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 ~400μm 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±10μm and 400±20μm, 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 1.50W/mK. The bonding strength of as-sprayed coatings was increased from 5.4 to 10.1MPa for CYSZ/Al₂O₃, and 8.7 to 11.5MPa 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.