Isothermal and thermal cyclic oxidation behaviour of thermal barrier coatings: Pt aluminide bond coats

beta-phase and gamma-gamma'-phase Pt aluminide, two diffusion bond coats, were applied respectively to CMSX4 and RR3000, two single-crystal Ni-base superalloys, with and without a yttria partially-stabilised zirconia, EB-PVD top coat. The oxide scales developed on RR3000/gamma-gamma'-phase Pt aluminide systems without YPSZ top coat were essentially alpha-Al2O3 at 1,200 degrees C and alpha-Al2O3 plus gamma-Al2O3 at 1,100 degrees C. The oxide scales developed during thermal-cycling oxidation on RR3000/gamma-gamma'-phase, Pt aluminide/YPSZ were found to be more resistant to spallation than the scales grown on CMSX4/beta-phase, Pt aluminide/YPSZ. Spallation of the oxide scale occurred mainly at the bond coat-oxide scale interface but also within the oxide and at the oxide-top coat interface.