Effect of the Superalloy Composition on the Isothermal Oxidation Behaviour of TBC Systems

The isothermal oxidation behaviour of TBC systems based on a first-generation superalloy, AM1 and a fourth-generation one, MCNG, was investigated and compared. The main difference between both is the addition of Re, Ru and Hf in the MCNG composition. The systems consisted of a Pt-modified nickel aluminide (Ni,Pt)Al bond coat deposited on the superalloy and with or without a yttria-stabilized zirconia ceramic top coat. Isothermal oxidations were performed at 1,100 °C in synthetic air for 10, 50, 500 and 1,000 h. The MCNG-based system exhibited a better spallation resistance than the AM1-based one and a lower oxidation rate. Spallation always occurred at the thermally grown oxide/bond coat interface. For both systems, transformation of the β-phase into the γ′-phase was observed. In the MCNG-based samples, the β-(Ni,Pt)Al was enriched in ruthenium and the secondary reaction zone strongly extends, whereas chromium precipitation occurred in the AM1-based ones.