CMAS deposition rate and sequence effects on cyclic life in gradient testing

Abstract

Thermal barrier coating (TBC) resistance to varied CMAS deposition rates was experimentally assessed using a temperature gradient rig using a CMAS precursor spray. TBCs were composed of EB-PVD YSZ. Five different deposition rates were tested quantifying life versus deposition rate. A high deposition rate and low deposition rate were selected from those tests for sequence testing. For sequence effect testing CMAS deposition occurred at the initial rate until the expected half-life and then switched to the other rate until failure, in the order of high deposition rate first followed by low deposition rate and vice versa. The results suggest that the order of deposition rates can affect ultimate failure behavior. Specifically applying the CMAS at the low deposition rate extended the life of the sample by a nearly a factor of 2 compared to a virgin sample. At the high deposition rate, the CMAS infiltrated all the way to the bond coat past the estimated freeze line. Data showing the coating life versus CMAS deposition rate and the existence of sequence effects in CMAS dosing are fundamentally important to coating life prediction.