Failure of physical vapor deposition/plasma-sprayed thermal barrier coatings during thermal cycling

ZrO2-7 wt.% Y2O3 plasma-sprayed (PS) coatings were applied on high-temperat ure Ni-based alloys precoated by physical vapor deposition with a thin, den se, stabilized zirconia coating (PVD bond coat). The PS coatings were appli ed by atmospheric plasma spraying (APS) and inert gas plasma spraying (IPS) at 2 bar for different substrate temperatures. The thermal barrier coating s (TBCs) were tested by furnace isothermal cycling and flame thermal cyclin g at maximum temperatures between 1000 and 1150 degrees C, The temperature gradients within the duplex PVD/PS thermal barrier coatings during the ther mal cycling process were modeled using an unsteady heat transfer program. T his modeling enables calculation of the transient thermal strains and stres ses, which contributes to a better understanding of the failure mechanisms of the TBC during thermal cycling. The adherence and failure modes of these coating systems were experimentally studied during the high-temperature te sting. The TBC failure mechanism during thermal cycling is discussed in lig ht of coating transient stresses and substrate oxidation.