 5.4 to 10.1 MPa for CYSZ/Al2O3, and 8.7 to 11.5 MPa for CYSZ/Al2O3 + YSZ coatings with the increasing number of layers. Existence of phase transformation (γ → α) for Al2O3 coating was observed after the thermal cycle test. The results indicated that the thermal conductivity and thermal cycle strength of CYSZ/Al2O3 + YSZ TBCs were higher than CYSZ/Al2O3 based thermal barrier coatings.