Functionally graded thermal barrier coatings (FG-TBCs) with a gradual composition change from the MCrAlY bond coat (BC) layer to the yttria stabilized zirconia (YSZ) TBC layer is one way to decrease the residual stresses at the BC/TBC interface during a thermal cycling process. At high temperatures, the oxidation resistance of TBCs is also important which would affect the cyclic life of the coatings. In this paper, two YSZ materials were used to make FG-TBCs and conventional duplex TBCs by applying air-plasma spray (APS) technique. The coated samples were thermal cycled with 24-hours heating at 1100 °C followed by air cooling. The results showed that the FG-TBCs performed earlier failure than the duplex ones. Microstructure study indicated that the poor oxidation resistance of the graded mixed layer was responsible for the coating failure. In addition, the influence of spraying parameters on the coating life was discussed.

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