Production and characterisation of GZ/CYSZ alternative thermal barrier coatings with multilayered and functionally graded designs

In this study multilayered and functionally graded Gd2Zr2O7/CYSZ thermal barrier coatings were designed and produced in 2,4,8, and 12 layers utilizing HVOF and APS processes to improve the thermal cycling performance of single layered Gd2Zr2O7. Microstructural, mechanical, and thermal properties of the coatings were investigated. The phase structure of the Gd2Zr2O7 was stable even after the coating and thermal cycling tests made at 1250 °C. The thermal conductivities and bonding strengths were between in 0.64-0.89 W/mK and 8.87-12.10 MPa, respectively. As far as thermal cycling performance of the designs are concerned while big spallation was observed (74%) in the single layered Gd2Zr2O7 coating after 160 cycles a significant improvement had been observed in cases of multilayered coatings and no failure was seen in functionally graded coatings even after 300 cycles. The results indicated that the thermal cycling performance of Gd2Zr2O7 coating was improved thanks to multilayered and especially functionally graded designs.