Isothermal and Cyclic Oxidation Performance of Vertically Cracked and Columnar TBC Structures Produced Using ASPS Process

Abstract

Oxidation performance of thermal barrier coatings (TBCs) deposited by the axial suspension plasma spraying (ASPS) method was evaluated under isothermal and cyclic conditions with a peak temperature of 1080°C. The TBC systems are based on two nickel-based superalloy substrates (CMSX-4 and IN738LC), platinum aluminide bond coat, and yttria stabilized zirconia (8YSZ) top coat of either vertically cracked (VC) or columnar structure. Samples with IN738LC substrate exhibited longer isothermal oxidation lives whereas the ones with CMSX-4 substrate showed greater cyclic oxidation lives. Outward diffusion of W and Ta in TBC systems containing CMSX-4 was found to have progressed to the interface between TGO and top coat; this has contributed to the reduced isothermal oxidation life. The longer cyclic oxidation lives of TBC systems with CMSX-4 were attributed to less CTE mismatch between coating layers (reduced strain energy) and better creep resistance of diffusional bond coat on CMSX-4, hence less TGO rumpling. TBC systems with columnar YSZ had longer isothermal oxidation lives while those with vertically cracked YSZ seemed to result in longer cyclic lives.