Isothermal and Cyclic Oxidation Performance of Vertically Cracked and Columnar Thermal Barrier Coating Structures Produced Using Axial Suspension Plasma Spraying 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 آ°C. The TBC systems are based on two nickelbased superalloy substrates (CMSX4 and IN738LC), platinum aluminide bond coat (BC), and yttriastabilized zirconia (8YSZ) top coat (TC) of either vertically cracked (VC) or columnar structure. Samples with IN738LC substrate exhibited longer isothermal oxidation lives whereas the ones with CMSX4 substrate showed greater cyclic oxidation lives. Outward diffusion of W and Ta in TBC systems containing CMSX4 was found to have progressed to the interface between thermally grown oxide (TGO) and TC; this has contributed to the reduced isothermal oxidation life. The longer cyclic oxidation lives of TBC systems with CMSX4 were attributed to less coefficient and thermal expansion (CTE) mismatch between coating layers (reduced strain energy) and better creep resistance of diffusional BC on CMSX4, hence less TGO rumpling. TBC systems with columnar YSZ had longer isothermal oxidation lives while those with VC YSZ seemed to result in longer cyclic lives.