Kinetics and mechanism of isothermal oxidation of compositionally graded yttria stabilized zirconia (YSZ) based thermal barrier coating

• Study of isothermal oxidation kinetics of YSZ based thermal barrier coating (TBC).
• Compositionally graded TBC shows lower oxidation kinetics than duplex one.
• Presence of Al2O3 and spinel oxides were found in the microstructure.
• Lower oxidation kinetics in graded TBC was due to reduced spinel oxides.

The present study concerns studying the isothermal oxidation behavior of compositionally graded thermal barrier coating (TBC) consisting of 100% CoNiCrAlY as bond coat developed by high velocity oxyfuel (HVOF) spraying on Inconel 718 substrate followed by several layers of CoNiCrAlY and YSZ in the weight ratios of 70:30, 50:50, 30:70, and 0:100 by plasma spraying. The kinetics of growth of the thermally grown oxide (TGO) layer developed due to oxidation of compositionally graded TBC was compared to the same grown during oxidation of conventional duplex TBC. The mechanism of oxidation was established. The residual stress developed on the surface before and after oxidation was studied in details.