LAUSR

Abstract The oxidation resistant diffusion PtAl coatings applied on the hot-section Ni-superalloy components of aero-engines exhibit phase transitions during thermal exposure in air: B2-NiAl➔B2-NiAl/L10-NiAl martensite+γ´-Ni3Al➔γ-Ni + γ´-Ni3Al. The present study correlates the oxidation-microstructure-tensile properties for DS CM-247LC superalloy coated with 60 and 90 μm thick inward grown PtAl bond coat. Cyclic oxidation of the superalloy, in the uncoated condition and after application of 60 and 90 μm thick PtAl coating, has been carried out at 1100 °C for various durations of 10, 100, 750 and 1000 h. The microstructure changes occurring in the coating and superalloy substrate during oxidation for various durations are examined. The concomitant tensile properties for the various oxidized samples are evaluated at 870 °C and their fracture behavior ascertained. Both coatings prevented surface degradation and imparted superior tensile properties, despite 750–1000 h of cyclic oxidation at 1100 °C. The morphology of the phases formed in the coatings affected the tensile properties of the coated superalloy. Cracks formed along the inter/intra-phase boundaries in the coatings. The predominant formation of martensitic L10 laths and films of single-phase γ´ at the prior B2/L10 phase boundaries in the thicker coating during intermediate-term oxidation, such as after 100 h, promoted the initiation of sharp cracks, which penetrated into the substrate and deteriorated the strength and ductility appreciably. On the other hand, if the B2/L10 martensitic phase was enveloped by the γ´ phase or the coating was comprised of γ´ surrounded by the γ phase, then the coating cracks had blunt tips and the tensile properties were not affected adversely. Albeit early phase transformations, the thin coating imparted superior tensile properties.